Quantitative pulse selection for photon-counting computed tomography scanning systems.

Abstract

To provide a photon-counting computed tomography (PCCT) scanning system and a method to be used in the system.SOLUTION: In a method for counting electric charge events detected by a pixel in a photon-counting computed tomography (PCCT) scanning system comprising a plurality of discriminators, each discriminator is associated with respective one of a plurality of threshold voltage levels. The method includes: detecting a signal output from one of the discriminators; incrementing a quantitative count corresponding to the threshold voltage level associated with the one of the discriminators if the detected discriminator output signal satisfies a first condition; and incrementing a qualitative count if the detected discriminator output signal satisfies at least one second condition.SELECTED DRAWING: Figure 2

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 300,953, filed January 19, 2022, entitled "QUANTITATIVE PULSE SELECTION FOR PHOTON-COUNTING COMPUTED TOMOGRAPHY SCANNING SYSTEMS," the entire contents of which are incorporated herein by reference for all purposes. [Technical Field]

[0002] The present disclosure relates generally to the field of photon-counting computed tomography (PCCT) scanning systems, and more particularly to quantitative pulse selection techniques for use in such systems. [Brief explanation of the drawings]

[0003] To provide a more complete understanding of the present disclosure and its features and advantages, please refer to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts and in which:

[0004] [Figure 1] 1 is an illustration of a schematic diagram of the operation of a conventional CT scanning system in accordance with features of certain embodiments described herein. [Figure 2] 1 is a schematic block diagram of an exemplary signal processing architecture for a PCCT scanning system in accordance with features of certain embodiments described herein. [Figure 3] 3 is a graph illustrating the results of an example simulation of the PCCT scanning system of FIG. 2 in accordance with features of certain embodiments described herein. [Figure 4A] 1 illustrates an example of a charge event pileup in accordance with features of certain embodiments described herein. [Figure 4B] 1 illustrates an example of charge sharing according to features of embodiments described herein. [Figure 5A] 1 is a flowchart illustrating the operation of a quantitative pulse selection (QPS) technique in accordance with features of embodiments described herein. [Figure 5B] 1 is a state machine implemented by QPS technology in accordance with aspects of embodiments described herein. [Figure 6A] 1 illustrates counting of charge events detected at a pixel-of-interest (POI) according to features of embodiments described herein. [Figure 6B] 1 illustrates counting of charge events detected at a pixel-of-interest (POI) according to features of embodiments described herein. [Figure 6C] 1 illustrates counting of charge events detected at a pixel-of-interest (POI) according to features of embodiments described herein. [Figure 7A] 10 shows quantitative and qualitative counting curves for various PCCT counting methods compared to ground truth in accordance with features of embodiments described herein. [Figure 7B] 10 shows quantitative and qualitative counting curves for various PCCT counting methods compared to ground truth in accordance with features of embodiments described herein. [Figure 7C] 10 shows quantitative and qualitative counting curves for various PCCT counting methods compared to ground truth in accordance with features of embodiments described herein. [Figure 7D] 10 shows quantitative and qualitative counting curves for various PCCT counting methods compared to ground truth in accordance with features of embodiments described herein. [Figure 8] 10 shows total counting curves for the QPS technique with and without time-over-threshold (ToT) compared to ground truth in accordance with features of embodiments described herein. [Figure 9A] 10 shows a series of estimates of bone thickness in a simulated dataset according to features of embodiments described herein. [Figure 9B]10 shows a series of estimates of bone thickness in a simulated dataset according to features of embodiments described herein. [Figure 10] FIG. 1 is a block diagram of a computer system that may be used to implement all or part of a PCCT scanning system in accordance with features of certain embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

[0005] For purposes of this disclosure, the phrase "A and / or B" means (A), (B), or (A and B). For purposes of this disclosure, the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). The term "between" when used in reference to a measurement range is inclusive of both ends of the measurement range. As used herein, the designation "A / B / C" means (A), (B), and / or (C).

[0006] The description uses phrases such as "in one embodiment" or "in an embodiment," which may each refer to one or more of the same or different embodiments. Furthermore, terms such as "comprising," "including," and "having," when used with respect to embodiments of the present disclosure, are synonymous. The present disclosure may use perspective descriptions such as "above," "below," "top," "bottom," and "side," which are used for ease of discussion and are not intended to limit the application of the disclosed embodiments. The accompanying drawings are not necessarily drawn to scale. Unless otherwise specified, the use of ordinal adjectives such as "first," "second," and "third" to describe common objects merely indicates that various instances of similar objects are being referred to and is not intended to imply that the objects so described must be in a given order, whether temporally, spatially, sequentially, or in any other manner.

[0007] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and which show, by way of example, embodiments that may be implemented. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense.

