WO2023015564A1

WO2023015564A1 - Determination of photon origination points using radiation detectors

Info

Publication number: WO2023015564A1
Application number: PCT/CN2021/112531
Authority: WO
Inventors: Peiyan CAO; Yurun LIU
Original assignee: Shenzhen Xpectvision Technology Co., Ltd.
Priority date: 2021-08-13
Filing date: 2021-08-13
Publication date: 2023-02-16
Also published as: TW202307463A; CN117795382A

Abstract

A method, comprising: receiving, with a first radiation sensor, a first photon from an object (520), the first radiation sensor comprising M sensing element groups (152), wherein each sensing element group (152) of the M sensing element groups (152) comprises multiple sensing elements (150), and wherein M is an integer greater than 1; determining a first subset of the M sensing element groups (152) based on electrical signals in the M sensing element groups (152) of the first radiation sensor; and determining a first estimated path of the first photon based on positions of the sensing element groups (152) in the first subset.

Description

DETERMINATION OF PHOTON ORIGINATION POINTS USING RADIATION DETECTORS

Background

A radiation detector is a device that measures a property of a radiation. Examples of the property may include a spatial distribution of the intensity, phase, and polarization of the radiation. The radiation measured by the radiation detector may be a radiation that has transmitted through an object. The radiation measured by the radiation detector may be an electromagnetic radiation such as infrared light, visible light, ultraviolet light, X-ray, or γ-ray. The radiation may be of other types such as α-rays and β-rays. An imaging system may include one or more image sensors each of which may have one or more radiation detectors.

Summary

Disclosed herein is a method, comprising: receiving, with a first radiation sensor, a first photon from an object, the first radiation sensor comprising M sensing element groups, wherein each sensing element group of the M sensing element groups comprises multiple sensing elements, and wherein M is an integer greater than 1; determining a first subset of the M sensing element groups based on electrical signals in the M sensing element groups of the first radiation sensor; and determining a first estimated path of the first photon based on positions of the sensing element groups in the first subset.

In an aspect, said determining the first subset comprises identifying sensing element groups of the M sensing element groups that have a photon presence signal.

In an aspect, said identifying comprises: determining a voltage of a dedicated electrode of each sensing element of the first radiation sensor; and combining the voltages of the dedicated electrodes of the multiple sensing elements of each sensing element group of the M sensing element groups resulting in a group voltage for said each sensing element group, wherein the photon presence signal in a sensing element group is an event of the group voltage of the sensing element group exceeding a pre-specified threshold voltage.

In an aspect, dedicated electrodes of the multiple sensing elements of each sensing element group of the M sensing element groups are electrically connected to a group node with metal lines, and wherein the photon presence signal in a sensing element group is an event of a voltage of the group node of the sensing element group exceeding a pre-specified threshold voltage.

In an aspect, said determining the first subset further comprises excluding sensing element groups from the first subset based on a temporal relationship among the photon presence signals in the sensing element groups in the first subset.

In an aspect, the temporal relationship is a temporal order of the photon presence signals in the sensing element groups in the first subset.

In an aspect, the first photon undergoes scattering inside the first radiation sensor.

In an aspect, the first estimated path of the first photon comprises a portion outside the first radiation sensor.

In an aspect, the sensing elements of the M sensing element groups are in multiple radiation absorption layers of the radiation sensor.

In an aspect, a layer opaque to the first photon separates any two adjacent radiation absorption layers of the multiple radiation absorption layers.

In an aspect, the first photon is a gamma ray photon or an X-ray photon.

In an aspect, all the M sensing element groups have a same number of sensing elements.

In an aspect, the method further comprises receiving, with a second radiation sensor, a second photon from the object, the second radiation sensor comprising N sensing element groups, wherein each sensing element group of the N sensing element groups comprises multiple sensing elements, and wherein N is an integer greater than 1; determining a second subset of the N sensing element groups based on electrical signals in sensing element groups of the second radiation sensor; and determining a second estimated path of the second photon based on positions of the sensing element groups in the second subset.

In an aspect, the method further comprises determining a position of a photon origination point of the first and second photons based on the first estimated path and the second estimated path.

In an aspect, the method further comprises rotating the first radiation sensor and the second radiation sensor around the object while keeping the first radiation sensor and the second radiation sensor stationary with respect to each other.

In an aspect, the method further comprises receiving, with the first radiation sensor, a second photon from the object; determining a second subset of the M sensing element groups based on electrical signals in sensing element groups of the first radiation sensor; and determining a second estimated path of the second photon based on positions of the sensing element groups in the second subset.

In an aspect, said determining the first estimated path of the first photon comprises: determining a straight line of best fit through the sensing element groups in the first subset resulting in the first estimated path.

In an aspect, the first radiation sensor comprises P signal processing chips and a stack of 2P radiation absorption layers, P being an integer greater than 1, wherein each of the P signal processing chips is dedicated to processing electrical signals in two adjacent radiation absorption layers of the 2P radiation absorption layers, and wherein at least one of the P signal processing chips is sandwiched between two radiation absorption layers of the 2P radiation absorption layers.

In an aspect, the two radiation absorption layers are separated by another radiation absorption layer of the 2P radiation absorption layers.

