JP4644292B2 - X-ray CT apparatus and image display method thereof - Google Patents

Description

  The present invention relates to an X-ray CT apparatus that controls an X-ray tube current (hereinafter abbreviated as tube current) during imaging to suppress the exposure dose of the subject, and in particular, considers the exposure dose and image quality of the subject. The present invention relates to an X-ray CT apparatus that can reset a change curve of tube current during imaging.

  Conventional X-ray CT apparatuses perform imaging under the same CT scan (hereinafter abbreviated as scan) conditions (X-ray tube voltage (hereinafter abbreviated as tube voltage), tube current, etc.) on the same tomographic plane. I am doing so. In recent years, a helical scan that scans and images a subject in a spiral manner has been widely used, but the scan condition in the body axis direction is also constant during the scan.

  Therefore, for example, when the cross section of the subject is an ellipse rather than a concentric circle with respect to the rotation axis of the CT scanner (hereinafter abbreviated as a scanner), the X-ray transmission length of the subject depends on the rotational angle position of the X-ray source. However, there was a problem that excessive and insufficient X-ray doses were transmitted within the same fault plane.

  In addition, the X-ray absorption coefficient differs greatly between low-density organs in the chest such as the lung and high-density organs in the abdomen such as the liver, so when scanning continuously from the chest to the upper abdomen, When the appropriate X-ray dose was set, there was a shortage in the liver, and when an X-ray dose appropriate for the liver was set, there was an excess in the lungs.

  When the transmitted X-ray dose is insufficient, the S / N (SN ratio) deteriorates due to a decrease in the amount of X-ray photons detected by an X-ray detector (hereinafter abbreviated as a detector), resulting in image reconstruction. The S / N of the entire tomographic image obtained by On the other hand, when the transmitted X-ray dose is too large, an invalid X-ray exposure is applied to the subject.

  As a method for solving these problems, a method for controlling the tube voltage disclosed in Patent Document 1 and a method for controlling the tube current disclosed in Patent Document 2 and Patent Document 3 have been proposed.

JP-A-53-110495 JP-A-9-108209 Japanese Patent Laid-Open No. 10-309271 Japanese Patent Laid-Open No. 2001-276040

  However, the method of controlling the tube voltage in Patent Document 1 has a problem that the CT value cannot be determined because the X-ray spectrum changes because the tube voltage is changed during scanning. For this reason, at present, the method of controlling the tube current has become the mainstream.

  As a method of optimally controlling the tube current according to the subject, as in Patent Document 3, a method of controlling the tube current using transmitted X-ray dose data before a half cycle of scanner rotation, and Patent Document 2 Thus, there is a method in which a pattern for controlling the tube current is determined in advance according to the position of the subject based on scanograms taken from two different directions.

  However, the method using the transmitted X-ray dose data half a cycle before the rotation of the scanner in Patent Document 3 has a problem that a deviation of the transmitted X-ray dose data becomes large particularly when the scan pitch is increased in the helical scan. In addition, it is impossible to cope with a region where the X-ray absorption characteristics of the subject greatly change, such as before and after the diaphragm.

  The method of acquiring scanograms from two different directions in Patent Document 2 increases unnecessary X-ray exposure to the subject by performing scanogram imaging twice, and reduces the exposure dose by tube current control. It is contrary to the purpose.

  The inventors of the present invention have also proposed in Patent Document 4 one method for optimally controlling the tube current according to the subject. The invention of Patent Document 4 relates to an X-ray CT apparatus that realizes low exposure of a subject by suppressing unnecessary X-ray exposure to the subject. A model showing the relationship between the two is stored in memory, and scan measurement is performed by irradiating the same subject with X-rays based on the set tube current for each rotation angle of the scanner determined from this model during scan measurement of the subject. And tomographic images are reconstructed.

  In the invention of Patent Document 4, emphasis is placed on the generation of an X-ray transmission length model of a subject and setting the tube current based on the X-ray transmission length of the X-ray transmission length model. The X-ray dose applied to the subject by X-ray and the X-ray exposure to the organ in the subject were not considered.

  In consideration of the above problems, in the present invention, the exposure dose inside and outside the subject is calculated from the tube current change pattern automatically set from the X-ray transmission length model of the subject, and the X-ray exposure of this subject is calculated. It is an object of the present invention to provide an X-ray CT apparatus in which the operator can reset the change pattern of the tube current in consideration of

To achieve the above object, the X-ray CT apparatus of the present invention, the X-ray detector for detecting transmitted X-ray amount of the subject arranged to face the X-ray source, a display device for displaying a scanogram image of the subject The X-ray source emits X-rays while rotating the X-ray source, and the X-ray detector detects the X-ray source while setting the X- ray source tomographic position on the displayed scanogram. and tomographic image reconstruction means for reconstructing a tomographic image from the transmitted X-ray amount of the subject was, in X-ray CT apparatus that includes a display device for displaying the reconstructed tomographic image, depending on the imaging position of the object In order to compare the tube current value and the imaging position, the tube current pattern for generating the X-rays generated in the X-ray source is displayed in parallel with the scanogram image or displayed on the display device.

In the X-ray CT apparatus of the present invention, the tube current pattern calculation means has transmission length calculation means for calculating the X-ray transmission length of the subject based on the scanogram image, and based on the X-ray transmission length and the scanning conditions. A tube current pattern may be calculated.

Further, the X-ray CT apparatus of the present invention further includes a dose calculation means for calculating a dose according to the tube current pattern, and the calculated dose may be displayed on the display device in parallel with or superimposed on the scanogram image. Good .

The image display method of the X-ray CT apparatus of the present invention, photographing position set to accept the results and display step of displaying a scanogram image of the subject, the imaging position of the tomographic image of the subject on the displayed scanogram image is set a step, the X-ray source emits a rotating article al X-ray, and the tomographic image reconstruction step of reconstructing a tomographic image from the transmitted X-ray amount of the subject detected by the X-ray detector, reconstituted In the image display method of the X-ray CT apparatus provided with a display step for displaying a tomographic image, a tube current pattern for generating an X-ray according to the imaging position of the subject in the X-ray source is expressed as a tube current value. In order to contrast with a photographing position, the method includes a step of displaying juxtaposed or superposed on a scanogram image.

Further, in the image display method of the X-ray CT apparatus of the present invention, the tube current pattern calculation step includes a transmission length calculation step of calculating the X-ray transmission length of the subject based on the scanogram image, The tube current pattern may be calculated based on the scan condition.

