Method, apparatus, non-transitory computer-readable medium, and program

Abstract

A method according to an embodiment includes: acquiring calibration data that is generated during a calibration procedure executed at a first time using an X-ray imaging system (10) having a photon counting detector (12), and is stored in a calibration data storage unit (320, 41); acquiring air scan data generated by an air scan executed at a second time after the first time using the X-ray imaging system (10); generating object scan data by executing, on an imaging object (P), an object scan at a third time after the second time using the X-ray imaging system (10); executing detector response correction on the basis of the air scan data and the calibration data using the object scan data; and reconstructing an image of the imaging object (P) on the basis of the detector response correction.

Description

Method, apparatus, non-transitory computer-readable medium and program

[0001] The embodiments disclosed in this specification and the drawings relate to a method, an apparatus, a non-transitory computer-readable medium and a program.

[0002] Computed tomography (CT) systems and methods are commonly used in medical imaging and diagnosis. CT systems typically create projection images through a body being imaged at a series of projection angles. A radiation source, such as an x-ray tube, irradiates the body being imaged with radiation to generate projection images at various angles. From the projection images, an image of the body being imaged can be reconstructed.

[0003] Traditionally, energy-integrating detectors (EIDs) and photon-counting detectors (PCDs) have been used to measure CT projection data. PCDs offer many advantages, including the ability to perform spectral CT. In this case, PCDs resolve incident x-ray counts into spectral components called energy bins, which collectively correspond to the energy spectrum of the x-ray beam. Unlike non-spectral CT, spectral CT generates information attributable to different materials that exhibit different x-ray attenuation as a function of x-ray energy. These differences allow the spectrally resolved projection data to be differentiated into different material components. For example, two material components for material decomposition can be bone and water.

[0004] Although PCDs have a fast response time, at high x-ray flux rates, such as those used in clinical x-ray imaging, multiple x-ray detection events can occur within the detector's time response for a single detector—a phenomenon known as pile-up. Left uncorrected, the pile-up effect can distort the PCD energy response and degrade images reconstructed from the PCD. Correcting for these effects allows spectral CT to offer numerous advantages over conventional CT. Because spectral CT extracts complete tissue characterization information from scanned objects, various clinical applications can benefit from spectral CT technology, including improved material discrimination.

[0005] U.S. Pat. No. 11,249,035 U.S. Pat. No. 1,165,3892 U.S. Pat. No. 1,944,484

[0006] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve the accuracy of correction related to a photon-counting detector. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems.

[0007] An embodiment of a method includes acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit, acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system, performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data, performing detector response correction using the object scan data based on the air scan data and the calibration data, and reconstructing an image of the imaging object based on the detector response correction.

[0008] FIG. 1 illustrates example bin response functions for a photon-counting detector (PCD), according to an embodiment, where each curve shows an example function for an energy bin. FIG. 2A illustrates an air scan performed during a full calibration procedure, according to an embodiment. FIG. 2B illustrates a slab scan performed during a full calibration procedure, according to an embodiment, where different combinations of known materials and thicknesses are used. FIG. 2C illustrates a slab scan performed during a full calibration procedure, according to an embodiment, where different combinations of known materials and thicknesses are used. FIG. 3 illustrates a block diagram of a detector response correction apparatus, according to an embodiment. FIG. 4 illustrates a flowchart of a detector response correction process, according to an embodiment. FIG. 5 illustrates a block diagram of a detector response correction circuit, according to an embodiment. FIG. 6 illustrates a flowchart of a detector response correction procedure, according to an embodiment. FIG. 7 illustrates a block diagram of a detector response correction circuit, according to an embodiment. FIG. 8 illustrates a flowchart of a detector response correction procedure, according to an embodiment. FIG. 9A illustrates an example normalized spectrum of an air scan, according to an embodiment. FIG. 9B illustrates an example normalized spectrum of an attenuation scan, according to an embodiment. FIG. 10 illustrates a scenario in which an effective energy threshold drift is calculated based on normalized air scan spectra, according to an embodiment. 11 is a block diagram of a detector response correction circuit according to an embodiment, FIG. 12 is a flowchart of a detector response correction procedure according to an embodiment, and FIG. 13 is a diagram of an example of a photon-counting computed tomography scanner system according to an embodiment.

[0009] Hereinafter, embodiments of a method, an apparatus, a non-transitory computer-readable medium, and a program will be described in detail with reference to the accompanying drawings.

[0010] The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the disclosure. Of course, these are merely examples and are not intended to be limiting.

[0011] For example, the order of description of different steps described herein is presented for clarity. In general, these steps can be performed in any suitable order. Furthermore, although different features, techniques, configurations, etc. herein may each be discussed in different places in this disclosure, it is contemplated that each of the concepts can be implemented independently of each other or in combination with each other. Thus, the present disclosure can be embodied and contemplated in many different ways.

[0012] Furthermore, as used herein, words such as "a" and "an" generally mean "one or more" unless otherwise specified.

[0013] Figure 1 shows an example of a bin response function for a photon counting detector (PCD). As shown, due to charge sharing, pulse pile-up effects, etc., the bin response function has a very wide distribution beyond the ideal bin energy window of each counter. For example, Patent Documents 1 to 3 propose PCD forward models and calibration methods for both counting and spectral modes. In general, a calibration procedure can be applied based on multiple transmission measurements of various known attenuation path lengths to refine the forward model to match the calibration measurements.

[0014] For example, when the number of energy bins is n, the PCD forward model is given by the following equation (1):

[0015]

[0016] In formula (1), E represents the incident energy. E' represents the measurement energy. N ｂ，ｊ represents the counts measured at a given detector pixel j for energy bin b. ｂ (E′) represents a binning function that models the functionality of a Data Acquisition System (DAS) (or ASIC) that generates digital data indicative of the counts detected by the detector. Φ ｂ (E') is expressed by, for example, the following formula (2).

[0017]

[0018] In addition, in formula (1), T ｂ and T ｂ＋１ are the low and high energy thresholds for energy bin b. ｍｉｎ and E ｍａｘ are the low and high energy thresholds of the incident spectral energy range. ０，ｊ is the incident beam spectrum, which can be expressed in terms of the air flux measured at detector pixel j using an air scan. ０，ｊ (E)D(E,E') is the detector response calibration term ("DR"). The portion of equation (1) shown below in equation (3) is the attenuated sample at detector pixel j.

[0019]

[0020] As mentioned above, a series of slab scans using known materials and thicknesses can be performed to calibrate the parameters of the forward model. ｂ，ｉ，ｊ Let ∑ j = ...

[0021]

[0022] The portion of equation (4) shown in equation (5) below calculates a specific air flux N based on equation (1) for energy bin b, slab i, and detector pixel j. ０，j Under the DR ｊ This is a count calculated using

[0023]

[0024] It should be noted that the above equations are designed for the spectral mode of photon-counting CT. When the photon-counting CT operates in counting mode, the calculations can be shortened as shown in equations (6), (7), and (8) below.

[0025]

[0026]

[0027]

[0028] For example, if the PCD calibration scan data is acquired using slabs "1, . . . , m", the procedure generates a series of measurements using the attenuation samples shown in equation (9) below.

[0029]

[0030] 2A, 2B, and 2C show air and slab scans using different combinations of known materials and thicknesses. In the examples shown in FIGS. 2B-2C, the PCD calibration slab scans utilize two base materials (i.e., K=2), such as solid water / aluminum, or other similar combinations (e.g., iodine, calcium, etc.), to cover the attenuation phase space that will be encountered in the target scan. Each of these data points N ｂ，ｉ，ｊ (In the case of spectrum mode or counting mode, N ｔｏｔ，ｉ，ｊ ) is used to calculate the cost function.

[0031] Typically, the material of the PDC sensor causes detector response drift, which can cause the measured bin counts to deviate from the original value obtained during full calibration for a given attenuation. One possible root cause of this behavior is that the effective energy threshold drifts from its initial value. As a result, in the forward model developed earlier, for slab i, pixel j, and energy bin b, N ｉ，ｊ，ｂ N ｉ，ｊ，ｂ ' and T ｊ，ｂ T ｊ，ｂ However, without a suitable isotope source, it is difficult to quantify these changes in the system. Therefore, when using this modified real forward model, the original calibration table is no longer accurate, leading to errors in the line integral generation of the object scan. If the errors reach a significant magnitude, they will result in visible artifacts in the reconstructed object image.

[0032] Furthermore, sensor materials can experience drift in energy response and changes in detection efficiency due to prolonged exposure to X-rays and environmental variables (e.g., fluctuations in temperature and humidity over time). While the sensor material may still produce acceptable measurements, it will exhibit a shifted response (D(E,E')). Recalibration of the forward model will be necessary to ensure high-quality images.

