WO2023077366A1

WO2023077366A1 - Imaging methods using radiation detectors in computer tomography

Info

Publication number: WO2023077366A1
Application number: PCT/CN2021/128743
Authority: WO
Inventors: Peiyan CAO; Yurun LIU
Original assignee: Shenzhen Xpectvision Technology Co., Ltd.
Priority date: 2021-11-04
Filing date: 2021-11-04
Publication date: 2023-05-11
Also published as: TW202319737A

Abstract

A imaging method, comprising: capturing first multiple 2D images of an object (1030, 1032) counting only incident photons with wavelengths shorter than or equal to a first wavelength (1210); reconstructing a first 3D image of the object (1030, 1032) from the first multiple 2D images (1220); capturing second multiple 2D images of the object (1030, 1032) counting only incident photons with wavelengths shorter than or equal to a second wavelength, wherein the second wavelength is shorter than the first wavelength (1230); reconstructing a second 3D image of the object (1030, 1032) from the second multiple 2D images (1240); and generating a third 3D image of the object (1030, 1032) from the first 3D image and the second 3D image (1250).

Description

IMAGING METHODS USING RADIATION DETECTORS IN COMPUTER TOMOGRAPHY

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 may be one that has interacted with an object. For example, the radiation measured by the radiation detector may be a radiation that has penetrated the object. The radiation 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: capturing first multiple 2D (2-dimensional) images of an object counting only incident photons with wavelengths shorter than or equal to a first wavelength; reconstructing a first 3D (3-dimensional) image of the object from the first multiple 2D images; capturing second multiple 2D images of the object counting only incident photons with wavelengths shorter than or equal to a second wavelength, wherein the second wavelength is shorter than the first wavelength; reconstructing a second 3D image of the object from the second multiple 2D images; and generating a third 3D image of the object from the first 3D image and the second 3D image.

In an aspect, the incident photons counted in said capturing the first multiple 2D images are X-ray photons, and the incident photons counted in said capturing the second multiple 2D images are X-ray photons.

In an aspect, an emission peak of a chemical element is between the first wavelength and the second wavelength.

In an aspect, there is no other emission peak of the chemical element between the first wavelength and the second wavelength.

In an aspect, the third 3D image is generated based on a differential between the first

3D image and the second 3D image.

In an aspect, the third 3D image is the differential between the first 3D image and the second 3D image.

In an aspect, said capturing the first multiple 2D images comprises: starting a time delay from a time at which an absolute value of a voltage of an electrode of a radiation absorption layer equals or exceeds an absolute value of a first threshold; activating a second circuit during the time delay; and if an absolute value of the voltage equals or exceeds an absolute value of a second threshold, increasing a count of photon incident on the radiation absorption layer by one, wherein if a photon with its wavelength equal to the first wavelength is incident on the radiation absorption layer, the incident photon would cause the absolute value of the voltage to be at most the absolute value of the second threshold.

In an aspect, said capturing the first multiple 2D images further comprises measuring the voltage upon expiration of the time delay.

In an aspect, said capturing the first multiple 2D images further comprises determining a photon energy based on a value of the voltage at expiration of the time delay.

In an aspect, a rate of change of the voltage is substantially zero at expiration of the time delay.

In an aspect, a rate of change of the voltage is substantially non-zero at expiration of the time delay.

In an aspect, said activating the second circuit is at a beginning or expiration of the time delay.

In an aspect, the second circuit is configured to compare the absolute value of the voltage to the absolute value of the second threshold.

In an aspect, said capturing the first multiple 2D images further comprises deactivating a first circuit at a beginning of or during the time delay.

In an aspect, the first circuit is configured to compare the absolute value of the voltage to the absolute value of the first threshold.

In an aspect, said capturing the first multiple 2D images further comprises deactivating the second circuit at an expiration of the time delay or at a time when the absolute value of the voltage equals or exceeds the absolute value of the second threshold.

In an aspect, said capturing the second multiple 2D images comprises: starting the time delay from a time at which the absolute value of the voltage equals or exceeds the absolute value of the first threshold; activating the second circuit during the time delay; and if the absolute value of the voltage equals or exceeds an absolute value of a third threshold, increasing a count of photon incident on the radiation absorption layer by one, wherein if a photon with its wavelength equal to the second wavelength is incident on the radiation absorption layer, the incident photon would cause the absolute value of the voltage to be at most the absolute value of the third threshold.

In an aspect, the second circuit is electrically connected to the electrode.

In an aspect, a semiconductor X-ray detector comprises the second circuit and the radiation absorption layer.

In an aspect, said capturing the first multiple 2D images comprises using the semiconductor X-ray detector to capture the first multiple 2D images, and said capturing the second multiple 2D images comprises using the semiconductor X-ray detector to capture the second multiple 2D images.

Brief Description of Figures

Fig. 1A schematically shows a semiconductor X-ray detector, according to an embodiment.

Fig. 1B shows a semiconductor X-ray detector 100, according to an embodiment.

Fig. 2 shows an exemplary top view of a portion of the detector in Fig. 1A, according to an embodiment.

Fig. 3A and Fig. 3B each show a component diagram of an electronic system of the detector in Fig. 1A or Fig. 1B, according to an embodiment.

Fig. 4 schematically shows a temporal change of the electric current flowing through an electrode (upper curve) of a diode or an electrical contact of a resistor of an X-ray absorption layer exposed to X-ray, the electric current caused by charge carriers generated by an X-ray photon incident on the X-ray absorption layer, and a corresponding temporal change of the voltage of the electrode (lower curve) , according to an embodiment.

Fig. 5 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by noise (e.g., dark current) , and a corresponding temporal change of the voltage of the electrode (lower curve) , in the electronic system operating in the way shown in Fig. 4, according to an embodiment.

