JP4909188B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT apparatus, and more particularly to an X-ray CT apparatus capable of appropriately identifying a diagnosis target even when a contrast examination is assumed.

  An X-ray CT apparatus irradiates a subject with X-rays of a fan beam (fan-shaped beam) or cone beam (conical or pyramidal beam), and based on the intensity of the X-ray transmitted through the subject, The distribution information of the linear absorption coefficient is imaged and plays an important role in the diagnosis of lesions.

  In the X-ray CT apparatus, in order to identify the diagnosis target in the obtained tomographic image, it is necessary to ensure sufficient contrast resolution. The contrast resolution depends on CNR (Contrast Noise Ratio) which is a kind of image quality index. Here, the CNR is defined as a value obtained by dividing the absolute value of the CT value difference (contrast) between the diagnosis target and its surroundings by the image SD (image standard deviation, image noise standard deviation value).

  Since the CNR is inversely proportional to the image SD, generally, the CNR is improved by increasing the dose and reducing the image SD. However, from the viewpoint of subject exposure, it is not always necessary to simply increase the dose in order to improve CNR. That is, in an actual scan, it is desirable to suppress the exposure dose of the subject as much as possible while ensuring an appropriate CNR according to the diagnostic purpose.

  In order to cope with this, Patent Document 1 discloses an X-ray condition in which an X-ray CT apparatus can reduce the exposure dose received by each patient while maintaining an appropriate CNR for identifying a diagnosis target, and achieve it. Describes a technique for simply and simply determining in advance before starting scanning.

  By the way, the contrast examination of the X-ray CT apparatus is performed for the purpose of qualitative diagnosis such as benign / malignant confirmation of a lesion. For this reason, it is important to perform a scan (main scan) for capturing a diagnostic image at a timing when the contrast agent administered to the subject flows into the imaging region.

  In order to cope with this, in Patent Document 2, the CT value of a specific part is monitored while performing a low-dose scan (monitoring scan) on the upstream side of the imaging part before the main scan, and the CT value is constant. A technique is described in which the monitoring scan is stopped when the threshold value of the value is exceeded and the main scan is automatically started.

In Non-Patent Document 1, the operator's weight, contrast agent concentration, contrast agent injection speed, contrast agent injection time, contrast agent injection amount, etc. are input by the operator in advance, and monitored by a monitoring scan. In addition, a technique for predicting a temporal change in the CT value of a specific region, that is, a temporal change in the CT value of a diagnosis target from the initial rising shape of the contrast agent is described.
Japanese Patent Application No. 2006-277699 JP 2002-191594 A Aortic and hepatic contrast medium enhancement at CT: Part I. Prediction with a computer model, Radiology, 1998, 207, 647-655.

  However, as described in Patent Document 2, the contrast between the diagnosis target and the surrounding tissue changes depending on the contrast phase. However, in the technique of Patent Document 1, the contrast between the diagnosis target and the surrounding tissue is determined as a constant value in consideration of the patient size, tube voltage, etc., and the contrast change due to the time phase of the contrast is not taken into consideration. . Therefore, in the technique of Patent Document 1, depending on the time phase of the contrast, there may be a case where the CNR that must be ensured for diagnosis is not satisfied, or conversely, an excessive CNR may occur. May cause disability and overexposure in making a correct diagnosis.

  The present invention has been made in view of the above circumstances, and provides an X-ray CT apparatus that performs a contrast examination while maintaining a CNR suitable for diagnosis even when a temporal change in contrast in a contrast scan is taken into consideration. For the purpose.

  In order to solve the above-mentioned problem, an X-ray CT apparatus according to claim 1, an X-ray source that irradiates a subject with X-rays, an X-ray detector that detects X-rays transmitted through the subject, and An X-ray CT apparatus for performing contrast imaging of an examination region of the subject by a scan that rotates the X-ray source and the X-ray detector around the subject into which a contrast medium has been injected. Predicting means for predicting a contrast corresponding to a time phase at the time of scanning, which is a contrast representing a difference between a density of a diagnostic object and a density of surrounding tissue that changes with time by injecting a contrast medium into the contrast medium, and the scan Calculation means for calculating an X-ray condition in a time phase of time so as to satisfy a contrast-noise ratio set in advance based on the predicted contrast, and the X-ray condition so as to satisfy the calculated X-ray condition source Is characterized by comprising a control means for controlling, the.