[0033] Furthermore, given that the response of the PCD may vary, the induced shift in bin count measurements may depend mostly on the measurement spectrum, which is determined by the beam path attenuation and flux (including pile-up effects). Furthermore, material inhomogeneities and local defects are likely to cause pixel-to-pixel variations.

[0034] Therefore, when typical Photon-Counting Computed Tomography (PCCT) systems are used in clinical settings, how to restore system performance, minimize downtime, and maintain image quality is a challenging problem before substantial material improvements can be made.

[0035] This disclosure provides a method and apparatus for estimating effective detector response drift and performing a pixel-by-pixel, energy-bin-by-energy-bin correction, thereby eliminating the need to repeat full calibrations. This approach significantly reduces system downtime while preserving image quality as much as possible.

[0036] To achieve this, the PCD's response drift can be captured or monitored by frequent air scans. Corrections can then be applied to the forward model using data acquired in the most recent air scan, without resorting to a recalibration procedure that involves measurements over the full range of attenuation samples.

[0037] 3 shows a block diagram of a detector response correction apparatus 300 according to an embodiment of the present disclosure. The detector response correction apparatus 300 includes air scan data acquisition circuitry 310, calibration data storage 320, object scan data acquisition circuitry 330, detector response correction circuitry 340, and object image reconstruction circuitry 350.

[0038] The air scan data acquisition circuitry 310 acquires the scan data generated during an air scan and transmits the data to the detector response correction circuitry 340. This air scan may be the most recent of multiple air scans performed on a regular or routine basis using the PCCT scanner, or may be performed when certain criteria are met.

[0039] For example, air scans can be scheduled daily, weekly, or monthly, and can be triggered when significant variations in the PCCT scanner operating conditions (such as environmental temperature) are detected and / or when different scan protocols (including, but not limited to, counting mode and material decomposition mode) are requested.

[0040] The calibration data storage unit 320 stores data generated by a full calibration procedure. A full calibration procedure is a calibration procedure that includes required procedures. For example, in a full calibration procedure, procedures typically required to achieve detector calibration are performed over the required time. A full calibration procedure is also referred to as a pre-calibration procedure. For example, this data can include calibration air scan data generated from air scans performed during the full calibration process and calibration slab scan data obtained from scans performed on multiple slabs during the full calibration. Calibration tables created based on the calibration air scan data and calibration slab scan data, such as those described in Patent Documents 1 and 3, are also stored in the calibration data storage unit 320.

[0041] The calibrated air scan data, calibrated slab scan data, and calibration tables stored in the calibration data storage unit 320 are examples of calibration data. The calibration data storage unit 320 may store all of the calibrated air scan data, calibrated slab scan data, and calibration tables, or may store only a portion of them. For example, in the embodiments of FIGS. 5 and 6 described below, the calibration data storage unit 320 does not need to store the calibrated slab scan data.

[0042] The object scan data acquisition circuitry 330 acquires scan data generated by the PCCT scanner during an object scan of the imaging object and transmits the data to the detector response correction circuitry 340 .

[0043] Detector response correction circuit 340 uses the calibration data read from calibration data storage 320 and the most recent air scan data received from air scan data acquisition circuit 310 to perform detector response correction on the object scan data received from object scan data acquisition circuit 330. The function and structure of detector response correction circuit 340 will be described below with reference to Figures 5-12.

[0044] Based on the corrections performed by detector response correction circuitry 340, object image reconstruction circuitry 350 reconstructs an image of the imaged object.

[0045] 4 shows a flowchart of a detector response correction process 400 according to an embodiment of the present disclosure. In step S410, data generated from a recent air scan is acquired. In step S420, calibration data created during a full calibration procedure is acquired. In step S430, a scan of the imaging object is performed with a PCCT scanner to generate object scan data. Next, in step S440, detector response correction is performed on the generated object scan data using the recent air scan data and the calibration data. Finally, in step S450, an image of the imaging object is reconstructed based on the detector response correction.

[0046] According to embodiments of the present disclosure, air scan correction ratios can be determined for each pixel and energy bin to account for differences in detector response between the original air scan (performed during the full calibration process) and the new air scan (performed after calibration). The correction ratios can then be used to modify the scan data from the object scan, thereby producing adjusted or corrected measurements of the imaged object as if the PCCT detector were still in its original state when the full calibration was performed.

[0047] 5 shows a block diagram of detector response correction circuitry 340 according to an embodiment of the present disclosure. Detector response correction circuitry 340 includes calibration air scan data acquisition circuitry 510, air scan correction ratio calculation circuitry 520, calibration table acquisition circuitry 530, object scan data correction circuitry 540, and line integral sinogram generation circuitry 550.

[0048] The calibration air scan data acquisition circuit 510 retrieves the scan data generated during the calibration air scan from the calibration data storage unit 320 and sends it to the air scan correction ratio calculation circuit 520. The air scan correction ratio calculation circuit 520 also receives the latest air scan data from the air scan data acquisition circuit 310. Based on the original and new air scan data, the air scan correction ratio calculation circuit 520 calculates air scan correction ratios for each pixel and energy bin.

[0049] To isolate other system-related variations, static scan conditions are used for air scans, meaning the mount remains stationary during the scan. For example, air scans can be performed routinely or initiated when certain criteria are met, using the same scan conditions used during the calibration air scan. This allows for accurate capture of detector response drift.

[0050] For pixel j and energy bin b, N ａｉｒ (j, b) represents the counts per integration time originally measured during the calibration air scan, and N ａｉｒLet '(j,b) denote the counts measured during the subsequent air scan. Assuming that the detector response drift is spectrally or flux independent, the air scan correction ratio for a particular pixel and energy bin can be calculated as follows:

[0051]

[0052] The target scan data correction circuit 540 receives the air scan correction ratio calculated from the air scan correction ratio calculation circuit 520 along with the target scan data from the target scan data acquisition circuit 330. Based on the received air scan correction ratio, the target scan data correction circuit 540 can modify or correct the target scan data.

[0053] In this disclosure, target scan data is always collected after both the calibration air scan and the most recent air scan. ｏｂｊ Let '(j,b,k) denote the counts per integration time measured during an object scan at pixel j and energy bin b, where k denotes the scan view index. The corresponding air scan correction ratio R ａｉｒ (j, b) is the target scan data N' ａｉｒ (j, b, k) can be applied as in the following equation (11).

[0054]

[0055] By performing this correction process, the detector response at full calibration is corrected as if it were in its original state, resulting in an adjusted measurement N ｏｂｊ (j, b, k) is derived.

[0056] The calibration table acquisition circuit 530 retrieves the calibration table from the calibration data storage unit 320 and transmits it to the line integral sinogram generation circuit 550. In addition to the calibration table, the line integral sinogram generation circuit 550 receives the adjusted object scan data from the object scan data correction circuit 540. Based on the calibration table, the line integral sinogram generation circuit 550 generates a line integral sinogram using the adjusted object scan data, which is transmitted to the object image reconstruction circuit 350 for image reconstruction.

[0057] 6 shows a flowchart of a detector response correction procedure 600 according to an embodiment of the present disclosure. In step S610, scan data acquired from a latest air scan is received. In step S620, scan data generated from an air scan performed during a full calibration is acquired. In step S630, air scan correction ratios are calculated for each pixel and energy bin based on the received air scan data and the acquired calibration air scan data. In step S640, object scan data generated from an object scan is received. In step S650, the received object scan data is corrected based on the calculated air scan correction ratios. In step S660, a calibration table is acquired. In step S670, a line integral sinogram is generated using the corrected object scan data based on the acquired calibration table.

[0058] In the embodiment shown in Figures 5-6, the air-scan correction ratios are used to adjust the object scan data as if the detector response remained the same as at full calibration. Alternatively, the calibration tables can be modified based on the air-scan correction ratios. For example, the air-scan correction ratios can be used to adjust the slab scan data to simulate slab calibration data generated with the current detector response, thereby generating a new set of detector response calibration tables. These new calibration tables can be used to generate line integral sinograms in place of the initial calibration tables created during full calibration.

[0059] 7 shows a block diagram of detector response correction circuit 340 according to an embodiment of the present disclosure. Detector response correction circuit 340 includes a calibration air scan data acquisition circuit 710, an air scan correction ratio calculation circuit 720, a calibration slab scan data acquisition circuit 730, a calibration table correction circuit 740, and a line integral sinogram generation circuit 750. The functionality of calibration air scan data acquisition circuit 710 and air scan correction ratio calculation circuit 720 is identical to the functionality of the corresponding components of detector response correction circuit 340 of FIG. 3.

