Nuclear imaging with a modified compton camera

Abstract

An apparatus, system and methods are provided for performing nuclear imaging with a modified Compton camera. The modified Compton camera features multiple gamma detectors for detecting gamma rays emanating from a subject (e.g., a human patient injected with a radiopharmaceutical), and a collimator for collimating incident gamma rays. Instead of the cone-shaped volume of space that a traditional Compton camera identifies as the origination of a given detected gamma ray, collimation of incoming rays allows the modified Compton camera to reduce the volume of uncertainty or probability to a planar volume. The resulting images of the subject benefit from higher signal-to-noise ratios compared to a traditional Compton camera.

Description

NUCLEAR IMAGING WITH A MODIFIED COMPTONCAMERAInventor: Brahim MehadjiRELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 708,014, filed 16 October 2024 (docket number UC24-9BX-1PSP), the contents of which are incorporated herein by reference.BACKGROUND

[0002] This disclosure relates to the fields of electrical engineering and medical devices. More specifically, a portable device or apparatus is offered that provides images having improved signal-to-noise ratio for radiotracer imaging using a modified Compton camera, and may be combined with other medical imaging technology such as an ultrasound detector.

[0003] Nuclear imaging methodologies (e.g., PET or Positron Emission Tomography, SPECT or Single Photon Emission Computed Tomography), also known as scintigraphy, use gamma radiation emitted by an injected radiopharmaceutical to map areas within a body where the substance accumulates. After the radiopharmaceutical (or radiotracer) is introduced to a subject’s body, external detectors detect gamma radiation emitted by the pharmaceutical and reveal the physiological function or status of the area(s) in the subject where the radiopharmaceutical has aggregated. Nuclear imaging is generally used to diagnose and / or aid in the treatment of disease, such as cancer and coronary artery disease. Furthermore, determining the depth of specific tissue within a human body is crucial for successful biopsies and surgeries. However, traditional methods of performing nuclear imaging require substantial preparation time (e.g., to introduce the radiopharmaceutical and allow it to distribute), and its use is limited to traditional radiological rooms equipped with the necessary detection apparatus, which is not portable.

[0004] Ultrasound imaging, also known as sonography and ultrasonography, uses sound waves to generate pictures of organs, tissues, and other anatomical structures inside a subject body. Ultrasound imaging is lower in cost than nuclear imaging, but has a limited field of view, requires a cooperative subject, and must be performed by a skilled operator. Ultrasound images tend to focus on specific bodily structures for diagnosis and / or as part of a therapeuticprocedure. For example, ultrasound may be used to guide needle biopsies for soft-tissue sarcoma and lymph nodes, but the false negative rate using ultrasound alone can be as high as 20%.

[0005] A Compton camera, like other gamma cameras, detects gamma radiation. Originally developed for astronomical observations, attempts have been made to employ it for medical imaging. However, the way it estimates the source of incident radiation allows for much uncertainty, and its wide field of view (FOV) means that it may collect a lot of noise while also capturing useful radiation, which decreases the accuracy of the resulting imagery.

[0006] Moreover, many or most existing nuclear medicine imaging devices and technologies do not permit simultaneous use of different imaging techniques (e.g., nuclear imaging and ultrasound), or cannot do so with high resolution. Therefore, there remains a need for a medical imaging scheme that is portable and easy to use, that can simultaneously deploy multiple imaging technologies, and that provides good resolution.SUMMARY

[0007] In some embodiments, a system, apparatus and methods are provided for improved nuclear imaging using a Compton camera, which may be co-located with another medical instrument, such as an ultrasound transducer. Configurations of the apparatus and system provided herein reduce the uncertainty regarding the origination of gamma radiation captured with the camera, thereby increasing the signal-to-noise ratio of the resulting images. In addition, the apparatus and system are portable, meaning that their use is not limited to existing radiology suites.

[0008] In these embodiments, a modified Compton camera features a relatively narrow aperture, thereby restricting the angles of incidence of incoming gamma rays and reducing the zones of probability or uncertainty regarding the points from which the gamma rays were emitted. More particularly, whereas traditional Compton cameras have wide fields of view that can only limit a gamma interaction incident to a three-dimensional cone of probability, in the presently discussed embodiments the restricted aperture of a given implementation can limit the uncertainty to, or almost to, a planar volume, thereby greatly increasing the signal-to-noise ratio of images and decreasing uncertainty as to the origin of a gamma ray.

[0009] In some implementations, an apparatus for performing nuclear imaging, possibly in connection with another imaging technique, features an elongated enclosure having a front end open to face a subject from which gamma radiation will be received. The rear end of the enclosure, which is substantially parallel to the front end, may be closed and / or may be configured with signal conduits for transmitting detection event data from the apparatus to a microprocessor or other controller.

