Photon Counting Detector System

Abstract

The photon counting detector system of the present invention collects the counts and cumulative threshold-crossing times of each energy level interval through a dedicated photon counting chip of the photon counting detector. When acquiring images under low-dose-rate X-ray conditions, it can count both the number of photons in each energy interval and the total energy of photons in each energy interval, providing richer energy information for energy spectrum images. When acquiring images under high-dose-rate X-ray conditions, it can determine the severity of photon stacking and calculate the average number of photons in each energy level based on the threshold-crossing time, thereby avoiding the impact of counter paralysis caused by photon stacking on energy spectrum characteristics. It can also significantly suppress and correct the counting nonlinearity caused by photon stacking, thereby solving the problem of energy spectrum distortion of the photon counting detector.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging equipment, and in particular to a photon counting detector system. Background Art

[0002] Photon counting detectors are a new type of energy spectrum image acquisition device and a core component of medical imaging equipment such as X-ray CT, DR, and digital subtraction angiography. A dedicated photon counting chip is the core processing unit of a photon counting detector. X-ray photons incident on the detector excite electron-hole pairs in the detector's semiconductor crystal material, generating charge pulses. The dedicated photon counting detector chip identifies the pulse energy and counts the number of photons in each energy range.

[0003] Conventional photon counting detectors are affected by the photon stacking effect, resulting in a nonlinear relationship between the output count and the number of incident photons. As the X-ray dose rate increases, the deviation in counts caused by stacking becomes more significant. The energy spectrum distortion caused by photon stacking degrades the quality of spectral images.

[0004] To address the photon stacking problem, the currently published mainstream literature and patents adopt the following methods:

[0005] 1. Through a priori testing, the counts under low-dose-rate conditions are pre-measured under pre-set X-ray tube voltage, tube current, and filtration conditions. At this low-dose-rate condition, the probability of photon stacking is low, and the detector output count can be considered equal to the number of incident photons. The tube current is gradually increased, while other conditions are fixed. The output counts under each tube current condition are recorded. The number of incident photons is proportional to the tube current, and a mapping relationship (incident photons-output counts) can be established based on this relationship. In actual detector use, the counts are corrected using a lookup table based on this mapping relationship. This method has the advantage of enabling nonlinear correction of counts without requiring additional circuitry. However, its disadvantage is that it establishes this mapping relationship based on test data without an attenuating object between the X-ray source and detector (or with a specific phantom acting as an attenuating object). When X-rays are attenuated by human tissue or any unspecified object, the mapping relationship deviates significantly from the results obtained under the a priori test conditions, resulting in low energy spectrum resolution.

[0006] 2. Presmatic Sensor AB's patent US20220082710A1 discloses a method that uses a counter and timer to simultaneously calculate the count and TTOT (Total Time Over Threshold) information, and then uses the TTOT information to correct the count. However, this solution has the disadvantage that the analog front-end output pulse is quasi-Gaussian, and the calculated threshold-crossing time and pulse energy have only a positive correlation, not a linear relationship.

[0007] 3. The dedicated chip's comparator is designed as a "non-paralyzed model." This means that if an analog pulse continuously exceeds the threshold for a period of time without falling below it, the comparator detects a buildup and quickly resets, generating an output digital pulse again. This non-paralyzed model offers some anti-buildup protection, improving the detector's count rate. However, its constant reset time prevents flexible optimization for different thresholds and crystal charge gains. Consequently, the counts in this model deviate from the actual photon energy distribution. Summary of the Invention

[0008] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a photon counting detector system for solving the above technical problems in the prior art.

[0009] To achieve the above-mentioned and other related objectives, the present invention provides a photon counting detector system, comprising: a photon counting detector including a conversion crystal for exciting electron-hole pairs in response to incident X-ray photons under conditions of image acquisition at a set X-ray dose rate; a dedicated photon counting chip having a pixel array structure, comprising: a plurality of arranged pixel structures for processing voltage pulse signals obtained by converting electron-hole pairs excited by the conversion crystal corresponding to a current pixel in the form of pixel charge signals to obtain quasi-triangular wave analog voltage pulse signals, and counting and outputting the number of digital pulse counts and accumulated threshold-crossing times in multiple energy intervals based on the quasi-triangular wave analog voltage pulse signals; and a photon number calculation module connected to the photon counting detector for calculating, when the X-ray dose rate is high, an average number of photons in each energy interval for each pixel based on the accumulated threshold-crossing times output by each pixel structure; and, when the X-ray dose rate is low, calculating the number of photons and the total photon energy in each energy interval for each pixel based on the number of digital pulses in each energy interval output by each pixel structure and the accumulated threshold-crossing times.