[0060] As previously described, instead of using air-scan correction ratios to refine the object scan data, detector response correction can be achieved through calibration table correction. Calibration slab-scan data acquisition circuit 730 acquires calibration slab-scan data from calibration data storage 320 and transmits it to calibration table correction circuit 740. In addition to the calibration slab-scan data, calibration table correction circuit 740 receives calibration air-scan data from calibration air-scan data acquisition circuit 710 and air-scan correction ratios from air-scan correction ratio calculation circuit 720. Based on the air-scan correction ratios, calibration table correction circuit 740 can adjust the received calibration slab-scan data and generate a set of corrected calibration tables based on the adjusted calibration slab-scan data and the received calibration air-scan data. That is, calibration table correction circuit 740 corrects the calibration slab-scan data based on the air-scan correction ratios and generates calibration tables based on the calibration air-scan data and the corrected calibration slab-scan data.

[0061] The line integral sinogram generation circuit 750 then obtains the adjusted calibration table from the calibration table correction circuit 740. Based on the adjusted calibration table, the line integral sinogram generation circuit 750 generates a line integral sinogram using the object scan data received from the object scan data acquisition circuit 330, and the line integral sinogram is sent to the object image reconstruction circuit 350 for image reconstruction.

[0062] For example, considering pixel j and energy bin b, the air scan correction ratio Rａｉｒ (j, b) is the calibration slab scan data N ｓｌａｂ (i, j, b) and adjusted calibration slab scan data N′ ｓｌａｂ (i, j, b) can be derived as in the following equation (12).

[0063]

[0064] Thus, in this embodiment, a new set of calibration tables for the forward model is generated based on the adjusted calibration slab scan data, while the object scan data remains unchanged.

[0065] 8 shows a flowchart of a detector response correction procedure 800 according to an embodiment of the present disclosure. In step S810, latest air scan data is received. In step S820, stored calibration air scan data is acquired. In step S830, air scan correction ratios are calculated for each pixel and each energy bin using the received and acquired calibration air scan data. In step S840, stored calibration slab scan data is acquired. In step S850, a corrected calibration table is generated based on the air scan correction ratios. In step S860, acquired object scan data is received. In step S870, a line integral sinogram is generated using the acquired object scan data based on the corrected calibration table.

[0066] The embodiments shown in Figures 5-6 and 7-8 can maintain consistent detector response, thereby facilitating the generation of corrected object scan line integrals and the reconstruction of high-quality object images. However, neither approach takes into account the spectral differences between air scans and attenuated scans. In contrast, alternative approaches that take such spectral differences into account are described with reference to Figures 9A-9B and 10-12.

[0067] 9A-9B show exemplary normalized spectra for air and attenuation scans according to embodiments of the present disclosure. As can be seen, the main difference is that with attenuation the measured spectrum becomes harder, with an increase in the high energy bin counts compared to the low energy bin counts.

[0068] To account for the spectral dependency in the detector response drift, for example, a weighting mechanism can be applied to account for the spectral differences between the air scan and the attenuation scan. This approach is implemented by adding a calculated air scan correction ratio R ａｉｒ (j, b) to estimate the attenuation scan correction ratio, so that the R is directly applied to the object scan data (or the calibration slab scan data). ａｉｒ Compared with the case where (j, b) is applied, a more accurate correction can be performed.

[0069] More specifically, data acquired from the slab scan during the full calibration procedure is used to calculate the air scan correction ratio R ａｉｒ Based on (j, b), slab-scan correction ratios can be calculated. When used to correct the detection response of an object scan, these slab-scan correction ratios (R ｓｌａｂ (j,b) can provide a reliable approximation of the attenuation scan correction ratio, which is generally valid since the attenuation scan spectrum is fairly stable for most detector pixels.

[0070] Figure 10 shows an example calculation of the effective energy threshold drift using the normalized air scan spectrum shown in Figure 9A. In this scenario, a linear interpolation method is applied to the measured bin counts of two adjacent energy bins to obtain an approximation of the measured spectrum, as shown in Figure 10. If the effective energy threshold drifts, a correction ratio for the attenuated spectrum can be estimated based on the corresponding air scan correction ratio.

[0071] As shown exemplarily in FIG. 10, for a given pixel, the measurement at the highest energy bin b is T ｂThe photons with greater energy are counted. The air scan correction ratio R calculated for this energy bin ａｉｒ (b) is less than 1 (R ａｉｒ (b) If < 1), it indicates that the most recent air scan has more counts in this energy bin, which is probably lower than the corresponding energy threshold T ｂ This is because the price is lower than before. ｂ represents the central energy of energy bin b, and E ｂ－１ Let denote the central energy of energy bin b-1. The air spectrum slope S around this energy region ｂ (air) can be calculated using the calibrated air scan data as follows:

[0072]

[0073] In formula (13), n ｂ (air) and n ｂ－１ (air) is the count normalized by the energy bin width. ｂ (air) and N ｂ－１ (air) is the count measured in two energy bins b and b-1 during the calibration air scan. The rest of the letters in equation (13) are as in equations (14), (15), (16), and (17) below.

[0074]

[0075]

[0076]

[0077]

[0078] Furthermore, the air scan correction ratio R ａｉｒ (b) Using the air scan normalized count drift δn ｂ can be calculated for energy bin b as shown in the following equation (18).

[0079]

[0080] Next, the effective energy threshold drift δT for energy bin b is calculated based on the calculations from Equations (13) and (18). ｂ can be derived as shown in the following equation (19).

[0081]

[0082] S ｂ In a similar manner to the calculation of (air), the attenuation spectral slope S in this energy region is calculated. ｂ (slab) can be calculated using the scan data generated by the slab scan during the calibration procedure as in equation (20) below.

[0083]

[0084] In formula (20), n ｂ (slab) and n ｂ－１ (slab) is the count normalized by the energy bin width. ｂ (slab) and N ｂ－１ (slab) are the counts measured for two energy bins b and b-1 during the calibration slab scan. The rest of the letters in equation (20) are as in equations (21) and (22) below.

[0085]

[0086]

[0087] Effective energy threshold drift δT calculated by equation (19) ｂ , and the attenuation spectral tilt S calculated by equation (20) ｂ (slab) to the attenuation scan count drift δN ｂ (slab) can be derived as in the following equation (23).

[0088]

[0089] Next, the attenuation scan correction ratio R is calculated by taking into account the difference between the air scan and attenuation scan spectra. ｓｌａｂ (b) can be calculated as in the following equation (24).

[0090]

[0091] Once the attenuation scan correction ratio is calculated for a particular pixel and a particular energy bin, the attenuation scan correction ratio can be substituted for the corresponding air scan correction ratio applied in equations (11) or (12) above to perform detector response correction. For example, in equation (12), the air scan correction ratio can be substituted for the attenuation scan correction ratio, and the calibration slab scan data can be corrected based on the attenuation scan correction ratio.

[0092] After accounting for the drift of the estimated high threshold for the selected energy bin measurements, the threshold for the lower energy bin, e.g., T ｂ－１ For example, the calculations of the following equations (25), (26), (27), (28), and (29) can be performed.

[0093]

[0094]

[0095]

[0096]

[0097]

[0098] The discussion so far has used linear interpolation of the measured spectrum. Alternatively, higher order polynomials and additional constraints including two or more adjacent bin counts can be used to fit the function parameters. In such cases, the slope S ｂ can be replaced, for example, by the first derivative of a polynomial function at the corresponding energy threshold.

[0099] 11 shows a block diagram of a detector response correction circuit 340 according to an embodiment of the present disclosure. The detector response correction circuit 340 includes a calibration air and slab scan data acquisition circuit 1112, an air scan correction ratio calculation circuit 1120, an energy threshold drift calculation circuit 1122, an attenuation scan correction ratio calculation circuit 1124, a calibration table acquisition circuit 1130, an object scan data correction circuit 1140, and a line integral sinogram generation circuit 1150.

[0100] The calibration air and slab scan data acquisition circuit 1112 acquires the calibration air scan data and the calibration slab scan data from the calibration data storage unit 320. The air scan correction ratio calculation circuit 1120 receives the calibration air scan data from the calibration air and slab scan data acquisition circuit 1112 and the latest air scan data from the air scan data acquisition circuit 310. Based on both sets of data, the air scan correction ratio calculation circuit 1120 calculates air scan correction ratios for each pixel and each energy bin.

[0101] The energy threshold drift calculation circuit 1122 receives the air scan correction ratios calculated by the air scan correction ratio calculation circuit 1120 and the calibrated air scan data from the calibrated air and slab scan data acquisition circuit 1112. Based on the air scan correction ratios and the calibrated air scan data, the energy threshold drift calculation circuit 1122 calculates the energy threshold drifts and sends them to the attenuation scan correction ratio calculation circuit 1124.