Fig. 6 schematically shows a temporal change of the electric current flowing through an electrode (upper curve) of the X-ray absorption layer exposed to X-ray, the electric current caused by charge carriers generated by an X-ray photon incident on the X-ray absorption layer, and a corresponding temporal change of the voltage of the electrode (lower curve) , when the electronic system operates to detect incident X-ray photons at a higher rate, according to an embodiment.

Fig. 7 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by noise (e.g., dark current) , and a corresponding temporal change of the voltage of the electrode (lower curve) , in the electronic system operating in the way shown in Fig. 6, according to an embodiment.

Fig. 8 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by a series of X-ray photons incident on the X-ray absorption layer, and a corresponding temporal change of the voltage of the electrode, in the electronic system operating in the way shown in Fig. 6 with RST expires before t _e, according to an embodiment.

Fig. 9A shows a flow chart for a method suitable for detecting X-ray using a system such as the electronic system operating as shown in Fig. 4, according to an embodiment.

Fig. 9B shows a flow chart for a method suitable for detecting X-ray using a system such as the electronic system operating as shown in Fig. 6, according to an embodiment.

Fig. 10A and Fig. 10B show an imaging system in operation, according to an embodiment.

Fig. 11 shows a photon spectrum curve for photons used in the imaging system, according to an embodiment.

Fig. 12 is a flowchart generalizing the operation of the imaging system.

Detailed Description

X-RAY DETECTOR

Fig. 1A schematically shows a semiconductor X-ray detector 100, according to an embodiment. The semiconductor X-ray detector 100 may include an X-ray absorption layer 110 and an electronics layer 120 (e.g., an ASIC) for processing or analyzing electrical signals incident X-ray generates in the X-ray absorption layer 110. In an embodiment, the semiconductor X-ray detector 100 does not comprise a scintillator. The X-ray absorption layer 110 may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the X-ray energy of interest. The X-ray 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 the intrinsic region 112. The discrete portions 114 are 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 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 in Fig. 1A, 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. 1A, the X-ray absorption layer 110 has a plurality of diodes having the first doped region 111 as a shared electrode. The first doped region 111 may also have discrete portions.

Fig. 1B shows the semiconductor X-ray detector 100, according to an alternative embodiment. The semiconductor X-ray detector 100 may include an X-ray absorption layer 110 and an electronics layer 120 (e.g., an ASIC) for processing or analyzing electrical signals incident X-ray generates in the X-ray absorption layer 110. In an embodiment, the semiconductor X-ray detector 100 does not comprise a scintillator. The X-ray absorption layer 110 may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the X-ray energy of interest. The X-ray absorption layer 110 may not include a diode but includes a resistor.

When an X-ray photon hits the X-ray absorption layer 110 including diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. An X-ray photon may generate 10 to 100000 charge carriers. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The field may be an external electric field. The electrical contact 119B may include discrete portions each of which is in electrical contact with the discrete regions 114. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single X-ray photon are not substantially shared by two different discrete regions 114 ( “not substantially shared” here means less than 5%, less than 2%or less than 1%of these charge carriers flow to a different one of the discrete regions 114 than the rest of the charge carriers) . In an embodiment, the charge carriers generated by a single X-ray photon can be shared by two different discrete regions 114.

Fig. 2 shows an exemplary top view of a portion of the device 100 with a 4-by-4 array of discrete regions 114. Charge carriers generated by an X-ray photon incident around the footprint of one of these discrete regions 114 are not substantially shared with another of these discrete regions 114. The area around a discrete region 114 in which substantially all (more than 95%, more than 98%or more than 99%of) charge carriers generated by an X-ray photon incident therein flow to the discrete region 114 is called a pixel associated with that discrete region 114. Namely, less than 5%, less than 2%or less than 1%of these charge carriers flow beyond the pixel. By measuring the drift current flowing into each of the discrete regions 114, or the rate of change of the voltage of each of the discrete regions 114, the number of X-ray photons absorbed (which relates to the incident X-ray intensity) and/or the energies thereof in the pixels associated with the discrete regions 114 may be determined. Thus, the spatial distribution (e.g., an image) of incident X-ray intensity may be determined by individually measuring the drift current into each one of an array of discrete regions 114 or measuring the rate of change of the voltage of each one of an array of discrete regions 114. The pixels may be organized in any suitable array, such as, a square array, a triangular array and a honeycomb array. The pixels may have any suitable shape, such as, circular, triangular, square, rectangular, and hexangular. The pixels may be individually addressable.

When an X-ray photon hits the X-ray absorption layer 110 including a resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. An X-ray photon may generate 10 to 100000 charge carriers. The charge carriers may drift to the

electrical contacts

119A and 119B under an electric field. The field may be an external electric field. The electrical contact 119B includes discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single X-ray photon are not substantially shared by two different discrete portions of the electrical contact 119B ( “not substantially shared” here means less than 5%, less than 2%or less than 1%of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers) . In an embodiment, the charge carriers generated by a single X-ray photon can be shared by two different discrete portions of the electrical contact 119B. Charge carriers generated by an X-ray photon incident around the footprint of one of these discrete portions of the electrical contact 119B are not substantially shared with another of these discrete portions of the electrical contact 119B. The area around a discrete portion of the electrical contact 119B in which substantially all (more than 95%, more than 98%or more than 99%of) charge carriers generated by an X-ray photon incident therein flow to the discrete portion of the electrical contact 119B is called a pixel associated with the discrete portion of the electrical contact 119B. Namely, less than 5%, less than 2%or less than 1%of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact 119B. By measuring the drift current flowing into each of the discrete portion of the electrical contact 119B, or the rate of change of the voltage of each of the discrete portions of the electrical contact 119B, the number of X-ray photons absorbed (which relates to the incident X-ray intensity) and/or the energies thereof in the pixels associated with the discrete portions of the electrical contact 119B may be determined. Thus, the spatial distribution (e.g., an image) of incident X-ray intensity may be determined by individually measuring the drift current into each one of an array of discrete portions of the electrical contact 119B or measuring the rate of change of the voltage of each one of an array of discrete portions of the electrical contact 119B. The pixels may be organized in any suitable array, such as, a square array, a triangular array and a honeycomb array. The pixels may have any suitable shape, such as, circular, triangular, square, rectangular, and hexangular. The pixels may be individually addressable.

