Specimen chamber for optical imaging of radiopharmaceuticals

Abstract

Apparatus for optical imaging of Cerenkov luminescence from an object subsequent to the object receiving a dose of a radiopharmaceutical, the apparatus comprising: a light tight enclosure within which the object can be received at a sample location; an imaging means; a means to mitigate direct particle impingement between the sample location and the imaging means; and one or more optical elements for transmitting Cerenkov photons from within the light tight enclosure to the imaging means.

Claims

1. Apparatus for optical imaging of Cerenkov luminescence from a sample subsequent to the sample receiving a dose of a radiopharmaceutical, the apparatus comprising: a light tight enclosure within which the sample can be received at a sample location; an imaging means outside of the enclosure, the imaging means for optical imaging of Cerenkov photons; a radiation shield disposed between the sample location in the enclosure and the imaging means, wherein the radiation shield is configured to protect the imaging means from radiation emitted from the sample; and one or more optical elements for guiding the light path of the Cerenkov photons emitted from the sample along a hollow optical conduit, the one or more optical components being arranged in the hollow optical conduit to turn the Cerenkov photons through an angle around the radiation shield, to the imaging means outside the enclosure.

2. Apparatus according to claim 1, wherein the imaging means is positioned and/or oriented relative to the sample location to minimise radiation impingement on the imaging means.

3. Apparatus according to claim 1, wherein the enclosure is a light tight specimen chamber.

4. Apparatus according to claim 3, where in the chamber comprises a door in a wall of the chamber that, when open, allows access to the inside of the chamber and when closed ensures a light tight seal with surrounding parts of the chamber to maintain the light tightness of the chamber interior for imaging the sample.

5. Apparatus according to claim 4, comprising a seal around the perimeter of the door to provide the light tight seal between the door and surrounding parts of the chamber wall when the door is closed.

6. Apparatus according to claim 5, wherein the position of the sample platform can be adjusted within the enclosure relative to the optical element.

7. Apparatus according to claim 3, comprising means within the chamber that can be used to confirm whether or not the chamber is light tight once the door is closed.

8. Apparatus according to claim 1, wherein the sample location is provided by a sample platform mounted within the enclosure on which the sample can be placed.

9. Apparatus according to claim 1, comprising a frame within which the sample is held at the sample location to prevent the sample from deforming and/or to spatially position and orient the sample.

10. Apparatus according to claim 1, wherein the imaging means is a CCD camera.

11. Apparatus according to claim 10, wherein the camera is an emCCD camera.

12. Apparatus according to claim 1, wherein the imaging means includes an image detector with a surface on which the Cerenkov photons impinge and the imaging means is oriented so that the image detector surface is substantially normal to a wall of the enclosure it is mounted adjacent to.

13. Apparatus according to claim 1, wherein the radiation shield surrounds a majority of the sides of the imaging means.

14. Apparatus according to claim 1, wherein the one or more optical elements for Cerenkov photons from within the light tight enclosure to the imaging means comprise a lens and a light tight optical conduit for Cerenkov photons collected by the lens to the imaging means.

15. Apparatus according to claim 14, wherein the focus of the lens can be varied and adjustment of the lens focus is motorised so that controls can be provided outside the enclosure to facilitate focusing the lens.

16. Apparatus according to claim 1, further comprising one or more lights within the enclosure that can illuminate the enclosure to facilitate acquisition of an illuminated image.

17. Apparatus according to claim 16, comprising a mechanical shutter to cover the light(s) during periods of CLI acquisition and to uncover the light(s) during periods of illuminated image acquisition.

18. Apparatus according to claim 17, wherein the mechanical shutter is arranged such that it is synchronised to an image acquisition sequence.

19. Apparatus according to claim 16, wherein the apparatus is controllably arranged such that duration on CLI acquisition periods is longer than illuminated image acquisition periods.

20. Apparatus according to claim 16, wherein the apparatus is controllably arranged such that there is a delay between illumination being removed from the enclosure and commencement of the CLI acquisition.

21. Apparatus according to claim 16, wherein the apparatus is controllably arranged such that a single imaging means is used to capture CLI images and illuminated images, the imaging means being switchable between an illuminated level image mode and a low light level image mode for capture of the illuminated and CLI images respectively.