The X-ray CT apparatus image display method of the present invention further includes a dose calculation step of calculating a dose according to the tube current pattern, and the calculated dose is juxtaposed with the scanogram image or superimposed on the display device. It may be displayed.

The X-ray CT apparatus image display method of the present invention obtains a scanogram image for obtaining a tomographic image of a subject, displays the scanogram image on the display device, and associates the displayed scanogram image with the displayed scanogram image. A step of displaying a change pattern of the supply current to the radiation source, a step of editing the change pattern of the supply current while referring to the scanogram, and a tomographic image of the subject based on the edited change pattern of the supply current And displaying the tomographic image on a display device.

An X-ray CT apparatus of the present invention is a scanogram image acquisition means for acquiring a scanogram image for obtaining a tomographic image of a subject, and a display device for displaying the scanogram image, in association with the displayed scanogram image. A display device that displays a change pattern of the supply current to the X-ray source, an editing means for editing the change pattern of the supply current while referring to the scanogram, and a subject based on the edited supply current change pattern Means for obtaining the tomographic image and displaying the tomographic image on a display device.

  As described above, in the X-ray CT apparatus of the present invention, operation means for setting the scanning conditions of the apparatus, scanogram analysis means for generating a three-dimensional X-ray transmission length model of the subject from the scanogram image data of the subject, Tube current setting means for automatically setting the tube current change pattern according to the imaging region of the subject from the scan conditions and the three-dimensional X-ray transmission length model of the subject, and the subject based on the tube current change pattern Since the dose calculation means for calculating and displaying the dose irradiated to the tube is provided, the tube current change pattern during the scan is automatically entered by inputting the maximum and minimum tube current values as the scan conditions. It can be set and X-ray exposure to the subject can also be evaluated. Furthermore, when there is a possibility that the X-ray exposure to the subject becomes excessive, it is possible to reset the change pattern of the tube current.

  Further, in the X-ray CT apparatus of the present invention, the dose distribution in the body of the subject is calculated and displayed based on the change pattern of the tube current during the scan and the three-dimensional CT value model data of the subject generated in advance. Since it has a distribution calculation means, it is possible to know in advance the dose distribution in the body of the subject by CT imaging, and to determine whether or not to perform scanning in consideration of the degree of X-ray exposure of the organ of interest it can.

  Further, in the X-ray CT apparatus of the present invention, the above three-dimensional CT value model data of the subject is generated based on the standard human CT value model data obtained by CT imaging of a human phantom or the like and the scanogram image data of the subject. CT image model data is generated only by acquiring one scanogram image data as a preliminary image, even for a sample that has not been subjected to CT imaging before. Can be generated.

  In the X-ray CT apparatus of the present invention, the scanogram image of the subject and the change pattern of the tube current are displayed side by side or superimposed on the same screen of the display means. However, the change pattern of the tube current can be edited, and the tube current suitable for the imaging region can be easily set.

1 is a block diagram showing the overall configuration of an X-ray CT apparatus according to the present invention. The principal part component of the X-ray CT apparatus which concerns on this invention. 6 is a flowchart of a series of operations in a first scan operation example using the X-ray CT apparatus according to the present invention. The figure which shows a response | compatibility with a scanogram image, a slice position, and the example of projection data. The figure which shows the model in the 1 slice position of a three-dimensional X-ray transmission length model. X-ray transmission length model at slice position Z. A display example of a change pattern of tube current. An example of a change pattern of tube current. 9 is a flowchart of a series of operations in a second scan operation example using the X-ray CT apparatus according to the present invention. A display example of a calculation result of a dose distribution in a subject. The figure for demonstrating the preparation procedure of a subject CT value model. The figure for demonstrating the procedure of irradiation X dose distribution calculation. A superposed display of the tube current change pattern on the scanogram image of the subject. The figure which showed the relationship between tube current and the thickness of a subject.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the overall configuration of an X-ray CT apparatus according to the present invention. As shown in FIG. 1, the X-ray CT apparatus mainly includes an X-ray source 12 and a detector 13, and a gantry 10 including a scanner 11 that can continuously rotate around the subject 15. A host computer 20 for generalizing the entire apparatus, a high voltage generator 22 for supplying a high voltage to the X-ray source 12, an image processing apparatus 24 for performing preprocessing of image data, image reconstruction processing, and various analysis processes The display device 25 includes an image display device 25, a table device 18 on which the subject 15 is placed, an operation means 21 for an operator to input scan conditions and the like. Since the scanner 11 and the subject 15 need only be able to rotate relatively, the subject 15 may be stationary and the scanner 11 may be rotated, or the scanner 11 may be stationary and the subject 15 may be rotated. May rotate.

  FIG. 2 shows the main components of the X-ray CT apparatus according to the present invention. First, details of the scanner 11 will be described with reference to FIG. In FIG. 2, the X-ray source 12 and the detector 13 are arranged in the scanner 11 in a positional relationship facing each other by 180 degrees. The X-ray beam 14 emitted from the X-ray source 12 is irradiated onto the subject 15 as a fan-shaped X-ray beam 14 whose beam width and thickness are limited by a collimator 19. The X-ray source 12 is controlled by the host computer 20 via the high voltage generator 22. The entire scanner 11 detects the rotation angle by the scanner angle detection means 17, and the host computer 20 controls the scanner drive means 16 based on the detected rotation angle to drive the scanner 11. The detector 13 detects the X-rays 14 that have passed through the subject 15, and the detection data is captured as projection data indicating the amount of X-ray attenuation by the subject 15. The projection data is collated with data such as the scanner angle of the host computer 20 in the image processing device 24, and after processing such as image reconstruction, it is displayed on the display device 25 as a tomographic image.

  Next, components other than the scanner 11 according to the present invention will be described. In FIG. 2, a host computer 20 that generalizes the entire apparatus includes a scanner 11 via a scanner driving means 16, an X-ray source 12 via a high voltage generator 22, and a detector 13 via an image processor 24. The operation means 21, tube current setting means 22, image processing device 24, and scanogram analysis means 26 are directly connected to each other. By connecting the host computer 20 to the scanner 11, the X-ray source 12, and the detector 13, the host computer 20 allows the X-ray irradiation to the subject 15 by the X-ray source 12 and the projection data (detection data) of the detector 13. Control uptake. The image processing device 24 sequentially reconstructs tomographic images based on the captured projection data in response to a command from the host computer 20.

