Image reconstructing apparatus

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an image reconstructing device that reconstructs the absorption coefficient distribution inside the subject from projection data obtained by measuring the dose distribution of radiation transmitted through the subject from a plurality of directions.

【0002】

[Conventional technology]

As is well known, the filtered back projection method is a method of reconstructing the absorption coefficient distribution inside the subject as an image from the projection data obtained by measuring the dose distribution of the radiation transmitted through the subject from multiple directions. It is commonly used. The current reconstruction method of X-ray CT equipment is different in that approximation is performed and a spatial filter is added to the correction filter in order to facilitate hardware conversion, but basically this is the case. The method is adopted.

【0003】

It takes about 1 second to reconstruct the absorption coefficient distribution as an image using this method using dedicated hardware.

【0004】

[Problems to be Solved by the Invention]

In recent years, there has been a demand for detailed observation of a three-dimensional distribution image of the absorption coefficient inside a subject. However, in order to reconstruct such a three-dimensional distribution image, it is necessary to reconstruct a large number of tomographic images. In particular, as shown in FIG. 20, a helical scan CT (helical scan CT) that spirally scans a subject placed on a top plate by moving the top plate while rotating an X-ray beam source such as an X-ray tube. (Also called spiral scan CT or spiral scan CT) or cone beam CT that generates a cone-shaped X-ray beam from the X-ray beam source and collects it with a two-dimensional detector as shown in Fig. 21. Since the number of fault planes to be generated increases dramatically and the reconstruction algorithm becomes complicated, there arises a problem that it takes an extremely large amount of time.

【0005】

For example, in 3D reconstruction, the reconstruction area is M.³If voxel and the number of projection directions are N, the three-dimensional back projection operation is M.³It is necessary to perform × N times, and it is impossible to use it in a clinical setting unless it is used even with a supercomputer (which has about 1000 times the arithmetic processing speed of normal hardware) until a reconstructed image is obtained. It will take some time.

【0006】

In addition, by continuously scanning an arbitrary tomography and reconstructing the cross section at high speed, it is possible to track the tip of the catheter and observe changes in the amount of inflow and outflow of contrast medium.

【0007】

In such a case, there is a demand for observing changes in CT values over time at a high speed of 1 frame or more (about 6 frames) per second. However, it takes a great deal of time to reconstruct such a moving image.

【0008】

For example, the reconstruction area of the moving image is set to M.²pixel, number of projection directions N, when trying to reconstruct L images per second, M²The operation of × N × L times must be performed in one second, which is impossible with the dedicated hardware. To meet this requirement, the size to be reconfigured is 512 x 512 pixels²From 256 x 256 pixel²The above-mentioned reconstruction speed is realized by reducing the amount to. However, since the size of one pixel becomes large, the image quality deteriorates by that amount, causing problems such as difficulty in seeing a moving object.

【0009】

The present invention has been made in view of the above problems, and provides an image reconstruction apparatus capable of shortening the time required for reconstruction processing without deteriorating the image quality of an area of interest or a target area. With the goal.

【0010】

[Means for solving problems]

In order to achieve the above object, the invention according to claim 1 obtains the X-ray absorption coefficient distribution in the subject by reconstructing the projection data obtained based on the dose distribution of X-rays transmitted through the subject. The first reconstruction means, the region extraction means for extracting the region of interest based on the X-ray absorption coefficient distribution obtained by the first reconstruction means, and the X-ray absorption coefficient distribution in the region of interest are the first. The gist is that the means for reconstructing the region of interest obtained with higher spatial resolution than one reconstructing means and the means for displaying the X-ray absorption coefficient distribution obtained by the means for reconstructing the region of interest as an image are provided.

【0011】

In the image reconstructing apparatus according to claim 1, the first reconstructing means is inside the subject by reconstructing the projection data obtained based on the dose distribution of X-rays transmitted through the subject. The X-ray absorption coefficient distribution of the above is obtained, and the region extraction means extracts the region of interest based on the X-ray absorption coefficient distribution obtained by the first reconstruction means. Then, the region of interest reconstructing means obtains the X-ray absorption coefficient distribution in the region of interest with a higher spatial resolution than the first reconstructing means, and the display means obtains the X-rays obtained by the region of interest reconstructing means. The absorption coefficient distribution is displayed as an image. As a result, it is possible to shorten the time required for the reconstruction process for the region of interest without deteriorating the image quality. Further, the first reconstructing means and the region of interest reconstructing means sequentially reconstruct the projection data that is continuous in time, and the region of interest reconstructing means repositions the position for obtaining the X-ray absorption coefficient. It is desirable that the images are sequentially switched for each constituent image.

【0012】

Further, the invention according to claim 3 is the first reconstitution for obtaining the X-ray absorption coefficient distribution in a subject by reconstructing the projection data obtained based on the dose distribution of X-rays transmitted through the subject. The constitutional means, the region extraction means for extracting the region of interest based on the X-ray absorption coefficient distribution obtained by the first reconstruction means, and the first reconstruction means for extracting the X-ray absorption coefficient in the region of interest. The gist is that it is equipped with means for reconstructing the region of interest that is required with higher accuracy.

【0013】

In the image reconstruction apparatus according to claim 3, the first reconstruction means is inside the subject by reconstructing the projection data obtained based on the dose distribution of X-rays transmitted through the subject. The X-ray absorption coefficient distribution of the above is obtained, and the region extraction means extracts the region of interest based on the X-ray absorption coefficient distribution obtained by the first reconstruction means. Then, the region of interest reconstructing means obtains the X-ray absorption coefficient in the region of interest with higher accuracy than the first reconstructing means. As a result, it is possible to shorten the time required for the reconstruction process for the region of interest without deteriorating the image quality.

【0014】

Further, the projection data is obtained by collecting outputs for each angle from a detector located at a position facing the X-ray tube when the X-ray tube is rotated about a subject by a predetermined angle. The reconstructing means reconstructs based on a part of the output in the X-ray detector, and the region of interest reconstructing means is the X used by the first reconstructing means for reconstructing. It is desirable that the reconstruction is performed based on the output of the line detector and the output of at least one X-ray detection element that the first reconstruction means does not use for the reconstruction.

【0015】

Further, for example, when the X-ray detector is composed of a plurality of X-ray detection elements and is rotated by a predetermined angle about the subject, the projection data is output for each angle from a detector located at a position facing the subject. It is desirable that the projection data used for the reconstruction by the region of interest reconstruction means has a smaller angular pitch than the projection data used for the reconstruction by the first reconstruction means.

