SYSTEM AND METHOD OF USING TEMPORAL MEASUREMENTS OF LOCALIZED RADIATION TO ESTIMATE THE MAGNITUDE, LOCATION, AND VOLUME OF RADIOACTIVE MATERIAL IN THE BODY

Abstract

A system and method for the measurement of radiation emitted from the body, for example, is presented. In one example, radiation sensors (e.g., gamma radiation sensors) may be used to measure activity proximate an injection site as a function of time. In some embodiments, one or more rangefinders may be employed to determine a size and/or position of a subject relative to the radiation sensors to better account for varying material densities within the system in estimating, for example, the amount of radioactive material in the tissue proximate the injection site. With an estimated function of radioactive material proximate the injection site as a function of time known, an estimated arterial input function may be determined, allowing for calculation of a correction factor that may be applied by a clinician during nuclear medical imaging. The magnitude, location, and volume of the radioactive source in the body may also be estimated.

Claims

1. A method for the ex vivo real-time determination over a period of time of one or more of the magnitude, location, and volume of radioactive material in the body by measuring radiation that decays in vivo emitted by a subject, the method comprising: (i) applying one or more ex vivo radiation measurement sensors proximate an area of interest on a patient; (ii) applying one or more rangefinders proximate an area of interest on a patient for determining a position of the subject relative to the one or more radiation measurement sensors; (iii) detecting radiation over a desired period of time and producing signal data associated with the desired period of time; (iii) amplifying the signal data using a signal amplifier in operable communication with the radiation measurement sensor, wherein the radiation measurement sensor has at least one sensor output for such amplified signal data, and outputting the amplified signal data; (iv) processing the amplified signal data using a computer processor in operative communication with a non-transient memory and the measurement sensor output by performing the steps of: (a) receiving the amplified signal data associated with the desired period of time; (b) comparing the amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes within a subject at the position determined by the one or more rangefinders; (c) determining one or more of a magnitude, location, and volume of the radioactive source in the body over the desired period of time by fitting the amplified signal data to the most likely set of expected signal data.

2. The method of claim 1, wherein a Maximum Likelihood Expectation Maximization method is used to fit the most likely magnitude, location, and volume of the radioactive source in the body.

3. The method of claim 1, further comprising the step of determining a dose of radioactivity to an area of tissue proximate the location of the radioactive source.

4. The method of claim 1, further comprising the step of using the determined one or more magnitude, location, and volume of radioactive source in the body to make one or more of a clinical decision or diagnosis.

5. The method of claim 1, wherein an array comprising two or more of the ex vivo radiation measurement sensors and two or more rangefinders are utilized.

6. The method of claim 5, wherein the array of two or more radiation measurement sensors and two or more rangefinders are disposed in a substantially symmetric geometry about the radioactive source in the body.

7. The method of claim 5, wherein the two or more sensors are disposed proximate one or more desired measurement location, and further wherein each desired measurement location comprises at least a first sensor disposed relatively closer to the radioactive source than a second sensor.

8. The method of claim 1, wherein one or more of a magnitude, location, or volume is determined for two or more radiation sources in the body.

9. The method of claim 8, further comprising the step of comparing the one or more determined magnitude, location, or volume of the two or more radioactive sources, and making a clinical decision or diagnosis based on the comparison.

10. The method of claim 9, wherein the clinical decision or diagnosis is also based on one or more prior determinations or comparisons of the subject patient.

11. The method of claim 9, wherein the clinical decision or diagnosis is further based on a comparison to a table comprising data from a population of other patients.

12. The method of claim 1, wherein the one or more rangefinders comprises an ultrasound transducer and detector.

13. The method of claim 1, wherein the one or more rangefinders comprises an optical detector.

14. The method of claim 1, wherein the one or more rangefinders comprises a camera and laser system for determining the position of the subject.

15. The method of claim 1, further comprising the step of utilizing the position of the subject to estimate a position of bone within the patient.

16. A system for the ex vivo real-time detection over a period of time of radiation emitted by a subject from the administration of a radioactive analyte that decays in vivo, the system comprising: two or more ex vivo radiation measurement sensors to detect radiation over a desired period of time and to produce signal data associated with the desired period of time, the ex vivo measurement sensors adapted to sensing radiation proximate to a point of administration on the subject of the radioactive analyte and disposed within a deformable cuff comprising two or more detector plates, wherein the two or more detector plates are joined by a pivot point between each pair of detector plates having a sensor for measuring a relative angle between the pair of detector plates in real time such that the relative positions of the two or more sensors disposed within the two or more detector plates are known in real time; a signal amplifier in operable communication with the two or more radiation measurement sensors, the signal amplifier adapted to amplify the signal data, the measurement sensors having at least one sensor output for such amplified signal data; at least one computer processor and a non-transient memory, the computer processor in operable communication with the non-transient memory and the measurement sensor output port; wherein the non-transient memory includes computer program code executable by the at least one computer processor, the computer program code configured for performing the steps of receiving the amplified signal data with the desired period of time, accessing a measured amount of radioactive material proximate the point of administration at a time t, and using the amplified signal data, estimating a function of radioactive material proximate the point of injection as a function of time from a time of injection to time t.

17. The system of claim 16, wherein the measured value of radioactive material proximate the point of administration at time t is measured using the two or more ex vivo radiation measurement sensors disposed on the two or more corresponding detector plates, wherein a distance from the array to a radiometric center of the radioactive material being measured can be determined, and further wherein a volume of the radioactive material being measured can be determined.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a chart illustrating an exemplary injection blood concentration showing concentration vs. time.

[0028] FIG. 2 is a chart showing an exemplary activity entering circulation as activity per unit time vs. time.

[0029] FIG. 3 is a chart showing an exemplary depiction of AIF for Extravasation resulting in a 50% AUC reduction.

[0030] FIG. 4 is an exemplary schematic of a measurement sensor according to some embodiments of the present disclosure.

[0031] FIG. 5 is an exemplary illustration of a measurement sensor according to some embodiments of the present disclosure.

[0032] FIG. 6 is an exemplary illustration of a measurement sensor according to some embodiments of the present disclosure.

[0033] FIG. 7 is an exemplary chart showing a time activity curve (TAC) with an exponential fit for estimating a clearance rate.

[0034] FIG. 8 is an exemplary illustration of a sensor configuration according to some embodiments of the present disclosure.

[0035] FIG. 9 is an exemplary illustration of a sensor configuration according to some embodiments of the present disclosure.

[0036] FIG. 10 is an exemplary illustration of a sensor configuration according to some embodiments of the present disclosure.

[0037] FIG. 11 is an exemplary sensor configuration according to some embodiments of the present disclosure.

[0038] FIG. 12 is an exemplary sensor configuration according to some embodiments of the present disclosure.

[0039] FIG. 13 is a simplified illustration of pixels and a sensor according to some embodiments of the present disclosure.

[0040] FIG. 14 is an exemplary sensor configuration according to some embodiments of the present disclosure.

[0041] FIG. 15A is an exemplary sensor configuration according to some embodiments of the present disclosure.

[0042] FIG. 15B is another view of the exemplary sensor configuration presented in FIG. 15A, viewed along a longitudinal axis.

[0043] FIG. 15C is another view of the exemplary sensor configuration presented in FIG. 15A, viewed from a side.

[0044] FIG. 16 is an exemplary sensor configuration according to some embodiments of the present disclosure.

[0045] FIG. 17 is an exemplary sensor configuration according to some embodiments of the present disclosure.

[0046] FIGS. 18A-C depict an exemplary sensor and rangefinder configuration according to some embodiments of the present disclosure.

[0047] FIGS. 19A-D depict various positions of a subject to be measured by an exemplary sensor and rangefinder configuration according to some embodiments of the present disclosure.

[0048] FIGS. 20A-B depict an exemplary laser and digital camera configuration that may be used to determine the size and location of an object to be measured in a system according to some embodiments of the present disclosure.

[0049] FIG. 21 illustrates an exemplary sensor and rangefinder configuration according to an alternative embodiment of the present disclosure.