22. Apparatus according to claim 21, wherein the apparatus is controllably arranged such that switching of the camera modes is synchronised with the switching on and off of the light(s) in the enclosure.

23. Apparatus according to claim 1, further comprising one or more ports in a wall of the enclosure that allow access for a hand or instrument without damaging the integrity of the light tight enclosure.

24. Apparatus according to claim 1, further comprising a Cerenkov radiator that can be placed over the sample in the enclosure.

25. The apparatus of claim 1, wherein the one or more optical components comprises a beam-splitter.

26. A method for optical imaging of Cerenkov luminescence from a sample subsequent to the sample receiving a dose of a radiopharmaceutical, the method comprising: placing the sample in a light tight enclosure; illuminating the interior of the enclosure with light and capturing an illuminated image of the sample in the enclosure whilst the interior of the enclosure is illuminated; and capturing a Cerenkov luminescence image of the sample in the enclosure when the interior of the enclosure is not illuminated, wherein capturing the Cerenkov luminescence image comprises using one or more optical elements to guide the light path of the Cerenkov photons emitted from the sample along a hollow optical conduit, the one or more optical components being arranged in the hollow optical conduit to turn the Cerenkov photons through an angle around a radiation shield, to impinge on an imaging means outside the enclosure; wherein the radiation shield is configured to protect the imaging means from radiation emitted from the sample.

27. A method according to claim 26, wherein a plurality of alternating illuminated and Cerenkov images are captured, the interior of the enclosure being intermittently illuminated, the illumination of the interior of the enclosure coinciding with capture of the illuminated images.

28. A method according to claim 26, wherein the illuminated image(s) and Cerenkov image(s) are overlaid.

29. A method according to claim 26, wherein the illuminated and Cerenkov images are captured by a single camera having two modes, one for capture of the illuminated image and one for capture of the Cerenkov image, the method comprising switching the camera between the two modes in synchronisation with the illumination of the interior of the enclosure.

30. A method according to claim 26 employing an apparatus in accordance with claim 1.

31. A method for optical imaging of Cerenkov luminescence from a sample subsequent to the sample receiving a dose of a radiopharmaceutical, the method comprising the steps of: placing the sample in a light tight enclosure; illuminating the sample with light from a light source located within the enclosure; capturing a first image with a first imaging means whilst the sample is illuminated with white light from the light source, the first imaging means having a first dynamic range; and capturing a second image with a second imaging means configured for Cerenkov luminescence imaging whilst the sample is not illuminated with light from the light source, the second imaging means having a second dynamic range; wherein light paths feeding the first and second imaging means pass through optical elements such that the first and second imaging means both image the same region of the sample.

32. The method of claim 31 wherein the first image and the second image are superimposed.

33. The method of claim 31 wherein the sample is illuminated with light having a wavelength of between 500-740 nm.

34. The method of claim 31, wherein the sample is illuminated with light having a wavelength of between 435-500 nm.

35. The method of claim 31, including the step of applying strobed or spectrally separated lighting.

36. An apparatus for optical imaging of Cerenkov luminescence from a sample subsequent to the sample receiving a dose of a radiopharmaceutical, wherein the sample is intermittently illuminated with white light, the apparatus comprising: a first imaging means for capturing a first image of the sample whilst the sample is illuminated, the first imaging means having a first dynamic range; and a second imaging means configured for Cerenkov luminescence imaging for capturing a second image of the sample whilst the sample is not illuminated with said light, the second imaging means having a second dynamic range; and one or more optical elements, wherein light paths feeding the first and second imaging means pass through the optical elements such that the first and second imaging means both image the same region of the sample.

37. The apparatus of claim 36 wherein the apparatus comprises processing means to superimpose the two images.

38. The apparatus of claim 36, wherein the imaging means comprises a monochromatic camera capable of applying sequential red, green and blue illumination in any order, to provide a full-colour image.

39. The apparatus of claim 36, wherein the one or more optical components comprises a beam-splitter and wherein the light paths feeding the first and second imaging means coincide with the beam-splitter.