[0010] Besides the front end that comprises apertures for one or more imaging chambers, and the bottom end, the enclosure is defined primarily by four walls. Two opposing walls of the apparatus may be longer than the other two opposing walls so that the enclosure is elongated along one axis. Scattering and absorbing gamma detectors are positioned within the enclosure, and extend substantially the entire distance between each of the four walls at different depths within the enclosure. A display component is also coupled to the apparatus to display images that recreate the events captured by the apparatus.

[0011] Testing of the apparatus confirms that it enables cross-sectional imaging of a radiopharmaceutical from a single position, thereby providing real-time nuclear imaging. In different configurations, the images may be two-dimensional or three-dimensional. For example, the apparatus may be rotated around the imaging subject or, as one alternative, the apparatus is configured with multiple imaging chambers that perform cooperative imaging to yield three- dimensional output.DESCRIPTION OF THE FIGURES

[0012] Figure 1 is a diagram of a traditional Compton camera.

[0013] Figures 2A-C illustrate a modified Compton camera according to some embodiments.

[0014] Figures 3A-B illustrate another modified Compton according to some embodiments.

[0015] Figure 4 is a diagram of the effect of a modified Compton camera, according to some embodiments.

[0016] Figures 5A-B illustrate a modified Compton camera configured to enable reconstruction of three-dimensional images, according to some embodiments.

[0017] Figures 6A-B comprise images of two radioactive point sources, according to some embodiments.

[0018] Figure 7 is a flowchart demonstrating a method of operating a modified Compton camera, according to some embodiments.DESCRIPTION

[0019] The following description is presented to enable any person skilled in the art to make and use the disclosed embodiments, and is provided in the context of one or more practical applications and their requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of those that aredisclosed. Thus, the present invention or inventions are not intended to be limited to the embodiments shown, but rather are to be accorded the widest scope consistent with the disclosure.

[0020] A device and methods are described herein for nuclear imaging that provides real-time cross-sectional images, low complexity setup, improved surgical workflow, fast acquisition time, and enhanced safety for both subjects and operators. In the disclosed embodiments, the device comprises a Compton camera that has been modified to overcome its historical limitations. The device is portable and in some embodiments is even hand-held, but is also effective in producing quality images from a stationary position.

[0021] Figure 1 depicts the principle of operation of a traditional Compton camera. A subject (a radiopharmaceutical introduced to a human subject) emits gamma ray 104 that is captured by Compton camera 110, which comprises two detectors - scatterer 112 and absorber 114. Collision of the gamma ray with scatterer 112 causes emission of a photon having a particular energy profile (i.e., 511 keV). That photon may interact with absorber 114. Based on the energies detected at the scatterer and the absorber, and the location at which the gamma ray and / or photon are detected, event cone 106 can be reconstructed to define a three-dimensional volume of space before the camera (e.g., and within the subject) from which the gamma ray emanated. The event cone’s vertex is the point of interaction of the gamma ray with scatterer 112, and the axis of the event cone is colinear with a line segment connecting the points of interaction within scatterer 112 and absorber 114. By calculating intersections between many overlapping event cones from many events, a map of the origination points of the events can be reconstructed and displayed. Because the event cones encompass large three-dimensional volumes, however, the resulting images are blurry and imprecise.

[0022] Embodiments of the invention provided herein, however, significantly reduce the uncertainty regarding the origination points of gamma events, almost to planes instead of cones. In these embodiments, barriers are employed to promote collimation of incident gamma rays, reduce noise, and ultimately reduce the uncertainty regarding their points of emanation. These barriers (e.g., extended walls, baffles, partitions) prevent gamma rays outside of a narrow range of angles from reaching an imaging chamber comprising the camera’s scatterer or absorber.

[0023] Therefore, incident gamma rays detected by the Compton camera provided herein necessarily emanate from locations directly before the camera and a short distance to either side. Gamma rays from other locations are blocked by the barriers. However, by moving (e.g., rotating, tilting, panning) the apparatus, different views are enabled that can reconstruct multiple areas of the subject and / or be combined to produce a three-dimensional view.Alternatively, in some embodiments, multiple sets of detectors and collimators are combined to increase the overall field of view.

[0024] Furthermore, in some implementations, a Compton camera features a second imaging technology, such as ultrasound. In these implementations, an ultrasound transducer is positioned near the front, open end of the camera to provide normal ultrasound imaging. The transducer is virtually transparent to incoming gamma rays.

[0025] Figures 2A-C illustrate a modified Compton camera according to some embodiments. In these embodiments, the configuration of camera 210 reduces noise and collimates incoming gamma rays as described previously. Figure 2A is a view of the front end of the camera (e.g., along the camera’s z-axis), Figure 2B is a view along the x-axis of the camera, while Figure 2C is a view along the y-axis.