[0050] FIGS. 22A-B depict an exemplary deformable sensor configuration according to some embodiments of the present disclosure.

[0051] FIG. 22C depicts an exemplary detector segment of the exemplary deformable sensor configuration of FIGS. 22A-B according to one exemplary embodiment of the present disclosure.

[0052] FIG. 23A depicts an exemplary detector configuration according to some embodiments of the present disclosure.

[0053] FIGS. 23B-C depict an alternative exemplary detector configuration according to some other embodiments of the present disclosure.

[0054] FIGS. 24A-F depict yet another exemplary detector plate configuration according to certain other embodiments of the present disclosure.

[0055] FIGS. 25A-D depict another exemplary detector configuration according to certain other aspects of the present disclosure.

DETAILED DESCRIPTION

[0056] The present disclosure teaches, among other things, systems and methods for using measurements of localized radiation to estimate the magnitude, location, and/or volume of radioactive source materials in the body. In some embodiments, such measurements may be repeated at various points in time to determine temporal changes in magnitude, location, and/or volume of radioactive materials in the body. In some embodiments, such information may be used to correct for non-bolus injections of radiopharmaceuticals. Such systems and methods may allow physicians to better measure, for example, cancer treatment effectiveness. In other embodiments, the systems, devices and methods may be used to validate organ dosimetry, or measure uptake of radiopharmaceuticals in tumors, organs or other areas of interest directly.

[0057] According to a first set of embodiments, and as introduced above, the SUV of a tumorfor example, the ratio of the amount of radio-labeled tracer in an area of interest compared to the level in the rest of the bodymay be calculated using, among other things, molecular imaging data. In general, SUV may be approximated as the integral of concentration of radiotracer in the bloodstream, multiplied by a constant K, plus a variability of distribution volume factor (V.sub.d). In the exemplary equation below, C.sub.T(t) represents the concentration of radiotracer in the tumor, C.sub.B(t) represents the concentration of radiotracer in the blood, K is a constant and V.sub.d is a dimensionless volume of distribution equivalent to a volume of blood that contains the same activity as 1 mL of tissue.

C.sub.T(t)=K.sub.0.sup.TC.sub.B(t)dt+V.sub.d

[0058] When the injection of radiotracer into the patient goes according to plan (i.e., there is no infiltration or extravasation during the injection and the entire dose of radiotracer goes promptly into the patient's bloodstream), the concentration of radiotracer in the blood can be assumed as the arterial input function. The arterial input function or AIF may be referred to as the impulse response for a typical bolus injection, and such impulse responses have been well-studied and measured. When the concentration of radiotracer in the blood cannot be assumed to be a typical bolus injection of known dosage, but instead varies over time as an infiltrated portion of a dose relatively slowly finds its way to the bloodstream, the measured concentration of radiotracer in the tumor becomes a function of both the radiotracer in the bloodstream from the initial (partial) bolus injection, and the later added radiotracer from the infiltration portion. Further, because the magnitude (i.e. the activity) of the infiltration depends on the nature of the infiltration itself (i.e. varies from infiltration to infiltration based on, for example, size of the infiltration, location of the infiltration, local tissue vascularization, etc.), the effective dose into the bloodstream from the bolus portion may be reduced by an unknown amount. The SUV of an area of interest (e.g., a tumor) is therefore altered by an amount proportional to the ratio of the bolus injection integral from a typical injection and the non-bolus injection integral, and may be expressed in some embodiments as follows (where SUV.sub.b is the SUV in the case of a typical bolus injection and SUV.sub.i is the SUV in the case of an infiltrated injection):

[00001]$\frac{{\mathrm{SUV}}_i}{{\mathrm{SUV}}_b}\frac{C_{\mathrm{Ti}}}{C_{\mathrm{Tb}}}\frac{K.Math.{}_0^T.Math.C_{\mathrm{Bi}}\left(t\right).Math.\mathrm{dt}+V_d}{K.Math.{}_0^T.Math.C_{\mathrm{Bb}}\left(t\right).Math.\mathrm{dt}+V_d}$

[0059] In general, the kinetics of radiotracer uptake can be considered a time-invariant linear system. In this exemplary case, a bolus injection could be the impulse and the normal AIF curve (i.e. concentration of radiotracer in the blood as a function of time) could then be the impulse response. The AIF for a typical bolus injection has been well-studied and measured, such that results and applicable measurements are readily available in the literature. Referring now to FIG. 1, an exemplary AIF curve 100 for an ideal injection is presented, showing concentration of radiopharmaceutical in the blood on the y-axis vs. time on the x-axis.

[0060] In the case of an extravasated or infiltrated injection, however, the AIF may be modeled as a convolution of the normal impulse response with the altered input signal that may comprise a decreased initial impulse (the bolus) followed by prolonged decaying exponential reabsorption. The reduced bolus portion may represent the amount of radiotracer that enters circulation immediately. The extended infusion portion may result from sequestered or infiltrated radiotracer being reabsorbed into circulation through, for example, the venous or lymphatic systems. Referring now to FIG. 2, an exemplary graphical representation of a non-typical injection 200 (e.g., one having an infiltration) is presented, where the activity measured per unit time (y-axis) is expressed as a function of time (x-axis). As illustrated, there is an initial spike 201 corresponding to the bolus portion, followed by a gradual decaying exponential reabsorption portion 202.

[0061] In cases of infiltration/extravasation, the injection is not a bolus, and thus the input to the linear system is not an impulse. If the true input to the linear system from an extravasated or infiltrated injection is known or can be determined, it may be possible to then calculate how the altered injection shape may impact the scan metrics such as, for example, SUV (e.g. from a PET scan). For example, it is possible to take the altered linear system input following an infiltrated or extravasated injection and convolve it with the known impulse response from a typical bolus injection, thereby yielding the anticipated blood concentration over time for the infiltrated (i.e. extravasation) injection. That convolution of functions can yield a function for concentration of radiotracer in the blood as a function of time (i.e. the Arterial Input Function or AIF) for any case of infiltration or extravasation. Referring now to FIG. 3, an exemplary graphical representation of an ideal bolus injection AIF (dotted line) alongside an AIF for an extravasation resulting in a 50% SUV (i.e. Area under the curve or AUC) reduction is presented.

[0062] To perform the methods outlined above, a user may need to know the amplitude (i.e. the activity) of the infiltration as well as the rate of reabsorption of the infiltrate (so as to produce the function of radiotracer entering circulation over time). One method of determining the amplitude of radioactivity in a particular region (e.g., the infiltration site) is to use nuclear medicine imaging data taken during an imaging session, which may yield an amplitude in a region at a time=t. This alone, however, cannot enable one to extrapolate the infiltrated amount at the time of injection (t=0), or the rate at which the radiotracer may have been reabsorbed into the bloodstream.

[0063] In some embodiments, localized radiation detectors such as those disclosed U.S. Pat. Nos. 9,939,533 and 9,002,438 may be used to measure activity at the injection site as a function of time (i.e. time-activity curve or TAC). Referring now to FIGS. 4-6, a measurement sensor 11 may be utilized that may include, for example, a scintillation material 20; a light detector 21; and a sensor processor 22 with associated non-transient sensor memory 30, logic or sensor software 26, and other circuitry supporting these components in operable communication, optionally with a printed circuit board 23P (FIG. 6). Such sensors may also include amplifier circuitry 33 and/or a temperature sensor 36. Measurement sensor 11 may utilize a scintillation material 20 to receive gamma radiation from positron emission decay and convert the radiation into photons, such as pulses of light, which may then be detected by the light detector 21. The sensor processor 22 may enable measurement and collection of the photons, such as the number of light pulses detected over a given amount of time. Optionally, noise rejection 37 may be included that may provide a filter for filtering amplified signal data based on the height or amplitude of such pulses. For example, noise rejection 37 may include a voltage comparator or an analog to digital converter with computer program code to compare the digital output to a reference level.

