JP2009011863A - X-ray computed tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a delay of the main scan start timing in an X-ray computed tomography apparatus. <P>SOLUTION: In an aspect, an X-ray computed tomography apparatus monitors the density of a contrast medium injected into a subject by a preparation scan so as to adjust the main scan start timing with a scan condition different from that of the main scan. The apparatus includes an X-ray tube 110, an X-ray detector 113, a high voltage generation unit 14 to apply a high voltage to the X-ray tube 110, a reconstruction unit 24 to reconstruct tomographic image data based on an output of the X-ray detector 113, an operation unit 26 to set a region of interest to the tomographic image data, and a control unit 21 to compare the average of CT values of a part of pixels in the region of interest with the threshold value and stop the preparation scan and start to execute the main scan or preparing the execution of the main scan when the average reaches or exceed the threshold value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an X-ray computed tomography apparatus having a function of monitoring contrast agent inflow to a region of interest by a prep scan.

  In contrast medium imaging, it is important to scan (main scan) at the timing when the contrast medium administered to the subject flows into the slice of interest. Therefore, before the main scan, the scan (prep scan) and low-resolution image reconstruction are repeated at a lower dose, and the radiographer visually confirms the contrast agent concentration (stain degree) of the region of interest in the tomographic image. When the density becomes high to some extent, a trigger for the main scan is input. When receiving the trigger, the apparatus stops the prep scan and starts the main scan.

  Further, in recent years, a technique called so-called real prep scan for automating the main scan start timing has been popularized. As shown in FIG. 15A, the CT value of the region of interest is extracted from the tomographic image data obtained by the prep scan, and the value or average value CTave. Is compared with the threshold value TH. At time t when the value or average value CTave. Exceeds the threshold value TH, the transition from the prep scan to the main scan is started.

  Here, in diagnosis, the interpreter examines the continuous tomographic images collected in the main scan as a moving image, and in many cases, the temporal variation of the contrast agent concentration in the region of interest is objectively expressed by a time concentration curve. Checking is done. This is the so-called dynamic study.

  The accuracy of this dynamic study is sensitive not only to the body movement of the subject but also to the movement of the tissue due to breathing and pulsation. The smaller the region of interest, the greater the influence.

  Therefore, before the main scan, the laboratory technician uses a loudspeaker or the like to instruct the subject to hold his breath or suppress body movement. There are also devices that automate this instruction. That is, voice data such as breath holding and body movement suppression is held, and the voice data is obtained at time t when the CT value or average value CTave. Exceeds the threshold value TH, as shown in FIG. Is played (voice guidance).

  However, in this case, there is a problem that the disclosure of the main scan is delayed by the time required to reproduce the audio data from the time t when the CT value or the average value CTave.

  An object of the present invention is to reduce a deviation in main scan start timing in an X-ray computed tomography apparatus.

  An aspect of the present invention is an X-ray computed tomography apparatus that measures the start timing of a main scan having different scan conditions from the prep scan by monitoring a contrast agent concentration administered to a subject by a prep scan. An X-ray detector, a high voltage generator for applying a high voltage to the X-ray tube, a reconstruction unit for reconstructing tomographic image data based on the output of the X-ray detector, and the tomographic image data When the operation unit for setting the region of interest and the average of CT values of some pixels in the region of interest are compared with a threshold value, and the average value reaches or exceeds the threshold value And an X-ray computed tomography apparatus including a control unit that stops the prep scan and starts execution of the main scan or preparation for execution.

  According to the present invention, in the X-ray computed tomography apparatus, it is possible to reduce the shift in the main scan start timing.

  Embodiments of an X-ray computed tomography apparatus (X-ray CT apparatus) according to the present invention will be described below with reference to the drawings. The X-ray CT apparatus has a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and a radiation detector are rotated as one body, and a large number of detection elements are arrayed in a ring shape. There are various types such as a fixed / rotation (STATIONARY / ROTATE) type in which only the X-ray tube rotates around the subject, and the present invention can be applied to any type. Here, the rotation / rotation type that currently occupies the mainstream will be described.

  In addition, to reconstruct one slice of tomographic image data, projection data for about 360 ° around the periphery of the subject is required, and projection data for 180 ° + view angle is also required in the half scan method. . Here, in order to increase the reconstruction rate, techniques described in Japanese Patent Publication No. 1-23136, Japanese Patent Application Laid-Open No. 4-266744, Japanese Patent Application Laid-Open No. 12-70257, and the like may be employed. The present invention can be applied to any reconstruction method. Here, the half scan method will be described as an example.

