Imaging guided ambient ionisation mass spectrometry

Abstract

A method is disclosed comprising obtaining or acquiring image or other data from one or more regions of a target using an imaging sensor. The image or other data may then be used to determine one or more regions of interest of the target. An ambient ionisation ion source may then be used to generate aerosol, smoke or vapour from one or more regions of the target.

Claims

1. A method comprising: obtaining or acquiring image data from one or more regions of a target; using said image data to determine one or more regions of interest of said target; using a first device to generate aerosol, smoke or vapour from said one or more regions of interest of said target; mixing said aerosol, smoke or vapour with a matrix and directing or aspirating at least some of said aerosol, smoke or vapour into a vacuum chamber of a mass spectrometer and/or ion mobility spectrometer; causing a mixture of said matrix and aerosol, smoke or vapour to impact upon a collision surface located within a vacuum chamber of said mass spectrometer and/or ion mobility spectrometer; and mass analysing and/or ion mobility analysing said aerosol, smoke or vapour or ions derived from said aerosol, smoke or vapour in order to obtain mass spectrometric data and/or ion mobility data.

2. The method as claimed in claim 1, wherein said image data comprises data selected from the group consisting of: (i) thermal, temperature or thermographic image data; (ii) microwave image data; (iii) radio-frequency (“RF”) image data; (iv) magnetic resonance imaging (“MRI”) image data; (v) ultrasonic or ultrasound image data; (vi) tomographic image data; (vii) optical or other absorption data; (viii) scattering coefficient data; (ix) oxyhemoglobin or deoxyhemoglobin absorbance data; (x) near infrared (NIR) image data; or (xi) magnetic data.

3. The method as claimed in claim 1, wherein said first device comprises or forms part of an ambient ion or ionisation source or wherein said first device generates said aerosol, smoke or vapour for subsequent ionisation by an ambient ion or ionisation source or other ionisation source.

4. The method as claimed in claim 1, wherein said target comprises native or unmodified target material.

5. The method as claimed in claim 1, wherein said step of using said first device to generate aerosol, smoke or vapour from one or more regions of said target further comprises: (i) contacting said target with one or more electrodes; (ii) irradiating said target with a laser; or (iii) directing ultrasonic energy into said target.

6. The method as claimed in claim 1, wherein the step of analysing said mass spectrometric data and/or ion mobility data further comprises analysing a profile of said aerosol, smoke or vapour or a profile of ions derived from said aerosol, smoke or vapour, wherein said profile is selected from the group consisting of: (i) a lipidomic profile; (ii) a fatty acid profile; (iii) a phospholipid profile; (iv) a phosphatidic acid (PA) profile; (v) a phosphatidylethanolamine (PE) profile; (vi) a phosphatidylglycerol (PG) profile; (vii) a phosphatidylserines (PS) profile; (viii) a phosphatidylinositol (PI) profile; or (ix) a triglyceride (TG) profile.

7. The method as claimed in claim 1, further comprising using one or more contrast agents to enhance said image data.

8. The method as claimed in claim 1, further comprising displaying said image data or data derived from said image data so as to assist a user to manually guide or direct one or more probes, ambient ionisation ion sources or said first device.

9. The method as claimed in claim 1, further comprising automatically or robotically guiding or directing one or more probes, ambient ionisation ion sources or said first device using a guidance system.

10. The method as claimed in claim 1, further comprising using said image data to determine the margins or bounds of one or more regions of interest of said target.

11. Apparatus comprising: a device arranged and adapted to obtain or acquire image data from one or more regions of a target; a control system arranged and adapted to use said image data to determine one or more regions of interest of said target; a first device for generating aerosol, smoke or vapour from said one or more regions of interest of said target; a mass analyser and/or ion mobility analyser for mass analysing and/or ion mobility analysing said aerosol, smoke or vapour or ions derived from said aerosol, smoke or vapour in order to obtain mass spectrometric data and/or ion mobility data; a device for mixing said aerosol, smoke or vapour with a matrix and directing or aspirating at least some of said aerosol, smoke or vapour into a vacuum chamber of a mass spectrometer and/or ion mobility spectrometer; and a device for directing a mixture of said matrix and aerosol, smoke or vapour to impact upon a collision surface located within a vacuum chamber of said mass spectrometer and/or ion mobility spectrometer so as to generate a plurality of analyte ions.

12. The apparatus as claimed in claim 11, wherein said image data comprises data selected from the group consisting of: (i) thermal, temperature or thermographic image data; (ii) microwave image data; (iii) radio-frequency (“RF”) image data; (iv) magnetic resonance imaging (“MRI”) image data; (v) ultrasonic or ultrasound image data; (vi) tomographic image data; (vii) absorption data; (viii) scattering coefficient data; (ix) oxyhemoglobin or deoxyhemoglobin absorbance data; (x) near infrared (NIR) image data; or (xi) magnetic data.

13. The apparatus as claimed in claim 11, wherein: (i) said first device is arranged and adapted to generate aerosol, smoke or vapour from one or more regions of said target by contacting said target with one or more electrodes; (ii) said first device comprises a laser for irradiating said target; or (iii) said first device is arranged and adapted to direct ultrasonic energy into said target.

14. The apparatus as claimed in claim 11, wherein said first device comprises a point of care (“POC”), diagnostic or surgical device.

15. The apparatus as claimed in claim 11, further comprising one or more sensors, detectors or devices for obtaining the image data, wherein said one or more sensors, detectors or devices comprise: (i) one or more thermal or temperature sensors, detectors or devices; (ii) one or more microwave or RF sensors, detectors or devices; (iii) an optical coherence tomography (“OCT”) device; (iv) one or more ultrasonic tomography devices; or (vi) an X-ray scattering device.

16. The apparatus as claimed in claim 11, further comprising a device for displaying the image data or data derived from the image data.

17. The apparatus as claimed in claim 11, further comprising a guidance system for manually, automatically or robotically guiding or directing one or more probes, surgical tools, diagnostic tools, ambient ionisation ion sources or the first device using the image data or data derived from the image data.

18. The method as claimed in claim 1, wherein the matrix comprises isopropanol.

19. The method as claimed in claim 1, wherein said image data comprises data selected from the group consisting of: (i) visual or optical image data; (ii) infra-red (“IR”) image data; and (iii) X-ray image data.

20. The apparatus as claimed in claim 11, further comprising one or more sensors, detectors or devices for obtaining the image data, wherein said one or more sensors, detectors or devices comprise: (i) a computed tomography device; (ii) a positron emission tomography (“PET”) device; (iii) a magnetic resonance imaging (“MRI”) device; or (iv) one or more optical imaging sensors, detectors or devices.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 illustrates a method of rapid evaporative ionisation mass spectrometry (“REIMS”) wherein an RF voltage is applied to bipolar forceps resulting in the generation of an aerosol or surgical plume which is captured through an irrigation port of the bipolar forceps and is then transferred to a mass spectrometer for ionisation and mass analysis;

(3) FIG. 2 illustrates a general embodiment wherein one or more imaging sensors or detectors are used to obtain image data from a target (e.g. in vivo tissue) prior to or whilst activating a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source to inter alia analyse the target and to determine, for example, whether or not the tissue may be cancerous;

(4) FIG. 3 shows a microwave reflectrometry sensor which may be used according to various embodiments in order to obtain imaging data;

(5) FIG. 4 shows a method of analysis that comprises building a classification model according to various embodiments;

(6) FIG. 5 shows a set of reference sample spectra obtained from two classes of known reference samples;

(7) FIG. 6 shows a multivariate space having three dimensions defined by intensity axes, wherein the multivariate space comprises plural reference points, each reference point corresponding to a set of three peak intensity values derived from a reference sample spectrum;

(8) FIG. 7 shows a general relationship between cumulative variance and number of components of a PCA model;

(9) FIG. 8 shows a PCA space having two dimensions defined by principal component axes, wherein the PCA space comprises plural transformed reference points or scores, each transformed reference point or score corresponding to a reference point of FIG. 6;

(10) FIG. 9 shows a PCA-LDA space having a single dimension or axis, wherein the LDA is performed based on the PCA space of FIG. 8, the PCA-LDA space comprising plural further transformed reference points or class scores, each further transformed reference point or class score corresponding to a transformed reference point or score of FIG. 8;

(11) FIG. 10 shows a method of analysis that comprises using a classification model according to various embodiments;

(12) FIG. 11 shows a sample spectrum obtained from an unknown sample;

(13) FIG. 12 shows the PCA-LDA space of FIG. 9, wherein the PCA-LDA space further comprises a PCA-LDA projected sample point derived from the peak intensity values of the sample spectrum of FIG. 11;

(14) FIG. 13 shows a method of analysis that comprises building a classification library according to various embodiments; and

(15) FIG. 14 shows a method of analysis that comprises using a classification library according to various embodiments.

DETAILED DESCRIPTION

(16) Various embodiments will now be described in more detail below which in general relate to obtaining imaging or other data from one or more regions of a target (e.g., in vivo tissue) and then generating an aerosol, surgical smoke or vapour from one or more regions of the target using an ambient ionisation ion source.

(17) The aerosol, surgical smoke or vapour is then aspirated into a vacuum chamber of a mass spectrometer and/or ion mobility spectrometer and is caused to impact upon a collision surface causing the aerosol, smoke or vapour to be ionised by impact ionisation which results in the generation of analyte ions.

(18) The resulting analyte ions (or fragment or product ions derived from the analyte ions) are then mass analysed and the resulting mass spectrometric data and/or ion mobility data may then be subjected to multivariate analysis in order to determine one or more properties of the target in real time.

(19) For example, the multivariate analysis may enable a determination to be made as to whether or not a portion of tissue which is currently being resected is cancerous or not.

(20) The use of imaging data enables tissue which is of potential concern to be identified either prior to and/or during a surgical procedure and enables a surgeon to have a greater confidence that all undesired or potentially cancerous tissue is both located and completely removed whilst at the same time ensuring that the minimum amount of healthy tissue is removed.

(21) Ambient Ionisation Ion Sources

(22) According to various embodiments a device is used to generate an aerosol, smoke or vapour from one or more regions of a target (e.g., in vivo tissue). The device may comprise an ambient ionisation ion source which is characterised by the ability to generate analyte aerosol, smoke or vapour from a native or unmodified target. For example, other types of ionisation ion sources such as Matrix Assisted Laser Desorption Ionisation (“MALDI”) ion sources require a matrix or reagent to be added to the sample prior to ionisation.

