JP4503265B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT apparatus useful for diagnosis of cardiac coronary artery calcification.

Fig. 1 shows a schematic diagram of the heart. 6 is the heart region, 7 is the right coronary artery, and 8 is the left coronary artery. If these coronary arteries 7 and 8 that supply the heart nourish, stenosis, etc., will cause serious ischemic diseases such as myocardial infarction.
Coronary artery calcification is said to have a deep relationship with coronary artery stenosis and ischemic disease, and the progress of calcification is positioned as a diagnostic index for ischemic heart disease of the heart.
This diagnosis of progression of coronary artery calcification includes a so-called calcium score. The most popular score calculation algorithm is a method using an electron beam scan CT that can be imaged at high speed, and is called an Agatston score.
In this method, the score is calculated based on the CT value of the coronary artery region of the cardiac tomographic image, and is the most standard score practically used.

Since the heart repeatedly beats once per second, motion artifacts due to heart beats occur in cardiac tomographic images at the scan speed (about 1 second) of conventional third-generation CT devices. Because of this artifact, information on coronary arteries running around the heart is lost, making it difficult to calculate the score.
For this reason, as described above, the calcium score has been performed by a CT apparatus capable of high-speed scanning (for example, 0.1 second scanning) such as electron beam scanning CT.

Recently, as described in Patent Document 1, a third-generation CT device (sub-second CT) that can scan in less than 1 second has appeared, so even if you do not prepare an electron beam scan CT separately, it is versatile The high-accuracy third-generation CT apparatus has made it possible to observe a tomographic image of the heart region, and a calcium score, which is a quantitative diagnosis method for coronary artery calcification, can be easily performed.
US6,233,304B1 Special table 2002-531199 gazette

In the above-described conventional technique, the calcium score of the coronary artery causing calcification indicates the value and position with numerals.
However, in the display method as described above, it is difficult for an operator to recognize how much calcification is occurring at which point in the two-dimensional and three-dimensional positions of the coronary artery where calcification is occurring.
In the prior art, the calcium score for determining whether the coronary artery has undergone calcification has been displayed in numerical values along with the image of the coronary artery.
However, in order to read numerically, it is difficult for the operator to recognize how much calcification is occurring at which point in the 2D and 3D positions of the coronary artery, and since it cannot be intuitively discriminated clinically Has become a disadvantage.

In order to solve the above problems, the present invention displays an axial image of a slice position where calcification has occurred, and also displays a scanogram image or a three-dimensional image of a heart region, and the coronary artery at any position in the body axis direction. Information on whether calcification is occurring is displayed.
Further, emphasis processing such as coloring of the calcified region, the calcium score value, and the degree of risk are displayed on the image, and the operator is warned.

That is, according to the first feature of the present invention, an X-ray source that emits X-rays and the X-ray source that is disposed opposite to the subject with the subject interposed therebetween and rotating around the X-ray source together with the X-ray source. An X-ray detector that detects transmitted X-rays transmitted through the subject, and creates at least one of a scanogram image, a tomographic image, and a three-dimensional image of the subject from the transmitted X-rays obtained by the X-ray detector. An X-ray CT apparatus having an image processing unit and an image display unit that displays at least one of the images created by the image processing unit,
The image processing unit extracts an image portion of a calcified coronary artery from an image of a heart region of a subject, assigns a color according to a calcium score for each pixel of the image portion of the calcified coronary artery, and the calcified coronary artery Means for displaying the color for each pixel on the image portion is provided .

  According to a second aspect of the present invention, the image processing device further includes position information of the image portion of the calcified coronary artery in the body axis direction, at least one of the scanogram image, the tomographic image, and the three-dimensional image. Display above.

  According to a third aspect of the present invention, in the image processing apparatus, the position information display in the body axis direction is indicated by a straight line, a broken line or an arrow, the thickness of the straight line, the roughness of the broken line, the size of the arrow, Or the severity of the calcium score is displayed by color.

  According to the fourth feature of the present invention, in the X-ray CT apparatus, when creating the tomographic image and the three-dimensional image of the subject from the transmitted X-rays detected by the X-ray detector, The tomographic image and the three-dimensional image are created based on the transmitted X-rays detected corresponding to a predetermined cardiac time phase by measuring with an electrocardiograph and synchronizing with the detection.

According to the present invention, an axial image of a slice position where calcification has occurred is displayed with a color or gradation, and a scanogram image, an MPR image, or a three-dimensional image of a heart region is displayed. It becomes easy to determine how much calcification the coronary artery has caused at the position.
For example, a calcified region can be projected on a scanogram image to display the density or color display according to the severity of calcification.