  In addition, the mechanism for converting incident X-rays into electric charges is based on an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator and the light is converted into electric charges by a photoelectric conversion element such as a photodiode, The generation of electron-hole pairs in semiconductors and their transfer to the electrode, that is, the direct conversion type utilizing a photoconductive phenomenon, is the mainstream. Any of these methods may be employed as the X-ray detection element, but here, the former indirect conversion type will be described.

  In recent years, the so-called multi-tube type X-ray CT apparatus in which a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has been advanced. The present invention can be applied to both a conventional single-tube X-ray CT apparatus and a multi-tube X-ray CT apparatus. Here, a single tube type will be described.

  FIG. 1 shows the configuration of the main part of the X-ray computed tomography apparatus according to this embodiment. The X-ray computed tomography apparatus according to this embodiment includes a scan gantry 1 and a computer apparatus 2. The scan gantry 1 is a component for collecting projection data relating to a subject, and the projection data is captured by the computer device 2 and used for processing such as image reconstruction and real prep. The computer apparatus 2 includes a real prep control unit 21, a preprocessing unit 23, an image reconstruction unit 24, a display unit 25, an operation console 26, and an audio data storage unit 27 connected to the real prep control unit 21 via a data / control bus 28. Consists of

  The subject is inserted into the cavity (imaging port) of the scan gantry 1 while being placed on the top plate 20 of the bed 10. The top plate 20 of the bed 10 is driven by the bed driving unit 17 and moves in the longitudinal direction. Usually, the bed 10 is installed such that the longitudinal direction thereof is parallel to a rotation axis RA (same as the body axis and the Z axis) described later. The scan gantry 1 is provided with an annular rotary gantry (not shown) that is driven by the gantry rotation drive unit 16 and rotates about the rotation axis RA. An X-ray tube device 110 and an X-ray detector 113 are mounted on the rotating mount in a facing relationship.

  The X-ray tube device 110 includes an X-ray tube 111 and an X-ray filter 112 for removing a low energy component for reducing exposure. In order to supply power to the X-ray tube 111, an inverter type high voltage generator 14 is provided. The high voltage generator 14 includes a high voltage transformer, a filament current generator, a rectifier, a tube voltage switch, a filament current switch, and the like for adjusting the tube voltage and the filament current arbitrarily or in stages. .

  The output of the X-ray detector 113 is supplied as projection data to the image reconstruction unit 24 via a data acquisition unit 114, a slip ring (not shown) that enables continuous rotation and a preprocessing unit 23, where the tomographic image data is output. It is used for the reconstruction process. This tomographic image data is displayed on the display unit 25 and also supplied to the real prep control unit 21 and used for processing for determining the voice guide generation timing and the main scan operation start timing as will be described later. Is called.

  The console 26 is provided for the operator to input various information and various instructions including, for example, scanning conditions and real prep conditions (two types of threshold values THguide and THmain and waiting time WT). The console 26 includes an operation screen. The operation screen or display unit 25 displays a setting screen suitably devised by the real prep control unit 21 to assist the operator in setting the real prep conditions.

  Hereinafter, the real prep photographing operation by the real prep control unit 21 will be described. Actually, prior to the real prep shooting operation, the imaging slice positioning, prep scan conditions (tube voltage, tube current, scan time, number of bundled channels), main scan conditions (tube voltage, tube current, scan time, The number of bundled channels) and real prep conditions (size and position of the region of interest ROI, two kinds of thresholds THguide and THmain, waiting time WT) are set. Typically, the tube voltage for the prep scan is set to be equivalent to the tube voltage for the main scan in order to obtain a uniform quality, and the tube current for the prep scan is lower than the tube current for the main scan in order to reduce the exposure dose. Is set. The setting of the real prep condition will be described later. First, the real prep shooting operation will be described.

  FIG. 2 shows this operation procedure. Please refer to FIG. 3 and FIG. 4 (a) together with FIG. First, a contrast medium is injected into the subject, and then, under the control of the real prep control unit 21, typically at least a lower dose and a lower resolution (may be bundled with adjacent channels) than the main scan. A real prep scan is performed under the scan conditions (S1). That is, while the X-ray tube apparatus 110 and the X-ray detector 113 continuously rotate around the subject with respect to the positioned slice, X-rays are generated continuously or in pulses at a low dose, and data collection is performed periodically. Repeated.