Description

BRIEF DESCRIPTION OF FIGURES

(1) Examples are now described with reference to the accompanying drawings, in which:

(2) FIG. 1 shows schematically a specimen imaging chamber in accordance with an embodiment of the invention;

(3) FIG. 2 schematically shows the effect of sample platform position on field of view for the specimen chamber of FIG. 1;

(4) FIG. 3 schematically illustrates an embodiment in which two imaging means are used, which could be used in combination with a specimen chamber of the type shown in FIG. 1;

(5) FIG. 4 shows an example embodiment of the invention that uses stroboscopic illumination;

(6) FIG. 5 shows an example sequence of stroboscopic illumination, Cerenkov image acquisition and structural image (e.g. illuminated) acquisition of an example embodiment of the invention;

(7) FIG. 6 is a schematic view of an optical light shield and camera setup used in experiments to illustrate the principles of embodiments of the invention;

(8) FIG. 7 shows the layout of sample wells used in the experiments;

(9) FIGS. 8a and 8b show Cerenkov images captured during the experiments;

(10) FIG. 9 is a graph of signal photon rate for each of the experimental wells;

(11) FIG. 10 schematically shows an arrangement that employs two cameras and an optical coupler and shutter to direct light to the two cameras;

(12) FIGS. 11a and 11b show two alternative arrangements for the optical coupler used in the arrangement of FIG. 10;

(13) FIG. 12a shows a plan view and FIG. 12b a cross-section of a rotating disc shutter that can be used to shutter a light source and an emCCD camera.

DETAILED DESCRIPTION

(14) FIG. 1 shows a specimen imaging chamber apparatus in accordance with an embodiment of the invention that can be used to image an object, for example a tissue sample, using CLI. The invention will be exemplified with reference to imaging a tissue sample but the skilled person will understand that other objects may be imaged.

(15) The apparatus includes a light tight chamber 2 in which a sample S can be supported on a sample platform 4. The chamber 2 has a door 6 that can be opened to give access to the interior of the chamber 2, for example for introduction of removal of a sample S. A seal 8, in this example a labyrinth seal, around the periphery of the door ensures the light tightness of the chamber when the door is closed.

(16) An imaging system is mounted on the top of the chamber. This system includes a lens 10 that collects light from within the chamber (including light from the sample) and a camera 12. In this example, the camera is an emCCD camera. The lens preferably has a motor-driven focus, so that it can be focussed using a remote controller external to the chamber 2.

(17) Light is transmitted from the lens 10 to the camera 12 through a light guide 14, which turns through a 90 degree angle. A mirror 16 in the light guide 14 deflects the light from the lens 10 to direct it onto an image detector (not shown) of the camera 12. With this arrangement, the surface of the image detector can be arrange to be normal to the top face of the chamber on which the camera is supported, so as to minimise the cross-section of the detector potentially exposed to x-rays or beta-particles escaping the chamber. To better protect the camera 12 from unwanted radiation, it is housed within a radiation shield 18.

(18) The interior of the chamber 2 can be illuminated with illuminated (e.g. white light or RGB light) by one or more light sources 20 within the chamber. The light sources may be LEDs. With the chamber illuminated, the camera 12 can capture illuminated images (video or still) of the sample S in the chamber.

(19) The illumination in the chamber 2 can be “switched off” by covering the light source(s) 20 with a mechanical shutter 22. In this example, the shutter is a rotatable disc that includes one or more openings 24. As the disc 22 is rotated is selectively uncovers and then covers the light source as the opening(s) 24 in the disc come into registration with the light source(s) 20. With the light source switched off, the imaging system can acquire low light level images such as Cerenkov images from a sample that has been dosed with a beta-emitting radiopharmaceutical.

(20) FIG. 5 shows an example sequence of the stroboscopic pulses and intervals. In an example embodiment, strobe illumination may be >100 Hz and the pulse duration (PD) may be 10-1000 microseconds in an example embodiment. Structural image (i.e. illuminated image) acquisition is performed during the stroboscopic pulse duration. In this example embodiment the time or gating offset (GO) between the strobe pulse and the acquisition of the second image is sufficiently long to allow for the decay of any induced tissue autofluorescence, and also for any charge on the CCD of the camera to be cleared. In an example embodiment, if the pulse duration (PD) is 1000 microseconds, the pulse interval (PI) is 9000 microseconds, and so the gating offset (GO) may be 2000 microseconds and the second (Cerenkov) image acquisition time is 7000 microseconds. In another example embodiment, if the pulse duration (PD) is 10 microseconds, the pulse interval (PI) is 9990 microseconds and so the gating offset (GO) may be 1990 microseconds and the second (Cerenkov) image acquisition time is 8000 microseconds.