[0010] In one embodiment of the present invention, each pixel structure includes: a charge amplifier, which is used to convert the electron-hole pairs excited by the capture crystal of the detector corresponding to the current pixel collected in the form of pixel charge signals into a voltage pulse signal; a shaper, connected to the charge amplifier, which is used to process the voltage pulse signal and output a quasi-triangular wave analog voltage pulse signal; and energy level output modules corresponding to one or more different energy level energy intervals, which are used to count the number of digital pulses in each energy interval and the accumulated threshold-crossing time and output them.

[0011] In one embodiment of the present invention, each energy level output module includes: a comparator corresponding to the current energy level interval, which is used to output a high level when the voltage value of the quasi-triangular wave analog voltage pulse signal is greater than the energy level voltage threshold corresponding to the current energy interval; a counter, connected to the comparator, which is used to count and output the number of digital pulses when the comparator outputs a high level; and a timer, connected to the comparator, which is used to count and output the accumulated threshold crossing time of the analog triangular wave when the comparator outputs a high level.

[0012] In one embodiment of the present invention, the timer uses an external high-speed sampling clock as the internal timing main frequency.

[0013] In one embodiment of the present invention, the unit of the accumulated threshold-crossing time is an external high-speed sampling clock cycle, and the external high-speed sampling clock cycle is set by an external crystal oscillator.

[0014] In one embodiment of the present invention, when the X-ray dose rate is a low X-ray dose rate, the quasi-triangular wave analog voltage pulse signal output by the shaper is a similar triangle.

[0015] In one embodiment of the present invention, when the X-ray dose rate is a high X-ray dose rate, the method for calculating the average number of photons in each energy interval of each pixel based on the number of digital pulse counts in each energy interval output by each pixel structure and the accumulated threshold-crossing time includes: when the X-ray dose rate is a high X-ray dose rate, the average pulse width of the photon pulse in each energy interval corresponding to each pixel obtained by the quasi-triangular wave analog voltage pulse signal obtained by each pixel structure and the accumulated threshold-crossing time in each energy interval of each pixel are calculated to obtain the average number of photons in each energy interval of each pixel.

[0016] In one embodiment of the present invention, when the X-ray dose rate is a low X-ray dose rate, the method for calculating the number of photons in each energy interval of each pixel and the total photon energy based on the number of digital pulses in each energy interval output by each pixel structure and the accumulated threshold-crossing time includes: when the X-ray dose rate is a low X-ray dose rate, using the number of digital pulses in each energy interval output by each pixel structure as the number of photons in each energy interval of each pixel, and based on the photon energy relationship, according to the threshold equivalent pulse width time in each energy interval corresponding to each pixel obtained by the quasi-triangular wave analog voltage pulse signal obtained by each pixel structure, the number of photons in each energy interval of each pixel, and the accumulated threshold-crossing time in each energy interval of each pixel to obtain the total photon energy in each energy interval of each pixel.

[0017] In one embodiment of the present invention, the photon energy relationship includes: E∝T1+A×T2; wherein E is the total photon energy, T1 is the accumulated threshold crossing time, A is the number of photons, and T2 is the average pulse width of the photon pulse.

[0018] In one embodiment of the present invention, each pixel structure transmits the number of digital pulse counts and the accumulated threshold-crossing time in multiple energy intervals to the photon counting module via an LVDS serial bus.

[0019] As described above, the present invention is a photon counting detector system having the following beneficial effects: the present invention collects the counts and cumulative over-threshold times of each energy level interval through a dedicated photon counting chip of the photon counting detector, so that when collecting images under low-dose rate X-ray conditions, it can count both the number of photons in each energy interval and the total energy of photons in each energy interval, providing richer energy information for the energy spectrum image; when collecting images under high-dose rate X-ray conditions, it can judge the severity of photon stacking, calculate the average number of photons in each energy level based on the over-threshold time, avoid the influence of counter paralysis caused by photon stacking on the energy spectrum characteristics, and can significantly suppress and correct the counting nonlinearity caused by photon stacking, thereby solving the problem of energy spectrum distortion of the photon counting detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown is a structural schematic diagram of a photon counting detector system according to an embodiment of the present invention.

