阅读说明：本技术 用于医学成像的近2π康普顿摄像机 (Near 2 pi compton camera for medical imaging ) 是由 M·罗德里格斯 R·E·马尔明 于 2018-08-07 设计创作，主要内容包括：为了用康普顿摄像机捕集更多的发射光子,散射检测器(12)相对于来自成像系统的等中心的径向而倾斜(非正交角度)。倾斜创建了用于散射相互作用的更大体积。为了捕集更多散射光子,捕集器检测器(13)是非平面的,例如至少部分地围绕散射检测器(12)之后的体积的多面检测器。在康普顿摄像机中,单独使用倾斜散射检测器(12)、单独使用非平面捕集器检测器(13)、或者使用倾斜散射检测器(12)和非平面捕集器检测器(13)。(In order to capture more emitted photons with the compton camera, the scatter detector (12) is tilted (non-orthogonal angle) with respect to the radial direction from the isocenter of the imaging system. The tilt creates a larger volume for the scattering interaction. To trap more scattered photons, the trap detector (13) is non-planar, e.g. a multi-faceted detector at least partially surrounding the volume behind the scatter detector (12). In a Compton camera, a tilted scatter detector (12) alone, a non-flat trap detector (13) alone, or both a tilted scatter detector (12) and a non-flat trap detector (13) are used.)

1. A Compton camera for medical imaging, the Compton camera comprising:

a bed (60) for a patient space having an isocenter axis;

a first module (11) having a first scatter detector (12) and a first trap detector (13) spaced apart from the first scatter detector (12), the first scatter detector (12) having an outer surface facing the isocenter axis, wherein the outer surface is at an angle of at least 20 degrees from orthogonal to a radial line extending perpendicularly from the isocenter axis through a center of the first scatter detector (12), the first trap detector (13) forming a substantially hemispherical enclosure behind the first scatter detector (12) with respect to the patient space;

an image processor (19) configured to determine an angle of incidence of Compton events from the first scatter detector (12) and the first trap detector (13).

2. Compton camera according to claim 1, wherein the first scatter detector (12) comprises a series of plates in a folded arrangement.

3. A compton camera according to claim 1, wherein said angle is at least 45 degrees.

4. Compton camera according to claim 1, wherein the first scatter detector (12) comprises an oblique arrangement with respect to the radial line.

5. Compton camera according to claim 1, wherein the substantially hemispherical enclosure comprises a five-sided cube with an open side adjacent to the first scatter detector (12).

6. Compton camera according to claim 1, wherein the substantially hemispherical enclosure comprises a plurality of planar trap substrates located on non-parallel planes within the first module (11).

7. Compton camera according to claim 1, further comprising an application specific integrated circuit or a field programmable gate array (122) for reading the first scatter detector (12), said application specific integrated circuit or field programmable gate array forming a plate positioned non-parallel to the outer surface.

8. Compton camera according to claim 1, further comprising a shielding material (114) on the side walls of the first module (11).

9. Compton camera according to claim 8, further comprising a second module (11) with a second scatter detector (12) and a second trap detector (13) spaced apart from the second scatter detector (12), the shielding material separating the first module (11) from the second module (11).

10. Compton camera according to claim 1, further comprising a second module (11) having a second scatter detector (12) and a second trap detector (13) spaced apart from the second scatter detector (12), the enclosure comprising the second trap detector (13).

11. Compton camera according to claim 1, further comprising an additional module (11) with an additional scatter detector (12) and an additional trap detector (13) spaced apart from the additional scatter detector (12), the first module (11) and the additional module (11) forming a ring or partial ring around the patient space.

12. Compton camera according to claim 1, wherein the image processor (19) is configured to generate a Compton image from the Compton events and angles and further comprises a display configured to display the Compton image.

13. A medical imaging system, comprising:

a compton camera comprising a scatter detector (12) arranged to receive emissions from a patient, the scatter detector (12) having an outer surface facing the patient, wherein the outer surface is at an angle of at least 20 degrees from being orthogonal to a radial line extending perpendicularly from a longitudinal axis of the patient through the scatter detector (12).

14. The medical imaging system of claim 13, wherein the compton camera further comprises a near 2 pi structure behind the scatter detector (12) relative to the patient.

15. The medical imaging system of claim 13, wherein the outer surface of the scatter detector (12) comprises a folded surface formed by abutting plates of the scatter detector (12).

16. The medical imaging system of claim 13, wherein the scatter detector (12) is in a module (11) and further comprising gamma ray shielding material on a side of the module (11).

17. A medical imaging system, comprising:

compton camera comprising a scatter detector (12) and a trap detector (13), the scatter detector (12) being arranged to receive emissions from a patient, the trap detector (13) being arranged to receive scatter from the scatter detector (12) due to the emissions from the patient, the trap detector (13) comprising a multi-sided detection surface located behind the scatter detector (12) with respect to the patient.

18. The medical imaging system of claim 17, wherein the scatter detector (12) has an outer surface facing the patient, wherein the outer surface is at an angle of at least 20 degrees from being orthogonal to a radial line extending perpendicularly from a longitudinal axis of the patient through the scatter detector (12).

19. The medical imaging system of claim 17, wherein the multi-sided detection surface includes a near 2 pi structure.

20. Medical imaging system according to claim 17, wherein the scatter detector (12) and the trap detector (13) are in a module (11) and further comprising a gamma ray shielding material on one side of the module (11).

Background

The present embodiments relate to medical imaging using the compton effect. The compton effect allows for higher imaging energies than used for Single Photon Emission Computed Tomography (SPECT). The compton imaging system is configured as a test platform, for example, the scattering layer is assembled, and then the trap layer is mounted to the metro frame. The electronic device is connected to detect compton-based events from the emission of the phantom (phantom). Compton imaging systems fail to address the design and constraints of practical use in any commercial clinical environment. Current proposals lack the ability to integrate into the imaging platform in the clinic or the design and constraint requirements (i.e., flexibility and scalability) to address the business and diagnostic needs.

A compton camera may have a low sensitivity ($) and poor Image Quality (IQ). The absolute number of scattered photons in the scattering layer is low due to geometry (e.g. source scattering solid angle Ω < 4 π), material (e.g. low scattering fraction in the detection material favoring the photoelectric effect), and detector manufacturing limitations (e.g. the actual detector thickness that can be fabricated for both the scattering layer and the trap layer is bounded, such as 1mm for a maximum of a Si detector and 2mm … 10 mm for a maximum of a CZT detector). The number of scattered photons trapped in the trap layer is low due to geometry (e.g., scatter trap solid angle Ω < 4 π). Doppler broadening degrades the image quality of a compton camera. The contribution of the Doppler spread to the Compton angle uncertainty depends on the incident photon energy E₀Scattering angle θ and the energy of the mobile electrons bound to the target atom. The limited detector energy resolution leads to additional compton angle uncertainty. Finite detector position separation in both scattering and trap layersThe resolution results in an additional compton cone ring offset.

Disclosure of Invention

By way of introduction, the preferred embodiments described below include methods and systems for medical imaging. To capture more emitted photons with the compton camera, the scatter detector is tilted (non-orthogonal angle) with respect to the radial direction from the isocenter of the imaging system. The tilting creates a larger volume for the scattering interaction. To trap more scattered photons, the trap detector is non-planar, such as a multi-faceted detector that at least partially surrounds the volume behind the scatter detector. The oblique scatter detectors alone, the non-flat trap detectors alone, or both are used in a compton camera.

In a first aspect, a compton camera for medical imaging is provided. The bed is used for a patient space having an isocenter axis. The first module has a first scatter detector and a first trap detector spaced apart from the first scatter detector. The first scatter detector has an outer surface facing the isocenter axis, wherein the outer surface is at an angle of at least 20 degrees from orthogonal to a radial line extending perpendicularly from the isocenter axis through a center of the first scatter detector. The first trap detector forms a substantially hemispherical enclosure behind the first scatter detector with respect to the patient space. The image processor is configured to determine an angle of incidence of compton events from the first scatter detector and the first trap detector.