In addition, the calcification position can be projected on the 3D image or MPR image, the density can be displayed, and the color can be displayed. When necessary, a tomographic image corresponding to the clicked slice position can be displayed and used for diagnosis by clicking and specifying a coronary artery causing calcification with a mouse or the like.
Further, similar projection and display can be simultaneously performed on a plurality of scanogram images, MPR images, and three-dimensional images.
As described above, since a clinical calcification position can be determined from a necessary viewpoint, a quick and accurate diagnosis can be performed.

Preferred embodiments of an image diagnostic apparatus according to the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 2, the X-ray CT apparatus according to the present invention includes a scanner unit 1, an image processing unit 2, and an image display unit 3. The scanner unit 1 includes an X-ray source 11 and an X-ray detector 13. These are arranged opposite to each other across the bed 12 and rotate together.

  The subject 14 is placed on the bed 12, and the bed is sent in the body axis direction of the subject, that is, the rotation axis direction of the scanner unit 1 while the subject 14 is placed. Simultaneously with the rotation of the scanner unit 1, X-rays are emitted from the X-ray source 11, and the X-ray detector 13 measures X-rays transmitted through the subject. By measuring the X-ray in this way while feeding the bed 13, it is possible to take an axial image of the subject, that is, a tomographic image, at a number of positions in the body axis direction of the subject. .

  Further, by transmitting only the bed while exposing the X-ray without rotating the scanner unit 1, for example, a fluoroscopic image for determining the photographing position can be obtained. An image obtained through such a perspective is called a scanogram image.

  The image processing unit 2 includes an image reconstruction function, and images the photographed X-ray detection value. The ECG device 4 such as an electrocardiograph measures the heartbeat waveform of the examinee, and the measurement result is recorded in synchronization with the imaging by the CT device. By reconstructing the image using only the data corresponding to the time, the calcium score is easily obtained.

FIG. 3 is a flowchart showing a process of photographing a heart region with a CT apparatus and displaying a calcium score.
In step 21, CT imaging of the heart region is started.
In step 22, the imaging range is determined using a fluoroscopy method such as a scanogram shown in FIG.
The scanogram is used to determine an imaging range, and the fluoroscope is seen through in the direction of the subject's body axis without rotating the scanner unit 1 to determine an imaging range where an image should be actually captured. For example, when imaging a heart region, as shown in FIG. 2, the scanogram imaging start position and the scanogram imaging end position are determined so as to include the heart region to be imaged.

In step 23, CT imaging is performed within the range thus determined.
For this imaging, a CT apparatus capable of imaging at a scan speed of about 100 ms, for example, which is sufficiently faster than the heart beat may be used.
Alternatively, using the above-mentioned third generation apparatus, attaching an electrocardiograph 4 to the subject, obtaining electrocardiogram information of the subject simultaneously with CT imaging, performing so-called ECG imaging, and using an ECG reconstruction algorithm, It is possible to obtain a cardiac tomographic image equivalent to that taken in 0.1 seconds like an electron beam scan CT.

  When imaging of the heart region of the patient is completed, a reconstruction process of the cardiac tomographic image is performed in step 24 to obtain a reconstructed image.

In step 25, a coronary artery causing calcification is extracted from the reconstructed cardiac tomographic image, and a calcium score is calculated. When the calculation of the calcium score is completed in this way, the CT imaging is terminated. The present invention relates to this calcium score processing step and will be described in detail below.
When the calcium score processing step is finished, the whole process is finished.

  The calcium score is calculated according to the following procedure. The procedure is shown in the flowchart of FIG. Beginning in step 31, a region of the heart including the coronary artery is extracted from the tomographic image including the heart in step 32. For the region extraction, a method is used in which a heart region is clicked with a few points, a CT value of the pixel is obtained, and only the heart region is extracted by threshold processing with surrounding pixel values based on that value. When extraction accuracy is poor, a more advanced extraction processing method is used. This processing method is as follows.

If the heart region cannot be extracted by threshold processing with the surrounding pixel values described above,
For example, when a vertebra or sternum is extracted as a heart region, it is dealt with by limiting the region to a rectangular region or the like in advance so that threshold processing is not performed outside the periphery of the heart.
As a more advanced heart extraction method, vertebra and sternum regions are extracted as preprocessing for extracting heart regions. The bone region can be easily extracted because the CT value is much higher than the surrounding soft tissue and lung region.
If the extracted bone region is subtracted from the original image and the heart is extracted using the subtracted image, the adjacent vertebra and sternum are not extracted, and only the heart region can be extracted.