【0016】

Further, the invention according to claim 7 reconstructs the X-ray absorption coefficient distribution in the subject from the projected data obtained based on the dose distribution of the X-ray transmitted through the subject to be less than a predetermined number of data. The reconstruction means of the above, the region extraction means for extracting the region to be diagnosed based on the data reconstructed by the first reconstruction means, and the target region extracted by the region extraction means are described above. Extracted by the second reconstruction means for reconstructing the X-ray absorption coefficient distribution in the subject based on the projection data and the region extraction means for all the pixels except the pixels reconstructed by the first reconstruction means. Regarding the target area, the data reconstructed by the first reconstructing means and the data reconstructed by the second reconstructing means are combined to obtain diagnostic data, and the area excluding the target area is used. Is gisted to have a synthetic means for using the data reconstructed by the first reconstructing means as diagnostic data.

【0017】

In the image reconstruction apparatus according to claim 7, the first reconstruction means is an X-ray absorption coefficient distribution in the subject from projection data obtained based on the dose distribution of X-rays transmitted through the subject. Is reconstructed to be less than a predetermined number of data, and the region extraction means extracts the region to be diagnosed based on the reconstructed data. In addition, the second reconstruction means projects the X-ray absorption coefficient distribution in the subject for all the pixels except the pixels reconstructed by the first reconstruction means for the extracted target region. Reconstruct based on. Then, the synthesizing means synthesizes the data reconstructed by the first reconstructing means and the data reconstructed by the second reconstructing means for the target region extracted by the region extracting means for diagnosis. For the area other than the target area, the data reconstructed by the first reconstructing means is used as the diagnostic data. As a result, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0018】

Further, the invention according to claim 8 is based on a reduction means for reducing the projection data obtained based on the dose distribution of X-rays transmitted through the subject and the projection data reduced by the reduction means. A first reconstruction means for reconstructing the X-ray absorption coefficient distribution in the region, a region extraction means for extracting a region to be diagnosed based on the data reconstructed by the first reconstruction means, and the region extraction means. For the target region extracted by the region extraction means, the second is to reconstruct the X-ray absorption coefficient distribution in the subject based on the projection data obtained based on the dose distribution of X-rays transmitted through the subject. For the reconstruction means and the target area extracted by the area extraction means, the data reconstructed by the second reconstruction means is used as diagnostic data, and the area other than the target area is the first reconstruction. The gist is to have a synthetic means for using the data reconstructed by the constituent means as the data for diagnosis.

【0019】

In the image reconstruction apparatus according to claim 8, the reduction means reduces the projection data obtained based on the dose distribution of X-rays transmitted through the subject, and based on the reduced projection data, the reduction means is used. The first reconstruction means reconstructs the X-ray absorption coefficient distribution in the subject, and based on the data reconstructed by the first reconstruction means, the region extraction means is the region to be diagnosed. Is extracted. In the second reconstruction means, for the target region extracted by this region extraction means, X in the subject is based on the projection data obtained based on the dose distribution of X-rays transmitted through the subject. Reconstruct the line absorption coefficient distribution. Then, the synthesis means uses the data reconstructed by the second reconstruction means as diagnostic data for the target region extracted by the region extraction means, and the first region excluding the target region. The data reconstructed by the reconstructing means is used as diagnostic data. As a result, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0020】

Further, the invention according to claim 9 reconstructs the X-ray absorption coefficient distribution in the subject from the projected data obtained based on the dose distribution of the X-ray transmitted through the subject to be less than a predetermined number of data. The reconstructing means of, the latest data reconstructed by the first reconstructing means, the subtracting means for subtracting the data reconstructed before this latest data, and the data subtracted by this subtracting means. With respect to the region extraction means for extracting the region to be diagnosed based on the above and the target region extracted by this region extraction means, all the pixels except the pixels reconstructed by the first reconstruction means are subject to the subject. The second reconstruction means for reconstructing the X-ray absorption coefficient distribution in the data based on the projection data, and the target region extracted by the region extraction means, the data reconstructed by the first reconstruction means. And, the data reconstructed by the second reconstructing means is combined into the data for diagnosis, and for the area other than the target area, the data reconstructed by the first reconstructing means is used as the data for diagnosis. The gist is to have a synthetic means.

【0021】

In the image reconstructing apparatus according to claim 9, the first reconstructing means is the X-ray absorption coefficient distribution in the subject from the projection data obtained based on the dose distribution of the X-ray transmitted through the subject. Is reconstructed to be less than a predetermined number of data, and the subtracting means subtracts the latest data reconstructed by this first reconstructing means and the data reconstructed before this latest data, and extracts the area. The means extracts a region to be diagnosed based on the data subtracted by the subtracting means. In addition, the second reconstruction means has an X-ray absorption coefficient distribution in the subject for all the pixels except the pixels reconstructed by the first reconstruction means for the target region extracted by the region extraction means. Is reconstructed based on the projection data. Then, the synthesizing means diagnoses the target region extracted by the region extracting means by synthesizing the data reconstructed by the first reconstructing means and the data reconstructed by the second reconstructing means. For the area other than the target area, the data reconstructed by the first reconstructing means is used as the diagnostic data. As a result, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0022】

Further, the invention according to claim 10 is based on a reduction means for reducing the projection data obtained based on the dose distribution of X-rays transmitted through the subject and the projection data reduced by the reduction means. Subtract the first reconstructing means to reconstruct the X-ray absorption coefficient distribution in, the latest data reconstructed by this first reconstructing means, and the data reconstructed before this latest data. X-rays transmitted through the subject for the subtraction means to be performed, the region extraction means for extracting the region to be diagnosed based on the data subtracted by the subtraction means, and the target region extracted by this region extraction means. About the second reconstruction means for reconstructing the X-ray absorption coefficient distribution in the subject based on the predetermined number of projection data obtained based on the dose distribution of, and the target region extracted by the region extraction means. Uses the data reconstructed by the second reconstructing means as the diagnostic data, and for the area other than the target area, the data reconstructed by the first reconstructing means is used as the diagnostic data. The gist is to have means.