In an aspect, a separation layer is sandwiched between any two adjacent radiation absorption layers of the 2P radiation absorption layers, and wherein the separation layer is configured to block gamma rays and X-rays.

In an aspect, the first radiation sensor comprises (A) a stack of Q radiation absorption layers, and (B) multiple signal processing chips for each of the Q radiation absorption layers, wherein the multiple signal processing chips for each radiation absorption layer of the Q radiation absorption layers and dedicated electrodes of all the sensing elements of said each radiation absorption layer are on a same side surface of said each radiation absorption layer, and wherein no straight line (A) that is perpendicular to said same side surface of said each radiation absorption layer and (B) that intersects a signal processing chip for said each radiation absorption layer intersects any dedicated electrode of any sensing element of said each radiation absorption layer.

In an aspect, a plurality of signal processing chips of the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are physically attached to a support substrate, and wherein the plurality of signal processing chips are sandwiched between the support substrate and the radiation absorption layer.

In an aspect, the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are in recesses of an adjacent radiation absorption layer of the Q radiation absorption layers.

In an aspect, the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are in recesses of a separation layer, and wherein the separation layer is configured to block gamma rays and X-rays.

Disclosed herein is a system, comprising a first radiation sensor configured to receive a first photon from an object, wherein the first radiation sensor comprises M sensing element groups, wherein each sensing element group of the M sensing element groups comprises multiple sensing elements, wherein M is an integer greater than 1, wherein the system is configured to determine a first subset of the M sensing element groups based on electrical signals in the M sensing element groups of the first radiation sensor, and wherein the system is configured to determine a first estimated path of the first photon based on positions of the sensing element groups in the first subset.

In an aspect, the system further comprises a second radiation sensor configured to receive a second photon from the object, wherein the second radiation sensor comprises N sensing element groups, wherein each sensing element group of the N sensing element groups comprises multiple sensing elements, wherein N is an integer greater than 1, wherein the system is configured to determine a second subset of the N sensing element groups based on electrical signals in sensing element groups of the second radiation sensor, and wherein the system is configured to determine a second estimated path of the second photon based on positions of the sensing element groups in the second subset.

In an aspect, the system is configured to determine a position of a photon origination point of the first and second photons based on the first estimated path and the second estimated path.

Brief Description of Figures

Fig. 1 schematically shows a radiation detector, according to an embodiment.

Fig. 2 schematically shows a simplified cross-sectional view of the radiation detector, according to an embodiment.

Fig. 3 schematically shows a detailed cross-sectional view of the radiation detector, according to an embodiment.

Fig. 4 schematically shows a detailed cross-sectional view of the radiation detector, according to an alternative embodiment.

Fig. 5 schematically shows a perspective view of a radiation sensor of a radiation sensing system in operation, according to an embodiment.

Fig. 6 shows a flowchart generalizing the operation of the radiation sensing system.

Fig. 7 schematically shows the radiation sensing system in further operation, according to an embodiment.

Fig. 8 schematically shows the radiation sensing system, according to an alternative embodiment.

Fig. 9 schematically shows a perspective view of the radiation sensor, according to an alternative embodiment.

Fig. 10 –Fig. 11 schematically show cross-sectional views of the radiation sensor of Fig. 9, according to embodiments.

Detailed Description

RADIATION DETECTOR

Fig. 1 schematically shows a radiation detector 100, as an example. The radiation detector 100 may include an array of pixels 150 (also referred to as sensing elements 150) . The array may be a rectangular array (as shown in Fig. 1) , a honeycomb array, a hexagonal array, or any other suitable array. The array of pixels 150 in the example of Fig. 1 has 4 rows and 7 columns; however, in general, the array of pixels 150 may have any number of rows and any number of columns.

Each pixel 150 may be configured to detect radiation from a radiation source (not shown) incident thereon and may be configured to measure a characteristic (e.g., the energy of the particles, the wavelength, and the frequency) of the radiation. A radiation may include particles such as photons and subatomic particles. Each pixel 150 may be configured to count numbers of particles of radiation incident thereon whose energy falls in a plurality of bins of energy, within a period of time. All the pixels 150 may be configured to count the numbers of particles of radiation incident thereon within a plurality of bins of energy within the same period of time. When the incident particles of radiation have similar energy, the pixels 150 may be simply configured to count numbers of particles of radiation incident thereon within a period of time, without measuring the energy of the individual particles of radiation.

Each pixel 150 may have its own analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of an incident particle of radiation into a digital signal, or to digitize an analog signal representing the total energy of a plurality of incident particles of radiation into a digital signal. The pixels 150 may be configured to operate in parallel. For example, when one pixel 150 measures an incident particle of radiation, another pixel 150 may be waiting for a particle of radiation to arrive. The pixels 150 may not have to be individually addressable.

The radiation detector 100 described here may have applications such as in an X-ray telescope, X-ray mammography, industrial X-ray defect detection, X-ray microscopy or microradiography, X-ray casting inspection, X-ray non-destructive testing, X-ray weld inspection, X-ray digital subtraction angiography, etc. It may be suitable to use this radiation detector 100 in place of a photographic plate, a photographic film, a PSP plate, an X-ray image intensifier, a scintillator, or another semiconductor X-ray detector.