  In parallel with the prep scan, the real prep control unit 21 controls the image reconstruction unit 24 to immediately reconstruct the attenuation coefficient distribution as tomographic image data from the projection data obtained by the prep scan (real time). CT (referred to as CT or CT fluoroscopy) (S2), CT values of a plurality of pixels in the region of interest ROI set in advance are extracted from the tomographic image data obtained in S2, and an average value CTave. Is calculated (S3 The calculated CT average value CTave. Is compared with a threshold value THguide for guidance set in advance to a value lower than the threshold value THmain for shifting to the main scan (S4). The CT average value CTave. Reflects the contrast agent concentration. As the contrast agent concentration itself, the mask image collected before injection of the contrast agent and real or live image data obtained by the prep scan are used. May be extracted, pixel values of a plurality of pixels in the region of interest ROI may be extracted from the difference image, and an average value thereof may be calculated.

  As a result of the comparison, when the CT average value CTave. Does not reach or exceed the guidance threshold value THguide, the degree of staining of the region of interest by the contrast agent is too low, and the above S1 to S4 Repeat the process. At time t1 when the CT average value CTave. Reaches or exceeds the guidance threshold value THguide, the real prep control unit 21 assumes that the degree of staining of the region of interest by the contrast medium is in the state immediately before the main scan. Reads voice data related to breath holding and body movement suppression from the voice data storage unit 27, converts the voice data into a voice signal, and supplies the voice signal to the speaker 19. Thereby, voice guidance regarding breath holding and body movement suppression is output from the speaker 19 to the subject (S5).

  Although it has been described that the guidance on breath holding and body movement suppression is performed by voice, instead of or in combination with it, the subject can be visually recognized and placed on a display placed at a position outside the X-ray exposure range. You may make it output the guidance regarding a stop and body movement suppression as a character message or a design.

  Subsequently, the prep scan (S6), the immediate image reconstruction (S7), and the calculation of the CT average value CTave. Of the pixels in the region of interest ROI (S8) are continued. Then, the threshold THmain for main scan transition set in advance to a value higher than the threshold THguide for guidance is compared (S9). As a result of the comparison, when the CT average value CTave. Does not reach or exceed the threshold THmain for the main scan transition, the degree of staining of the region of interest by the contrast agent is too low for the main scan transition. As described above, the processes of S6 to S9 are repeated. At the time t2 when the CT average value CTave. Reaches or exceeds the threshold THmain for the main scan transition, the degree of staining of the region of interest by the contrast medium satisfies the transition state to the main scan, The real prep control unit 21 stops the prep scan (S10).

  Then, the real prep control unit 21 terminates the voice guidance at the time t2 when the CT average value CTave. Reaches or exceeds the threshold THmain for the main scan transition, and holds the breath hold and body for the subject. It is determined whether or not the waiting time WT prepared as a preparation period for the movement suppression has elapsed since the end of the voice guidance (S11), and when the voice guidance is completed and the waiting time WT has elapsed since then, the main scan is performed. Is started (S13).

  On the other hand, the real prep control unit 21 determines that the voice guidance has not ended or the waiting time WT has ended the voice guidance at the time t2 when the CT average value CTave. Reaches or exceeds the threshold THmain for the main scan transition. When the time has not elapsed, as shown in FIG. 4 (b), the main scan is not immediately started at time t2, but the main guidance is waited until the voice guidance is finished and the waiting time WT elapses thereafter. (S12). Such a situation occurs when the threshold THmain for shifting to the main scan is too low, or conversely, the threshold THguide for guidance is relatively high. It is important to avoid such a situation in order to avoid the delay of the main scan. For this reason, a method for setting the threshold THmain for shifting to the main scan and conversely, the threshold value THguide for guidance is devised. ing. This will be described later.

  In this scan, the scheduled duration, scheduled number of rotations, contrast agent concentration (CT average value) drops to the scheduled value, or if the helical scan is completed, data collection for the scheduled helical scan range is completed. It continues until it satisfies (S14), and when the condition is satisfied, the main scan ends (S15).

  As described above, according to the present embodiment, not only the threshold THmain for the main scan but also the threshold THguide for voice guidance lower than that is set, and the CT average value becomes the threshold THguide for guidance. Since the guidance is output at the time t1 when it reaches or exceeds, the delay from the time t2 when the CT average value reaches or exceeds the threshold THmain for the main scan to the start of the main scan is eliminated. Can do. Further, even when the guidance or waiting time has not elapsed at the time t2 when the CT average value reaches or exceeds the threshold THmain for the main scan, the delay time from the time t2 to the start of the main scan Can always be shorter than the total time of the guidance time and the waiting time.