The electronics layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by X-ray photons incident on the X-ray 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 microprocessors, and memory. The electronic system 121 may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system 121 may include an amplifier dedicated to each pixel and a microprocessor shared among all the pixels. The electronic system 121 may be electrically connected to the pixels 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 X-ray absorption layer 110. Other bonding techniques are possible to connect the electronic system 121 to the pixels without using vias.

ELECTRONIC SYSTEM

Fig. 3A and Fig. 3B each show a component diagram of the electronic system 121, according to an embodiment. The electronic system 121 may include a first voltage comparator 301, a second voltage comparator 302, a counter 320, a switch 305, a voltmeter 306 and a controller 310.

The first voltage comparator 301 is configured to compare the voltage of an electrode of a diode 300 to a first threshold. The diode may be a diode formed by the first doped region 111, one of the discrete regions 114 of the second doped region 113, and the optional intrinsic region 112. Alternatively, the first voltage comparator 301 is configured to compare the voltage of an electrical contact (e.g., a discrete portion of electrical contact 119B) to a first threshold. The first voltage comparator 301 may be configured to monitor the voltage directly, or calculate the voltage by integrating an electric current flowing through the diode or electrical contact over a period of time. The first voltage comparator 301 may be controllably activated or deactivated by the controller 310. The first voltage comparator 301 may be a continuous comparator. Namely, the first voltage comparator 301 may be configured to be activated continuously, and monitor the voltage continuously. The first voltage comparator 301 configured as a continuous comparator reduces the chance that the system 121 misses signals generated by an incident X-ray photon. The first voltage comparator 301 configured as a continuous comparator is especially suitable when the incident X-ray intensity is relatively high. The first voltage comparator 301 may be a clocked comparator, which has the benefit of lower power consumption. The first voltage comparator 301 configured as a clocked comparator may cause the system 121 to miss signals generated by some incident X-ray photons. When the incident X-ray intensity is low, the chance of missing an incident X-ray photon is low because the time interval between two successive photons is relatively long. Therefore, the first voltage comparator 301 configured as a clocked comparator is especially suitable when the incident X-ray intensity is relatively low. The first threshold may be 5-10%, 10%-20%, 20-30%, 30-40%or 40-50%of the maximum voltage one incident X-ray photon may generate in the diode or the resistor. The maximum voltage may depend on the energy of the incident X-ray photon (i.e., the wavelength of the incident X-ray) , the material of the X-ray absorption layer 110, and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV, or 200 mV.

The second voltage comparator 302 is configured to compare the voltage to a second threshold. The second voltage comparator 302 may be configured to monitor the voltage directly, or calculate the voltage by integrating an electric current flowing through the diode or the electrical contact over a period of time. The second voltage comparator 302 may be a continuous comparator. The second voltage comparator 302 may be controllably activate or deactivated by the controller 310. When the second voltage comparator 302 is deactivated, the power consumption of the second voltage comparator 302 may be less than 1%, less than 5%, less than 10%or less than 20%of the power consumption when the second voltage comparator 302 is activated. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term “absolute value” or “modulus” |x| of a real number x is the non-negative value of x without regard to its sign. Namely, |x|= x if x >=0, and |x| = -x if x <0.

The second threshold may be 200%-300%of the first threshold. The second threshold may be at least 50%of the maximum voltage one incident X-ray photon may generate in the diode or resistor. For example, the second threshold may be 100 mV, 150 mV, 200 mV, 250 mV or 300 mV. The second voltage comparator 302 and the first voltage comparator 310 may be the same component. Namely, the system 121 may have one voltage comparator that can compare a voltage with two different thresholds at different times.

The first voltage comparator 301 or the second voltage comparator 302 may include one or more op-amps or any other suitable circuitry. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the system 121 to operate under a high flux of incident X-ray. However, having a high speed is often at the cost of power consumption.

The counter 320 is configured to register a number of X-ray photons reaching the diode or resistor. The counter 320 may be a software component (e.g., a number stored in a computer memory) or a hardware component (e.g., a 4017 IC and a 7490 IC) .

The controller 310 may be a hardware component such as a microcontroller and a microprocessor. The controller 310 is configured to start a time delay from a time at which the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold (e.g., the absolute value of the voltage increases from below the absolute value of the first threshold to a value equal to or above the absolute value of the first threshold) . The absolute value is used here because the voltage may be negative or positive, depending on whether the voltage of the cathode or the anode of the diode or which electrical contact is used. The controller 310 may be configured to keep deactivated the second voltage comparator 302, the counter 320 and any other circuits the operation of the first voltage comparator 301 does not require, before the time at which the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The time delay may expire before or after the voltage becomes stable, i.e., the rate of change of the voltage is substantially zero. The phase “the rate of change of the voltage is substantially zero” means that temporal change of the voltage is less than 0.1%/ns. The phase “the rate of change of the voltage is substantially non-zero” means that temporal change of the voltage is at least 0.1%/ns.

The controller 310 may be configured to activate the second voltage comparator during (including the beginning and the expiration) the time delay. In an embodiment, the controller 310 is configured to activate the second voltage comparator at the beginning of the time delay. The term “activate” means causing the component to enter an operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc. ) . The term “deactivate” means causing the component to enter a non-operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by cut off power, etc. ) . The operational state may have higher power consumption (e.g., 10 times higher, 100 times higher, 1000 times higher) than the non-operational state. The controller 310 itself may be deactivated until the output of the first voltage comparator 301 activates the controller 310 when the absolute value of the voltage equals or exceeds the absolute value of the first threshold.

The controller 310 may be configured to cause the number registered by the counter 320 to increase by one, if, during the time delay, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold.