Fig. 2 schematically shows a simplified cross-sectional view of the radiation detector 100 of Fig. 1 along a line 2-2, according to an embodiment. Specifically, the radiation detector 100 may include a radiation absorption layer 110 and an electronics layer 120 (which may include one or more ASICs (application-specific integrated circuits) or programmable logic devices) for processing or analyzing electrical signals which incident radiation generates in the radiation absorption layer 110. The radiation detector 100 may or may not include a scintillator (not shown) . The radiation absorption layer 110 may include a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor material may have a high mass attenuation coefficient for the radiation of interest.

Fig. 3 schematically shows a detailed cross-sectional view of the radiation detector 100 of Fig. 1 along the line 2-2, as an example. Specifically, the radiation absorption layer 110 may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region 111, one or more discrete regions 114 of a second doped region 113. The second doped region 113 may be separated from the first doped region 111 by an optional intrinsic region 112. The discrete regions 114 may be separated from one another by the first doped region 111 or the intrinsic region 112. The first doped region 111 and the second doped region 113 may have opposite types of doping (e.g., region 111 is p-type and region 113 is n-type, or region 111 is n-type and region 113 is p-type) . In the example of Fig. 3, each of the discrete regions 114 of the second doped region 113 forms a diode with the first doped region 111 and the optional intrinsic region 112. Namely, in the example in Fig. 3, the radiation absorption layer 110 has a plurality of diodes (more specifically, 7 diodes corresponding to 7 pixels 150 of one row in the array of Fig. 1, of which only 2 pixels 150 are labeled in Fig. 3 for simplicity) . The plurality of diodes may have an electrode 119A as a shared (common) electrode. The first doped region 111 may also have discrete portions.

The electronics layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by the radiation incident on the radiation absorption layer 110. The electronic system 121 may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessor, and memory. The electronic system 121 may include one or more ADCs (analog to digital converters) . The electronic system 121 may include components shared by the pixels 150 or components dedicated to a single pixel 150. For example, the electronic system 121 may include an amplifier dedicated to each pixel 150 and a microprocessor shared among all the pixels 150. The electronic system 121 may be electrically connected to the pixels 150 by vias 131. Space among the vias may be filled with a filler material 130, which may increase the mechanical stability of the connection of the electronics layer 120 to the radiation absorption layer 110. Other bonding techniques are possible to connect the electronic system 121 to the pixels 150 without using the vias 131.

When radiation from the radiation source (not shown) hits the radiation absorption layer 110 including diodes, particles of the radiation may be absorbed and generate one or more charge carriers (e.g., electrons, holes) by a number of mechanisms. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The electric field may be an external electric field. The electrode 119B may include discrete portions each of which is in electrical contact with the discrete regions 114. The term “electrical contact” may be used interchangeably with the word “electrode. ” The electrode 119B may also be called the dedicated electrode 119B because it is dedicated to a pixel 150. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete regions 114 ( “not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow to a different one of the discrete regions 114 than the rest of the charge carriers) . Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete regions 114 are not substantially shared with another of these discrete regions 114. A pixel 150 associated with a discrete region 114 may be an area around the discrete region 114 in which substantially all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%of) charge carriers generated by a particle of the radiation incident therein flow to the discrete region 114. Namely, less than 2%, less than 1%, less than 0.1%, or less than 0.01%of these charge carriers flow beyond the pixel 150.

Fig. 4 schematically shows a detailed cross-sectional view of the radiation detector 100 of Fig. 1 along the line 2-2, according to an alternative embodiment. More specifically, the radiation absorption layer 110 may include a resistor of a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does not include a diode. The semiconductor material may have a high mass attenuation coefficient for the radiation of interest. In an embodiment, the electronics layer 120 of Fig. 4 is similar to the electronics layer 120 of Fig. 3 in terms of structure and function.

When the radiation hits the radiation absorption layer 110 including the resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. A particle of the radiation may generate 10 to 100,000 charge carriers. The charge carriers may drift to the

electrodes

119A and 119B under an electric field. The electric field may be an external electric field. The electrode 119B may include discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete portions of the electrode 119B ( “not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers) . Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete portions of the electrode 119B are not substantially shared with another of these discrete portions of the electrode 119B. A pixel 150 associated with a discrete portion of the electrode 119B may be an area around the discrete portion in which substantially all (more than 98%, more than 99.5%, more than 99.9%or more than 99.99%of) charge carriers generated by a particle of the radiation incident therein flow to the discrete portion of the electrode 119B. Namely, less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrode 119B.

RADIATION SENSING SYSTEM AND RADIATION SENSOR

Fig. 5 schematically shows a perspective view of a radiation sensing system 500, according to an embodiment. In an embodiment, the radiation sensing system 500 may include a radiation sensor 510. In an embodiment, the radiation sensor 510 may include a stack of 12 radiation absorption layers 110 and 6 signal processing chips 122 as shown.

In an embodiment, each signal processing chip 122 may be similar to the electronics layer 120 of Fig. 2 -Fig. 4 in terms of function and structure. For example, each signal processing chip 122 may be an ASIC chip or a programmable logic device for processing and analyzing electrical signals which incident radiation generates in the sensing elements 150 of the radiation absorption layer 110 served by the signal processing chip 122.