  FIG. 6 shows real prep conditions (size and position of the region of interest ROI, two kinds of threshold values THguide displayed on the operation screen of the console 26 or the display unit 25 under the control of the real prep control unit 21. , THmain, waiting time WT) setting screen. For example, a tomographic image 32 photographed in advance for condition setting is displayed in the right column of the screen, and a time density curve 31 is displayed in the lower left column of the screen. As the time density curve 31, after the prep scan is started, the time variation of the CT average value of the real-time image obtained by the prep scan is displayed. A time concentration curve model is displayed.

  The data of the time concentration curve model is stored in the storage unit 27 or the like in association with the part. A mark 33 of the region of interest ROI is superimposed on the tomographic image 32, and the operator can move to a desired position on the image using a pointing device and set the desired size.

  Further, in the upper left column of the setting screen, a box for inputting the threshold values THguide and THmain and the waiting time WT is displayed. The operator can set the thresholds THguide and THmain and the waiting time WT by inputting arbitrary numerical values in each box. The waiting time WT after the end of the guidance is arbitrarily set by the laboratory technician according to the age, physical condition, etc. of the subject, and in some cases, the waiting time WT may be set to zero. When the main scan threshold THmain is set, the guidance threshold THguide is automatically input as a default value, for example, 30% of the threshold THmain, and the guidance threshold THguide is manually input only when necessary. To do.

  The reference lines 37 and 38 on the time density curve model move up and down according to the threshold values THguide and THmain input in these boxes. The operator can refer to this information to check whether each value is appropriate, and to determine the approximate time width from t1 to t2, and approximate the threshold values THguide and THmain to the optimum values. .

  Here, when the optimum values of the threshold values THguide and THmain are defined, as shown in FIG. 5, the CT average value CTave. Is required for guidance output from the time t1 when the guidance threshold value THguide is reached or exceeded. At the time when the total time of the time and the waiting time WT has elapsed, the CT average value CTave. Is defined as a state in which the time t2 when reaching or exceeding the main scanning threshold value THmain coincides. In this state, the restraint time for holding the breath of the subject can be minimized. However, the actual time-concentration curve varies among individuals, and even for the same individual, it changes due to uncertain factors such as physical condition. It is practically impossible to set the threshold values THguide and THmain as optimum values. Is possible. However, the threshold values THguide and THmain are set while referring to the time density curve model, and the recommended value of the guidance threshold value THguide is automatically input in the recommended percentage with respect to the main scan threshold value THmain. Thus, it is possible to approximate the optimum value rather than the case without such support.

  Also, as shown in FIG. 7A, when the pull-down menus 39 and 40 are written in the thresholds THguide and THmain boxes 34 and 35 and pressed, a plurality of recommended values are displayed in a pull-down menu. You may make it select from the inside by an inspection engineer. Further, instead of the recommended value, a plurality of examination site menus may be displayed as shown in FIG. 7B. In this case, recommended values of the threshold values THguide and THmain are set for each examination site.

  In the above method, as shown in FIG. 8, the region of interest ROI is set at an appropriate concentration monitoring site (such as the descending aorta) upstream from the slice of the main scan, and the average value of CT values of pixels in the region of interest ROI is calculated. The average value is calculated and compared with threshold values THguide and THmain. However, there is a possibility that the body movement accompanying the breathing stop will remove the region of interest ROI from the concentration monitoring site. This is because the region of interest ROI is fixed in the coordinate system of the screen, but the concentration monitoring region moves with respiratory motion. If the region of interest ROI deviates from the concentration monitoring part, the concentration monitoring accuracy is lowered. A method for solving this will be described below.

  FIG. 9 shows an operation procedure for reducing a decrease in concentration monitoring accuracy due to respiratory motion. First, as shown in FIG. 10, the region of interest ROI is set for the concentration monitoring site (for example, the descending aorta) by the operation of the console 26 by the operator (S21). The region of interest ROI is not limited to a circle, and can be set to other shapes or arbitrary shapes. The operator estimates a range in which the concentration monitoring part moves with respiration, and sets the region of interest ROI larger than the area of the concentration monitoring part so as to include the estimated movement range of the concentration monitoring part. As a result, the concentration monitoring region before movement is inherent in the region of interest ROI, and the concentration monitoring region after movement is also inherent in the region of interest ROI. In addition, since the high CT value of the bone lowers the threshold processing accuracy, the operator should carefully adjust the position, shape and size of the region of interest ROI avoiding the region of bone (such as the spine).