In a second aspect, a medical imaging system includes a compton camera having a scatter detector arranged to receive emissions from a patient. The scatter detector has an outer surface facing the patient, wherein the outer surface is at an angle of at least 20 degrees from orthogonal to a radial line extending perpendicularly from a longitudinal axis of the patient through the scatter detector.

In a third aspect, a medical imaging system includes a compton camera having a scatter detector and a trap detector. A scatter detector is arranged to receive emissions from the patient. The trap detector is arranged to receive scatter from the scatter detector due to emissions from the patient. The trap detector includes a multi-sided detection surface positioned behind the scatter detector relative to the patient.

The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Other aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments and may be claimed later, either individually or in combination.

Drawings

The components and figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a perspective view of a plurality of modules of a Compton camera in accordance with one embodiment;

FIG. 2 illustrates an exemplary scatter detector;

FIG. 3 illustrates an exemplary trap detector;

FIG. 4A is a side view of one embodiment of a Compton camera, FIG. 4B is an end view of the Compton camera of FIG. 4A, and FIG. 4C is a detailed view of a portion of the Compton camera of FIG. 4B;

FIG. 5 is a perspective view of one embodiment of a Compton camera in a medical imaging system;

FIG. 6 is a perspective view of one embodiment of a complete loop Compton camera in a medical imaging system;

FIG. 7 is a perspective view of one embodiment of a partial loop Compton camera in a medical imaging system;

FIG. 8 is a perspective view of one embodiment of a full-ring Compton camera with an axially extending partial ring in a medical imaging system;

FIG. 9 is a perspective view of one embodiment of a single module based Compton camera in a medical imaging system;

FIG. 10 is a flow chart of an exemplary embodiment of a method for forming a Compton camera;

FIG. 11 illustrates one embodiment of a module having a tilted scatter detector and a near 2 π trap detector;

FIG. 12A shows one embodiment of a tilted scatter detector with parallel application specific integrated circuits, and FIG. 12B shows a tilted scatter detector with application specific integrated circuits arranged in a non-parallel arrangement;

fig. 13A and 13B show orthogonal cross-sectional views of a multi-loop configuration of a module in a compton camera according to a first embodiment;

fig. 14A and 14B show orthogonal cross-sectional views of a multi-loop configuration of a module in a compton camera according to a second embodiment;

FIG. 15 illustrates different tilts of scatter detectors in different modules according to an embodiment; and

fig. 16A shows an exemplary plot of the full-width, half-maximum (FWHM) of the scatter angle of compton imaging, and fig. 16B shows an exemplary scatter angle.

Detailed Description

Fig. 1-9 are directed to a multi-modal compatible compton camera. The modular design is used to form a compton camera for use with various other imaging modalities. Fig. 11-15 are directed to a compton camera with a tilted scatter detector and/or a near 2 pi trap detector. Oblique scatter detectors and/or near 2 pi trap detectors are used in the modules of fig. 1-9, in other modules, or without modules. After summarizing the oblique scatter detector and/or near 2 π trap detector embodiments, the Compton camera of FIGS. 1-9 is described. Many of the features and components of the compton camera of fig. 1-9 may be used in the tilted scatter detector and/or near 2 pi trap detector embodiments described later with respect to fig. 11-15.

The oblique scatter detector and/or the near 2 pi trap detector provide a more efficient compton camera. The sensitivity ($) and/or the Image Quality (IQ) can be improved. Synchronization and triggering limitations between modules can be avoided by trapping photons at a higher rate within the modules. Tilting the scatter detector and/or using a near 2 π trap detector can increase the sensitivity ($) by a factor of 15 compared to the parallel plate scatter detector and trap detector of FIG. 1. The absolute number of scattered photons can be increased by-3-5 times using an oblique scatter detector, and the number of trapped photons can be increased by-3-5 times using a near 2 pi trap detector.

The oblique scatter detector and/or the near 2 pi trap detector may be applied to any compton camera regardless of the detection material used, the readout electronics, and/or the size of the imaged object. Given that the quantified number of different modules can be swapped in the system for different tasks during design, the design configuration of each module can be rearranged and optimized for different imaging tasks. The use of modular smaller compton cameras forming larger imaging systems with reduced or near zero cross talk between modules due to shielding results in lower requirements on electronics (e.g., ASIC/FPGA) cross talk and inter-module triggering at high rates.

Referring to fig. 1-9, a medical imaging system includes a multi-modality compatible compton camera having a segmented detection module. The compton camera (e.g. compton camera ring) is segmented into modules that house the detection units. Each module is independent and when assembled into a ring or partial ring, the modules can communicate with each other. The modules are independent but can be assembled into a multi-module unit that produces a compton scatter-based image. A cylindrically symmetric module or a spherical shell segmented module may be used.

The scatter trap allows for a modular arrangement that is efficient to manufacture, serviceable in the field, and cost and energy efficient. The modules allow design freedom to vary the radius of each radial detection unit, the angular span and/or the axial span of a module. The scatter trap is multi-modal compatible to the modules and/or forms a modular loop compton camera for clinical emission imaging. This design allows flexibility so that the compton camera can be added to existing Computed Tomography (CT), Magnetic Resonance (MR), Positron Emission Tomography (PET), or other medical imaging platforms as an axially separate system or as a fully integrated system. Each module may address heat dissipation, data collection, calibration, and/or allow for efficient assembly and servicing.

Each scatter trap pair module is formed from a commercially suitable solid-state detector module (e.g., Si, CZT, CdTe, HPGe, or the like), allowing an energy range of 100-. Compton imaging can be set with a wider range of isotope energies (> 2 MeV) to enable new tracers/labels by selecting the scatter trap detector. Modularity allows individual modules to be removed or replaced, allowing time and cost efficient service. The modules may operate and isolate independently or may be linked for crosstalk, allowing for improved image quality and higher efficiency when detecting compton events using the scatter detector of one module and the trap detector of another module.

The modularity allows for a flexible design geometry optimized for individual needs, such as using a partial ring for integration with a CT system (e.g., connected between an X-ray source and a detector), several modules (e.g., tiles) for integration with a single photon emission computed tomography gamma camera or other spatially limited imaging system, or a complete ring. Functional imaging based on compton detection events can be added to other imaging systems (e.g., CT, MR, or PET). Multiple full or partial rings may be placed adjacent to each other for greater axial coverage of the compton camera. A dedicated or stand-alone compton-based imaging system may be formed. In one embodiment, the module includes a collimator of lower energy (e.g., < 300 keV), providing multi-channel and multiplexed imaging (e.g., high energy using a scatter trap detector for Compton events and low energy using one of the detectors for SPECT or PET imaging). The module may be stationary or rapidly rotating (0.1 rpm < omega < 240 rpm). Dimensional, installation, service, and/or cost constraints are addressed by the scatter trap pairing module.

Fig. 1 shows an embodiment of a module 11 for a compton camera. Four modules 11 are shown, but additional or fewer modules may be used. The compton camera is formed of one or more modules, depending on the desired design of the compton camera.

Compton cameras are used for medical imaging. A space for the patient relative to the module is provided such that the module is positioned to detect photons emitted from the patient. The radiopharmaceutical in the patient includes a radioisotope. Photons are emitted from the patient as a result of the decay of the radioisotope. The energy from the radioisotope may be 100-3000keV, depending on the material and structure of the detector. Any of a variety of radioisotopes may be used to image a patient. Modules 11 optimized for different isotopes may be staggered to cover any range of the energy spectrum (e.g., the entire range). For example, the first module is used for 100-400keV, the second module is used for 300-600keV, the third module is used for more than 500 keV, and the fourth module is used for 100-400keV, … to cover the entire ring and/or partially fill the ring.