In an embodiment, the 12 radiation absorption layers 110 may be divided into 6 pairs, each pair having two adjacent radiation absorption layers 110. In an embodiment, each pair of two adjacent radiation absorption layers 110 may share a signal processing chip 122. In other words, the shared signal processing chip 122 is dedicated to processing and analyzing electrical signals generated in the sensing elements 150 of the two adjacent radiation absorption layers 110.

For example, the signal processing chip 122.1 is dedicated to processing and analyzing electrical signals generated in the two adjacent radiation absorption layers 110.1a and 110.1b. In other words, the signal processing chip 122.1 is for the two radiation absorption layers 110.1a and 110.1b. As another example, the signal processing chip 122.6 is for the two adjacent radiation absorption layers 110.6a and 110.6b.

In an embodiment, most signal processing chips 122 may be sandwiched between two radiation absorption layers 110. For example, the signal processing chip 122.6 is sandwiched between the radiation absorption layers 110.5b and 110.6b. Note that these 2 radiation absorption layers 110.5b and 110.6b are separated by the radiation absorption layer 110.6a.

In an embodiment, for each of the 12 radiation absorption layers 110, its dedicated electrodes 119B are on its right side surface and its common electrode 119A is on its left side surface. For example, the radiation absorption layer 110.1a have 4×6 = 24 sensing elements 150, and all the 24 dedicated electrodes 119B of the 24 sensing elements 150 of the radiation absorption layer 110.1a are on the right side surface 110s of the radiation absorption layer 110.1a. The common electrode 119A of the 24 sensing elements 150 of the radiation absorption layer 110.1a is on the left side surface of the radiation absorption layer 110.1a but is not shown for simplicity.

In an embodiment, transmission lines (not shown) that electrically connect the sensing elements 150 of both the radiation absorption layers 110.1a and 110.1b to the associated signal processing chip 122.1 run on the right side surface of the radiation absorption layer 110.1b. In an embodiment, the arrangements of transmission lines in the other pairs of radiation absorption layers 110 and their associated signal processing chips 122 may be similar.

In an embodiment, the sensing elements 150 of the radiation sensor 510 may be divided into sensing element groups 152 each of which may have multiple sensing elements 150. In an embodiment, all the sensing element groups 152 of the radiation sensor 510 may have the same number of sensing elements 150. For example, all the sensing element groups 152 of the radiation sensor 510 may have 2 sensing elements 150. As a result, the 24 sensing elements 150 of the radiation absorption layer 110.1a are divided into 12 sensing element groups 152 as shown.

OBJECT TO BE ANALYZED

In an embodiment, an object 520 may be positioned such that a photon originating from the object 520 and traveling toward the radiation sensor 510 would incident (i.e., hit) the radiation sensor 510 on a side of the radiation sensor 510 where there is no

electrode

119A or 119B (as shown) .

For example, a photon 521 originating from the object 520 and traveling toward the radiation sensor 510 along a path 521p hits the side of the radiation sensor 510. In an embodiment, this side of the radiation sensor 510 does not have any

electrode

119A or 119B.

PHOTON PRESENCE SIGNAL –GROUP VOLTAGE

In an embodiment, the photon 521 after incident on the radiation sensor 510 may undergo scattering (e.g., Compton scattering) inside the radiation sensor 510. As a result, the photon 521 may cause electrical signals in some sensing elements 150 of the radiation sensor 510. As a result, the voltages of the dedicated electrodes 119B of some sensing elements 150 in the radiation sensor 510 may rise.

In an embodiment, the photon 521 may be considered present in a sensing element group 152 of the radiation sensor 510 if the combined voltage (e.g., the sum) of the voltages of the two dedicated electrodes 119B of the two sensing elements 150 (called group voltage for short) of the sensing element group 152 exceeds a pre-specified threshold voltage.

The event of the group voltage of a sensing element group 152 exceeding the pre-specified threshold voltage can be referred to as the photon presence signal in the sensing element group 152.

For example, the photon 521 may be considered present in the sensing element group 152 (4, 1) if the signal processing chip 122.1 determines the voltages of the 2 dedicated electrodes 119B of the 2 sensing elements 150 of the sensing element group 152 (4, 1) , and then determines that the group voltage of the sensing element group 152 (4, 1) exceeds the pre-specified threshold voltage.

SYSTEM OPERATION -DETERMINATION OF ESTIMATED PATH OF PHOTON

As an example, assume that photon presence signals appear in the sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) . These 3 sensing element groups are in grey in Fig. 5 for easy view. As a result, in an embodiment, the photon 521 may be considered present in these 3 sensing element groups 152. These 3 sensing element groups make a subset of all the sensing element groups 152 of the radiation sensor 510. Note that in essence, the 3 sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) of the subset are identified based on the electrical signals in sensing element groups 152 of the radiation sensor 510. Specifically, the 3 sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) of the subset are identified because they have the photon presence signals.

In an embodiment, an estimated path 521p’ of the photon 521 may be determined based on the positions of the sensing element groups 152 in the subset which includes the sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) .

In an embodiment, the estimated path 521p’ may be a straight line of best fit through all the 3 sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) in the subset.