The controller 310 may be configured to cause the voltmeter 306 to measure the voltage upon expiration of the time delay. The controller 310 may be configured to connect the electrode to an electrical ground, so as to reset the voltage and discharge any charge carriers accumulated on the electrode. In an embodiment, the electrode is connected to an electrical ground after the expiration of the time delay. In an embodiment, the electrode is connected to an electrical ground for a finite reset time period. The controller 310 may connect the electrode to the electrical ground by controlling the switch 305. The switch may be a transistor such as a field-effect transistor (FET) .

In an embodiment, the system 121 has no analog filter network (e.g., a RC network) . In an embodiment, the system 121 has no analog circuitry. The voltmeter 306 may feed the voltage it measures to the controller 310 as an analog or digital signal.

The system 121 may include a capacitor module 309 electrically connected to the electrode of the diode 300 or the electrical contact, wherein the capacitor module is configured to collect charge carriers from the electrode. The capacitor module can include a capacitor in the feedback path of an amplifier. The amplifier configured as such is called a capacitive transimpedance amplifier (CTIA) . CTIA has high dynamic range by keeping the amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. Charge carriers from the electrode accumulate on the capacitor over a period of time ( “integration period” ) (e.g., as shown in Fig. 4, between t ₀ to t ₁, or t ₁-t ₂) . After the integration period has expired, the capacitor voltage is sampled and then reset by a reset switch. The capacitor module can include a capacitor directly connected to the electrode.

ELECTRODE CURRENT AND VOLTAGE

Fig. 4 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by an X-ray photon incident on the diode or the resistor, and a corresponding temporal change of the voltage of the electrode (lower curve) . The voltage may be an integral of the electric current with respect to time. At time t ₀, the X-ray photon hits the diode or the resistor, charge carriers start being generated in the diode or the resistor, electric current starts to flow through the electrode of the diode or the resistor, and the absolute value of the voltage of the electrode or electrical contact starts to increase. At time t ₁, the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller 310 starts the time delay TD1 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD1. If the controller 310 is deactivated before t ₁, the controller 310 is activated at t ₁. During TD1, the controller 310 activates the second voltage comparator 302. The term “during” a time delay as used here means the beginning and the expiration (i.e., the end) and any time in between. For example, the controller 310 may activate the second voltage comparator 302 at the expiration of TD1. If during TD1, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold V2 at time t ₂, the controller 310 causes the number registered by the counter 320 to increase by one. At time t _e, all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. At time t _s, the time delay TD1 expires. In the example of Fig. 4, time t _s is after time t _e; namely TD1 expires after all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. The rate of change of the voltage is thus substantially zero at t _s. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD1 or at t ₂, or any time in between.

The controller 310 may be configured to cause the voltmeter 306 to measure the voltage upon expiration of the time delay TD1. In an embodiment, the controller 310 causes the voltmeter 306 to measure the voltage after the rate of change of the voltage becomes substantially zero after the expiration of the time delay TD1. The voltage at this moment is proportional to the amount of charge carriers generated by an X-ray photon, which relates to the energy of the X-ray photon. The controller 310 may be configured to determine the energy of the X-ray photon based on voltage the voltmeter 306 measures. One way to determine the energy is by binning the voltage. The counter 320 may have a sub-counter for each bin. When the controller 310 determines that the energy of the X-ray photon falls in a bin, the controller 310 may cause the number registered in the sub-counter for that bin to increase by one. Therefore, the system 121 may be able to detect an X-ray image and may be able to resolve X-ray photon energies of each X-ray photon.

After TD1 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode to flow to the ground and reset the voltage. After RST, the system 121 is ready to detect another incident X-ray photon. Implicitly, the rate of incident X-ray photons the system 121 can handle in the example of Fig. 4 is limited by 1/ (TD1+RST) . If the first voltage comparator 301 has been deactivated, the controller 310 can activate it at any time before RST expires. If the controller 310 has been deactivated, it may be activated before RST expires.

Fig. 5 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by noise (e.g., dark current, background radiation, scattered X-rays, fluorescent X-rays, shared charges from adjacent pixels) , and a corresponding temporal change of the voltage of the electrode (lower curve) , in the system 121 operating in the way shown in Fig. 4. At time t ₀, the noise begins. If the noise is not large enough to cause the absolute value of the voltage to exceed the absolute value of V1, the controller 310 does not activate the second voltage comparator 302. If the noise is large enough to cause the absolute value of the voltage to exceed the absolute value of V1 at time t ₁ as determined by the first voltage comparator 301, the controller 310 starts the time delay TD1 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD1. During TD1 (e.g., at expiration of TD1) , the controller 310 activates the second voltage comparator 302. The noise is very unlikely large enough to cause the absolute value of the voltage to exceed the absolute value of V2 during TD1. Therefore, the controller 310 does not cause the number registered by the counter 320 to increase. At time t _e, the noise ends. At time t _s, the time delay TD1 expires. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD1. The controller 310 may be configured not to cause the voltmeter 306 to measure the voltage if the absolute value of the voltage does not exceed the absolute value of V2 during TD1. After TD1 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode as a result of the noise to flow to the ground and reset the voltage. Therefore, the system 121 may be very effective in noise rejection.

Fig. 6 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by an X-ray photon incident on the diode or the resistor, and a corresponding temporal change of the voltage of the electrode (lower curve) , when the system 121 operates to detect incident X-ray photons at a rate higher than 1/ (TD1+RST) . The voltage may be an integral of the electric current with respect to time. At time t ₀, the X-ray photon hits the diode or the resistor, charge carriers start being generated in the diode or the resistor, electric current starts to flow through the electrode of the diode or the electrical contact of resistor, and the absolute value of the voltage of the electrode or the electrical contact starts to increase. At time t ₁, the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller 310 starts a time delay TD2 shorter than TD1, and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD2. If the controller 310 is deactivated before t ₁, the controller 310 is activated at t ₁. During TD2 (e.g., at expiration of TD2) , the controller 310 activates the second voltage comparator 302. If during TD2, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold V2 at time t ₂, the controller 310 causes the number registered by the counter 320 to increase by one. At time t _e, all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. At time t _h, the time delay TD2 expires. In the example of Fig. 6, time t _h is before time t _e; namely TD2 expires before all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. The rate of change of the voltage is thus substantially non-zero at t _h. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD2 or at t ₂, or any time in between.

