Photon counting radiodiagnostic apparatus, method, and program

Abstract

To reduce a data amount while maintaining image quality.SOLUTION: Provided is a photon counting radiodiagnostic apparatus includes: a photon counting detector having a plurality of detector pixels arranged in a channel direction and a segment direction; and a processing circuit. The processing circuit processes first data detected at a first detector pixel in the plurality of detector pixels with a first energy bin setting and processes second data detected at a second detector pixel in the plurality of detector pixels with a second energy bin setting having a greater number of energy bins than the first energy bin setting.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a photon counting type radiological diagnostic apparatus, method, and program.

[0002] The present disclosure relates to X-ray imaging systems based on photon-counting detectors. [Background technology]

[0003] Material decomposition is a useful technique employed in Computed Tomography (CT) to identify and quantify materials. It exploits the energy dependence of the linear attenuation coefficients of different materials and requires at least two energy bins. Dual-energy CT systems generally incorporate material decomposition as a feature that may be performed on the image or projection database.

[0004] For example, a Photon-Counting CT (PCCT) system has three or more energy bins. Therefore, the PCCT system is suitable for material decomposition. Moreover, material decomposition of the projection database can play a very important role in the calibration process of the PCCT system.

[0005] However, the amount of data required increases proportionally to the number of energy bins used: to achieve high image quality, more energy bins are needed, which in turn places higher demands on data memory or storage and data transfer rates.

[0006] It would therefore be desirable to overcome the above-mentioned problems and other issues associated with current material decomposition techniques. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Pat. No. 10,905,388 [Patent Document 2] U.S. Patent No. 10,034,652 Summary of the Invention [Problem to be solved by the invention]

[0008] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to reduce the amount of data while maintaining image quality. 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 later can also be positioned as other problems. [Means for solving the problem]

[0009] A photon-counting radiological diagnostic device according to an embodiment includes a photon-counting detector having a plurality of detector pixels arranged in a channel direction and a segment direction, and a processing circuit, which processes first data detected at a first detector pixel in the plurality of detector pixels with a first energy bin setting, and processes second data detected at a second detector pixel in the plurality of detector pixels with a second energy bin setting having a larger number of energy bins than the first energy bin setting. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example bin response function Sb(E) of a photon-counting detector (PCD), where each curve shows a response function corresponding to an energy bin. [Diagram 2] FIG. 2 shows hypothetical monochromatic energy reconstructions at 50, 70, and 135 keV for a photon-counting CT (PCCT) system using five and two energy bins, respectively. [Diagram 3]FIG. 3 illustrates a scenario where a single value of the energy bin number NEbins is adopted in the channel direction across the entire projection views. [Figure 4] FIG. 4 is a block diagram illustrating an apparatus for performing material decomposition implementing pixel-based energy binning according to an embodiment. [Diagram 5] FIG. 5 is a flow chart illustrating a procedure for performing material decomposition implementing pixel-based energy binning according to an embodiment. [Figure 6] FIG. 6 illustrates an example approach where higher values ​​of NEbins are used for central regions in the channel direction of a detector and lower values ​​of NEbins are used for peripheral regions in the channel direction of a detector according to an embodiment. [Figure 7] FIG. 7 illustrates an example approach where higher values ​​of NEbins are used in both the channel and channel directions for inner regions of a detector in accordance with an embodiment, and lower values ​​of NEbins are used in both the channel and channel directions for outer regions of the detector. [Figure 8] FIG. 8 illustrates an exemplary approach when incorporating more than two values ​​of NEbins with no overlap of NEbins values ​​between adjacent NChMD ranges according to an embodiment. [Figure 9] FIG. 9 illustrates an exemplary approach when more than two values ​​of NEbins are incorporated with overlapping NEbins values ​​between adjacent NChMD ranges. [Figure 10] FIG. 10 illustrates an example approach using asymmetric division of NEbins in the channel direction for projection views at 0 degrees and 180 degrees according to an embodiment. [Figure 11] FIG. 11 is a diagram illustrating another example approach using asymmetric division of NEbins in the channel direction for projection views at 0 degrees and 180 degrees according to an embodiment. [Figure 12] FIG. 12 illustrates an example technique for using different splitting between adjacent detector channels according to an embodiment. [Figure 13]FIG. 13 is a diagram illustrating an example of the configuration of a photon counting X-ray CT apparatus according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In one exemplary embodiment, a photon-counting imaging system including a photon-counting detector and a processing circuit is disclosed. The photon-counting detector acquires projection data of a plurality of projection views from an imaging object. The photon-counting detector has a plurality of detector pixels arranged in both a channel direction and a segment direction on a surface of the photon-counting detector. The processing circuit acquires the projection data obtained by the photon-counting detector. The projection data includes first projection data and second projection data. The processing circuit processes the first projection data using a first energy bin setting, the first energy bin setting indicating the use of m energy bins, and processes the second projection data using a second energy bin setting, the second energy bin setting indicating the use of n energy bins, where n>m. The processing circuit generates a material-decomposed image of the imaging object based on the processed first projection data and the processed second projection data.

[0012] In another exemplary embodiment, a method for performing pixel-based energy bin number adjustment in a photon counting imaging system is also disclosed. The photon counting imaging system includes a photon counting detector that acquires projection data of a plurality of projection views from an imaging object. The photon counting detector has a plurality of detector pixels arranged in both channel and segment directions on a surface of the photon counting detector. The method includes acquiring projection data acquired by the photon counting detector, the projection data including first projection data and second projection data, processing the first projection data with a first energy bin setting, the first energy bin setting indicating the use of m energy bins, processing the second projection data with a second energy bin setting, the second energy bin setting indicating the use of n energy bins, where n>m, and generating a material decomposition image of the imaging object based on the processed first projection data and the processed second projection data.

