Scintillator detectors and methods for positron emission tomography
A positron emission tomography (PET) scanner includes a plurality of gamma radiation detector modules arranged to form a detector ring. Each detector module includes an array of scintillator detectors. Each scintillator detector comprises a monolithic scintillation crystal and a plurality of photodetector arrays, such as silicon photomultipliers (SiPMs). A photodetector array is positioned on at least two nonparallel faces of each scintillation crystal. In some examples, a photodetector array is positioned on each of three orthogonal faces of each scintillation crystal.
1. A gamma radiation scintillator detector comprising:
a cuboid monolithic scintillator with six faces, including a first end-face to receive a gamma photon, a second end-face opposing the first end-face, and four lateral faces, including a first lateral face opposing a third lateral face and a second lateral face opposing a fourth lateral face;
arrays of silicon photomultipliers (SiPMs) on only three orthogonal faces of the scintillator, including:
a first two-dimensional array of SiPMs on the second end-face of the monolithic scintillator;
a second two-dimensional array of SiPMs on the first lateral face of the monolithic scintillator;
a third two-dimensional array of SiPMs on the second lateral face of the monolithic scintillator;
reflective material positioned on the three orthogonal faces of the scintillator without an array of SiPMs, including reflective material on at least the first end-face, the third lateral face, and the fourth lateral face, such that each face with an array of SiPMs is opposed by a face with reflective material;
a position module to calculate location information of a scintillation event based on detection signals from the SiPM arrays on the three orthogonal faces of the scintillator;
a processing circuit comprising:
a first timing channel to generate a first side event timing signal for the second end-face based on combined detection signals from the first two-dimensional array of SiPMs;
a second timing channel to generate a second side event timing signal for the first lateral face based on combined detection signals from the second two-dimensional array of SiPMs; and
a third timing channel to generate a third side event timing signal for the second lateral face based on combined detection signals from the third two-dimensional array of SiPMs; and
a time correction module to adjust the first, second, and third side event timing signals based on the calculated location information of the scintillation event, thereby generating:
a first adjusted side event timing signal for the second end-face;
a second adjusted side event timing signal for the first lateral face; and
a third adjusted side event timing signal for the second lateral face.
2. The scintillator detector of claim 1 , wherein each two-dimensional array of SiPMs comprises a plurality of subarrays of SiPMs, and wherein each timing channel comprises:
an analog subarray combining circuit for each of the plurality of subarrays of SiPMs to combine the detection signals thereof; and
an analog pulse shaping module to shape analog signals from each analog subarray combining circuit.
3. The scintillator detector of claim 1 , wherein each of the first, second, and third timing channels comprises:
an analog combing circuit to combine analog detection signals from all the SiPMs in the respective two-dimensional array of SiPMs;
a leading-edge discriminator; and
a time-to-digital converter (TDC).
4. The scintillator detector of claim 3 , wherein the analog combing circuit of each timing channel comprises a multistage cascaded combiner circuit.
5. The scintillator detector of claim 1 , wherein each two-dimensional array of SiPMs comprises multiple rows of SiPMs and multiple columns of SiPMs, and
wherein each timing channel comprises an analog subarray combining circuit for each row of SiPMs in each respective two-dimensional array of SiPMs to combine analog detection signals thereof.
6. The scintillator detector of claim 5 , wherein each timing channel further comprises an analog pulse shaping module to shape analog signals from each analog subarray combining circuit.
7. The scintillator detector of claim 1 , further comprising an energy module to determine a total energy of a scintillation event.
8. The scintillator detector of claim 1 , wherein each two-dimensional array of SiPMs comprises a plurality of subarrays of SiPMs, wherein each subarray of SiPMs comprises at least two SiPMs, wherein each timing channel comprises a subarray combining circuit for each subarray of SiPMs, each subarray combining circuit configured to sum analog detection signals of the SiPMs in a respective subarray of SiPMs and generate a subarray analog detection signal.
9. The scintillator detector of claim 8 , wherein each timing channel comprises at least one two-stage combining circuit, each two-stage combining circuit comprising:
a comparator for each of at least two subarrays of SiPMs, each comparator configured to receive the subarray analog detection signal of one of the subarrays of SiPMs and generate a binary time-mark signal based on the subarray analog detection signal exceeding a subarray trigger threshold; and
a combining comparator to combine the binary time-mark signals from each comparator of each of the at least two subarrays of SiPMs to generate an intermediate binary time-mark signal.
10. The scintillator detector of claim 9 , wherein each two-dimensional array of SiPMs comprises at least four subarrays of SiPMs, and wherein each timing channel comprises at least two two-stage combining circuits,
wherein each timing channel comprises at least one subsequent-stage combining circuit, each subsequent-stage combining circuit comprising:
a subsequent-stage combining comparator to combine the binary time-mark signals from at least two two-stage combining circuits to generate a subsequent binary time-mark signal.