  According to the image processing apparatus of claim 1, the contrast represents a difference between the density of the diagnosis target and the density of the surrounding tissue that changes with time by injecting the contrast medium into the subject, and the contrast at the time of scanning. The contrast corresponding to the phase, that is, the contrast at a certain point in time of scanning is predicted. An X-ray condition that satisfies a preset contrast-to-noise ratio (CNR) based on the predicted contrast is calculated. Scanning is performed by controlling the X-ray source so that the calculated X-ray condition is satisfied. Thereby, even when a temporal change in contrast in a contrast scan is taken into consideration, a CNR suitable for diagnosis can be maintained.

  The X-ray CT apparatus according to claim 1, wherein a monitoring scan is performed at a dose lower than that at the time of scanning the imaging region to be diagnosed or a specific region upstream of the imaging region, and the time concentration obtained thereby Based on a curve (TDC: Time Density Curve), the relationship between the time phase at the time of scanning and the contrast at that time phase may be predicted. Thereby, the main scan can be performed at a more reliable shooting timing. In addition, by performing a monitoring scan, a time contrast curve (TCC: Time Contrast) representing a difference between a time concentration curve of a diagnosis target that changes in time by injecting a contrast medium into a subject and a time concentration curve of surrounding tissues. Curve) can be predicted more reliably.

  According to the present invention, a contrast examination can be performed while maintaining a CNR suitable for diagnosis even when a temporal change in contrast in a contrast scan is taken into consideration.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is an external view showing the overall configuration of the X-ray CT apparatus 100 according to the first embodiment of the present invention, and FIG. 2 is a block configuration diagram of the X-ray CT apparatus 100. Although the case where there is one X-ray tube is described here, the present invention can also be applied to a multi-ray source type X-ray CT apparatus. In addition, the X-ray CT apparatus irradiates a wide fan beam that covers the entire subject, and rotates / rotates (Rotate / Rotate) method in which the X-ray tube and the detector are integrally rotated, and an electron beam is electrically applied. Various methods have been established so far, such as an electron beam scanning method in which the light beam is deflected to a target electrode, but the present invention can be applied to any method. Here, a case where the present invention is applied to a rotation / rotation method that occupies the mainstream will be described. In addition, in order to reconstruct one slice of tomographic image data, a full scan method that requires projection data of about 360 degrees for one rotation of the subject and a half scan method that requires projection data for 180 degrees + view angle. There is. The present invention can be applied to any reconstruction method.

  As shown in FIG. 1, an X-ray CT apparatus 100 mainly includes a gantry 1, a patient table 2, an operation console 3, a top 4 provided on the patient table 2, a display device 5, and an operation device. 6. When the subject 7 fixed on the top 4 on the patient table 2 is carried into the gantry 1 and scanned, X-ray absorption coefficient distribution information inside the subject 7 is acquired.

  As shown in FIG. 2, the gantry 1 mainly includes an X-ray tube 10, a high voltage generator 11, a slip ring 12, a collimator 13, an X-ray detector 14, a data acquisition circuit 15, and a gantry drive. The unit 16 includes a drive frame 17 and a tube voltage / tube current measuring device 18.

  The X-ray tube 10 irradiates the subject 7 with X-rays, and in order to irradiate the X-rays, power is supplied from the high voltage generator 11 to the X-ray tube 10 via the slip ring 12, Thereby, X-rays are emitted from the X-ray tube 10 intermittently or continuously. The tube voltage / tube current supplied to the X-ray tube 10 is always measured by the tube voltage / tube current measuring device 18, and the high voltage generator 11 reflects the result to the tube supplied to the X-ray tube 10. Controls voltage and tube current.

  The collimator 13 irradiates the subject 7 with X-rays radiated from the X-ray tube 10 as, for example, a pyramidal X-ray beam, that is, a cone beam X-ray.

  The X-ray detector 14 detects X-rays emitted from the X-ray tube 10 and transmitted through the subject 7.

  The data collection circuit 15 is connected to the X-ray detector 14 and collects detection data of individual X-ray detection elements of the X-ray detector 14.

  The drive frame 17 includes the X-ray tube 10, the high voltage generator 11, the slip ring 12, the collimator 13, the X-ray detector 14, the data collection circuit 15, and the tube voltage / tube current measuring device. 18 are mounted. The drive frame 17 is rotated by the driving force transmitted from the gantry driving unit 16 controlled by the system control device 20.

  As shown in FIG. 2, the patient table 2 mainly includes a top plate 4, a table control device 21, and a top plate drive device 22.

  The table control device 21 controls the top plate driving device 22 to control the height of the top plate 4 and the back and forth movement of the top plate 4. Thereby, the subject 7 is carried into and out of the X-ray irradiation space of the gantry 1.