Each module 11 includes the same or many identical components. Scatter detector 12, trap detector 13, circuit board 14 and baffle 15 are disposed in the same housing 21. Additional, different or fewer components may be provided. For example, scatter detector 12 and trap detector 13 are disposed in housing 21 without other components. As another example, fiber optic data lines 16 are provided in all or a subset of the modules 11.

The modules 11 are shaped for stacking together. The modules 11 mate with each other, for example with matching recesses and extensions, latches, tongue and groove, or clips. In other embodiments, flat or other surfaces are provided for abutting each other or against the divider. Latches, clips, bolts, tongue and groove or other attachment mechanisms are provided for attaching the module 11 to any adjacent module 11. In other embodiments, the modules 11 are attached to a rack or other frame with or without direct connection to any adjacent modules 11.

The connection to other modules 11 or stands may be releasable. The module 11 is connected and can be disconnected. The connection may be releasable, allowing removal of one module 11 or a group of modules 11 without removing all modules 11.

In order to form a compton camera from more than one module 11, the housing 21 and/or the outer shape of the module 11 is wedge-shaped. Due to the wedge shape, the modules 11 may be stacked around the shaft to form a ring or partial ring. The portions closer to the axis have a narrower width dimension along a dimension perpendicular to the axis than the width dimension of the portions further away from the axis. In the module 11 of fig. 1, the housing 21 has the widest portion furthest from the axis. In other embodiments, the widest portion is closer to the shaft, but spaced from the narrowest portion that is closest to the shaft. In the wedge shape, scatter detector 12 is closer to the narrower portion of the wedge than trap detector 13. The wedge shape in cross section along a plane normal to the shaft allows the modules 11 to be adjacently stacked and/or connected in an abutting position to form at least a portion of a ring around the shaft.

The taper of the wedge provides a number N of modules 11 to form a complete ring around the shaft. Any number N may be used, e.g., N =10-30 modules. The number N may be configurable, for example using different housings 21 for different numbers N. The number of modules 11 for a given compton camera may vary depending on the design of the compton camera (e.g., the partial ring). The wedge shape may be arranged along other dimensions, for example having a wedge shape in a cross section parallel to the axis.

The stacked modules 11 are cylindrically symmetric, such as in connection with a gantry of a medical imaging system. The narrowest end of the wedge-shaped cross-section is closest to a patient space of the medical imaging system, and the widest end of the wedge-shaped cross-section may be furthest from the patient space. In alternative embodiments, other shapes than wedges may be provided that allow stacking together to provide a ring or generally curved shaped stack.

The housing 21 is of metal, plastic, fiberglass, carbon (e.g., carbon fiber), and/or other material. In one embodiment, different portions of the housing 21 are of different materials. For example, tin is used for the housing around the circuit board 14. Aluminum is used to hold scatter detector 12 and/or trap detector 13. In another example, the housing 12 is of the same material, such as aluminum.

The housing 21 may be formed of different structures, such as end plates having a wedge shape, ground plane sheets that house the circuit board 14, and separate structures for holding the walls of the scatter detector 12 and the trap detector 13, wherein the separate structures are formed of a material (e.g., aluminum or carbon fiber) through which photons of the desired energy from a compton event can pass. In an alternative embodiment, no walls are provided for modules 11 between the end plates for the areas where scatter detectors 12 and/or trap detectors 13 are placed, thereby avoiding the transfer of interfering photons from scatter detectors 12 of one module 11 to trap detectors 13 of another module 11. The housing 21 beside the detectors 12, 13 and/or for holding the detectors 12, 13 is made of a low attenuation material, such as aluminum or carbon fiber.

The housing 21 may enclose the module or include an opening. For example, openings for airflow are provided, such as at the top of the widest portion of the wedge at the circuit board 14. The housing 21 may include holes, slots, tabs, latches, clips, seats, bumpers, or other structures for mounting, mating, and/or stacking.

Each solid state detector module 11 includes both a scatter detector 12 and a trap detector 13 of the compton sensor. By stacking each module, the size of the compton sensor is increased. A given module 11 may itself be a compton sensor, since both scatter detector 12 and trap detector 13 are included in the module.

The module 11 may be separately removed and/or added to the compton sensor. For a given module 11, scatter detector 12 and/or trap detector 13 may be removable from module 11. For example, the module 11 is removed for service. The faulty detector or detectors 12, 13 are removed from the module 11 for replacement. Once replaced, the refurbished module 11 is placed back into the medical imaging system. Bolts, clips, latches, tongue and groove, or other releasable connectors may connect the detectors 12, 13 or a portion of the housing 21 for the detectors 12, 13 to the rest of the module 11.

Scatter detector 12 is a solid state detector. Any material may be used, such as Si, CZT, CdTe, HPGe, and/or other materials. Scatter detector 12 is created by wafer fabrication at any thickness, for example about 4 mm for CZT. Any size, for example about 5 x 5 cm, may be used. Fig. 2 shows a square shape for scatter detector 12. Other shapes than square, such as rectangular, may also be used. For module 11 of fig. 1, scatter detector 12 may be rectangular in shape extending between two wedge-shaped end plates.

In module 11, scatter detector 12 has any range. For example, scatter detectors 12 extend from one wedge-shaped end wall to the other. A smaller or larger extent may be provided, for example extending between mounts within the module 11, or axially beyond one or both end walls. In one embodiment, scatter detector 12 is at, on, or beside one end wall, and does not extend to the other end wall.

Scatter detectors 12 form a sensor array. For example, the 5 × 5 cm scatter detector 12 of fig. 2 is a 21 × 21 pixel array having a pixel pitch of about 2.2 mm. Other numbers of pixels, pixel pitches, and/or array sizes may be used.

Scatter detector 12 includes a semiconductor formatted for processing. For example, scatter detector 12 includes an Application Specific Integrated Circuit (ASIC) for sensing photon and electron interactions in scatter detector 12. The ASIC is collocated with pixels of scatter detector 12 (colocate). The ASIC may have any thickness. Multiple ASICs may be provided, for example 9 in a 3 x 3 grid of scatter detectors 12.

Scatter detector 12 may operate at any count rate, for example >100 kcps/mm. Due to the interaction, electricity is generated by the pixels. The electricity is sensed by an application specific integrated circuit. Position, time and/or energy are sensed. The sensed signal may be conditioned (e.g., amplified) and transmitted to one or more circuit boards 14. A flex circuit, wire or other communication path carries the signal from the ASIC to the circuit board 14.

Compton sensing operates without collimation. Instead, the angle of a photon entering scatter detector 12 is determined using a fixed relationship between the energy, location, and angle of photon interaction at scatter detector 12 relative to photon interaction at trap detector 13. The compton process is applied using a scatter detector 12 and a trap detector 13.

The trap detector 13 is a solid state detector. Any material may be used, such as Si, CZT, CdTe, HPGe, and/or other materials. The trap detector 13 is formed by wafer fabrication at any thickness, for example about 10 mm for CZT. Any size, for example about 5 x 5 cm, may be used. This dimension may be larger in at least one dimension than scatter detector 12 due to the wedge shape and the spaced apart position of scatter detector 12 and trap detector 13. Fig. 3 shows a rectangular shape of the trap detector 13, but other shapes may be used. For module 11 of fig. 1, trap detector 13 may be a rectangle extending between two end plates, wherein the length is the same as scatter detector 12 and the width is larger than scatter detector 12.

The trap detector 12 forms a sensor array. For example, the 5 × 6 cm trap detector 13 of fig. 3 is a 14 × 18 pixel array with a pixel pitch of about 3.4 mm. The pixel size is larger than the pixel size of scatter detector 12. The number of pixels is smaller than the number of pixels of scatter detector 12. Other numbers of pixels, pixel pitches, and/or array sizes may be used. Other relative pixel sizes and/or numbers of pixels may be used.