[0064] Possible scintillation materials 20 include, but are not limited to: Bismuth Germanate (BOO); Gadolinium Oxyorthosilicate (GSO); Cerium-doped Lutetium Oxyorthosilicate (LSO); Cerium-doped Lutetium Yttrium Orthosilicate (LYSO); Thallium-doped Sodium Iodide (NaI(T1)); Plastic Scintillator (Polyvinyltoluene); or Cadmium Zinc Telluride (CZT). In an exemplary embodiment of a measurement sensor 11, multiple scintillation materials 20 adapted to measure different radioisotopes may be used. In another embodiment of a measurement sensor 11, scintillation materials 20 that do not require the use of a light detector 21 may be used. In another embodiment of a measurement sensor, multiple scintillation materials 20, each with their own detection circuitry, may be included to enable a two or three dimensional array of measurements. In some embodiments, the sensor(s) are capable of detecting alpha particles, beta particles, x-rays, gamma rays, and/or other particles/energy indicative of radioactive material.

[0065] Of course, other radiation sensors known in the art may be utilized as desired. For example, radiation sensors capable of detecting alpha particles, beta particles, x-rays, gamma rays or any other kind of radioactive decay particle/energy may be utilized depending on the desired application. Measurement of beta particles, for example, may be advantageous when assessing delivery of a radio-therapeutic to an area of the body as such drugs sometimes release beta particles. It may similarly be advantageous to ensure that certain beta particle (or other particle) emitting drugs or other substances not be reaching a certain part of the body. Thus, sensors could be used to confirm the absence of such substances. All that is typically necessary for the sensors, in some embodiments, is that the sensor be capable of detecting emissions from radioactive material, and further capable of transmitting or otherwise sharing information about those emissions to the system for processing. It may also be desirable, in some embodiments, that the sensors and/or system generally be able to measure an energy level associated with the detected emissions, or filter received energy above or below a certain threshold.

[0066] Utilizing measured data, the rate of reabsorption into the bloodstream may be calculated by observing the activity at the detector as a function of time (i.e. the rate at which radioactive activity leaves the infiltration site). Knowing from the TAC the amount of radioactive material at a time t, and the rate at which it left the infiltration site, an estimate of the initial amount of radioactive material infiltrated may be determined. Knowing this information, the altered injection curve and the reduction of the initial bolus may be plotted, and a function of concentration of radiotracer in the blood as a function of time determined. With that function known, a correction factor for SUV or the like may be applied and the clinician may better diagnose treatment efficacy, etc. Referring now to FIG. 7, an exemplary TAC with Exponential Fit Curve is presented.

[0067] As introduced above, the many constraints on nuclear imaging apparatus (e.g. PET scanners) such as availability, cost, operational resources, etc., make determining the size and/or magnitude of a radioactive source in the body using such apparatuses not always possible. For example, taking a measurement of an infiltration area that may otherwise be outside the field of view and/or otherwise not of interest at the time of the scan is not always feasible. It would also be advantageous to have an understanding of the magnitude and scope of any infiltration from the time of the injection forward, rather than having to wait until the patient is moved to the scanner. The ability to determine the magnitude of an infiltration without using a nuclear imaging scanner may also be desirable because it could eliminate the need to use such a scanner at all where the scope of the infiltration is deemed large enough to render a scan unproductive, thereby saving the patient from additional unnecessary radiation exposure (e.g., from a computerized tomography (CT) scan, or the like).

[0068] It may also be advantageous to measure the area and/or magnitude of radioactive material uptake in an area of interest generally, without having to depend on the availability of more complex and expensive nuclear imaging apparatuses. To determine the efficacy of a treatment to eliminate a tumor, for example, a physician may want to know whether the tumor is shrinking over a period of time (e.g., days, weeks, months, etc.). Requiring a patient to undergo successive nuclear imaging scans and face exposure to the requisite radiation on multiple occasions is, at best, not ideal, and in some cases is prohibitory.

[0069] One way to overcome the difficulties outlined above is, for example, to utilize multiple detectors that may be arranged in a known geometry. Each sensor may measure radioactivity coming from a given source of material, and each sensor may have a known sensitivity thereby enabling it to provide information about intensity measured for each event. Such intensity may depend, for example, on the sensor's distance from the source, material-specific attenuation between source and sensor, as well as intensity of the source itself. As noted above, a determination of each sensor's distance from the source may not be determinable on a sensor by sensor basis because the measured intensity at any given distance depends on an unknown intensity at the source. However, by utilizing data from an array of sensors, and measuring intensity of the same area of different but known relative distances, information regarding both magnitude, location, and/or size of the source may ultimately be determined at each unit of time.

[0070] In some embodiments, and as just one example, a method known as trilateration may be used in combination with the disclosures herein to determine the distance of each sensor from a radiometric center. Trilateration is similar in some respects to triangulation but utilizes distance instead of angles. In some embodiments, each sensor could calculate an estimated distance R to the source based on the measured intensity of each count. The direction of the source, however, would be unknown. Thus, the determined distance dictates only that the source must lie somewhere on a sphere of radius R centered about the sensor. Having such a sphere for multiple sensors (e.g., four) positioned in 3-D space, however, a point where the four spheres intersect could identify the radiometric center of the source material, and allow for the system to know the distance between a radiometric center of the source material and the sensor.

[0071] Referring now to FIG. 8, an exemplary representation of one trilateration model is presented according to some embodiments. In this exemplary embodiment, and with further reference to FIG. 9, a set of sensors 910 may be disposed in a known three-dimensional configuration. Because both distance and source intensity would be unknown, an iterative process may be utilized to determine values that satisfy the system's given constraints. For example, various parameters could be employed to determine the values wherein the highest number of spheres best intersect. Certain assumptions may be employed including estimates for expected activity, assumptions about the material-specific attenuation between the source and each sensor, and distance range approximations to aid the iterative process. While measurement noise could make finding exact intersection points difficult, a best fit may be employed to ultimately find a sufficiently precise distance estimate, and determine an estimate for a radiometric center (e.g., point 805). Knowing this distance, the system could then calculate the amount of radioactive material present based on the intensity of the measurements at any given time (including situations where the source at a time T.sub.2 has shifted relative to an earlier time T.sub.1).

[0072] Various different sensors capable of measuring counts in the presence of radioactive material are available and known in the art. These include, but are not limited to: the sensors disclosed hereinabove with reference to FIGS. 4-6; TLDthermo-luminescent device; OSLoptically stimulated luminescence device; Radiation sensitive film; RADFETradiation sensitive field-effect transistor; PIN Dioderadiation sensitive diode; Ionization chamber; Geiger counter; and Scintillation crystals, among others. It will be appreciated that the array of sensors discussed herein may be of one type or may be a combination of different types if desired. The system need only know the relative sensitivity of each sensor to appropriately calibrate the measurements.

[0073] As noted above, the relative geometry of the sensor array must be known, but that geometry is otherwise generally unrestrained, both in space and time. In some embodiments, so long as the relative geometry of the sensors is known at each time t, the relative distances of each sensor to the radiometric center be determined. Note, however, that in some embodiments it may be necessary that the sensors be disposed in a three-dimensional array, rather than all residing, for example, on a similar two-dimensional plane, or in a one-dimensional line.

[0074] Referring now to FIG. 9, an exemplary four-sensor array is presented according to some embodiments. As illustrated, the various sensors 910 may be arranged in a three-dimensional configuration. In certain other embodiments, and with reference to FIG. 10, various sensors 1010 could be disposed in a three-dimensional L-bracket configuration. FIGS. 9 and 10 represent just two of many different potential sensor arrangements and geometries that may be utilized.

[0075] In some embodiments, the various sensors discussed herein that may be arranged in an array to determine a radiometric center of a radiation source that may be the same sensor(s) that measure the time-activity curve (TAC) discussed above. Accordingly, as disclosed herein, the sensors may be utilized to detect an infiltration, measure the time-activity curve at the injection/infiltration site, and even measure the magnitude of the infiltration so as to yield information about the SUV, for example, of an area of interest (e.g. tumor) ultimately measured by a nuclear imaging device (e.g., PET scan) and any correction factor that may need be applied in view of, for example, an imperfect injection of radiotracer.