[0102] The attenuation scan correction ratio calculation circuit 1124 calculates an attenuation scan correction ratio corresponding to each air scan correction ratio based on the energy threshold drift received from the energy threshold drift calculation circuit 1122 and the calibrated slab scan data received from the calibrated air and slab scan data acquisition circuit 1112. That is, for each specific air scan correction ratio in the air scan correction ratios calculated by the air scan correction ratio calculation circuit 1120, the energy threshold drift calculation circuit 1122 and the attenuation scan correction ratio calculation circuit 1124 calculate a corresponding attenuation scan correction ratio based on the specific air scan correction ratio, the calibrated air scan data, and the calibrated slab scan data.

[0103] The object scan data correction circuit 1140 receives the object scan data from the object scan data acquisition circuit 330, receives the attenuation scan correction ratio from the attenuation scan correction ratio calculation circuit 1124, and adjusts the object scan data based on the attenuation scan correction ratio.

[0104] The calibration table acquisition circuit 1130 retrieves the calibration table from the calibration data storage unit 320 and sends it to the line integral sinogram generation circuit 1150. In addition to the calibration table, the line integral sinogram generation circuit 1150 receives the adjusted object scan data from the object scan data correction circuit 1140. Based on the calibration table, the line integral sinogram generation circuit 1150 generates a line integral sinogram using the adjusted object scan data, which is then sent to the object image reconstruction circuit 350 for image reconstruction.

[0105] 12 shows a flowchart of a detector response correction procedure 1200 according to an embodiment of the present disclosure. In step S1210, the latest air scan data is received. In step S1220, stored calibration air and slab scan data is obtained. In step S1230, air scan correction ratios are calculated for each pixel and energy bin based on the latest air scan data and the calibration air scan data.

[0106] In step S1240, an energy threshold drift is calculated based on the air scan correction ratio and the calibrated air scan data. In step S1250, an attenuated scan correction ratio is calculated based on the energy threshold drift and the calibrated slab scan data. In step S1260, acquired object scan data is received. In step S1270, the received object scan data is corrected based on the calculated attenuated scan correction ratio. In step S1280, a calibration table is obtained. In step S1290, a line integral sinogram is generated using the corrected object scan data based on the calibration table.

[0107] 7-8, in this embodiment, detector response correction can be performed by modifying the calibration table instead of the object scan data. That is, the object scan data can be left untouched, and the calibration slab scan data can be adjusted based on the attenuation scan correction ratio. A new calibration table for the forward model can then be generated based on the adjusted calibration slab scan data and used to generate the line integral sinogram.

[0108] As described above, the correction ratio calculated using the calibration slab scan data is used during detector response correction for the object scan to account for spectral differences between the air scan and the attenuation scan. Depending on the estimated attenuation path length of the object scan, scan data acquired using a slab with the closest path length can be selected to calculate the slab scan correction ratio. For example, for each view of the object scan data, data acquired from a slab with a path length closest to the attenuation path length of that view can be selected from slab scan data previously collected using multiple slabs during full calibration.

[0109] Furthermore, to reduce the flux dependency in the calculation of the slab scan correction ratio, an appropriate tube current can be selected for the air scan to produce a count rate that matches the count rate of the slab scan, thereby improving the accuracy of the detector response correction and reducing the flux dependency due to pile-up effects.

[0110] Furthermore, since target scans can be performed with various tube currents, the above-described calculation of the correction ratios can also be performed for slab scans performed with multiple different tube currents. Calculating the correction ratios from slab scans using the same tube currents as those used in the target scan can further improve the correction accuracy.

[0111] In connection with the various embodiments described above, one challenge to more effectively using semiconductor-based photodetectors for spectral CT is to perform material decomposition of projection data in a robust and efficient manner. For example, pile-up correction in the detection process may be imperfect, and these imperfections degrade the material components resulting from material decomposition.

[0112] In photon-counting CT systems, semiconductor-based detectors using direct conversion are designed to resolve the energy of individual incident photons and measure multiple energy bin counts for each integration period. However, due to the detection physics of such semiconductor materials (e.g., CdTe / CZT), the detector's energy response is significantly degraded / distorted by charge sharing, k-escape, and scattering effects in the energy accumulation and charge induction process, as well as electronic noise in the associated front-end electronics. As mentioned above, due to the finite signal induction time, pulse pileup also distorts the energy response under high count rate conditions.

[0113] Due to the heterogeneity of the sensor material and the complexity of the integrated detection system, it is difficult to accurately model the detector response of a PCD solely based on physical theory or Monte Carlo simulations using specific modeling of the signal-inducing process, which determines the accuracy of the forward model for each measurement. Furthermore, uncertainties in modeling the incident X-ray tube spectrum introduce additional errors into the forward model. All of these factors ultimately reduce the attenuation line integral accuracy (in counting mode) or material decomposition accuracy (in spectral mode) obtained from the PCD measurement, thereby affecting the quality of the generated spectral image.

[0114] US Patents 5,629,703, 5,729,730, 5,740,760, 5,750,770, 5,760,780, 5,770,790, 5,780,790, 5,79 ...

[0115] Compared with conventional EID scintillators, PCD sensor materials often exhibit high sensitivity to environmental variables such as temperature, humidity, and radiation exposure. As a result, the detector's response typically drifts gradually over time or with use. Without an appropriate correction mechanism, this drift leads to a gradual degradation of image quality, necessitating a full recalibration using multiple slabs. However, a full calibration procedure is typically time-consuming and labor-intensive. Performing such recalibrations frequently can significantly hinder the system's use in a clinical environment.

[0116] Therefore, it is desirable to develop a rapid recalibration or correction approach for detector response in order to maintain the image quality of photon-counting CT systems for as long as possible.

[0117] In contrast, the methods, apparatus, non-transitory computer-readable media, or programs according to the above-described embodiments provide a rapid recalibration or correction approach for detector response, thereby improving the accuracy of the correction.

[0118] The present disclosure relates to detector response correction for use in a photon-counting CT scanner system, the CT scanner system comprising one or more X-ray tubes for emitting X-ray radiation and an array of detector pixels for receiving the X-ray radiation propagating through a field of view (FOV) of the CT scanner system. The detector response correction scheme can be applied to both the photon-counting model and the spectral-forward model.

[0119] The detector response correction approach can be implemented in a photon-counting CT scan system, as will be described later with reference to Fig. 13. The X-ray CT apparatus 1 shown in Fig. 13 includes a gantry 10, a bed 30, and a console 40 that executes processing of a medical imaging processing apparatus. For ease of explanation, Fig. 13 shows multiple gantry 10. The gantry 10 shown in Fig. 13 is an example of an X-ray imaging system having a photon-counting detector.

[0120] In this embodiment, the rotation axis of the rotating frame 13 in a non-inclined state, i.e., the longitudinal direction of the tabletop 33 of the bed 30, is defined as the "Z-axis direction," the axis direction perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the "X-axis direction," and the axis direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the "Y-axis direction."

[0121] For example, the gantry 10 and the couch 30 are installed in a CT examination room, and the console 40 is installed in a control room adjacent to the CT examination room. The console 40 is not necessarily installed in the control room. For example, the console 40 can be installed in the same room as the gantry 10 and the couch 30. In any case, the gantry 10, the couch 30, and the console 40 are connected to each other so that they can communicate with each other via wires or wirelessly.

[0122] The gantry 10 is a scanner configured to perform X-ray CT imaging on a subject (or imaging target) P. The gantry 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge filter 16, a collimator 17, and a data acquisition system (DAS) 18.

[0123] The X-ray tube 11 is a vacuum tube that generates X-rays by emitting thermoelectrons from a cathode (filament) to an anode (target) in response to the application of high voltage and the supply of filament current from the X-ray high voltage generator 14. Specifically, X-rays are generated when the thermoelectrons collide with the target. An example of the X-ray tube 11 is a rotating anode type X-ray tube that generates X-rays by causing a rotating anode to emit thermoelectrons. The X-rays generated by the X-ray tube 11 are shaped into a cone beam by, for example, a collimator 17 and applied to the subject P.

[0124] The X-ray detector 12 detects X-rays that are irradiated by the X-ray tube 11 and have passed through the subject P, and outputs an electrical signal corresponding to the X-ray dose to the DAS 18. The X-ray detector 12 includes, for example, a plurality of X-ray detection element rows, each including a plurality of X-ray detection elements aligned in the channel direction (X-axis direction, i.e., row direction) along an arc centered on the focal point of the X-ray tube 11. The X-ray detector 12 has an array structure in which a plurality of X-ray detection element rows, each including a plurality of X-ray detection elements aligned in the channel direction, are aligned in the segment direction (Z-axis direction, i.e., row direction).

[0125] Specifically, the X-ray detector 12 may be, for example, a direct conversion detector including a semiconductor element that converts incident X-rays into an electrical signal. The X-ray detector 12 is an example of a PCD according to this embodiment and is also referred to as a "PCD 12."