(21) The sample platform 4 can be raised and lowered using a scissor jack 26 powered by an electric motor (not shown). The height of the platform can be adjusted to change the distance between the sample platform 4 (and hence the sample S on it) and the lens 10. As illustrated in FIG. 2, in this example this distance can be adjusted between 50 cm and 15 cm with a corresponding change in the field of view. As the field of view decreases, the physical resolution of the image increases.

(22) The chamber also includes a light tight access port 28 through which the sample S can be accessed with an instrument of a gloved hand for example whilst maintaining the light tightness of the chamber 2. This access port may be a glove port for example.

(23) As noted above, the specimen chamber apparatus uses an emCCD camera to acquire low light level images. Illuminated images are also captured with the same camera. To achieve this with the emCCD camera, one important aspect of the approach is to thermally cycle the camera when switching between low and high light levels. This is to ensure the camera does not experience high light levels when it is cooled in order to prevent ghost imaging. This is because the lifetime of photoelectrons is greatly enhanced at cold temperatures and the read out of stray photoelectrons from a bright image can be seen as noise in subsequent frames. This effect is long lasting and can adversely affect the signal to noise for many hours after exposure to illuminated.

(24) The following is an exemplary procedure for acquiring images using the apparatus of FIG. 1.

(25) 1. Switch on camera and imaging software that drives it.

(26) 2. Open the door and adjust the sample stage to the desired height. This will depend on the desired field of view.

(27) 3. Load the sample

(28) 4. Ensure the door is properly closed to achieve a light tight enclosure.

(29) Initially it may be useful to use a continuous (video) image from the camera in order to guide the choice of stage height used.

(30) For Normal Illuminated Imaging:

(31) 5. Ensure the cooler for the camera is switched off.

(32) 6. Use camera settings suitable for normal light level imaging.

(33) Typical Normal Illuminated Level Imaging Settings (Ambient Temperature)

(34) TABLE-US-00001 Readout rate 3 MHz Conventional Pre-Amplifier Gain 3x Vertical shift speed 3.3 μs Vertical clock voltage Normal EM gain Disabled Exposure time 0.01 s
7. Acquire a continuous live video image.
8. Switch on the internal lights—the light level is preferably adjustable so that it can be set such that the camera receives enough light without saturation.
9. Use the external focus controller to bring the target sample into sharp focus.
10. The image capture software may enable the image orientation to be changed if desired.
11. When happy, acquire a single still illuminated image.
12. Save the image.

(35) For Low Light Level Imaging:

(36) 13. Ensure the door is properly closed and ensure that the internal lights are switched off.

(37) 14. Switch on the camera cooler and set the temperature to −80° C.

(38) 15. Change the camera settings for low light level imaging.

(39) Typical Low Light Level Imaging Settings (−80° C.)

(40) TABLE-US-00002 Readout rate 1 MHz Electron Multiplying Pre-Amplifier Gain 3x Vertical shift speed 0.5 μs Vertical clock voltage +1 EM gain 300.sub.3 Exposure time 5 s
16. Before acquiring an image ensure the temperature has reached −80° C. and is stable.
17. Acquire an image.
18. The image quality can be enhanced by introducing on chip binning (e.g. 8×8 on chip binning for fast acquisition times). For higher resolution, the acquisition time can be increased.
19. For long integration times, when many photons per pixel can be collected, better results can often be obtained by using the conventional CCD mode:

(41) Typical Long Integration Time Settings (−80° C.)

(42) TABLE-US-00003 Readout rate 80 kHz Conventional Pre-Amplifier Gain 3x Vertical shift speed 3.3 μs Vertical clock voltage Normal EM gain Disabled Exposure time >100 s
20. Save the low light image.
21. Ensure EM gain is switched off before opening the door. The cooler should also be disabled to prevent ghosting during the next low light level acquisition.