[0076] In certain other embodiments of the present disclosure, the system may utilize arrays of sensors in combination with other estimation techniques to, for example, quantify and/or measure the magnitude and/or location/size of a radioactive area of interest. In some embodiments, and referring now to exemplary FIG. 11, an area of interest 1101, which may contain a volume of radioactive source material 1103, may be surrounded by a one or a plurality of sensors 1110, forming a sensor array. The area of interest 1101 may be within, for example, a patient 1160 (e.g., an infiltrated radiopharmaceutical injection, a tumor being treated with radiopharmaceuticals, an organ desired to be dosed with a precise amount of radiopharmaceutical, etc.), but may more generically be any volume of area that may include radioactive material, whether located in a body, within some other container/vessel, or standing alone. In this exemplary embodiment, the sensor(s) 1110 may be positioned outside the body of patient 1260 in various geometries relative to the area of interest 1101.

[0077] The array of sensors 1110 may include any number of sensors, including in some embodiments as few as one or two, or as many as four, eight, ten, twenty, thirty, fifty, one-hundred, or more or anywhere in between. Further, each of the plurality of sensors 1110 that make up the array may be identical sensors to one another, or one or more may have unique characteristics relative to one or more other of the sensors 1110. Such distinguishing characteristics may include, but are not limited to, different shielding configurations, different energy threshold settings for detection, different size/shape for given locations or applications, etc. Other varying characteristics may also be utilized, some of which are discussed in greater detail elsewhere in this disclosure.

[0078] In some embodiments, each sensor 1110 may detect particles/energy emitted from the radioactive area of interest 1103. In some embodiments, the sensors 1110 may detect the emitted particles as discussed hereinabove (e.g., through use of scintillation material that emits light when impacted with radioactive particles (e.g., alpha particles, beta particles, or the like) in the sensor and circuitry capable of counting the number of hits per unit time). As noted above, however, other sensor configurations and detection methods may be used.

[0079] In general, the array of sensors 1110 may be arranged in any desired geometry relative to each other and relative to the area of interest 1101. In some embodiments, it may be advantageous to utilize a known geometry of sensors, and it may be further advantageous to arrange the sensors 1110 such that the location of each sensor 1110 may be known relative to each of the other sensors 1110 in the array.

[0080] Using techniques known to those having skill in the art, it is possible to estimate the radioactive activity expected at a given location (e.g., at the location of a specific sensor 1110) given certain information, including for example a known amount of radioactive material centered about a known point in space. For example, if the radiometric center, and amount and type of radioactive material is known, and information about the density and composition of the material through which the emitted particles will pass to reach the sensor 1110 (e.g., water, tissue, bone, etc.), one may determine a likelihood that a particle emitted from the radiation source would be detected at a given point in space. Using these techniques, a set of expected measurements can be generated for radioactive sources of various magnitudes, locations, and volumes.

[0081] Accordingly, by inversing such calculations, measurements of activity taken at various points in space relative to a source of radioactive material may be used to estimate characteristics about the radioactive material source itself, for example, magnitude, location, volume, etc. In one example, activity at various locations about a radioactive source may be measured as a function of time. Then, knowing the likelihood of measuring the activity actually measured relative to radioactive sources of various magnitudes and locations, a least squares regression analysis may be used to estimate the magnitude, location, and/or volume of the actual radioactive material source. Using such techniques, and assuming a distribution, for example Gaussian, of radioactive material, an accurate determination of the amount of radioactive material present can be determined (i.e., the magnitude), and the radiometric center of the radioactive material (i.e., location), and/or distribution of radioactive material (i.e., size of the source of radioactive material) may be determined.

[0082] According to one exemplary method of using the system disclosed herein, and referring again to FIG. 11, the system 1100 may assume the presence of a blob of radioactive material (e.g., radioactive area of interest 1103) positioned relative to the array made of sensors 1110. The radioactive material's location and magnitude may be unknown, but the radioactive material emits radioactive energy/particles and/or decays into other particles/energy (e.g., alpha particles, beta particles, x-rays, gamma rays, positrons etc.) that may be measured by each of the sensors 1110. In particular, each sensor 1110 may detect those particles that intercept it. In some embodiments, by measuring the energies of the particles, the system may eliminate unwanted hits (e.g., deflected particles), and utilize knowledge of the material through which the particles traveled (i.e., water, bone, etc.) to gain an understanding about the magnitude and/or volume (among other things) of the radioactive source.

[0083] Having measured the activity of direct hits per unit time at each known location, the least squares regression analysis can be applied to find the magnitude (A), mean location () and standard deviation () of the radioactive source which minimizes the error between actual counts (c.sub.n) and estimated counts (.sub.n) associated with the various possibilities of radioactive sources. In some embodiments, the system or method may assume a Gaussian distribution of the radioactive material of interest, but other distributions are possible. Knowing such information, it may be possible to diagnose certain conditions, determine a dose of radiation to tissue in the body proximate the radioactive source, analyze whether a desired dosage of therapeutic radiopharmaceutical has been delivered to an area of interest (or is not present in an area of interest or below some acceptable threshold), and by capturing such exact measurements, it may be possible to compare results for a single patient over multiple visits to track efficacy of treatments, etc.

[00002]${\mathrm{argmin}}_{A,,}\left(\underset{n=0}{\overset{N}{.Math.}}.Math..Math.{\left(c_n-{\hat{c}}_n\right)}^2\right)$

[0084] One drawback to this technique may be that the standard deviation of the distribution is sometimes difficult to determine accurately. For example, the counts or hits measured by an array made of sensors 1110 may be the same for a collection of radioactive material distributed over a first volume as it would for a collection of the same amount of radioactive material distributed over a second volume. Accordingly, while the magnitude of the source (i.e., how much radioactive material is present) and radiometric center of the source (i.e., the location about which the radioactive source is centered) may be determined, the volume of space that the source occupies may be more difficult to estimate according to some techniques. While magnitude and location can provide significantly advantageous information in some circumstances (e.g., determining the size and location of an infiltration and using that information to aid in interpretation of medical imaging, for example), it is not always sufficient to determine, for example, the radioactive dose to surrounding tissue, as the distribution of the radioactive material (i.e. the standard deviation discussed above) in the tissue would be needed.

[0085] Accordingly, it would be advantageous to modify and/or supplement the techniques described hereinabove to determine not only the magnitude and location of a radioactive area of interest (e.g., 1103), but also gain an understanding of the volume/distribution of the material.

[0086] According to additional embodiments of the present disclosure, sensor arrays not unlike those discussed hereinabove may be used in combination with other methods to obtain even more robust estimates of the magnitude, location, and/or volume of a radioactive area of interest. Referring now to FIG. 12, an exemplary system 1200 is presented where a volume of interest 1201 may be defined and divided into a plurality of three-dimensional voxels (analogous to two-dimensional pixels, see FIG. 13 below). In some embodiments these voxels may be of uniform size and shape, while other embodiments may include voxels of varying size, shape, arrangement, etc. Within volume of interest 1201 may lie a radioactive area of interest 1203 of unknown magnitude, location, and volume. Spaced about the volume of interest 1201 may be a plurality of sensors 1210 forming a sensor array.

[0087] Similar to the sensor array discussed hereinabove, each of the sensors 1210 may be positioned proximate a known location relative to the plurality of other sensors 1210. The sensors 1210 may be arranged at random known locations about the volume of interest 1201, or in preferred embodiments, may be positioned in mathematically advantageous geometries about the volume of interest 1201, including for example, in triangular, cubic, hemispherical or spherical orientations about the volume of interest 1201, among others. In some embodiments, the arrangements may be symmetrical. In the exemplary embodiment illustrated in FIG. 12, the sensors are arranged in a substantially cubic configuration about area of interest 1201. It should also be understood that in some embodiments, the relative locations of sensors in space may change over time, and techniques could be employed to measure or otherwise determine the relative positions of the plurality of sensors 1210 at each time t.