[0126] The rotating frame 13 supports the X-ray generator and the X-ray detector 12 rotatably about a rotation axis. Specifically, the rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 so that the X-ray tube 11 faces the X-ray detector 12, and rotates the X-ray tube 11 and the X-ray detector 12 under the control of a control device 15 (described later). The rotating frame 13 is rotatably supported by a fixed frame (not shown) made of metal such as aluminum. Specifically, the rotating frame 13 is connected to an end of the fixed frame via bearings. The rotating frame 13 receives power from a driver of the control device 15 and rotates at a predetermined angular velocity about the rotation axis Z.

[0127] In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 includes and supports an X-ray high-voltage device 14 and a DAS 18. The rotating frame 13 is housed in a substantially cylindrical housing in which an opening (bore) 19 that forms an imaging space is formed. The opening substantially coincides with the FOV. The central axis of the opening coincides with the rotation axis Z of the rotating frame 13. The detection data generated by the DAS 18 is transmitted to a receiver (not shown) from a transmitter (not shown) disposed in a non-rotating part of the gantry (such as a fixed frame, not shown in FIG. 13 ), for example, and transferred to the console 40.

[0128] The X-ray high voltage device 14 includes a high voltage generator that includes electrical circuits such as a transformer and a rectifier and has the function of generating a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11, and an X-ray controller configured to control the output voltage in accordance with the X-rays irradiated by the X-ray tube 11. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13, which will be described later, or on a fixed frame (not shown) of the gantry 10.

[0129] The control device 15 includes a processing circuit including a central processing unit (CPU) and drivers for motors, drive devices, and the like. The processing circuit includes, as hardware resources, a processor such as a CPU or microprocessor (MPU) and memory such as read-only memory (ROM) or random access memory (RAM). The control device 15 can be implemented using an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other complex programmable logic device (CPLD) or simple programmable logic device (SPLD). The control device 15 controls the X-ray high-voltage generator 14, the DAS 18, and the like in accordance with commands from the console 40. The processor performs the above control by reading and executing programs stored in memory.

[0130] The CPU may execute a computer program including a set of computer-readable instructions that perform the functions described herein, the program being stored in any of the non-transitory electronic memory and / or hard disk drives, CDs, DVDs, flash drives, or other known storage media described above. Further, the computer-readable instructions may be provided as a utility application, a background daemon, or an operating system component, or a combination thereof, and executed in conjunction with a processor and operating system known to those skilled in the art. Furthermore, the CPU may be implemented as multiple processors operating cooperatively in parallel to execute instructions.

[0131] The control device 15 also has a function of controlling the operation of the gantry 10 and the bed 30 in response to input signals from an input interface 43 (described later) attached to the console 40 or the gantry 10. For example, the control device 15 controls the rotation of the rotating frame 13, the tilt of the gantry 10, or the operation of the bed 30 and the tabletop 33 in response to the input signals. The control of tilting the gantry 10 is performed by the control device 15 rotating the rotating frame 13 around an axis parallel to the X-axis direction based on tilt angle information input via the input interface 43 attached to the gantry 10. The control device 15 can be provided in either the gantry 10 or the console 40. The control device 15 can be configured by directly incorporating a program into the circuitry of a processor rather than storing the program in a memory. In this case, the processor executes the above-described control by reading and executing the program embedded in the circuitry.

[0132] The wedge filter 16 is a filter for adjusting the dose of X-rays irradiated from the X-ray tube 11. Specifically, the wedge filter 16 is a filter that transmits X-rays irradiated from the X-ray tube 11 and attenuates the X-rays so that the X-rays irradiated from the X-ray tube 11 to the subject P exhibit a predetermined distribution. For example, the wedge filter 16 (or bowtie filter) is a filter obtained by processing aluminum to have a predetermined target angle and a predetermined thickness.

[0133] The collimator 17 is a lead plate or the like for narrowing the application range of the X-rays transmitted through the wedge filter 16, and includes slits formed by combining lead plates or the like. The collimator 17 is sometimes called an "X-ray aperture."

[0134] The DAS 18 generates digital data (also called "detection data") indicating the count of X-rays detected by the X-ray detector 12 for each of a plurality of energy bands (also called "energy bins" or simply "bins"). The detection data is a set of count data identified by the channel number and row number of the X-ray detection element that generated the data, the view number indicating the acquired view (also called the projection angle), and the energy bin number. The DAS 18 is realized, for example, by an application specific integrated circuit (ASIC) that implements circuit elements capable of generating detection data. The detection data is transferred to the console 40.

[0135] The bed 30 is a device for moving the subject P while placing the subject P thereon for scanning, and includes a base 31, a bed driving device 32, a top board 33, and a support frame .

[0136] The base 31 is a housing that supports the support frame 34 so that the support frame 34 can move in the vertical direction.

[0137] The bed driving device 32 is a motor or driving device that moves the tabletop 33, on which the subject P is placed, in the longitudinal direction of the tabletop 33. The bed driving device 32 moves the tabletop 33 under control of the console 40 or the control device 15. For example, the bed driving device 32 moves the tabletop 33 in a direction perpendicular to the subject P so that the body axis of the subject P placed on the tabletop 33 coincides with the central axis of the bore of the rotating frame 13. The bed driving device 32 can also move the tabletop 33 in the body axis direction of the subject P in accordance with X-ray CT imaging performed using the gantry 10. The bed driving device 32 generates electricity by rotating at a rotational speed that corresponds to the duty ratio of a drive signal from the control device 15. The bed driving device 32 is realized by a motor such as a direct drive motor or a servo motor.

[0138] The tabletop 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. The bed driving device 32 can move not only the tabletop 33 but also the support frame 34 in the longitudinal direction of the tabletop 33.

[0139] The console 40 includes a memory 41, a display 42, an input interface 43, and a processing circuit 44. Data communication between the memory 41, the display 42, the input interface 43, and the processing circuit 44 is performed via a bus. Although the console 40 is described as being separate from the gantry 10, the gantry 10 may include the console 40 or some of the components of the console 40.

[0140] Console 40 is an example of an apparatus for performing a method including detector response correction. For example, console 40 includes processing circuitry 44 that acquires calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having X-ray detector 12 and stored in memory 41, acquires air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system, performs an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data, performs detector response correction using the object scan data based on the air scan data and the calibration data, and reconstructs an image of the imaging object based on the detector response correction.

[0141] The memory 41 is a storage device such as a hard disk drive (HDD), a solid state drive (SSD), or an integrated circuit storage device, and stores various types of information. The memory 41 stores, for example, projection data and reconstructed image data. The memory 41 is not limited to an HDD, an SSD, or the like, and may be, for example, a portable storage medium such as a CD, a DVD, or a flash memory, or a driver that reads and writes various types of information from and to a semiconductor memory such as a random access memory (RAM). The storage area of ​​the memory 41 may be provided within the X-ray CT apparatus 1 or may be provided in an external storage device connected via a network. For example, the memory 41 stores data of CT images or display images. The memory 41 also stores a control program according to this embodiment.

[0142] The memory 41 is an example of a calibration data storage unit, and stores, for example, calibration data such as calibration air scan data, calibration slab scan data, and a calibration table.

[0143] The display 42 displays various types of information. For example, the display 42 outputs medical images (CT images) generated by the processing circuitry 44 and a graphical user interface (GUI) for receiving various operations from the operator. The display 42 may be, for example, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OELD), a plasma display, or any other suitable display. The display 42 may be provided on the gantry 10. The display 42 may be a desktop type or may be configured as a tablet terminal capable of wireless communication with the console 40.

[0144] The input interface 43 accepts various input operations from the operator, converts the accepted input operations into electrical signals, and outputs the electrical signals to the processing circuitry 44. For example, the input interface 43 accepts from the operator acquisition conditions for acquiring projection data, reconstruction conditions for reconstructing CT images, image processing conditions for generating post-processed images from CT images, and the like. The input interface 43 may be, for example, a mouse, keyboard, trackball, switch, button, joystick, touchpad, or touch panel display, as appropriate. In this embodiment, the input interface 43 does not necessarily include physical operating components such as a mouse, keyboard, trackball, switch, button, joystick, touchpad, or touch panel display. For example, the input interface 43 may also include an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device provided separately from the apparatus and outputs the electrical signals to the processing circuitry 44. The input interface 43 may be provided on the gantry 10. The input interface 43 may be configured as a tablet terminal capable of wireless communication with the console 40.

[0145] The processing circuitry 44 controls the overall operation of the X-ray CT apparatus 1 in response to electrical signals of input operations output from the input interface 43. For example, the processing circuitry 44 includes, as hardware resources, a processor such as a CPU, an MPU, or a graphics processing unit (GPU), and memory such as ROM or RAM. The processing circuitry 44 executes a system control function 441, a preprocessing function 442, a reconstruction function 443, and a display control function 444 by using the processor to execute programs loaded into the memory. Each of the functions (the system control function 441, the preprocessing function 442, the reconstruction function 443, and the display control function 444) is not necessarily realized by a single processing circuit. A processing circuit can be configured by combining multiple independent processors, and the processors can execute their respective programs to realize the functions.