[0013] In another exemplary embodiment, a non-transitory computer readable medium is also disclosed that stores a program that, when executed by a processing circuit, causes the processing circuit to perform a method for performing pixel-based energy bin number adjustment in a photon counting imaging system. The photon counting imaging system includes a photon counting detector that acquires projection data of a plurality of projection views from an imaging object. The photon counting detector has a plurality of detector pixels arranged in both a channel direction and a segment direction on a surface of the photon counting detector. The method includes acquiring projection data obtained by a photon counting detector, the projection data including first projection data and second projection data; processing the first projection data using a first energy bin setting, the first energy bin setting indicating the use of m energy bins; processing the second projection data using a second energy bin setting, the second energy bin setting indicating the use of n energy bins, where n>m; and generating a material decomposition image of the imaged object based on the processed first projection data and the processed second projection data.

[0014] It should be noted that the above-described exemplification of embodiments does not identify all embodiments and / or incrementally novel aspects of the present disclosure or claimed invention. Instead, the exemplification provides only a preliminary discussion of various embodiments and equivalent novelties. For further details and / or possible aspects of the present disclosure and embodiments, please refer to the detailed description and corresponding drawings of the present disclosure, which are further described below.

[0015] The present application will be better understood in the light of the description given in a non-limiting manner, accompanied by the accompanying drawings, in which:

[0016] The following disclosure presents many different embodiments, or examples, for implementing various features of the presented subject matter. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting.

[0017] For example, the order of description of different procedures as described herein is presented for clarity. Generally, these procedures can be performed in any suitable order. Also, although each of the different features, techniques, and configurations herein may be described in various places in this disclosure, it is intended that each of the concepts can be implemented independently of each other or in combination with each other. Thus, this disclosure can be embodied and viewed in many different ways.

[0018] Additionally, as used herein, the terms "a," "an," and the like, are generally intended to mean "one or more," unless otherwise specified.

[0019] The present disclosure relates to pixel-based energy bin number adjustment used in a photon-counting computed tomography (PCCT) system, which includes one or more x-ray tubes for emitting x-rays and an array of detector pixels for detecting the x-rays propagating through an image field of view (FOV) of a scanning system. The array of detector pixels is linearly arranged on a surface of the detector in both channel and segment directions. The energy bin number adjustment scheme can be applied to a material decomposition mode of the PCCT system.

[0020] The PCCT system uses a direct conversion photon counting detector (PCD) to discriminate the energy of each incident photon and generate multiple energy bin count measurements per integration period. The transmission forward model of this energy discriminating PCD can be formulated as shown in Equation (1) below:

[0021]

number

[0022] Here, "S" in formula (1) b (E)” denotes the bin response function defined by the following equation (2), “N0” denotes the total flux in the air scan, and “μ m " and "l m " indicates the linear attenuation coefficient and path length of the mth principal component material, and "w(E)" indicates the normal incidence X-ray spectrum. In addition, "R(E,E')" in equation (2) indicates the detector response function, and "E bL " and "E bH " indicates the low and high energy thresholds for each counting bin.

[0023]

number

[0024] In PCCT systems, three or more energy bins may be available and these energy bins may be used in the discrimination of the projection database. Figure 1 shows an example bin response function, “S b (E)." Each curve in Figure 1 shows the response function corresponding to each of the five energy bins.

[0025] Figure 2 shows a comparison of hypothetical monoenergetic energy reconstructions at 50, 70, and 135 keV for a PCCT system using five and two energy bins. As shown in Figure 2, the image quality of PCCT material decomposition is improved when more energy bins are used.

[0026] Furthermore, Table 1 below shows the measured noise standard deviation (SD) within the ROI (arrow) of FIG. 2. The table compares the noise SD measured for a hypothetical monochromatic energy reconstruction of five energy bins and two energy bins. If only two energy bins were used instead of five energy bins, the resulting noise during reconstruction would increase by 24.5%, 20.5%, and 22.0% at 50, 70, and 135 keV, respectively. Note that Table 1 shows the noise SD measured in the ROI of FIG. 2 between discrimination into five energy bins and discrimination into two energy bins.

[0027] [Table 1]

[0028] Material decomposition of the projection database is performed at the level of individual detector pixels. Specifically, for each pixel, a number of energy bins, N EBins Only a single value of N is used in the material decomposition process, and this value is applied uniformly to all pixels in one projection view. Figure 3 illustrates this commonly adopted approach, where N EBins A single value of ", e.g., "5", is used in the channel direction across the entire projection view. Segment directions are not depicted in FIG.

[0029] It is desirable to achieve the highest possible image quality, which means using the maximum number of energy bins, however this results in the largest amount of data, which in turn requires high data storage and fast data transfer rates, thus requiring extensive memory or disk space and slower processing times.

[0030] In general, the amount of data required for the material decomposition process is EBins " and the total number of data values ​​"N values" can be calculated using the following formula (3).

[0031]

number

[0032] In formula (3), "N ch " and "N seg " represent the number of detector channels and the number of detector segments, respectively. Compared to a PCCT system using two energy bins, for example, a five bin system requires more than 2.5 times as much data. The challenge is therefore to maintain the highest image quality while reducing the amount of data required by the maximum amount of energy bins.

[0033] 4 shows a block diagram of an apparatus 400 for performing material decomposition according to the present embodiment. As shown in FIG. 4, the apparatus 400 includes a first projection data processing circuit 410, a second projection data processing circuit 420, and a material decomposition image generating circuit 430.

[0034] The first projection data processing circuit 410 and the second projection data processing circuit 420 receive projection data obtained from the imaging object by the PCD. Since not all projection data are obtained from the region of interest (corresponding to the FOV part with high image quality requirements) in the imaging object, the projection data may be processed differently based on the position of the image pixel to be reconstructed. This allows a larger number of energy bins to be utilized for processing the projection data from the region of interest, while at the same time using a smaller number of energy bins for processing the projection data from other regions (e.g., FOV parts with low image quality requirements). By doing so, it is possible to reduce the amount of data without compromising the quality of the reconstructed image.