  As described above, since the region of interest ROI is set larger than the region of the concentration monitoring region, the region of interest ROI includes the contrast agent flowing into the concentration monitoring region and the surrounding tissue. Therefore, the average value of the CT values of the pixels included in the region of interest ROI is pulled down by the CT value of the surrounding tissue and becomes low.

  In order to solve the problem, as shown in FIG. 11, the real prep control unit 21 extracts the CT values of the upper few percent or the upper tens of percent from the CT value distribution (histogram) of the pixels in the region of interest ROI. And a function of calculating an average value of the CT values of the extracted top few percent or top tens percent. The above percentage is called the extraction rate.

  Along with the setting of the region of interest ROI, the extraction rate is set by the operator via the console 26 (S22). The initial value of the extraction rate is set to 20%, for example, which is expected to have high versatility. When changing the extraction rate from the initial value to an arbitrary value, the operator inputs a desired number from the numeric keypad provided on the console 26. The control unit 21 provides a pull-down menu for the input part of the extraction rate. There are various numbers on the pull-down menu. The operator operates a pointing device provided on the console 26 to input a desired number from the pull-down menu.

  When the above preparation is completed, a contrast medium is injected into the subject, and then a real prep scan is performed under the control of the real prep control unit 21 (S23), and the image reconstruction unit 24 performs tomographic image data. Is reconfigured (S24).

  The control unit 21 extracts, from the tomographic image data, CT values of the upper X percent set as the extraction rate from a plurality of pixels in the relatively large region of interest ROI set in advance (S25), and the average value CTave. ' Is calculated (S26).

  The CT average value CTave. 'Is compared with the threshold value THguide (S27). When the CT average value CTave. 'Has not reached or exceeded the threshold value THguide, the processing of S23 to S27 is repeated. When the CT average value CTave. 'Reaches or exceeds the threshold value THguide, a voice guide relating to breath holding and body movement suppression is output from the speaker 19 under the control of the real prep control unit 21 (S28).

  Subsequently, prep scan (S29), image reconstruction (S30), extraction of CT values of the upper X percent from pixels in the region of interest ROI (S31), calculation of the average value CTave. 'Of the extracted CT values (S32), and A series of processing of the comparison of the CT average value CTave. 'To the threshold value THmain (S33) is repeated until the CT average value CTave.' Reaches or exceeds the threshold value THmain. At this time, the prep scan is stopped (S34), waits for the waiting time WT to elapse as required (S35, S36), and the main scan is started (S37). In this scan, the scheduled duration, scheduled number of rotations, contrast agent concentration (CT average value) drops to the scheduled value, or if the helical scan is completed, data collection for the scheduled helical scan range is completed. It continues until it satisfies (S38), and when the condition is satisfied, the main scan ends (S39).

  In this way, by setting the region of interest ROI larger than the concentration monitoring region, calculating the average value of the CT values of the upper X percent of the pixels in the region of interest ROI, and executing threshold processing with the average value The error of the guidance output timing and the main scan start timing due to the deviation of the region of interest ROI with respect to the concentration monitoring site by the breathing operation can be reduced.

  Here, as described above, the operator should carefully adjust the position, shape, and size of the region of interest ROI while avoiding the region of the bone (such as the spine), but in reality, the amplitude of the respiratory motion is large. There is an individual difference, and therefore, a bone region may enter the region of interest ROI. In this case, since the bone has a high CT value, a situation occurs in which the guidance output timing and the main scan start timing are unexpectedly advanced.

  In order to avoid this situation, as shown in FIG. 9, the control unit 21 has a CT value higher than a predetermined value from the CT value distribution of the pixels in the region of interest ROI in the previous stage of the CT value extraction processes S25 and S31. The value is removed (S40, S41). Generally, bone CT values are distributed within a range of 250-1,000. The predetermined value is set to a CT value slightly higher than the lowest CT value (250) of bone, for example, 300. By setting the predetermined value to a value slightly higher than the lowest CT value (250) of the bone, a slight margin can be given to the situation where the CT value of the contrast agent is removed together with the CT value of the bone.

  In S22 of FIG. 9, particularly when the region of interest ROI is set to a complicated shape, the extraction rate may be significantly deviated from the optimum value. When the extraction rate is too high, the guidance output timing and the main scan start timing may be unexpectedly early, and when the extraction rate is too low, the guidance output timing and the main scan start timing may be unexpectedly delayed. There is sex.