(23) It will be apparent that the requirement to add a matrix or a reagent to a sample prevents the ability to perform in vivo analysis of tissue and also, more generally, prevents the ability to provide a rapid simple analysis of target material.

(24) In contrast, therefore, ambient ionisation techniques are particularly advantageous since firstly they do not require the addition of a matrix or a reagent (and hence are suitable for the analysis of in vivo tissue) and since secondly they enable a rapid simple analysis of target material to be performed.

(25) A number of different ambient ionisation techniques are known and are intended to fall within the scope of the present invention. As a matter of historical record, Desorption Electrospray Ionisation (“DESI”) was the first ambient ionisation technique to be developed and was disclosed in 2004. Since 2004, a number of other ambient ionisation techniques have been developed. These ambient ionisation techniques differ in their precise ionisation method but they share the same general capability of generating gas-phase ions directly from native (i.e. untreated or unmodified) samples. A particular advantage of the various ambient ionisation techniques which are intended to fall within the scope of the present invention is that the various ambient ionisation techniques do not require any prior sample preparation. As a result, the various ambient ionisation techniques enable both in vivo tissue and ex vivo tissue samples to be analysed without necessitating the time and expense of adding a matrix or reagent to the tissue sample or other target material.

(26) A list of ambient ionisation techniques which are intended to fall within the scope of the present invention are given in the following table:

(27) TABLE-US-00001 Acronym Ionisation technique DESI Desorption electrospray ionization DeSSI Desorption sonic spray ionization DAPPI Desorption atmospheric pressure photoionization EASI Easy ambient sonic-spray ionization JeDI Jet desorption electrospray ionization TM-DESI Transmission mode desorption electrospray ionization LMJ-SSP Liquid microjunction-surface sampling probe DICE Desorption ionization by charge exchange Nano-DESI Nanospray desorption electrospray ionization EADESI Electrode-assisted desorption electrospray ionization APTDCI Atmospheric pressure thermal desorption chemical ionization V-EASI Venturi easy ambient sonic-spray ionization AFAI Air flow-assisted ionization LESA Liquid extraction surface analysis PTC-ESI Pipette tip column electrospray ionization AFADESI Air flow-assisted desorption electrospray ionization DEFFI Desorption electro-flow focusing ionization ESTASI Electrostatic spray ionization PASIT Plasma-based ambient sampling ionization transmission DAPCI Desorption atmospheric pressure chemical ionization DART Direct analysis in real time ASAP Atmospheric pressure solid analysis probe APTDI Atmospheric pressure thermal desorption ionization PADI Plasma assisted desorption ionization DBDI Dielectric barrier discharge ionization FAPA Flowing atmospheric pressure afterglow HAPGDI Helium atmospheric pressure glow discharge ionization APGDDI Atmospheric pressure glow discharge desorption ionization LTP Low temperature plasma LS-APGD Liquid sampling-atmospheric pressure glow discharge MIPDI Microwave induced plasma desorption ionization MFGDP Microfabricated glow discharge plasma RoPPI Robotic plasma probe ionization PLASI Plasma spray ionization MALDESI Matrix assisted laser desorption electrospray ionization ELDI Electrospray laser desorption ionization LDTD Laser diode thermal desorption LAESI Laser ablation electrospray ionization CALDI Charge assisted laser desorption ionization LA-FAPA Laser ablation flowing atmospheric pressure afterglow LADESI Laser assisted desorption electrospray ionization LDESI Laser desorption electrospray ionization LEMS Laser electrospray mass spectrometry LSI Laser spray ionization IR-LAMICI Infrared laser ablation metastable induced chemical ionization LDSPI Laser desorption spray post-ionization PAMLDI Plasma assisted multiwavelength laser desorption ionization HALDI High voltage-assisted laser desorption ionization PALDI Plasma assisted laser desorption ionization ESSI Extractive electrospray ionization PESI Probe electrospray ionization ND-ESSI Neutral desorption extractive electrospray ionization PS Paper spray DIP-APCI Direct inlet probe-atmospheric pressure chemical ionization TS Touch spray Wooden-tip Wooden-tip electrospray CBS-SPME Coated blade spray solid phase microextraction TSI Tissue spray ionization RADIO Radiofrequency acoustic desorption ionization LIAD-ESI Laser induced acoustic desorption electrospray ionization SAWN Surface acoustic wave nebulization UASI Ultrasonication-assisted spray ionization SPA-nanoESI Solid probe assisted nanoelectrospray ionization PAUSI Paper assisted ultrasonic spray ionization DPESI Direct probe electrospray ionization ESA-Py Electrospray assisted pyrolysis ionization APPIS Ambient pressure pyroelectric ion source RASTIR Remote analyte sampling transport and ionization relay SACI Surface activated chemical ionization DEMI Desorption electrospray metastable-induced ionization REIMS Rapid evaporative ionization mass spectrometry SPAM Single particle aerosol mass spectrometry TDAMS Thermal desorption-based ambient mass spectrometry MAII Matrix assisted inlet ionization SAII Solvent assisted inlet ionization SwiFERR Switched ferroelectric plasma ionizer LPTD Leidenfrost phenomenon assisted thermal desorption

(28) According to an embodiment the ambient ionisation ion source may comprise a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source wherein a RF voltage is applied to one or more electrodes in order to generate an aerosol or plume of surgical smoke by Joule heating.

(29) However, it will be appreciated that other ambient ion sources including those referred to above may also be utilised. For example, according to another embodiment the ambient ionisation ion source may comprise a laser ionisation ion source. According to an embodiment the laser ionisation ion source may comprise a mid-IR laser ablation ion source. For example, there are several lasers which emit radiation close to or at 2.94 μm which corresponds with the peak in the water absorption spectrum. According to various embodiments the ambient ionisation ion source may comprise a laser ablation ion source having a wavelength close to 2.94 μm on the basis of the high absorption coefficient of water at 2.94 μm. According to an embodiment the laser ablation ion source may comprise a Er:YAG laser which emits radiation at 2.94 μm.

(30) Other embodiments are contemplated wherein a mid-infrared optical parametric oscillator (“OPO”) may be used to produce a laser ablation ion source having a longer wavelength than 2.94 μm. For example, an Er:YAG pumped ZGP-OPO may be used to produce laser radiation having a wavelength of e.g. 6.1 μm, 6.45 μm or 6.73 μm. In some situations it may be advantageous to use a laser ablation ion source having a shorter or longer wavelength than 2.94 μm since only the surface layers will be ablated and less thermal damage may result. According to an embodiment a Co:MgF.sub.2 laser may be used as a laser ablation ion source wherein the laser may be tuned from 1.75-2.5 μm. According to another embodiment an optical parametric oscillator (“OPO”) system pumped by a Nd:YAG laser may be used to produce a laser ablation ion source having a wavelength between 2.9-3.1 μm. According to another embodiment a CO.sub.2 laser having a wavelength of 10.6 μm may be used to generate the aerosol, smoke or vapour.

(31) According to other embodiments the ambient ionisation ion source may comprise an ultrasonic ablation ion source which generates a liquid sample which is then aspirated as an aerosol. The ultrasonic ablation ion source may comprise a focused or unfocussed source.

(32) According to an embodiment the first device for generating aerosol, smoke or vapour from one or more regions of a target may comprise an electrosurgical tool which utilises a continuous RF waveform. According to other embodiments a radiofrequency tissue dissection system may be used which is arranged to supply pulsed plasma RF energy to a tool. The tool may comprise, for example, a PlasmaBlade®. Pulsed plasma RF tools operate at lower temperatures than conventional electrosurgical tools (e.g. 40-170° C. c.f. 200-350° C.) thereby reducing thermal injury depth. Pulsed waveforms and duty cycles may be used for both cut and coagulation modes of operation by inducing electrical plasma along the cutting edge(s) of a thin insulated electrode.

(33) Rapid Evaporative Ionisation Mass Spectrometry (“REIMS”)

(34) FIG. 1 illustrates a method of rapid evaporative ionisation mass spectrometry (“REIMS”) wherein bipolar forceps 1 may be brought into contact with in vivo tissue 2 of a patient 3. In the example shown in FIG. 1, the bipolar forceps 1 may be brought into contact with brain tissue 2 of a patient 3 during the course of a surgical operation on the patient's brain. An RF voltage from an RF voltage generator 4 may be applied to the bipolar forceps 1 which causes localised Joule or diathermy heating of the tissue 2. As a result, an aerosol or surgical plume 5 is generated. The aerosol or surgical plume 5 may then be captured or otherwise aspirated through an irrigation port of the bipolar forceps 1. The irrigation port of the bipolar forceps 1 is therefore reutilised as an aspiration port. The aerosol or surgical plume 5 may then be passed from the irrigation (aspiration) port of the bipolar forceps 1 to tubing 6 (e.g. ⅛″ or 3.2 mm diameter Teflon® tubing). The tubing 6 is arranged to transfer the aerosol or surgical plume 5 to an atmospheric pressure interface 7 of a mass spectrometer and/or ion mobility spectrometer 8.

(35) According to various embodiments a matrix comprising an organic solvent such as isopropanol may be added to the aerosol or surgical plume 5 at the atmospheric pressure interface 7. The mixture of aerosol 3 and organic solvent may then be arranged to impact upon a collision surface within a vacuum chamber of the mass spectrometer and/or ion mobility spectrometer 8. According to one embodiment the collision surface may be heated. The aerosol is caused to ionise upon impacting the collision surface resulting in the generation of analyte ions. The ionisation efficiency of generating the analyte ions may be improved by the addition of the organic solvent. However, the addition of an organic solvent is not essential.

(36) Analyte ions which are generated by causing the aerosol, smoke or vapour 5 to impact upon the collision surface are then passed through subsequent stages of the mass spectrometer and/or ion mobility spectrometer and are subjected to mass analysis (and/or ion mobility analysis) in a mass analyser (and/or ion mobility analyser). The mass analyser may, for example, comprise a quadrupole mass analyser or a Time of Flight mass analyser.

(37) FIG. 2 illustrates a general embodiment wherein one or more imaging sensors 20 are used to obtain imaging data from a target 2 (e.g. in vivo tissue) prior to activating a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source 1 which inter alia samples tissue 2 and enables a determination to be made, for example, as to whether or not the issue is cancerous.