[0146] The system control function 441 controls each function of the processing circuitry 44 based on input operations received from the operator via the input interface 43. Specifically, the system control function 441 reads out a control program stored in the memory 41, loads it into the memory in the processing circuitry 44, and controls each part of the X-ray CT apparatus 1 in accordance with the loaded control program. For example, the processing circuitry 44 executes each function of the processing circuitry 44 based on input operations received from the operator via the input interface 43. For example, the system control function 441 acquires a two-dimensional positioning image of the subject P and determines the scan range, imaging conditions, etc. The positioning image is also sometimes called a "scanogram" or a "scout image."

[0147] The pre-processing function 442 generates acquired data by performing pre-processing on the detection data output from the DAS 18, such as logarithmic conversion, offset correction, inter-channel sensitivity correction, beam hardening correction, and correction for detector calibration, detector nonlinearity, polarity effect, noise balance, and material decomposition. The data before pre-processing (detection data) and the data after pre-processing may be collectively referred to as "projection data." The pre-processing function 442 is an example of a pre-processor.

[0148] The reconstruction function 443 generates CT image data by performing reconstruction processing using a filtered back projection method, an iterative reconstruction method, a stochastic image reconstruction method, or the like on the projection data generated by the preprocessing function 442. The reconstruction function 443 is an example of a reconstruction processor. Image filtering, smoothing, volume rendering, or image subtraction processing can be applied to the CT image data as needed. The display control function 444 converts the CT image data generated by the reconstruction function 443 into tomographic image data of a predetermined cross section, i.e., three-dimensional image data using a known method, based on an input operation received from the operator via the input interface 43. The three-dimensional image data can be generated directly by the reconstruction function 443. The display control function 444 is an example of a display control device.

[0149] The reconstruction function 443 can also perform detector response correction according to the embodiment. For example, the reconstruction function 443 acquires calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having an X-ray detector 12 and stored in the memory 41. The reconstruction function 443 also acquires air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system. The reconstruction function 443 also generates object scan data by performing an object scan on the imaging object at a third time after the second time using the X-ray imaging system. The reconstruction function 443 also performs detector response correction based on the air scan data and the calibration data using the object scan data. The reconstruction function 443 then reconstructs an image of the imaging object based on the detector response correction.

[0150] In one embodiment, the X-ray tube 11 is a single source emitting a wide spectrum of X-ray energies, and the PCD 12 can use semiconductor-based direct X-ray radiation detectors, such as cadmium telluride (CdTe), cadmium zinc telluride (CZT), silicon (Si), mercury iodide (HgI), and gallium arsenide (GaAs). As mentioned above, semiconductor-based direct X-ray detectors generally have a much faster time response than indirect detectors, such as scintillator detectors. While the fast time response of direct detectors allows for the resolution of individual X-ray detection events, some pileup of detection events may occur at high X-ray fluxes typical of clinical X-ray applications. The energy of the detected X-rays is proportional to the signal generated by the direct detector, and the detection events can be organized into energy bins to obtain spectrally resolved X-ray data for spectral CT.

[0151] Numerous modifications and variations of the embodiments presented herein are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the application may be practiced otherwise than as specifically described herein. The invention is not limited to the examples just described. In particular, features of the illustrated examples may be combined with one another in variations not shown.

[0152] The components of each device according to the above-described embodiments are conceptual and functionally independent, and are not necessarily physically configured as shown in the drawings. In other words, the specific form of distribution and integration of each device is not limited to that shown in the drawings, and all or part of the devices can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc. Furthermore, all or any part of the processing functions performed by each device can be realized by a CPU and a program analyzed and executed by the CPU, or can be realized as hardware using wired logic.

[0153] The method described in the above embodiment can be realized by executing a prepared program on a computer such as a personal computer or a workstation. This program can be distributed via a network such as the Internet. This program can also be recorded on a non-transitory computer-readable recording medium such as a hard disk, flexible disk (FD), CD-ROM, MO, or DVD, and executed by being read from the recording medium by a computer.