[0035] In particular, the first projection data processing circuit 410 may process projection data from a subset of detector pixels using a first energy bin setting with a small number of energy bins, while the second projection data processing circuit 420 may process projection data from another subset of detector pixels using a second energy bin setting with a large number of energy bins.

[0036] For example, the second energy bin setting may use all five energy bins, which is determined by a set of predefined energy thresholds in the PCCT system, and the first energy bin setting may use fewer energy bins, for example, two energy bins. The reduced number of energy bins can be obtained through recombination of the original five energy bins.

[0037] For example, in one recombination scenario, bin 1 and bin 2 may be merged to form one energy bin, while bin 3, bin 4, and bin 5 may be merged to create another energy bin. Alternatively, in a different recombination scenario, bins 1, 2, and 4 may be combined as one energy bin, and bins 3 and 5 may be combined as another. These exemplary scenarios are not limiting, and many other possible recombination scenarios are contemplated.

[0038] The material decomposition image generation circuitry 430 receives the data processed by the first projection data processing circuitry 410 and the second projection data processing circuitry 420, and generates a material decomposition image of the imaged object.

[0039] 5 shows a flow chart of a procedure 500 for performing material decomposition according to the present invention. The procedure 500 begins at step S510, where projection data obtained from an imaging object by a PCD is acquired.

[0040] In step S520, first projection data acquired by detector pixels within the first detector region may be processed using a first energy bin setting having fewer energy bins.

[0041] In step S530, second projection data acquired by detector pixels within the second detector region may be processed using a second energy bin setting having more energy bins.

[0042] Finally, in step S540, a material decomposition image of the imaged object is generated based on the processed first projection data and the processed second projection data.

[0043] FIG. 6 shows the energy bin number “N” for various values ​​at different pixel regions on the detector surface according to the present embodiment. Ebins In FIG. 6, an example method is shown in which "N Ebins A larger value of N (e.g., 5) is used for the central part of the detector in the channel direction, where high image quality is required. Ebins A smaller value of " (eg, 2) is used for the two peripheral parts of the detector in the channel direction where lower image quality is acceptable.

[0044] The total amount of data required, N values " can be calculated using the following formula (4).

[0045]

number

[0046] Here, "N chLow ” is the lower energy bin number “N EbinsLow " indicates the number of channels having "N chHi " is a higher energy bin number "N EbinsHi " indicates the number of channels having "N seg " indicates the number of detector segments.

[0047] In the example of FIG. 6, for any reconstructed image pixel “i,j” (represented by a square in FIG. 6), “N Ebins " remains the same for all projection views. By using a higher number of energy bins to process the projection data detected by the central region of the detector (corresponding to the high Image Quality (IQ) center of the FOV) and a lower number of energy bins to process the projection data detected by the remaining detector regions (corresponding to the lower IQ periphery of the FOV), it is possible to maintain image quality while reducing the overall data requirements.

[0048] High "N" on the detector EBins The range of "N" can be determined based on the size of the center of the high IQ of the FOV. ch " represents the total number of detector channels, and "FOV Hi Let "N" denote the central diameter of the high IQ, "SOD" denote the source isocenter distance, and "FanAng" denote the fan angle. EBins ” is the higher number of detector channels and “N EBins The number of detector channels for which ' is lower can be calculated as follows, using equations (5) and (6), respectively:

[0049]

number

[0050]

number

[0051] In the embodiment shown in FIG. Ebins" is split in the channel direction. However, in an alternative approach, the split can be in the segment direction instead of the channel direction. Furthermore, these two embodiments can be combined, which allows splitting in both the segment and channel directions simultaneously, as shown by way of example in FIG. 7.

[0052] FIG. 7 shows the "N" in both the segment and channel directions for the inner region of the detector according to this embodiment. Ebins A higher value of N is used, while a lower value of N is used for the outer regions of the detector in both the segment and channel directions. Ebins 13 shows an example approach where a lower value of " is used.

[0053] In this case, the total amount of data required is N values " can be calculated using the following equation (7).

[0054]

number

[0055] Here, "N ChLow " and "N SegLow ” is the lower energy bin number “N EbinsLow " indicates the number of channels and segments (corresponding to the low IQ peripheral volume of the imaging subject) with "N ChHi " and "N SegHi " is a higher energy bin number "N EbinsHi " indicates the number of channels and the number of segments (corresponding to the central volume of high IQ of the imaged subject).

[0056] In this embodiment, the high IQ imaging volume corresponds to the center of the detector. The axial height of the high IQ FOV is defined as "d Hi ” and the physical height of the detector is “H Det ” the source-detector distance is denoted by “SDD” and the total number of detector segments is denoted by “N seg" Also, "N segLowU " = "N segLowL " = "N segLow " Suppose, "N segHi " and "N segLow " can be calculated using the following equations (8) and (9), respectively.

[0057]

number

[0058]

number

[0059] Those skilled in the art will appreciate that in an alternative embodiment, Hi " does not need to be centered relative to the height of the detector, "N segLowU " is "N segLowL " may differ from the

[0060] The above figures 6 and 7 show the Ebins This illustrates a scenario where two values ​​are embedded in "N Ebins The "N" value may be used to provide a smooth transition in image quality from the center to the edge of the detector. FIG. 8 shows the "N Ebins 13 shows an exemplary method when more than two values ​​of " are implemented along the channel.

[0061] The total amount of data required in this case is N values " can be calculated as shown in the following equation (10).

[0062]

number

[0063] Here, "N seg " indicates the number of detector segments, and "N ChMD[n]" is the number of energy bins "N Ebins The number of channels is indicated with "[n]", where "n" ranges from "0" to "N-1".

[0064] In this embodiment, when "n=0, 1, ..., N-1", "N Ebins [n]" and "N ChMD For any reconstructed image pixel “i,j” (represented by a square in Fig. 8), “N Ebins " remains the same for all projection views. Although Fig. 8 shows the case in the channel direction, the same concept can be applied in the segment direction as well.