  As shown in FIG. 2, the console 3 mainly includes a display device 5, an operation device 6, a system control device 20, an image reconstruction device 23, a storage device 24, a scan planning device 25, a TDC • A TCC prediction device 26 and a contrast medium injection control device 27 are included.

  The display device 5 is connected to the system control device 20 and displays a reconstructed image output from the image reconstruction device 23 and various information handled by the system control device 20.

  The operation device 6 is connected to the system control device 20, and inputs various instructions, information, and the like to the system control device 20 by an operator. The operator can interactively operate the X-ray CT apparatus using the display device 5 and the operation device 6.

  The system controller 20 is connected to the gantry 1 and the patient table 2, and includes a high voltage generator 11, a collimator controller (not shown), a data acquisition circuit 15, and an X-ray detector 14 in the gantry 1. Control the table controller 21 in the patient table 2.

  The image reconstruction device 23 receives data collected by the data collection circuit 15 in the gantry 1 under the control of the system control device 20, and scanogram projection data (subject fluoroscopy data) collected by the data collection circuit 15 at the time of scanogram imaging. ) To create a scanogram image, and at the time of scanning, CT image reconstruction is performed using projection data of a plurality of views collected by the data collection circuit 15.

  The storage device 24 is connected to the system control device 20, and a program for realizing the functions of the scanogram image, the reconstructed CT image, the various data, and the X-ray CT apparatus created by the image reconstruction device 23. Etc. are stored.

  The scan planning device 25 is connected to the system control device 20, and an operator creates a scan condition advance plan using an instruction input from the operation device 6 and a scanogram image read from the storage device 24. To do. That is, the scanogram image read from the storage device 24 is displayed on the display device 5, and the operator uses the operation device 6 on the displayed subject scanogram image to perform a CT image reconstruction position (hereinafter referred to as a slice position). By specifying the coordinates, it is possible to set the slice position at the time of scanning. Further, the information on the slice position set here is stored in the storage device 24, and is also used by the scan planning device 25 for making a plan such as X-ray dose control conditions. Various known techniques can be used for the function of planning an optimum X-ray dose for a subject that has been previously scanned.

  The TDC / TCC prediction device 26 predicts TDC and TCC at the imaging region based on information such as the physique of the subject inputted in advance and information obtained by the monitoring scan. Further, a contrast agent injection control device 27 for appropriately injecting a contrast agent is connected to the TDC / TCC prediction device 26. TDC and TCC will be described later in detail.

  The X-ray CT apparatus 100 configured as described above operates as follows.

  The X-ray emission range of the X-ray emitted from the X-ray tube 10 is controlled by the collimator 13, for example, a fan beam (fan beam) or a cone beam (conical or pyramidal beam) X-ray, and the subject 7 Is irradiated. The scan range set by the photographer is adjusted by controlling the position of the top plate 4 with the top plate driving device 22 and the table control device 21.

  X-rays transmitted through the subject 7 are detected by the X-ray detector 14. In general, in the case of a multi-slice CT apparatus, the X-ray detector 14 has a curved surface structure in which X-ray detection elements having 2 to several hundred rows in the body axis direction and several hundred to 1000 channels in the body width direction are arranged. The detection data converted into an electrical signal by such a detector 14 is transmitted to a data acquisition circuit 15 called DAS (Data Acquisition System), converted to AD, and stored in the storage device 24 under the control of the system controller 20. Is done. Based on the accumulated collected data, the image reconstruction device 23 reconstructs the CT image and displays it on the display device 5 as an image. At the time of scanogram imaging before the main imaging (main scan), a scanogram image is reconstructed by the image reconstruction device 23 using the projection data of the subject acquired by the data acquisition circuit 15, and at the time of the main scan. In the image reconstruction device 23, image reconstruction is performed using projection data of a plurality of views acquired by the data collection circuit 15.

  The scanogram image created by the image reconstruction device 23 and the reconstructed CT image are stored in the storage device 24.

  In the present embodiment, it is important to scan the diagnostic image at the timing when the contrast agent administered to the subject flows into the imaging region in order to appropriately identify the diagnosis target.

  Hereinafter, TDC / TCC when the liver is imaged will be described with reference to FIG. FIG. 3 is a diagram showing TDC and TCC when a contrast scan is performed, (a) shows TDC of abdominal aorta, bloody tumor (diagnosis target) and liver parenchyma (surrounding tissue), (b) Abdominal aorta, ischemic tumor and hepatic parenchyma TDC are shown, (c) shows hepatic parenchymal polycytic tumor TCC (absolute value of CT value), and (d) shows hepatic parenchymal ischemic tumor TCC.