[0154] With respect to the above embodiment, the following supplementary note is disclosed as an aspect and optional feature of the invention: (Supplementary note 1) A method including: acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit, acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system, performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data, performing detector response correction based on the air scan data and the calibration data using the object scan data, and reconstructing an image of the imaging object based on the detector response correction. (Supplementary Note 2) The method may further include acquiring calibration air scan data generated by a calibration air scan performed during the calibration procedure and stored in the calibration data storage unit, and a calibration table stored in the calibration data storage unit; calculating air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the calibration air scan data and the air scan data; correcting the object scan data based on the air scan correction ratios; performing the detector response correction by generating a line integral sinogram using the corrected object scan data based on the calibration table; and reconstructing the image of the imaging object based on the generated line integral sinogram.(Supplementary Note 3) The method may include acquiring calibrated air scan data generated by a calibrated air scan performed during the calibration procedure and stored in the calibration data storage unit, and calibrated slab scan data generated by a calibrated slab scan performed during the calibration procedure and stored in the calibration data storage unit, calculating air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the calibrated air scan data and the air scan data, correcting the calibrated slab scan data based on the air scan correction ratios, generating a calibration table based on the calibrated air scan data and the corrected calibrated slab scan data, performing the detector response correction by generating a line integral sinogram using the object scan data based on the calibration table, and reconstructing the image of the imaging object based on the generated line integral sinogram. (Supplementary Note 4) The method may include acquiring calibrated air scan data generated by a calibrated air scan performed during the calibration procedure and stored in the calibration data storage unit, calibrated slab scan data generated by a calibrated slab scan performed during the calibration procedure and stored in the calibration data storage unit, and a calibration table stored in the calibration data storage unit; calculating air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the calibrated air scan data and the air scan data; calculating a corresponding attenuated scan correction ratio for each specific air scan correction ratio in the air scan correction ratios based on the specific air scan correction ratio, the calibrated air scan data, and the calibrated slab scan data; correcting the object scan data based on the attenuated scan correction ratio; performing the detector response correction by generating a line integral sinogram using the corrected object scan data based on the calibration table; and reconstructing the image of the imaging object based on the generated line integral sinogram.(Supplementary Note 5) For each of the specific air scan correction ratios, an energy bin threshold drift of the energy bin corresponding to the specific air scan correction ratio may be calculated based on linear interpolation or a high-order polynomial function of the calibration air scan data associated with the energy bin and adjacent energy bins, and the attenuation scan correction ratio may be calculated based on the energy bin threshold drift and the calibration slab scan data. (Supplementary Note 6) Scan data generated by a calibration slab scan performed on a specific slab having an attenuation path length closest to the attenuation path length of the imaging target may be acquired as the calibration slab scan data, among scan data generated by multiple calibration slab scans performed on multiple slabs having different attenuation path lengths. (Supplementary Note 7) A tube current may be applied during the calibration air scan so that a difference between a first detector counting rate occurring during the calibration air scan and a second detector counting rate occurring during the calibration slab scan is equal to or less than a predefined threshold, and a tube current applied during the air scan may be set so that a difference between a third detector counting rate occurring during the air scan and the second detector counting rate occurring during the calibration slab scan is equal to or less than the predefined threshold. (Supplementary Note 8) Scan data generated by a calibration slab scan having a specific tube current closest to the tube current applied in the target scan may be acquired as the calibration slab scan data from among scan data generated by a plurality of calibration slab scans performed on slabs to which a plurality of different tube currents are applied.(Supplementary Note 9) The method may include acquiring calibrated air scan data generated by a calibrated air scan performed during the calibration procedure and stored in the calibration data storage unit, and calibrated slab scan data generated by a calibrated slab scan performed during the calibration procedure and stored in the calibration data storage unit, calculating air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the calibrated air scan data and the air scan data, calculating a corresponding attenuation scan correction ratio for each specific air scan correction ratio in the air scan correction ratios based on the specific air scan correction ratio, the calibrated air scan data, and the calibrated slab scan data, correcting the calibrated slab scan data based on the attenuation scan correction ratio, generating a calibration table based on the calibrated air scan data and the corrected calibrated slab scan data, performing the detector response correction by generating a line integral sinogram using the object scan data based on the calibration table, and reconstructing the image of the imaging object based on the generated line integral sinogram. (Supplementary Note 10) The air scan data generated by the air scan performed when a predefined criterion is met may be obtained, and the predefined criterion may be at least one of: a predefined period of time has elapsed since the calibration procedure; a difference between the conditions under which the X-ray imaging system operates and the conditions under which the calibration procedure is performed is greater than or equal to a predefined threshold; and a scan protocol applied using the X-ray imaging system is different from a scan protocol applied when the calibration procedure is performed.(Supplementary Note 11) An apparatus comprising: an X-ray imaging system having a photon-counting detector; acquiring calibration data generated during a calibration procedure performed at a first time and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction. (Supplementary Note 12) A non-transitory computer-readable medium having stored therein instructions, which when executed by one or more processors, cause the one or more processors to perform a method including detector response correction, the method including: acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction.(Supplementary Note 13) A program that causes a computer to perform each of the following processes: acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; generating object scan data by performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction.(Supplementary Note 14) A method for performing detector response correction in an X-ray imaging system having a photon-counting detector, the method comprising: acquiring calibration data stored in a calibration data storage unit, the calibration data being generated during a calibration procedure performed using the X-ray imaging system at a first time; acquiring air scan data generated by an air scan performed using the X-ray imaging system at a second time, the second time being after the first time; performing an object scan on an imaging object using the X-ray imaging system at a third time to generate object scan data, the third time being after the second time; performing detector response correction using the generated object scan data based on the acquired air scan data and the acquired calibration data; and reconstructing an image of the imaging object based on the performed detector response correction. (Supplementary Note 15) The acquiring step may further include acquiring calibration air scan data and a calibration table stored in the calibration data storage unit, the calibration air scan data being generated by a calibration air scan performed during the calibration procedure; the performing step may further include: calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins on a pixel-by-pixel, energy bin-by-energy bin basis based on the acquired calibration air scan data and the acquired air scan data; correcting the generated object scan data based on the calculated air scan correction ratios; and using the corrected object scan data to generate a line integral sinogram based on the acquired calibration table; and the reconstructing step may further include reconstructing the image of the imaging object based on the generated line integral sinogram.(Supplementary Note 16) The acquiring step may further include acquiring calibration air scan data and calibration slab scan data stored in the calibration data storage unit, wherein the calibration air scan data is generated by a calibration air scan performed during the calibration procedure, and the calibration slab scan data is generated by a calibration slab scan performed during the calibration procedure; the performing step may further include: calculating air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the acquired calibration air scan data and the acquired air scan data; correcting the acquired calibration slab scan data based on the calculated air scan correction ratios; generating a calibration table based on the acquired calibration air scan data and the corrected calibration slab scan data; and using the generated object scan data to generate a line integral sinogram based on the generated calibration table; and the reconstructing step may further include reconstructing the image of the imaging object based on the generated line integral sinogram.(Supplementary Note 17) The acquiring step further includes acquiring calibration air scan data, calibration slab scan data, and a calibration table stored in the calibration data storage unit, wherein the calibration air scan data is generated by a calibration air scan performed during the calibration procedure, and the calibration slab scan data is generated by a calibration slab scan performed during the calibration procedure; and the performing step further includes: calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins on a pixel-by-pixel and energy bin-by-energy bin basis based on the acquired calibration air scan data and the acquired air scan data; for each specific air scan correction ratio of the calculated air scan correction ratios, calculating a corresponding attenuation scan correction ratio based on the specific air scan correction ratio, the acquired calibration air scan data, and the acquired calibration slab scan data; correcting the generated object scan data based on the calculated attenuation scan correction ratio; and using the corrected object scan data to generate a line integral sinogram based on the acquired calibration table. The reconstructing step may further include reconstructing the image of the imaging object based on the generated line integral sinogram. (Supplementary Note 18) The calculating step may further include: for each particular air scan correction ratio of the calculated air scan correction ratios, calculating an energy bin threshold drift for the energy bin corresponding to the particular air scan correction ratio based on a linear interpolation or a higher-order polynomial function of the acquired calibration air scan data associated with the energy bin and an adjacent energy bin; and calculating the corresponding attenuated scan correction ratio based on the calculated energy bin threshold drift and the acquired calibration slab scan data.(Supplementary Note 19) The acquiring step may further include selecting, as the acquired calibration slab scan data, calibration slab scan data generated by a calibration slab scan performed on a specific slab having an attenuation path length closest to an attenuation path length of the imaging target, from among calibration slab scan data generated by a plurality of calibration slab scans performed on a plurality of slabs having different attenuation path lengths. (Supplementary Note 20) A tube current is applied during the calibration air scan such that a difference between a detector counting rate generated during the calibration air scan and a detector counting rate of the calibration slab scan is equal to or less than a predefined threshold, and the acquiring step may further include setting a tube current applied during the air scan such that a difference between a detector counting rate generated during the air scan and the detector counting rate of the calibration slab scan is equal to or less than the predefined threshold. (Supplementary Note 21) The acquiring step may further include selecting, from among calibration slab scan data generated by a plurality of calibration slab scans performed on a slab to which a plurality of different tube currents are applied, calibration slab scan data generated by a calibration slab scan having a specific tube current closest to the tube current applied in the target scan as the acquired calibration slab scan data.(Supplementary Note 22) The acquiring step further includes acquiring calibrated air scan data and calibrated slab scan data stored in the calibration data storage unit, wherein the calibrated air scan data is generated by a calibrated air scan performed during the calibration procedure, and the calibrated slab scan data is generated by a calibrated slab scan performed during the calibration procedure; and the performing detector response correction step includes: calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins based on the acquired calibrated air scan data and the acquired air scan data; for each specific air scan correction ratio of the calculated air scan correction ratios, calculating a corresponding attenuation scan correction ratio based on the specific air scan correction ratio, the acquired calibrated air scan data, and the acquired calibrated slab scan data; correcting the acquired calibrated slab scan data based on the calculated air scan correction ratios; and generating a calibration table based on the acquired calibrated air scan data and the corrected calibrated slab scan data. and using the generated object scan data to generate a line integral sinogram based on the generated calibration table, and the reconstructing step may further include reconstructing the image of the imaging object based on the generated line integral sinogram. (Supplementary Note 23) The acquiring step may further include acquiring the air scan data generated by the air scan performed when a predefined criterion is satisfied, and the predefined criterion may be satisfied when a predefined period of time has elapsed since the calibration procedure, when a difference between a condition under which the X-ray imaging system operates and the condition under which the calibration procedure is performed is equal to or greater than a predefined threshold, and / or when a scan protocol applied using the X-ray imaging system differs from a scan protocol applied when the calibration procedure is performed.(Supplementary Note 24) An apparatus for performing detector response correction in an X-ray imaging system having a photon-counting detector, the apparatus comprising: a processing circuit configured to: acquire calibration data stored in a calibration data storage unit, the calibration data being generated during a calibration procedure performed using the X-ray imaging system at a first time; acquire air scan data generated by an air scan performed using the X-ray imaging system at a second time, the second time being after the first time; perform an object scan on an imaging object at a third time using the X-ray imaging system to generate object scan data, the third time being after the second time; perform detector response correction using the generated object scan data based on the acquired air scan data and the acquired calibration data; and reconstruct an image of the imaging object based on the performed detector response correction. (Supplementary Note 25) The processing circuitry may be further configured to: retrieve calibration air scan data and a calibration table stored in the calibration data storage unit, the calibration air scan data being generated by a calibration air scan performed during the calibration procedure; calculate air scan correction ratios for a plurality of pixels and a plurality of energy bins on a pixel-by-pixel, energy bin-by-energy bin basis based on the acquired calibration air scan data and the acquired air scan data; correct the generated object scan data based on the calculated air scan correction ratios; use the corrected object scan data to generate a line integral sinogram based on the acquired calibration table; and reconstruct the image of the imaging object based on the generated line integral sinogram.(Supplementary Note 26) The processing circuitry may be further configured to: acquire calibration air scan data and calibration slab scan data stored in the calibration data storage unit, the calibration air scan data being generated by a calibration air scan performed during the calibration procedure, and the calibration slab scan data being generated by a calibration slab scan performed during the calibration procedure; calculate air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the acquired calibration air scan data and the acquired air scan data; correct the acquired calibration slab scan data based on the calculated air scan correction ratios; generate a calibration table based on the acquired calibration air scan data and the corrected calibration slab scan data; use the generated object scan data to generate a line integral sinogram based on the generated calibration table; and reconstruct the image of the imaging object based on the generated line integral sinogram.(Supplementary Note 27) The processing circuitry may be further configured to: acquire calibration air scan data, calibration slab scan data, and a calibration table stored in the calibration data storage unit, the calibration air scan data being generated by a calibration air scan performed during the calibration procedure, and the calibration slab scan data being generated by a calibration slab scan performed during the calibration procedure; calculate air scan correction ratios for each pixel and each energy bin for a plurality of pixels and a plurality of energy bins based on the acquired calibration air scan data and the acquired air scan data; for each particular one of the calculated air scan correction ratios, calculate a corresponding attenuation scan correction ratio based on the particular air scan correction ratio, the acquired calibration air scan data, and the acquired calibration slab scan data; correct the generated object scan data based on the calculated attenuation scan correction ratio; use the corrected object scan data to generate a line integral sinogram based on the acquired calibration table; and reconstruct the image of the imaging object based on the generated line integral sinogram. (Supplementary Note 28) The processing circuitry may be further configured to: calculate, for each particular air scan correction ratio of the calculated air scan correction ratios, an energy bin threshold drift for the energy bin corresponding to the particular air scan correction ratio based on a linear interpolation or a higher order polynomial function of the acquired calibration air scan data associated with the energy bin and adjacent energy bins; and calculate the corresponding attenuation scan correction ratio based on the calculated energy bin threshold drift and the acquired calibration slab scan data.(Supplementary Note 29) The processing circuit may be further configured to: select, as the acquired calibration slab scan data, calibration slab scan data generated by a calibration slab scan performed on a specific slab having an attenuation path length closest to an attenuation path length of the imaging target, from among calibration slab scan data generated by a plurality of calibration slab scans performed on a plurality of slabs having different attenuation path lengths. (Supplementary Note 30) A tube current is applied during the calibration air scan such that a difference between a detector counting rate generated during the calibration air scan and a detector counting rate of the calibration slab scan is equal to or less than a predefined threshold; and the processing circuit may be further configured to set a tube current applied during the air scan such that a difference between a detector counting rate generated during the air scan and the detector counting rate of the calibration slab scan is equal to or less than the predefined threshold. (Supplementary Note 31) The processing circuit may be further configured to select, as the acquired calibration slab scan data, calibration slab scan data generated by a calibration slab scan having a specific tube current closest to the tube current applied in the target scan, from among calibration slab scan data generated by a plurality of calibration slab scans performed on slabs to which a plurality of different tube currents were applied.(Supplementary Note 32) The processing circuitry: acquires calibrated air scan data and calibrated slab scan data stored in the calibration data storage unit, the calibrated air scan data being generated by calibrated air scans performed during the calibration procedure, and the calibrated slab scan data being generated by calibrated slab scans performed during the calibration procedure; calculates air scan correction ratios for a plurality of pixels and a plurality of energy bins based on the acquired calibrated air scan data and the acquired air scan data; for each particular air scan correction ratio of the calculated air scan correction ratios, calculates a corresponding attenuation scan correction ratio based on the particular air scan correction ratio, the acquired calibrated air scan data, and the acquired calibrated slab scan data; corrects the acquired calibrated slab scan data based on the calculated air scan correction ratio; generates a calibration table based on the acquired calibrated air scan data and the corrected calibrated slab scan data; and uses the generated object scan data to generate a line integral sinogram based on the generated calibration table. The imaging device may be further configured to reconstruct the image of the imaging object based on the generated line integral sinogram.33. A non-transitory computer-readable medium having stored thereon instructions that, when executed by one or more processors, cause the one or more processors to perform a method for performing detector response correction in an X-ray imaging system having a photon-counting detector, the method comprising: acquiring calibration data stored in a calibration data storage unit, the calibration data generated during a calibration procedure performed using the X-ray imaging system at a first time; acquiring air scan data generated by an air scan performed using the X-ray imaging system at a second time, the second time being after the first time; performing an object scan on an imaging object at a third time using the X-ray imaging system to generate object scan data, the third time being after the second time; performing detector response correction using the generated object scan data based on the acquired air scan data and the acquired calibration data; and reconstructing an image of the imaging object based on the performed detector response correction.