[0065] In Figure 8, each combination {N ChMD [n],N Ebins [n]} is the adjacent "N ChMD Between the range of "N Ebins 9, the {N ChMD [n],N Ebins [n]} and {N ChMD [n+1],N Ebins [n+1]} may overlap.

[0066] FIG. 9 shows adjacent “N ChMD Between the range of "N Ebins " value is duplicated, "N Ebins ” is incorporated. On the detector, the solid line area represents the N Ebins [n] represents the channel that is used, and the shaded area represents the channel that is used Ebins [n] and N Ebins The i,j channels represent the channels when both i and j are used, where n ranges from 0 to N-1. Thus, the reconstructed image pixel i,j in the overlap region is the i,j channel. EbinsFor example, overlapping regions may be affected by two values ​​of "N Ebins ” and reconstructed using one value of “N Ebins The data may be reconstructed using different values ​​of " and then averaged.

[0067] As in the embodiment shown in FIG. 8, for n=0, 1, . . . , N-1, Ebins [n] and "N ChMD [n]" is symmetrical about the central X-ray. Although FIG. 9 shows the case in the channel direction, the same concept can be applied in the segment direction as well.

[0068] The pixel-based energy bin number adjustment described in this disclosure is the “N Ebins Note that the present invention is not limited to a symmetric division of "N Ebins It is possible to implement an asymmetric split of

[0069] FIG. 10 shows the “N” projection view of the channel direction at 0 degrees (left) and 180 degrees (right), respectively, according to the present embodiment. Ebins FIG. 13 illustrates an exemplary approach using an asymmetric division of two values ​​of “.”

[0070] As shown in FIG. 10, for any given pixel “i,j” in the image to be reconstructed, “N Ebins " may vary depending on the view angle. For example, the 0 degree projection view (left side of Figure 10) has a higher value of "N EbinsHi " is applied to the upper half of the detector, while the lower value "N EbinsLow " is applied to the lower half. In the 180 degree projection view (right side of Figure 10), the lower value "N EbinsLow " is applied to the top half of the detector, while the higher value "N EbinsHi " is applied to the lower half.

[0071] Therefore, in this embodiment, "N EbinsThe data associated with the two values ​​of "IQ" is effectively "blended" across the 360° of the projection view, resulting in a reconstructed image that does not contain distinct high and low IQ regions, but rather has an IQ that is approximately halfway between the high and low values.

[0072] FIG. 11 shows the K value “N” in the channel direction for the projection view at 0 degrees (left) and 180 degrees (right), respectively, according to the present embodiment. Ebins ” shows a more generalized case using an asymmetric partition of

[0073] Similar to the embodiment shown in FIG. 10, in this embodiment, for any given pixel “i,j” in the image to be reconstructed, “N Ebins " may also vary with view angle. The left diagram of FIG. 11 shows the projection view at 0 degrees, and the right diagram of FIG. 11 shows the projection view at 180 degrees. Again, "N Ebins " Data associated with the K values ​​is effectively "blended" across 360° of the projection view, resulting in a reconstructed image that does not contain distinct high or low IQ regions, but rather has an IQ that is approximately halfway between high and low.

[0074] In the above embodiment, "N Ebins The division and number of "N" are implemented within the range of the projection view and remain constant across different views. Ebins The division and number of " may vary from view to view, rather than within a single projection view. For example, for even projection views, five energy bins may be used, while for odd projection views, two energy bins may be used. Other divisions and numbers of energy bins are also contemplated. For example, the projection views may be divided into three or more groups, with a different number of energy bins used in each group.

[0075] In addition, for detector regions with lower energy bin numbers, EbinsThe splitting of " may be mixed between adjacent detector channels, segments, and / or projection views. Figure 12 illustrates an example approach using different energy splitting between adjacent detector channels according to the present embodiment.

[0076] The expanded window in Figure 12 shows the division [E bin1 ,E bin2 ] and [E bin3 ,E bin4 ] are applied alternately in the channel direction. Specifically, in the peripheral part of the detector, two energy bins, bin 1 and bin 2, may be applied to channels 0, 2, 4, ..., while two energy bins, bin 3 and bin 4, may be applied to channels 1, 3, 5, ..., where bins 1 and 2 can be obtained by recombining the original bins 1 to 5 in one way, and bins 3 and 4 can be obtained by recombining the original bins 1 to 5 in another way.

[0077] Although Figure 12 illustrates two different types of division, three or more types of division may be used. Additionally, although Figure 12 illustrates at the channel level, the same concepts may be applied at the segment level and / or projection view level as well.

[0078] Those skilled in the art will recognize that various combinations of the above-described embodiments are possible without departing from the scope of the present disclosure. For example, in the embodiment shown in FIG. 10 and FIG. 11, "N" is used between adjacent detector regions. Ebins The "N" values ​​are not overlapping, but overlap at the transition zone to achieve smoothing of the image quality. Ebins " value may also be applied. As another example, the asymmetric split within the projection views shown in Figures 10 and 11 may also be implemented in the segment direction, or in both the channel and segment directions.

[0079] The pixel-based energy bin number adjustment may be implemented in a photon-counting CT scanning system (X-ray CT device) as described below with reference to Fig. 13. The X-ray CT device 1 shown in Fig. 13 includes a gantry 10, a bed 30, and a console 40 that executes processing of a medical imaging processing device. For the purpose of explanation, Fig. 13 shows multiple gantries 10.

[0080] In this embodiment, the rotation axis of the rotating frame 13 when not tilted, or the longitudinal direction of the table top surface 33 of the bed 30 is defined as the "Z-axis direction", the axial direction perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the "X-ray direction", and the axial direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the "Y-axis direction".

[0081] For example, the gantry 10 and the bed 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 may be installed in the same room as the gantry 10 and the bed 30. In any case, the gantry 10, the bed 30, and the console 40 are connected to be able to communicate with each other by wires or wirelessly.