In an embodiment, the radiation sensing system 500 may further include a computer 530 electrically connected to all the 6 signal processing chips 122 of the radiation sensor 510. In an embodiment, the computer 530 may determine the straight line of best fit through all the three sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) .

In an embodiment, the estimated path 521p’ extends outside the radiation sensor 510 to infinity in both opposite directions. As a result, the estimated path 521p’ includes a portion outside the radiation sensor 510.

In the example described above, for simple illustration, all the sensing element groups 152 that have photon presence signals (i.e., the 3 sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) ) are in the same radiation absorption layer 110 (i.e., the radiation absorption layers 110.1a) . In general, the sensing element groups 152 that have photon presence signals may be in multiple radiation absorption layers 110.

FLOWCHART GENERALIZING SYSTEM OPERATION

Fig. 6 shows a flowchart 600 generalizing the operation of the radiation sensing system 500, according to an embodiment. In step 610, a radiation sensor receives a photon from an object, the radiation sensor including M sensing element groups, wherein M is an integer greater than 1. For example, in the embodiments described above, the radiation sensor 510 receives the photon 521 from the object 520. The radiation sensor 510 includes multiple sensing element groups 152. If the other radiation absorption layers 110 are similar to the radiation absorption layer 110.1a, then M = 12 layers × 12 groups/layer = 144 sensing element groups 152.

In addition, in step 610, each sensing element group of the M sensing element groups includes multiple sensing elements. For example, in the embodiments described above, each sensing element group 152 of the 144 sensing element groups 152 of the radiation sensor 510 includes 2 sensing elements 150.

In step 620, a subset of the M sensing element groups is determined based on electrical signals in sensing element groups of the radiation sensor. For example, in the embodiments described above, the subset including the 3 sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) is determined based on the electrical signals in sensing element groups 152 of the radiation sensor 510.

In step 630, an estimated path of the photon is determined based on positions of the sensing element groups in the subset. For example, in the embodiments described above, the estimated path 521p’ of the photon 521 is determined based on the positions of the 3 sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) in the subset.

ADDITIONAL EMBODIMENTS

TEMPORAL RELATIONSHIP OF PHOTON PRESENCE SIGNALS

In an embodiment, with respect to step 620 of Fig. 6, the determination of the subset may further include excluding sensing element groups from the subset based on a temporal relationship among the photon presence signals in the sensing element groups in the subset.

In the example described above, the determination of the subset may further include excluding sensing element groups 152 from the subset based on the temporal relationship among the photon presence signals in the sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) .

For example, assume that the photon presence signal occurs in the sensing element group 152 (2, 3) , then in the sensing element group 152 (4, 1) , and then in the sensing element group 152 (3, 2) . Because the photon 521 is likely to travel deeper into the radiation sensor 510 as time progresses, the photon presence signal in the sensing element group 152 (3, 2) is likely not caused by the photon 521. Therefore, in an embodiment, the sensing element group 152 (3, 2) may be excluded from the subset. Then, the determination of the estimated path 521p’ of the photon 521 may be based on the remaining sensing element groups 152 in the subset (i.e., based on the sensing element groups 152 (2, 3) and 152 (4, 1) ) .

In other words, the determination of the subset further includes excluding sensing element groups 152 from the subset based on the temporal order of the photon presence signals in the sensing element groups 152 (2, 3) , 152 (3, 2) , and 152 (4, 1) of the subset.

SEPARATION LAYERS BETWEEN RADIATION ABSORPTION LAYERS

In an embodiment, with reference to Fig. 5, the radiation sensor 510 may further include 11 separation layers (not shown) between the 12 radiation absorption layers 110 such that a separation layer is sandwiched between and thereby separates any 2 adjacent radiation absorption layers 110. For example, with reference to Fig. 11, the separation layer 117 is sandwiched between and thereby separates the 2 adjacent radiation absorption layers 110.1a and 110.1b.

In an embodiment, the 11 separation layers may be opaque to the photon 521. In other words, if the photon 521 hits any of the 11 separation layers, the photon 521 is blocked and absorbed by the separation layer.

In an embodiment, the photon 521 may be a gamma ray photon or an X-ray photon. In an embodiment, the 11 separation layers may comprise tungsten which blocks and absorbs gamma ray photons and X-ray photons.

ESTIMATED PATH OF SECOND PHOTON

With reference to Fig. 7, assume that a second photon 522 originating from the object 520 and traveling toward the radiation sensor 510 along a path 522p hits a side of the radiation sensor 510. Note that this side of the radiation sensor 510 does not have any

electrode

119A or 119B.

In an embodiment, the computer 530 may determine an estimated path 522p’ of the second photon 522. In an embodiment, the determination of the estimated path 522p’ of the second photon 522 may be similar to the determination of the estimated path 521p’ of the first photon 521 described above.

PHOTON ORIGINATION POINT

In an embodiment, the computer 530 may analyze whether the estimated path 521p’ and the estimated path 522p’ intersect each other. Assume the computer 530 determines that the estimated path 521p’ and the estimated path 522p’ intersect each other at an intersection point 525. As a result, this intersection point 525 may be considered a photon origination point of both the first photon 521 and the second photon 522. It can be said that the determination of the photon origination point 525 of the first photon 521 and the second photon 522 is based on the first estimated path 521p’ of the first photon 521 and the second estimated path 522p’ of the second photon 522.