  In the X-ray CT apparatus according to the present invention, various preparation operations are performed to set scan conditions before a main scan for acquiring a tomographic image of a subject. This preparatory operation includes scanning of a scanogram image for positioning the subject, analysis of scanogram image data for tube current setting, determination of a change pattern of tube current as a scan condition, etc. Done in the original.

  Main components involved in these preparatory operations are, in FIG. 2, a host computer 20, an operation means 21, a scanogram analysis means 26, a tube current setting means 22, an X-ray source 12, and a detector 13. Etc. In this preparation operation, first, the operation means 21 mainly inputs a scan condition such as a set value (maximum value, minimum value) of the tube current to the system. The X-ray source 12 and the detector 13 take a scanogram image without rotating the scanner 11 and store the image data in the host computer 20. The scanogram analysis means 26 analyzes the scanogram image data, and models the X-ray transmission length of the subject as three-dimensional shape data that can be calculated for each slice position in the body axis direction and for each rotation angle of the scanner. (Referred to as a three-dimensional X-ray transmission length model of the subject) is stored in the host computer 20. Based on the tube current setting value input from the operation means 21 and the data of the three-dimensional X-ray transmission length model of the subject, the tube current setting means 22 determines the X-ray transmission length of the imaging region of the subject during the scan. A series of tube current values that change with time according to the change, that is, a change pattern of the tube current is automatically determined. The tube current change pattern determined in this way is stored in the host computer 20 and is sequentially called according to the imaging region of the subject during the main scan to change the tube current of the X-ray source 12.

  In the present invention, based on the change pattern of the tube current determined as described above, the X-ray dose irradiated to the subject 15 is calculated in advance before the main scan. In X-ray equipment, the mAs value is used as the amount corresponding to the normal X-ray dose, but this calculation also uses the mAs value. This mAs value is the product of the tube current (mA) and the irradiation time (s) .If the tube voltage is constant (the tube voltage is often used at a constant value in the X-ray CT system), X Since it is proportional to the total X-ray dose irradiated from the radiation source 12, it is used as a reference for the X-ray dose. The X-ray dose irradiated to the subject 15 calculated here is evaluated by the operator as the predicted exposure dose to the subject 15.

  FIG. 3 shows a flowchart of a series of operations of the first scanning operation using the X-ray CT apparatus according to the present invention. This scanning operation is characterized by three-dimensional data generation in steps 103, 106, and 108, tube current pattern generation in step 110, mAs calculation in step 111, and mAs display in step 114. Hereinafter, the details of the first scanning operation of FIG. 3 will be described with reference to FIG.

  In FIG. 3, first, in the scanogram imaging process of step 101, a scanogram image of the subject 15 is captured. The configuration for capturing a scanogram image of the subject 15 and the configuration for capturing a tomographic image are basically the same. In this step, scanogram image data is obtained by irradiating the subject 15 with X-rays 14 from the front direction without rotating the scanner 11 and capturing the detection data by the detector 13. The scanogram image obtained at this time is in the front direction. This scanogram image data is sent from the detector 13 to the host computer 20. The scanogram image data is used not only for positioning the subject 15 during the main scan, but also for determining the change pattern of the tube current for tube current control in the present invention.

  Next, in the scanogram data analysis step of step 102 and the first three-dimensional data generation step of step 103, the scanogram image data is analyzed by the scanogram analysis means 26 connected to the host computer 20, and the subject 15 A three-dimensional X-ray transmission length model is generated. This three-dimensional X-ray transmission length model is a model showing the relationship between the position of the subject 15 and the X-ray transmission length when the subject 15 is subjected to CT imaging. A method for creating a three-dimensional X-ray transmission length model of the subject 15 is also disclosed in Patent Document 4.

Hereinafter, an example of a method for creating a three-dimensional X-ray transmission length model of the subject 15 will be described. FIG. 4 is a diagram showing a correspondence between a scanogram image, a slice position, and an example of projection data, and FIG. 5 is a diagram showing a model at one slice position of a three-dimensional X-ray transmission length model. FIG. 4 (a) shows a scanogram image 29 of the subject imaged in step 101. In this scanogram image 29, an area from the chest to the middle position of the abdomen is an imaging area. A slice position is selected from the imaging region of such a scanogram image. In the case shown in the figure, n slice positions are selected. In the _{figure, P 1, ···, P i} , ···, P j, ···, is P _n is the slice position.

4 (b), 4 (c), and 4 (d) are explanatory diagrams of model determination of a three-dimensional X-ray transmission length model. Assuming that the CT tomograms at any two slice positions P _i and P _j are as shown in Fig. 4 (b), the projection data of the X-ray attenuation in the vertical direction (vertical direction in the figure) is It should look like Figure 4 (c). Since the cross section of the trunk of the human body is usually close to an ellipse, assuming that CT tomograms at arbitrary slice positions P _i and P _j in Fig. 4 (b) are considered to have no significant error. Is done. Therefore, the projection data in FIG. 4 (c) is converted into X-ray transmission length data, and then integrated along the horizontal axis to obtain the area. At this time, in converting the X-ray attenuation amount into the X-ray transmission length of the projection data, the data is converted assuming that the human body is equivalent to water for simplicity. X-ray attenuation to c, and X-ray transmission length b, when the linear attenuation coefficient of water was mu _w, the relationship between them is expressed by b = log c / μ _w. Further, the horizontal axis is converted so that the width of the entire region where the X-ray attenuation data exists matches the width dimension of the human body. FIG. 4D is a distribution diagram of X-ray transmission length data of the subject 15 at the slice positions P _i and P _j converted from the projection data of FIG. 4C. In FIG. 4D, the maximum X-ray transmission lengths at the slice positions P _i and P _j are b _i and b _j , and the areas are S _i and S _j . In the X-ray transmission length data of FIG. 4D, when attention is paid to the maximum X-ray transmission lengths b _i and b _j and the areas S _i and S _j , b _i and S _i are X of the tomographic image at the slice position P _i. Reflecting the line transmission state, b _j and S _j can be regarded as values reflecting the X-ray transmission state of the tomographic image at the slice position P _j .

Therefore, as a three-dimensional X-ray transmission length model of the subject 15, the slice cross section at each slice position is modeled as an ellipse 30 as shown in FIG. In this modeling, the areas of the elliptic models 30 _i and 30 _{j at} the slice positions P _i and P _j are S _i and S _j , and the short axes are b _i and b _j . As a result, if the major axes of the elliptic models 30 _i and 30 _j are a _i and a _j , the area of the elliptic models 30 _i and 30 _j is expressed by [Equation 1]

長軸a_i、a_jは［数2］によって求められる。

The major axes a _i and a _j are obtained by [Equation 2].