  The TDC indicates a change in the concentration of the contrast agent with time, and is represented by a function of time and EU (Enhancement Unit). The EU is a value obtained by subtracting the CT value before contrast from the CT value after contrast. Further, TH (Threshold) in the figure is a threshold value in the monitoring scan.

  When scanning the liver, usually, a contrast medium is injected into a subject intravenously in a radial vein, and a monitoring scan is performed on the abdominal aorta located upstream from the liver. The monitoring scan is performed before the main scan, and the CT value can be acquired and is performed with the lowest possible X-ray dose.

  By analyzing the initial rising shape of the TDC from the EU measured by the monitoring scan, it is possible to predict the TDC of the liver and a desired diagnosis target (such as various tumors). In addition, the timing for starting the main scan can be measured from the EU measured by the monitoring scan. That is, the contrast scan of the liver is started after the EU measured by the monitoring scan exceeds the dark value TH, that is, after the time t has elapsed since the monitoring scan was started.

  In this case, the operator inputs the conditions such as the subject's body weight, imaging region, contrast agent concentration, contrast agent injection speed, contrast agent injection time, contrast agent injection amount, etc. in advance. Predict TDC of surrounding tissue. About this, the well-known technique as shown in the above-mentioned nonpatent literature 1 can be used. Further, the time t also varies depending on the above conditions.

  Further, the TCC is calculated from the predicted TDC of the diagnosis target and the TDC of the surrounding tissue and used for determining the scanning condition. That is, the TCC can be calculated by setting the contrast value between the diagnosis target and the surrounding tissue at a predetermined time as an absolute value of the difference between the EU of the diagnosis target and the EU of the surrounding tissue at the predetermined time.

  Next, a series of scan operations in the present embodiment will be described with reference to FIG.

  First, scanogram imaging of the subject 7 is performed (step S1), and based on the scanogram obtained in step S1, a scan region including a diagnosis target is input by the operator via the operation device 6 (step S2). ). Here, a slice thickness, a scan time, a reconstruction filter function, a visual field size, a window condition, and the like are input as scan conditions for slice positions. Further, a monitoring scan position is set based on the scanogram obtained in step S1 (step S3).

  An imaging time phase to be scanned is input by the operator via the operation device 6 (step S4). In the input of the contrast time phase in step S4, the TDC or TCC stored in the storage device 24 is called by the scan protocol, and the TDC or TCC as shown in FIG. It is good to show in Here, the scan protocol is a scanning procedure set in the X-ray CT apparatus 100 and imaging conditions corresponding to the physique and imaging region of the subject. The TDC or TCC used for this processing may be any of data acquired using a standard human body phantom, data acquired by volunteer shooting of a healthy person, data acquired by the user in the past, and the like. However, it is preferable to extract data having the same physique and physical characteristics as the subject based on the subject information input by the operator.

  Here, a method for setting the time phase of the contrast to be scanned when the TCC is shown as in FIG. 5 will be described.

  Based on the TCC as shown in FIG. 5 displayed on the display device 5, the operator inputs a contrast time phase to be visually scanned using, for example, a GUI. Various input methods such as a method of directly pointing the mouse on the displayed TCC and a method of inputting by providing a pull-down menu can be used.

  A, B, and C in FIG. 5 show examples of time phases set when a plurality of liver regions are intermittently scanned. A assumes the time phase Tl (early arterial phase) of 1/2 (1 / 2C_maX) of the maximum contrast in the predicted TCC, and B indicates the time phase T2 where the contrast is maximum (C_maX). (Late arterial phase) is assumed, and C is assumed to be in the vicinity of the time phase (equilibrium phase) after the time T3 has elapsed since the start of imaging. In addition, the areas shown in the band shapes of the scans A, B, and C in FIG. 5 indicate rough scan times in the respective time phases. Generally, when the whole liver is imaged by MDCT (multi-slice CT), imaging can be performed in about 5 to 10 seconds. The contrast time phase may be one or plural, but in this embodiment, three time phases as shown in FIG. 5 are input.

  The display device 5 may display not only the TCC but also the TDC of the liver tumor (diagnosis target) or liver parenchyma (surrounding tissue) familiar to the operator. Even with other display methods, the displayed TDC and TCC may be modified in any way without departing from the spirit of the present invention.