The controller 310 may be configured to extrapolate the voltage at t _e from the voltage as a function of time during TD2 and use the extrapolated voltage to determine the energy of the X-ray photon.

After TD2 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode to flow to the ground and reset the voltage. In an embodiment, RST expires before t _e. The rate of change of the voltage after RST may be substantially non-zero because all charge carriers generated by the X-ray photon have not drifted out of the X-ray absorption layer 110 upon expiration of RST before t _e. The rate of change of the voltage becomes substantially zero after t _e and the voltage stabilized to a residue voltage VR after t _e. In an embodiment, RST expires at or after t _e, and the rate of change of the voltage after RST may be substantially zero because all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110 at t _e. After RST, the system 121 is ready to detect another incident X-ray photon. If the first voltage comparator 301 has been deactivated, the controller 310 can activate it at any time before RST expires. If the controller 310 has been deactivated, it may be activated before RST expires.

Fig. 7 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by noise (e.g., dark current, background radiation, scattered X-rays, fluorescent X-rays, shared charges from adjacent pixels) , and a corresponding temporal change of the voltage of the electrode (lower curve) , in the system 121 operating in the way shown in Fig. 6. At time t ₀, the noise begins. If the noise is not large enough to cause the absolute value of the voltage to exceed the absolute value of V1, the controller 310 does not activate the second voltage comparator 302. If the noise is large enough to cause the absolute value of the voltage to exceed the absolute value of V1 at time t ₁ as determined by the first voltage comparator 301, the controller 310 starts the time delay TD2 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD2. During TD2 (e.g., at expiration of TD2) , the controller 310 activates the second voltage comparator 302. The noise is very unlikely large enough to cause the absolute value of the voltage to exceed the absolute value of V2 during TD2. Therefore, the controller 310 does not cause the number registered by the counter 320 to increase. At time t _e, the noise ends. At time t _h, the time delay TD2 expires. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD2. After TD2 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode as a result of the noise to flow to the ground and reset the voltage. Therefore, the system 121 may be very effective in noise rejection.

Fig. 8 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by a series of X-ray photons incident on the diode or the resistor, and a corresponding temporal change of the voltage of the electrode (lower curve) , in the system 121 operating in the way shown in Fig. 6 with RST expires before t _e. The voltage curve caused by charge carriers generated by each incident X-ray photon is offset by the residue voltage before that photon. The absolute value of the residue voltage successively increases with each incident photon. When the absolute value of the residue voltage exceeds V1 (see the dotted rectangle in Fig. 8) , the controller starts the time delay TD2 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD2. If no other X-ray photon incidence on the diode or the resistor during TD2, the controller connects the electrode to the electrical ground during the reset time period RST at the end of TD2, thereby resetting the residue voltage. The residue voltage thus does not cause an increase of the number registered by the counter 320.

OPERATION FLOWCHARTS

Fig. 9A shows a flow chart for a method suitable for detecting X-ray using a system such as the system 121 operating as shown in Fig. 4. In step 901, compare, e.g., using the first voltage comparator 301, avoltage of an electrode of a diode or an electrical contact of a resistor exposed to X-ray, to the first threshold. In step 902, determine, e.g., with the controller 310, whether the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1. If the absolute value of the voltage does not equal or exceed the absolute value of the first threshold, the method goes back to step 901. If the absolute value of the voltage equals or exceeds the absolute value of the first threshold, continue to step 903. In step 903, start, e.g., using the controller 310, the time delay TD1. In step 904, activate, e.g., using the controller 310, a circuit (e.g., the second voltage comparator 302 or the counter 320) during the time delay TD1 (e.g., at the expiration of TD1) . In step 905, compare, e.g., using the second voltage comparator 302, the voltage to the second threshold V2. In step 906, determine, e.g., using the controller 310, whether the absolute value of the voltage equals or exceeds the absolute value of the second threshold V2. If the absolute value of the voltage does not equal or exceed the absolute value of the second threshold, the method goes to step 910. If the absolute value of the voltage equals or exceeds the absolute value of the second threshold, continue to step 907. In step 907, cause, e.g., using the controller 310, the number registered in the counter 320 to increase by one. In optional step 908, measure, e.g., using the voltmeter 306, the voltage upon expiration of the time delay TD1. In optional step 909, determine, e.g., using the controller 310, the X-ray photon energy based the voltage measured in step 908. There may be a counter for each of the energy bins. After measuring the X-ray photon energy, the counter for the bin to which the photon energy belongs can be increased by one. The method goes to step 910 after step 909. In step 910, reset the voltage to an electrical ground, e.g., by connecting the electrode of the diode or an electrical contact of a resistor to an electrical ground.

Steps

908 and 909 may be omitted, for example, when neighboring pixels share a large portion (e.g., >30%) of charge carriers generated from a single photon.

Fig. 9B shows a flow chart for a method suitable for detecting X-ray using the system such as the system 121 operating as shown in Fig. 6. In step 1001, compare, e.g., using the first voltage comparator 301, a voltage of an electrode of a diode or an electrical contact of a resistor exposed to X-ray, to the first threshold. In step 1002, determine, e.g., with the controller 310, whether the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1. If the absolute value of the voltage does not equal or exceed the absolute value of the first threshold, the method goes back to step 1001. If the absolute value of the voltage equals or exceeds the absolute value of the first threshold, continue to step 1003. In step 1003, start, e.g., using the controller 310, the time delay TD2. In step 1004, activate, e.g., using the controller 310, a circuit (e.g., the second voltage comparator 302 or the counter 320) during the time delay TD2 (e.g., at the expiration of TD2) . In step 1005, compare, e.g., using the second voltage comparator 302, the voltage to the second threshold. In step 1006, determine, e.g., using the controller 310, whether the absolute value of the voltage equals or exceeds the absolute value of the second threshold V2. If the absolute value of the voltage does not equal or exceed the absolute value of the second threshold, the method goes to step 1010. If the absolute value of the voltage equals or exceeds the absolute value of the second threshold, continue to step 1007. In step 1007, cause, e.g., using the controller 310, the number registered in the counter 320 to increase by one. The method goes to step 1010 after step 1007. In step 1010, reset the voltage to an electrical ground, e.g., by connecting the electrode of the diode or an electrical contact of a resistor to an electrical ground.