上記によって、各スライス位置での断層画像に対応するX線透過長モデルとしての楕円形モデル30が求められたので、これらの楕円形モデル30を体軸方向に配列することによって3次元的X線透過長モデル30を作成することができる。体軸方向のスライス位置のピッチが粗いときには、例えば隣り合う楕円形モデル間で最小自乗法により、その途中の1つ又は2つ以上の楕円形モデルを補間で求める。以上の如き手順により被検体15の3次元的X線透過長モデル30のデータとして、3次元座標(X、Y、Z)系での被検体15のX線透過長データT＝T(X、Y、Z)が生成される。

As described above, the elliptical model 30 as the X-ray transmission length model corresponding to the tomographic image at each slice position is obtained. By arranging these elliptical models 30 in the body axis direction, three-dimensional X-rays are obtained. A transmission length model 30 can be created. When the pitch of slice positions in the body axis direction is coarse, for example, one or two or more elliptical models in the middle are obtained by interpolation by the least square method between adjacent elliptical models. As described above, the data of the three-dimensional X-ray transmission length model 30 of the subject 15 as the data of the subject 15 in the three-dimensional coordinate (X, Y, Z) system X-ray transmission length data T = T (X, Y, Z) is generated.

  Next, in the process from Step 104 to Step 110, the change pattern of the tube current to be applied to the X-ray source 12 is set using the above three-dimensional X-ray transmission length model 30, but before that, A method of obtaining the tube current using the three-dimensional X-ray transmission length model 30 will be described. The three-dimensional X-ray transmission length model 30 obtained in FIGS. 4 and 5 reflects the X-ray transmission length of the tomographic image at each slice position of the subject. Since the data of the three-dimensional X-ray transmission length model 30 is once stored in the memory including the register of the host computer 20, when scanning conditions such as the imaging range and table pitch are determined, the model data in that range is retrieved from the memory. The second and third three-dimensional data are generated and the change pattern of the tube current is determined.

  The tube current is determined by the tube current setting means 23 based on the X-ray transmission length obtained from the three-dimensional X-ray transmission length model 30 for each scanner rotation angle at each slice position. FIG. 6 shows the X-ray transmission length model 30 at the slice position (position in the body axis direction) Z. Further, the tube current at a certain scanner rotation angle is usually determined in association with the maximum value of the X-ray transmission lengths of the three-dimensional X-ray transmission length model at the scanner rotation angle. Since the X-ray transmission length indicating the maximum value is obtained by a path passing through the center 0 of the elliptic model 30 in FIG. 6, when setting the tube current, the center 0 of the elliptic model 30 is set for each scanner rotation angle. Only the X-ray transmission length of the path passing through the image needs to be considered. Accordingly, in FIG. 6, when the slice position is Z and the scanner rotation angle is θ (the start point of θ is the short axis direction of the elliptical model 30), the maximum X-ray transmission length T at that position is Z and θ. It can be expressed as T = T (Z, θ) as a function.

  This maximum X-ray transmission length T (Z, θ) is the length of the path passing through the center position 0 of the elliptical model 30. Therefore, when the major axis is a, the minor axis is b, and the scanner rotation angle is θ , [Equation 3].

ここで、a、bは［数1］、［数2］のa_i、a_j、及びb_i、b_jと対応する。

Here, a and b correspond to a _i and a _j and b _i and b _{j in} [Equation 1] and [Equation 2].

Next, an example of a tube current setting method will be described. First, let T _{max be} the maximum value of the path (maximum value of the path among all slice positions P1 to Pn) in the entire range in which the subject is scanned, and T _min be the minimum value (similarly, the minimum value of the path). These values are known when the three-dimensional X-ray transmission length model 30 is created. When changing the tube current in the range of the maximum value I _max (mA) and the minimum value I _min (mA), in this example, the maximum value of the tube current, the minimum value and the maximum value of the path, respectively, correspond to each other, A linear relationship is established between the tube current and the path. The relationship between the tube current I and the path T is expressed as [Equation 4].

ここで、パスTはT(Z、θ)に対応するので、管電流Iは(Z、θ)の1次関数となり、スライス位置Z及びスキャナ回転角度θごとに求められる。

Here, since the path T corresponds to T (Z, θ), the tube current I is a linear function of (Z, θ), and is obtained for each slice position Z and scanner rotation angle θ.

  Next, returning to the flowchart of FIG. In steps 104 and 105, the operator inputs a table pitch and a scan start position as scan conditions from the operation means 21 with reference to the scanogram image. With these data, the CT imaging range, slice position, and scan rotation angle of the subject are determined. The coordinate system at this time is preferably the (Z, θ) coordinate system as described above, and the scan condition data is preferably input as data in the (Z, θ) coordinate system.

  Next, in the process of step 106, data of a second three-dimensional X-ray transmission length model is generated. The data generated in this step is the maximum X-ray transmission length for each slice position Z and scan rotation angle θ, and can be obtained from [Expression 3] from the data of the first three-dimensional X-ray transmission length model. Therefore, the data of the first three-dimensional X-ray transmission length model is called from the memory of the host computer 20 and calculated. The calculation result is expressed as T = T (Z, θ).

  Next, in step 107, a scan time as a scan condition is input from the operation means 21. When the scan start position, table pitch, and scan time are determined, the position (Z, θ) of the X-ray source 12 during the scan can be expressed as a function of the elapsed time t after the start of the scan. The second three-dimensional X-ray transmission length model of the subject 15, that is, the maximum X-ray transmission length T can also be expressed as a function T = T (t) of time t. Therefore, in the third three-dimensional X-ray transmission length model generation step 108, the function of the maximum X-ray transmission length T is converted from T = T (Z, θ) to T = T (t). .

Next, in the step of inputting the tube current set value in step 109, the operator inputs the set value of the tube current, for example, the maximum value I _max and the minimum value I _min of the tube current during scanning, from the operation means 21. In the tube current pattern generation process of step 110, the tube current setting means 23 calls the data T (t) of the three-dimensional X-ray transmission length model from the host computer 20, and based on the tube current setting value, the subject 15 The tube current change pattern corresponding to the imaging region is automatically determined. At this time, the value of the tube current during scanning is set in association with the X-ray transmission length T (t), but when the X-ray transmission length T (t) is minimum, the minimum tube current is set, When the X-ray transmission length T (t) is the maximum, the change pattern of the tube current is determined so as to set the maximum tube current. In addition to the linear function shown in [Equation 4], there are various relationships between the X-ray transmission length T (t) and the tube current value (however, T in [Equation 4] is T (t )).