When the heart region is extracted, the process proceeds to the next step 33. In step 33, the coronary artery causing calcification is extracted from the image of the heart region including the coronary artery, and the calcium score is calculated.
Since the coronary artery in which calcification has occurred has a CT value that is significantly different from that in a normal case, it can be performed by simple threshold processing.

In step 34, the calcium score of the calcified coronary artery extracted with the threshold value is calculated.
In calculating the calcium score, an Agatston score, which is a standard calculation algorithm, may be used.

When the calculation of the calcium score is completed, in step 35, the calcium score and the area of the calcified region are displayed on the image. In step 36, the process is completed.
The extraction of the heart region and the calculation of the calcium score are not limited to a single processing, but the heart region extraction processing of the tomographic images of all slices is performed by simultaneously processing the cardiac tomographic images at different slice positions.
In step 36, the process is completed.

The above is the explanation of the calculation of the calcium score, which is illustrated in FIG. 6, and the flowchart of FIG. 5 is illustrated. FIG. 6 (a) is an example in which a cardiac region including a coronary artery is depicted from a cardiac tomographic image. FIG. 6 (b) shows an example in which only the coronary artery is extracted from the extracted heart region, and FIG. 6 (c) shows an example in which the calculated calcium score is displayed on the image. In FIG. 5 (c), the calcium score is displayed in black and white in the extracted image of the outline of the coronary artery, but the same display may be performed at the stage of the image in FIG. 6 (b).

Since FIG. 6 (c) is a black-and-white display, the portion where calcification has occurred due to density is displayed in grayscale, that is, the density of black, but the color of the pixel causing calcification is colored according to the score. The operator can be informed of the severity of the problem by color-coding and displaying.
In addition, in the attached figure, the calcification area | region which has a calcium score with high black shall show the area | region where a calcium score is so low that it is light.
For color display, for example, a portion having a high calcium score is assigned red, and a portion having a low calcium score is assigned blue, and in the meantime, a corresponding color may be applied from an arbitrary hue color map that goes from blue to red.
In addition, the case where the calcium score is high is red and the low calcium score is blue, and another hue may be used.

  As shown in Fig. 6 (c), the calcified portion of the image is color-converted according to the calcium score and the score value is shown on the image. Therefore, as shown in FIG. 7, for example, if a plurality of tomographic images causing calcification are displayed at a time by an image viewer capable of simultaneously displaying four images, it is three-dimensional for the operator and observer. This makes it easier to understand which part of the coronary artery is calcified.

Further, in the present invention, this is realized by displaying as shown in FIG. 8 in order to facilitate a three-dimensional understanding of which position of the coronary artery is calcified. A three-frame tomographic image and a scanogram image of one heart image or a three-dimensionally reconstructed three-dimensional image are displayed on a four-screen viewer that simultaneously shows four images shown in FIG. For example, a scanogram or three-dimensional image display of the heart region obtained in step 24 of FIG. 3 is performed at the position shown in FIG. 8 (d).
It should be noted that the scano image or the three-dimensional image display is not limited to the position (d) but can be at other positions, and the number of viewer screens is not limited to four.

  When the image shown in FIG. 8 (d) is a scanogram image, for example, the calcification position information in the body axis direction is transmitted to the operator by a straight line, a broken line, or the like at a slice position having a coronary artery causing calcification. . Furthermore, by displaying the color of straight lines and broken lines according to the severity of the calcium score, the surgeon can determine which position in the body axis direction coronary artery or severe calcification has occurred. It becomes easy to do. In addition to the color, the severity of calcification can also be indicated by the roughness of the dotted dot line. This is illustrated in FIG.

  In addition, when the operator designates a straight line or a broken line displayed on the scanogram image of FIG. 9 (d) by, for example, clicking with a mouse or the like, a tomographic image corresponding to the slice position of the straight line or the broken line is designated. Display immediately at the position shown in FIG. 9 (a). A plurality of straight lines and broken lines can be selected. For example, when three slice positions are selected, the images at the positions shown in FIGS. 9A, 9B, and 9C are immediately updated and displayed.

As shown in FIGS. 11 and 12, it is possible to indicate the severity of the calcium score by the thickness of the line or the size of the arrow.
For example, if the calcium score is high, the thickness of the line is increased, and if it is an arrow, the size of the arrow is increased.
Furthermore, in the case of a broken line, the broken line is thickened and the interval between the broken lines is made dense to warn that the score value is high.
On the contrary, when the calcium score is low, the operator can be informed that the severity of the calcium score is low by reducing the thickness of the broken line and making the interval between the broken lines sparse.