  After inputting the imaging time phase, the CNR (CNR_d) that can identify the diagnosis target is called from the storage device 24 (step S5). Then, an optimal scan condition that satisfies CNR_d is preliminarily calculated for each inputted contrast time phase (step S6). The optimum scanning conditions here are a tube voltage and a tube current that satisfy CNR_d while minimizing the exposure of the subject. In this embodiment, the tube voltage is constant during scanning regardless of the contrast time phase, but the tube current is adaptively changed in the body axis direction of the subject and the rotation direction of the X-ray tube. As the optimum scanning condition set in step S6 and accompanying information, the image SD, the exposure dose, and the like may be displayed on the display device 5 to be shown to the operator.

  In the present embodiment, an example in which CNR_d that can identify a diagnosis target is called from the storage device 24 in step S5 is described. However, CNR_d is calculated using an arithmetic function provided in the system control device 20, It can also be calculated by the method described in Patent Document 1 (steps S304 to S310 of Patent Document 1) filed earlier by the inventors of the present application. The same applies to the second and third embodiments described later.

  When the preliminary scan conditions are calculated, a monitoring scan is performed on the monitoring scan position set under the scan conditions, and the TDC / TCC prediction device 26 performs an abdominal aorta, a polycytic tumor (diagnosis target), and liver parenchyma. The TDC and TCC of (surrounding tissue) are predicted, and the optimal scan condition used when performing the actual scan is calculated based on the TCC predicted by the monitoring scan (step S7). The TDC and TCC for setting the time phase of contrast input in step S4 are reflected in the TCC predicted in step S7. Thereby, the contrast of the diagnostic object assumed by the contrast and the surrounding tissue is predicted for each time phase.

  Here, the predicted TCC is at the time of a standard tube voltage (for example, 120 kV), but the information of the optimum tube voltage calculated in this step is taken in and the X-ray spectrum is taken into consideration as shown in FIG. Therefore, it is better to change the shape of the TCC as appropriate. Here, FIG. 6 shows the corrected shape of the abdominal aorta TDC and liver parenchyma TCC, and (a) shows the TDC when the height and weight of the subject are constant and the contrast agent injection rate is changed. (B) is the TCC of the liver parenchyma when the X-ray spectrum is changed by changing the scan tube voltage. Thus, it is expected that the TCC accuracy is improved by taking into account the subject information and the X-ray spectrum, and the imaging dose is controlled to obtain a desired image quality. Further, depending on the scanning speed of the X-ray CT apparatus 100 in the body axis direction, the TCC calculated in step S7 may not be achieved. Therefore, a technique for scanning the vicinity of the contrast time phase that provides the operator's desired contrast over the entire scanning range as described in JP-A-2006-296493 may be used.

  Then, after the EU measured by the monitoring scan exceeds the dark value TH, that is, after the time t has elapsed since the monitoring scan was started, a scan (main scan) of a preset scan area is performed. Based on the TCC predicted in step S7, scanning is performed under a scanning condition that satisfies CNR_d according to the contrast between the diagnosis target and the surrounding tissue in each inputted contrast time phase (step S8) (step S8). Step S9). For example, when the operator has set three time phases of the liver as shown in FIG. 5, the image is taken so as to obtain an image SD corresponding to the contrast in each time phase of A, B, and C. Conditions are controlled. Specifically, since the CNR is defined as a value obtained by dividing the contrast by the image SD, the image SD to be satisfied in each time phase of A and B is 1 / 2C_max / in the time phase T1 set by the operator. It is obtained as CNR_d, and is obtained as C_max / CNR_d in the time phase T2. The tube current may be controlled to satisfy this. Actually, the scan conditions may be controlled so that the CNR takes into account the change in contrast with the scan speed and the scan time. Thereby, it is possible to perform photographing under more appropriate photographing conditions.

  FIG. 7 is an example of an imaging protocol in the case of volume scanning. FIG. 7A shows a case where a contrast scan of the liver is performed, and (i), (ii), and (iii) in the figure correspond to the time phases of A, B, and C in FIG. In this case, the monitoring scan position is set at the lower part of the liver and in the vicinity of the abdominal aorta, and a method of scanning in the body axis direction as indicated by an arrow is preferable. FIG. 7B shows a case where the chest and abdomen are subjected to a non-contrast scan and the liver is subjected to a contrast scan. In FIG. 7B, (i) is a simple image, and (ii), (iii), and (iv) are The contrast imaging corresponds to the time phases A, B, and C in FIG. In this case, considering the examination time and the burden on the subject, the monitoring scan is started after the non-contrast scan (simple imaging) of the chest and abdomen and the monitoring scan position is reached, and prediction of TDC / TCC It is more appropriate to start a contrast scan by injecting a contrast agent later. In this way, the operator can scan an arbitrary area, and the location of the monitoring scan can be set to an appropriate location by a technique. By performing simple imaging as shown in FIG. 7B, diagnostic performance can be improved.