(38) Other embodiments are contemplated wherein the target 2 may more generally comprise an organic target including materials such as plastics. The target 2 may be imaged (e.g. using X-ray imaging) to determine regions of density change in the target 2. Regions of interest may then be identified and subjected to ambient ionisation analysis. For example, a determination may be made that one or more regions of a plastic target have a different density which may be indicative of an organic or other contaminant. The regions of interest may then be analysed and the potential contaminant identified.

(39) According to various embodiments the one or more sensor devices 20 may be used to obtain imaging (or other closely related) data from the target (e.g. either in vivo or ex vivo biological tissue). The one or more imaging sensor devices 20 may be arranged, for example, to obtain from the target: (i) thermal, temperature or thermographic image data; (ii) microwave image data; (iii) visual or optical image data; (iv) infra-red (“IR”) image data; (v) radio-frequency (“RF”) image data; (vi) X-ray image data; (vii) magnetic resonance imaging (“MRI”) image data; (viii) ultrasonic or ultrasound image data; (ix) tomographic image data; (x) optical or other absorption data; (xi) optical or other scattering coefficient data; (xii) oxyhemoglobin or deoxyhemoglobin absorbance data; (xiii) near infrared (NIR) image data; or (xiv) magnetic data.

(40) A number of different embodiments are contemplated and will be described in more detail below wherein imaging (or other closely related) data is acquired from one or more imaging sensors or devices 20 and wherein the imaging data may then be used, for example, to guide a user (e.g. a surgeon) performing a surgical, diagnostic or other procedure utilising an ambient ionisation ion source to one or more regions of particular interest on a target (e.g. in vivo or ex vivo tissue).

(41) By way of example only, the one or more imaging sensors or devices 20 may be utilised to determine regions of tissue of a patient which have a different thermal, temperature or thermographic profile, microwave profile, visual or optical profile, infra-red (“IR”) profile, radio-frequency (“RF”) profile, X-ray profile, magnetic resonance imaging profile, ultrasonic or ultrasound profile, tomographic profile, optical or other absorption profile, optical or other scattering coefficient profile, oxyhemoglobin or deoxyhemoglobin absorbance profile, near infrared (NIR) profile or magnetic profile compared to surrounding tissue. As will be appreciated, portions of tissue which have a different thermal, temperature or thermographic profile, microwave profile, visual or optical profile, infra-red (“IR”) profile, radio-frequency (“RF”) profile, X-ray profile, magnetic resonance imaging profile, ultrasonic or ultrasound profile, tomographic profile, optical or other absorption profile, optical or other scattering coefficient profile, oxyhemoglobin or deoxyhemoglobin absorbance profile, near infrared (NIR) profile or magnetic profile compared to surrounding tissue may comprise diseased or potentially cancerous tissue. It is known, for example, that potentially cancerous tissue may be denser than healthy tissue and may have a highly vascular nature. Accordingly, potentially cancerous tissue may have a different water content to that of surrounding healthy tissue, may have a higher or different temperature to that of healthy tissue and have different dielectric and physical properties to that of surrounding healthy tissue.

(42) According to an embodiment the additional or confirmatory information provided by the one or more imaging sensors 20 may be used to help determine the margins or bounds of healthy, potentially cancerous, cancerous, potentially diseased or diseased biological tissue or the margins or bounds of a tumour.

(43) The cancerous biological tissue or the tumour may comprise: (i) grade I, grade II, grade III or grade IV cancerous tissue; (ii) metastatic cancerous tissue; (iii) mixed grade cancerous tissue; or (iv) a sub-grade cancerous tissue.

(44) The one or more imaging sensors 20 may be used to help determine physical, chemical or other data and in particular may be used to determine the margins or bounds between different types or grades of diseased or cancerous tissue.

(45) The different grades of cancerous tissue may be selected from the group consisting of: (i) grade I cancerous tissue; (ii) grade II cancerous tissue; (iii) grade III cancerous tissue; and (iv) grade IV cancerous tissue.

(46) According to various embodiments a determination from the imaging or other data may be made to determine either: (i) one or more physical properties of the target; (ii) one or more chemical properties of the target; (iii) one or more physico-chemical properties of the target; or (iv) one or more mechanical properties of the target.

(47) Optimised Operational Parameters of an Ambient Ionisation Surgical or Diagnostic Tool May be Programmed or Set Dependent Upon Data Acquired from One or More Imaging Sensors

(48) According to an embodiment one or more operational parameters of an ambient ionisation surgical or diagnostic tool may be arranged to vary or otherwise be optimised during a surgical or diagnostic procedure based upon the acquired physical or non-mass spectrometric data, chemical data, imaging data or other data.

(49) For example, according to an embodiment the energy dissipated into surrounding tissue may be arranged to reduce as the surgical or diagnostic device approaches a vital organ.

(50) According to various embodiments one more operational parameters of an ambient ionisation ion source may be varied or controlled depending upon the specific type of tissue which is being probed. The type of tissue may be known in advance or may be determined from imaging, chemical, physical or other data. For example, according to an embodiment if a tissue or tumour has a soft or gelatinous texture or the probe is in close proximity to a sensitive region of the body (e.g. the probe is in close proximity to important nerves) than the power and/or duty cycle of the ambient ionisation ion source may be reduced, varied or otherwise altered.

(51) According to another embodiment, one or more operational parameters of an ambient ionisation surgical or other tool may be set based upon the acquired chemical, physical or imaging data. For example, one or more operational parameters of an ambient ionisation surgical tool may be set based upon the type or grade of cancerous tissue identified by the one or more physical, chemical, imaging or other sensors or devices 20 or based upon the nature of the diseased tissue identified by the one or more physical, chemical, imaging or other sensors or devices 20.

(52) Different operational parameters may be used depending upon whether operating upon healthy tissue, clearly cancerous tissue or at the cancer margin.

(53) According to various embodiments the physical data, non-mass spectrometric data, chemical data, imaging data or other data may include spatial information and hence the variation of tissue as a function of depth within an organ may be determined. Accordingly, previously acquired physical data, non-mass spectrometric data, chemical data, imaging data or other data may be used to set various operational parameters of an ambient ionisation surgical tool as the surgical tool moves deeper into (or out of) an organ or closer to (or away from) an organ or specific tissue types.

(54) Furthermore, various ionisation parameters may be varied as the ambient ionisation surgical tool moves deeper into (or out of) an organ or closer to (or away from) an organ or specific tissue types.

(55) As the ambient ionisation surgical tool makes an initial cut into an organ one or more ionisation parameters (e.g. the composition of a matrix added to the aerosol, smoke or vapour released from the tissue, the temperature of a ionisation collision surface, the voltage applied to an ionisation collision surface etc.) may be optimised for the surgical conditions (e.g. initial blood loss, tissue composition) experienced when cutting into the organ. As the ambient ionisation surgical tool moves deeper into (or out of) the organ or closer to (or away from) an organ or specific tissue types the optimum ionisation parameters for the surgical tool may change reflecting e.g. a different degree of blood loss and a different composition of the tissue. Accordingly, one or more ionisation parameters (e.g. the composition of matrix added to aerosol, smoke or vapour released from the tissue, the temperature of a ionisation collision surface, the voltage applied to an ionisation collision surface etc.) may be arranged also to change or vary in order to match the changing surgical conditions and optionally based upon the acquired chemical data.

(56) Numerous different embodiments are contemplated wherein various operational parameters of a surgical device or diagnostic tool which incorporates an ambient ionisation ion source (e.g. a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source) may be varied based upon the acquired physical non-mass spectrometric data, chemical data, imaging data or other data.

(57) According to various embodiments an ion mode of the mass spectrometer and/or ion mobility spectrometer may be selected based upon chemical, physical, imaging or other data taken or determined from the cutting site.

(58) According to further embodiments one or more operational parameters of the mass spectrometer and/or ion mobility spectrometer may be changed or altered based upon, subsequent to or during the process of making a diagnosis (e.g. of cancerous or healthy tissue). For example, one or more operational parameters may be changed upon confirmation. The one or more operational parameters which may be changed or optimised depending upon the stage of analysis (e.g. exploratory, diagnosis or confirmation) include optimisation of: (i) inlet conditions including inlet voltages, type and flow rate of optional matrix added to aerosol flow, Venturi suction etc.; (ii) fragmentation conditions for aerosol including flow rates and temperature of collision surface, heated coil parameters etc.; (iii) downstream ion optics including ion path; and (iv) mass analysis steps including selection of mass peak(s) for further diagnosis, performing MS/MS experiments, fragmenting analyte ions of interest and mass analysing subsequent daughter, fragment or product ions.

(59) Thermal Imaging

(60) Intraoperative Thermal Imaging (“ITI”) is an imaging technique which can be used to locate the margins of primary and metastatic tumours. For example, in the case of brain tumours there may be a temperature difference of >3° C. between a brain tumour core (having a temperature of e.g. 36.4° C.) and surrounding normal tissue having a lower temperature of e.g. 33.1° C.

(61) The temperature of human body tissue is influenced by a number of complex factors including the degree of vasculature. Tumours may be highly vascular in nature and hence may be detected by being hyperthermic i.e. having a higher temperature than that of surrounding tissue. It is known, for example, to use thermography as a simple and non-invasive method of screening for potential breast tumours.

(62) Brain, corneal and ocular tumours and malignant melanomas may be detected on the basis of having a hyperthermic profile relative to surrounding normal tissue.

(63) In some instances tumours may have a lower temperature than that of surrounding tissue and certain tumours may be hypothermic. Major factors which can contribute to hypothermia include: (i) low density in tumour microvessels; (ii) edema in surrounding tissues due to the growth of the tumour; (iii) lower metabolism; and (iv) tumour necrosis which can result in a reduction of tumour vasculature and metabolic activity.

(64) Thermal or infrared emission from tissue may be absorbed by fluid or glass. Ideally, therefore, the surgical site should be dried to remove any fluids including blood prior to thermal imaging.

(65) ITI is essentially a technology for determining the surface temperature of tissue and the technology has a low effective penetration into the body or the tissue.

(66) One advantage of ITI is that it is non-invasive and can be used with patients who have an implant which prevents the use of intra-operative MRI.

(67) Various embodiments are contemplated wherein thermal imaging data of a target (e.g. in vivo tissue) may be obtained and may be used in combination with an ambient ionisation ion source.