【0023】

In the image reconstruction apparatus according to claim 10, the reduction means reduces the projected data obtained based on the dose distribution of X-rays transmitted through the subject, and the first reconstruction means reduces the reduction. The X-ray absorption coefficient distribution in the subject is reconstructed based on the projection data reduced by the means, and the subtraction means is the latest data reconstructed by the first reconstructing means and the latest data. The previously reconstructed data is subtracted, and the region extraction means extracts the region to be diagnosed based on the data subtracted by the subtraction means. In addition, the second reconstruction means has a target region extracted by the region extraction means in the subject based on a predetermined number of projection data obtained based on the dose distribution of X-rays transmitted through the subject. Reconstruct the X-ray absorption coefficient distribution of. Then, the synthesis means uses the data reconstructed by the second reconstruction means as diagnostic data for the target region extracted by the region extraction means, and the first region excluding the target region. The data reconstructed by the reconstructing means is used as diagnostic data. As a result, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0024】

The first aspect of claim 11 is to reconstruct the X-ray absorption coefficient distribution in a subject from projection data obtained based on the dose distribution of X-rays transmitted through the subject by using an arbitrary interpolation method. The reconstructing means, the subtracting means for subtracting the latest data reconstructed by the first reconstructing means and the data reconstructed before this latest data, and the data subtracted by this subtracting means. For the area extraction means that extracts the area to be diagnosed based on the area and the target area extracted by this area extraction means, a more accurate interpolation method than the interpolation method used by the first reconstruction means is used. The second reconstructing means and the target area extracted by the area extraction means are reconstructed by the data reconstructed by the first reconstructing means and the second reconstructing means. The gist is to have a synthesis means for synthesizing the data to obtain diagnostic data, and for the region other than the target area, the data reconstructed by the first reconstruction means is used as the diagnostic data.

【0025】

Further, the invention according to claim 12 is based on a region extraction means for extracting a region to be diagnosed based on projection data obtained based on the dose distribution of X-rays transmitted through a subject, and the region extraction means. The extracted target region has a reconstruction means for reconstructing the X-ray absorption coefficient distribution in the subject based on the projection data obtained based on the dose distribution of X-rays transmitted through the subject. It is a summary.

【0026】

In the image reconstruction apparatus according to claim 12, the region extraction means extracts a region to be diagnosed based on projection data obtained based on the dose distribution of X-rays transmitted through the subject. Then, the reconstructing means refers to the X-ray absorption coefficient distribution in the subject based on the projection data obtained based on the dose distribution of the X-rays transmitted through the subject for the target region extracted by the region extraction means. To reconstruct. As a result, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0027】

Further, the invention according to claim 13 is a subtraction in which the latest projection data obtained based on the dose distribution of X-rays transmitted through the subject and the projection data obtained before the latest projection data are subtracted. For the means, the region extraction means for extracting the region to be diagnosed based on the data subtracted by the subtraction means, and the target region extracted by this region extraction means, the dose of X-rays transmitted through the subject. The gist is to have a second reconstruction means for reconstructing the X-ray absorption coefficient distribution in the subject based on a predetermined number of projection data obtained based on the distribution.

【0028】

Further, the invention according to claim 14 is a subtraction in which the latest projection data obtained based on the dose distribution of X-rays transmitted through the subject and the projection data obtained before the latest projection data are subtracted. For the means, the region extraction means for extracting the region to be diagnosed based on the data subtracted by the subtraction means, and the target region extracted by this region extraction means, the dose of X-ray transmitted through the subject. Obtained based on the second reconstruction means that reconstructs the X-ray absorption coefficient distribution in the subject based on the predetermined number of projection data obtained based on the distribution, and the dose distribution of X-rays that have passed through the subject. By the reduction means for reducing the projected projection data, the third reconstruction means for reconstructing the X-ray absorption coefficient distribution in the subject based on the projection data reduced by the reduction means, and the region extraction means. For the extracted target area, the data reconstructed by the second reconstruction means is used as diagnostic data, and for the area other than the target area, the data reconstructed by the third reconstruction means is diagnosed. The gist is to have a synthetic means to use the data for the purpose.

【0029】

In the image reconstructing apparatus according to claim 14, the subtraction means is the latest projection data obtained based on the dose distribution of X-rays transmitted through the subject and the projection obtained on the latest projection data. The data is subtracted, the area extraction means extracts the area to be diagnosed based on the data subtracted by the subtraction means, and the second reconstruction means is the target area extracted by this area extraction means. The X-ray absorption coefficient distribution in the subject is reconstructed based on a predetermined number of projection data obtained based on the dose distribution of X-rays transmitted through the subject. Further, the reduction means reduces the projection data obtained based on the dose distribution of X-rays transmitted through the subject, and the third reconstruction means reduces the projection data obtained based on the projection data reduced by the reduction means. Reconstruct the X-ray absorption coefficient distribution in the sample. Then, the synthesis means uses the data reconstructed by the second reconstruction means as diagnostic data for the target region extracted by the region extraction means, and the third region excluding the target region. The data reconstructed by the reconstructing means is used as diagnostic data. As a result, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0030】

Further, the invention according to claim 15 is a subtraction in which the latest projection data obtained based on the dose distribution of X-rays transmitted through the subject and the projection data obtained before the latest projection data are subtracted. For the means, the region extraction means for extracting the region to be diagnosed based on the data subtracted by the subtraction means, and the target region extracted by this region extraction means, the dose of X-ray transmitted through the subject. A second reconstruction means for reconstructing the X-ray absorption coefficient distribution in the subject based on a predetermined number of projection data obtained based on the distribution, and an interpolation method with lower accuracy than this second reconstruction means. For the third reconstruction means for reconstructing the X-ray absorption coefficient distribution using the data and the target region extracted by the region extraction means, the data reconstructed by the second reconstruction means is used as the diagnostic data. The gist of the region other than the target region is to have a synthesis means for using the data reconstructed by the third reconstruction means as the diagnostic data.

【0031】

In the invention according to claim 16, the region extraction means includes a range designation unit that specifies a range of values of the X-ray absorption coefficient distribution as a target region, and data reconstructed by the first reconstruction means. The gist is to have an extraction unit that extracts an area within the range specified by the range designation unit.

【0032】

A gist of the invention according to claim 17 is that the region of interest reconstructing means reconstructs a highly accurate X-ray absorption coefficient distribution by using a higher interpolation method than the first reconstructing means. ..

【0033】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the image reconstruction apparatus according to the present invention.

【0034】

As shown in FIG. 1, the image reconstruction device 1 of the first embodiment includes a detector 3, an analog / digital conversion unit (hereinafter referred to as an A / D conversion unit) 5, and a first reconstruction means. The first reconstruction processing unit 7, the interpolation processing unit 9, the first image memory unit 11, the area extraction unit 13 as the area extraction means, the area of interest reconstruction means, and the second as the second reconstruction means. Reconstruction processing unit 15, second image memory unit 17, image composition unit 19 as a composition means, composition image memory unit 21, digital / analog conversion unit (hereinafter referred to as D / A conversion unit) 23, It has a display unit 25.

【0035】

The detector 3 has 512 X-ray detection elements arranged in an arcuate row, and emits X-rays that have been exposed from an X-ray beam source (not shown) and have passed through the subject. The projection data detected by the detection element sequence and converted into an electric signal is obtained. The A / D converter 5 converts the projection data (analog signal) obtained by the detector 3 into a digital signal.