(43) FIG. 10 shows an alternative camera arrangement that could be used with the embodiment of FIG. 1, in which two cameras are used, an emCCD camera for CLI and a colour video camera for illuminated (e.g. anatomical) imaging. An optical coupler and shutter direct light to the two cameras and shutter is emCCD camera during periods when the interior of the chamber is illuminated. The shutter is controlled by a shutter controller to be synchronised with the illumination.

(44) FIG. 11a shows one exemplary configuration for the optical coupler and shutter. In this example a single aspheric lens is used for coupling out of the fibre bundle and focussing on to both cameras. A high transmittance beam splitter option is shown.

(45) FIG. 11b shows another option for the configuration of the optical coupler. In this example, a modular setup is used with a collimating lens coupling out of the fibre bundle and a focussing lens attached to each camera. The high transmittance beam splitter option is shown in this example too.

(46) FIGS. 12a and 12b show an alternative shutter arrangement that can be used to shutter both the light source and the emCCD camera in embodiments where these two components are located adjacent to one another. The shutter is a rotating disc that is configured to cover both the light source and the emCCD lens. The disc is driven by a motor and as it rotates, windows in the disc, aligned respectively with the light source and the emCCD lens (which are at different radii) mean that the light source and the emCCD camera lens are selectively covered and uncovered. The relative positions of the windows ensure that the emCCD lens is covered when the light source is uncovered. As best seen in FIG. 12a, the emCCD windows are longer than the windows for the light source, to give a longer CLI acquisition period compared with the illuminated image acquisition period.

(47) Turning to FIG. 3, we now discuss another embodiment of the invention. This example embodiment allows CLI to be performed under lit conditions. In this example embodiment, the background lighting is completely eliminated, and monochromatic red LED lighting is used to illuminate the object. However, the various features discussed, especially image acquisition using two cameras, could be used in embodiments of the invention using a specimen chamber as discussed above.

(48) In this example embodiment, an object is injected with .sup.18F-Fluorodeoxyglucose (FDG) (a common beta-emitting radiopharmaceutical). The radiopharmaceutical may be injected systemically, or locally. The injection may be intratumoral, peritumoral, or to the local arterial supply. Commonly, there is a narrow time window of around 60 to 90 minutes post-injection for a scan to be performed. This is a result of the use of radiopharmaceutical. Local injection directly has the advantage that it can lead to an earlier time window for performing CLI, and lower radiopharmaceutical dosage. A surgeon, for example, may choose to perform an image before carrying out a procedure, or perform a procedure then carry out imaging subsequently. The former may be useful, for example, for obtaining or confirming particulars, while the latter may be useful for checking the success of the procedure, for example.

(49) Two separate cameras (C1 and C2) are used to image the illuminated image and the Cerenkov image respectively. Using two separate cameras allows for the spectral response and dynamic range to be selected separately for each image. The second camera (C2) is an ultra-sensitive camera such as a cooled CCD camera, which may be a cryogenically cooled CCD camera. For the first camera (C1), one or more monochromatic or colour cameras may be used. By rapidly applying (in any order) sequential red, green and blue illumination and then composing the image, full colour imaging can be provided. The speed at which the illumination is applied is determined by the desired frame rate of the video image.

(50) In alternative embodiments, use of very low levels of illumination and a single camera may be used to take advantage of the sensitivity of the CLI camera. This illumination could be flashed red, green and blue if a colour image is required.

(51) A CLI camera may have a light collector and/or lens to collect weak light. The light collector and/or lens may be built in to the camera. The lens may be a Fresnel lens. The light collector may be a shaped mirror. The mirror may be parabolic.

(52) The light collector may be made of a material which has low scintillation for beta and gamma radiation. Scintillation is undesirable as it results in light being emitted that interferes with the signal.

(53) A large aperture lens with low f number is preferred. This arrangement means that more light can be collected. Usually this is undesirable because it leads to distortions. However, it has surprisingly been found that the spatial resolution is sufficiently maintained for CLI, which generally has a comparatively poor spatial resolution, so that the improvement in light input outweighs the loss of spatial resolution.