[0021] Figure 2 Shown is a schematic structural diagram of a dedicated photon counting chip according to an embodiment of the present invention.

[0022] Figure 3 FIG. 1 is a schematic structural diagram of a pixel structure according to an embodiment of the present invention.

[0023] Figure 4 Shown is a schematic diagram of counting+timing energy spectrum data at a single-threshold low X-ray dose rate in one embodiment of the present invention.

[0024] Figure 5 Shown is a schematic diagram of counting+timing spectrum data at two threshold low X-ray dose rates in one embodiment of the present invention.

[0025] Figure 6 Shown is a schematic diagram of counting+timing energy spectrum data at three threshold low X-ray dose rates in one embodiment of the present invention.

[0026] Figure 7 FIG2 is a schematic diagram of counting+timing spectrum data at a high X-ray dose rate according to an embodiment of the present invention.

[0027] Figure 8 It is a schematic diagram showing the description of the threshold equivalent pulse width time in one embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0029] It should be noted that in the following description, reference is made to the accompanying drawings, which describe several embodiments of the present invention. It should be understood that other embodiments may be used and that mechanical, structural, electrical and operational changes may be made without departing from the spirit and scope of the present invention. The following detailed description should not be considered restrictive, and the scope of the embodiments of the present invention is limited only by the claims of the published patents. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. Spatially related terms, such as "upper", "lower", "left", "right", "below", "below", "lower", "above", "upper", etc., may be used in the text to facilitate the description of the relationship between one element or feature shown in the figure and another element or feature.

[0030] Throughout this specification, when a part is said to be "connected" to another part, this includes not only "direct connection" but also "indirect connection" with other elements interposed therebetween. Furthermore, when a part is said to "include" a certain component, unless otherwise stated, this does not exclude the other component but rather implies that the other component may be included.

[0031] The terms "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or segments, but are not intended to be limiting. These terms are used solely to distinguish one part, component, region, layer, or segment from another. Therefore, a reference to a first part, component, region, layer, or segment below may also refer to a second part, component, region, layer, or segment without departing from the scope of the present invention.

[0032] Furthermore, as used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms "comprise", "include" indicate the presence of the described features, operations, elements, components, items, kinds, and / or groups, but do not exclude the presence, occurrence, or addition of one or more other features, operations, elements, components, items, kinds, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean any one or any combination. Thus, "A, B, or C" or "A, B, and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B, and C". Exceptions to this definition occur only when the combination of elements, functions, or operations is inherently mutually exclusive in some way.

[0033] The present invention provides a photon counting detector system. A dedicated photon counting chip of the photon counting detector collects the counts and accumulated cross-threshold time of each energy level interval. When acquiring images under low-dose rate X-ray conditions, the system can count both the number of photons in each energy interval and the total energy of photons in each energy interval, providing richer energy information for energy spectrum images. When acquiring images under high-dose rate X-ray conditions, the system can determine the severity of photon stacking and calculate the average number of photons in each energy level based on the cross-threshold time, thereby avoiding the impact of counter paralysis caused by photon stacking on energy spectrum characteristics. The system can also significantly suppress and correct the counting nonlinearity caused by photon stacking, thereby solving the problem of energy spectrum distortion of the photon counting detector.

[0034] The following is a detailed description of the embodiments of the present invention with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. The present invention can be embodied in many different forms and is not limited to the embodiments described herein.

[0035] like Figure 1 A schematic structural diagram of a photon counting detector system in an embodiment of the present invention is shown.

[0036] The structure includes:

[0037] A photon counting detector 1 includes: a conversion crystal 11 for exciting electron-hole pairs in response to incident X-ray photons under conditions of image acquisition at a set X-ray dose rate; a dedicated photon counting chip 12 having a pixel array structure, including: a plurality of arranged pixel structures 121 for processing voltage pulse signals obtained by converting electron-hole pairs excited by the conversion crystal corresponding to a current pixel in the form of pixel charge signals to obtain quasi-triangular wave analog voltage pulse signals; and based on the quasi-triangular wave analog voltage pulse signals, counting and outputting the number of digital pulse counts and the accumulated threshold crossing time in multiple energy intervals;

[0038] The photon number calculation module 2 is connected to the photon counting detector 1 and is used to calculate the average number of photons in each energy interval of each pixel based on the accumulated threshold-crossing time output by each pixel structure when the X-ray dose rate is a high X-ray dose rate; when the X-ray dose rate is a low X-ray dose rate, the photon number and total photon energy in each energy interval of each pixel are calculated based on the number of digital pulses in each energy interval output by each pixel structure and the accumulated threshold-crossing time.