【0036】

The first reconstruction processing unit 7 has several elements (pixels) in the discretized reconstruction space based on the projection data converted into a digital signal by the A / D conversion unit 5, for example, X every other pixel. The line absorption coefficient distribution is reconstructed as reconstructed data. The pixels used in the following description include "pixels", which are the smallest units in two dimensions, and "voxels", which are the smallest units in three dimensions.

【0037】

The interpolation processing unit 9 interpolates the pixels not reconstructed by the first reconstruction processing unit 7 by using the values of the pixels around the pixels. The first image memory unit 11 stores the reconstruction data reconstructed by the first reconstruction processing unit 7 and the data interpolated by the interpolation processing unit 9 for each pixel.

【0038】

The area extraction unit 13 is in the range of the value set in advance by the operator using the input device (not shown) in the reconstruction data reconstructed by the first reconstruction processing unit 7, and next to it. A region that is a certain pixel and has not been reconstructed by the first reconstruction processing unit 7 is extracted as a reconstruction region.

【0039】

The second reconstruction processing unit 15 reconstructs the X-ray absorption coefficient distribution of the reconstruction region extracted by the region extraction unit 13 based on the projection data converted into a digital signal by the A / D conversion unit 5. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body. The second image memory unit 17 stores the reconstructed data reconstructed by the second reconstructed processing unit 15 and the data having a value λ without being reconstructed for each pixel.

【0040】

The image synthesizing unit 19 checks the data of each pixel stored in the second image memory unit 17, and if the value is λ, the value of the same pixel stored in the first image memory unit 11 is the value of that pixel. If the value is other than λ, the value stored in the second image memory unit 17 as it is is used as the value of the pixel.

【0041】

The composite image memory unit 21 stores the data synthesized by the image synthesis unit 19 for each pixel. The D / A conversion unit 23 reads the data stored in the image synthesis memory unit 21 and converts it into analog data. The display unit 25 includes a display (not shown), converts the data converted into analog data by the D / A conversion unit 23 into data that can be displayed on the display, and displays the data on the display.

【0042】

Next, the operation of the image reconstruction device 1 of the first embodiment will be described. First, in an X-ray CT apparatus (not shown), X-rays are irradiated in a fan shape while rotating an X-ray beam source (not shown).

【0043】

When X-rays are irradiated, the detector 3 detects the irradiated X-rays and obtains projection data of 1200 patterns (for one rotation) of, for example, 0.3 degrees each. The projection data of the 1200 patterns is converted into a digital signal by the A / D conversion unit 5 and supplied to the first reconstruction processing unit 7 and the second reconstruction processing unit 15.

【0044】

When the projection data converted into a digital signal is supplied, the first reconstruction processing unit 7 reconstructs the X-ray absorption coefficient distribution for every few discretized elements (pixels) based on the projection data. Reconstruct as. For example, as shown by the diagonal lines in FIGS. 2 and 3, the X-ray absorption coefficient distribution (CT value with 0 for water and -1000 for air) is reconstructed every other pixel. As a reconstruction method, for example, after applying a predetermined convolution filter to the projection data of 1200 patterns, a back projection operation (back projection) is performed on the data of every other pixel. The reconstructed region is defined as, for example, a circle inscribed in all the X-ray bundles emitted from the X-ray beam generation source.

【0045】

When reconstruction is performed every other pixel by the first reconstruction processing unit 7, the interpolation processing unit 9 uses the values of the pixels around the pixels that were not reconstructed by the first reconstruction processing unit 7. To interpolate. For example, in the example shown in FIG. 2, the average value of the four pixels on the top, bottom, left, and right is taken as the value of the pixel to be interpolated, centering on the pixel to be interpolated. Further, in the example shown in FIG. 3, the average value of four pixels of diagonally upper right, diagonally lower right, diagonally upper left, and diagonally lower left, or the average value of two pixels above and below or left and right is used as the pixel value to be interpolated. The interpolated data and the reconstructed data reconstructed by the first reconstructed processing unit 7 are stored in the first image memory unit 11 for each pixel.

【0046】

On the other hand, when reconstruction is performed every other pixel by the first reconstruction processing unit 7, the area extraction unit 13 is within the range of values previously input by the input device (not shown) in the reconstruction data. The area and the area adjacent to the area and not reconstructed by the first reconstruction processing unit 7 are extracted as the reconstruction area. For example, in the example shown in FIG. 4, when the pixel A is within the above range, the four pixels on the top, bottom, left, and right indicated by the triangles in the figure centering on the pixel A are extracted as the reconstruction area. Further, in the example shown in FIG. 5, when the pixel A is within the above range, the top, bottom, left and right, diagonally upper right, diagonally lower right, diagonally upper left, and diagonally lower left 8 shown by triangles in the figure centering on pixel A. Pixels are extracted as a reconstruction area.

【0047】

When the reconstruction area is extracted by the area extraction unit 13, the second reconstruction processing unit 15 absorbs X-rays from the reconstruction area based on the projection data converted into a digital signal by the A / D conversion unit 5. The coefficient distribution is reconstructed as reconstructed data. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body. This value λ and the reconstruction data reconstructed by the second reconstruction processing unit 15 are stored in the second image memory unit 17 for each pixel.

【0048】

When the value λ and the reconstruction data are stored in the second image memory unit 17, the image synthesis unit 19 checks the data of each pixel stored in the second image memory unit 17, and if the value is λ, the image synthesis unit 19 checks the data of each pixel. The value of the same pixel stored in the first image memory unit 11 is used as the value of the pixel, and if the value is other than the value λ, the value stored in the second image memory unit 17 is used as the value of the pixel. As a result, the data stored in the first image memory unit 11 and the data stored in the second image memory unit 17 are combined. The synthesized data is stored in the composite image memory unit 21.

【0049】

When the data is stored in the composite image memory unit 21, the D / A conversion unit 23 reads the data stored in the image synthesis memory unit 21 and converts it into analog data. Then, the data converted into the analog data is converted into image data that can be displayed on the display by the display unit 25, and is displayed on the display.

【0050】

As described above, in the image reconstruction device 1 of the first embodiment, all the pixels are reconstructed in the predetermined area, and the data of every other pixel is reconstructed in the areas other than the area. Therefore, the time required for the reconstruction process can be shortened without deteriorating the image quality.