  As described above, the tube current is determined as a function of time t in accordance with the three-dimensional X-ray transmission length model of the subject 15. Therefore, the change pattern of the tube current can be expressed as I = I (t). The tube current change pattern I = I (t) determined in this way is stored in the host computer 20 and is sequentially called in accordance with the imaging region of the subject 15 during the main scan, via the high voltage generator 22. Control the tube current during the scan.

  FIG. 7 shows a display example of the tube current change pattern (in the following display examples of the tube current change pattern including this example, for the sake of simplicity, an approximately periodic tube current change due to the change in the scanner rotation angle θ is shown. The change is omitted and only the change due to the slice position is shown). This is displayed in contrast to the scanogram image 29 on the screen of the display device 25. In the tube current change pattern 31, the vertical axis represents the tube current value (mA), and the horizontal axis represents the elapsed time t after the start of scanning. In the case of the display example, the tube current has a medium value at the beginning of the scan (abdomen), a minimum value at the middle period (between the abdomen and the chest), and a maximum value at the end (chest). As shown in this display example, the tube current change pattern 31 and the scanogram image 29 are juxtaposed on the same screen so that the tube current value and the imaging region can be compared at a glance. It is effective for judgment.

  Next, in the step of calculating mAs in step 111, the X-ray dose irradiated to the subject 15 during the scan is calculated based on the change pattern of the tube current determined in step 110. Here, as a reference for the X-ray dose irradiated to the subject 15, mAs, which is the product of the tube current (mA) and the irradiation time (s), is used as described above. Therefore, in this step, the tube current change pattern I = I (t) is integrated over time to obtain the X-ray dose mAs irradiated to the subject 15. This integration is performed by [Equation 5].

ここで求めたmAs値は、あくまでも被検体15に照射されるX線量に相当する量であるので、実験等によってX線量とmAs値との正確な対応をとり、両者の間の換算ができるようにしておく必要がある。

Since the mAs value obtained here is an amount corresponding to the X-ray dose irradiated to the subject 15 only, the X-ray dose and the mAs value can be accurately matched by experiments, etc. It is necessary to keep it.

  Taking the tube current change pattern 31 shown in FIG. 7 as an example, let us consider calculating the irradiation X-ray dose mAs to the subject 15. In this case, the tube current change pattern 31 is I = I (t) and is a function of time, so calculating the mAs by integrating this calculates the area of the tube current change pattern 31 figure. Therefore, the area S in the diagram of the tube current change pattern 31 corresponds to mAs.

  Next, in the step of displaying the calculated mAs value in step 112, the calculated value of mAs obtained in step 111 is displayed on the screen of the display device 25. In step 111, when a change pattern of the tube current is generated, mAs corresponding to the X-ray dose irradiated to the subject over the entire region of the scan range of the subject 15 is calculated. The value is presented to the operator as data for the operator to determine whether or not to start scanning.

  In the step of determining mAs in step 113, the operator determines the validity of the mAs as a whole. That is, the operator weighs the benefits of CT imaging to be performed in the future and the disadvantages of X-ray exposure to the subject 15 to determine whether or not the overall mAs is too large. If it is determined that is too large, the set value of the tube current is lowered. In this case, the process returns to step 109, the tube current set value is input again, and the change pattern of the tube current is reset.

FIG. 8 shows an example of a change pattern of the tube current. The tube current change pattern 31a shown in Fig. 8 (a) is the case where the normal tube current is constant (I0), and the minimum value (I _min ) and the maximum value (I _max ) of the tube current are the same I0. It is an example. In the graph of the tube current change pattern 31a in FIG. 8A, mAs is the area Sa. Next, in FIG. 8 (b) shows the tube current change pattern 31b, the tube current in the same I0 and 8 early (a), the mid-term to the minimum value I _min next lower I0, higher than I0 at the end The maximum value is I _max . The mAs in the graph of the tube current change pattern 31a in FIG. 8 (b) is the area Sb, but this area Sb is smaller than the area Sa in FIG. 8 (a), and the exposure dose of the subject 15 is reduced. is doing.

In the tube current change pattern 31c shown in FIG. 8 (c), the maximum value I _max at the end is made smaller than that in the graph of FIG. 8 (b) and is almost the same as I0. In this case, the tube current is suppressed to a low level for the entire scan. The mAs in the graph of the tube current change pattern 31c in FIG.8 (c) is the area Sc, but this area Sc is smaller than the area Sb in FIG.8 (b), and the exposure dose of the subject 15 is Further reduction.

In the tube current change pattern 31d shown in FIG. 8 (d), the minimum value I _{min in the} middle period is further reduced as compared with FIG. 8 (b), and I _min is greatly reduced with respect to I0. is there. The mAs in the tube current change pattern 31d in FIG. 8 (d) is the area Sd, but is smaller than the area Sc in FIG. 8 (c).

  When the maximum value of the tube current set value is lowered as in FIG. 8 (c), the tube current is reduced at the portion where the subject 15 is thick, that is, the portion where the X-ray transmission length is large. . Therefore, the tube current change pattern 31c in FIG. 8 (c) is particularly suitable when the image quality in a low-density region such as the lung is emphasized and the exposure dose in a high-density region such as the abdomen is desired to be reduced. .

  When the minimum value of the tube current set value is lowered as in the case of FIG. 8 (d), the tube current is reduced in the portion where the subject 15 is thin, that is, the portion where the X-ray transmission length is small. . Therefore, the tube current change pattern 31d in FIG. 8 (d) is particularly suitable when the image quality in a high-density region such as the bone periphery or the substantial part is emphasized and the exposure dose in a low-density region is desired to be reduced. .

In FIG. 8 (c) and FIG. 8 (d), only one of the maximum value I _{max and the} minimum value I _min of the tube current set value is reduced, but both are reduced so that the whole of the subject 15 is reduced. It is also possible to reduce the exposure dose on average for the region. For the tube current change pattern newly set as described above, mAs is calculated again, and if there is no problem, it is adopted as it is.

  Next, in the scanning process of step 114, the operator executes scanning under the scanning conditions including the tube current change pattern determined above.