As described above, the image processing apparatus according to the present invention enables an operator to observe a cardiac tomographic image and obtain a calcium score, and at the same time to grasp the calcification position in the body axis direction of the coronary artery on the scanogram image. It works effectively for early detection of blood heart disease.
Although the above example shows a method of displaying a scanogram image and grasping the position of the coronary artery calcification in the body axis direction, it is of course possible to implement this with a three-dimensional image or an MPR image. Alternatively, both the scanogram image and the three-dimensional image may be displayed simultaneously.
Further, the extracted calcified region may be projected onto a scanogram image and further displayed in color.

As described above, when the three-dimensional image of the heart region is arranged at the position shown in FIG. 10 (d), the coronary artery is also displayed on the three-dimensional image along the heart wall.
The coronary artery where the calcification is occurring is color-coded according to the severity of calcification as described above, and the calcification position in the body axis direction is the same as when using a scanogram for the operator. Can be clearly shown to the surgeon.
In addition, in the case of a three-dimensional image as shown in FIG. 10 (d), the heart can be observed from many directions based on the image characteristics, that is, the coronary artery where calcification has occurred can be observed by rotating the three-dimensional image. it can. Even in the case of a three-dimensional image, a tomographic image corresponding to the slice position can be obtained by clicking on the coronary artery causing calcification with a mouse, for example, as shown in Fig. 10 (c). Can be displayed immediately.

Schematic of heart region showing coronary artery. The block diagram of CT apparatus concerning one Example of this invention. The heart region imaging | photography flowchart concerning one Example of this invention. Explanatory drawing of a scanogram concerning one Example of this invention. The flowchart of the scanogram imaging | photography concerning one Example of this invention. (a) A tomographic image of a subject, (b) is a diagram in which coronary arteries are extracted from the heart region in (a), and (c) is a diagram in which the calculated calcium score is displayed on the coronary artery portion. (a), (b), (c), and (d) are tomographic images of the heart region at four different positions according to the present invention. (a), (b), and (c) are examples of calcium score display on tomographic images at three different positions according to the present invention, and (d) a scanogram image displaying the calcium score. (a) (b) (c) is a calcium score display example on a tomographic image at three different positions according to the present invention, and (d) is a scanogram image displaying the calcium score. (a) (b) is a calcium score display example on a tomographic image according to the present invention, (c) is an MPR image of (a) and (b), (d) is a three-dimensional image of (a) and (b) . The example of a display which shows the seriousness and position of the calcium score concerning this invention. The example of a display which shows the seriousness and position of the calcium score concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Scanner part of X-ray CT apparatus, 2 ... Image processing part, 3 ... Image display part, 4 ... Electrocardiograph, 6 ... Heart region, 7 ... Right coronary artery, 8 ... Right coronary artery, 9 ... Lung, 10 ... spine, 11 ... X-ray source, 12 ... bed, 13 ... X-ray detector

Claims (4)

An X-ray source that emits X-rays, and an X-ray source that is disposed opposite to the X-ray source with the subject interposed therebetween, and detects transmitted X-rays that pass through the subject while rotating around the X-ray source and the periphery of the X-ray source A line detector, an image processing unit that generates at least one of a scanogram image, a tomographic image, and a three-dimensional image of a subject from transmitted X-rays obtained by the X-ray detector, and the image processing unit An X-ray CT apparatus having an image display unit for displaying at least one of images,
The image processing unit extracts a calcified coronary image portion from an image of a heart region of a subject, and determines positional information of the image portion in the body axis direction of at least the scanogram image, the tomographic image, and the three-dimensional image. An X-ray CT apparatus characterized in that a display form of the position information is changed according to a calcium score calculated on the basis of a pixel value for each pixel of the image portion, which is indicated by a straight line, a broken line, or an arrow above one . The X-ray CT apparatus according to claim 1,
The image processing unit displays the severity of the calcium score by the thickness of the straight line or the broken line, the roughness of the broken line, the size of the arrow, or the color of the straight line, the broken line, or the arrow. X-ray CT apparatus characterized by this. The X-ray CT apparatus according to claim 2,
The image processing unit assigns a color according to the calcium score for each pixel of the calcified image portion in the cross-sectional layer image, characterized in the allocated colors by displaying the image portion X-ray CT apparatus . In creating the tomographic image and the three-dimensional image of the subject from the transmitted X-rays detected by the X-ray detector, the heart region is measured with an electrocardiograph and synchronized with the detection to obtain a predetermined cardiac time. X-ray CT apparatus according to any one of claims 1 to 3, characterized in that to create the tomogram image and the three-dimensional image based on the transmitted X-rays detected corresponding to the phase.

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