【0051】

The first reconstruction processing unit 7 of the first embodiment reconstructs every other pixel, but the present invention is not limited to this, and for example, as shown in FIG. 6, 2 rows and 2 columns. The X-ray absorption coefficient distribution at the center position of each pixel (2 × 2 pixels) may be reconstructed based on the projection data. In this case, since the X-ray absorption coefficient distribution at the center position of the 2 × 2 pixel is reconstructed, the oversight of the information to be extracted is reduced. In this case, the interpolation processing unit 9 performs two-dimensional first-order interpolation (Bi-Linear interpolation). In this two-dimensional first-order interpolation, as shown in FIG. 7, the value on the center line (dotted arrow) of the desired pixel is sandwiched between the values at the two adjacent center positions (solid line arrow) and the desired pixel. Two points are obtained, and the value of the desired pixel (the value at the center position of the desired pixel; the value at the position indicated by the circle in the figure) is obtained from the values of these two points. Since the amount of calculation increases when this two-dimensional first-order interpolation is performed, if the interpolation function is set to the 0th order, that is, the value at the closest position is set to the value of that pixel, the value at the center of 2 × 2 pixels is adopted. Is the value of all 2 × 2 pixels, and the amount of calculation for interpolation processing can be reduced.

【0052】

Next, a second embodiment of the image reconstruction apparatus according to the present invention will be described with reference to FIG. In FIG. 8, the same ones shown in FIG. 1 are given the same symbols and detailed explanations are omitted.

【0053】

As shown in FIG. 8, the image reconstruction apparatus 30 of the second embodiment includes a detector 3, an A / D conversion unit 5, a reduction processing unit 31 as a reduction means, and a first reconstruction means. (1) Reconstruction processing unit 33, enlargement processing unit 35, first image memory unit 37, area extraction unit 13 as area extraction means, second reconstruction processing unit 15 as second reconstruction means, and It has a second image memory unit 17, an image composition unit 19 as a composition means, a composition image memory unit 21, a D / A conversion unit 23, and a display unit 25, and is reconstructed after reducing the projected data. , A predetermined area is extracted.

【0054】

The reduction processing unit 31 reduces the number of projection data converted into digital signals by the A / D conversion unit 5 from, for example, 512 to 256. Here, reduction means reduction in image processing technology. For example, by taking the average of the values of two adjacent pixels, the value of two pixels is represented by the average value.

【0055】

The first reconstruction processing unit 33 reconstructs 2 × 2 pixels as one pixel as shown in FIG. 9 based on the projection data reduced by the reduction processing unit 31. Here, 2 x 2 pixels are reconstructed as one pixel, but if this size is increased, the amount of calculation will be reduced and high-speed processing will be possible, but on the contrary, objects smaller than that size will be overlooked. There is a possibility that it will end up. Therefore, 2 × 2 pixels are suitable.

【0056】

The enlargement processing unit 35 returns the value of one pixel of 2 × 2 pixels by the first reconstruction processing unit 33 to the original 2 × 2 pixel by using the enlargement processing of the image processing technique. The first image memory unit 37 stores the data enlarged by the enlargement processing unit 35 for each pixel.

【0057】

Next, the operation of the image reconstruction device 30 of the second embodiment will be described. First, in an X-ray CT apparatus (not shown), X-rays are irradiated in a fan shape while rotating an X-ray beam source (not shown).

【0058】

When X-rays are irradiated, the detector 3 detects the irradiated X-rays and obtains projection data. This projection data is converted into a digital signal by the A / D conversion unit 5, and is supplied to the reduction processing unit 31 and the second reconstruction processing unit 15.

【0059】

When the projection data converted into a digital signal is supplied, the reduction processing unit 31 reduces the number of the supplied projection data from, for example, 512 to 256. Then, the reduction processing unit 31 supplies the reduced projection data to the first reconstruction processing unit 33.

【0060】

When the reduced projection data is supplied, the first reconstruction processing unit 33 reconstructs the 2 × 2 pixels as one pixel as shown in FIG. 9 based on the reduced projection data. Then, the first reconstruction processing unit 33 supplies the reconstructed data to the expansion processing unit 35 and the area extraction unit 13.

【0061】

When the reconstruction data is supplied from the first reconstruction processing unit 33, the enlargement processing unit 35 sets the value of 2 × 2 pixels as one pixel by the first reconstruction processing unit 33 to be the original 2 × 2. Return to pixel. At this time, the value of each pixel may be the value of one of the reconstructed pixels (all four pixels have the same value), or the reconstructed value is used as the value of the center position of the 2 × 2 pixels. It may be obtained in the same manner as the interpolation process shown in FIG. Then, the enlargement processing unit 35 stores the enlarged data in the first image memory unit 37 for each pixel.

【0062】

On the other hand, when reconstruction is performed by the first reconstruction processing unit 33, the area extraction unit 13 uses an input device (not shown) in advance in the reconstruction data to set a range of values set by the operator. The area inside is extracted as a reconstruction area. Then, the area extraction unit 13 instructs the second reconstruction processing unit 15 of this reconstruction area.

【0063】

The value (CT value) to be set has a certain range, for example, 500 to 3000 when bone is to be extracted, and 0 to 100 when soft tissue is to be extracted.

【0064】

When the reconstruction area is extracted by the area extraction unit 13, the second reconstruction processing unit 15 determines the X-ray absorption coefficient for this reconstruction area based on the projection data converted into a digital signal by the A / D conversion unit 5. Reconstruct the distribution as reconstructed data. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body. This value λ and the reconstruction data reconstructed by the second reconstruction processing unit 15 are stored in the second image memory unit 17 for each pixel.

【0065】

When the value λ and the reconstruction data are stored in the second image memory unit 17, the image synthesis unit 19 checks the data of each pixel stored in the second image memory unit 17, and if the value is λ, the image synthesis unit 19 checks the data of each pixel. The value of the same pixel stored in the first image memory unit 37 is used as the value of the pixel, and if the value is other than the value λ, the value stored in the second image memory unit 17 as it is is used as the value of the pixel. As a result, the data stored in the first image memory unit 37 and the data stored in the second image memory unit 17 are combined.

【0066】

After that, the data synthesized by the image synthesizing unit 19 is displayed on the display of the display unit 25 by operating in the same manner as the image reconstructing device 1 of the first embodiment.

【0067】

As described above, in the image reconstruction apparatus 30 of the second embodiment, the predetermined area is reconstructed for all pixels based on the projection data that is not reduced, and the other areas are 2 × based on the reduced projection data. Since the two pixels are reconstructed as one pixel, the time required for the reconstructing process can be shortened without deteriorating the image quality in the area.