[0008] The following disclosure describes various exemplary embodiments and examples for implementing the features and functionality of the present disclosure. While specific components, arrangements, and / or features are described below in connection with various exemplary embodiments, these are merely examples used to simplify the disclosure and are not intended to be limiting. Of course, it will be understood that in the development of any actual embodiment, many implementation-specific decisions must be made to achieve the developer's particular goals, including compliance with system, business, and / or legal constraints, which may vary from implementation to implementation. It will also be understood that such a development effort may be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0009] Reference may be made herein to spatial relationships between various components and the spatial orientation of various aspects of components, as depicted in the accompanying drawings. However, as one of ordinary skill in the art would recognize after fully reading this disclosure, the devices, components, members, apparatuses, etc. described herein may be positioned in any desired orientation. Accordingly, because the components described herein may be oriented in any desired direction, the use of terms such as "upper," "lower," "top," "lower," "top," "bottom," and the like, or other similar terms to describe the spatial relationships between various components or the spatial orientation of aspects of such components, should be understood to describe the relative relationships between the components or the spatial orientation of aspects of such components, respectively. When used to describe a range of dimensions or other characteristics (e.g., time, pressure, temperature, length, width, etc.) of elements, operations, and / or conditions, the phrase "between X and Y" represents a range that includes X and Y.

[0010] Furthermore, the present disclosure may repeat reference numerals and / or characters in various instances. This repetition is for the purposes of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed. Example embodiments that can be used to implement the features and functionality of the present disclosure will now be described with more particular reference to the accompanying figures.

[0011] 1, a conventional computed tomography (CT) scanning system 100 employs x-rays 101 generated by an x-ray source 102 and passed through an object of interest 104. The x-rays are converted by a collimator and scintillator 106 into light 108 that is captured by a detector implemented as a photodiode array 110. The photodiode array 110 converts the light 108 into an analog electrical signal 112, which is converted to a digital signal 114 using an analog-to-digital (A / D) converter 116. The digital signal output from the A / D converter is used to generate a grayscale image referred to as a CT scan.

[0012] PCCT imaging may offer significant advantages and improvements over the existing CT imaging techniques described above. PCCT systems employ photon-counting detectors (PCDs), which include semiconductor layers for implementing an array of detector pixels that register individual photon interactions with the PCD. By tracking the accumulated energy of each interaction, the detector pixels of the PCD record not only the photon intensity but also the approximate energy spectrum, making PCCT a spectral or energy-resolved CT technique. In contrast, conventional CT scanners use energy-integrating detectors (EIDs), which register the total energy from one or more photons and the electronic noise accumulated in the pixel over a period of time. Thus, EIDs register only photon intensity, similar to monochrome photography. In contrast, PCDs register both photon intensity and spectral information, similar to color photography.

[0013] PCCT imaging transforms the three-step process described above into a more streamlined direct conversion of x-rays to electrical charge via a semiconductor layer comprising a PCD. Specifically, the semiconductor material used to efficiently implement the PCD transforms each x-ray photon into a burst of electrical charge proportional to the x-ray's energy. The benefits of this technology include improved signal-to-noise, reduced x-ray dose to the patient due to higher resolution that can be achieved with the same x-ray dose, improved spatial resolution, and the ability to distinguish between multiple contrast agents and multiple types of materials / tissues through the use of several "energy bins."

[0014] When a photon interacts within a PCD, the height of the resulting electrical pulse is roughly proportional to the photon's energy. By comparing each pulse generated within a pixel with a suitable low-energy threshold, contributions from low-energy events (arising from both photon interactions and electronic noise) can be filtered out. As a result, PCDs have higher signal-to-noise and contrast-to-noise ratios compared to EIDs, allowing for improved image quality at the same x-ray exposure level or reduced patient x-ray dose for the same image quality.

[0015] Introducing more energy thresholds above a low energy threshold allows for the division of PCD into several distinct energy bins. Each registered photon is assigned to a specific bin according to its energy, such that each pixel measures a histogram of the incident X-ray spectrum. This spectral information allows for a qualitative determination of the material composition of each pixel in the reconstructed CT image, as opposed to the estimated average linear attenuation coefficient obtained in conventional CT scans. Additionally, the use of three or more energy bins allows for discrimination of dense bone and calcifications from heavier elements commonly used as contrast agents, reducing the need for a reference scan before contrast injection, thereby further reducing the X-ray dose received by the patient.

[0016] FIG. 2 shows a schematic diagram of an exemplary signal processing architecture for a PCCT system 200 with a PCD including multiple detector pixels, represented in FIG. 2 by a single pixel. During operation, pulses of current enter from a sensor 202, are amplified by a charge-sensitive amplifier (CSA) 204, and are shaped by a pulse shaper (PS) 206. The voltage pulses output from the PS 206 are input to a set of N discriminators (or comparators) 208, which each compare the pulse to N increasing voltage thresholds. The set of discriminators 208 produces a pulsed digital output in "thermometer code." Pulses may be counted at each level or threshold by a counter 210, and the resulting count value (which may be temporarily stored in a result register 212) represents the number of x-ray hits occurring at each of the N thresholds. It will be appreciated that the thresholds are set to correspond to different voltages corresponding to different energy photons. According to a feature of the embodiments described herein, in addition to quantitative counters corresponding to each of the N thresholds, the counter 210 includes a qualitative counter for purposes described in more detail below.