[0082] The gantry 10 is a scanner having a configuration for performing X-ray CT imaging on a subject (or an imaging object) 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.

[0083] The X-ray tube 11 is a vacuum tube that generates X-rays by emitting thermal electrons from a cathode (filament) to an anode (target) in response to application of a high voltage and supply of a filament current from an X-ray high voltage device 14. Specifically, X-rays are generated by thermal electrons colliding with a target. An example of the X-ray tube 11 is a rotating anode type X-ray tube that generates X-rays by emitting thermal electrons to a rotating anode. The X-rays generated by the X-ray tube 11 are formed into a cone beam by a collimator 17, for example, and irradiated onto the target P.

[0084] The X-ray detector 12 detects X-rays emitted by the X-ray tube 11 and passing through the object P, and outputs an electrical signal according 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 a channel direction (X-axis direction or cylindrical 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 or column direction).

[0085] 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."

[0086] The rotating frame 13 supports the X-ray generator and the X-ray detector 12 rotatably around 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 the X-ray tube 11 and the X-ray detector 12 rotate 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 a metal such as aluminum. Specifically, the rotating frame 13 is connected to an end of the fixed frame via a bearing. The rotating frame 13 rotates at a predetermined angular velocity around the rotation axis Z while receiving power from a driver of the control device 15.

[0087] In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 includes and supports the X-ray high voltage device 14 and the DAS 18. Such a rotating frame 13 is housed in a substantially cylindrical housing with a bore 19 that defines an imaging space. The bore corresponds approximately to the FOV. The central axis of the bore coincides with the rotation axis Z of the rotating frame 13. Detection data generated by the DAS 18 is transmitted, for example, from a transmitter (not shown) to a receiver (not shown) installed in a non-rotating part of the gantry (such as a fixed frame not shown in FIG. 13), and then transferred to the console 40.

[0088] The X-ray high voltage device 14 includes a high voltage generator including electric circuits such as a transformer and a rectifier, and having a function of generating a high voltage applied to the X-ray tube 11 and a filament current supplied to the X-ray tube 11, and an X-ray control device configured to control an output voltage due to X-rays emitted by the X-ray tube 11. The high voltage generator can be of a transformer type or an inverter type. The X-ray high voltage device 14 may be installed on the rotating frame 13 described below or on a fixed frame (not shown) of the gantry 10.

[0089] The control device 15 includes a processing circuit including a central processing unit (CPU) and the like, and a driver for a motor or an actuator and the like. The processing circuit includes a processor such as a CPU or a micro processing unit (MPU) and a memory such as a read only memory (ROM) or a random access memory (RAM) as hardware resources. The control device 15 can be realized by an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or another complex programmable logic device (CPLD) or simple programmable logic device (SPLD). The control device 15 controls the X-ray high voltage device 14 and the DAS 18 and the like according to instructions from the console 40. The processor performs the above control by reading and executing a program stored in the memory.

[0090] 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 either the non-transitory electronic memory mentioned above and / or a hard disk drive, a CD, a DVD, a FLASH drive, or any other known storage medium. Furthermore, the computer readable instructions may be provided as a utility application, a background daemon, or a component of an operating system, or a combination thereof, and executed in conjunction with a processor and an operating system known to those skilled in the art. Furthermore, the CPU may be implemented as multiple processors working together in parallel to perform the instructions.

[0091] The control device 15 also has a function of controlling the operation of the gantry 10 and the bed 30 in response to an input signal from an input interface 43 (described later) connected 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 table top surface 33 in response to the input signal. 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 through the input interface 43 connected to the gantry 10. The control device 15 may be installed in either the gantry 10 or the console 40. The control device 15 may be configured by directly incorporating a program into the circuit of the processor instead of storing the program in a memory. In this case, the processor performs the above-mentioned control by reading and executing the program incorporated in the circuit.

[0092] The wedge filter 16 is a filter for adjusting the dose of X-rays emitted from the X-ray tube 11. Specifically, the wedge filter 16 is a filter that transmits the X-rays emitted from the X-ray tube 11 and attenuates the X-rays so that the X-rays emitted from the X-ray tube 11 show a predetermined distribution with respect to the object P. For example, the wedge filter 16 (or a bowtie filter) is a filter obtained by processing aluminum so as to have a predetermined target angle and a predetermined thickness.

[0093] The collimator 17 is a lead plate or the like for narrowing the irradiation range of the X-rays transmitted through the wedge filter 16, and includes a slit formed in combination with the lead plate or the like. The collimator 17 is also called an "X-ray aperture."

[0094] The DAS 18 generates digital data (also referred to as "detection data") indicating the count of X-rays detected by the X-ray detector 12 for each of a plurality of energy bands (called "energy bins" or simply "bins"). The detection data is a set of count value data identified by a channel number and a row number of the source X-ray detection element, a view number indicating the collected view (also referred to as a projection angle), and an energy bin number. The DAS 18 is executed, for example, by an application specific integrated circuit (ASIC) equipped with circuit elements capable of generating the detection data. The detection data is transferred to the console 40.

[0095] The bed 30 is a device on which an object P to be scanned is placed and which moves the object P, and includes a base 31, a bed actuator 32, a table top surface 33, and a support frame .

[0096] The base 31 is a housing that supports the support frame 34 so that the support frame 34 is vertically movably.

[0097] The bed actuator 32 is a motor or actuator that moves the table top 33 on which the subject P is placed in the longitudinal direction of the table top 33. The bed actuator 32 moves the table top 33 in response to control by the console 40 or control by the control device 15. For example, the bed actuator 32 moves the table top 33 in a direction perpendicular to the subject P so that the body axis of the subject P placed on the table top 33 coincides with the central axis of the bore of the rotating frame 13. The bed actuator 32 can also move the table top 33 in the body axis direction of the subject P in response to X-ray CT imaging performed using the gantry 10. The bed actuator 32 generates electricity by driving at a rotation speed according to the duty ratio of a drive signal from the control device 15. The bed actuator 32 is implemented by a motor such as a direct drive motor or a servo motor.