[0088] In some embodiments, a system for estimating the magnitude, location, and volume of a radioactive area within a volume of interest, such as for example the system 1200 illustrated in FIG. 12, may utilize an estimation method known as Maximum Likelihood Expectation Maximization (MLEM). Referring now to a simplified exemplary two-dimensional configuration shown in FIG. 13, MLEM methods may be used to calculate a probability for each cell or pixel 1305 that a particle 1320 having a certain energy measured at a given location (i.e., the location of one of the sensors 1310) originated from each particular cell 1305. Put another way, for each cell 1305, a probability may be determined that a particle 1320 originating from each cell 1305 would arrive at the location of the sensor 1310. Using the same methods, probabilities for each voxel in a three-dimensional space (e.g., volume of interest 1201) can be determined.

[0089] For example, and referring again to FIG. 13, consider a sensor (e.g., sensor 1310) positioned at a location relative to an area of interest 1301 divided into a plurality of pixels 1305. Sensor 1310 may receive a hit from a particle 1320 emitted by the radioactive material located within the area of interest 1301. Specifically, particle 1320 measured by sensor 1310 may have originated from any one of the pixels 1305.

[0090] Particles released from radioactive material travel in random directions from their source, and therefore there is only a chance that any particular particle (e.g., particle 1320) will travel in the direction of a given sensor (e.g., sensor 1310). Further, the greater the distance between the source of the particle 1320 and the sensor 1310, the more likely it is that the particle 1320 will collide with some intervening material (e.g., water molecule, bone, etc.) and scatter to a different trajectory. When scattered, the particles lose energy, and therefore it is possible to calibrate the sensors to disregard scattered particles that may be received at a sensor, if desired, as counting scattered particles may introduce error.

[0091] Accordingly, referring again to FIG. 13, the probability that a sensor 1310 is hit by a particle 1320 that originated in cell B may be lower, for example, than the probability that the particle 1320 originated in cell A. This is because, in this example, the physical distance between cell B and the sensor 1310 is greater than the distance between cell A and the sensor 1310, thereby not only reducing the solid angle created by the sensor with respect to the pixel, but also introducing a greater chance that the particle will be scattered from its original trajectory by intervening material. Knowing the distances between the sensor 1310 and each pixel 1305, the density and other characteristics of the material(s) through which the particle must travel to reach the sensor 1310, and the characteristics of the radioactive material of interest itself, among other things, the system may determine a set of such probabilities of a particle hitting a sensor 1310 for each pixel 1305, and may determine such sets relative to each sensor 1310 for each pixel 1305.

[0092] The same is true for a three-dimensional configuration, such as for example the configuration illustrated in FIG. 12. In general, the probability that a particle 1220 counted by sensor 1210 originated from a relatively close voxel within area of interest 1201 is greater than a probability that particle 1220 originated from a relatively distant voxel in area of interest 1201. As above, a set of probabilities for each voxel may be determined for each sensor. This information may be used to generate, or may itself be characterized as, a set of expected signal data associated with radioactive sources of various magnitudes, locations, and/or volumes.

[0093] Knowing these probabilities, the system 1200 may be used to take actual measurements of hits per unit time observed at each sensor 1210 and estimate, among other things, the magnitude, location, and/or volume of a radioactive source. In some embodiments, because the radioactive material releases particles in all directions, each sensor 1210 should register some number of hits if a sufficient amount of radioactive material is present within volume of interest 1201. Each hit at each sensor 1210 corresponds to a set of probabilities across the voxels 1205 in the volume of interest 1201 corresponding to the likelihood that the particle (e.g., 1220) intercepting a particular sensor 1210 originated in each voxel 1205. In some embodiments, the system may analyze the sets of probabilities for each hit at each sensor 1210 and iterate over time to determine the most likely distribution of radioactive material 1203 within the volume of interest 1201 that would generate the hits observed. The system may also iterate over various energy levels, providing additional detail.

[0094] Generally speaking, increasing the number of available sensors (e.g., 1210) positioned about the radioactive material source (e.g., 1203) may increase the accuracy with which the system 1200 can estimate the magnitude, location, and/or volume of the source. Similarly, increasing the number of voxels used in the calculations (i.e., more voxels comprising smaller and smaller volumes each) may increase the system's accuracy. However, as the number of sensors and/or voxels increases, the number of required calculations and processing requirements of the system generally increases significantly. It may therefore be advantageous, in some embodiments, to take advantage of certain sensor positioning arrangements that may simplify calculations or aid in the iterative convergence of the calculations, including for example using symmetrical sensor configurations, among other things. Such configurations may also shorten the time and/or reduce the number of calculations required to achieve acceptable iterative convergence. Various distributions of voxel size may also be utilized, such that smaller voxels are utilized closer to and within the radioactive source material 1203 and larger voxels are utilized elsewhere, for example.

[0095] In some embodiments, in may also be advantageous to include two or more sensors proximate each of the fixed points about a volume of interest. An exemplary configuration illustrating an exemplary dual-sensor approach is illustrated in FIG. 14. As shown in the exemplary configuration there, a concentric-cubic configuration may be used, where a first set of sensors 1410 may be positioned at each of eight points on a first, inner cube surrounding the area of interest 1401, and a second set of sensors 1410 may be positioned at each of eight points on a second, outer cube surrounding the same area of interest 1201. Proximate each of the eight known points 1430 positioned about the volume of interest 1401, two sensors 1410 may then be provided, for a total of sixteen sensors in the system. Of course, each fixed location 1430 may include more than two sensors 1410 if desired (e.g., a third cube of greater dimensions), and/or any number of fixed locations 1430 may be utilized (including for example, one, two, four, eight, sixteen, twenty-four, or more, or any number in between, as desired). Utilizing two or more sensors 1410 at each location 1430 may have the advantage of aiding, among other things, an iterative convergence. More particularly, by having a second sensor 1410 slightly farther away from the source of radioactive material 1403 relative to the first sensor 1410 at each location 1430, they system may more efficiently arrive at an iterative convergence.

[0096] In some embodiments, it may be advantageous to detect particles from plurality of radioactive sources. For example, by introducing two or more radiopharmaceuticals with distinguishable radioactive characteristics (e.g., different energy levels, different uptake rates, etc.), additional information may be detected. Sensors in such systems may be tuned to detect particles of one or more different energy levels, thereby providing additional information. For example, the amount or rate of uptake of one drug associated with a first radiopharmaceutical relative to the amount rate of uptake of a second drug associated with a second radiopharmaceutical may provide useful information to a clinician.

[0097] Referring now to FIGS. 15A to 15C, an application of the present disclosure is presented according to one exemplary embodiment in system 1500. In some embodiments, a plurality of sensors 1510 may be arranged in a substantially cylindrical array to form, for example a cuff 1550. Cuff 1550 may be sized to fit, for example, around a portion of a patient's body, for example, a patient's arm 1560. In some embodiments, cuff 1550 may be positioned about, for example, the location where a patient is or was injected with a radiopharmaceutical or the like. In some embodiments, cuff 1550 may include a deformable transition layer 1555 that may be utilized to maintain a consistent or otherwise known material composition and/or density between a radioactive source 1503 and the sensors 1510, such as for example, to substantially eliminate air gaps. In some embodiments, the transition layer 1555 may include water, saline, and/or various other gels or materials. In some embodiments, the materials may be substantially similar in density to human tissue and/or bone.

[0098] In some embodiments, the sensors 1510 of cuff 1550 may also be arranged to provide for substantially stacked sensors at various locations on cuff 1550. For example, and similar to the exemplary cubic configuration discussed above with reference to FIG. 14, the plurality of sensors 1510 may be arranged to have a first, inner substantially cylindrical configuration and a second, outer substantially cylindrical configuration, thereby providing for two or more sensors 1510 proximate a plurality of desired locations, with one of the sensors 1510 being relatively farther away from the source 1503 than another sensor 1510.

[0099] In the event of an infiltration, for example, the system 1500 could be used according to some or all of the methods taught hereinabove to estimate the magnitude, location, and/or volume of the infiltrated radioactive material in the patient. Advantageously, the system may also be utilized, in some embodiments, to provide estimates of the magnitude, location, and volume over time, thereby providing critical information to healthcare providers regarding, among many other things, the rate at which radioactive material is being introduced into the bloodstream and therefore affecting, for example, nuclear imaging, and to quantify the patient's tissue exposure to the infiltrated radiation at or around the injection site, to name just a few.