(68) Total En Bloc Spondylectomy (“TES”)

(69) Conventionally, curettage or piecemeal excision has been the usual approach to vertebral tumours. This approach, however, can increase the risk of tumour cell contamination to the surrounding structures and residual tumour tissue at the site due to the difficulty in demarcating tumour from healthy tissue. These contribute to incomplete resection of the tumour as well as high local recurrence rates of the spinal malignant tumour. To reduce local recurrence and to increase survival, a procedure known as total en bloc spondylectomy (“TES”) may be used. In this method, the entire vertebra or vertebrae containing the malignant tumour are resected, together with en bloc laminectomy, en bloc corpectomy, and bilateral pediculotomy using a T-saw through the posterior approach. Using this technique, it is possible to excise the tumour mass together with a wide or marginal margin.

(70) Various embodiments are contemplated wherein an ambient ionisation surgical or diagnostic tool may be used to perform a total en bloc spondylectomy and wherein, in particular, imaging data may first be obtained according to various embodiments in order to help determine one or more regions of vertebra which should be resected and in order to reduce the amount of healthy vertebra which is removed.

(71) Infrared Thermography

(72) According to an embodiment an infrared thermal camera may be used to record the thermal profile of a target, surgical site or tissue. The camera may comprise, for example, an array of 340×240 pixels and may comprise an uncooled micro-barometer Focal Plane Array (“FPA”) detector which is arranged to provide a high spatial resolution (e.g. 7.5 to 13 μm). The detector may be arranged to have a thermal sensitivity of e.g. 0.06° C. at an ambient temperature of 30° C.

(73) The resolution of a thermal imaging camera having 340×240 pixels is greater than the resolution of conventional magnetic resonance imaging (“MRI”) which has a resolution of 256×256 pixels.

(74) Intraoperative Magnetic Resonance Imaging (“iMRI”)

(75) Intraoperative Magnetic Resonance Imaging (“iMRI”) technology is known which provides surgeons with intraoperative image guidance during tumour resections as it provides various surgically relevant parameters such as the location of the tumor and its borders as well as vascular parameters.

(76) According to various embodiments an intraoperative magnetic resonance imaging device may be used to acquire imaging data and may be used in conjunction with an ambient ionisation surgical or diagnostic tool.

(77) NIR Optical Tomography of In Vivo Tissue

(78) According to an embodiment a number of different NIR optical tomography techniques may be used in order to obtain imaging data. For example, according to various embodiments continuous wave (“CW”), time domain photon migration (“TDPM”) and frequency domain photon migration (“FDPM”) imaging techniques may be utilised in order to obtain imaging data.

(79) Continuous wave imaging utilises a light source wherein the intensity of the light source is arranged to remain substantially constant with time. The light source may be focused onto the target which may comprise in vivo tissue. The time invariant distribution of light may then be detected at various positions on the target surface.

(80) Regions of abnormal, diseased or potentially cancerous tissue may be detected by wavelength dependent light absorption properties and/or wavelength dependent light scattering properties. For example, cancerous tissue may have a higher vascular density and an increased number of larger nuclei. As a result, both the light absorption and scattering properties of the diseased tissue will be different from that of healthy tissue and hence the two different tissue types can be differentiated.

(81) Continuous wave imaging sensors or devices have the advantage of being relatively simple and require just a light source and a basic detector.

(82) Time domain photon migration (“TDPM”) imaging is a more complex imaging technique which involves directing very short pulses of light (e.g. pulses having a duration of picoseconds or femtoseconds at full width half maximum (FWHM)) at the target surface.

(83) The pulses of light will broaden as they pass through the tissue. A detector may be positioned to detect the pulse of light as it passes through the tissue and the point-spread function of the detected pulse of light may be determined.

(84) In essence, the distribution of the times of flight of photons as detected using very fast photon counting techniques or a streak camera detector may be used to infer optical properties of the tissue.

(85) Embodiments are contemplated wherein an optical system comprising a pulsed laser source, a streak camera detector or a single photon counting detection system may be provided. Other embodiments are also contemplated wherein time gating techniques may be used to determine the total number of photons that arrive at a detector within a certain period of time.

(86) Other embodiments are contemplated wherein frequency domain photon migration (“FDPM”) imaging techniques may be used, wherein the light intensity emitted from e.g. a laser diode or LED light source is sinusoidally modulated at frequencies of the order of 10 MHz to 1 GHz. The light propagates through tissue and is amplitude and phase-shifted relative to the source wave. The phase delay and amplitude attenuation relative to the intensity of the incident light may be detected at a point on the tissue surface some distance away from its source. The location, size and optical contrast of heterogeneities within a tissue volume may be determined.

(87) According to various embodiments NIR absorption signatures for healthy and diseased tissue may be generated and which look in particular at the absorbance of optical light due to melanin, oxyhemoglobin, deoxyhemoglobin, water and fat.

(88) Contrast Agents and Nanoparticles

(89) The near-infrared (“NIR”) may be used to interrogate tissues in combination with NIR excitable dyes or contrast agents.

(90) Various embodiments are contemplated wherein endogenous or exogenous contrast agents may be used to enhance image data, physical data, chemical data or other data which may be acquired according to various embodiments.

(91) A number of different contrast agents may be used to enhance image data, physical data, chemical data or other data which, for example, may fluorescence when illuminated with infrared radiation having a wavelength in the range 700-900 nm. The wavelength range 700-900 nm may be considered to comprise a therapeutic window since in vivo tissue exhibits a low absorbance in this wavelength range. Absorption occurs primarily from tissue chromophores of oxy- and deoxyhemoglobin, fat, melanin and water.

(92) It will be understood that the ability to detect potentially abnormal or diseased tissue by imaging, chemical, physical or other techniques depends principally upon there being a contrast between healthy and diseased tissue.

(93) Alternatively, abnormal or diseased tissue can be differentiated from healthy tissue on the basis of the two different tissue types having different scattering properties.

(94) Although the wavelength range 700-900 nm is of particular interest due to the low absorbance in this wavelength range, infrared radiation in this wavelength range can also exhibit a relatively high scattering coefficient.

(95) Embodiments are contemplated wherein imaging data, chemical data, physical data or other data may be obtained by detecting differences in the scattering of infrared radiation within the wavelength range 700-900 nm between healthy and diseased tissue.

(96) Embodiments are also contemplated wherein one or more exogenous contrast agents may be used to analyse in vivo, ex vivo or in vitro tissue samples, biological matter, organic matter (including plastics), one or more bacterial colonies or one or more fungal colonies. According to an embodiment one or more exogenous fluorescence contrast agents may be provided or added to the tissue in order to augment endogenous contrast.

(97) The one or more contrast agents may comprise one or more fluorescent contrast agents.

(98) The one or more contrast agents may comprise one or more visible dyes.

(99) The one or more contrast agents may comprise one or more radiocontrast agents.

(100) The one or more contrast agents may comprise one or more optical, near infrared (“NIR”), fluorescent, autofluorescent or diagnostic contrast agents.

(101) According to various embodiments the one or more contrast agents may be selected from the group consisting of: (i) indocyanine green (“ICG”) and derivatives or conjugates of indocyanine green including indotricarbocyanine; (ii) diethylthiatricarbocyanine iodide (“DTTCI”) and derivatives or conjugates of diethylthiatricarbocyanine iodide; (iii) rhodamine B and derivatives or conjugates of rhodamine B; (iv) photodynamic therapy (“PDT”) agents including hexylpyropheophorbide (“HPPH”); (v) a cyanine dye including Cy 5.5 dyes; and (vi) bifunctional contrast agents.

(102) Indocyanine green (“ICG”) is of particular interest since it has FDA approval for systemic administration. Indocyanine is excited at about 780 nm and emits at 830 nm. Indocyanine green will dissolve in blood and will bind to proteins such as albumin and lipoproteins. ICG is a nonspecific agent and is cleared rapidly from the blood. However, ICG tends to collect in regions of dense vascularity through extravascation. ICG may be administered to a patient at a dose of 0.2 mg/kg intravenously. Derivatives and conjugates of ICG may also be used.

(103) Various embodiments are contemplated wherein ICG is excited using a 780 nm laser and fluorescent spectra at 830 nm are detected using a gain modulated image intensified charge coupled camera (ICCD).

(104) Other embodiments are contemplated wherein magnetic nanoparticles (“MNPs”) may be used as a contrast agent. The magnetic nanoparticles may comprise ferromagnetic iron oxide i.e. magnetite (Fe.sub.3O.sub.4) or maghemite (γ-Fe.sub.2O.sub.3) having a diameter in the range 1-100 nm. According to an embodiment the nanoparticles may have a diameter in the range 1-10, 10-20, 20-30, 30-40, 40-50, 50-60, 60-70, 70-80, 80-90 or 90-100 nm. In particular, various embodiments are contemplated wherein nanoparticles having a core diameter in the range of 5-15 nm may be used as contrast agents. In particular, as the size of the nanoparticles is reduced then the characteristics of the nanoparticles changes from having multi-domain ferromagnetic characteristics to having single domain characteristics and finally to having superparamagnetic characteristics. In particular, small nanoparticles having a diameter in the range 5-15 nm exhibit superparamagnetic properties having no hysteresis losses and will generate heat as a result of relaxational losses, mainly Néel relaxation loss. The inherent ferromagnetic properties of magnetic nanoparticles provides contrast enhancement with magnetic resonance (“MR”) imaging. For example, accumulation of magnetic nanoparticles in brain tumours appears as a hypointensity on T2-weighted imaging including gradient echo imaging.

(105) Magnetic nanoparticles may also be functionalised to target cancer cells thereby enabling cancerous tissue to be identified by magnetic resonance imaging.

(106) According to an embodiment ultrasmall superparamagnetic iron oxide nanoparticles (“USPIONPs”) may be used.

(107) In addition to using nanoparticles to accumulate within cancerous tissue, according to further embodiments the nanoparticles may be heated by applying a magnetic field and in particular an alternating magnetic field (“AMF”) which produces heat via relaxational loss via the Brownian Néel relaxation process or by hysteresis loss. As a result, potentially cancerous tissue can be identified on the basis of having an elevated or hyperthermic temperature relative to surrounding normal healthy tissue. Accordingly, thermal detection techniques in conjunction with the heating of nanoparticles which have accumulated in cancerous tissue may be used to visualise, image or target potentially cancerous tissue.