RADIOTRACER AS SOURCE OF GAMMA RAY PHOTONS

In an embodiment, the object 520 may contain a radiotracer that emits positrons. Each emitted positron may collide and combine with an electron nearby resulting in one or more gamma ray photons. In an embodiment, these gamma ray photons may include the

photons

521 and 522 described above.

ALTERNATIVE EMBODIMENTS

SECOND RADIATION SENSOR TO RECEIVE SECOND PHOTON

In the embodiments described above, with reference to Fig. 7, the radiation sensor 510 receives both the

photons

521 and 522. In an alternative embodiment, with reference to Fig. 8, the radiation sensing system 500 may further include another radiation sensor 512 which receives the second photon 522 whereas the first radiation sensor 510 receives the first photon 521 as shown.

In an embodiment, the radiation sensor 512 may be similar to the radiation sensor 510 in terms of structure and function. The

radiation sensors

510 and 512 do not necessarily have the same number of radiation absorption layers 110 or the same number of sensing elements 150 or the same number of sensing element groups 152.

In an embodiment, the signal processing chips 122 (not shown) of the radiation sensor 512 may be electrically connected to the computer 530.

In an embodiment, the determination of the photon origination point 525 of the

photons

521 and 522 using 2 radiation sensors 510 and 512 (Fig. 8) may be similar to the determination of the photon origination point 525 of the

photons

521 and 522 using only the radiation sensor 510 as described above (Fig. 7) .

ROTATION OF THE RADIATION SENSORS

In an embodiment, with reference to Fig. 8, the

radiation sensors

510 and 512 may be rotated around the object 520 as the

radiation sensors

510 and 512 scan the entire object 520 from different angles. In an embodiment, while the

radiation sensors

510 and 512 are rotated around the object 520, the

radiation sensors

510 and 512 may be stationary with respect to each other.

SIDE OF DEDICATED ELECTRODES 119B

In the embodiments described above, with reference to Fig. 5, in the pair of radiation absorption layers 110.1a and 110.1b, the dedicated electrodes 119B of the radiation absorption layer 110.1b are on the right side surface of the radiation absorption layer 110.1b and the common electrode 119A of the radiation absorption layer 110.1b is on the left side surface of the radiation absorption layer 110.1b; and the dedicated electrodes 119B of the radiation absorption layer 110.1a are on the right side surface of the radiation absorption layer 110.1a and the common electrode 119A of the radiation absorption layer 110.1a is on the left side surface of the radiation absorption layer 110.1a.

In an alternative embodiment, in the first pair of radiation absorption layers 110.1a and 110.1b, the dedicated electrodes 119B of the radiation absorption layer 110.1b are still on the right side surface of the radiation absorption layer 110.1b and the common electrode 119A of the radiation absorption layer 110.1b is still on the left side surface of the radiation absorption layer 110.1b; but the dedicated electrodes 119B of the radiation absorption layer 110.1a are on the left side surface of the radiation absorption layer 110.1a and the common electrode 119A of the radiation absorption layer 110.1a is on the right side surface of the radiation absorption layer 110.1a.

PHOTON PRESENCE SIGNAL –VOLTAGE OF GROUP NODE

In the embodiments described above, with reference to Fig. 5, the photon presence signal is defined such that the photon presence signal occurs in a sensing element group 152 if the group voltage of the sensing element group 152 exceeds the pre-specified threshold voltage.

In an alternative embodiment, the dedicated electrodes 119B of the sensing elements 150 of each sensing element group 152 of the radiation sensor 510 may be electrically connected to a group node with metal lines. For example, with reference to the sensing element group 152 (4, 2) , the 2 dedicated electrodes 119B of the sensing element group 152 (4, 2) are electrically connected to a group node 154 with metal lines 156. The other sensing element groups 152 of the radiation sensor 510 may have similar connections.

In this alternative embodiment, the photon presence signal may be defined such that the photon presence signal occurs in a sensing element group 152 if the voltage of the group node 154 of the sensing element group 152 exceeds the pre-specified threshold voltage.

SIGNAL PROCESSING CHIPS AND DEDICATED ELECTRODES ARE ON SAME SIDE SURFACE OF RADIATION ABSORPTION LAYER

In the embodiments described above, with reference to Fig. 5, the signal processing chip 122.1 for the radiation absorption layer 100.1a and the dedicated electrodes 119B of the radiation absorption layer 100.1a are not on the same side surface 110s of the radiation absorption layer 110.1a.

In an alternative embodiment, with reference to Fig. 9, the multiple (e.g., 4) signal processing chips 122 for the radiation absorption layer 100.1a and the 24 dedicated electrodes 119B of the radiation absorption layer 100.1a may be on the same side surface 110s of the radiation absorption layer 110.1a as shown.

In an embodiment, the footprints of the signal processing chips 122 for the radiation absorption layer 100.1a do not overlap the dedicated electrodes 119B of the radiation absorption layer 100.1a. In other words, no straight line (A) that is perpendicular to the side surface 110s of the radiation absorption layer 110.1a and (B) that intersects a signal processing chip 122 for the radiation absorption layer 110.1a intersects any dedicated electrode 119B of the radiation absorption layer 110.1a.