[0098] The table top surface 33, which is installed on the upper surface of the support frame 34, is a plate on which the object P is placed. The bed actuator 32 can move not only the table top surface 33 but also the support frame 34 in the longitudinal direction of the table top surface 33.

[0099] 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 will be 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.

[0100] The memory 41 is a storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various kinds of information. The memory 41 stores, for example, projection data and reconstructed image data. The memory 41 may be not only an HDD or SSD, but also a driver that writes various kinds of information to, for example, a portable storage medium such as a CD, a DVD, or a flash memory, or a semiconductor memory such as a random access memory (RAM), and reads it from the portable storage medium. The storage area of ​​the memory 41 may be in the X-ray CT apparatus 1 or in an external storage device connected via a network. For example, the memory 41 stores data of a CT image or a display image. The memory 41 also stores a control program according to this embodiment.

[0101] The display 42 displays various kinds of information. For example, the display 42 outputs medical images (CT images) generated by the processing circuit 44 and a graphical user interface (GUI) for receiving various kinds of operations from an operator. As the display 42, for example, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OELD), a plasma display, or any other display may be appropriately used. The display 42 may be installed in the gantry 10. The display 42 may be a desktop type or may be configured by a tablet device capable of wirelessly communicating with the console 40.

[0102] The input interface 43 receives various types of input operations from an operator, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuitry 44. For example, the input interface 43 receives from the operator acquisition conditions for acquiring projection data, reconstruction conditions for reconstructing CT images, and image processing conditions for generating post-processed images from CT images. As the input interface 43, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad, or a touch panel display may be appropriately used. In this embodiment, the input interface 43 does not necessarily include a physical operation component such as a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad, or a touch panel display. For example, the input interface 43 also includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device installed separately from the apparatus and outputs the electrical signal to the processing circuitry 44. The input interface 43 may be installed in the gantry 10. The input interface 43 may be configured by a tablet device capable of wirelessly communicating with the console 40.

[0103] The processing circuit 44 controls the overall operation of the X-ray CT device 1 in response to an electrical signal of an input operation output from the input interface 43. For example, the processing circuit 44 includes a processor such as a CPU or an MPU, or a graphics processing unit (GPU), and a memory such as a ROM or a RAM as hardware resources. Together with the processor that executes a program loaded in the memory, the processing circuit 44 performs a system control function 441, a pre-processing function 442, a reconstruction function 443, and a display control function 444. Each of the functions (the system control function 441, the pre-processing function 442, the reconstruction function 443, and the display control function 444) is not necessarily implemented by a single processing circuit. The processing circuit can be configured by combining multiple independent processors, and the processor can execute a corresponding program to execute the function.

[0104] The system control function 441 controls each function of the processing circuit 44 based on an input operation received from an 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 circuit 44, and controls each part of the X-ray CT device 1 according to the loaded control program. For example, the processing circuit 44 performs each function of the processing circuit 44 based on an input operation received from an operator via the input interface 43. For example, the system control function 441 obtains a two-dimensional positioning image of the object P and determines a scan range, imaging conditions, etc. The positioning image may also be called a "scanogram" or a "scout image."

[0105] The pre-processing function 442 generates acquired data by performing pre-processing such as logarithmic conversion, offset correction, inter-channel sensitivity correction, beam hardening correction, as well as detector calibration, detector nonlinearity, polarity effect, noise balance, and material decomposition correction on the detection data output from the DAS 18. 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.

[0106] The reconstruction function 443 generates CT image data by performing reconstruction processing on the projection data generated by the pre-processing function 442 using a filtered back projection method, an iterative reconstruction method, a stochastic image reconstruction method, or the like. The reconstruction function 443 is an example of a reconstruction processing. If necessary, image filtering, smoothing, volume rendering, or image subtraction processing can be applied to the CT image data. The display control function 444 converts the CT image data generated by the reconstruction function 443 into tomographic image data or three-dimensional image data of a given cross section by a known method based on an input operation received from an operator via the input interface 43. The generation of the three-dimensional image data may be performed directly by the reconstruction function 443. The display control function 444 is an example of a display control device.

[0107] In one implementation, the X-ray tube 11 is a single source that emits a broad spectrum of X-ray energy, and the PCD 12 can use direct X-ray radiation detectors based on semiconductors such as cadmium telluride (CdTe), cadmium zinc telluride (CZT), silicon (Si), mercuric iodide (HgI2) and gallium arsenide (GaAs). As previously mentioned, semiconductor-based direct X-ray detectors generally have a faster time response than indirect detectors such as scintillator detectors. The fast time response of direct detectors allows for the resolution of individual X-ray detection events, but at high X-ray fluxes typical of clinical X-ray applications, several multiple collisions of detection events may occur. The energy of the detected X-rays is proportional to the signal generated by the direct detector, and the detection events can be grouped into energy bins that result in the spectrally resolved X-ray data of the spectral CT.

[0108] Numerous modifications and variations of the implementations presented herein are possible in light of the above teachings. It will therefore be understood that, within the scope of the appended claims, the application may be practiced otherwise than as specifically described herein. The present invention is not limited to the examples described, and it is particularly possible to combine features of the illustrated examples with one another in variations not illustrated.

[0109] Regarding the embodiments of the present disclosure, the following supplementary notes are disclosed as one aspect and optional features of the invention.

[0110] (1) A photon counting imaging system comprising: a photon counting detector configured to acquire projection data of a plurality of projection views from an imaging object, the photon counting detector having a plurality of detector pixels arranged in both a channel direction and a segment direction on a surface of the photon counting detector; and a processing circuit configured to acquire projection data acquired by the photon counting detector, the projection data including first projection data and second projection data, process the first projection data using a first energy bin setting, the first energy bin setting indicating the use of m energy bins, and process the second projection data using a second energy bin setting, the second energy bin setting indicating the use of n energy bins, where n>m; and generate a material resolved image of the imaging object based on the processed first projection data and the processed second projection data.