[0017] FIG. 3 is a graph illustrating the results of an example simulation of the PCCT system shown in FIG. 2, with no overlapping charge events. A first waveform 300 represents the stimulation current from the sensor 202, and a second waveform 302 represents the corresponding shaper voltage from the PS 206 versus the boosted voltage discriminator threshold voltage (vth[0] through vth[4]) expressed in millivolts (mV). Waveform 304 represents the corresponding pulses counted at each level by the counter 210. Finally, waveform 306 represents the output of the discriminator 208 input to the counter 210. It can be seen from FIG. 3 that for each pulse of current, a voltage pulse from the pulse shaper generates an output on the discriminator 208. The counting by the counter 210 of the peak discriminator output for each pulse is the desired response.

[0018] When all pulses occur far enough apart in time, there are several ways to effectively implement a counter to count and "bin" the pulses. These include two common techniques: asynchronous edge (asynch_edge) counting and peak zero (peak_zero) counting. Using asynchronous edge counting, an asynchronous counter is associated with each discriminator output. As a result, the counter increments for any energy level above the associated discriminator's threshold level. When a "binned" value is desired, for each counter, the count of the higher threshold level counter must be subtracted from the count to determine the correct count for the threshold level. For example, the counter associated with discriminator 0 is also incremented every discriminator 1-N count; therefore, to obtain the accurate level 0 count, the count for discriminator 1-N must be subtracted from the count for discriminator 0. Similarly, the counter associated with discriminator 1 is also incremented every discriminator 2-N count; therefore, to obtain the accurate level 1 count, the count for discriminator 2-N must be subtracted from the count for discriminator 1.

[0019] By using peak-zero counting, the edge of the signal output from Discriminator 0 is used to determine which counter to increment. The method basically increments only the largest discriminator count that occurs between the rising and falling edges of Discriminator 0.

[0020] Both asynchronous edge counting and peak-zero counting work fairly well when the events being counted are spaced apart without any overlap. In the absence of other charge events, there will always be an orderly sequence beginning and ending with the rising and falling edges of discriminator 0. There will also be rising edges of all levels below the discriminator with maximum switching.

[0021] In practice, charge events can occur too close in time to be distinguished from one another, which can result in multiple charge events being counted as a single charge event with the wrong energy. This phenomenon is typically referred to as a "pileup," an example of which is shown in FIG. 4A. Referring to FIG. 4A, graph 400 illustrates two cases of pileup, designated by reference numerals 402a and 402b. Specifically, case 402a corresponds to the pileup of two overlapping charge events 404a and 404b. Case 402b corresponds to the pileup of three overlapping charge events 406a-406c.

[0022] Additionally, charge events can occur on boundaries between adjacent pixels, resulting in charge energy being split between (or within) the pixels. This phenomenon is typically referred to as "charge sharing," an example of which is shown in FIG. 4B. Referring to FIG. 4B, charge event 410 occurs on boundary 412 between pixels 414 and 416, resulting in charge sharing between those pixels. In contrast, charge event 418 occurs entirely within the boundary of pixel 420.

[0023] Both pile-up and charge sharing can cause errors when measuring photon energies: over a measurement frame, some events may suffer from pile-up and / or charge sharing, while other events may not.

[0024] Various charge event counting techniques have been proposed and implemented. For example, a technique referred to herein as a "tickdown" counter employs an asynchronous state machine to count "downtick" events and maximize the likelihood of agreement with the total event count. Another method employed is referred to as a Time of Test (ToT) technique, in which if a spectral threshold is exceeded for a longer period than expected for a single event, the event at that threshold is immediately counted and the timer is reset. The ToT technique provides improved counting performance, especially at high fluxes. A method that reduces the effects of charge sharing may be referred to as a "coincidence counter" method, which attempts to correct individual events for the effects of charge sharing.

[0025] According to features of embodiments described herein for implementing a QPS system, if incidents of pileup and / or charge sharing can be detected, the corresponding charge events can be tallied by a qualitative counter, which aims to maintain an accurate record of the total count. Only events that do not measurably suffer from pileup and / or charge sharing are binned by an energy-sensitive quantitative detector. As long as a statistically significant number of qualitative events can be measured during a measurement frame, the overall energy spectrum can be estimated without systematic errors resulting from charge sharing and pileup. In certain embodiments, the QPS technique is combined with the Time of Threshold technique to improve performance. Unlike coincidence counter methods, in the QPS method described herein, charge sharing is detected and the corresponding events are ignored for the purpose of estimating the energy spectrum.

[0026] FIG. 5A is a flowchart illustrating an exemplary operation of one embodiment of a QPS system. As shown in FIG. 5A, an event detected at a pixel (step 500) is quantized (step 502), and then, in step 504, it is determined whether the quantized event exhibits a monotonic rising-falling characteristic, indicating that the detected event is not affected by pileup. Specifically, this condition is met if and only if the quantized event consists solely of a series of low-to-high transitions starting from a baseline level, followed by a series of high-to-low transitions ending at the baseline level. If not (indicating that the detected charge event is affected by pileup), in step 506, the event is counted by a qualitative counter; if not, in step 510, it is determined whether a ToT parameter has been exceeded. If the ToT parameter has been exceeded, the event is counted by a qualitative counter in step 506 (or the event is counted depending on the length of time the ToT parameter has been exceeded); if not, in step 512, it is determined whether an overlapping event has been detected by any adjacent pixel 514, indicating a charge-sharing situation. If it is determined that an overlapping event is detected by one or more adjacent pixels 516, the event is counted by a qualitative counter in step 506; otherwise, the event is binned by a quantitative counter in step 516.