The semiconductor X-ray detector 100 may be used for phase-contrast X-ray imaging (PCI) (also known as phase-sensitive X-ray imaging) . PCI encompasses techniques that form an image of an object at least partially using the phase shift (including the spatial distribution of the phase shift) of an X-ray beam caused by that object. One way to obtain the phase shift is transforming the phase into variations in intensity.

PCI can be combined with tomographic techniques to obtain the 3D-distribution of the real part of the refractive index of the object. PCI is more sensitive to density variations in the object than conventional intensity-based X-ray imaging (e.g., radiography) . PCI is especially useful for imaging soft tissues.

IMAGING SYSTEM

Fig. 10A shows a perspective view of an imaging system 1000, according to an embodiment. In an embodiment, the imaging system 1000 may include a radiation source 1015, a mask 1020, and the semiconductor X-ray detector 100. The mask 1020 may include a mask window 1022.

In an embodiment, an object 1030+1032 may be positioned between the mask 1020 and the semiconductor X-ray detector 100. For example, the object 1030+1032 may include a carton box 1030 and a silver spoon 1032 inside the carton box 1030.

In an embodiment, the radiation source 1015 may be configured to generate radiation (e.g., X-ray) toward the mask 1020. The portion of the radiation from the radiation source 1015 incident on the mask window 1022 of the mask 1020 may be allowed to pass through the mask 1020 (for example, the mask window 1022 may be transparent or not opaque) , while the portion of the radiation from the radiation source 1015 incident on other parts of the mask 1020 may be blocked. As a result, after passing through the mask window 1022 of the mask 1020, the radiation from the radiation source 1015 incident on the mask 1020 becomes a radiation beam represented by an arrow 1011 (hence hereafter this radiation beam may be referred to as the radiation beam 1011) .

In an embodiment, the mask window 1022 of the mask 1020 may have a rectangular shape as shown in Fig. 10A. As a result, the radiation beam 1011 has the shape of a truncated pyramid as shown in Fig. 10A. In an embodiment, the radiation source 1015, the mask 1020, and the semiconductor X-ray detector 100 may be in a first system arrangement as shown in Fig. 10A.

FIRST 2D (2-DIMENSIONAL) IMAGE CAPTURE

In an embodiment, while the imaging system 1000 is in the first system arrangement as shown in Fig. 10A, the semiconductor X-ray detector 100 may capture a first 2D image (not shown) of the object 1030+1032. Specifically, in an embodiment, radiation of the radiation beam 1011 after interacting with and passing through the object 1030+1032 may be incident on the semiconductor X-ray detector 100. Using this incident radiation of the radiation beam 1011, the semiconductor X-ray detector 100 may capture the first 2D image of the object 1030+1032.

SECOND 2D IMAGE CAPTURE

In an embodiment, after the semiconductor X-ray detector 100 captures the first 2D image of the object 1030+1032, the imaging system 1000 may be rotated around the object 1030+1032 to a second system arrangement as shown in Fig. 10B.

In an embodiment, while the imaging system 1000 is in the second system arrangement as shown in Fig. 10B, the semiconductor X-ray detector 100 may capture a second 2D image (not shown) of the object 1030+1032. Specifically, in an embodiment, radiation of radiation beam 1012 after interacting with and passing through the object 1030+1032 may be incident on the semiconductor X-ray detector 100. Using this incident radiation of the radiation beam 1012, the semiconductor X-ray detector 100 may capture the second 2D image of the object 1030+1032.

In an embodiment, the radiation beam 1012 may be generated in a manner similar to the manner in which the radiation beam 1011 (Fig. 10A) is generated.

FIRST 3D (3-DIMENSIONAL) IMAGE RECONSTRUCTION

In an embodiment, after the semiconductor X-ray detector 100 captures the first and second 2D images of the object 1030+1032 as described above, the semiconductor X-ray detector 100 may reconstruct a first 3D image of the object 1030+1032 from the first and second 2D images of the object 1030+1032.

SECOND 3D IMAGE RECONSTRUCTION

In an embodiment, a second 3D image of the object 1030+1032 may be obtained in a manner similar to the manner in which the first 3D image is obtained. Specifically, in an embodiment, the semiconductor X-ray detector 100 may capture a third 2D image and a fourth 2D image (not shown) of the object 1030+1032 in a manner similar to the manner in which the semiconductor X-ray detector 100 captures the first 2D image and the second 2D image, respectively. Next, in an embodiment, after the semiconductor X-ray detector 100 captures the third and fourth 2D images, the semiconductor X-ray detector 100 may reconstruct the second 3D image from the third and fourth 2D images.

PHOTON SPECTRUM CURVE

Fig. 11 shows a photon spectrum curve 1100 for photons propagating from the silver spoon 1032 (Fig. 10A and Fig. 10B) toward the semiconductor X-ray detector 100. With reference to Fig. 10A –Fig. 11, the photon spectrum curve 1100 is a combination of some emission peaks and a regular curve.

The emission peaks result from characteristic photons of chemical element silver. As a result, the emission peaks are at the wavelengths of these silver characteristic photons. For example, the emission peak K _α is at the wavelength (0.45 nm) of a photon generated by the transition of an electron from level L (n=2) down to level K (n=1) in the silver atom. For another example, the emission peak L _β is at the wavelength (0.60 nm) of a photon generated by the transition of an electron from level N (n=4) down to level L (n=2) in the silver atom.