【0068】

In the image reconstruction device 30 of the second embodiment, the reduction processing unit 31 reduces the projection data, and the first reconstruction processing unit 33 reconstructs the 2 × 2 pixels as one pixel. The present invention is not limited to this, and the reduction processing unit 31 and the enlargement processing unit 35 are eliminated, and the first reconstruction processing unit 33 uses less projection data and reconstructs all the pixels. (Ii) The reconstruction processing unit 15 may reconstruct the reconstruction area using the total projection data. For example, when the projection data is collected every 0.3 degrees, the first reconstruction processing unit 33 reconstructs all the pixels based on the projection data every one direction, that is, every 0.6 degrees, and the second reconstruction. The configuration processing unit 15 reconstructs all the pixels in the reconstruction region based on the projection data every 0.3 degrees.

【0069】

Next, a third embodiment of the image reconstruction apparatus according to the present invention will be described with reference to FIG. In FIG. 10, the same ones shown in FIG. 1 are given the same symbols and detailed explanations are omitted.

【0070】

As shown in FIG. 10, the image reconstruction apparatus 40 of the third embodiment includes a detector 3, an A / D conversion unit 5, an area extraction unit 41 as an area extraction means, and a first reconstruction means. It has a first reconstruction processing unit 43, a second reconstruction processing unit 45 as a second reconstruction means, an image memory unit 47, a D / A conversion unit 23, and a display unit 25, and has projection data. A predetermined region is extracted based on the above.

【0071】

The area extraction unit 41 sets the area corresponding to the range of values set by the operator in advance using an input device (not shown) in the projection data converted into a digital signal by the A / D conversion unit 5. Extracted as an area on the detector (detector 3) projected by the target part (for example, bone or contrasting blood vessel), the projection data of this extracted area is "1", and the other projection data is "0". ". Here, since the projected data is a line integral of the X-ray dose, when the contrast agent is injected into the extraction target, the extraction target is included before the contrast agent is injected, as shown in FIG. A mask image image memory unit 51 that stores data obtained by photographing a subject, and a live image image memory unit 53 that stores data photographed at the same projection angle as the data stored in the mask image image memory unit 51 after injection of a contrast agent. And a subtractor 55 for subtracting the data stored in the mask image image memory unit 51 and the data stored in the live image image memory unit 53 is provided, and the data before the contrast agent injection and the data after the contrast agent injection are provided. The area may be extracted from the value obtained by subtracting.

【0072】

The first reconstruction processing unit 43 uses the binary projection data in the 1200 directions as shown in FIG. 12 to set the region reproduced by the back projection and the logical product processing as the reconstruction region, and reconstructs the region. Instruct the second reconstruction processing unit 45.

【0073】

Here, assuming that the target portion is completely determined on the detector (detector 3) surface, the target portion is never projected except for the region extracted by the region extraction unit 41. Since the area other than the reconstructed area shown in FIG. 12 is projected to the area other than the area extracted by the area extraction unit 41 depending on the projection direction, it is determined that the target part is not in this area.

【0074】

Further, the reconstructed region shown in FIG. 12 is an region in the image region in which the back projections of the regions extracted by the region extraction unit 41 overlap in all directions. This can be obtained by determining whether the back projection line of the target portion passes through this pixel in all directions when considering any pixel. That is, assuming that "1" is used when passing in any direction and "0" is used when not passing, the logical product of the values (1 or 0) in all directions is used to check whether or not all areas are passed. It is required by taking.

【0075】

The second reconstruction processing unit 45 reconstructs the X-ray series coefficient distribution as reconstruction data for the region instructed by the first reconstruction processing unit 43 based on the total projection data.

【0076】

The image memory unit 47 stores the reconstruction data reconstructed by the second reconstruction processing unit 45 for each pixel.

【0077】

Next, the operation of the image reconstruction device 40 of the third embodiment will be described. First, in an X-ray CT apparatus (not shown), X-rays are irradiated in a fan shape while rotating an X-ray beam source (not shown).

【0078】

When X-rays are irradiated, the detector 3 detects the irradiated X-rays and obtains projection data. This projection data is converted into a digital signal by the A / D conversion unit 5, and is supplied to the region extraction unit 41 and the first reconstruction processing unit 43.

【0079】

When the projection data is supplied from the A / D conversion unit 5, the area extraction unit 41 uses an input device (not shown) in advance in the projection data supplied from the A / D conversion unit 5 by the operator. The area corresponding to the set value range is extracted as the reconstruction area by the second reconstruction processing unit 45, and the projection data of this extracted area is set to "1" and the other projection data is set to "0". ..

【0080】

Here, when the contrast agent is injected into the extraction target, as shown in FIG. 11, after storing the subject including the extraction target in the mask image image memory unit 51 before injecting the contrast agent. , The data taken at the same projection angle as the data stored in the mask image image memory unit 51 is stored in the live image image memory unit 53. Then, the subtractor 55 subtracts the data stored in the mask image image memory unit 51 and the data stored in the live image image memory unit 53 to extract the area.

【0081】

When the region is extracted by the region extraction unit 41 using the projection data, the first reconstruction processing unit 43 reproduces the region by back projection and logical product processing using the binary projection data in the 1200 directions as shown in FIG. The area is set as the reconstruction area, and the second reconstruction processing unit 45 is instructed to reconstruct the area.

【0082】

When the region is specified by the first reconstruction processing unit 43, the second reconstruction processing unit 45 calculates the X-ray series coefficient distribution for the region specified by the first reconstruction processing unit 43 based on the total projection data. Reconstruct as reconstructed data. Then, this reconstruction data is stored in the image memory unit 47 and displayed on the display of the display unit 25.

【0083】

As described above, in the image reconstruction apparatus 40 of the third embodiment, a predetermined region is extracted based on the projection data, and only the extracted region is reconstructed by the second reconstruction processing unit 45. For the above-mentioned area, the time required for the reconstruction process can be shortened without deteriorating the image quality.

【0084】

In the image reconstruction apparatus 40 of the third embodiment, the region extraction unit 41 extracts the region using all the projection data, but the present invention is not limited to this, and the collected projections are not limited to this. The region extraction may be performed using only a part of the data, for example, the projection data having projection angles of 0 degrees, 45 degrees, 90 degrees, and 135 degrees. In this case, the amount of calculation can be reduced.

【0085】

Further, in the area extraction by the area extraction unit 41 and the first reconstruction processing unit 43, if the ratio occupying the pixel is low, the pixel is not extracted as the boundary of the area, so that it may be estimated to be slightly smaller than the original boundary. There is. Therefore, the area may be expanded by a predetermined amount before the reconstruction is performed by the second reconstruction processing unit 45. In this case, for example, as shown in FIG. 13, the binarization processing unit 61 that binarizes the area extracted by the area extraction unit 41 and the first reconstruction processing unit 43 to 1 and the others to 0. And the filtering processing unit 63 that performs the convolution calculation using the convolution kernel as shown in FIG. 14 on the data binarized by the binarization processing unit 61, and the convolution by this filtering processing unit 63. Threshold processing is performed on the calculated data, and a threshold processing unit 65 instructing the second reconstruction processing unit 45 is provided with an area other than "0" as a reconstruction area.