  According to the present embodiment, even when a temporal change in contrast in a contrast scan is considered, the exposure dose of the subject is maintained while maintaining a CNR suitable for diagnosis and maintaining an image SD that can achieve the CNR. Can be minimized.

  Further, according to the present embodiment, since the scan dose is controlled using not only the image SD but also the CNR in consideration of the contrast effective for diagnosis, an image more suitable for diagnosis can be obtained.

  Further, according to the present embodiment, since the scan is not performed in a time phase where the operator does not pay attention, it is possible to reduce the exposure dose of the subject.

  Further, according to the present embodiment, since the time when the EU exceeds the dark value TH is measured by performing the monitoring scan, the TCC is predicted more reliably, and the main scan is performed at a more reliable shooting timing. It can be performed.

  In the present embodiment, it is assumed that the monitoring scan is performed, but the monitoring scan can be omitted. In this case, TDC and TCC may be predicted in advance using the information on the subject when the subject information and protocol are input. As a result, there is no need for a monitoring scan, so a further effect of reducing exposure can be expected.

  In the present embodiment, the tube voltage is constant during scanning regardless of the contrast time phase. However, the tube voltage may be changed at each time phase. By changing the tube voltage in each time phase, it is possible to scan with the contrast desired by the operator.

  Further, the dose control by the view may be added to the control of the scanning condition such as the tube current according to the TCC described in the present embodiment. Thereby, more appropriate control can be performed.

  Further, in this embodiment, there are a plurality of contrast time phases that can be input by the operator, but it is of course possible to input only one. In this case, since the photographing is completed in one volume scan, a significant exposure reduction effect can be expected.

  Note that in the identification, visualization, and diagnosis of hepatocellular carcinoma, imaging is generally performed in three to four phases including simple imaging. In actual clinical settings, hepatic arterial phase around 40 seconds after the start of contrast agent injection, portal vein phase around 80 seconds, and equilibrium phase around 120 seconds are widely taken. It is used for. Here, the setting of T1, T2, and T3 indicates a method in which the operator selects with the mouse. However, these three to four phases are stored in advance as a protocol, and the photographing timing is determined without input by the operator. A method to do this is also possible. This increases the work efficiency of the operator and enables easier shooting. At this time, it is desirable to appropriately correct the imaging timing in consideration of the contrast agent injection speed, the physique of the subject, and the like.

<Second Embodiment>
The first embodiment is a case of performing a volume scan of the liver at each imaging time phase when performing a contrast scan of the liver, but the embodiment of the contrast scan is not limited to this.

  In the second embodiment, when the liver is contrast-scanned, the liver is dynamically scanned at each imaging time phase. In the following description, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 8 is a flowchart showing the flow of processing in the second embodiment.

  After the scanogram imaging is completed (step S1), the scan position including the diagnosis target is input by the operator via the input device 5 based on the obtained scanogram (step S11). In this embodiment, scanning means dynamic scanning in which scanning is performed at the same slice position. At the same time, a slice thickness, a scan time, a reconstruction filter function, a field size, a window condition, and the like are input as scan conditions for slice positions.

  After inputting the scan position, the position of the monitoring scan is set (step S3), and then the contrast time phase to be scanned is input by the operator via the operation device 6 (step S4).

  After inputting the imaging time phase, the CNR (CNR_d) that can identify the diagnosis target is called from the protocol stored in the storage device 24 (step S5). Then, an optimal scan condition corresponding to the image SD satisfying CNR_d is preliminarily calculated for each inputted contrast time phase (step S6).

  Next, a monitoring scan is performed at the set monitoring scan position under the above-described preliminary scanning conditions, and the TDC and TCC prediction device 26 performs TDC of the abdominal aorta, multi-blood tumor (diagnosis target) and liver parenchyma (surrounding tissue) and A TCC is predicted, and an optimal scan condition used when an actual scan is performed is calculated based on the TCC predicted by the monitoring scan (step S7).

  Then, after the EU measured by the monitoring scan exceeds the dark value TH, that is, after the time t has elapsed since the monitoring scan was started, scanning at a preset scan position is started (step S8) Based on the TCC predicted in step T7, the scan position set in step T2 under the scan condition satisfying CNR_d according to the contrast between the diagnosis target and the surrounding tissue in the contrast time phase input by the operator A dynamic scan is performed (step S12).