[0027] 5B is a state machine illustrating an example operation of a QPS system according to embodiments described herein. The state variables of the state machine of FIG. 5B are defined as follows: disc_nz: The discriminator output is non-zero (aka disc_out[0]) neighbor_nz: At least one neighboring (N, S, E, W) discriminator output is non-zero or all neighbors' disc_nz disc_dir: final direction of discriminator output 0 → The final discriminator output was higher 1 → The final discriminator output was lower t_over_t: Time over threshold indicator 0 → Default 1->Threshold exceedance timer expired

[0028] The outputs of the state machine of FIG. 5B are defined as follows: +QUAL_CT: Incremental qualitative pulse counter +QUANT_CT[N]: Incremental quantitative pulse counter for bin N

[0029] After the counter is incremented, t_over_t is reset to zero. Note that more internal state variables than defined above may be needed to keep track of the state history.

[0030] 6A illustrates the counting of a POI-detected event 600 according to features of embodiments described herein for implementing a QPS counting method. As shown in FIG. 6A, the event 600 is not subject to pile-up (i.e., the POI discriminator output waveform is monotonic rise and fall and does not exceed ToT) or charge sharing (no activity on the waveform corresponding to the orthogonal adjacent discriminator output), and therefore the event 600 is counted by the quantitative counter corresponding to bin 2 (represented by waveform 602).

[0031] 6B illustrates counting of events 610 detected at a POI according to features of embodiments described herein for implementing a QPS counting method. As shown in FIG. 6B, event 610 is not subject to pileup (i.e., the POI discriminator output waveform is monotonic rise and fall and does not exceed ToT), but event 610 is subject to charge sharing, as indicated by activity on at least one of the waveforms corresponding to orthogonal adjacent discriminator outputs (i.e., waveform 612). As a result, event 610 is counted by a qualitative counter (represented by waveform 614).

[0032] 6C illustrates the counting of an event 620 detected at a POI according to features of embodiments described herein for implementing a QPS counting method. As shown in FIG. 6C, event 620 is not affected by charge sharing (no activity on the waveforms corresponding to the orthogonal adjacent discriminator outputs), but event 620 is affected by pileup, as indicated by the ToT of bin 4 exceeding two (waveform 622). As a result, event 620 is counted twice by the quantitation counter (represented by waveform 624).

[0033] Figures 7A-7D show quantitative and qualitative counting curves for various PCCT counting methods, including tickdown (Figure 7A), QPS (Figure 7B), tickdown with ToT (Figure 7C), and QPS with ToT (Figure 7D), compared to ground truth. Note that the QPS with ToT method significantly improves the correlation between estimated and actual total counts, and between the percentage of estimated and actual counts per bin.

[0034] For comparison purposes, Figure 8 shows the total counting curves for QPS with and without ToT. As the flux rate increases, the number of quantitative counts increases monotonically, while the number of qualitative counts decreases. Measurements at the high end of the flux range contain little or no spectral information. This is a useful feature of the QPS method, as a low ratio of qualitative counts to total counts can be used to indicate that a signal does not contain useful spectral information. In some embodiments, it may be beneficial to ignore measured spectra based on such indicators rather than providing inaccurate spectral estimates.

[0035] Charge sharing causes spectral shifts, primarily due to high-energy photons entering the POI in lower bins from neighboring pixels that share a large portion of the charge. The QPS technique described herein can distinguish some of these events, resulting in improved accuracy for low-flux spectra. Specific results will depend on the choice of discriminator threshold. QPS largely prevents spectral shifts due to pileup, in which high-bin (e.g., bin 4) counts increase at the expense of other (lower) bins. Above approximately 10 megacounts per second (Mcps), the number of quantified counts is so low that the information can be ignored. As a result, systems employing QPS technology can detect conditions in which nearly all charge events in a measurement frame are affected by either charge sharing or pileup, rendering the frame's spectral information highly corrupted and virtually useless. Other systems may use corrupted spectral information to falsely present inaccurate results as reliable.

[0036] The ultimate goal of a CT scan is to produce a 3D image of a subject that can distinguish between different materials. Therefore, one way to benchmark a PCCT counting method is to use it to perform a material discrimination task. For example, counting data from a single pixel can be used to estimate the proportion of different materials present along a simulated linear X-ray photon trajectory.

[0037] 9A and 9B show the results of such a material discrimination experiment, where the simulated data correspond to an X-ray beam passing through 10 cm of water (which has similar X-ray absorption to human tissue) and 1 cm of bone. Because water and bone have different X-ray absorption properties, the received photon counts can be used to estimate the proportion of water and bone along the simulated trajectory.