  In order to reduce this possibility, as shown in FIGS. 13 and 14, two types of regions of interest ROI1 and ROI2 are set (S42), and the area ratio (ROI2 / ROI1) is calculated by the control unit 21. (S43) The area ratio may be set as the extraction rate. The area ratio may actually be calculated as a ratio of the number of pixels.

One region of interest ROI1 is set to a relatively large size including the density monitoring region, as in FIG. The other region of interest ROI2 is set to a relatively small size surrounding the concentration monitoring region. The control unit 21 calculates the area of the first region of interest ROI1. Further, the control unit 21 calculates the area of the second region of interest ROI2. The control unit 21 calculates the ratio of the area of the second region of interest ROI2 to the area of the first region of interest ROI1. For example, assuming that the area of the first region of interest ROI1 is 40 mm ² and the area of the second region of interest ROI2 is 10 mm ² , the extraction rate is set to 10/40, that is, 25 percent.

  By setting the extraction rate in this way, it is possible to reduce the deviation between the guidance output timing and the main scan start timing due to the extraction rate error.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Furthermore, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some constituent requirements may be deleted from all the constituent requirements shown in the embodiment.

The block diagram of the principal part of the X-ray computed tomography apparatus which concerns on embodiment of this invention. The flowchart which shows the real prep operation | movement by this embodiment. In this embodiment, the figure which shows the time concentration curve of a region of interest, and two types of threshold values set with respect to it. The figure which shows typically the real prep operation | movement by this embodiment with progress of time. The figure which shows typically the ideal state in the real prep operation | movement by this embodiment. The figure which shows the example of the threshold value setting screen displayed on the operation screen of a console or a display part under control of the real prep control part of FIG. The figure which shows the other example of the threshold value setting screen displayed on the operation screen of a console, or a display part under control of the real prep control part of FIG. The figure which shows the example of the region of interest ROI set via the console of FIG. The flowchart which shows the other real prep operation by this embodiment. The figure which shows the example of the region of interest ROI set by S21 of FIG. FIG. 10 is a supplementary diagram of the process of S25 of FIG. The flowchart which shows the further another real prep operation by this embodiment. The flowchart which shows the further another real prep operation by this embodiment. FIG. 14 is a supplementary diagram of the process of S42 of FIG. The figure which shows the conventional real prep operation | movement typically with time progress.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Scan gantry, 110 ... X-ray tube apparatus, 111 ... X-ray tube, 112 ... X-ray aperture apparatus, 113 ... X-ray detector, 114 ... Data collection part, 14 ... High voltage generation part, 16 ... Stand rotation drive , 17 ... bed driving unit, 10 ... bed, 20 ... top plate, 2 ... computer device, 21 ... real prep control unit, 23 ... pre-processing unit, 24 ... image reconstruction unit, 25 ... display unit, 26 ... operation Table 27, voice data storage unit 28, data / control bus.

Claims (6)

In the X-ray computed tomography apparatus for measuring the start timing of the main scan having different scan conditions from the prep scan by monitoring the contrast agent concentration administered to the subject by the prep scan,
An X-ray tube;
An X-ray detector;
A high voltage generator for applying a high voltage to the X-ray tube;
A reconstruction unit for reconstructing tomographic image data based on the output of the X-ray detector;
An operation unit for setting a region of interest for the tomographic image data;
An average of CT values of some pixels in the region of interest is compared with a threshold value. When the average value reaches or exceeds the threshold value, the prep scan is stopped and the main scan is performed. An X-ray computed tomography apparatus comprising: a control unit that starts execution or preparation for execution. 2. The X according to claim 1, wherein the control unit extracts a CT value occupying a predetermined upper percentage from the CT value distribution of pixels in the region of interest, and calculates an average value of the extracted CT values. Line computed tomography equipment. The X-ray computed tomography apparatus according to claim 1, wherein the control unit removes CT values greater than or equal to a predetermined value from the CT value distribution of pixels in the region of interest. The control unit removes CT values greater than or equal to a predetermined value from the CT value distribution of pixels in the region of interest, and extracts and extracts CT values that occupy a predetermined upper percentage from the distribution of remaining CT values. The X-ray computed tomography apparatus according to claim 1, wherein an average value of CT values is calculated. The X-ray computed tomography apparatus according to claim 2, wherein the control unit sets a ratio of the area of the concentration monitoring region to the area of the region of interest to the predetermined percentage. 6. The X-ray computed tomography apparatus according to claim 5, wherein another region of interest smaller than the region of interest is set in order to limit the region of the concentration monitoring region.

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