(108) Further embodiments are contemplated wherein nanoparticles which have accumulated in cancerous tissue may be heated up to temperatures >40° C. in order to selectively target and kill cancerous cells. For example, heating cancerous cells to a temperature around 45° C. can cause cancer cells to undergo apoptosis or necrosis. Furthermore, locally heating cancerous cells can increase the blood flow to the cancerous cells which can, for example, result in an improved delivery of chemotherapeutic agents to the cancerous cells. Also, cancer cells are more heat sensitive than normal tissue and so heat can be selectively applied to cancer cells in order to kill cancer cells without damaging surrounding normal or healthy tissue.

(109) According to an embodiment the nanoparticles may comprise a polysiloxane matrix (Si) wherein chelating species such as diethylene triamine pentaacetic acid (DTPA) at the surface of the particles allows the complexation of metallic elements such as gadolinium (Gd), silicon (Si), calcium (Ca) and iron (Fe).

(110) According to other embodiments the nanoparticles may be heated by radiofrequency capacitive heating wherein, for example, an alternating electrical current at 8 MHz may be applied and the temperature of tissues located between the electrodes increases. Magnetite cationic liposomes (MCLs) may be used and when injected into cancer cells the cancerous tissue may reach a temperature which is 2-3° C. above that of healthy tissue.

(111) Other embodiments are contemplated wherein antibodies containing a ferromagnetic component may be used as a contrast agent.

(112) The one or more contrast agents may be exogenous or endogenous to the target.

(113) As is well known, fluorophores may be activated to an excited state by absorbing a photon and may then relax to a ground state in a non-radiative manner. Alternatively, the fluorophore may relax to the ground state in a radiative (fluorescence) manner. The fluorescence lifetime T is equivalent to the mean time that a fluorophores remains in its activated state and the quantum efficiency is the proportion of relaxations which occur radiatively.

(114) Other mechanisms are known wherein the excited state can undergo intersystem crossing to an intermediate excited state wherein the spin state of the electron is flipped and the relaxation of the intermediate excited state is forbidden until the electron spin is reversed. The lifetimes of the intermediate excited state may be of the order of microseconds to milliseconds and are termed phosphorescence.

(115) Fluorescence radiative decay can be affected by pH, oxygenation, free ion concentrations, glucose and other analytes. Fluorescence can therefore provide an optical imaging ability which is not otherwise directly detectable.

(116) According to an embodiment the fluorescence spectra of tissue may be analysed in order to determine the pH, oxygenation level or quantum efficiency of the tissue.

(117) Other embodiments are contemplated wherein gamma ray imaging may be performed and optionally a technetium-99 sulfur colloid may be injected into the target tissue for analysis.

(118) According to various embodiments gold nanoparticles (“Au NPs” or “GNPs”) may be used as contrast agents. Gold nanoparticles may be formed by a laser ablation method wherein a gold target in water is subjected to pulsed laser irradiation. Colloidal gold can also be prepared by citrate reduction. Various other physical methods of producing gold nanoparticles are known including inert gas condensation, thermolysis of gold(I) complex, radiolysis of gold salts, photochemistry and sonochemistry. Chemical methods of producing gold nanoparticles are known including emulsification, reduction of gold ions in the presence of a disperant, seed-mediated growth, use of reverse micelles and phase transfer reactions. Gold nanoparticles may also be biosynthesised by certain types of fungi including Fusarium oxysporum, Verticillium sp. and Colletotrichum sp. Gold nanoparticles have also been synthesized within HEK-293, HeLa, SiHa and SKNSH cells.

(119) Gold nanoparticles may be readily functionalised generally through thiol linkages to provide functionalised gold nanoparticles (fGNPs) The surface of gold nanoparticles may be functionalised with e.g. cyclodextrin as a drug pocket having hydrophobic cavities, antibodies as a targeting moiety and poly(ethleneglycol) (PEG) as an anti-fouling shell. Anti-cancer drugs may be encapsulated into the hydrophobic cavity of the cyclodextrin and the gold nanoparticles may therefore be used as a drug delivery system (DDS).

(120) According to various embodiments gold nanoparticles and in particular functionalised gold nanoparticles as described above may be used as contrast agents.

(121) Gold nanoparticles cause local heating when irradiated with light (800-1200 nm) and hence gold nanoparticles may be used in the photothermal destruction of tumours according to various embodiments.

(122) Plasmonic gold nanoparticles may be used for cancer diagnosis and photothermal therapy. Surface plasmon resonance (“SPR”) leads to strong electromagnetic fields on the surface of gold nanoparticles which enhances all radiative properties such as absorption and scattering. In particular, Raman scattering is enhanced. Additionally, strongly absorbed light may be quickly converted to heat via a series of nonradiative processes.

(123) Gold nanoparticles can be optically tuned by shape and structure and for example gold nanorods having different optical properties to gold nanospheres can be produced. The aspect ratio can be precisely controlled by changing experimental parameters in a seed-mediation growth method.

(124) Gold nanoshells (comprising a silica core around 100 nm with a thin shell of gold a few nanometers thick) and gold nanocages may also be produced. Gold nanospheres, nanorods, nanostars and nanoshells may be used as contrast agents according to various embodiments.

(125) According to an embodiment gold nanoparticles may be used for cancer imaging. It is known that gold nanoparticles scatter strongly and the scattering properties depend upon the size, shape and structure of the nanoparticles. According to an embodiment gold nanoparticles having a diameter 30-100 nm may be used. Such nanoparticles scatter intensely and can be detected using a microscope under dark field illumination conditions. The gold nanoparticles may be conjugated with, for example, anti-epidermal growth factor receptors (anti-EGFR) antibodies (or other antibodies) to recognise the EGFR proteins (or other proteins) of cancer cells and tissues. The regular or well organised scattering pattern of nanoparticles bound to cancer cells can be readily distinguished from the random distribution of nanoparticles around healthy cells and this difference in scattering pattern may be utilised according to various embodiments.

(126) The nanoparticles may be excited by white light from a halogen lamp.

(127) According to an embodiment, functionalised gold nanoparticles may be distributed across the surface of a target (such as biological in vivo or ex vivo tissue) and the gold nanoparticles may preferentially bind to cancerous cells. As a result, cancerous regions of tissue can be identified by illuminating the target and either analysing the scattering pattern or measuring the scattered intensity of light.

(128) For example, gold nanoparticles may have a strong surface plasmon resonance (“SPR”) around 540 nm on the cell monolayer with the result that the nanoparticles scatter strongly in the green to yellow range of the visible spectrum. Similarly, gold nanorods may be constructed which exhibit a strong surface plasmon resonance (“SPR”) around 800 nm giving an intense red colour.

(129) Accordingly, gold nanoparticles may be used as imaging, physical or chemical contrast agents according to various embodiments.

(130) Surface plasmon resonance (“SPR”) effects also enhance the Raman scattering of adjacent molecules because the Raman intensity is directly proportional to the square of the field intensity imposed on the molecules. This phenomenon is termed as surface enhanced Raman scattering (“SERS”).

(131) According to an embodiment gold nanoparticles may be utilised in order to enhance Raman scattering of adjacent molecules. The gold nanoparticles may be either symmetric or asymmetric. According to an embodiment the gold nanoparticles may be asymmetric (e.g. nanorods) since asymmetric nanoparticles provide a larger Raman enhancement due to the lightening rod effect.

(132) One particular advantage of using gold nanoparticles and surface enhance Raman scattering is that this approach greatly enhances detection sensitivity and decreases signal acquisition time.

(133) According to another embodiment a Raman tag may be used as a spectroscopic imaging probe. The Raman tag may comprise organic dye molecules with aromatic structures which have relatively high Raman cross sections. Its fluorescence is quenched when they are adsorbed on to metallic nanoparticles and thus Raman signals are able to be detected.

(134) The Raman tags may be physically adsorbed or chemically conjugated with both Raman tag and cancer targeting ligands.

(135) According to other embodiments levan nanoparticles may be utilised for targeted cancer imaging. Levan is a biocompatible carbohydrate polymer that consists of β-D-fructofuranose attached by β-(2,6) linkages and is used in biomedical applications. According to an embodiment Indocyanine green (ICG) may be encapsulated in levan nanoparticles by self-assembly and the levan-ICG nanoparticles may be used for cancer imaging.

(136) Various embodiments are contemplated wherein a target which may comprise biological tissue may be subjected to Raman or laser imaging (transmission or fluorescence) using nanoparticles such as gold nanoparticles are described above as contrast agents. One or more regions of interest may then be identified and the regions of interest may then be subjected to analysis using a first device to generate aerosol, smoke or vapour. The first device may comprise an ambient ionisation ion source such as a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source.

(137) Other embodiments are contemplated wherein chemical tags (such as luminescent tags) may be used in combination with an ambient ionisation ion source such as a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source. For example, according to an embodiment a luminescent imaging, physical or chemical contrast agent may be modified with the inclusion of a ligand that is readily ionisable by an ambient ionisation ion source such as a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source. The contrast agents, tags or nanoparticles may be detected by mass spectrometry if an undesired (or desired) target or undesired (or desired) tissue is ablated. The tagging chemical may have fluorescent, magnetic, chemical, physical or other imaging properties and a part of the molecule may be arranged so as to ionise well for mass spectrometry analysis. For example, as described above, Indocyanine green (ICG) may be encapsulated into levan nanoparticles or more generally in functionalised nanoshells which are functionalised so as to target cancerous tissue or other undesired target material. Embodiments are contemplated wherein ICG (or other chemicals) which may be encapsulated within functionalised nanoparticles or nanoshells (which may be functionalised so as to target cancerous tissue) may be detected by mass spectrometry. Other embodiments are contemplated wherein one or more different markers other than ICG may be encapsulated into nanoparticles which target cancerous tissue. These one or more markers may then identified by mass spectrometry and a determination may be made that the tissue which is currently being analysed comprises cancerous tissue or otherwise comprises undesired target material.

(138) Embodiments are contemplated wherein target experiments may be performed wherein a target is subjected to mass spectrometry analysis with a view to seeking to identify portions of target or tissue which include (or conversely do not include) a contrast agent, chemical tag, marker or nanoparticle wherein the contrast agent, chemical tag, marker or nanoparticle has been functionalised so as to target a particular target e.g. cancerous tissue. According to various embodiment identifying the presence of the contrast agent, chemical tag, marker or nanoparticle thereby enables a determination to be made that the target or tissue which is currently being analysed comprises cancerous tissue (or otherwise desired or undesired target material).