(54) The light reflected from the object is passed through a beam splitter (BS) such as a dichroic prism that directs the red light to the first camera and the non-red light to the second camera. The second camera is also equipped with a band-pass filter (BP) to block any residual red light. The need for the band-pass filter will depend on the performance of the beam-splitter. The role of red and blue may be reversed to allow, for example, a surgeon to see deeper into tissue.

(55) C2 is also enclosed within a radiation shield (e.g., lead shielding) (RS) to block any interference from x-rays or beta-particles. The plane of the camera chip within C2 may also be placed parallel to the incoming light to minimize the cross-section exposed to x-rays or beta-particles.

(56) Image processing (P) is applied to the two images (I1 and I2) to calibrate the intensity windowing and apply image registration, if required. To further segment the Cerenkov image, additional imaging processing can be performed on I2 including both spectral and spatial information. For example, it can be specified that the Cerenkov image only comes from a restricted field-of-view (such as the surgical site) within I2. Another example is that the signal within a pixel should fit the expected Cerenkov spectrum. The final image (I) is generated by superimposing the calibrated Cerenkov image (I2) on the illuminated image (I1).

(57) In another embodiment of the invention, CLI can be performed in intervals between stroboscopic pulses of light. In this example embodiment, the object is illuminated by automatic stroboscopic illumination. In this embodiment the illumination is white-light illumination with a gated shutter using a digital micro-mirror apparatus (DMD). Other methods of shuttering are contemplated within the scope of the invention. In some embodiments, the strobed, or spectrally separated, lighting may be provided within an optical shroud. In some embodiments, the strobed, or spectrally separated, lighting may be provided in the room.

(58) This embodiment uses a similar apparatus setup to the embodiment described above. In this example embodiment the acquisition of the second image is gated off of a signal from the stroboscopic illumination system, as shown by FIG. 4. The gated acquisition is performed using a digital micro-mirror apparatus (DMD). In this example where stroboscopic illumination is used, a trigger (TR) connects the DMD to the light source. Connecting the light source and the DMD by the trigger allows light to be directed to one of two cameras for separate imaging of the Cerenkov or structural images.

(59) FIG. 5 shows an example sequence of the stroboscopic pulses and intervals. In an example embodiment, strobe illumination may be >100 Hz and the pulse duration (PD) may be 10-1000 microseconds in an example embodiment. Structural image (i.e. illuminated image) acquisition is performed during the stroboscopic pulse duration. In this example embodiment the time or gating offset (GO) between the strobe pulse and the acquisition of the second image is sufficiently long to allow for the decay of any induced tissue autofluorescence, and also for any charge on the CCD of the camera to be cleared. In an example embodiment, if the pulse duration (PD) is 1000 microseconds, the pulse interval (PI) is 9000 microseconds, and so the gating offset (GO) may be 2000 microseconds and the second (Cerenkov) image acquisition time is 7000 microseconds. In another example embodiment, if the pulse duration (PD) is 10 microseconds, the pulse interval (PI) is 9990 microseconds and so the gating offset (GO) may be 1990 microseconds and the second (Cerenkov) image acquisition time is 8000 microseconds.

(60) In another embodiment of the invention, the camera system may also be implemented in an endoscope or “chip-in-tip” application, as shown in FIG. 4. In this embodiment, C1 is mounted within a fibre optic (FO). C1 is placed near the distal end of the endoscope, and light is transmitted to the proximal end to be read by C2. The beam-splitter may be placed on the distal end of the endoscope.

(61) FIG. 6 shows a schematic view of an exemplary optical light shield and camera setup in line with the present invention and used for the experiments discussed below. In this example, an iXon camera is positioned directly above a sample to be imaged (not shown) on a metal mounting plate b. An f/1.8 lens c is located beneath the camera and metal mounting plate b. A plastic (PVC) tube d extends between the metal mounting plate b and the sample to be imaged. The plastic tube d is lined with a low reflectance flock lining e. The sample is surrounded by packing foam g, which is covered with a neoprene rubber sponge lining g, in turn covered with stretched elastic h.

(62) In some embodiments, a phantom, or testing replica, for ultra-weak light may be used to calibrate the light system. The phantom may use a light emitting diode (LED) with a stack or layers of neutral density filters. If necessary, the LED may be driven with a modulated waveform to further and controllably reduce the output of the LED. Such a phantom may also or alternatively be useful for maintenance and quality control of the light system.