  Next, in the step of displaying the mAs integrated value in step 115, the integrated value of mAs during scanning is sequentially calculated according to the above [Formula 5], displayed in real time on the screen of the display device 25, and presented to the operator. . As the mAs integrated value display method, either a method of displaying a relative value as a ratio to the mAs value as a whole or a method of displaying an absolute value of the mAs integrated value can be selected. Of course, both can be displayed simultaneously.

  Next, a second scanning operation example of the X-ray CT apparatus according to the present invention will be described. FIG. 9 shows a flowchart of a series of operations of the second scan operation example. In this scan operation example, with respect to the flowchart of the first scan operation example in FIG. 3, the steps of calculating and displaying the dose distribution in the subject 15 are performed after the mAs calculation in step 111 and the mAs display step in step 112. In addition, the operator can also determine the scan execution by looking at the dose distribution in the subject 15. For this reason, in the description of this operation example, the process of calculating and displaying the dose distribution in the subject 15 in steps 201 to 205 will be mainly described.

  Hereinafter, step 201 to step 205 in the second scan operation example of FIG. 9 will be described. Before entering the description of the contents of the step, a display example of the calculation result of the dose distribution in the subject 15 is shown in FIG. Show. FIG. 10 (a) is a display example of the dose distribution on the cross section 35 of the subject, and FIG. 10 (b) is a display example of the dose distribution on the side surface 36 in the body axis direction of the subject. In both figures, isodose lines 38a to 38c and 39a to 39c having the same distributed dose in the subject 15 are shown, and the closer to the body surface, the higher the dose. In the present operation example, since the dose distribution of the subject 15 is presented to the operator, the operator can perform a more detailed evaluation on the X-ray exposure of the subject.

  In this operation example, before calculating the dose distribution in the subject in step 203, as a preparation, the CT value model of the subject is generated in step 201, the μ model of the subject is generated in step 202, and then The dose distribution in the subject is calculated based on the μ model data of the subject and the X-ray dose data irradiated on the subject.

  First, in the subject CT value model generation step of step 201, standard human CT value distribution model (hereinafter referred to as standard human CT value model) data is acquired in advance and stored in the storage means of the host computer 20. The standard human body CT value model data is corrected based on the scanogram image data of the subject 15 acquired in step 101, whereby the CT value model of the subject 15 (hereinafter referred to as the subject CT value model). ). As the standard human CT value model data, for example, three-dimensional CT value distribution data obtained from a tomographic image obtained by CT imaging of a standard human phantom or the like is used. The tomographic image represents the distribution of CT values, and the distribution of the linear attenuation coefficient for effective energy (usually 60 keV) X-rays, so the three-dimensional CT value distribution data obtained by reconstructing this tomographic image in three dimensions is This is data of the three-dimensional spatial distribution of the line attenuation coefficient, and can be used to calculate the amount of attenuation of X-rays irradiated to the subject.

  Next, an example of a method for generating a subject CT value model will be described with reference to FIG. In this example, the subject CT representing the three-dimensional CT value distribution of the subject 15 from the scanogram image data obtained by photographing the subject 15 in step 101 and actually measured, and the standard human CT value model data described above. Generate value model data. In generating the subject CT value model, the scanogram image data of the subject 15 and the scanogram image data of the standard human body are used as a medium.

  FIG. 11 is a diagram for explaining a procedure for creating a subject CT value model in step 201. In FIG. 11, FIG. 11 (a) is an example of the standard human CT value model data 41, and FIG. 11 (b) is a scanogram image of the standard human body calculated from the standard human CT value model data 41 of FIG. 11 (a). FIG. 11 (c) shows an example of the data 42, FIG. 11 (d) shows an example of the actually measured scanogram image data 43, and FIG. 11 (d) shows an example of the subject CT value model data 44 obtained by calculation. The standard human CT value model data 41 in Fig. 11 (a) is a CT value distribution model of the trunk of a standard human body such as a human phantom, and shows the CT value distribution model of the cross section at each slice position from the shoulder to the abdomen. ing.

  Since the scanogram image can be generated by calculation from the three-dimensional CT value distribution model, the standard human body scanogram data 42 in FIG. 11 (b) is a front view of the standard human CT value model data 41 in FIG. 11 (a). It is obtained by obtaining data projected from the direction. The measured scanogram image data 43 of the subject in FIG. 11 (c) is scanogram image data obtained by photographing the same area as the standard human scanogram image data 42 from the front direction of the trunk of the subject 15. This image is hereinafter referred to as a subject scanogram image.

  In FIG. 11, the standard human body scanogram image data 42 of the trunk and the subject scanogram image data 43 are shown so as to be juxtaposed, but they are different from each other in normal dimensions and CT values. For this reason, while comparing the standard human body scanogram image data 42 and the subject scanogram image data 43, based on the difference between the two, the matching portions are left as they are, and the different portions are deformed to fit the subject 15. Then, the standard human body CT value model data 41 is corrected to generate the subject CT value model data 44.

  In the example of the trunk in FIG. 11, first, the body axis direction is divided into the length A from the shoulder to the diaphragm and the length B from the diaphragm to the intestinal tract of the standard human scanogram image data 42 and the subject scanogram image data 43. Based on these differences, the standard human CT value model data 41 is interpolated, expanded, thinned out, or shortened, so that the CT value distribution in the body axis direction of the standard human CT value model data 41 is covered. The actual condition of the specimen 15 is approximated. Similarly, in the left-right direction, the left and right sides are divided with respect to the body axis, and the left and right spreads are corrected based on the respective differences to approximate the actual state of the subject 15. With respect to the front-rear direction, based on the X-ray transmission length in the front-rear direction estimated from the subject scanogram image data 43, the data in the front-rear direction of the standard human CT value model data 41 is linearly interpolated. In this manner, the subject CT value model data 44 is generated by matching the standard human CT value model data 41 with the actual subject 15 based on the two scanogram image data 42 and 43.

  Next, in the process of generating the subject μ model in step 202, the CT value of the subject CT value model data 44 generated in step 201 is converted into a linear attenuation coefficient μ, and the three-dimensional μ value distribution of the subject 15 is converted. Generate a model. Conversion from the CT value to the linear attenuation coefficient μ is performed as follows.

The CT value is determined by the linear attenuation coefficient for X-rays of effective energy (usually using 60 keV), and is defined as water = 0, air = 1000, average bone = 1000. Now, assuming that the CT value at the position x of the subject CT value model is CT _x , the linear attenuation coefficient μ _x at the effective energy (60 keV) at the position x is expressed by [Equation 6] and [Equation 7].