In an embodiment, the features described above with respect to the radiation absorption layer 110.1a and its 4 associated signal processing chips 122 also apply to the other 11 radiation absorption layers 110 and their associated signal processing chips 122 of the radiation sensor 510.

SIGNAL PROCESSING CHIPS IN RECESSES OF AN ADJACENT RADIATION ABSORPTION LAYER

Fig. 10 shows a cross-sectional view of the radiation sensor 510 of Fig. 9 along a plane 10. In an embodiment, with reference to Fig. 10, the multiple signal processing chips 122 for the radiation absorption layer 110.1b may be in recesses 116 of the adjacent radiation absorption layer 110.1a as shown.

SIGNAL PROCESSING CHIPS IN RECESSES OF SEPARATION LAYER

Fig. 11 shows a cross-sectional view of the radiation sensor 510 of Fig. 9 along the plane 10 in case a separation layer 117 is sandwiched between any two adjacent absorption layers 110 of the radiation sensor 510. In an embodiment, with reference to Fig. 11, the multiple signal processing chips 122 for the radiation absorption layer 110.1b may be in recesses 118 of the separation layer 117 as shown.

In an embodiment, the separation layers 117 of the radiation sensor 510 may be configured to block gamma rays and X-rays.

SUPPORT SUBSTRATE FOR SIGNAL PROCESSING CHIPS

In an embodiment, with reference to Fig. 9, the 2 left signal processing chips 122 for the radiation absorption layer 110.1a may be physically attached to a first support substrate 122s such that the 2 left signal processing chips 122 are sandwiched between the first support substrate 122s and the radiation absorption layer 110.1a.

Similarly, in an embodiment, the 2 right signal processing chips 122 for the radiation absorption layer 110.1a may be physically attached to a second support substrate (not shown for simplicity) such that the 2 right signal processing chips 122 are sandwiched between the second support substrate and the radiation absorption layer 110.1a.

In an embodiment, the signal processing chips 122 for the other 11 radiation absorption layers 110 of the radiation sensor 510 may have similar features (i.e., support substrates for signal processing chips 122) .

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

A method, comprising:

receiving, with a first radiation sensor, a first photon from an object, the first radiation sensor comprising M sensing element groups,

wherein each sensing element group of the M sensing element groups comprises multiple sensing elements, and

wherein M is an integer greater than 1;

determining a first subset of the M sensing element groups based on electrical signals in the M sensing element groups of the first radiation sensor; and

determining a first estimated path of the first photon based on positions of the sensing element groups in the first subset.
The method of claim 1, wherein said determining the first subset comprises identifying sensing element groups of the M sensing element groups that have a photon presence signal.
The method of claim 2, wherein said identifying comprises:

determining a voltage of a dedicated electrode of each sensing element of the first radiation sensor; and

combining the voltages of the dedicated electrodes of the multiple sensing elements of each sensing element group of the M sensing element groups resulting in a group voltage for said each sensing element group,

wherein the photon presence signal in a sensing element group is an event of the group voltage of the sensing element group exceeding a pre-specified threshold voltage.
The method of claim 2,

wherein dedicated electrodes of the multiple sensing elements of each sensing element group of the M sensing element groups are electrically connected to a group node with metal lines, and

wherein the photon presence signal in a sensing element group is an event of a voltage of the group node of the sensing element group exceeding a pre-specified threshold voltage.
The method of claim 2, wherein said determining the first subset further comprises excluding sensing element groups from the first subset based on a temporal relationship among the photon presence signals in the sensing element groups in the first subset.
The method of claim 5, wherein the temporal relationship is a temporal order of the photon presence signals in the sensing element groups in the first subset.
The method of claim 1, wherein the first photon undergoes scattering inside the first radiation sensor.
The method of claim 1, wherein the first estimated path of the first photon comprises a portion outside the first radiation sensor.
The method of claim 1, wherein the sensing elements of the M sensing element groups are in multiple radiation absorption layers of the radiation sensor.
The method of claim 9, wherein a layer opaque to the first photon separates any two adjacent radiation absorption layers of the multiple radiation absorption layers.
The method of claim 1, wherein the first photon is a gamma ray photon or an X-ray photon.
The method of claim 1, wherein all the M sensing element groups have a same number of sensing elements.
The method of claim 1, further comprising:

receiving, with a second radiation sensor, a second photon from the object, the second radiation sensor comprising N sensing element groups,

wherein each sensing element group of the N sensing element groups comprises multiple sensing elements, and

wherein N is an integer greater than 1;

determining a second subset of the N sensing element groups based on electrical signals in sensing element groups of the second radiation sensor; and

determining a second estimated path of the second photon based on positions of the sensing element groups in the second subset.
The method of claim 13, further comprising determining a position of a photon origination point of the first and second photons based on the first estimated path and the second estimated path.
The method of claim 13, further comprising rotating the first radiation sensor and the second radiation sensor around the object while keeping the first radiation sensor and the second radiation sensor stationary with respect to each other.
The method of claim 1, further comprising:

receiving, with the first radiation sensor, a second photon from the object;