[0038] Figure 9A shows a series of estimates of bone thickness in a simulated data set. In Figure 9A, the first column, labeled "GT (analysis)," shows the actual thickness of the bone used to generate the simulated data. The other columns represent estimates of this bone thickness based on a series of Monte Carlo simulations using three different hypothetical photon counters. The second column, labeled "GT (simulation)," represents an estimate based on an ideal photon counter that obtains the correct energy from each photon event, uncorrupted by pileup and charge sharing. Errors in this estimate are caused by a limited sample size of photons arriving at the detector within a finite time frame. The third column, labeled "Tick down," shows an estimate based on a simulated photon counter using the "tick down" method. The fourth column, labeled "QPS," represents an estimate based on a simulated photon counter using the QPS method.

[0039] Figure 9B shows the results of the same experiment when the thickness of the water in the simulated data set was estimated.

[0040] The experimental results of Figures 9A and 9B show that the QPS method performs the material discrimination task with better accuracy than the tickdown method.

[0041] 10 is a block diagram illustrating an exemplary system 1100 that may be configured to implement at least a portion of the techniques in accordance with embodiments described herein, and more particularly, as illustrated in the figures described above. As shown in FIG. 10, the system 1100 may include at least one processor 1102, e.g., a hardware processor 1102, coupled to a memory device 1104 via a system bus 1106. Thus, the system may store program code and / or data in the memory device 1104. The processor 1102 may also execute program code accessed from the memory device 1104 via the system bus 1106. In one aspect, the system may be implemented as a computer suitable for storing and / or executing program code. However, it should be understood that the system 1100 may be implemented in the form of any system including a processor and memory capable of performing the functions described in this disclosure.

[0042] In some embodiments, the processor 1102 may execute software or algorithms to perform activities as discussed herein, particularly activities related to the embodiments described herein. The processor 1102 may include any combination of hardware, software, or firmware providing programmable logic, including, by way of non-limiting example, a microprocessor, a DSP, a field programmable gate array (FPGA), a programmable logic array (PLA), an integrated circuit (IC), an application-specific IC (ASIC), or a virtual machine processor. The processor 1102 may be communicatively coupled to the memory device 1104, for example, in a direct memory access (DMA) configuration, such that the processor 1102 may read from or write to the memory device 1104.

[0043] In general, memory device 1104 may include any suitable volatile or non-volatile memory technology, including double data rate (DDR) random access memory (RAM), synchronous RAM (SRAM), dynamic RAM (DRAM), flash, read-only memory (ROM), optical media, virtual memory area, magnetic or tape memory, or any other suitable technology. Unless otherwise specified, any of the memory devices discussed herein should be construed as being encompassed within the broad term “memory.” Information measured, processed, tracked, or transmitted to or from any of the components of system 1100 may be provided in any database, register, control list, cache, or storage structure, all of which may be referenced in any suitable time frame. Any of such storage options may be included within the broad term “memory” as used herein. Similarly, any of the potential processing elements, modules, and machines described herein should be construed as being encompassed within the broad term “processor.” Each element shown in this figure may also include a suitable interface for receiving, transmitting, and / or otherwise communicating data or information in a network environment so that it can communicate, for example, with a system having hardware similar to or identical to another one of these elements.

[0044] In certain exemplary implementations, mechanisms for implementing the embodiments outlined herein may be implemented by logic encoded in one or more tangible media, which may include non-transitory media, such as embedded logic provided in an ASIC, DSP instructions, software executed by a processor (potentially including object code and source code), or other similar machine. In some of these cases, a memory element, such as memory element 1104 shown in FIG. 10 , may store data or information used in the operations described herein. This includes memory elements that can store software, logic, code, or processor instructions that are executed to perform the activities described herein. A processor may execute any type of instruction associated with data or information to accomplish the operations detailed herein. In one example, a processor, such as processor 1102 shown in FIG. 10 , may transform an element or item (e.g., data) from one state or thing to another. In another example, the activities outlined herein may be implemented using fixed logic or programmable logic (e.g., software / computer instructions executed by a processor), and the elements identified herein may be some type of programmable processor, programmable digital logic (e.g., FPGA, DSP, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM)), or ASIC containing digital logic, software, code, electronic instructions, or any suitable combination thereof.

[0045] The memory elements 1104 may include, for example, one or more physical memory devices, such as local memory 1108, and one or more mass storage devices 1110. Local memory may refer to RAM or other non-persistent memory devices typically used during the actual execution of program code. The mass storage device may be implemented as a hard drive or other persistent data storage device. The processing system 1100 may also include one or more cache memories (not shown) that provide temporary storage of at least some program code to reduce the number of times the program code must be retrieved from the mass storage device 1110 during execution.

[0046] As shown in FIG. 10 , memory element 1104 may store energy bin event counting module 1120. In various embodiments, module 1120 may be stored in local memory 1108, in one or more mass storage devices 1110, or remotely from local memory and mass storage devices. It should be understood that system 1100 may further execute an operating system (not shown in FIG. 10 ) that may facilitate execution of module 1120. Module 1120, implemented in the form of executable program code and / or data, may be read from, written to, and / or executed by system 1100, for example, by processor 1102. In response to reading from, writing to, and / or executing module 1120, system 1100 may be configured to perform one or more operations or method steps described herein.