11. The scintillator detector of claim 8 , wherein each timing channel comprises at least one programmable two-stage dual-trigger combining circuit, wherein each programmable two-stage dual-trigger combining circuit is configurable to selectively trigger an output binary time-mark signal in response to a selectable number of subarrays of SiPMs exceeding a subarray trigger threshold.
12. The scintillator detector of claim 8 , wherein each timing channel comprises at least one programmable two-stage dual-trigger combining circuit, each programmable two-stage dual-trigger combining circuit comprising:
a comparator for each of at least two subarrays of SiPMs, each comparator configured to receive the subarray analog detection signal of one of the subarrays of SiPMs and generate a binary time-mark signal based on the subarray analog detection signal exceeding a subarray trigger threshold; and
a combining comparator to combine the binary time-mark signals from each comparator of a selectable number of subarrays of SiPMs to generate an output binary time-mark signal.
13. A gamma radiation detector module comprising an array of scintillator detectors, wherein each scintillator detector includes:
a cuboid monolithic scintillator with six faces, including a first end-face to receive a gamma photon, a second end-face opposing the first end-face, and four lateral faces, including a first lateral face opposing a third lateral face and a second lateral face opposing a fourth lateral face;
photodetector arrays on only three orthogonal faces of the scintillator, including:
a first two-dimensional array of silicon photomultipliers (SiPMs) on the second end-face of the monolithic scintillator;
a second two-dimensional array of SiPMs on the first lateral face of the monolithic scintillator;
a third two-dimensional array of SiPMs on the second lateral face of the monolithic scintillator;
reflective material positioned on the three orthogonal faces of the scintillator without a photodetector array, including reflective material on at least the first end-face, the third lateral face, and the fourth lateral face, such that each face with an array of SiPMs is opposed by a face with reflective material;
a position module to calculate location information of a scintillation event based on detection signals from the photodetector arrays on the three orthogonal faces of the scintillator;
a processing circuit comprising:
a first timing channel to generate a first side event timing signal for the second end-face based on combined detection signals from the first two-dimensional array of SiPMs;
a second timing channel to generate a second side event timing signal for the first lateral face based on combined detection signals from the second two-dimensional array of SiPMs; and
a third timing channel to generate a third side event timing signal for the second lateral face based on combined detection signals from the third two-dimensional array of SiPMs; and
a time correction module to adjust the first, second, and third side event timing signals based on the calculated location information of the scintillation event, thereby generating:
a first adjusted side event timing signal for the second end-face;
a second adjusted side event timing signal for the first lateral face; and
a third adjusted side event timing signal for the second lateral face.
14. A positron emission tomography (PET) scanning system, comprising:
a plurality of gamma radiation detector modules, wherein each detector module comprises an array of scintillator detectors, each of which includes:
a cuboid monolithic scintillator with six faces, including a first end-face to receive a gamma photon, a second end-face opposing the first end-face, and four lateral faces, including a first lateral face opposing a third lateral face and a second lateral face opposing a fourth lateral face;
photodetector arrays on only three orthogonal faces of the scintillator, including:
a first two-dimensional array of silicon photomultipliers (SiPMs) on the second end-face of the monolithic scintillator;
a second two-dimensional array of SiPMs on the first lateral face of the monolithic scintillator;
a third two-dimensional array of SiPMs on the second lateral face of the monolithic scintillator;
reflective material positioned on the three orthogonal faces of the scintillator without a photodetector array, including reflective material on at least the first end-face, the third lateral face, and the fourth lateral face, such that each face with an array of SiPMs is opposed by a face with reflective material;
a position module to calculate location information of a scintillation event based on detection signals from the photodetector arrays on the three orthogonal faces of the scintillator;
a processing circuit comprising:
a first timing channel to generate a first side event timing signal for the second end-face based on combined detection signals from the first two-dimensional array of SiPMs;
a second timing channel to generate a second side event timing signal for the first lateral face based on combined detection signals from the second two-dimensional array of SiPMs; and
a third timing channel to generate a third side event timing signal for the second lateral face based on combined detection signals from the third two-dimensional array of SiPMs;
a time correction module to adjust the first, second, and third side event timing signals based on the calculated location information of the scintillation event, thereby generating:
a first adjusted side event timing signal for the second end-face
a second adjusted side event timing signal for the first lateral face; and
a third adjusted side event timing signal for the second lateral face; and
an imaging system to generate an image based on electronic outputs from the plurality of detector modules.