determining a second subset of the M sensing element groups based on electrical signals in sensing element groups of the first radiation sensor; and

determining a second estimated path of the second photon based on positions of the sensing element groups in the second subset.
The method of claim 16, further comprising determining a position of a photon origination point of the first and second photons based on the first estimated path and the second estimated path.
The method of claim 1, wherein said determining the first estimated path of the first photon comprises:

determining a straight line of best fit through the sensing element groups in the first subset resulting in the first estimated path.
The method of claim 1,

wherein the first radiation sensor comprises P signal processing chips and a stack of 2P radiation absorption layers, P being an integer greater than 1,

wherein each of the P signal processing chips is dedicated to processing electrical signals in two adjacent radiation absorption layers of the 2P radiation absorption layers, and

wherein at least one of the P signal processing chips is sandwiched between two radiation absorption layers of the 2P radiation absorption layers.
The method of claim 19, wherein the two radiation absorption layers are separated by another radiation absorption layer of the 2P radiation absorption layers.
The method of claim 19,

wherein a separation layer is sandwiched between any two adjacent radiation absorption layers of the 2P radiation absorption layers, and

wherein the separation layer is configured to block gamma rays and X-rays.
The method of claim 1,

wherein the first radiation sensor comprises (A) a stack of Q radiation absorption layers, and (B) multiple signal processing chips for each of the Q radiation absorption layers,

wherein the multiple signal processing chips for each radiation absorption layer of the Q radiation absorption layers and dedicated electrodes of all the sensing elements of said each radiation absorption layer are on a same side surface of said each radiation absorption layer, and

wherein no straight line (A) that is perpendicular to said same side surface of said each radiation absorption layer and (B) that intersects a signal processing chip for said each radiation absorption layer intersects any dedicated electrode of any sensing element of said each radiation absorption layer.
The method of claim 22,

wherein a plurality of signal processing chips of the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are physically attached to a support substrate, and

wherein the plurality of signal processing chips are sandwiched between the support substrate and the radiation absorption layer.
The method of claim 22, wherein the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are in recesses of an adjacent radiation absorption layer of the Q radiation absorption layers.
The method of claim 22,

wherein the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are in recesses of a separation layer, and

wherein the separation layer is configured to block gamma rays and X-rays.
A system, comprising a first radiation sensor configured to receive a first photon from an object,

wherein the first radiation sensor comprises M sensing element groups,

wherein each sensing element group of the M sensing element groups comprises multiple sensing elements,

wherein M is an integer greater than 1,

wherein the system is configured to determine a first subset of the M sensing element groups based on electrical signals in the M sensing element groups of the first radiation sensor, and

wherein the system is configured to determine a first estimated path of the first photon based on positions of the sensing element groups in the first subset.
The system of claim 26, further comprising a second radiation sensor configured to receive a second photon from the object,

wherein the second radiation sensor comprises N sensing element groups,

wherein each sensing element group of the N sensing element groups comprises multiple sensing elements,

wherein N is an integer greater than 1,

wherein the system is configured to determine a second subset of the N sensing element groups based on electrical signals in sensing element groups of the second radiation sensor, and

wherein the system is configured to determine a second estimated path of the second photon based on positions of the sensing element groups in the second subset.
The system of claim 27, wherein the system is configured to determine a position of a photon origination point of the first and second photons based on the first estimated path and the second estimated path.
The system of claim 26,

wherein the first radiation sensor comprises P signal processing chips and a stack of 2P radiation absorption layers, P being an integer greater than 1,

wherein each of the P signal processing chips is dedicated to processing electrical signals in two adjacent radiation absorption layers of the 2P radiation absorption layers, and

wherein at least one of the P signal processing chips is sandwiched between two radiation absorption layers of the 2P radiation absorption layers.
The system of claim 29, wherein the two radiation absorption layers are separated by another radiation absorption layer of the 2P radiation absorption layers.
The system of claim 29,

wherein a separation layer is sandwiched between any two adjacent radiation absorption layers of the 2P radiation absorption layers, and

wherein the separation layer is configured to block gamma rays and X-rays.
The system of claim 26,

wherein the first radiation sensor comprises (A) a stack of Q radiation absorption layers, and (B) multiple signal processing chips for each of the Q radiation absorption layers,

wherein the multiple signal processing chips for each radiation absorption layer of the Q radiation absorption layers and dedicated electrodes of all the sensing elements of said each radiation absorption layer are on a same side surface of said each radiation absorption layer, and

wherein no straight line (A) that is perpendicular to said same side surface of said each radiation absorption layer and (B) that intersects a signal processing chip for said each radiation absorption layer intersects any dedicated electrode of any sensing element of said each radiation absorption layer.
The system of claim 32,

wherein a plurality of signal processing chips of the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are physically attached to a support substrate, and

wherein the plurality of signal processing chips are sandwiched between the support substrate and the radiation absorption layer.
The system of claim 32, wherein the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are in recesses of an adjacent radiation absorption layer of the Q radiation absorption layers.
The system of claim 32,

wherein the multiple signal processing chips for a radiation absorption layer of the Q radiation absorption layers are in recesses of a separation layer, and

wherein the separation layer is configured to block gamma rays and X-rays.