[0039] In one embodiment, the photon counting dedicated chip 12 with a pixel array structure includes a plurality of arranged pixel structures 121, such as Figure 2 As shown; wherein each pixel structure corresponds to a pixel;

[0040] like Figure 3 As shown, each pixel structure 121 includes:

[0041] The charge amplifier 31 is used to convert the electron-hole pairs excited by the capture crystal of the detector corresponding to the current pixel, which are collected in the form of pixel charge signals, into voltage pulse signals;

[0042] a shaper 32 connected to the charge amplifier 31 and configured to process the voltage pulse signal and output a quasi-triangular wave analog voltage pulse signal;

[0043] The energy level output modules corresponding to one or more different energy level intervals are used to count the number of digital pulses in each energy interval and the accumulated threshold crossing time and output them.

[0044] When the X-ray dose rate is low, that is, when no stacking occurs, the pixel structure uses a charge amplifier and a shaper to make the output analog pulses all similar triangles (without considering the photon stacking situation), the photon pulse energy is proportional to the quasi-triangular wave pulse width time, and the pulse peak is linearly related to the photon energy.

[0045] When the X-ray dose rate is high, due to photon stacking, the quasi-triangular wave pulses output by the shaper also stack up. However, after photon stacking occurs, the threshold-crossing time continues to increase, and the correlation between the threshold-crossing time and energy is higher than the correlation between counts and energy.

[0046] In a specific embodiment, if Figure 3 As shown, each energy level output module includes:

[0047] The comparator 331 corresponding to the current energy level interval is configured to output a high level when the voltage value of the quasi-triangular wave analog voltage pulse signal is greater than the energy level voltage threshold corresponding to the current energy interval; specifically, the comparator 331 is configured to set an energy level voltage threshold. When the analog pulse is greater than the set threshold, the comparator outputs a high level, otherwise it outputs a low level.

[0048] The counter 332 is connected to the comparator 331 and is used to count and output the number of digital pulses when the comparator outputs a high level; specifically, the counter counts the number of digital pulses output by the comparator within a period of acquisition time.

[0049] The timer 333 is connected to the comparator 331 and is used to count and output the accumulated threshold-crossing time of the analog triangle wave when the comparator outputs a high level. Specifically, the timer is enabled by the comparator outputting a high level, and counts and outputs the accumulated threshold-crossing time of the analog triangle wave.

[0050] In one embodiment, the timer 333 uses an external high-speed sampling clock as its internal timing frequency. Specifically, the timer 333 is enabled by a high-level comparator output, and the comparator output pulse controls the timer's enable. A high-level enable signal continuously timers the timer, while a low-level enable signal pauses the timer. Triggered by the external high-speed clock, the timer 333 calculates the cumulative threshold-crossing time of the simulated triangle wave. Preferably, the unit of the cumulative threshold-crossing time is the external high-speed sampling clock cycle, which is set by an external crystal oscillator. Specifically, the unit of the total threshold-crossing time is the number of high-speed sampling clocks, which is set by the user via the external crystal oscillator. The number of clocks multiplied by the number of clock cycles represents the physical time. The accuracy of the threshold-crossing time measurement depends on the timer's external high-speed clock. A higher clock frequency results in a smaller quantization error and higher temporal resolution.

[0051] In one embodiment, a dedicated chip uses a charge amplifier and a shaper to make the output analog pulses all similar triangles (regardless of the photon stacking situation), and the photon pulse energy is proportional to the quasi-triangular wave pulse width time. The "threshold equivalent pulse width time" refers to the quasi-triangular wave voltage pulse width with a peak value exactly equal to the set threshold, which is obtained from the energy spectrum distribution characteristics. For example, Figure 4 As shown, it is the "counting + timing" energy spectrum data output. When there is only one energy level output module, if the number of digital pulses in the energy interval output by each received pixel structure is 3 and the accumulated threshold crossing time is 8+15+12=35 clock cycles.