[0026] In these figures, aperture 216 in the front end of camera 210 is defined by walls 226a, 226b, and elongated walls 228a, 228b. Gamma rays that are captured by the camera enter aperture 216 and imaging chamber 230, and impinge upon scatterer 212. Imaging chamber 230 is defined by the four walls enumerated above, plus rear wall 224, which may be parallel to the front end. The portions of walls 226, 228 that extend forward from scatterer 212 may be referred to as the camera’s collimator because they are responsible for blocking gamma rays received from relatively wide angles.

[0027] Compton camera 210 may thus be described as an enclosure defined by the five walls that form imaging chamber 230 which, in turn, comprises scatterer 212 and absorber 214. It should be noted that walls 226a, 226b and walls 228a, 228b may or may not be parallel with each other. Although not shown in Figures 2A-C, wires, optical links, and / or other data or imaging conduits may pierce rear wall (or some other wall) to couple the camera to external equipment for relaying signals captured by the camera, processing the signals, assembling an image of a subject from which gamma rays were captured, displaying the image, and / or other actions.

[0028] Walls 226, 228, and possibly rear end 224, comprise tungsten, gold, lead, or some other element or composition that prevents entry of a gamma particle or ray into imaging chamber 230 from any direction other than the front end. Gamma ray detectors 212, 214 may comprise scintillation crystals coupled to photodetectors (e.g., silicon photomultipliers (SiPMs)) or, in other embodiments, may comprise semiconductors.

[0029] In different implementations, the components of Compton camera 210 may be of different sizes, and it should be understood that Figures 2A-C are not intended to replicate the scale of these components in any specific embodiment. By way of illustration, walls (e.g., walls 226, elongated walls 228, rear wall 224) may be approximately 2-10 mm thick, scatterer 212 maybe located approximately 1-5 cm into imaging chamber 230 from the surface of the front end of camera 210, and scatterer 212 and absorber 214 may be separated by approximately 1-7 cm. Lengths and widths of walls of Compton camera 210, and lengths, widths, and depths of scatterer 212 and absorber 214 may vary and / or depend upon a desired application or environment in which the camera is deployed.

[0030] Figures 3A-B illustrate another modified Compton camera, according to some embodiments. Figure 3A is a view along the x-axis of the camera, while Figure 3B is a view along the y-axis. In these embodiments, camera 310 may be similar or identical to camera 210 of Figures 2A-C, but is enhanced by the addition of ultrasound transducer 350 to imaging chamber 330.

[0031] Transducer 350 may be of any suitable dimensions and may be located at any position in imaging chamber 330 in front of scatterer 212. The transducer may extend completely between the two elongated walls, but need extend the full distance between the other walls (walls 326a, 326b).

[0032] Figure 4 is a diagram of the effect of a modified Compton camera, according to some embodiments. In Figure 4, the enclosure of modified Compton camera 410, which encloses scatterer 412, absorber 414, and collimator 418, is omitted in the interest of clarity. However, reconstruction plane or sheet 422 is illustrated, which depicts the volume in front of modified Compton camera 410 in which gamma ray events can be reconstructed. The thickness of plane 422 depends upon the thickness of the gap between the elongated walls of the camera.

[0033] The reconstruction cone of a traditional Compton camera is illustrated as cone 460, which reflects the volume of space in which events could be reconstructed in a Compton camera that omitted collimator 418. Furthermore, intersection 462 between reconstruction plane 422 and Compton cone 460 is delineated to show the significant reduction in the volume of uncertainty regarding the origination points of captured gamma events. Thus, whereas a traditional Compton camera could identify only an expanding cone of space for a given gamma event, modified Compton camera 410 reduces the uncertainty to a small section of a thin plane.

[0034] Figures 5A-B illustrate a modified Compton camera configured to enable reconstruction of three-dimensional images, according to some embodiments. Figure 5A is a perspective view of camera 510, while Figure 5B is a view along the x-axis of the camera. In these embodiments, camera 510 comprises multiple apertures 516 that each provides access to a separate imaging chamber 530. Every imaging chamber shares scatterer 512 and absorber 514, but adjacent chambers are separated by collimators 518 that are substantially parallel to elongated walls 228 and that extend completely or substantially the distance between walls 526. Note that, in Figure 5B, wall 526a is omitted to enhance the visibility of collimators 518.

[0035] Simultaneous operation of all imaging chambers 530 enables reconstruction of a three-dimensional image without relocating or repositioning modified Compton camera 510. As one alternative, a camera having a single imaging chamber (e.g., camera 210 of Figures 2A- C) may be repositioned to view a subject from multiple angles and thereby produce a composite three-dimensional reconstruction.

[0036] Figures 6A-B are reconstructed images of two radioactive point sources, according to some embodiments. Figure 6A comprises image 610, which was reconstructed from events captured by a traditional Compton camera (without collimation). Figure 6B comprises image 620, which was constructed from events captured by a Compton camera modified as described above (with collimation). Image 620 provides better resolution and contains less noise than image 610. These images were each captured from a single detector position (i.e., without moving the modified Compton camera).