(139) According to an embodiment the step of using physical or other non-mass spectrometric data to determine one or more regions of interest may comprise the use of targeted nanoparticles containing or comprising a metal which is intended to change the electrical impedance of a targeted tissue type. As detailed above, metallic nanoparticles may be functionalised so that they adhere to specific types of tissue or other surfaces. One or more regions of interest of a target may be identified by determining one or more regions of a target (e.g., tissue) having a different impedance to other target areas due to the presence of targeted or functionalised nanoparticles which preferentially adhere to certain specific target areas (e.g., cancerous tissue).

(140) Photothermal Therapy (PTT)

(141) Gold nanoparticles absorb light much more strongly than organic dye molecules. Nearly 100% adsorbed light is converted to heat via nonradiative properties. Accordingly, gold nanoparticles may be used as photothermal contrast agents for photothermal therapy wherein photon energy is converted to heat sufficient to induce cellular damage via thermal effects such as hyperthermia, coagulation and evaporation.

(142) Photothermal therapy may be performed using spherical gold nanoparticles in conjunction with either pulsed or continuous wave lasers.

(143) Nanosecond pulsed lasers may be used in conjunction with PTT to provide highly selective and localised damage to cancer cells without affecting neighbouring healthy cells which may be only a few nanometers to tens of micrometers away.

(144) For in vivo therapy of tumours under the skin or deeply seated tumours within tissue near infrared (NIR) light may be used because of its deep penetration ability due to minimal absorption by hemoglobin and water molecules.

(145) According to an embodiment PEGylated gold nanoshells may used in conjunction with an ambient ionisation ion source since the absorption of gold nanoshells can be tuned to the NIR region. A continuous wave (cw) diode laser e.g. emitting at 820 nm with an irradiance of e.g. 35 W/cm.sup.2 for 4 mins may be used to illuminate the gold nanoshells in order to cause cancer cell death of targeted cells.

(146) The gold nanoshells may according to various embodiments be injected into the blood stream of a patient or spread upon the surface of a target or tissue sample.

(147) Other embodiments are contemplated wherein PTT may be performed using gold nanorods. According to an embodiment a cw Ti:Saphhire laser emitting at 800 nm may be used in conjunction with gold nanorods.

(148) According to an embodiment the target may be illuminated with either linearly polarized light or circularly polarized light. Illuminating gold nanorods with circularly polarized light is particularly beneficial as the light absorption by gold nanorods is enhanced leading to an ultra-low energy threshold for cancer killing.

(149) It has been determined that a laser fluence of 30 J/cm.sup.2 can result in an increase in temperature of the cells by about 10° C. which is sufficient to induce heat-stress cell death. Accordingly, a laser fluence of 30 J/cm.sup.2 may be utilised according to various embodiments.

(150) According to an embodiment gold nanorods may be conjugated to methoxy-poly (ethylene-glycol)-thiol having an average MW 5,000 (mPEG-SH-5000) and may be injected into a patient either intravenously and/or subcutaneously. Tumours or cancerous cells can be identified using transmission imaging of a NIR laser with a camera due to the NIR light absorption by the nanorods in the tumour.

(151) Intraoperative Computer Tomography (“CT”), Intraoperative Ultrasound and Surgical Guidance Systems

(152) According to an embodiment a mobile CT device may be used to acquire intraoperative images during a procedure such as a tumour resection.

(153) According to another embodiment an intra-operative 3D ultrasound (“3D-iUS”) guidance system may be used.

(154) Various embodiments are contemplated wherein an ambient ionisation probe, surgical device or diagnostic device may be manually, automatically or robotically guided or directed using a guidance system.

(155) The guidance system may comprise a magnetic resonance imaging (“MRI”) guidance system or an ultrasound or ultrasonic guidance system such as an intraoperative ultrasound (“IOUS”) guidance system.

(156) Other embodiments are contemplated wherein the guidance system may comprise a guidewire localization (“GWL”), a wire localization (“WL”) or a wire-guided localization (“WGL”) device.

(157) According to another embodiment the guidance system may comprise a radioguided occult lesion localization (“ROLL”) guidance system.

(158) A yet further embodiment is contemplated wherein a nuclear radiotracer is injected or otherwise introduced into one or more regions of the target (e.g. tissue). The nuclear radiotracer may comprise .sup.99mTc.

(159) According to an embodiment a gamma ray detection probe may be used to detect gamma rays emitted by the decay of the nuclear radiotracer thereby enabling the target region to be located and/or visualised.

(160) Other guidance system may be used including radioactive seed localization (“RSL”) systems. For example, one or more radioactive seeds may be inserted or implanted into the target. Various different forms of radioactive seeds may be used including radioactive seeds having a titanium shell which optionally houses .sup.125I. A gamma ray detection probe may be used to detect gamma rays emitted by the decay of the radioactive seed thereby enabling a target region of interest to be located and/or visualised.

(161) The guidance system may comprise a mammography guidance system.

(162) According to other embodiments the guidance system may comprise a computed tomography (“CT”) guidance system, a positron emission tomography (“PET”) guidance system or a radiographic guidance system.

(163) According to other embodiments the guidance system may comprise a magnetic or magnetism sensing guidance system or a superconducting quantum interference device (“SQUID”) guidance system for detecting magnetic particles or magnetic nanoparticles or a guidance system for detecting nanoparticles.

(164) Compton X-Ray Scattering

(165) Other embodiments are contemplated wherein an X-ray scattering device may be used to obtain image or other data.

(166) The method may comprise directing X-rays onto one or more regions of the target and measuring the wavelength or frequency of scattered X-rays from the target.

(167) The X-ray scattering device may comprise a Compton X-ray scattering device which is arranged to measure scattered signals due to incoherent X-ray scattering. The X-rays may have an energy ≥50 keV.

(168) According to another embodiment the X-ray scattering device may comprise a Rayleigh X-ray scattering device which is arranged to measure scattered signals due to coherent X-ray scattering. The X-rays may have an energy ≤30 keV.

(169) RF or Microwave Sensors

(170) According to an embodiment one or more RF or microwave sensors or devices may be used to obtain image or other data from one or more regions of a target.

(171) FIG. 3 shows an RF or microwave sensor or device 30 which may be used to acquire image data according to an embodiment. The RF or microwave sensor 30 may comprise a coaxial line probe 31 such that a microwave load 32 is directed into a target 33 which may comprise in vivo tissue such as lung or breast tissue. The microwave load 32 results in an electrical field 34 which penetrates a short distance into the target 33. A reflected signal 35 is captured by the coaxial line probe 31 and is detected by the RF or microwave sensor or device 30. One or more physical or image properties of the target or target tissue 33 may then be determined.

(172) In particular, the RF sensor or device 30 may utilise microwaves at RF frequencies. In the case of breast tissue, normal breast tissue is substantially translucent to microwaves and there is a high dielectric contrast between malignant breast tumours and normal breast tissue. As a result, according to an embodiment a RF or microwave sensor 30 may be used to detect regions of e.g. breast tissue which are potentially cancerous. As a result, the image data obtained by the RF or microwave sensor 30 may be used to direct a surgeon to specific areas of breast tissue which may then be subjected to a surgical procedure using an ambient ionisation ion source such as a rapid evaporative ionisation mass spectrometry (“REIMS”) ion source. In particular, the image data obtained by the RF or microwave sensor 30 may be used in conjunction with the ambient ionisation ion source to help determine the margins or bounds of potentially cancerous tissue with a high level of precision.

(173) It will be appreciated that being able to determine to a high level of certainty that all undesired (e.g. potentially cancerous) tissue has been removed from a surgical site without also unnecessarily removing healthy tissue can have a significant positive impact upon potential surgical outcomes.

(174) A pulsed confocal technique may be used together with time-gating in order to enhance the detection of tumours whilst suppressing the effects of tissue heterogeneity and absorption.

(175) It is known to perform X-ray mammograms. However, there are concerns that repeated X-ray mammograms can result in an increased risk of cancer.

(176) Therefore, one advantage of utilising RF or microwave technology according to various embodiments is that it avoids subjecting a patient to any increased risk (whether perceived or real) of cancer and also can be performed in a more relaxing and flexible environment which puts the patient at ease.

(177) It is known that microwaves interact with biological tissue according to the water content of the tissue and that this interaction is quite different to the interaction of X-rays with biological tissue. In particular, using a microwave sensor or device 30 according to an embodiment can result in an order of magnitude improvement in terms of contrast compared to using either X-rays or ultrasound.

(178) According to various embodiments the dielectric permittivity of a target which may comprise a specific type of tissue such as healthy in vivo breast or lung tissue may be determined in advance or may be determined during an initial procedure. The presence or absence of fluid (e.g., water) at the target or tissue 33 will impact upon the dielectric polarization. The microwave reflection coefficient will depend upon the dielectric properties of the target 33 and hence as a result the intensity of the reflected microwave signal will depend upon the fluid or water content of the tissue 33 which is being probed. As a result, the fluid or water content of the target or tissue 33 of interest can be determined and in particular areas of the target or tissue 33 which have a suspect fluid or water content can be identified.

(179) In the case of lung tissue, for example, microwave reflectrometry measurements of the lung tissue enable the total tissue water content of the lung tissue to be determined. This can be useful in determining whether or not potentially cancerous lung tissue may be present. For example, healthy lung tissue may have a first water content (e.g., 77%) and cancerous lung tissue may have a second (higher) water content (e.g., 85%).

(180) Furthermore, this approach can be useful in identifying the margins of a tumour in lung tissue. For example, the margins of the tumour may have a third (intermediate) water content (e.g., 82%) which is intermediate between the first water content of healthy tissue (77%) and the second water content of cancerous tissue (85%).

(181) According to embodiments a microwave generator may be used to generate the microwave signal and the frequency of the signal emitted by the microwave generator may be varied from e.g. 5 MHz to e.g. 3 GHz as desired.

(182) Embodiments are contemplated wherein the RF or microwave sensor 30 may be set to generate microwaves at a fixed frequency. Other embodiments are contemplated wherein the RF or microwave sensor or device 30 may be arranged to vary the frequency of microwaves which are output by the microwave sensor or device 30. For example, a target or tissue 33 may be probed by scanning the surface with a range of difference microwave frequencies and then determining the response or profile of the intensity of reflected microwaves as a function of the input frequency of the microwaves.

(183) Malignant tumours may have significantly different dielectric constants to that of normal tissue and the high dielectric contrast may cause malignant tumours to have significantly greater microwave scattering cross sections compared to normal tissue.