In module 11, the trap detector 13 has any range. For example, the trap detector 13 extends from one wedge-shaped end wall to the other. A smaller or larger extent may be provided, for example extending between mounts within the module 11, or axially beyond one or both end walls. In one embodiment, the trap detector 13 is located at, on or beside one end wall, without extending to the other end wall.

The trap detector 13 comprises a semiconductor formatted for processing. For example, trap detector 13 includes an ASIC for sensing the interaction of photons and electrons in trap detector 13. The ASIC is juxtaposed with the pixels of the trap detector 13. The ASIC may have any thickness. Multiple ASICs may be provided, for example 6 in a 2 x 3 grid of trap detectors 13.

The trap detector 13 may operate at any count rate, for example >100 kcps/mm. Due to the interaction, electricity is generated by the pixels. The electricity is sensed by the ASIC. Position, time and/or energy are sensed. The sensed signal may be conditioned (e.g., amplified) and transmitted to one or more circuit boards 14. A flex circuit, wire or other communication path carries the signal from the ASIC to the circuit board 14.

Trap detector 13 is spaced from scatter detector 12 by any distance along a radial line from the axis or normal to parallel scatter detector 12 and trap detector 13. In one embodiment, the spacing is about 20 cm, but greater or lesser spacing may be provided. The space between trap detector 13 and scatter detector 12 is filled with air, other gases, and/or other materials that have low attenuation for photons at the desired energy.

The circuit board 14 is a printed circuit board, but a flexible circuit or other material may be used. Any number of circuit boards 14 for each module may be used. For example, one circuit board 14 is provided for scatter detector 12 and another circuit board 14 is provided for trap detector 13.

The circuit board 14 is within the housing 21, but may extend outside the housing 21. The housing 21 may be grounded, thereby acting as a ground plane for the circuit board 14. The circuit boards 14 may be mounted parallel to each other or non-parallel, e.g., spread apart in a wedge shape. The circuit board is positioned generally orthogonal to the catcher detector 13. Typically to account for any expansion due to the wedge shape. Brackets, bolts, screws, and/or standoffs with each other and/or with the housing 21 are used to hold the circuit board 14 in place.

Circuit board 14 is connected to the ASICs of scatter detector 12 and drip catcher detector 13 by flex circuits or wires. The ASIC outputs a detection signal. The circuit board 14 is acquisition electronics that processes the detection signals to provide parameters to the compton processor 19. Any parameterization of the detection signal may be used. In one embodiment, energy, time of arrival, and location in three dimensions are output. Other acquisition processes may be provided.

The circuit boards 14 output to each other, to the data bridge 17 and/or to the fiber optic data link 16, for example, through electrical connections within the module 11. The fiber optic data link 16 is a fiber optic interface for converting electrical signals to optical signals. One or more fiber optic cables provide acquisition parameters for the events detected by scatter detector 12 and trap detector 13 to compton processor 19.

Data bridge 17 is a circuit board, wire, flex circuit, and/or other material for electrical connection to allow communication between modules 11. A housing or protective plate may cover the data bridge 17. The data bridge 17 is releasably connected to one or more modules 11. For example, a plug or mating connector of the data bridge 17 mates with a corresponding plug or mating connector on the housing 21 and/or the circuit board 14. Latches, clips, tongue and groove, screws, and/or bolt connections may be used to releasably hold data bridge 17 in place with respect to module 11.

The data bridge 17 allows communication between the modules. For example, the fiber optic data link 16 is disposed in one module 11 but not in another module 11. Avoiding the cost of the fibre optic data link 16 in each module 11. Instead, the parameters output by another module 11 are provided to the module 11 with the fiber optic data link 16 via the data bridge 17. One or more circuit boards 14 of a module 11 having a fiber optic data link 16 route parameter outputs to the fiber optic data link 16, reporting detection events from more than one module 11 using the fiber optic data link 16. In an alternative embodiment, each module 11 includes a fiber optic data link 16, and thus no data bridge 17 is provided or data bridge 17 carries other information.

Data bridge 17 may connect other signals between modules 11. For example, the data bridge 17 includes conductors for power. Alternatively, different bridges provide power to the modules 11, or the modules 11 are individually powered. As another example, a data bridge 17 is used to transfer clock and/or synchronization signals between modules 11.

In the embodiment of fig. 1, a separate clock and/or synchronization bridge 18 is provided. Clock and/or synchronization bridge 18 is a circuit board, wire, flex circuit, and/or other material for electrical connection to allow communication of clock and/or synchronization signals between modules 11. A housing or protective plate may cover the clock and/or synchronization bridge 18. A clock and/or synchronization bridge 18 is releasably connected to one or more modules 11. For example, a plug or mating connector of clock and/or synchronization bridge 18 mates with a corresponding plug or mating connector on housing 21 and/or circuit board 14. Latches, clips, tongue and groove, screws and/or bolt connections may be used to releasably hold the clock and/or synchronization bridge 18 in place with respect to the module 11.

The clock and/or synchronization bridge 18 may be connected to the same or a different set of modules 11 as the data bridge 17. In the embodiment shown in fig. 1, a data bridge 17 is connected between pairs of modules 11 and a clock and/or synchronization bridge 18 is connected over groups of four modules 11.

The clock and/or synchronization bridge 18 provides a common clock signal and/or synchronization signal for synchronizing the clocks of the modules 11. One of the parameters formed by the circuit board 14 of each module 11 is the detection time of the event. Compton detection relies on event pairs (scatter events and trap events). The timing is used to pair events from different detectors 12, 13. The common clock and/or synchronization allows accurate pairing in case event pairs are detected in different modules 11. In an alternative embodiment, only scatter events and trap events detected in the same module 11 are used, and thus the clock and/or synchronization bridge 18 may not be provided.

Other links or bridges between different modules 11 may be provided. Since the bridges 17, 18 are removable, individual modules 11 can be removed for service while leaving the remaining modules 11 in the rack.

Each module 11 is air-cooled. Holes may be provided to force air through the module 11 (i.e., inlet and outlet holes). One or more baffles 15 may be provided to direct air within the module 11. Water, conductive transfer, and/or other cooling may alternatively or additionally be provided.

In one embodiment, the top of the wedge module 11 or housing 21 is open (i.e., there is no cover on the side furthest from the patient area). One or more baffles 15 are disposed along the center of the one or more circuit boards 14 and/or the housing 21. The fan and heat exchanger 20 forces cooling or ambient temperature air into each module 11, for example, half way along the module 11 at a location spaced from the trap detector 13 (e.g., the top of the module 11). Baffle 15 and/or circuit board 14 direct at least some air to the space between scatter detector 12 and trap detector 13. The air then passes over the baffles 15 and/or circuit board 14 on another portion (e.g., the other half) of the module 11 to exit to the heat exchanger 20. Other routes of air may be provided.

The heat exchanger and fan 20 is provided for each individual module 11 and may therefore be wholly or partly within the module 11. In other embodiments, ducts, baffles or other structures direct air to the plurality of modules 11. For example, a group of four modules 11 share a common heat exchanger and fan 20 mounted to a rack or other frame for cooling the group of modules 11.

To form a compton sensor, one or more modules 11 are used. For example, two or more modules 11 are positioned relative to a patient bed or imaging space to detect photon emissions from the patient. The arrangement of a greater number of modules 11 may allow a greater number of emissions to be detected. By using a wedge shape, the modules 11 may be positioned against, adjacent to and/or connected to each other to form an arc around the patient space. The arc may have any range. The modules 11 are in direct contact with each other or through spacers or stands with a small spacing (e.g., 10 cm or less) between the modules 11.