【0086】

The method of expanding the area by a predetermined amount before the reconstruction by the second reconstruction processing unit 45 described above is the same for each embodiment (from the first embodiment described above to the seventh embodiment described later). Needless to say, it can be applied to.

【0087】

Next, a fourth embodiment of the image reconstruction apparatus according to the present invention will be described with reference to FIG. In FIG. 15, the same ones shown in FIG. 1 are given the same symbols and detailed explanations are omitted.

【0088】

As shown in FIG. 15, the image reconstruction apparatus 70 of the fourth embodiment includes a detector 3, an A / D conversion unit 5, a first reconstruction processing unit 71 as a first reconstruction means, and a first. The image memory unit 73, the interpolation processing unit 75, the subtractor 77 as the subtraction means, the area extraction unit 79 as the area extraction means, the second reconstruction processing unit 81 as the second reconstruction means, and the second (Ii) It has an image memory unit 83, an image composition unit 85 as a composition means, a composition image memory unit 21, a D / A conversion unit 23, and a display unit 25.

【0089】

The first reconstruction processing unit 71 creates an X-ray absorption coefficient distribution for every discretized number of elements (pixels), for example, every other pixel, based on the projection data converted into a digital signal by the A / D conversion unit 5. Reconstruct as reconstructed data. The first image memory unit 73 temporarily holds the reconstructed data reconstructed by the first reconstructed processing unit 71. The interpolation processing unit 75 interpolates the pixels not reconstructed by the first reconstruction processing unit 7 by using the values of the pixels around the pixels.

【0090】

The subtractor 77 subtracts the reconstruction data converted into a digital signal by the first reconstruction processing unit 71 and the reconstruction data one frame before the reconstruction data stored in the first image memory unit 73. ..

【0091】

The region extraction unit 79 extracts, as a reconstruction region, a region equal to or larger than a threshold set by the operator using an input device (not shown) in advance from the data (absolute value) subtracted by the subtractor 77.

【0092】

The second reconstruction processing unit 81 uses the X-ray absorption coefficient distribution as reconstruction data based on the projection data obtained by converting the reconstruction region extracted by the region extraction unit 79 into a digital signal by the A / D conversion unit 5. Reconfigure. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body. The second image memory unit 83 stores the reconstructed data reconstructed by the second reconstructed processing unit 15 and the data having a value λ without being reconstructed for each pixel.

【0093】

The image composition unit 85 checks the data of each pixel stored in the second image memory unit 83, and if the value is λ, the value of the same pixel supplied from the interpolation processing unit 75 is used as the value of that pixel. If the value is other than λ, the value stored in the second image memory unit 83 as it is is used as the pixel value.

【0094】

Next, the operation of the image reconstructing device 70 of the fourth embodiment will be described. First, in an X-ray CT apparatus (not shown), X-rays are irradiated in a fan shape while rotating an X-ray beam source (not shown).

【0095】

When X-rays are irradiated, the detector 3 detects the irradiated X-rays and obtains projection data of 1200 patterns (for one rotation) of, for example, 0.3 degrees each. The projection data of the 1200 patterns is converted into a digital signal by the A / D conversion unit 5 and supplied to the first reconstruction processing unit 71 and the second reconstruction processing unit 81.

【0096】

When the projection data converted into a digital signal is supplied, the first reconstruction processing unit 71 reconstructs the X-ray absorption coefficient distribution for every few discretized elements (pixels) based on the projection data. Reconstruct as. For example, as shown by the diagonal lines in FIGS. 2 and 3, the X-ray absorption coefficient distribution (CT value with 0 for water and -1000 for air) is reconstructed every other pixel. As a reconstruction method, for example, after applying a predetermined convolution filter to the projection data of 1200 patterns, a back projection operation (back projection) is performed on the data of every other pixel. The reconstructed region is defined as, for example, a circle inscribed in all the X-ray bundles emitted from the X-ray beam generation source.

【0097】

Then, the first reconstruction processing unit 71 stores the reconstruction data in the first image memory unit 73 and supplies the reconstruction data to the subtractor 77.

【0098】

When the reconstruction data is temporarily held in the first image memory 73, the interpolation processing unit 75 uses the values of the pixels around the pixels that have not been reconstructed by the first reconstruction processing unit 71, and the first image memory 73 uses the values of the pixels around it. 1 Interpolation is performed in the same manner as in the interpolation processing unit 9 of the embodiment. Then, the interpolation processing unit 75 supplies the interpolated data and the reconstruction data reconstructed by the first reconstruction processing unit 71 to the image composition unit 85.

【0099】

On the other hand, the subtractor 77 combines the reconstruction data converted into a digital signal by the first reconstruction processing unit 71 and the reconstruction data one frame before the reconstruction data stored in the first image memory unit 73. It is subtracted and supplied to the region extraction unit 79.

【0100】

When the subtracted data is supplied from the subtractor 77, the area extraction unit 79 uses the input device (not shown) in advance in the subtracted data (absolute value) to set a threshold value set by the operator. The above area is extracted as a reconstruction area. Then, the reconstruction area is instructed to the second reconstruction processing unit 81.

【0101】

When the reconstruction area is instructed by the area extraction unit 79, the second reconstruction processing unit 81 projects the reconstruction area extracted by the area extraction unit 13 and converted into a digital signal by the A / D conversion unit 5. Based on the data, the X-ray absorption coefficient distribution is reconstructed as reconstructed data. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body. This value λ and the reconstruction data reconstructed by the second reconstruction processing unit 81 are stored in the second image memory unit 83 for each pixel.

【0102】

When the value λ and the reconstruction data are stored in the second image memory unit 83, the image synthesis unit 85 checks the data of each pixel stored in the second image memory unit 83, and if the value is λ, the image synthesis unit 85 checks the data of each pixel. , The value of the same pixel supplied from the interpolation processing unit 75 is used as the value of that pixel, and if the value is other than the value λ, the value stored in the second image memory unit 83 as it is is used as the value of that pixel. As a result, the data supplied from the interpolation processing unit 75 and the data stored in the second image memory unit 83 are combined. The synthesized data is stored in the composite image memory unit 21.