[0052] That is, when the X-ray dose rate is a low X-ray dose rate, the number of digital pulses in each energy interval output by each pixel structure is used as the number of photons in each energy interval of each pixel, and based on the similar triangle law, the threshold equivalent pulse width time corresponding to each energy interval of each pixel, the number of photons in each energy interval of each pixel, and the accumulated threshold crossing time in each energy interval of each pixel obtained according to the quasi-triangular wave analog voltage pulse signal obtained by each pixel structure are calculated to obtain the total photon energy in each energy interval of each pixel.

[0053] Preferably, according to the similar triangle rule, pulse width time = threshold crossing time + threshold equivalent pulse width time;

[0054] Under low-dose rate image acquisition conditions, the total photon energy collected at a certain energy level within a period of time has the following relationship.

[0055] Total photon energy ∝ cumulative threshold crossing time + number of pulses x threshold equivalent pulse width time;

[0056] Right now,

[0057] E∝T1+A×T2;(1)

[0058] Where E is the total photon energy, T1 is the cumulative threshold time, A is the number of photons, and T2 is the average pulse width of the photon pulse.

[0059] For example, if Figure 5 As shown, the number of photons at energy level 1 = 3; the number of photons at energy level 2 = 2; the threshold crossing time of energy level 1 = 6+16+14 = 36 clock cycles; the threshold crossing time of energy level 2 = 9+6 = 15 clock cycles; the equivalent pulse width time T1 of threshold 1 = 6 clock cycles; the equivalent pulse width time T1 of threshold 2 = 13 clock cycles; the total energy of photons at energy level 1 ∝ 36+3x6 = 54 clock cycles; the total energy of photons at energy level 2 ∝ 15+2x13 = 41 clock cycles.

[0060] In one embodiment, during high-dose-rate image acquisition, photon stacking causes stacking of the quasi-triangular wave pulses output by the shaper. After photon stacking occurs, the analog pulse remains above the threshold, the comparator output remains high, and the counter does not increment, resulting in a missed count. Therefore, when the X-ray dose rate is high, the average photon count in each energy interval for each pixel is calculated based on the average pulse width of the photon pulses in each energy interval corresponding to each pixel, as determined by the quasi-triangular wave analog voltage pulse signal obtained by each pixel structure, and the accumulated threshold-crossing time in each energy interval for each pixel.

[0061] Preferably, after photon stacking occurs, the threshold crossing time continues to increase, and the correlation between the threshold crossing time and energy is higher than the correlation between the count and energy. In this case, the following method is used to correct the photon count:

[0062] Step 1: Expose and collect the number of digital pulses in each energy interval and the accumulated threshold crossing time;

[0063] Step 2: Determine the average pulse width of the photon pulse in each energy range according to the energy spectrum distribution characteristics of the ray source;

[0064] Step 3: Divide the total threshold-crossing time in each energy region by the average pulse width of the photon pulse in the energy region to obtain the average photon count in the energy region.

[0065] This method differs from conventional "non-paralyzed model" photon counting in that it uses a set comparator reset time as the average pulse width of the photon pulse, with the average pulse width of all energy levels being the same. This makes it impossible to set the optimal average pulse width for different thresholds, resulting in significant deviations from the actual physical model. With the method described in this invention, different average pulse widths can be selected for each threshold based on the energy spectrum distribution characteristics of the radiation source.

[0066] In one embodiment, each pixel structure transmits the number of digital pulse counts and the accumulated threshold-crossing time in multiple energy intervals to the photon number calculation module via an LVDS serial bus.

[0067] In order to better illustrate the above-mentioned photon counting detector system, the present invention provides the following specific embodiments.

[0068] Example 1: A photon counting detector;

[0069] The invention comprises a photon counting dedicated chip with a pixel array structure, wherein each pixel comprises a charge amplifier, a shaper, several threshold comparators, several counters and several timers.

[0070] When X-ray photons strike a photon-counting detector, they excite electron-hole pairs in the detector crystal. The electrons and holes move in a directional manner under an applied electric field bias, generating a charge signal. This signal is collected by pixels on a dedicated photon-counting chip. After passing through a charge-sensitive amplifier, the charge signal outputs an analog pulse voltage. This voltage is then processed by a shaper to produce a quasi-triangular analog voltage pulse. This quasi-triangular pulse is compared with the thresholds of each comparator. If the pulse amplitude exceeds the comparator's threshold, a high level is output; otherwise, a low level is output.

[0071] In this embodiment, each pixel has three energy detection intervals, and each comparator output is connected to a set of counters and timers. The counters detect the number of comparator output pulses. The timers use an external high-speed clock as their internal timing frequency, and the comparator output pulses control the timer enable. A high enable signal continuously timers, while a low enable signal pauses timers.