[0047] Input / output (I / O) devices, depicted as input device(s) 1112 and output device(s) 1114, may optionally be coupled to the system. Examples of input devices may include, but are not limited to, a keyboard or a pointing device such as a mouse. Examples of output devices may include, but are not limited to, a monitor or display, or a speaker. In some implementations, the system may include a device driver (not shown) for the output device(s) 1114. The input and / or output devices 1112, 1114 may be coupled to the system 1100 either directly or through an intervening I / O controller. Additionally, sensors 1115 may be coupled to the system 1100 either directly or through an intervening controller and / or driver.

[0048] In one embodiment, the input and output devices may be implemented as a combined input / output device (illustrated in FIG. 10 by the dashed line surrounding input device 1112 and output device 1114). One example of such a composite device is a touch-sensitive display, sometimes referred to as a "touchscreen display" or simply a "touchscreen." In one such embodiment, input to the device may be provided by the movement of a physical object, such as a stylus or a user's finger, on or near the touchscreen display.

[0049] Optionally, a network adapter 1116 may also be coupled to system 1100 to enable system 1100 to couple to other systems, computer systems, remote network devices, and / or remote storage devices over intervening private or public networks. The network adapter may comprise a data receiver for receiving data transmitted by the system, device, and / or network to system 1100, and a data transmitter for transmitting data from system 1100 to the system, device, and / or network. Modems, cable modems, and Ethernet cards are examples of various types of network adapters that may be used in system 1100.

[0050] Example 1 provides a method for counting charge events detected by pixels in a photon-counting computed tomography (PCCT) scanning system including a plurality of discriminators, each discriminator associated with a respective one of a plurality of threshold voltage levels, the method including: detecting a signal output from one of the discriminators; incrementing a quantitative count corresponding to the threshold voltage level associated with one of the discriminators if the detected discriminator output signal satisfies a first condition; and incrementing a qualitative count if the detected discriminator output signal satisfies at least one second condition.

[0051] Example 2 provides the method of example 1, wherein the at least one second condition includes expiration of a Time Over Threshold (ToT) timer.

[0052] Example 3 provides the method of example 2, further comprising incrementing a qualitative count and resetting the ToT timer upon expiration of the ToT timer.

[0053] Example 4 provides the method of example 1, wherein the at least one second condition includes a signal output from one of the discriminators overlapping with a signal output from a discriminator associated with an adjacent pixel.

[0054] Example 5 provides the method of Example 1, wherein the at least one second condition includes a signal output from one of the discriminators including only one monotonic series of low-to-high transitions and only one monotonic series of high-to-low transitions.

[0055] Example 6 provides the method of Example 1, wherein the first condition includes the absence of at least one second condition.

[0056] Example 7 provides the method of example 1, wherein the plurality of discriminators includes five discriminators.

[0057] Example 8 provides the method of example 1, wherein the plurality of threshold voltage levels includes five threshold voltage levels.

[0058] Example 9 provides the method of Example 1, wherein each of the discriminators compares the voltage signal input to the discriminator to a threshold voltage level associated with the discriminator.

[0059] Example 10 provides the method of example 9, wherein the output of each of the discriminators is driven high when the voltage signal input to the discriminator exceeds a threshold voltage level associated with the discriminator.

[0060] Example 11 provides the method of Example 1, where the spectral information is ignored if the total number of qualitative counts does not reach a certain threshold.

[0061] Example 12 provides a method for counting charge events detected by pixels in a photon-counting computed tomography (PCCT) scanning system having a plurality of discriminators, each discriminator associated with a respective one of a plurality of threshold voltage levels, the method including detecting a signal output from one of the discriminators and incrementing a qualitative count or otherwise incrementing a quantitative count corresponding to the threshold voltage level associated with one of the discriminators when at least one of: a time-over-threshold (ToT) timer expires; the signal output from one of the discriminators overlaps with a signal output from a discriminator associated with an adjacent pixel; and the signal output from one of the discriminators includes only one monotonic low-to-high transition and one monotonic high-to-low transition.

[0062] Example 13 provides the method of example 12, further comprising incrementing the qualitative count upon expiration of the ToT timer and resetting the ToT timer.

[0063] Example 14 provides a photon-counting computed tomography (PCCT) scanning system comprising: a plurality of discriminators, each discriminator associated with a respective one of a plurality of threshold voltage levels; and a counting circuit configured to detect a signal output from one of the discriminators, increment a quantitative count corresponding to the threshold voltage level associated with one of the discriminators if the detected discriminator output signal satisfies a first condition, and increment a qualitative count if the detected discriminator output signal satisfies at least one second condition.

[0064] Example 15 provides the PCCT scanning system of example 14, wherein the at least one second condition includes expiration of a time over threshold (ToT) timer.

[0065] Example 16 provides the PCCT system of Example 15, further comprising incrementing the qualitative count and resetting the ToT timer upon expiration of the ToT timer.

[0066] Example 17 provides the PCCT system of Example 14, wherein the at least one second condition includes a signal output from one of the discriminators overlapping with a signal output from a discriminator associated with an adjacent pixel.