The regular curve of the photon spectrum curve 1100 results from the photons from the silver spoon 1032 other than the silver characteristic photons described above. The photons corresponding to the regular curve may include inter alia (A) the photons of the radiation source 1015 that pass through the silver spoon 1032, and (B) Bremsstrahlung photons that emit from the silver spoon 1032 due to the acceleration of photons that interact with atoms of the silver spoon 1032.

FIRST SELECTIVE PHOTON COUNTING SCHEME

In an embodiment, with reference to Fig. 10A –Fig. 11, while the semiconductor X-ray detector 100 captures the first and second 2D images of the object 1030+1032, the semiconductor X-ray detector 100 may be configured to count only incident photons with wavelengths shorter than or equal to a first wavelength (i.e., not count incident photons with wavelengths longer than the first wavelength) . This counting scheme can be called the first selective photon counting scheme.

In an embodiment, the first selective photon counting scheme may be implemented as follow. Assume that a photon with its wavelength equal to the first wavelength is incident on the radiation absorption layer 110 of the semiconductor X-ray detector 100 and that the incident photon causes the absolute value of the voltage of the electrode of the diode 300 (Fig. 3A &Fig. 3B) of the radiation absorption layer 110 to be at most 2V. Then, the second threshold may be set to 2V (i.e., the second voltage comparator 302 is configured to trigger a photon count increment when the absolute value of the voltage of the electrode equals or exceeds 2V) .

As a result, while the semiconductor X-ray detector 100 captures the first and second 2D images of the object 1030+1032, an incident photon with its wavelength shorter than or equal to the first wavelength would cause the absolute value of the voltage to equal or exceed the absolute value of the second threshold (2V) thereby causing the second voltage comparator 302 to trigger a photon count increment (hence the first selective photon counting scheme is implemented) .

SECOND SELECTIVE PHOTON COUNTING SCHEME

In an embodiment, with reference to Fig. 10A –Fig. 11, while the semiconductor X-ray detector 100 captures the third and fourth 2D images of the object 1030+1032, the semiconductor X-ray detector 100 may be configured to count only incident photons with wavelengths shorter than or equal to a second wavelength (i.e., not count incident photons with wavelengths longer than the second wavelength) . This counting scheme can be called the second selective photon counting scheme.

In an embodiment, the second selective photon counting scheme may be implemented as follow. Assume that a photon with its wavelength equal to the second wavelength is incident on the radiation absorption layer 110 of the semiconductor X-ray detector 100 and that the incident photon causes the absolute value of the voltage of the electrode of the diode 300 (Fig. 3A &Fig. 3B) of the radiation absorption layer 110 to be at most 3V. Then, the second threshold may be set to 3V (i.e., the second voltage comparator 302 is configured to trigger a photon count increment when the absolute value of the voltage of the electrode equals or exceeds 3V) .

To avoid confusion, hereafter, the value of 3V (of V2) is referred to as the third threshold, whereas the value of 2V (of V2) is referred to as the second threshold (meaning the second threshold and the third threshold are values or constants, not variables) .

As a result, while the semiconductor X-ray detector 100 captures the third and fourth 2D images of the object 1030+1032, an incident photon with its wavelength shorter than or equal to the second wavelength would cause the absolute value of the voltage to equal or exceed the absolute value of the third threshold (3V) thereby causing the second voltage comparator 302 to trigger a photon count increment (hence the second selective photon counting scheme is implemented) .

EMISSION PEAK UTILIZATION

In an embodiment, the first wavelength may be longer than the second wavelength, and the emission peak K _α may be between the first wavelength and the second wavelength. For example, with the emission peak K _α being at 0.45 nm, the first wavelength and the second wavelength can be chosen to be 0.5 nm and 0.4 nm, respectively so that the emission peak K _α (λ=0.45 nm) is between the first and second wavelengths as shown in Fig. 11.

In an embodiment, only one emission peak of silver (e.g., the emission peak K _α) is between the first and second wavelengths (i.e., the other emission peaks of silver are not between the first and second wavelengths) . For example, with reference to Fig. 11, only the emission peak K _α (λ=0.45 nm) is between the first wavelength (λ=0.5 nm) and the second wavelength (λ=0.4 nm) whereas the other emission peaks of silver (e.g., K _β, L _α, L _β , etc. ) are not between the first and second wavelengths.

DIFFERENTIAL OF TWO 3D IMAGES

In an embodiment, after the first and second 3D images of the object 1030+1032 are reconstructed as described above, a third 3D image of the object 1030+1032 may be generated from the first and second 3D images. In an embodiment, the third 3D image may be generated based on the differential between the first 3D image and the second 3D image. In an embodiment, the third 3D image of the object 1030+1032 may be generated by the semiconductor X-ray detector 100.

In an embodiment, the third 3D image may be the differential between the first 3D image and the second 3D image. In other words, each picture element of the third 3D image is the difference between (A) the corresponding picture element of the first 3D image and (B) the corresponding picture element of the second 3D image. For example, assume a picture element of the first 3D image has a value of 55, and the corresponding picture element of the second 3D image has a value of 46. Then, the corresponding picture element of the third 3D image has a value of 55 –46 = 9.

With (A) the semiconductor X-ray detector 100 being configured to count only incident photons with wavelengths shorter than or equal to the first wavelength while capturing the first and second 2D images, (B) the semiconductor X-ray detector 100 being configured to count only incident photons with wavelengths shorter than or equal to the second wavelength while capturing the third and fourth 2D images, and (C) an emission peak of silver (K _α) being between the first and second wavelengths, the value of each picture element of the third 3D image indicates the quantity of silver at the corresponding location in the object 1030+1032. In other words, the third 3D image shows only the silver spoon 1032.