  In this case, only in the contrast time phase set by the operator, the scanning conditions are controlled so that the image SD satisfies CNR_d. For example, referring to FIG. 5, as a condition to be satisfied by the image SD, scanning is performed so as to be 1 / 2C_max / CNR_d in the time phase T1 and C_max / CNR_d in the time phase T2. Further, when there are three set time phases, it means that the scan is performed three times.

  According to the present embodiment, even when a temporal change in contrast in a contrast scan is taken into consideration, the exposure dose of the subject is maintained while maintaining a CNR suitable for diagnosis and maintaining an image SD that can achieve the CNR. Can be minimized.

  Further, according to the present embodiment, since the desired CNR can always be satisfied in the time phase set by the operator, an improvement in diagnostic ability when focusing on a specific time phase can be expected. That is, in a slice to be diagnosed, an optimal CNR at a notable time phase can be achieved. Exposure can be further reduced when shooting with attention to a time phase having a high contrast.

  In the present embodiment, it is assumed that a monitoring scan is performed. However, as in the first embodiment, the monitoring scan can be omitted.

  As a modification of the present embodiment, dynamic scanning in all time phases can be considered. In this case, it is possible to obtain diagnostic images of all time phases at the same slice position by sequentially controlling the image SD so as to satisfy CNR_d according to the predicted shape of the TCC.

<Third Embodiment>
The first embodiment is a case of performing a volume scan of the liver at each imaging time phase when performing a contrast scan of the liver, but the embodiment of the contrast scan is not limited to this.

  In the third embodiment, imaging is performed only when the predicted contrast is equal to or higher than a predetermined value in the contrast scan of the liver. In the following description, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 9 is a flowchart showing the flow of processing in the third embodiment.
First, scanogram imaging of the subject 7 is performed (step S1), and based on the scanogram obtained in step S1, a scan region including a diagnosis target is input by the operator via the operation device 6 (step S2). ). Here, a slice thickness, a scan time, a reconstruction filter function, a visual field size, a window condition, and the like are input as scan conditions for slice positions. Further, a monitoring scan position is set based on the scanogram obtained in step S1 (step S3).

  When the monitoring scan position is set, the operator inputs a threshold value in the time phase of the contrast to be scanned through the input device 6 (step S21). Specifically, as shown in FIG. 10, ½C_max, which is a half value of the maximum contrast value, is input as a threshold value. In this case, only the time phase in which the contrast exceeds the threshold value (the time phase surrounded by the oblique line A) is scanned. In step S21, it is desirable that the TCC is previously shown to the operator via the display device 5 by the scan protocol. This process may be performed by calling a TCC stored in the storage device 24. The displayed TCC and the contrast time phase input by the operator may be the same as those in the first embodiment.

  When the threshold value is input, a CNR (CNR_d) that can identify the diagnosis target is called from the protocol stored in the storage device 24 (step S5). Then, an optimal scan condition that satisfies CNR_d is preliminarily calculated for each inputted contrast time phase (step S6). Next, a monitoring scan is performed at the set monitoring scan position under a preliminary scan condition, and the TDC / TCC prediction device 26 performs TDC and TCC of the abdominal aorta, multi-blood tumor (diagnosis target), and liver parenchyma (surrounding tissue). Is predicted, and an optimum scan condition used in actual scanning is calculated based on the TCC predicted in the monitoring scan (step S7).

  When the scan condition is calculated, it is determined whether the current time phase contrast exceeds the threshold value input in step S21 based on the TCC predicted in step S7 (step S22).

If the contrast does not exceed the threshold value input in step S21 (NO in step S22), the process returns to step S7, and the scan is postponed until the expected time phase.
If the contrast exceeds the threshold value input in step S21 (YES in step S22), scanning is executed (step S23). That is, based on the TCC predicted in step S7, the scan area is scanned under a scan condition that satisfies the CNR corresponding to the contrast between the diagnosis target and the surrounding tissue only in the contrast time phase in which the contrast is greater than or equal to the threshold value. . In this embodiment, volume scanning is assumed, but dynamic scanning can also be applied.

  According to the present embodiment, even when a contrast examination is performed, since the scan is performed only at a time phase that is equal to or higher than the contrast desired by the operator, an improvement in diagnostic ability and a reduction in exposure can be expected. Further, exposure is reduced by not performing scanning at a time phase lower than the desired contrast (low contrast).