(184) According to an embodiment microwaves having a frequency in the range 4-10 GHz may be focused and pulsed into tissue 33 (e.g. human breast). Microwave energy will be backscattered upon encountering a tumour since the tumour has a significantly greater dielectric permittivity and conductivity compared to normal tissue. Backscattered energy may be collected or otherwise detected by a sensor or detector. A three dimensional image of the tumour can thus be constructed.

(185) It is known that high water content tissue will have a different permittivity response as a function of frequency compared to low water content tissue.

(186) The relative dielectric permittivity c and conductivity a of high water content tissue (such as muscle or malignant tumours) is about an order of magnitude higher than lower water content tissue (such as fat or normal breast tissue). This contrast between high and low water content tissue persists over a wide range of microwave frequencies and enables diseased tissue to be differentiated from healthy tissue.

(187) Analysing Sample Spectra

(188) A list of analysis techniques which are intended to fall within the scope of the present invention are given in the following table:

(189) TABLE-US-00002 Analysis Techniques Univariate Analysis Multivariate Analysis Principal Component Analysis (PCA) Linear Discriminant Analysis (LDA) Maximum Margin Criteria (MMC) Library Based Analysis Soft Independent Modelling Of Class Analogy (SIMCA) Factor Analysis (FA) Recursive Partitioning (Decision Trees) Random Forests Independent Component Analysis (ICA) Partial Least Squares Discriminant Analysis (PLS-DA) Orthogonal (Partial Least Squares) Projections To Latent Structures (OPLS) OPLS Discriminant Analysis (OPLS-DA) Support Vector Machines (SVM) (Artificial) Neural Networks Multilayer Perceptron Radial Basis Function (RBF) Networks Bayesian Analysis Cluster Analysis Kernelized Methods Subspace Discriminant Analysis K-Nearest Neighbours (KNN) Quadratic Discriminant Analysis (QDA) Probabilistic Principal Component Analysis (PPCA) Non negative matrix factorisation K-means factorisation Fuzzy c-means factorisation Discriminant Analysis (DA)

(190) Combinations of the foregoing analysis approaches can also be used, such as PCA-LDA, PCA-MMC, PLS-LDA, etc.

(191) Analysing the sample spectra can comprise unsupervised analysis for dimensionality reduction followed by supervised analysis for classification.

(192) By way of example, a number of different analysis techniques will now be described in more detail.

(193) Multivariate Analysis—Developing a Model for Classification

(194) By way of example, a method of building a classification model using multivariate analysis of plural reference sample spectra will now be described.

(195) FIG. 4 shows a method 1500 of building a classification model using multivariate analysis. In this example, the method comprises a step 1502 of obtaining plural sets of intensity values for reference sample spectra. The method then comprises a step 1504 of unsupervised principal component analysis (PCA) followed by a step 1506 of supervised linear discriminant analysis (LDA). This approach may be referred to herein as PCA-LDA. Other multivariate analysis approaches may be used, such as PCA-MMC. The PCA-LDA model is then output, for example to storage, in step 1508.

(196) The multivariate analysis such as this can provide a classification model that allows an aerosol, smoke or vapour sample to be classified using one or more sample spectra obtained from the aerosol, smoke or vapour sample. The multivariate analysis will now be described in more detail with reference to a simple example.

(197) FIG. 5 shows a set of reference sample spectra obtained from two classes of known reference samples. The classes may be any one or more of the classes of target described herein. However, for simplicity, in this example the two classes will be referred as a left-hand class and a right-hand class.

(198) Each of the reference sample spectra has been pre-processed in order to derive a set of three reference peak-intensity values for respective mass to charge ratios in that reference sample spectrum. Although only three reference peak-intensity values are shown, it will be appreciated that many more reference peak-intensity values (e.g., ˜100 reference peak-intensity values) may be derived for a corresponding number of mass to charge ratios in each of the reference sample spectra. In other embodiments, the reference peak-intensity values may correspond to: masses; mass to charge ratios; ion mobilities (drift times); and/or operational parameters.

(199) FIG. 6 shows a multivariate space having three dimensions defined by intensity axes. Each of the dimensions or intensity axes corresponds to the peak-intensity at a particular mass to charge ratio. Again, it will be appreciated that there may be many more dimensions or intensity axes (e.g., ˜100 dimensions or intensity axes) in the multivariate space. The multivariate space comprises plural reference points, with each reference point corresponding to a reference sample spectrum, i.e., the peak-intensity values of each reference sample spectrum provide the co-ordinates for the reference points in the multivariate space.

(200) The set of reference sample spectra may be represented by a reference matrix D having rows associated with respective reference sample spectra, columns associated with respective mass to charge ratios, and the elements of the matrix being the peak-intensity values for the respective mass to charge ratios of the respective reference sample spectra.

(201) In many cases, the large number of dimensions in the multivariate space and matrix D can make it difficult to group the reference sample spectra into classes. PCA may accordingly be carried out on the matrix D in order to calculate a PCA model that defines a PCA space having a reduced number of one or more dimensions defined by principal component axes. The principal components may be selected to be those that comprise or “explain” the largest variance in the matrix D and that cumulatively explain a threshold amount of the variance in the matrix D.

(202) FIG. 7 shows how the cumulative variance may increase as a function of the number n of principal components in the PCA model. The threshold amount of the variance may be selected as desired.

(203) The PCA model may be calculated from the matrix D using a non-linear iterative partial least squares (NIPALS) algorithm or singular value decomposition, the details of which are known to the skilled person and so will not be described herein in detail. Other methods of calculating the PCA model may be used.

(204) The resultant PCA model may be defined by a PCA scores matrix S and a PCA loadings matrix L. The PCA may also produce an error matrix E, which contains the variance not explained by the PCA model. The relationship between D, S, L and E may be:
D=SL.sup.T+E  (1)

(205) FIG. 8 shows the resultant PCA space for the reference sample spectra of FIGS. 5 and 6. In this example, the PCA model has two principal components PC.sub.0 and PC.sub.1 and the PCA space therefore has two dimensions defined by two principal component axes. However, a lesser or greater number of principal components may be included in the PCA model as desired. It is generally desired that the number of principal components is at least one less than the number of dimensions in the multivariate space.

(206) The PCA space comprises plural transformed reference points or PCA scores, with each transformed reference point or PCA score corresponding to a reference sample spectrum of FIG. 5 and therefore to a reference point of FIG. 6.

(207) As is shown in FIG. 8, the reduced dimensionality of the PCA space makes it easier to group the reference sample spectra into the two classes. Any outliers may also be identified and removed from the classification model at this stage.

(208) Further supervised multivariate analysis, such as multi-class LDA or maximum margin criteria (MMC), in the PCA space may then be performed so as to define classes and, optionally, further reduce the dimensionality.

(209) As will be appreciated by the skilled person, multi-class LDA seeks to maximise the ratio of the variance between classes to the variance within classes (i.e., so as to give the largest possible distance between the most compact classes possible). The details of LDA are known to the skilled person and so will not be described herein in detail.

(210) The resultant PCA-LDA model may be defined by a transformation matrix U, which may be derived from the PCA scores matrix S and class assignments for each of the transformed spectra contained therein by solving a generalised eigenvalue problem.

(211) The transformation of the scores S from the original PCA space into the new LDA space may then be given by:
Z=SU  (2)
wherein the matrix Z contains the scores transformed into the LDA space.

(212) FIG. 9 shows a PCA-LDA space having a single dimension or axis, wherein the LDA is performed in the PCA space of FIG. 8. As is shown in FIG. 9, the LDA space comprises plural further transformed reference points or PCA-LDA scores, with each further transformed reference point corresponding to a transformed reference point or PCA score of FIG. 8.

(213) In this example, the further reduced dimensionality of the PCA-LDA space makes it even easier to group the reference sample spectra into the two classes. Each class in the PCA-LDA model may be defined by its transformed class average and covariance matrix or one or more hyperplanes (including points, lines, planes or higher order hyperplanes) or hypersurfaces or Voronoi cells in the PCA-LDA space.

(214) The PCA loadings matrix L, the LDA matrix U and transformed class averages and covariance matrices or hyperplanes or hypersurfaces or Voronoi cells may be output to a database for later use in classifying an aerosol, smoke or vapour sample.

(215) The transformed covariance matrix in the LDA space V′.sub.g for class g may be given by:
V′.sub.g=U.sup.TV.sub.gU  (3)
wherein V.sub.g are the class covariance matrices in the PCA space.

(216) The transformed class average position z.sub.g for class g may be given by:
s.sub.gU=z.sub.g  (4)
wherein s.sub.g is the class average position in the PCA space.
Multivariate Analysis—Using a Model for Classification

(217) By way of example, a method of using a classification model to classify an aerosol, smoke or vapour sample will now be described.

(218) FIG. 10 shows a method 2100 of using a classification model. In this example, the method comprises a step 2102 of obtaining a set of intensity values for a sample spectrum. The method then comprises a step 2104 of projecting the set of intensity values for the sample spectrum into PCA-LDA model space. Other classification model spaces may be used, such as PCA-MMC. The sample spectrum is then classified at step 2106 based on the project position and the classification is then output in step 2108.

(219) Classification of an aerosol, smoke or vapour sample will now be described in more detail with reference to the simple PCA-LDA model described above.

(220) FIG. 11 shows a sample spectrum obtained from an unknown aerosol, smoke or vapour sample. The sample spectrum has been pre-processed in order to derive a set of three sample peak-intensity values for respective mass to charge ratios. As mentioned above, although only three sample peak-intensity values are shown, it will be appreciated that many more sample peak-intensity values (e.g., ˜100 sample peak-intensity values) may be derived at many more corresponding mass to charge ratios for the sample spectrum. Also, as mentioned above, in other embodiments, the sample peak-intensity values may correspond to: masses; mass to charge ratios; ion mobilities (drift times); and/or operational parameters.

(221) The sample spectrum may be represented by a sample vector d.sub.x, with the elements of the vector being the peak-intensity values for the respective mass to charge ratios. A transformed PCA vector s.sub.X for the sample spectrum can be obtained as follows:
d.sub.xL=s.sub.x  (5)

(222) Then, a transformed PCA-LDA vector z.sub.X for the sample spectrum can be obtained as follows:
s.sub.xU=z.sub.x  (6)

(223) FIG. 12 again shows the PCA-LDA space of FIG. 9. However, the PCA-LDA space of FIG. 12 further comprises the projected sample point, corresponding to the transformed PCA-LDA vector z.sub.x, derived from the peak intensity values of the sample spectrum of FIG. 11.