[0067] Example 18 provides the PCCT system of Example 14, wherein the at least one second condition includes a signal output from one of the discriminators including only one monotonic consecutive low-to-high transition and one monotonic consecutive high-to-low transition.

[0068] Example 19 provides the PCCT system of Example 14, wherein the first condition includes the absence of at least one second condition.

[0069] Example 20 provides the PCCT system of Example 14, wherein the plurality of discriminators includes five discriminators.

[0070] Example 21 provides the PCCT system of Example 14, wherein the plurality of threshold voltage levels includes five threshold voltage levels.

[0071] Example 22 provides the PCCT system of Example 14, wherein each of the discriminators compares a voltage signal input to the discriminator with a threshold voltage level associated with the discriminator.

[0072] Example 23 provides the PCCT system of Example 14, wherein the output of each of the discriminators is driven high when the voltage signal input to the discriminator exceeds a threshold voltage level associated with the discriminator.

[0073] It should be noted that all specifications, dimensions, and relationships (e.g., numbers of elements, operations, steps, etc.) outlined herein are presented for illustrative and instructional purposes only. Such information may be significantly changed without departing from the spirit of the disclosure or the scope of the appended claims. The specifications apply only to one non-limiting example, and therefore, they should be construed as such. In the foregoing description, exemplary embodiments are described with reference to particular component arrangements. Various modifications and changes may be made to such embodiments without departing from the scope of the appended claims. Accordingly, the description and drawings should be regarded in an illustrative sense, and not a restrictive sense.

[0074] It should be noted that in many of the examples provided herein, interactions may be described with reference to two, three, four, or more electrical components. However, this is done for purposes of clarity and example only. It should be understood that systems may be integrated in any suitable manner. According to similar design alternatives, any of the illustrated components, modules, and elements of the figures may be combined into a variety of possible configurations, all of which are clearly within the broad scope of this specification. In some cases, one or more functions of a given set of flows may be simply described by reference to only a limited number of electrical elements. It should be understood that the illustrated electrical circuits and their teachings are readily expandable to accommodate many components and more complex / sophisticated arrangements and configurations. Thus, the provided examples should not limit or inhibit the broad teachings of the electrical circuits as they potentially apply to countless other architectures.

[0075] It should also be noted that, in this specification, references to various features (e.g., elements, structures, modules, components, steps, operations, characteristics, etc.) included in "one embodiment," "an embodiment," "another embodiment," "some embodiments," "various embodiments," "other embodiments," "alternative embodiments," etc., are intended to mean that any such features are included in one or more embodiments of the present disclosure, but may or may not necessarily be combined in the same embodiment.

[0076] It should also be noted that the functions associated with the circuit architecture represent only some of the possible circuit architecture functions that may be performed by or within the system depicted in the figures. Some of these operations may be omitted or removed, as appropriate, or these operations may be significantly modified or changed without departing from the scope of the present disclosure. Additionally, the timing of these operations may be significantly altered. The foregoing operational flow is presented for purposes of example and discussion. Substantial flexibility is provided by the embodiments described herein in that any suitable arrangement, timeline, configuration, and timing mechanism may be provided without departing from the teachings of the present disclosure.

[0077] Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained by those skilled in the art, and it is intended that this disclosure encompass all such changes, substitutions, variations, alterations, and modifications as fall within the scope of the appended claims.

[0078] It should be noted that all optional features of the above devices and systems may also be implemented for the methods or processes described herein, and details in the examples may be used anywhere in one or more embodiments.

[0079] The "means for" in these examples (above) may include, but is not limited to, using any suitable components discussed herein in conjunction with any suitable software, circuitry, hubs, computer code, logic, algorithms, hardware, controllers, interfaces, links, buses, communication paths, etc.

[0080] It should be noted that in the example provided above, and in many other examples provided herein, interactions could be described in terms of two, three, or four network elements. However, this is done for purposes of clarity and example only. In some cases, it may be easier to explain one or more functions of a given set of flows by referencing only a limited number of network elements. It should be understood that the topologies shown and described with reference to the accompanying figures (and their teachings) are readily extensible and can accommodate many components and more complex / sophisticated arrangements and configurations. Thus, the examples provided should not limit or inhibit the broad teachings of the topologies shown, as they potentially apply to countless other architectures.

[0081] It is also important to note that the steps in the foregoing flow diagrams represent only some of the possible signaling scenarios and patterns that may be performed by or within the communications system depicted in the figures. Some of these steps may be omitted or eliminated, or these steps may be significantly modified or altered without departing from the scope of the present disclosure. In addition, some of these operations are described as being performed simultaneously with or in parallel with one or more additional operations. However, the timing of these operations may be significantly altered. The foregoing operational flows are presented for purposes of example and discussion. Substantial flexibility is provided by the communications system depicted in the figures, in that any suitable arrangement, timeline, configuration, and timing mechanism may be provided without departing from the teachings of the present disclosure.

[0082] While the present disclosure has been described in detail with reference to particular arrangements and configurations, these example configurations and arrangements may be varied considerably without departing from the scope of the present disclosure. For example, while the present disclosure has been described with reference to particular communication exchanges, the embodiments described herein may be applicable to other architectures.