[0072] Among them, Figure 6 This example demonstrates the acquisition of data at a low X-ray dose rate. Based on the energy spectrum distribution characteristics, the equivalent pulse widths of thresholds 1 to 3 are pre-measured. In this example, it is known that:

[0073] Threshold 1 equivalent pulse width time = 6 clock cycles;

[0074] Threshold 2 equivalent pulse width time = 13 clock cycles;

[0075] Threshold 3 equivalent pulse width time = 24 clock cycles;

[0076] After a period of low-dose exposure, the detector collects the counts measured by the counter and the cumulative threshold-crossing time measured by the timer as follows:

[0077] threshold1 count = 3;

[0078] threshold2count=2;

[0079] threshold3 count = 0;

[0080] Threshold 1 cumulative threshold crossing time = 36 clock cycles;

[0081] Threshold 2 cumulative threshold crossing time = 15 clock cycles;

[0082] Threshold 3 cumulative threshold crossing time = 0 clock cycles;

[0083] According to the law of similar triangles:

[0084] Total energy of photons at energy level 1 ∝ 36 + 3*6 = 54 clock cycles;

[0085] Total energy of photons at energy level 2 ∝ 15 + 2 * 13 = 41 clock cycles;

[0086] The total energy of level 3 photons = 0.

[0087] Attachment Figure 7 This example demonstrates the acquisition of data at a high X-ray dose rate. Based on the known energy spectrum distribution characteristics, the average pulse width of the photon pulses at energy levels 1 to 3 is pre-calculated. This example pre-converts the data to:

[0088] Average pulse width of energy level 1 photon pulse = 18 clock cycles;

[0089] Average pulse width of energy level 2 photon pulse = 13 clock cycles;

[0090] Average pulse width of energy level 3 photon pulse = 4 clock cycles;

[0091] After a period of high-dose exposure, the detector collects data and the cumulative threshold-crossing time measured by the counter is as follows:

[0092] Threshold 1 cumulative threshold crossing time = 54 clock cycles;

[0093] Threshold 2 cumulative threshold crossing time = 38 clock cycles;

[0094] Threshold 3 cumulative threshold crossing time = 8 clock cycles;

[0095] The number of photons at each energy level is calculated as:

[0096] threshold1averagecount=3;

[0097] threshold2averagecount=3;

[0098] Threshold 3 Average Count = 2.

[0099] Example 2: A dedicated chip for photon counting;

[0100] The photon counting chip consists of 64 arranged pixels, each containing a charge amplifier, a shaper, three threshold comparators, three counters, and three timers. The charge amplifier and shaper combine to output a quasi-triangular analog voltage pulse, with the peak value linearly related to the photon energy. After the pulse and threshold are distinguished by the comparator, the number of digital pulses output by the comparator is detected by the counter, and the total time the digital pulses cross the threshold is detected by the timer. At low doses, the count value is close to the actual number of photons; at high doses, the count value is significantly lower than the actual value due to stacking.

[0101] like Figure 8 As shown in the figure, when the X-ray dose rate is a low X-ray dose rate, the threshold 1 equivalent pulse width time T1 is calculated based on the pixel amplifier shaper gain and the high-speed sampling clock frequency; the threshold 1 crossing time is detected by the timer as 36 clock cycles; wherein, the total photon energy is proportional to the 3 pulse bottom edge widths. In this example, the chip detection count value is 3, based on which it can be known that the total photon energy ∝ 36 + 3xT1 = 54 clock cycles.

[0102] In summary, the photon counting detector system of the present invention collects the counts and cumulative threshold crossing times of each energy level interval through the photon counting dedicated chip of the photon counting detector. When collecting images under low-dose rate X-ray conditions, it can count both the number of photons in each energy interval and the total energy of photons in each energy interval, providing richer energy information for the energy spectrum image. When collecting images under high-dose rate X-ray conditions, it can judge the severity of photon stacking and calculate the average number of photons in each energy level based on the threshold crossing time, thereby avoiding the impact of counter paralysis caused by photon stacking on energy spectrum characteristics. It can also significantly suppress and correct the counting nonlinearity caused by photon stacking, thereby solving the problem of energy spectrum distortion of the photon counting detector. Therefore, the present invention effectively overcomes the various shortcomings of the existing technology and has high industrial utilization value.