[0111] (2) The system described in (1), wherein the n energy bins are determined by a set of predetermined energy thresholds of the photon counting imaging system, and the m energy bins are determined by rearranging the n energy bins in a predetermined manner.

[0112] (3) The system of (1), wherein the photon counting detector is further configured to acquire first projection data from detector pixels within a first region of the photon counting detector and to acquire second projection data from detector pixels within a second region of the photon counting detector different from the first region.

[0113] (4) The photon counting detector is further configured to obtain first projection data from a first region of the imaging object, where the required image quality is lower than a pre-determined threshold, from detector pixels within a first region of the photon counting detector, and to obtain second projection data from a second region of the imaging object, where the required image quality is equal to or higher than the pre-determined threshold, from detector pixels within a second region of the photon counting detector, for the system described in (3).

[0114] (5) The first region of the photon counting detector corresponds to a peripheral portion of the photon counting detector in at least one of the channel direction and the segment direction, and the second region of the photon counting detector corresponds to a central portion of the photon counting detector in at least one of the channel direction and the segment direction, for the system described in (4).

[0115] (6) The first region of the photon counting detector and the second region of the photon counting detector are located in parallel on the surface of the photon counting detector in at least one of the channel direction and the segment direction, for the system described in (3).

[0116] (7) A transition zone is arranged around a boundary between the first region and the second region of the photon counting detector, and the processing circuit is further configured to process projection data obtained by detector pixels within the range of the transition zone using both a first energy bin setting and a second energy bin setting, for the system described in (3).

[0117] (8) The first region of the photon counting detector includes k sub-regions, detector pixels within each of the k sub-regions obtain k subsets of the first projection data, and the processing circuit is further configured to process each of the k subsets of the first projection data using k sub-settings of energy bins, where, when 1 ≦ i ≦ k, the i-th sub-setting of energy bins indicates the use of the m i -th energy bin, and m i < n, for the system described in (3).

[0118] (9) The system of (8), wherein, for 1≦j≦k-1, a transition zone is located around a boundary between the jth subregion and the (j+1)th subregion of the photon counting detector, and the processing circuitry is further configured to process projection data acquired by detector pixels within the transition zone between the jth subregion and the (j+1)th subregion using the jth energy bin subsetting and the (j+1)th energy bin subsetting.

[0119] (10) The system described in (3), wherein the processing circuitry is further configured to process the first projection data in a channel-based, segment-based, or view-based manner using a predetermined group of p energy bin sub-settings.

[0120] (11) The system of (10), wherein the processing circuitry is further configured to process projection data obtained by the xth pixel channel of each of p consecutive pixel channels within the first region using an xth energy bin sub-setting of the predetermined group, where 1≦x≦p.

[0121] (12) The system of (10), wherein the processing circuitry is further configured to process projection data obtained by an x-th pixel segment of each of p consecutive pixel segments within the first region using an x-th energy bin sub-setting of the predetermined group, where 1≦x≦p.

[0122] (13) The system described in (10), wherein the processing circuitry is further configured to process first projection data obtained for an x-th projection view of each of p consecutive projection views using an x-th energy bin sub-setting of a predetermined group, where 1≦x≦p.

[0123] (14) The system described in (1), wherein the photon counting detector is further configured to acquire first projection data for a first subset of the plurality of projection views and acquire second projection data for a second subset of the plurality of projection views.

[0124] (15) The system described in (14), wherein a first subset of the plurality of projection views includes an even number of projection views while a second subset of the projection views includes an odd number of projection views, or wherein the first subset of the plurality of projection views includes an odd number of projection views while a second subset of the projection views includes an even number of projection views.

[0125] (16) A method of performing pixel-based energy bin number adjustment in a photon counting imaging system, the photon counting imaging system including a photon counting detector acquiring projection data of a plurality of projection views from an imaging object, the photon counting detector having a plurality of detector pixels arranged in both a channel direction and a segment direction on a surface of the photon counting detector, the method including: acquiring projection data acquired by the photon counting detector, the projection data including first projection data and second projection data; processing the first projection data using a first energy bin setting, the first energy bin setting indicating the use of m energy bins; processing the second projection data using a second energy bin setting, the second energy bin setting indicating the use of n energy bins, where n>m; and generating a material decomposed image of the imaging object based on the processed first projection data and the processed second projection data.

[0126] (17) The method of (16), wherein the n energy bins are determined by a set of predetermined energy thresholds of a photon counting imaging system, and the m energy bins are determined by shuffling the n energy bins in a predetermined manner.

[0127] (18) The method of (16), wherein the acquiring step further includes obtaining first projection data from detector pixels within a first region of the photon counting detector, and obtaining second projection data from detector pixels within a second region of the photon counting detector.

[0128] (19) The method of (16), wherein the acquiring step further includes obtaining first projection data for a first subset of the plurality of projection views, and obtaining second projection data for a second subset of the plurality of projection views.

[0129] (20) A non-transitory computer readable medium storing a program, the program, when executed by a processing circuit, causing the processing circuit to execute a method of performing pixel-based energy bin number adjustment in a photon counting imaging system, the photon counting imaging system including a photon counting detector that acquires projection data of a plurality of projection views from an imaging object, the photon counting detector having a plurality of detector pixels arranged in both a channel direction and a segment direction on a surface of the photon counting detector, the method including acquiring projection data acquired by the photon counting detector, the projection data being a first projection data, and processing the first projection data using a first energy bin setting, the first energy bin setting indicating the use of m energy bins; and processing the second projection data using a second energy bin setting, the second energy bin setting indicating the use of n energy bins, where n>m; and generating a material decomposition image of the imaged object based on the processed first projection data and the processed second projection data.