In one example, four modules 11 are positioned together, sharing a clock and/or synchronization bridge 18, one or more data bridges 17, and a heat exchanger and fan 20. One, two or four fibre optic data links 16 are provided for groups of modules 11. Groups of a plurality of such modules 11 may be arranged to be spaced apart or adjacent to each other for the same patient space.

Due to the modular approach, any number of modules 11 may be used. By constructing multiple identical assemblies, manufacturing is more efficient and cost effective, although any given module 11 is used in a different arrangement than for other modules 11.

The fibre optic data link 16 of the module 11 or group of modules 11 is connected to a compton processor 19. The compton processor 19 receives values of parameters for different events. Using energy and timing parameters, scatter events and trap events are paired. For each pair, the spatial location and energy of the event pair are used to find the angle of incidence of the photon on scatter detector 12. In one embodiment, the event pairs are limited to events in the same module 11. In another embodiment, trap events from the same or different modules 11 may be paired with scatter events from a given module 11. More than one compton processor 19 may be used, for example, for pairing events from different parts of the part ring 40.

Once the pair-wise events are linked, the compton processor 19 or another processor may perform computed tomography to reconstruct the distribution in two or three dimensions of the detected emissions. The angle of incidence or line of incidence for each event is used in the reconstruction. The reconstructed distribution of the emissions is used to generate a compton image.

The display 22 is a CRT, LCD, projector, printer or other display. The display 22 is configured to display a compton image. The image or images are stored in a display plane buffer and read out to the display 22. The images may be displayed separately or combined, for example displaying a compton image overlapping or adjacent to the SPECT image.

Fig. 4A-6 illustrate one exemplary arrangement of the module 11. The modules 11 form a ring 40 around the patient space. Fig. 4A shows four such rings 40 stacked axially. Fig. 4B shows scatter detectors 12 and corresponding trap detectors 13 of modules 11 in ring 40. Fig. 4C shows a detail of a portion of the ring 40. Three modules 11 provide corresponding pairs of scatter detectors 12 and trap detectors 13. Other dimensions than those shown may be used. Any number of modules 11 may be used to form the ring 40. The ring 40 completely surrounds the patient space, but may provide a gap having a width less than 1/2 modules. Within the housing of the medical imaging system, the ring 40 is connected to a gantry 50 or another frame, as shown in FIG. 5. The ring 40 may be positioned to allow the patient bed 60 to move the patient into the ring 40 and/or through the ring 40. Fig. 6 shows an example of this configuration.

The ring may be used for compton-based imaging of emissions from a patient. Fig. 7 shows an example using the same type of module 11 but in a different configuration. Forming part of the ring 40. One or more gaps 70 are provided in the ring 40. This may allow for the use of other components in the gap and/or a less expensive system to be manufactured by using fewer modules 11.

Fig. 8 shows another configuration of the module 11. The ring 40 is a complete ring. Additional partial rings 80 are stacked axially relative to the couch 60 or patient space, extending the axial extent of the detected emissions. Instead of the two gaps 70 of fig. 7, the partial ring 80 is distributed with every other or group of N modules 11 (e.g., N = 4). The additional ring may be a complete ring. The complete ring 40 may be a partial ring 80. The different rings 40 and/or partial rings 80 are axially stacked with little or no (e.g., 1/2 less than the axial extent of the module 11) separation. Wider spacing may be provided, for example with a gap greater than the axial extent of one module 11.

Fig. 9 shows yet another configuration of the module 11. One module 11 or a single group of modules 11 is located beside the patient space or bed 60. A plurality of spaced apart individual modules 11 or groups (e.g., groups of four) may be disposed at different locations relative to the couch 60 and/or the patient space.

In either configuration, the module 11 is held in place by attachment to a rack, multiple racks, and/or other frame. The retention is releasable, for example using bolts or screws. A desired number of modules 11 are used to assemble a desired configuration for a given medical imaging system. The aggregated module 11 is installed in the medical imaging system, defining or relative to the patient space. The result is a compton sensor for imaging a patient.

The couch 60 may move the patient to scan different portions of the patient at different times. Alternatively or additionally, the gantry 50 moves the module 11 forming the compton sensor. The gantry 50 translates axially along the patient space and/or rotates the compton sensor around the patient space (i.e., rotates around the long axis of the couch 60 and/or the patient). Other rotations and/or translations may be provided, such as rotating the module 11 about an axis that is not parallel to the long axis of the couch 60 or patient. Combinations of different translations and/or rotations may be provided.

A medical imaging system with a compton sensor is used as a stand-alone imaging system. Compton sensing is used to measure the distribution of a radiopharmaceutical in a patient. For example, a full ring 40, partial ring 40, and/or axially stacked rings 40, 80 are used as a compton-based imaging system.

In other embodiments, the medical imaging system is a multi-modality imaging system. The compton sensor formed by the modules 11 is one modality and another modality is also provided. For example, another modality is a Single Photon Emission Computed Tomography (SPECT), PET, CT, or MR imaging system. The complete ring 40, partial ring 40, axially stacked rings 40, 80 and/or individual modules 11 or groups of modules 11 are combined with sensors for other types of medical imaging. The compton sensor may share the bed 60 with other modalities, such as being positioned along the long axis of the bed 60, wherein the bed positions the patient in one direction in the compton sensor and in the other modality along the other direction.

The compton sensor may share an external housing with other modalities. For example, the full ring 40, partial ring 40, axially stacked rings 40, 80, and/or individual modules 11 or groups of modules 11 are arranged within the same imaging system housing for one or more sensors of other modalities. The couch 60 positions the patient within the imaging system housing relative to the desired sensors. The compton sensor may be positioned axially adjacent to other sensors and/or in a gap at the same axial position. In one embodiment, partial ring 40 is used in a computed tomography system. The gantry holding the X-ray source and X-ray detector also holds the modules 11 of the partial ring 40. The X-ray source is in one gap 70 and the detector is in another gap 70. In another embodiment, a single module 11 or sparsely populated modules 11 are connected to the gantry of the SPECT system. The module 11 is placed adjacent to the gamma camera so that the gantry of the gamma camera can move the module 11. Alternatively, a collimator may be located between the module 11 and the patient or between the scatter detector 12 and the trap detector 13, allowing the scatter detector 12 and/or the trap detector 13 of the module 11 to be used for photoelectric event detection for SPECT imaging, instead of or in addition to the detection of compton events.

The module-based segmentation of the compton sensor allows the same design of module 11 to be used in any of the different configurations. Thus, different numbers of modules 11, module locations, and/or configurations of modules 11 may be used for different medical imaging systems. For example, one arrangement is provided for use with one type of CT system, while a different arrangement (e.g., number and/or location of modules 11) is used for a different type of CT system.

The module-based segmentation of the compton sensor allows for more efficient and cost-effective services. Instead of replacing the entire compton sensor, any module 11 may be disconnected and repaired or replaced. The modules 11 may be connected and disconnected separately from each other and/or from the gantry 50. Any bridges are removed and then the module 11 is removed from the medical imaging system, leaving the other modules 11. It is cheaper to replace the individual modules 11. The amount of time of service may be reduced. Individual components of a defective module 11, such as the scatter detector 12 or the trap detector 13, can be easily replaced while leaving the other. The module 11 may be configured to operate with different radioisotopes (i.e., different energies) by using corresponding detectors 12, 13.

FIG. 10 illustrates one embodiment of a flow chart of a method for forming, using, and repairing a Compton camera. The compton camera is formed in a segmented method. Rather than manually assembling the entire camera in place, a scatter detector and a trap detector pair are positioned relative to each other to form the desired configuration of the compton camera. Such a segmentation approach may allow for different configurations of the same components to be used, easy assembly, easy repair, and/or integration with other imaging modalities.