In general, with reference to Fig. 11, any emission peak of silver (e.g., K _β, L _α, etc. ) may be chosen, and then the first and second wavelengths can be chosen such that the chosen emission peak is between the first and second wavelengths. However, in the embodiments described above, the emission peak K _α is chosen because this emission peak is the highest emission peak counting from the regular curve.

FLOWCHART FOR GENERALIZATION

Fig. 12 is a flowchart 1200 generalizing the operation of the imaging system 1000 of Fig. 10A and Fig. 10B. Specifically, with reference to Fig. 10A –Fig. 12, in step 1210, first multiple 2D images of an object may be captured counting only incident photons with wavelengths shorter than or equal to a first wavelength. For example, in the embodiments described above, the first and second 2D images of the object 1030+1032 are captured wherein only incident photons with wavelengths shorter than or equal to the first wavelength (e.g., 0.5 nm) are counted.

In step 1220, a first 3D image of the object may be reconstructed from the first multiple 2D images. For example, in the embodiments described above, the first 3D image of the object 1030+1032 is reconstructed from the first and second 2D images as described above.

In step 1230, second multiple 2D images of the object may be captured counting only incident photons with wavelengths shorter than or equal to a second wavelength, wherein the second wavelength is shorter than the first wavelength. For example, in the embodiments described above, the third and fourth 2D images of the object 1030+1032 are captured wherein only incident photons with wavelengths shorter than or equal to the second wavelength (e.g., 0.4 nm) are counted, and wherein the second wavelength (0.4 nm) is shorter than the first wavelength (0.5 nm) .

In step 1240, a second 3D image of the object may be reconstructed from the second multiple 2D images. For example, in the embodiments described above, the second 3D image of the object 1030+1032 is reconstructed from the third and fourth 2D images as described above.

In step 1250, a third 3D image of the object may be generated from the first 3D image and the second 3D image. For example, in the embodiments described above, the third 3D image of the object 1030+1032 is generated from the first 3D image and the second 3D image as described above.

ALTERNATIVE EMBODIMENTS

In the embodiments described above, the semiconductor X-ray detector 100 captures all the 2D images. In general, the 2D images may be captured by different semiconductor X-ray detectors 100.

In the embodiments described above, the semiconductor X-ray detector 100 reconstructs and generates the 3D images. In general, the 3D images may be reconstructed and generated by different semiconductor X-ray detectors 100.

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:

capturing first multiple 2D (2-dimensional) images of an object counting only incident photons with wavelengths shorter than or equal to a first wavelength;

reconstructing a first 3D (3-dimensional) image of the object from the first multiple 2D images;

capturing second multiple 2D images of the object counting only incident photons with wavelengths shorter than or equal to a second wavelength, wherein the second wavelength is shorter than the first wavelength;

reconstructing a second 3D image of the object from the second multiple 2D images; and

generating a third 3D image of the object from the first 3D image and the second 3D image.
The method of claim 1,

wherein the incident photons counted in said capturing the first multiple 2D images are X-ray photons, and

wherein the incident photons counted in said capturing the second multiple 2D images are X-ray photons.
The method of claim 1, wherein an emission peak of a chemical element is between the first wavelength and the second wavelength.
The method of claim 3, wherein there is no other emission peak of the chemical element between the first wavelength and the second wavelength.
The method of claim 1, wherein the third 3D image is generated based on a differential between the first 3D image and the second 3D image.
The method of claim 5, wherein the third 3D image is the differential between the first 3D image and the second 3D image.
The method of claim 1, wherein said capturing the first multiple 2D images comprises:

starting a time delay from a time at which an absolute value of a voltage of an electrode of a radiation absorption layer equals or exceeds an absolute value of a first threshold;

activating a second circuit during the time delay; and

if an absolute value of the voltage equals or exceeds an absolute value of a second threshold, increasing a count of photon incident on the radiation absorption layer by one,

wherein if a photon with its wavelength equal to the first wavelength is incident on the radiation absorption layer, the incident photon would cause the absolute value of the voltage to be at most the absolute value of the second threshold.
The method of claim 7, wherein said capturing the first multiple 2D images further comprises measuring the voltage upon expiration of the time delay.
The method of claim 7, wherein said capturing the first multiple 2D images further comprises determining a photon energy based on a value of the voltage at expiration of the time delay.
The method of claim 7, wherein a rate of change of the voltage is substantially zero at expiration of the time delay.
The method of claim 7, wherein a rate of change of the voltage is substantially non-zero at expiration of the time delay.
The method of claim 7, wherein said activating the second circuit is at a beginning or expiration of the time delay.
The method of claim 7, wherein the second circuit is configured to compare the absolute value of the voltage to the absolute value of the second threshold.
The method of claim 7, wherein said capturing the first multiple 2D images further comprises deactivating a first circuit at a beginning of or during the time delay.
The method of claim 14, wherein the first circuit is configured to compare the absolute value of the voltage to the absolute value of the first threshold.
The method of claim 7, wherein said capturing the first multiple 2D images further comprises deactivating the second circuit at an expiration of the time delay or at a time when the absolute value of the voltage equals or exceeds the absolute value of the second threshold.
The method of claim 7, wherein said capturing the second multiple 2D images comprises:

starting the time delay from a time at which the absolute value of the voltage equals or exceeds the absolute value of the first threshold;

activating the second circuit during the time delay; and

if the absolute value of the voltage equals or exceeds an absolute value of a third threshold, increasing a count of photon incident on the radiation absorption layer by one,

wherein if a photon with its wavelength equal to the second wavelength is incident on the radiation absorption layer, the incident photon would cause the absolute value of the voltage to be at most the absolute value of the third threshold.
The method of claim 17, wherein the second circuit is electrically connected to the electrode.
The method of claim 17, wherein a semiconductor X-ray detector comprises the second circuit and the radiation absorption layer.
The method of claim 19,

wherein said capturing the first multiple 2D images comprises using the semiconductor X-ray detector to capture the first multiple 2D images, and

wherein said capturing the second multiple 2D images comprises using the semiconductor X-ray detector to capture the second multiple 2D images.