ここで、μ_wは水の線源弱係数(＝0.206cm-1)、μ_airは空気の線減弱係数(＝0.00025cm-1)、μ_boneは骨の線減弱係数(＝0.567cm-1、ただし密度1.8g/cm3の場合)である。

Here, mu _w is the source weak coefficient of water (= 0.206cm-1), μ air is linear attenuation coefficient of air (= 0.00025cm-1), μ bone is linear attenuation coefficient of bone (= 0.567cm-1 However, the density is 1.8 g / cm3).

  Next, in the dose distribution calculation process of step 203, as shown in FIG. 12, data of the X-ray dose irradiated to the subject obtained in step 111 (FIG. 12 (a)) and the subject μ obtained in step 202 are obtained. Using the model data 45 (FIG. 12 (b)), the dose distribution in the subject 15 (FIG. 12 (c)) is calculated. In the calculation of step 203, the attenuation of X-rays in the subject 15 is calculated in consideration of the energy spectrum of the X-rays irradiated to the subject, and the spatial distribution of the dose in the subject 15 is calculated. . The amount of X-ray attenuation when subject 15 is irradiated with X-rays from any direction can be analyzed analytically by using subject μ model data that is a model of the subject's three-dimensional linear attenuation coefficient (μ). Such calculation methods have already been carried out in other fields, for example, in the field of radiation therapy planning devices (Reference 1, Kiyoya Inagi, Radiation therapy planning system, P. 90-92, P. 113-115, Shinohara Publishing, April 20, 1992).

In calculating the attenuation of X-rays, first, an effective distance δ through which X-rays pass from the target position x in the subject 15 toward the X-ray source 12 is calculated. The effective distance is defined as 1 that is attenuated to 1 / e by the medium through which X-rays pass. When the X-ray energy spectrum is not taken into consideration, the medium of composition i has a real distance d _i (cm) from the target position x to the X-ray source 12, and the linear attenuation coefficient of composition i is μ _i (cm-1 ), The effective distance δ is expressed by [Equation 8].

しかし、X線のエネルギースペクトルを考慮すると実効距離はX線のエネルギーに応じて異なる値となる。組成_iのX線のエネルギー_jに対する線減弱係数をμ_ij(cm-1)とすると、X線のエネルギー_jに対する実効距離δ_jは［数9］で表される。

However, considering the X-ray energy spectrum, the effective distance varies depending on the X-ray energy. When the linear attenuation coefficient with respect to the energy _j of the X-ray of the composition _i is μ _ij (cm−1), the effective distance δ _{j with} respect to the energy _j of the X-ray is expressed by [Equation 9].

ここで、μ_ijは組成_iのエネルギー_jのX線に対する線減弱系数(cm-1)、d_iは組成_i中のX線の透過距離(cm)である。μ_ijについては、X線のエネルギー_jに応じて被検体15のμ値モデルから求める必要がある。

Here, μ _ij is the linear attenuation _coefficient (cm −1) for X-rays of energy _j of composition _i , and d _i is the transmission distance (cm) of X-rays in composition _i . μ _ij needs to be obtained from the μ value model of the subject 15 according to the energy _j of the X-ray.

Next, the dose at the target position x in the subject 15 is calculated. The distance from the X-ray source 12 to the target position x is r _x (m), and the dose at a distance of 1 m is I0 (C / kg: C is Coulomb). For example, I0 is obtained experimentally. When the energy spectrum of X-rays, that is, the component ratio of energy _j is S _j , the dose I _x (C / kg) at the target position x is expressed by [Equation 10].

ここで、I0は線量(X線源12から単位距離における空中の線量、単位C/kg)、r_xはX線源12から注目位置xまでの距離、単位m)、S_jはX線のエネルギースペクトルである。

Where I0 is the dose (dose in the air at a unit distance from the X-ray source 12, unit C / kg), r _x is the distance from the X-ray source 12 to the target position x, unit m), and S _j is the X-ray It is an energy spectrum.

  As a result of the calculation by [Equation 10], a dose at an arbitrary position x in the subject 15 when the X-ray source 12 is at a certain position Q (Z, θ) is obtained. The dose at an arbitrary position x when the X-ray source 12 is rotated once is obtained by rotating the position Q (Z, θ) of the X-ray source 12 around the subject 15 and the above dose for one rotation (θ = 0 to 2π) obtained by integrating. The dose distribution in the subject 15 at the slice position Z can be obtained by performing calculation at each set position in the subject 15 by the procedure as described above. In addition, dose distributions at other slice positions can be obtained by calculation in the same manner, so that the three-dimensional dose in the subject 15 can be calculated by proceeding with the calculation of the entire region of the imaging region in the body axis direction of the subject 15. Distribution is obtained.

  When taking a 1-slice tomographic image (in the case of 2D), the distribution of the dose in the subject 15 can be accurately obtained by the above calculation, but when performing CT imaging of multiple slices during one scan. In the case of (three-dimensional), there is a risk that the calculation accuracy may be lowered unless taking the scattered X-ray image. In the X-ray CT apparatus, since the energy of the X-ray is on the order of 100 keV or less, only Compton scattering needs to be considered as the scattered radiation (see Reference 1). Considering this Compton scattering, the calculation accuracy can be further increased.

  By calculating the dose at each set point at each slice position in the subject 15 by the procedure as described above, the calculated three-dimensional dose distribution of the subject 15 is obtained. The calculation result of the dose distribution of the subject 15 is temporarily stored in the host computer 20, and is displayed in a diagram that is easy to see for an operator, for example, a diagram as shown in FIG.

  Next, in the dose distribution display process of step 204, the calculation result of step 203 is displayed on the display device 25. As a display example in the present embodiment, the dose distribution in the tomographic plane 35 of the subject 15 as shown in FIG. 10 (FIG. 10 (a)) or the dose distribution on the side surface 36 of the subject 15 (FIG. 10 (b) )) Is raised. In these figures, since the isodose lines indicating the organs and dose distribution of the subject 15 are displayed in an overlapping manner, the doses to each organ can be recognized at a glance, so the X-rays to the subject 15 It is effective in evaluating exposure.

  Next, in the step of determining the exposure dose in step 205, the operator looks at the calculation result of the dose distribution in the subject 15 displayed in step 204, and the X-ray exposure to the organ in the subject 15 is excessive. If yes, proceed to the scan execution process in step 114 and start scanning. If no, enter the tube current setting value in step 109. Returning to the process, the tube current set value is re-input and the tube current pattern is re-examined.