[0083] Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained by those skilled in the art, and the present disclosure is intended to include all such changes, substitutions, variations, alterations, and modifications that fall within the scope of the appended claims. In order to assist the United States Patent and Trademark Office (USPTO), and further, any reader of any patent issued on this application, in interpreting the claims appended hereto, Applicant wishes to note that (a) Applicant does not intend any appended claims to invoke 35 U.S.C. § 142, paragraph 6, as they exist on the filing date of this application, unless the terms "means for" or "step for" are specifically used in a particular claim, and (b) nothing in this specification intends to limit the present disclosure in any manner not specifically reflected in the appended claims.

Claims

1. A method for counting charge events in a photon-counting computed tomography (PCCT) scanning system, said method comprising: detecting a signal output from one discriminator of a plurality of discriminators included in the PCCT scanning system, the discriminator being associated with a pixel in the PCCT scanning system, and each discriminator of the plurality of discriminators being associated with a respective one of a plurality of threshold voltage levels; incrementing a quantitative count corresponding to a threshold voltage level associated with the one discriminator in response to the detected signal output satisfying a first condition; incrementing a qualitative count in response to the detected signal output satisfying at least one second condition, the qualitative count defining a number of pile-up charge events, charge-sharing charge events, or a combination thereof; The method, wherein the first condition comprises the absence of the at least one second condition.

2. The method of claim 1 , wherein the at least one second condition comprises expiration of a Time Over Threshold (ToT) timer.

3. Upon expiration of the ToT timer, incrementing the qualitative count; The method of claim 2 , further comprising: resetting the ToT timer.

4. 2. The method of claim 1 , wherein the at least one second condition includes the signal output from the one of the discriminators overlapping with a signal output from a discriminator associated with an adjacent pixel.

5. 2. The method of claim 1 , wherein the at least one second condition includes the signal output from the one of the discriminators including only one monotonic series of low-to-high transitions and only one monotonic series of high-to-low transitions.

6. The method of claim 1 , wherein the plurality of discriminators comprises five discriminators.

7. The method of claim 1 , wherein the plurality of threshold voltage levels comprises five threshold voltage levels.

8. The method of claim 1 , wherein each of the discriminators compares a voltage signal input to the discriminator to the threshold voltage level associated with the discriminator.

9. 9. The method of claim 8, wherein the output of each of the discriminators is driven high when the voltage signal input to the discriminator exceeds the threshold voltage level associated with the discriminator.

10. The method of claim 1 , wherein the spectral information is ignored if the total number of qualitative counts does not reach a certain threshold.

11. 1. A method for counting charge events detected by pixels in a photon-counting computed tomography (PCCT) scanning system comprising a plurality of discriminators, each discriminator associated with a respective one of a plurality of threshold voltage levels, the method comprising: detecting a signal output from one of the discriminators; the expiration of a Time Over Threshold (ToT) timer; the signal output from said one of said discriminators overlaps with the signal output from a discriminator associated with an adjacent pixel; and incrementing a qualitative count when the signal output from said one of said discriminators includes at least one monotonic low-to-high transition and only monotonic high-to-low transitions; otherwise, incrementing a quantification count corresponding to the threshold voltage level associated with the one of the discriminators.

12. Upon expiration of the ToT timer, incrementing the qualitative count; The method of claim 11 , further comprising: resetting the ToT timer.

13. 1. A photon-counting computed tomography (PCCT) scanning system, comprising: a plurality of discriminators; A counting circuit, detecting a signal output from one discriminator of the plurality of discriminators included in the PCCT scanning system, the discriminator being associated with a pixel in the PCCT scanning system, and each discriminator of the plurality of discriminators being associated with a respective one of a plurality of threshold voltage levels; incrementing a quantitative count corresponding to a threshold voltage level associated with the one discriminator in response to the detected signal output satisfying a first condition; and a counting circuit configured to increment a qualitative count in response to the detected signal output satisfying at least one second condition, the qualitative count defining a number of pile-up charge events, charge-sharing charge events, or a combination thereof; the first condition comprises the absence of the at least one second condition; Photon-counting computed tomography (PCCT) scanning system.

14. 14. The PCCT scanning system of claim 13, wherein the at least one second condition comprises expiration of a Time Over Threshold (ToT) timer.

15. Upon expiration of the ToT timer, incrementing the qualitative count; The PCCT scanning system of claim 14, further comprising: resetting the ToT timer.

16. 14. The PCCT scanning system of claim 13, wherein the at least one second condition includes the signal output from the one of the discriminators overlapping with a signal output from a discriminator associated with an adjacent pixel.

17. 14. The PCCT scanning system of claim 13, wherein the at least one second condition includes the signal output from the one of the discriminators including only one monotonic consecutive low-to-high transition and one monotonic consecutive high-to-low transition.

18. 14. The PCCT scanning system of claim 13, wherein each of the discriminators compares a voltage signal input thereto with the threshold voltage level associated with the discriminator, and an output of each of the discriminators is driven high when the voltage signal input thereto exceeds the threshold voltage level associated with the discriminator.

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