Other embodiments form a combination of a compton camera and a SPECT camera. The segmentation module 11 of fig. 11 is used. The modules of fig. 13-16 may be used to form a SPECT camera. The detector arrangement of figure 11 may be used.

The method may be implemented by the system of fig. 1 to assemble a compton sensor as shown in any of fig. 4-9. The method may be implemented by the system of fig. 11 to assemble a compton sensor as shown in any of fig. 13-16. Other systems, modules and/or configurations of compton sensors may be used.

The actions are performed in the order shown (i.e., top to bottom or numerically) or in other orders. For example, act 108 may be performed as part of act 104.

Additional, different, or fewer acts may be provided. For example, acts 102 and 104 are provided for assembling a Compton camera without performing acts 106 and 108. As another example, act 106 is performed without performing other acts.

In act 102, the scatter detector and the trap detector pair are housed in separate housings. Modules are assembled, wherein each module includes both a scatter detector and a trap detector. The machine and/or human creates the housing.

The module is shaped to abut scatter and trap detector pairs of different housings in a non-planar position. For example, a wedge shape and/or positioning is provided such that the detector pair forms an arc, as shown in FIG. 4C. This shape allows and/or forces an arc when the modules are positioned against each other.

In act 104, the shells are abutted. A person or machine assembles the compton sensor from the housing. By stacking the shells adjacent to each other in direct contact or in contact through spacers, stands or frames, the adjoining shells form an arc. A complete ring or partial ring is formed around and at least partially defines the patient space. Based on the design of the compton camera or compton-SPECT camera, any number of housings with corresponding scatter and trap detector pairs are positioned together to form the camera.

The housing may abut as part of a multi-modality system or form a single imaging system. For multi-modality systems, the housing is located in the same external housing and/or relative to the same bed as the sensors for the other modalities (e.g., SPECT, PET, CT, or MR imaging systems). The same or different gantry or support frame may be used for the housing of the compton camera and for the sensors of other modalities. For other embodiments, the module provides multimodality by providing both a compton camera and a SPECT imaging system.

The configuration or design of the compton camera defines the number and/or location of the housings. Once abutted, the housing may be connected for communication, such as through one or more bridges. The housing may be connected to other components, such as an air cooling system and/or a compton processor.

In act 106, the assembled compton camera detects the emission. A given emitted photon interacts with a scatter detector. The result is that another photon scatters at a particular angle to the incident line of the emitted photon. The secondary photon has a smaller energy. The secondary photons are detected by a trap detector. Based on the energy and timing of both the detected scatter and trap events, the events are paired. The position and energy of the event pairs provide the ray and scatter angle between the detectors. As a result, the incident ray (e.g., compton cone of incidence) of the emitted photon is determined.

To increase the probability of detecting secondary photons, a trap event from one shell may be paired with a scatter event of another shell. Due to the angle, scatter from one scatter detector may be incident on a pair of trap detectors in the same housing or on a trap detector in another housing. By opening the housing in the detector area and/or using low photon attenuation materials, a greater number of compton events can be detected.

The detected events are counted or collected. The lines of response or along which different compton events occur are used in the reconstruction. The distribution in three dimensions of the emissions from the patient can be reconstructed based on compton sensing. The reconstruction does not require a collimator because the compton sensing accounts for or provides the angle of incidence of the emitted photons.

The detected events are used to reconstruct the position of the radioisotope. Compton and/or photoelectric images are generated from the detected events and corresponding line information from the events.

In act 108, a human or machine (e.g., a robot) removes one of the shells. The housing may be removed when one of its detectors or associated electronics fails or is to be replaced for detection at a different energy. The other housing remains in the medical imaging system. This allows for easier repair and/or replacement of the housing and/or detector without the cost of greater disassembly and/or replacement of the entire compton camera.

Fig. 11-15 are directed to a compton camera with a tilted scatter detector and/or a near 2 pi trap detector. Using the module of fig. 1-9 or another compton camera, the scattering layer and/or the trap layer are arranged to trap a greater percentage of emissions and/or scatter from the patient. The scattering layer is configured in a tilted configuration. The trap layer is formed as a near 2 pi trap layer. Collimation can be used between modules to eliminate large compton angle events that degrade image quality, thereby improving signal-to-noise ratio in the image and reducing the need for ASICs/FPGAs.

Fig. 11 shows an embodiment of a module 11 for a compton camera of a medical imaging system. A tilted scattering layer and a near 2 pi trap layer are provided. The oblique scattering layer results in a larger volume for scattering. Near 2 pi trap detectors create a greater chance of trapping scattered photons by trapping scatter over a wider angular range.

The module 11 may be a complete compton camera or a plurality of such modules 11 form a compton camera. The module 11 of the medical imaging system includes a tilted scattering layer of scatter detectors 12, bottom trap detectors 13A and side trap detectors 13B, inter-module shielding 112 for reducing cross-talk, and inter-module slits and/or slats (i.e., collimators) 114 for blocking large scatter compton angle events and reducing loading on the ASICs or FPGAs of the detectors 12, 13. Additional, different, or fewer components may be provided. For example, the tilted scatter detector 12 is provided without the near 2 π trap detectors 13A, 13B, and vice versa. As another example, no shield 112 and/or slits or slats 114 are provided. In another example, an ASIC or FPGA, circuit board, housing, or other component is provided.

The dimensions in the drawings are arbitrary and are sized for illustration. Other relative dimensions may be used. Since fig. 11 is a cross-sectional view, other components may be provided in front of or before fig. 11. For example, the side wall trap detector 13B, the shield 112, and/or the slit or slat 114 are provided on the side wall parallel to the drawing plane. In other embodiments, one or more sidewalls do not include sidewall trap detectors 13B, shields 112, and/or slits or slats 114.

The module 11 is positioned relative to a patient space, a bore (bore) of a medical imaging system, and/or a couch 60, as discussed above with respect to fig. 5-9 or another configuration. The patient bed 60 supports a patient in a patient space. The couch 60 may be movable, such as a robot or roller system for moving a patient into and out of the medical imaging system. The medical imaging system and/or the outer shell of the scattering layer create a bore in which the patient bed 60 is positioned. The bore defines a patient space for imaging a patient. The bore may be of any size, for example 70cm, in cross-section orthogonal to the longitudinal or iso-centre axis. The center of the bore or the center of the patient space along the longitudinal axis of the cylindrical bore is the isocentric axis. The bed 60 moves along an isocenter axis.

The scatter detector 12 is arranged to receive emissions from the patient. In fig. 11, gamma rays directed parallel to the front face of the scatter detector 12 are shown. The gamma rays emitted from the patient are not all parallel and therefore may reach the front face at any of a variety of angles. The module 11 is positioned such that gamma rays directed to the module 11 may intersect the scatter detector 12 before the trap detector 13. Scatter detector 12 has an outer surface facing toward the isocenter axis.

Due to the tilt, the outer surface deviates from normal by an angle of at least 10-80 degrees (e.g., at least 20, 30, or 45 degrees) from a radial line extending perpendicularly from the isocenter through the center or other portion of scatter detector 12. Any angle may be used, for example 35, 45, 65 or 75 degrees. In case the scatter detector 12 is a plate orthogonal to the radial line, a given area may be fitted in the module 11. By the inclination, the outer surface facing the patient can have a larger area. This results in a greater probability of scattering as the volume for interaction becomes larger. Larger angles result in larger areas and volumes of the faces of detector 12, resulting in a greater probability of scattering for any given photon.

The tilt is relative to the radial direction, which is taken perpendicular to the isocenter axis. No tilt corresponds to scatter detector 12 being a plate orthogonal to the radial direction, which is perpendicular to the isocenter axis. The tilt may be relative to the front or rear surface of the module 11, or the back or rear wall trap detector 13A.