[0037] The collimator of the modified Compton camera used to capture image 620 was 3 cm thick and composed of lead, and the camera features a 3 mm aperture. The point sources comprised Cesium- 137 with similar activity of 140 kBq. The point sources were located at the same positions, in each image, relative to the cameras. The camera was positioned approximately 5cm beneath the point sources. Acquisition time was 12.8 seconds and reconstruction of the images involved a custom version of the List- Mode Maximum Likelihood Expectation Maximation (LM-MLEM) algorithm, with 20 iterations.

[0038] Figure 7 depicts a method of nuclear imaging according to an embodiment of the invention. In this method, a radiotracer or radiopharmaceutical is introduced to a subject (e.g., a patient) and accumulates in a location to be imaged.

[0039] In operation 702, a portable modified Compton camera is positioned to capture the nuclear images and, in operation 704, multiple gamma ray interactions are captured. Each capture involves the collision of a gamma ray emanated from the subject with a scatterer detector, release of a photon by the scatterer, and capture of the photon by an absorber detector. For each capture, the associated energies of the collisions with the absorber and detector are recorded, as well as their locations within the detectors.

[0040] In operation 706, for each captured event, a planar volume from which the associated gamma ray may have emanated is identified. In operation 708, from the multiple planar volumes identified for the multiple interactions, an image (two-dimensional or three- dimensional) is reconstructed to show the points of origin of the gamma rays within the subject.

[0041] In operation 710 the image is displayed, recorded, printed and / or otherwise rendered.

[0042] The foregoing embodiments have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit this disclosure to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. The scope is defined by the appended claims, not the preceding disclosure.

Claims

What Is Claimed Is:

1. An apparatus, comprising: an enclosure defined by: a first pair of opposing walls separated by a first distance, a second pair of opposing walls separated by a second distance, and a bottom wall; wherein the first distance is shorter than the second distance; multiple detectors positioned within the enclosure; and one or more signal conductors.

2. The apparatus of claim 1, wherein: a first signal conductor of the one or more signal conductors couples the apparatus to a controller; and via the first signal conductor, the controller receives signals associated with interaction of an incident gamma ray with one or more of the multiple detectors.

3. The apparatus of claim 2, wherein: the apparatus further comprises a display; and the controller reconstructs, on the display, a view of a subject being imaged with the apparatus.

4. The apparatus of claim 2, wherein the first distance forms an aperture that restricts a field of view of the apparatus.

5. The apparatus of claim 4, wherein the aperture prevents detection of incident gamma rays originating from beyond the field of view.

6. The apparatus of claim 1 , wherein one or more of the walls of the enclosure comprise at least one metal.

7. The apparatus of claim 6, wherein the at least one metal comprises one or more of tungsten, gold, and lead.

8. The apparatus of claim 1, wherein the multiple detectors are gamma ray detectors.

9. The apparatus of claim 1 , wherein the multiple detectors comprise scintillation crystals coupled to silicon photomultipliers (SiPMs).

10. The apparatus of claim 1, wherein the multiple detectors comprise semiconductors.

11. The apparatus of claim 1 , wherein the multiple detectors comprise at least one ultrasound detector.

12. An imaging system, comprising: a housing having multiple partitions that define multiple apertures and multiple imaging chambers; multiple gamma ray detectors; and at least one signal conductor coupled to one or more external devices.

13. The imaging system of claim 12, wherein the housing comprises: a first pair of opposing and parallel walls, a second pair of opposing and parallel walls, and a rear wall.

14. The imaging system of claim 12, further comprising one or more ultrasound detectors.

15. The imaging system of claim 14, wherein the distance from the apertures to the one or more ultrasound detectors is less than the distance from the apertures to the multiple gamma ray detectors.

16. The imaging system of claim 12, wherein each aperture receives different incident gamma rays.

17. The imaging system of claim 12, wherein the housing is composed of tungsten.

18. A method of imaging a subject, the method comprising: detecting gamma ray interactions emanating from a subject comprising aradiopharmaceutical substance with a portable imaging device that comprises: a first pair of walls separated by a first distance, a second pair of walls separated by a second distance, a rear wall, and multiple detectors positioned within the enclosure; processing data collected during said detections; and displaying an image of the subject from the processed data.

19. The method of claim 18, further comprising: capturing an ultrasound image of the subject; wherein the portable imaging device further comprises an ultrasound transducer.

20. The method of claim 18, wherein said processing comprises: for each gamma ray interaction, identifying a planar volume from which the gamma ray may have originated; and based on the planar volumes identified for the gamma ray interactions, reconstructing an image of the originations of the gamma rays.

Images