  Further, as a method of generating CT value model data of the subject 15 in step 201, in addition to the method of using the standard human CT value model data described above, a method of using CT imaging data of the same subject 15 taken in the past Can also be implemented. In this case, since the CT value distribution data of the same subject 15 is actually used, there is an advantage that a procedure for correcting the shape of the standard human CT value model data 41 is not necessary. However, since it is not suitable for the first CT imaging, the case where the CT imaging for the second time or later is performed on the subject that has been CT imaging in the past is targeted.

  As described above, the dose distribution in the body of the subject 15 is calculated by simulation before the CT scan, and the calculation result is displayed as shown in FIG. 10, for example. It becomes possible to know the dose distribution in the body approximately.

  As a result, for example, instead of simply reducing the dose uniformly for all tissues of the subject, the dose is reduced especially for tissues with high radiation sensitivity such as bone marrow and lungs. For tissues with relatively low radiation sensitivity, it is possible to make detailed settings such as maintaining the exposure dose level to the extent that image quality is satisfactory.

  Next, an editing example of a change pattern of tube current for CT imaging of a subject will be described with reference to FIG. FIG. 13 shows a tube current change pattern superimposed on a scanogram image of a subject. In FIG. 12, the scanogram image data 29a is for the trunk, and the tube current change patterns are an initial tube current change pattern 46a before editing and a modified tube current change pattern 46b after editing.

  In the editing process of the tube current change pattern, with respect to the initially set tube current change pattern 46a displayed on the scanogram image 29a on the screen of the display device 25, while referring to the scanogram image data 29a, In some cases, the irradiation dose distribution inside the subject 15 is referred to, the operation means 21 is used for correction, and a new tube current change pattern 46b is edited. By this editing operation, the change pattern of the tube current at an arbitrary part is reset.

  In this editing operation, for example, in the automatic tube current change pattern setting, the tube current is set to an average value in a region where the density changes greatly as in the vicinity of the diaphragm, but even if the exposure dose increases. In areas where image quality needs to be improved, the tube current is set to be partially high. Since the change pattern of the tube current is a function of only the time t if the scan condition is set as described above, the value of the tube current at an arbitrary time can be changed. In the example of FIG. 13, the tube current change pattern 46b after correction is obtained by slightly reducing the tube current in the lung region and slightly increasing the tube current in the diaphragm region with respect to the initial tube current change pattern 46a. I am editing it.

  FIG. 14 is a diagram showing the relationship between the tube current and the thickness of the subject (corresponding to the X-ray transmission length). In the description of the step 110 above, the maximum value and the minimum value of the tube current are matched with the maximum value and the minimum value of the thickness of the object, and it is described as having a linear relationship between the two. Regarding the relationship between the two, it is possible to have a non-linear relationship by setting of the operator. The relationship between the tube current I and the thickness T of the subject shown in FIG. 14 is expressed by [Equation 11].

ここで、I_max、I_minは管電流の最大値と最小値、T_max、T_minは被検体の厚さの最大値と最小値、γは定数である。γについては以下ガンマと呼ぶことにする。

Here, I _max and I _min are the maximum and minimum values of the tube current, T _max and T _min are the maximum and minimum values of the thickness of the subject, and γ is a constant. Hereinafter, γ will be referred to as gamma.

  In FIG. 14, the graph 50 shows a case where gamma = 1, and the relationship between the tube current and the thickness of the subject is linear, the graph 51 shows a case where gamma <1, and the graph 52 shows a case where gamma> 1, both in the tube. The relationship between the current and the thickness of the subject is non-linear. In the case of FIG. 14, the relationship between the tube current and the thickness of the subject is uniquely determined by determining the value of gamma. Therefore, by incorporating a relational expression such as [Equation 11] into the apparatus, the operator can By inputting the value of gamma from the operating means 21, the relationship between the tube current I and the thickness T of the subject can be changed as shown in FIG. In actual operation, for example, in an initial setting in which no special setting is made by the operator, the maximum value and the minimum value of the tube current are matched with the maximum value and the minimum value of the thickness of the subject, and a linear relationship is established. By inputting gamma according to the operator's setting, a non-linear relationship can be obtained. In FIG. 14, when gamma = 1 is used as a reference, when gamma> 1, it is considered that the reduction in exposure of the subject is emphasized, and when gamma <1, it is considered that the image quality is emphasized.

  10 Gantry, 11 CT scanner (scanner), 12 X-ray source, 13 X-ray detector (detector), 14 X-ray beam (X-ray), 15 Subject, 16 Scanner drive means, 17 Scanner angle detection means, 18 Table, 19 Collimator, 20 Host computer, 21 Operating means, 22 High voltage generator, 23 Tube current setting means, 24 Image processing device, 25 Display device, 26 Scanogram analysis means, 29, 29a Scanogram image, 30 X-ray transmission length Model (elliptical model), 31, 31a, 31b, 31c, 31d, 47a, 47b Change pattern of tube current, 35 Cross section of subject, 36 Side surface of subject, 38a, 38b, 38c, 39a, 39b, 39c, 39d 46a, 46b, 46c isodose line, 41 standard human CT value model data, 42 calculated scanogram image data, 43 measured scanogram image data, 44 subject CT value model data, 45 subject μ model data, 51, 52, 53 Graph

Claims (1)

An X-ray source for irradiating the subject with X-rays;
An X-ray detector disposed opposite to the X-ray source to detect the transmitted X-ray dose of the subject;
A display device for displaying a scanogram image of the subject;
An imaging position setting means for setting an imaging position of a tomographic image of the subject on the displayed scanogram image;
A tomographic image reconstruction means for irradiating an X-ray from the X-ray source while rotating the X-ray source and reconstructing a tomographic image from the transmitted X-ray dose of the subject detected by the X-ray detector;
E Bei a display device for displaying the reconstructed tomographic image,
A tube current pattern for generating X-rays corresponding to the imaging position of the subject on the X-ray source is displayed on the display device so as to be superimposed or juxtaposed with the scanogram image in order to compare the tube current value and the imaging position, X-ray CT apparatus capable of editing the tube current value at a specific imaging position on the tube current pattern while referring to the imaging position, and displaying the tube current pattern based on the edited tube current value In
Dose calculating means for calculating the dose according to the tube current pattern by integrating the tube current pattern with time so that the calculated dose can be displayed on the display device in juxtaposition with or overlapping the scanogram image. An X-ray CT apparatus characterized by that.

Images