The absolute number of scattered photons increases by: a) using a scattering layer detector material that favors compton scattering over the photoelectric effect (low Z material, where low Z is 30 or less); b) adding more scattering material in the scattering layer; and c) maximizing the number of scatter events that contribute to better overall image quality by eliminating Compton events with large Compton angle uncertainties using physical or digital collimation. By increasing the number of scattered photons (tilt) that escape from the scattering layer and reach the trap layer, the probability of compton events escaping from the scattering layer is increased by reducing the mean free path of these events at the scattering layer. The increase in scattering increases the number of scattered photons that reach the trap layer. Due to the larger escape probability using the tilted geometry, fewer scatter detector modules (per absolute number of scatter events reaching the trap layer) may be used. The tilt results in a larger number of pixels in the projection orthogonal to the radial direction in scatter detector 12, thereby increasing resolution.

In the embodiment shown in FIG. 11, scatter detector 12 is formed from a plurality of plates positioned in a folded arrangement. To increase the number of scatter events, the plates of scatter detector 12 are configured in a tilted configuration, with no gaps between the detector plates. The panels abut to create a folded arrangement. In other embodiments a gap may be provided. The plates are inclined in a repeating sequence of two angles. Other arrangements in the sequence of three or more plates and three or more corresponding angles may be used. In an alternative embodiment, the scatter detector is a tilted single plate. In yet other embodiments, one or more plates of the detector are orthogonal to the radial direction (e.g., parallel to back wall trap detector 13A), while the other plates are tilted. Alternatively, the plates do not abut, but all slope at the same angle and parallel to each other (see fig. 15).

The same arrangement extends between the side walls into and out of the plane of the figure, using a panel and folding arrangement. In other embodiments, scatter detector 12 varies in angle or tilt into and out of the plane of the figure and through a cross-section of the figure. Any 3D surface that is not planar may be used.

The tilt maximizes the absolute number of scattered photons by the scattering layer, thereby increasing the absolute number of scattered photons reaching the trap layer. Because scattering is more likely to occur due to tilt, a greater variety of detector materials may be used, such as Si, HPGe, CdTe, CZT, GaAs, TlBr, etc., due to the inherent ease of fabricating more uniform detectors with thinner thicknesses. The tilt offsets some of the loss of scattering volume in the thinner detector. Due to the larger escape probability using the tilted geometry, fewer scatter detector modules are required per absolute number of scatter events that reach the trap. Due to the tilt, the pixel density of the scatter detector is large compared to viewing from the isocenter. The use of the slanted geometry improves the position resolution due to the larger number of pixels per unit projected area (ASIC channels) along the radial direction.

Trap detector 13 is positioned spatially behind scatter detector 12 with respect to the patient. Trap detector 13 is spaced apart from scatter detector 12 so that a volume is formed between detectors 12, 13. One or more portions of trap detector 13 may contact one or more portions of scatter detector 12, for example at a side of module 11. A gap may be provided between scatter detector 12 and trap detector 13 without contact. Drip catcher detector 13 may extend to the same z-depth as part of scatter detector 12, for example due to tilting of scatter detector 12 and/or due to the surrounding shape of drip catcher detector 13.

The trap detector 13 forms a substantially hemispherical enclosure behind the scatter detector 12 with respect to the patient space. Substantially to account for gaps at the junction, excluding one or both of the four sides of sidewall trap detector 13B, sidewall trap detector 13B begins at a z-depth (i.e., along a radial direction perpendicular to the isocenter axis) that is 30 degrees or less from a plane orthogonal to the radial direction at a depth of the deepest portion of scatter detector 12, and/or sidewall trap detector 13B begins at a z-depth (i.e., along a radial direction perpendicular to the isocenter axis) that is 10 cm or less deeper than the plane orthogonal to the radial direction at the depth of the deepest portion of scatter detector 12. A multi-sided detector front is provided. The trap detector 13 is non-planar. The front face or surface through which scattered photons enter detector 13 is non-planar. The trap detector 13 is formed in a cup-shape, box-shape or three or more sided hemisphere to at least partially (i.e. substantially) surround the volume behind the scatter detector 12. This provides a near 2 pi structure behind the scatter detector 12 with respect to the patient.

In one embodiment, the substantially hemispherical enclosure is formed by a plurality of flat plates, such as a back wall trap detector 13A and two or more side wall trap detectors 13B (e.g., back wall trap detector 13A and four side wall trap detectors 13B form a five-sided cube with one open side directed toward scatter detector 12). The plates may be at right angles to each other, but may also be provided at greater or lesser angles. The plates are substrates that lie in non-parallel planes within the module 11. A semiconductor or other process for forming the detector as a slab may be used to form the plate, which is then positioned in the module 11 to provide a substantially hemispherical enclosure. A four sided square or rectangular plate is used in fig. 11, but three, five, six or other numbers of sides may be used.

The catcher layer geometry at least partially surrounds the space behind the scattering layer, providing a near 2 pi solid angle geometry. Such a surrounding may result in trapping more scattered photons. For example, a scatter/trap ratio of close to 100% can be achieved by adding a trap layer between the modules (i.e., sidewall trap detectors 13B). Providing a larger field of view of the compton camera in the Z direction (bed direction). The absolute number of photons scattered/trapped is increased by: a) increasing a solid angle between the scattering layer and the catcher layer; b) increasing the area of the catcher layer; c) reducing the distance between the scattering layer and the catcher layer; d) increasing the effective thickness of the catcher layer; e) and/or selecting a material that favors photoelectric effect versus compton scattering in the trap layer. The solid angle may be increased by shaping the drip catcher detector 13 as a polygonal surround of the volume behind the scatter detector 12, the area of the front face of the drip catcher detector is increased, the distance between the scatter detector 12 and the drip catcher detector 13 may be decreased, and the effective thickness of the drip catcher layer is increased.

The shield 112 is a shielding material such as lead or tungsten. The shield 112 is a gamma ray shield. The material and thickness that is opaque for a given percentage (e.g., 75-100%) of the isotope energy emission is located at a sidewall (e.g., a covered portion or the entire wall) or is a sidewall of the module 11. Shielding material is provided over the entire sidewall (e.g., adjacent ends) and over the z-axis extent (i.e., depth along the radial direction) of scatter detector 12 and trap detector 13. In other embodiments, the shielding material has a smaller extent, for example starting on the sidewall at the deepest extent of scatter detector 12 to trap detector 13 or to the deepest part of trap detector 13.

The shielding 112 may be on all walls except the side of the module 11 facing the patient space. Alternatively, one or more of the side walls and/or the back wall do not include the shield 112. In the case where a plurality of modules 11 abut each other, one shield 112 may be provided therebetween without abutting shields 112 from two modules 11. The shielding material separates the modules 11. Cross talk between modules is reduced by adding inter-module shields.

The slits and/or slats 114 are collimators formed by the plates. The plates are positioned parallel to each other, forming a slit through which photons can pass. In other embodiments, the slits and/or slats 114 are collimators with apertures at desired angles. Any size aperture may be used.

The slits and/or slats 114 are angled to allow photons at certain angles to pass through and to absorb or block photons at other angles. For example, the slits and/or slats 114 are angled to absorb large angle scattered photons (e.g., 80-110 degrees from radial). Large angle scattered photons contain large angle uncertainties and can be noise to neighboring modules. The slits and/or slats 114 may improve image quality and reduce ASIC or FPGA 122 requirements by reducing noise-related photons.

The slits and/or slats 114 are disposed adjacent to the scatter detectors 12, such as having the same depth range on two or more sidewalls of the module 11. Other ranges or locations may be provided. The slits and/or slats 114 may be part of the modules 11 or located between the modules 11.

Scatter detector 12 includes an Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA) for reading scatter detector 12. A separate ASIC or FPGA is provided for each group of pixels in scatter detector 12. An ASIC or FPGA is formed as part of the substrate with scatter detector 12 or may be formed separately. An ASIC or FPGA 122 is positioned parallel to scatter detector 12, as shown in FIG. 12A. At this location, some scattered photons are trapped in the ASIC or FPGA 122, which results in the loss of the compton event.