[0100] In certain other embodiments, similar arrangements of sensors may be utilized in other configurations for use in other areas of the body. For example, referring now to FIG. 16, a larger cuff-like configuration 1650 may be utilized to surround the torso or pelvic region of a patient 1260, for example. Such arrangements may enable users to estimate, for example, radiopharmaceutical uptake in a tumor or organ (i.e. organ dosimetry) in the body. As presented above, any arrangement of sensors may be used, and therefore other configurations of sensors may be utilized as needed to fit the nature of the area to be measured. For example, a horseshoe figuration, a flexible sheet configuration, or any other.

[0101] Referring now to FIG. 17, yet another exemplary configuration of a system 1700 of the present disclosure is presented. In some embodiments, it may be desirable to estimate the uptake of radioactive material in all or a portion(s) of the brain. According to some embodiments, then, a plurality of sensors 1710 may be arranged in a helmet-like article 1750 such that the sensors 1710 may be arranged about a patient's head 1760. The sensors 1710 may be arranged in any manner about the helmet 1750, including in those several configurations discussed herein. In the exemplary embodiment illustrated in FIG. 17, the sensors 1710 may be disposed about the helmet 1750 in a generally hemispherical configuration and may in some embodiments also include two sensors 1710 at each measurement location 1730. In some embodiments, helmet 1750 may include a first set of sensors 1710 disposed in a first hemispherical configuration, and a second set of sensors 1710 disposed in a second hemispherical configuration, with the second hemispherical configuration having a slightly larger radius than the first. Accordingly, in some embodiments, there may be two (or more) sensors 1710 about a plurality of desired locations 1730 where one sensor 1710 at each location 1730 is slightly farther away from source 1703 than a second sensor 1710.

[0102] The helmet 1750 may also include a transition layer similar to layer 1555 in FIG. 15 comprising material(s) of known composition and/or density (e.g., water, saline, or gel(s) having a density and other properties similar to that of brain tissue, other tissue, bone (e.g., skull), etc., as desired), thereby eliminating air gaps that could, in some circumstances, complicate the estimations and/or introduce undesirable error.

[0103] In each of these various embodiments, the relative distance between sensors may initially be unknown given the need to modify the cuff 1550, 1650 or helmet 1750 to fit the various sizes and shapes of patients presented. To calibrate the various systems 1500, 1600, and/or 1700 (and others) before use, the systems and methods taught herein may be modified to introduce known radioactive elements at known locations. For example, relatively small doses of cesium, for example, may be introduced at a known location, from which the relative locations of each sensor may be determined by the system.

[0104] In another example, known amounts of cesium (or some other radioactive material) may be introduced to determine the specific density of a patient's body through which the particles released from a radiopharmaceutical may travel.

[0105] By determining reliable estimates of one or more of the magnitude, location, and/or volume of a radioactive source material in the body, it may be possible to, among many other things, evaluate treatment efficacy, make clinical decisions or diagnoses, identify or eliminate medical conditions, compare different areas of the body (e.g., different hemispheres of the bran) and make clinical decisions and/or diagnoses based on such measurements and/or by comparing such measurements to past measurements of the patient and/or measurements of the general population, among many other things. The systems and methods taught herein are expected not only to provide such estimates, but to use such estimates to aid clinicians in their diagnosis and treatment, and even suggest or determine appropriate clinical decisions and/or diagnosis.

Attenuation Estimations and Corrections

[0106] In some embodiments, the systems and methods taught hereinabove may further include mechanisms for measuring and/or estimating a position of different materials within a measurement region of interest so as, for example, to better understand the various densities and resulting attenuation through the system. In doing so, the system and method can more accurately account for different materials having relatively different densities in the system, thereby better estimating a particle's energy loss as it travels along a path from its origin to a sensor.

[0107] More particularly, and referring again to the exemplary system depicted in FIGS. 15A-15C, a plurality of sensors 1510 may be arranged in a substantially cylindrical array to form, for example a cuff 1550. Cuff 1550 may be sized to fit, for example, around a portion of a patient's body, for example, a patient's arm 1560. In some embodiments, cuff 1550 may be positioned about, for example, the location where a patient is or was injected with a radiopharmaceutical or the like. As discussed above, in some embodiments, cuff 1550 may include a deformable transition layer 1555 that may be utilized to maintain a relatively consistent or otherwise known material composition and/or density between a radioactive source 1503 and the sensors 1510, such as for example, to substantially eliminate air gaps where the material density encountered by a particle may be significantly different than the tissue or tissue-like material through which the particle otherwise travels.

[0108] In some circumstances, however, it may be more difficult, impracticable, or otherwise less desirable to rely on having a deformable transition layer 1555 to aid in maintaining a relatively uniform density between the radiation source 1503 and the sensor 1510. In many cases, for example, one or more air gaps may be unavoidable, and/or a system configuration may be desired where air gaps of known or unknown size may be necessary to facilitate, for example, patient comfort, system design, cost considerations, etc.

[0109] Referring now to FIG. 18A, an alternative and modified arm cuff system 1800 is presented. In exemplary cuff system 1800, radiation detectors 1810 may be positioned substantially about a radioactive source of interest 1803 positioned in, for example a patient's arm 1860. Patient's arm 1860 may also include, among other materials of varying density, bone 1865. Like other embodiments disclosed herein, cuff system 1800 may also include one or more sensors 1810 positioned about and/or proximate to the radioactive source of interest 1803. In some embodiments, the sensors 1810 may be disposed within, for example, a housing area that may be made of another material (e.g., plastic 1880). In some embodiments, such as the exemplary configuration in FIG. 18A, the sensors 1810 may be disposed about the radioactive source of interest 1803 such that a particle emitted from radioactive source of interest 1803 may travel through one or more of arm tissue 1860, bone 1865, plastic 1880, and/or air 1890. As would be known to a person having ordinary skill in the art, the modified system 1800 is not limited to an arm cuff, but may include any configuration of sensors 1810 positioned proximate to or about a radioactive source of interest, including any such source in any portion of a patient's body, for example, including but not limited to any of the exemplary configurations presented and contemplated hereinabove.

[0110] Referring again to the exemplary system presented in FIG. 18A, if the position of the patient's arm 1860 within the system 1800 is unknown, then the path of any particle detected by any of the one or more sensors 1810 may vary significantly. For example, particles (e.g., photons) originating at Point 1 could be detected by any of the ring's detectors or sensors 1810, with lines A, B and C demonstrating three exemplary paths. Traveling along line A, for example, a particle may first pass through tissue (1860), then air (1890), then plastic (1880), and finally air (1890) again before impacting the detector 1810. Along line B, the particle may encounter the same materials, but in significantly different proportions (e.g. substantially more tissue 1860 and less air 1890 relative to path A), and along line C, the particle may travel through bone 1865, but may encounter little or no air 1890. These differences may be significant, as the density of air, bone, plastic, and tissue, among other potential materials encountered, have different densities. As a particle travels through these materials, it loses energy through attenuation at a rate proportional to the density of the material in which it is traveling. Accordingly, a particle having a particular energy level when released from Point 1 will have a different energy level when measured at different sensors 1810 depending on which path the particle traveled (e.g., A, B, or C). If the distribution of material densities in the relevant measurement region are unknown, the accuracy of the estimation techniques disclosed hereinabove (e.g, MLEM, etc.) may be reduced.

[0111] One current (and often cost prohibitive) method for accounting for such varying material densities and attenuation along a particle's path is to use computed tomography (CT). CT consists of multiple x-ray images taken from various angles to build a 3D image of the patient's anatomy in terms of density. Then, the CT image can be used to correct for the photon energy lost due to absorption between any point and any detector. But for the system disclosed herein, size and cost are two of several important design requirements. Incorporation of CT imaging would be disadvantageous to both. It is therefore a further object of the present invention to provide systems and methods for better estimating various densities throughout the area within, for example, cuff system 1800, so as to better account for a particle's attenuation as it travels from a point of origin (e.g. Point 1) to a measurement sensor 1810.