(224) In this example, the projected sample point is to one side of a hyperplane between the classes that relates to the right-hand class, and so the aerosol, smoke or vapour sample may be classified as belonging to the right-hand class.

(225) Alternatively, the Mahalanobis distance from the class centres in the LDA space may be used, where the Mahalanobis distance of the point z.sub.x from the centre of class g may be given by the square root of:
(z.sub.x−z.sub.g).sup.T(V′.sub.g).sup.−1(z.sub.x−z.sub.g)  (7)
and the data vector d.sub.x may be assigned to the class for which this distance is smallest.

(226) In addition, treating each class as a multivariate Gaussian, a probability of membership of the data vector to each class may be calculated.

(227) Library Based Analysis—Developing a Library for Classification

(228) By way of example, a method of building a classification library using plural input reference sample spectra will now be described.

(229) FIG. 13 shows a method 2400 of building a classification library. In this example, the method comprises a step 2402 of obtaining plural input reference sample spectra and a step 2404 of deriving metadata from the plural input reference sample spectra for each class of sample. The method then comprises a step 2406 of storing the metadata for each class of sample as a separate library entry. The classification library is then output, for example to electronic storage, in step 2408.

(230) A classification library such as this allows an aerosol, smoke or vapour sample to be classified using one or more sample spectra obtained from the aerosol, smoke or vapour sample. The library based analysis will now be described in more detail with reference to an example.

(231) In this example, each entry in the classification library is created from plural pre-processed reference sample spectra that are representative of a class. In this example, the reference sample spectra for a class are pre-processed according to the following procedure:

(232) First, a re-binning process is performed. In this embodiment, the data are resampled onto a logarithmic grid with abscissae:

(233) $\begin{array}{cc}{x}_i=.Math.N_{\mathrm{chan}}\log \frac{m}{M_{\min }}\text{/}\log \frac{M_{\max }}{M_{\min }}.Math.& \left(8\right)\end{array}$
wherein N.sub.chan is a selected value and └x┘ denotes the nearest integer below x. In one example, N.sub.chan is 2.sup.12 or 4096.

(234) Then, a background subtraction process is performed. In this embodiment, a cubic spline with k knots is then constructed such that p % of the data between each pair of knots lies below the curve. This curve is then subtracted from the data. In one example, k is 32. In one example, p is 5. A constant value corresponding to the q % quantile of the intensity subtracted data is then subtracted from each intensity. Positive and negative values are retained. In one example, q is 45.

(235) Then, a normalisation process is performed. In this embodiment, the data are normalised to have mean y.sub.i. In one example, y.sub.i=1.

(236) An entry in the library then consists of metadata in the form of a median spectrum value μ.sub.i and a deviation value D.sub.i for each of the N.sub.chan points in the spectrum.

(237) The likelihood for the i'th channel is given by:

(238) $\begin{array}{cc}\mathrm{Pr}\left(y_i|{\mu }_i,D_i\right)=\frac{1}{D_i}\frac{C^{C-1/2}\Gamma \left(C\right)}{\sqrt{\pi }\Gamma \left(C-1\text{/}2\right)}\frac{1}{{\left(C+\frac{{\left(y_i-{\mu }_i\right)}^2}{D_i^2}\right)}^C}& \left(9\right)\end{array}$
where ½≤C<∞ and where Γ(C) is the gamma function.

(239) The above equation is a generalised Cauchy distribution which reduces to a standard Cauchy distribution for C=1 and becomes a Gaussian (normal) distribution as C.fwdarw.∞. The parameter D.sub.i controls the width of the distribution (in the Gaussian limit D.sub.i=σ.sub.i is simply the standard deviation) while the global value C controls the size of the tails.

(240) In one example, C is 3/2, which lies between Cauchy and Gaussian, so that the likelihood becomes:

(241) $\begin{array}{cc}\mathrm{Pr}\left(y_i|{\mu }_i,D_i\right)=\frac{3}{4}\frac{1}{D_i}\frac{1}{{\left(3\text{/}2+{\left(y_i-{\mu }_i\right)}^2\text{/}{D}_i^2\right)}^{3/2}}& \left(10\right)\end{array}$

(242) For each library entry, the parameters μ.sub.i are set to the median of the list of values in the i'th channel of the input reference sample spectra while the deviation D.sub.i is taken to be the interquartile range of these values divided by √2. This choice can ensure that the likelihood for the i'th channel has the same interquartile range as the input data, with the use of quantiles providing some protection against outlying data.

(243) Library Based Analysis—Using a Library for Classification

(244) By way of example, a method of using a classification library to classify an aerosol, smoke or vapour sample will now be described.

(245) FIG. 14 shows a method 2500 of using a classification library. In this example, the method comprises a step 2502 of obtaining a set of plural sample spectra. The method then comprises a step 2504 of calculating a probability or classification score for the set of plural sample spectra for each class of sample using metadata for the class entry in the classification library. The sample spectra are then classified at step 2506 and the classification is then output in step 2508.

(246) Classification of an aerosol, smoke or vapour sample will now be described in more detail with reference to the classification library described above.

(247) In this example, an unknown sample spectrum y is the median spectrum of a set of plural sample spectra. Taking the median spectrum y can protect against outlying data on a channel by channel basis.

(248) The likelihood L.sub.s for the input data given the library entry s is then given by:
L.sub.s=Pr(y|μ,D)=Π.sub.i=1.sup.N.sup.chanPr(y.sub.i|μ.sub.i,D.sub.i)  (11)
wherein μ.sub.i and D.sub.i are, respectively, the library median values and deviation values for channel i. The likelihoods L.sub.s may be calculated as log likelihoods for numerical safety.

(249) The likelihoods L.sub.s are then normalised over all candidate classes ‘s’ to give probabilities, assuming a uniform prior probability over the classes. The resulting probability for the class {tilde over (s)} is given by:

(250) $\begin{array}{cc}\mathrm{Pr}\left(\tilde{s}|y\right)=\frac{L_s^{\left(1/F\right)}}{\underset{s}{.Math.}{L}_s^{\left(1/F\right)}}& \left(12\right)\end{array}$

(251) The exponent (1/F) can soften the probabilities which may otherwise be too definitive. In one example, F=100. These probabilities may be expressed as percentages, e.g., in a user interface.

(252) Alternatively, RMS classification scores R.sub.s may be calculated using the same median sample values and derivation values from the library:

(253) $\begin{array}{cc}{R}_s\left(y,\mu ,D\right)=\sqrt{\frac{1}{N_{\mathrm{chan}}}\underset{i=1}{\overset{N_{\mathrm{chan}}}{.Math.}}\frac{{\left(y_i-{\mu }_i\right)}^2}{D_i^2}}& \left(13\right)\end{array}$

(254) Again, the scores R.sub.s are normalised over all candidate classes ‘s’.

(255) The aerosol, smoke or vapour sample may then be classified as belonging to the class having the highest probability and/or highest RMS classification score.

(256) Multivariate Analysis of Imaging Data

(257) Various further embodiments are contemplated wherein the imaging data may itself be subjected to multivariate analysis in order to assist, for example, in the identification of the target and/or to filter out outliers.

(258) Methods of Medical Treatment, Surgery and Diagnosis and Non-Medical Methods

(259) Various different embodiments are contemplated. According to some embodiments the methods disclosed above may be performed on in vivo, ex vivo or in vitro tissue. The tissue may comprise human or non-human animal tissue. Embodiments are contemplated wherein the target may comprise biological tissue, a bacterial or fungal colony or more generally an organic target such as a plastic).

(260) Various embodiments are contemplated wherein analyte ions generated by an ambient ionisation ion source are then subjected either to: (i) mass analysis by a mass analyser such as a quadrupole mass analyser or a Time of Flight mass analyser; (ii) ion mobility analysis (IMS) and/or differential ion mobility analysis (DMA) and/or Field Asymmetric Ion Mobility Spectrometry (FAIMS) analysis; and/or (iii) a combination of firstly (or vice versa) ion mobility analysis (IMS) and/or differential ion mobility analysis (DMA) and/or Field Asymmetric Ion Mobility Spectrometry (FAIMS) analysis followed by secondly (or vice versa) mass analysis by a mass analyser such as a quadrupole mass analyser or a Time of Flight mass analyser. Various embodiments also relate to an ion mobility spectrometer and/or mass analyser and a method of ion mobility spectrometry and/or method of mass analysis. Ion mobility analysis may be performed prior to mass to charge ratio analysis or vice versa.

(261) Various references are made in the present application to mass analysis, mass analysers, mass analysing, mass spectrometric data, mass spectrometers and other related terms referring to apparatus and methods for determining the mass or mass to charge of analyte ions. It should be understood that it is equally contemplated that the present invention may extend to ion mobility analysis, ion mobility analysers, ion mobility analysing, ion mobility data, ion mobility spectrometers, ion mobility separators and other related terms referring to apparatus and methods for determining the ion mobility, differential ion mobility, collision cross section or interaction cross section of analyte ions. Furthermore, it should also be understood that embodiments are contemplated wherein analyte ions may be subjected to a combination of both ion mobility analysis and mass analysis i.e. that both (a) the ion mobility, differential ion mobility, collision cross section or interaction cross section of analyte ions together with (b) the mass to charge of analyte ions is determined. Accordingly, hybrid ion mobility-mass spectrometry (IMS-MS) and mass spectrometry-ion mobility (MS-IMS) embodiments are contemplated wherein both the ion mobility and mass to charge ratio of analyte ions generated e.g. by an ambient ionisation ion source are determined. Ion mobility analysis may be performed prior to mass to charge ratio analysis or vice versa. Furthermore, it should be understood that embodiments are contemplated wherein references to mass spectrometric data and databases comprising mass spectrometric data should also be understood as encompassing ion mobility data and differential ion mobility data etc. and databases comprising ion mobility data and differential ion mobility data etc. (either in isolation or in combination with mass spectrometric data).

(262) Various surgical, therapeutic, medical treatment and diagnostic methods are contemplated.

(263) However, other embodiments are contemplated which relate to non-surgical and non-therapeutic methods of mass spectrometry which are not performed on in vivo tissue. Other related embodiments are contemplated which are performed in an extracorporeal manner such that they are performed outside of the human or animal body.

(264) Further embodiments are contemplated wherein the methods are performed on a non-living human or animal, for example, as part of an autopsy procedure.

(265) Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.