Fig. 12B shows another embodiment. An ASIC or FPGA 122 is electrically connected to the scatter detector 12 by traces on the flex circuit material or by wires. The ASIC or FPGA 122 is positioned parallel to a radial line from the isocenter axis to minimize the area interacting with the scatter. ASIC or FPGA 122 is a board or substrate that is positioned non-parallel to the outer or forward facing surface of scatter detector 12. In other embodiments, the ASIC or FPGA 122 of the scatter detector 12 is removed from the field of view, for example, behind the trap detector 13 with respect to the patient. The ASIC or FPGA 122 is positioned to reduce the impact on compton kinematics.

Fig. 11 shows one module 11. The compton camera is formed by a single module 11 or a plurality of modules 11. Each module 11 comprises a tilted scatter detector 12 and/or a near 2 pi trap detector 13. The modules 11 may have a housing shape that is stacked or abutted to form a ring or partial ring, for example having the wedge shape of fig. 1. Other shapes may be used.

For a multi-module compton camera, the scattering layer is formed by a plurality of scatter detectors 12, for example using the modular system of fig. 1-9. Similarly, the trap layer 13 is formed of a plurality of trap detectors 13. For example, eighteen modules 11 provide eighteen pairs of scatter detectors 12 and trap detectors 13. More or fewer modules 11 may be used. The modules 11 may have any arrangement, such as one or more axially spaced rings and/or partial rings or one or more sparsely distributed modules 11 or groups of modules. The module 11 may be part of a multi-modality imaging system or a system for a compton-only camera. Scatter detector 12 and trap detector 13 (e.g., module 11) are positioned to receive emissions from a patient on patient bed 60 or otherwise in patient space.

The modules 11 may be positioned not adjacent to other modules 11, adjacent to one, two, three or four other modules 11. Where scatter detectors 12 are tilted in a repeating pattern along one dimension, modules 11 may be positioned adjacent to each other along two sides. Where scatter detectors 12 are tilted in a repeating pattern along two dimensions, modules 11 may be positioned adjacent to each other along four sides. In other embodiments, the modules 11 may abut along 1-4 sides regardless of the angled arrangement.

In one embodiment, the modules 11 are positioned to form one or more axially spaced partial or complete rings. Fig. 13A and 13B show at least three complete or partial rings around the patient space and the patient bed 60. Additional or fewer rings and/or partial rings may be provided. Fig. 13A is a cross-sectional view normal to the isocenter axis at one of the rings or partial rings. Fig. 13B is a cross-sectional view of a plane parallel to bed 60 and along the isocenter axis.

The module's near 2 pi trap detector 13 includes a sidewall trap detector 13B located on a side adjacent to the module 11 in the same ring and the module 11 of the other ring. Each module 11 operates independently so that scatter from one module 11 does not pair with a trap in the trap detector 13 of the other module 11. Timing, power, or other information may or may not be shared between the modules. Since the modules 11 are completely isolated modules, the modules 11 may be stacked or abutted on any one of the four sides.

In an alternative embodiment, a compton event may be formed by scattering from one module 11 and trapping of scattered photons in another module 11. Fig. 14A and 14B show cross sections in which the sidewall trap detectors 13B for the sides adjacent to other rings or partial rings are removed or not provided. The modules 11 within a given ring or partial ring are isolated from each other. Adjacent modules 11 across the ring share a common synchronization and/or clock for event detection by the ASICs or FPGAs of the detectors 12, 13, allowing the use of compton event pairs of scattering in one module 11 and trapping of scattered photons in the other module 11. The surround of trap detector 13 in the axially outer or partial ring module has sidewall trap detectors 13B on three sides. The trap detectors 13 in the axially inner ring or partial ring have side wall trap detectors 13B on both sides (the sides of adjacent modules 11 in the same ring or partial ring). In an alternative embodiment, the modules are not isolated within a ring or partial ring, but between rings or partial rings. In still other embodiments, one or more modules 11 may not be isolated within and between rings. The near 2 pi trap layer is formed by the trap detectors 13 of the plurality of modules 11.

Fig. 15 shows a partial ring of modules 11. The modules 11 have a wedge shape for closer stacking. Fig. 13 and 14 show a cube shape in which the gap is provided at least further away from the isocenter axis when the modules 11 are stacked adjacent to each other in a ring or partial ring.

In fig. 15, scatter detector 12 is tilted. The detector plates forming the tilted scatter detector 12 are arranged in parallel planes. All plates of scatter detector 12 in module 11 are tilted in the same direction or towards a given side. Within a ring or partial ring, the scatter detectors 12 of different modules 11 are tilted in the same direction or in different directions. Different patterns or slanted arrangements may be provided between different modules 11 or in groups of modules 11, for example every other opposite slanted pattern between adjacent modules 11 of fig. 15.

The pattern or grouping may correspond to isolation or crosstalk between the modules 11. For example, pairs of modules 11 having oppositely tilted scatter detectors 12 share a synchronization signal and/or clock, but are isolated from other pairs. Sidewall trap detectors 13B between modules 11 that do not provide shared synchronization signals and/or clocks (i.e., with crosstalk). Sidewall trap detectors 13B between ungrouped modules 11 are provided. In other embodiments, pairs or groups of modules 11 used for crosstalk have the same skew as each other. The tilt for the other groups is the same and/or different.

A compton processor 19 (e.g., an image processor) is configured to generate a compton image from the compton events detected from the oblique scatter detector 12 and the near 2 pi trap detector 13. The electronics of the module 11 or other electronics output events detected from the detectors 12, 13. The location, energy and time of the event are received by the compton processor 19. These events are paired using location, energy, and/or time. Based on the pair, position and energy, the angle of incidence of the emission from the patient onto scatter detector 12 is determined. The angle may be expressed in probability, for example, incident on a cone. A reconstruction from a number of detected compton events and angles of incidence is used to determine the spatial distribution of emissions in the patient or object space. The compton image is rendered from the spatial distribution.

The display 22 displays a compton image. Other images may be displayed with the compton image. The tilted scatter detector 12 and/or the near 2 pi trap detector 13 cause a greater number of compton events to be trapped and therefore the resulting compton image has more information. This better image quality results in diagnostically improved images.

The compton processor 19 is configured to perform digital collimation. Once the events are paired, the scatter angle from scatter detector 12 for a given event is determined. The relationship of the energy and angle and position of the pair event indicates the angle of the scattered photon. Compton events may be rejected based on angle, such as applying one or more scatter angle thresholds. A compton image is generated from the non-rejected compton event. In other embodiments, digital collimation may not be used.

FIG. 16A shows the angular uncertainty in Compton angle as a function of Compton angle. Compton events with some scatter angles may result in poorer image quality. For example, the FWHM of the back projection cone will be at a desired level, e.g. as indicated by the horizontal dashed line. The FWHM for a given compton event is above or below the desired FWHM based on the scatter angle. For example, angles between 40 and 120 degrees provide information with sufficient FWHM. Fig. 16B shows the emission given orthogonal to the different scatter angles of the scatter detector. Compton events for small (e.g., less than 40 degrees) and/or large (e.g., greater than 120 degrees) scatter angles are not used (i.e., rejected by digital collimation). The remaining compton events are used to generate a compton image.

In one example, CZT scatter detector 12 and CZT trap detector 13 have a distance of 30cm between the scatter layer and the trap layer, with a bore diameter of 70 cm. By rejecting events with Compton angles greater than 40, PSFs with FWHM < 40.0mm are generated. Other thresholds may be used.

Although the invention has been described above with reference to various embodiments, it should be understood that many changes and modifications may be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.