[0130] According to at least one of the embodiments described above, it is possible to reduce the amount of data while maintaining image quality.

[0131] Specific embodiments of the subject matter have been described. Other embodiments are within the scope of the claims of the present invention. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. By way of example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous. It is apparent that 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 claims, the present disclosure may be practiced in ways other than as specifically described herein. [Explanation of symbols]

[0132] 1 X-ray CT device 11 X-ray tube 12 X-ray detector 44 Processing circuit 400 equipment 410 First projection data processing circuit 420 Second projection data processing circuit 430 Material Decomposition Image Generation Circuit

Claims

1. a photon-counting detector having a plurality of detector pixels arranged in a channel direction and a segment direction; a processing circuit that processes first data detected at a first detector pixel in the plurality of detector pixels with a first energy bin setting and processes second data detected at a second detector pixel in the plurality of detector pixels with a second energy bin setting having a greater number of energy bins than the first energy bin setting; A photon counting type radiation diagnostic apparatus comprising:

2. a number of energy bins in the second energy bin set is determined by a set of predefined energy thresholds; The photon counting radiological diagnostic device of claim 1 , wherein the number of energy bins in the first energy bin setting is determined by rearranging the number of energy bins in the second energy bin setting in a predetermined manner.

3. 2. The photon counting radiation diagnostic device of claim 1, wherein the processing circuit processes first projection data acquired by the first detector pixel included in a first region of the photon counting detector with the first energy bin setting, and processes second projection data acquired by the second detector pixel included in a second region of the photon counting detector different from the first region with the second energy bin setting.

4. 4. The photon-counting radiation diagnostic device according to claim 3, wherein the photon-counting detector acquires the first projection data of an imaging object having a desired image quality lower than a predetermined threshold from the first detector pixels included in the first region, and acquires the second projection data of an imaging object having a desired image quality equal to or higher than the predetermined threshold from the second detector pixels included in the second region.

5. the first region corresponds to a peripheral portion of the photon-counting detector in at least one of the channel direction and the segment direction; The photon-counting radiation diagnostic device according to claim 4 , wherein the second region corresponds to a central portion of the photon-counting detector in at least one of the channel direction and the segment direction.

6. 4. The photon counting radiation diagnostic device according to claim 3, wherein the first region and the second region are positioned in parallel on a surface of the photon counting detector in at least one of the channel direction and the segment direction.

7. the photon counting detector includes a transition zone disposed about a boundary between the first region and the second region; 4. The photon counting radiological diagnostic device of claim 3, wherein the processing circuitry processes projection data acquired by detector pixels included in the transition zone using both the first energy bin setting and the second energy bin setting.

8. the first region includes k sub-regions; Detector pixels in each of the k sub-regions acquire k subsets of the first projection data; the processing circuitry processes each of the k subsets of the first projection data using k energy bin subsets; The i-th (1≦i≦k) energy bin sub-set in the k energy bin sub-sets is a number (m) that is proportional to the number (m) of energy bins in the first energy bin set. i ), where m i The photon counting radiation diagnostic device according to claim 3 , wherein n is the number of energy bins in the second energy bin setting.

9. a transition zone is disposed around a boundary between a jth sub-region and a (j+1)th sub-region in the photon-counting detector, where 1≦j≦k−1; 9. The photon counting radiological diagnostic device of claim 8, wherein the processing circuitry processes projection data acquired by detector pixels included in the transition zone between the jth sub-region and the (j+1)th sub-region using a jth energy bin sub-setting and a (j+1)th energy bin sub-setting.

10. 4. The photon counting radiological diagnostic device of claim 3, wherein the processing circuitry processes the first projection data in a channel-based, segment-based, or view-based manner using a predefined group of p energy bin sub-sets.

11. 11. The photon counting radiological diagnostic device of claim 10, wherein the processing circuitry processes projection data acquired by an x-th pixel channel of p consecutive pixel channels included in the first region using an x-th energy bin sub-setting of the predetermined group (1≦x≦p).

12. 11. The photon counting radiological diagnostic device of claim 10, wherein the processing circuitry processes projection data acquired by an xth pixel segment of p consecutive pixel segments included in the first region using an xth (1≦x≦p)th energy bin sub-setting of the predetermined group.

13. 11. The photon counting radiological diagnostic device of claim 10, wherein the processing circuitry processes the first projection data obtained for an xth projection view of p consecutive projection views using an xth energy bin sub-setting of the predefined group (1≦x≦p).

14. 2. The photon-counting radiological diagnostic device of claim 1, wherein the photon-counting detector acquires the first data for a first subset of a plurality of projection views and acquires the second data for a second subset of the plurality of projection views.

15. the first subset includes an even number of projection views and the second subset includes an odd number of projection views; or 15. The photon-counting radiological diagnostic apparatus of claim 14, wherein the first subset includes odd-numbered projection views and the second subset includes even-numbered projection views.

16. 16. The photon counting radiological diagnostic device according to claim 1, wherein the processing circuitry generates a material decomposition image of the imaging object based on the first data processed with a first energy bin setting and the second data processed with a second energy bin setting.

17. 1. A method performed by a photon-counting radiological diagnostic device having a photon-counting detector having a plurality of detector pixels arranged in a channel direction and a segment direction, comprising: processing first data detected at a first detector pixel in the plurality of detector pixels with a first energy bin setting, and processing second data detected at a second detector pixel in the plurality of detector pixels with a second energy bin setting having a greater number of energy bins than the first energy bin setting; The method includes:

18. A computer that controls a photon-counting type radiation diagnostic apparatus having a photon-counting type detector having a plurality of detector pixels arranged in a channel direction and a segment direction, processing first data detected at a first detector pixel in the plurality of detector pixels with a first energy bin setting, and processing second data detected at a second detector pixel in the plurality of detector pixels with a second energy bin setting having a greater number of energy bins than the first energy bin setting; A program that executes a process.

Images