[0103] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, any equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A photon counting detector system, characterized in that: include: The photon counting detector includes: a conversion crystal for exciting electron-hole pairs in response to incident X-ray photons under the condition of collecting images at a set X-ray dose rate; a photon counting dedicated chip with a pixel array structure, including: A plurality of arranged pixel structures are used to respectively process voltage pulse signals obtained by converting electron-hole pairs excited by the conversion crystal corresponding to the current pixel in the form of pixel charge signals to obtain quasi-triangular wave analog voltage pulse signals, and to count and output the number of digital pulses and the accumulated threshold crossing time in multiple energy intervals based on the quasi-triangular wave analog voltage pulse signals; a photon number calculation module, connected to the photon counting detector, for calculating, when the X-ray dose rate is a high X-ray dose rate, an average number of photons in each energy interval of each pixel based on the accumulated threshold-crossing time output by each pixel structure; and, when the X-ray dose rate is a low X-ray dose rate, calculating, based on the number of digital pulses in each energy interval output by each pixel structure and the accumulated threshold-crossing time, the number of photons in each energy interval of each pixel and the total photon energy, in accordance with the following method: when the X-ray dose rate is low, using the number of digital pulses in each energy interval output by each pixel structure as the number of photons in each energy interval of each pixel, and calculating, based on the photon energy relationship, a threshold equivalent pulse width time corresponding to each energy interval of each pixel obtained from the quasi-triangular wave analog voltage pulse signal obtained by each pixel structure, the number of photons in each energy interval of each pixel, and the accumulated threshold-crossing time in each energy interval of each pixel to obtain the total photon energy in each energy interval of each pixel; the threshold equivalent pulse width time being the width of the quasi-triangular wave voltage pulse whose peak value is exactly equal to the set threshold, obtained from the energy spectrum distribution characteristics; The photon energy relationship includes: E∝T1+A×T2; Where E is the total photon energy, T1 is the cumulative threshold crossing time, A is the number of photons, and T2 is the threshold equivalent pulse width time.

2. The photon counting detector system according to claim 1, wherein: Each pixel structure includes: A charge amplifier, configured to convert the electron-hole pairs excited by the capture crystal of the detector corresponding to the current pixel, which are collected in the form of pixel charge signals, into voltage pulse signals; a shaper, connected to the charge amplifier, for processing the voltage pulse signal and outputting a quasi-triangular wave analog voltage pulse signal; The energy level output modules corresponding to one or more different energy level intervals are used to count the number of digital pulses in each energy interval and the accumulated threshold crossing time and output them.

3. The photon counting detector system according to claim 2, wherein: Each energy level output module includes: a comparator corresponding to the current energy level interval, configured to output a high level when the voltage value of the quasi-triangular wave analog voltage pulse signal is greater than the energy level voltage threshold corresponding to the current energy interval; a counter connected to the comparator, configured to count and output the number of digital pulses when the comparator outputs a high level; A timer is connected to the comparator and is used to count and output the accumulated threshold crossing time of the analog triangle wave when the comparator outputs a high level.

4. The photon counting detector system according to claim 3, wherein: The timer uses an external high-speed sampling clock as the internal timing main frequency.

5. The photon counting detector system according to claim 4, characterized in that The unit of the accumulated threshold crossing time is the external high-speed sampling clock period, and the external high-speed sampling clock period is set by an external crystal oscillator.

6. The photon counting detector system according to claim 2, wherein: When the X-ray dose rate is a low X-ray dose rate, the quasi-triangular wave analog voltage pulse signal output by the shaper is a similar triangle.

7. The photon counting detector system according to claim 1, wherein: When the X-ray dose rate is high, the method for calculating the average number of photons in each energy interval of each pixel based on the number of digital pulse counts in each energy interval output by each pixel structure and the accumulated threshold crossing time includes: When the X-ray dose rate is a high X-ray dose rate, the average number of photons in each energy interval of each pixel is calculated based on the average pulse width of the photon pulse in each energy interval corresponding to each pixel obtained from the quasi-triangular wave analog voltage pulse signal obtained by each pixel structure and the accumulated threshold crossing time in each energy interval of each pixel.

8. The photon counting detector system according to claim 1, wherein: Each pixel structure transmits the number of digital pulse counts in multiple energy intervals and the accumulated threshold-crossing time to the photon number calculation module through a low-voltage differential signal data bus.

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