[0155] According to at least one of the embodiments described above, the accuracy of correction relating to the photon-counting detector can be improved.

[0156] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims.

Claims

1. A method comprising: acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction.

2. The method of claim 1, further comprising: acquiring calibration air scan data generated by a calibration air scan performed during the calibration procedure and stored in the calibration data storage unit; and a calibration table stored in the calibration data storage unit; calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins based on the calibration air scan data and the air scan data, for each pixel and each energy bin; correcting the object scan data based on the air scan correction ratios; performing the detector response correction by generating a line integral sinogram using the corrected object scan data based on the calibration table; and reconstructing the image of the imaging object based on the generated line integral sinogram.

3. The method of claim 1, further comprising: acquiring calibrated air scan data generated by a calibrated air scan performed during the calibration procedure and stored in the calibration data storage unit, and calibrated slab scan data generated by a calibrated slab scan performed during the calibration procedure and stored in the calibration data storage unit; calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins based on the calibrated air scan data and the air scan data; correcting the calibrated slab scan data based on the air scan correction ratios; generating a calibration table based on the calibrated air scan data and the corrected calibrated slab scan data; performing the detector response correction by generating a line integral sinogram using the object scan data based on the calibration table; and reconstructing the image of the imaged object based on the generated line integral sinogram.

4. The method of claim 1, further comprising: acquiring calibrated air scan data generated by a calibrated air scan performed during the calibration procedure and stored in the calibration data storage unit, calibrated slab scan data generated by a calibrated slab scan performed during the calibration procedure and stored in the calibration data storage unit, and a calibration table stored in the calibration data storage unit; calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins based on the calibrated air scan data and the air scan data; calculating a corresponding attenuation scan correction ratio for each specific air scan correction ratio in the air scan correction ratios based on the specific air scan correction ratio, the calibrated air scan data, and the calibrated slab scan data; correcting the object scan data based on the attenuation scan correction ratio; performing the detector response correction by generating a line integral sinogram using the corrected object scan data based on the calibration table; and reconstructing the image of the imaged object based on the generated line integral sinogram.

5. The method of claim 4, further comprising: calculating, for each of the specific air scan correction ratios, an energy bin threshold drift for the energy bin corresponding to the specific air scan correction ratio based on a linear interpolation or a higher order polynomial function of the calibration air scan data associated with the energy bin and adjacent energy bins; and calculating the attenuation scan correction ratio based on the energy bin threshold drift and the calibration slab scan data.

6. The method of claim 4, wherein scan data generated by a calibration slab scan performed on a specific slab having an attenuation path length closest to the attenuation path length of the imaging object is acquired as the calibration slab scan data from among scan data generated by multiple calibration slab scans performed on multiple slabs having different attenuation path lengths.

7. The method of claim 4, wherein a tube current is applied during the calibration air scan such that a difference between a first detector counting rate occurring during the calibration air scan and a second detector counting rate of the calibration slab scan is less than or equal to a predefined threshold, and wherein the tube current applied during the air scan is set such that a difference between a third detector counting rate occurring during the air scan and the second detector counting rate of the calibration slab scan is less than or equal to the predefined threshold.

8. The method of claim 4, wherein scan data generated by a calibration slab scan having a specific tube current closest to the tube current applied in the target scan is acquired as the calibration slab scan data from among scan data generated by a plurality of calibration slab scans performed on a slab to which a plurality of different tube currents are applied.

9. The method of claim 1, further comprising: acquiring calibrated air scan data generated by calibrated air scans performed during the calibration procedure and stored in the calibration data storage unit, and calibrated slab scan data generated by calibrated slab scans performed during the calibration procedure and stored in the calibration data storage unit; calculating air scan correction ratios for a plurality of pixels and a plurality of energy bins based on the calibrated air scan data and the air scan data; calculating a corresponding attenuation scan correction ratio for each specific air scan correction ratio in the air scan correction ratios based on the specific air scan correction ratio, the calibrated air scan data, and the calibrated slab scan data; correcting the calibrated slab scan data based on the attenuation scan correction ratio; generating a calibration table based on the calibrated air scan data and the corrected calibrated slab scan data; performing the detector response correction by generating a line integral sinogram using the object scan data based on the calibration table; and reconstructing the image of the imaged object based on the generated line integral sinogram.

10. The method of claim 1, further comprising acquiring the air scan data generated by the air scan performed when predefined criteria are met, the predefined criteria being at least one of: a predefined period of time has elapsed since the calibration procedure; a difference between the conditions under which the X-ray imaging system operates and the conditions under which the calibration procedure is performed is greater than or equal to a predefined threshold; and a scan protocol applied using the X-ray imaging system is different from the scan protocol applied when the calibration procedure is performed.

11. An apparatus comprising: processing circuitry for acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction.

12. A non-transitory computer-readable medium having stored thereon instructions that, when executed by one or more processors, cause the one or more processors to perform a method including detector response correction, the method including: acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system to generate object scan data; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction.

13. A program causing a computer to perform the following processes: acquiring calibration data generated during a calibration procedure performed at a first time using an X-ray imaging system having a photon-counting detector and stored in a calibration data storage unit; acquiring air scan data generated by an air scan performed at a second time after the first time using the X-ray imaging system; generating object scan data by performing an object scan on an imaging object at a third time after the second time using the X-ray imaging system; performing detector response correction using the object scan data based on the air scan data and the calibration data; and reconstructing an image of the imaging object based on the detector response correction.

Images