[0112] Referring now to FIG. 18B, exemplary cuff system 1800 may further include one or more rangefinders 1895. In some embodiments, rangefinders 1895 may be positioned proximate to or about a radioactive area of interest 1803 in a patient's body (e.g., arm 1860). Rangefinders 1895 may also be arranged in various arrangements depending on, for example, the size of the system relative to the size of the object to be measured, and anticipated location of the object to be measured relative to the size and shape of the system. For example, if it is anticipated that the object to be measured will typically be located in a lower half of the systems (e.g., the lower half of an arm cuff where a patient may resent the arm), then the measurement sensors may be arranged and/or directed to better target and measure such locations. Rangefinders 1895 may also be adjustable (either manually or automatically) so as to maximize the ability of the range finders to measure the relative distance to objects (e.g., arm 1860) in the system (e.g., cuff system 1800). In certain other embodiments, a sufficient number of rangefinders 1895 may be utilized in the system such that all areas of the system (e.g., cuff 1800) may be sufficiently measured without having any undesired dead zones, and an accurate determination of the area within cuff 1800 filled with, for example, tissue 1860 relative to air 1890 can be made.

[0113] In some embodiments, rangefinders 1895 may include one or more devices which measure a straight-line distance between itself and an object in front of it. Such rangefinders 1895 may utilize different known technologies, including for example, ultrasonic and optical designs, but are not so limited and may include any method of determining or calculating a distance relative to the rangefinder 1895.

[0114] In one example, ultrasonic detectors, for example, may be based on the principle of time-of-flight and can be similar to SONAR. In some embodiments, a pulse of ultrasonic energy may be emitted from the device. Then, the time required for an echo of that pulse to be received back at the device may be measured. The measured time can relate to a distance based on the known speed of ultrasonic transmission through the intervening medium (e.g., air 1890). Ultrasonic time-of-flight rangefinder devices may have several advantages, including among others relatively low power consumption, relatively high distance range, little impact from target color or transparency, and relatively low cost. Disadvantages of ultrasound time-of-flight may include relatively low measurement resolution, relatively low measurement rate, relatively large physical size, susceptibility to ambient ultrasonic noise and echoes, among others.

[0115] In another example, optical range-finding devices may operate in one of two exemplary manners, among others. In one example, triangulation may be used. To use triangulation, an optical emitter and receiver may be required. The emitter may generate a beam of light, for example in the infrared spectrum. The receiver may then record the angle at which the emitted light is reflected. The angle of reflection may be related directly to a distance. Advantages of optical triangulation may include relatively small size, relatively high measurement rate, commercial availability of relatively short- and long-range versions, and relatively good spatial resolution to name a few.

[0116] In another example, optical time-of-flight may be used, which is similar in many respects to ultrasonic time-of-flight, but instead uses light. The light used may be in the infrared spectrum or any other spectrum. Optical time-of-flight systems may utilize so-called light detection and ranging systems (e.g. LIDAR) and/or vertical cavity surface emitting lasers (VCSEL), to name just a few. Advantages of such systems may include, among others, high measurement rates, long range, high accuracy, and good spatial resolution.

[0117] In one exemplary embodiment, a VCSEL optical rangefinder may be utilized. As will be known by a person having ordinary skill in the art, rangefinders based on VCSEL modules may be available with a measurement range of near zero to approximately 1 meter with accuracy of approximately 2-4 mm. Their measurement rate may typically be about 10 samples/second. They may be designed to be positioned behind a protective glass surface, and as such may include features to ignore reflected light from that surface.

[0118] Referring now to FIG. 18C, the exemplary system of FIG. 18A is presented with an exemplary arrangement of rangefinders 1895 included (A-H). In this exemplary embodiment, a size and position of the patient's arm 1860 may be estimated relative to an interior area 1801 of the cuff 1800, and relative to the one or more measurement sensors 1810. According to some embodiments, a location and relative angle of each rangefinder 1895 could be known. Using this information and corresponding distance measurements taken by the one or more rangefinders 1895, the system 1800 could determine a set of points on the surface of the patient's arm 1860. Using the set of points, an estimate of the overall size and shape of arm 1860 may be determined.

[0119] In one example, the system may use a least-squares method to fit a geometrical shape (e.g. circle or ellipse). In other embodiments, other estimation techniques known in the art may be utilized to generally determine which portions of the interior area 1801 are filled by the patient's arm 1860 and which portions of interior area 1801 include, for example, only air 1890. Accordingly, the system 1800 would be able to determine the location of the arm 1860 relative to each of the one or more radiation sensors 1810 at any given point in time, thereby enabling the system to account for the relative differences in attenuation of a particle emitted from a radioactive area of interest 1803 as it travels to a sensor 1810. This additional information may be used to improve upon the estimation techniques disclosed hereinabove.

[0120] As noted above, the exemplary systems and methods disclosed hereinabove are not limited to a patient's arm (e.g., arm 1860), but any portion of the body or any area or region surrounding any radioactive area of interest. For example, the exemplary embodiments disclosed in, for example, FIGS. 16 and 17, among others, may be modified to include rangefinders (e.g., rangefinders 1895) and estimate size and shape of varying material densities within the measurement area.

[0121] In certain additional embodiments, systems and methods disclosed herein may further estimate the size and/or location of bone proximate an area of interest within the body and account for its relatively dense characteristics relative to tissue or air. Referring again to FIGS. 18A to 18C, for example, having determined the general size and position of, for example, a patient's arm 1860, it may be possible to estimate the relative size and location of bone 1865 within the arm 1860. Referring now to FIG. 19, various examples of tissue 1860 and bone 1865 placement within a measurement area (e.g. cuff 1800) are presented. FIG. 19A shows an example of an upper arm 1860 with bone 1865 positioned substantially in the center. FIG. 19B shows an example of lower arm 1860 with bone 1865 positioned substantially in the center, wherein the lower arm includes the radius and ulna, for example. FIG. 19C shows an example of upper arm 1860 positioned in a lower portion of cuff 1860 with bone 1865 substantially in the center. FIG. 18D illustrates, for example, a hand portion of arm 1860 positioned in a lower portion of cuff 1800 with estimates for the multiple bones of the hand depicted. Once again, by informing the system of what portion of the body is within the measurement area (e.g., cuff 1800), and measuring the relative size and location of the body within the system, the system can further estimate the location of bone and better account for particle attenuation as it travels from a radiation source (e.g. 1803) to a sensor 1810. This is true for other configurations as well, including for example the exemplary system 1600 presented in FIG. 16, and the system 1700 presented in FIG. 17. In FIG. 17, for example, a distance from the sensors 1710 to the head 1760 may be determined, and using such information, the system may estimate a thickness and/or position, etc. of the skull and account for the bone density relative to the brain tissue and/or air that a particle may encounter along its path to a sensor 1710.

[0122] Further, in some embodiments, the various arrangements of one or more rangefinders 1895 may be arranged not only in the 2-D configurations depicted in, for example, FIGS. 18A-18C, but also in 3-D configurations commensurate with the various sensor configurations disclosed hereinabove. For example, multiple rings of rangefinders 1895 or other 3-D arrangements may be utilized as desired to best survey an area of interest within the measurement area.

[0123] Additionally, in certain other embodiments, various other methods for estimating the size and/or shape of the tissue within a measurement area (e.g., the size and shape of arm 1860 within cuff 1800) may be utilized. For example, in some embodiments, one or more rangefinders 1895 may be utilized that are capable of scanning across an area of interest, thereby enabling measurements to be taken across various angles known angles within the system to capture more information and detail for determining the position and/or size of tissue/bone, etc. within the measurement region.