(63) The skilled person will appreciate that various modification to the specifically described embodiment are possible without departing from the invention. The following examples are used to support certain aspects of embodiments the invention.

Example

(64) In vitro measurements of Cerenkov radiation emitted from F18 FDG were conducted using an iXon Ultra 897 emCCD camera.

(65) The camera was set up so that the experiment could be conducted inside a lead enclosure with the operation of the laptop on the other side of a room. The camera had the following settings: 50 mm f/1.8 lens CCD temperature: −80° C. 1 MHz pre-amplifier with a gain setting 3 0.5 μs vertical shift speed 300×EM Gain The field of view is 47×47 mm

(66) F18 was diluted and distributed into six 0.2 mL experimental wells inside a Perspex™ (PMMA) block. Three control wells with inactive material were also prepared. FIG. 7 illustrates the layout of the experimental wells.

(67) The liquid volume and initial activity concentration in the active wells is shown in the table below.

(68) TABLE-US-00004 Activity concentration Activity (μCi) Volume (μl) (nCi/μl) No. wells 2 200 10 4 1 100 10 1 0.5 200 2.5 1

(69) One control well and one active well with activity 2 μCi were covered with 6 mm thick BK7 glass. One control well and one active well with activity 2 μCi were covered with 6 mm thick BK7 glass and black masking tape. The BK7 glass is inset, with the wells under it 6 mm below the level of the other wells as viewed by the camera. The black masking tape was placed between the wells and the glass, leaving the glass open for viewing.

(70) The sample block was prepared and placed under the shielded camera, which was then lowered into place and draped to give a light tight enclosure. Images with the following settings were acquired: 1. 1 s integration time, 16×16 resolution (32×32 binning) 2. 3 s integration time, 16×16 resolution (32×32 binning) 3. 5 s integration time, 32×32 resolution (16×16 binning)

(71) Further images with the same settings were taken, with the room lights on and off, at regular intervals throughout the experiment.

(72) After the experiment each image was exported and the raw data in counts is converted to a signal in photo-electrons (or detected photons) using the following formula:

(73) $\mathrm{Signal}\left(\mathrm{photoelectrons}\right)=\frac{\left(\mathrm{Signal}\left(\mathrm{counts}\right)-\mathrm{Bias}\mathrm{Offset}\right)\times \mathrm{Conversion}\mathrm{Factor}}{\mathrm{EM}.\mathrm{Gain}}$
Bias Offset=200 counts
Conversion Factor=4.27 electrons/count
EM Gain=300
Results

(74) FIG. 8a shows a set of images taken approximately 15 minutes into the experiment with the lights on and lights off. The positions of the wells have been circled in the top left image using the same scheme as FIG. 6. It can be seen that a higher resolution of 32×32 is obtainable in 5 seconds. In addition to the Cherenkov emission interference from high energy rays can be seen as random white pixels that have a signal level beyond the scale used.

(75) FIG. 8b shows set of images taken approximately 180 minutes into the experiment. Even with the lower signal levels there is no discernible difference due to the room lights. The higher activity wells are still easily visible and the lowest activity well is still discernible.

(76) FIG. 9 shows the signal photon rate for each active sample well, after correcting for the background by subtracting the corresponding control signal. Each point on the graph represents an image of the sample. The measured decay constant corresponds to a half-life of 108 minutes.

(77) All three control samples showed no signal. The signal from the open wells was proportional to their initial activity. The signals showed exponential decay with a half-life matching that of the F18 FDG (110 minutes). Therefore, it was concluded that Cerenkov radiation due to activity of F18 FDG was being measured.

(78) The active well covered by glass but not masked produced a similar signal to the open active wells. The masked well showed no visible signal, and was quantified to be 10% of the signal obtained from the unmasked well. Therefore it was concluded that the scintillation in optical BK7 glass was insignificant.

(79) There was significant interference from gamma rays. However, it was shown in principle that higher resolutions are possible if the sensor is shielded from gamma rays and direct particle impingement. Further, it was possible to detect activities as low as 160 nCi (0.8 nCi/μl) with a spatial resolution down to 400 μm.