  In this embodiment, scanning is performed only when the contrast is equal to or higher than a predetermined threshold. However, the region where the operator has a desired contrast phase (Tl to T2) as indicated by the hatched line B in FIG. Can also be set.

  Further, in the present embodiment, it is assumed that a monitoring scan is performed, but it is also possible to omit the monitoring scan as in the first and second embodiments.

  Although the present invention has been described based on the three examples, the technical scope of the present invention is not limited to the above-described embodiments. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

1 is an overall overview diagram of an X-ray CT apparatus 100 according to the present invention. 1 is an overall configuration diagram of the X-ray CT apparatus 100. FIG. It is a figure which shows TDC and TCC at the time of performing contrast scan, (a) shows TDC of abdominal aorta, bloody tumor (diagnosis object), and liver parenchyma (surrounding tissue), (b) shows abdominal aorta, poor The hepatic tumor and hepatic parenchyma TDC are shown, (c) shows hepatic parenchymal and polycytic tumor contrast (absolute value of CT value difference), and (d) shows hepatic parenchymal and ischemic tumor contrast. 3 is a flowchart showing a flow of processing of the first embodiment of the X-ray CT apparatus 100. It is an example in the case of setting a photographing time phase on TCC. It is a figure which shows TDC and TCC at the time of performing a contrast scan, (a) is TDC and TCC when a subject's height and weight are constant and a contrast agent injection rate is changed, (b) is a scan tube TDC and TCC when the X-ray spectrum is changed by changing the voltage. It is an example of the scanning protocol in the case of performing a volume scan. It is a flowchart which shows the flow of a process of 2nd Embodiment of the said X-ray CT apparatus. It is a flowchart which shows the flow of a process of 3rd Embodiment of the said X-ray CT apparatus. This is an example of setting a shooting time phase by setting a threshold on the TCC.

Explanation of symbols

1: gantry, 2: patient table, 3: console, 4: top panel, 5: display device, 6: operation device, 10: X-ray tube, 11: high voltage generator, 12: slip ring, 13 collimator: , 14: X-ray detector, 15: data acquisition circuit, 16: gantry drive unit, 17: drive frame, 18: tube voltage / tube current measuring device, 20: system control device, 21: table control device, 22: sky Plate drive device 23: Image reconstruction device 24: Storage device 25: Scan planning device 26: TDC / TCC prediction device 27: Contrast medium injection control device

Claims (5)

An X-ray source for irradiating the subject with X-rays and an X-ray detector for detecting X-rays transmitted through the subject, and a contrast agent is injected into the X-ray source and the X-ray detector In the X-ray CT apparatus for performing contrast imaging of the examination site of the subject by a scan rotated around the subject,
Prediction means for predicting contrast corresponding to a time phase at the time of scanning, which is a contrast representing a difference between the density of the examination site and the density of surrounding tissue, which changes with time by injecting a contrast medium into the subject. When,
Calculation means for calculating an X-ray condition in a time phase at the time of scanning so as to satisfy a contrast noise ratio set in advance based on the predicted contrast;
Control means for controlling the X-ray source so as to satisfy the calculated X-ray condition;
An X-ray CT apparatus comprising: Means for monitoring and scanning the examination site or a specific site upstream of the examination site at a lower dose than during the scan,
The prediction means is based on a time density curve obtained by the monitoring scan after injecting a contrast medium into the subject , and a relationship between the time phase at the time of the scan at the examination site of the subject and the contrast at the time phase. The X-ray CT apparatus according to claim 1, wherein: The predicting means retains standard data of a time contrast curve representing a difference between a time concentration curve of the examination site and a time concentration curve of surrounding tissue, which changes with time by injecting a contrast medium into the subject, Corresponding to the time phase at the time of scanning using a time contrast curve obtained by transforming the standard data based on the scanning protocol of angiography, the physical feature of the subject, or the X-ray condition The X-ray CT apparatus according to claim 1, wherein a contrast is predicted .   The predicting means calculates a time contrast curve representing a difference between a time density curve of the examination site and a time density curve of surrounding tissue, which changes with time by injecting a contrast medium into the subject;
  The X-ray CT apparatus further includes an input unit that displays the calculated time contrast curve and inputs a time phase for performing the scan based on the displayed time contrast curve.
  The X-ray CT apparatus according to claim 1, 2, or 3.   The X-ray CT apparatus performs the scan in a time phase where the predicted contrast exceeds a predetermined value.
  The X-ray CT apparatus according to claim 1, 2, 3, or 4.

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