[0124] Alternatively, a system of lasers and/or cameras may be utilized to determine the size and/or location of tissue in the area of interest (e.g. arm 1860 in cuff 1800). Referring now to FIGS. 20A and 20B, an exemplary 3-D scanning arrangement using a laser line is depicted. FIG. 20A shows an example of a laser 2036 projecting a line of laser light 2037 onto an object (e.g. arm 1860). Positioned at a known offset angle, a digital camera 2038, for example, may view the same object with the line projected onto it. FIG. 20B illustrates an exemplary perspective of a camera 2038, with a line of projected laser light visible. Software algorithms may then be used to determine the curvature of the line, and by knowing the angle between projection and viewing, may reconstruct the object's size/shape in 3D for use in refining the estimate techniques disclosed hereinabove. Similarly, other types of light can be projected onto the object, including for example, structured light 3D scanning. In another example, a series of visible reference marks could be placed within the detector system (e.g., cuff 1800) and then viewed by one or more internal cameras. By inputting the relative location of each reference mark, the system could then determine the size and shape of an object placed into the system based on which reference marks were obscured.

[0125] Referring now to FIG. 21, yet another embodiment is presented wherein rangefinders 1895 may be utilized both to measure relative distances to areas of interest within, for example, cuff 1800, but also to other parts of a patient, including for example torso 1861. For example, rangefinders 1895 may be positioned relative to cuff 1800 for measuring, for example, an arm 1860 internal to cuff 1800, and also positioned externally for measuring, for example, the distance to, for example, torso 1861 external to cuff 1800. In such configurations, the system may, for example, account for the size and/or location of other portions of the body and/or other sources of radiation and account for the relevant attenuation of such outside particles (i.e. particles emitted from areas outside an area of interest (e.g., 1803) that may be measured by sensors 1810 (not pictured in FIG. 21), thereby providing a better estimate of, for example, a radioactive area of interest positioned within cuff 1800 when outside radiation sources may also be present.

[0126] As will be appreciated by those having ordinary skill in the art, substantially symmetrical (e.g. cylindrical) systems may not always be most advantageous for use with the varying shapes and sizes of the human anatomy or any other radioactive area of interest. For example, while not limited to such configurations, the depicted cylindrical configurations depicted in, for example, FIG. 18 may not always be desirable, and a non-symmetrical and/or deformable configuration may be desired to, for example, better fit the many different shapes/sizes of various patients, for example. One complication that may be introduced in such deformable systems is the non-uniform and/or unknown relative spacing between and among, for example, sensors 1810 and rangefinders 1895 that could be introduced. Absent a method for determining these relative positions and distances, the accuracy of the desired measurements and estimations to be conducted may be undesirably affected. It is therefore a further object of the present disclosure to provide systems and methods for providing, for example, deformable measurement cuffs or similar apparatus wherein the relative positions of the measurement sensors (e.g. sensors 1810) and/or rangefinders (e.g. 1895) can be determined for any desired measurement configuration and/or throughout a measurement period (e.g, when a patient is moving).

[0127] Referring now to FIGS. 22A-22C an exemplary wrap-around detector ring design is presented according to some embodiments. In some embodiments, a series of operatively connected detector plates 2205 may be utilized. Each detector plate 2205 may include one or more sensors or detector elements 2210. In some embodiments, the relative location of sensor(s) 2210 and a pivot point 2215 may be known through, for example, the design of the system (e.g., L1, L2, L3, etc.). When wrapped, for example, around an arm 2260 or other area of interest, an angle between detector plates 2205 may be determined using for example an angle measurement sensor positioned at or about pivot point 2215, and ultimately, the relative position/angle of the detector plates 2205 relative to the object about which they are surrounded (e.g., arm 2260), may be determined using lengths L1, L2, and L3 and trigonometric functions. Of course, there is no requirement that each detector plate be uniform in length, and/or that sensors 2210 be uniformly spaced in plates 2205, so long as the relative locations are known and/or determinable to the system by design. Further, by minimizing the length of plates 2205, and increasing the number of plates 2205, the closer the deforming wrap may align with the area of interest, thereby minimizing air gaps and other undesirable components of the system. Regardless, by knowing the length of the plates 2205 and positions of sensors 2210, it may be possible to estimate the area within the system filled by tissue (for example) relative to the remaining area filled with air (for example), and account for the differing densities as disclosed hereinabove.

[0128] Other such arrangements are also contemplated by the present disclosure. For example, and referring now to FIG. 23A, one or more sensors (e.g., 1810) may be positioned along a top detector plate 2301, and a bottom detector plate 2302. In such a configuration, plates 2301 and 2302 may be configured to translate, for example, up and/or down so as to rest on a top and bottom, for example, of an area of interest (e.g, arm 2260). In this configuration, the distance between the two plates could be altered in a known manner based on, for example, the size of the arm or other portion of the body or area of interest being measured.

[0129] In certain other embodiments, plates 2301 and 2302 may be curved as depicted, for example, in FIG. 23B, such that the curved plates generally conform to the shape of the area of interest to be measured (e.g, arm 2360). In such embodiments, where the relative distance between plates 2301 and 2302 is known, the relative positions of sensors (e.g. 1810) disposed with plates 2301 and 2302 may be known, thereby enabling the attenuation estimates disclosed hereinabove. The system may also be rotatable relative to a z-axis as illustrated in FIG. 23C.

[0130] In certain other embodiments, a combination of the arrangements disclosed in FIGS. 22A-22C and FIGS. 23A-23B may be utilized, such as, for example, system 2400 depicted in FIGS. 24A-F. In some embodiments, a system 2400 may include a fixed end track 2403 and a movable end track 2404, and one or more detector segments 2405. An area of interest to be measured (e.g., an arm 1860) may be positioned within system 2400 and movable end track 2404 adjusted such that the arm 1860 may be fit proximate to tracks 2403 and 2404. In doing so, detector segments 2405 may also be positioned proximate the arm 1860, in a manner such that the relative positions of sensors (e.g., sensor 1810) and/or rangefinders (e.g., rangefinder 1865) that may be disposed within detector plates 2205 are known, and estimation techniques disclosed herein may be utilized. FIGS. 24A-C illustrate three exemplary positions of a system with two detector segments 2405. FIGS. 24D-F illustrate three exemplary positions of a system with three or more detector segments, illustrating the finer radius that may be achieved as the number of segments is increased.

[0131] The present disclosure is non-limiting and may further include any other manner or means for determining the position of an object (e.g., a patient's arm, torso, or head) within a measurement area. Further examples may include any mechanisms for tracking the position of multiple targets in 3-D space, including optical tracking systems that use, for example, cameras and/or one or more light emitters; magnetic tracking systems that may utilize one or more magnetic detectors; radio-frequency (RF) tracking systems (e.g., radar); acoustic tracking systems; image recognition systems (e.g., 3d pose estimation and/or articulated body pose estimation); 3D scanning systems; and the like.

[0132] In certain other embodiments, a contour gauge system such as the exemplary systems 2500 disclosed in FIGS. 25A-D could also be utilized. In one example, a series of detector modules may be arranged such that they can move freely in one direction may be placed over the arm. The assembly may then be lowered over the area of interest (e.g., arm 2560), and each detector could conform to the surface of the arm 2560, for example, as contacted. A linear displacement along a z-axis, for example, of each detector could be determined and an understanding of the relative geometry within a measurement area of interest revealed. Combining the exemplary system of FIG. 25A-D with a corresponding set of detector elements under the arm may be advantageous as well. The various rods may also be motorized and/or include non-contact mechanisms such as distance measurement sensors that allow for the size and location of objects in the area of interest (e.g. arm 2560) to be determined without actually making contact. Such embodiments could be used in real-time to continuously determine the size/location such as, for example, when a patient is moving.

[0133] In certain other embodiments, mechanisms for determining the location of, for example, an arm 2560 may be utilized that account for clothing or other objects that may otherwise interfere with the detection systems described hereinabove. In one example, rods such as those depicted in FIG. 25A-D may include motors and force detectors such that each rod can be extended with a desired force to closely contact arm 2560for example, pressing clothing close to arm 2560 to get a better sense of the position/size of the arm 2560. In some embodiments (e.g., FIGS. 25C-D), a fixed detector array 2502 that includes one or more detectors (e.g., detectors/sensors 1810) may be included.

[0134] Other methods for determining a relationship between a detector rod and arm surface may also be utilized, including for example electrical skin conductivity, capacitance, inductance, ambient light, temperature, electrical signals from the body, heart beat detection, and others.

[0135] The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the claims of the application rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.