【0103】

When the data is stored in the composite image memory unit 21, the D / A conversion unit 23 reads the data stored in the image synthesis memory unit 21 and converts it into analog data. Then, the data converted into the analog data is converted into image data that can be displayed on the display by the display unit 25, and is displayed on the display. As described above, in the image reconstruction apparatus 70 of the fourth embodiment, the latest reconstruction data and the reconstruction data one frame before are subtracted to extract a predetermined area from the data, and the predetermined area is extracted. Since all the pixels are reconstructed and the data of every other pixel is reconstructed except for the area, the time required for the reconstruction process can be shortened for the area without deteriorating the image quality. In particular, in the image reconstruction apparatus 70 of the fourth embodiment, a predetermined region is extracted from the data obtained by subtracting the latest reconstruction data and the reconstruction data one frame before, so that an arbitrary fault is continuously scanned. However, by reconstructing the cross section at high speed, it is highly effective in tracking the tip of the catheter and observing changes in the inflow and outflow of the contrast medium.

【0104】

Next, a fifth embodiment of the image reconstruction apparatus according to the present invention will be described with reference to FIG. In FIG. 16, the same ones shown in FIG. 15 are given the same symbols and detailed explanations are omitted.

【0105】

As shown in FIG. 16, the image reconstruction apparatus 90 of the fifth embodiment includes a detector 3, an A / D conversion unit 5, a reduction processing unit 91 as a reduction means, and a first reconstruction means. (1) Reconstruction processing unit 93, first image memory unit 95, enlargement processing unit 97, subtractor 99 as subtraction means, area extraction unit 101 as area extraction means, and second reconstruction means. It has a second reconstruction processing unit 103, a second image memory unit 105, an image composition unit 107 as a composition means, a composition image memory unit 21, a D / A conversion unit 23, and a display unit 25. The projected data is reduced and then reconstructed to extract a predetermined area.

【0106】

The reduction processing unit 91 reduces the number of projection data converted into digital signals by the A / D conversion unit 5 from, for example, 512 to 256. The first reconstruction processing unit 93 reconstructs 2 × 2 pixels as one pixel as shown in FIG. 9 based on the projection data reduced by the reduction processing unit 91. Here, 2 x 2 pixels are reconstructed as one pixel, but if this size is increased, the amount of calculation will be reduced and high-speed processing will be possible, but on the contrary, objects smaller than that size will be overlooked. There is a possibility that it will end up. Therefore, 2 × 2 pixels are suitable.

【0107】

The first image memory unit 95 temporarily holds the reconstructed data reconstructed by the first reconstructed processing unit 93. The enlargement processing unit 97 returns the value of one pixel of 2 × 2 pixels to the original 2 × 2 pixels by the first reconstruction processing unit 91. The subtractor 99 subtracts the reconstruction data converted into a digital signal by the first reconstruction processing unit 93 and the reconstruction data one frame before the reconstruction data stored in the first image memory unit 95. .. The region extraction unit 101 extracts, as a reconstruction region, a region equal to or larger than a threshold set by the operator using an input device (not shown) in advance from the data (absolute value) subtracted by the subtractor 99.

【0108】

The second reconstruction processing unit 103 uses the X-ray absorption coefficient distribution as reconstruction data based on the projection data obtained by converting the reconstruction region extracted by the region extraction unit 101 into a digital signal by the A / D conversion unit 5. Reconfigure. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body.

【0109】

The second image memory unit 105 stores the data reconstructed by the second reconstruction processing unit 103 and the data having a value λ without being reconstructed for each pixel. The image composition unit 107 checks the data of each pixel stored in the second image memory unit 105, and if the value is λ, the value of the same pixel supplied from the enlargement processing unit 97 is used as the value of that pixel. If the value is other than λ, the value stored in the second image memory unit 105 as it is is used as the pixel value.

【0110】

Next, the operation of the image reconstructing device 90 according to the fifth embodiment will be described. First, in an X-ray CT apparatus (not shown), X-rays are irradiated in a fan shape while rotating an X-ray beam source (not shown).

【0111】

When X-rays are irradiated, the detector 3 detects the irradiated X-rays and obtains projection data of 1200 patterns (for one rotation) of, for example, 0.3 degrees each. The projection data of the 1200 patterns is converted into a digital signal by the A / D conversion unit 5 and supplied to the reduction processing unit 91 and the second reconstruction processing unit 103.

【0112】

When the projection data converted into a digital signal is supplied, the reduction processing unit 91 reduces the number of the supplied projection data from, for example, 512 to 256. Then, the reduction processing unit 91 supplies the reduced projection data to the first reconstruction processing unit 93.

【0113】

When the reduced projection data is supplied, the first reconstruction processing unit 93 reconstructs the 2 × 2 pixels as one pixel as shown in FIG. 9 based on the reduced projection data. Then, the first reconstruction processing unit 93 temporarily holds the reconstruction data in the first image memory unit 95 and supplies it to the subtractor 99.

【0114】

When the reconstruction data is temporarily held in the first image memory 73, the enlargement processing unit 97 sets the value of 2 × 2 pixels as one pixel by the first reconstruction processing unit 93 to obtain the original 2 × 2. Return to pixel. At this time, the value of each pixel may be the value of one of the reconstructed pixels (all four pixels have the same value), or the reconstructed value is the value of the center position of the 2 × 2 pixels. It may be obtained in the same manner as the interpolation process shown in FIG. Then, the enlargement processing unit 97 supplies the enlarged data to the image synthesis unit 107.

【0115】

On the other hand, the subtractor 99 combines the reconstruction data converted into a digital signal by the first reconstruction processing unit 93 and the reconstruction data one frame before the reconstruction data stored in the first image memory unit 95. It is subtracted and supplied to the region extraction unit 101.

【0116】

When the subtracted data is supplied from the subtractor 99, the area extraction unit 101 uses an input device (not shown) in advance in the subtracted data (absolute value) to set a threshold value set by the operator. The above area is extracted as a reconstruction area. Then, the reconstruction area is instructed to the second reconstruction processing unit 103.

【0117】

When the reconstruction area is instructed by the area extraction unit 101, the second reconstruction processing unit 103 projects the reconstruction area extracted by the area extraction unit 101 and converted into a digital signal by the A / D conversion unit 5. Based on the data, the X-ray absorption coefficient distribution is reconstructed as reconstructed data. At this time, the pixel that is not reconstructed here is set to a value λ (for example, 9999) that cannot exist inside the human body. This value λ and the reconstruction data reconstructed by the second reconstruction processing unit 103 are stored in the second image memory unit 105 for each pixel.

【0118】

When the value λ and the reconstruction data are stored in the second image memory unit 105, the image synthesis unit 107 checks the data of each pixel stored in the second image memory unit 105, and if the value is λ, the image synthesis unit 107 checks the data of each pixel. The value of the same pixel supplied from the enlargement processing unit 97 is used as the value of that pixel, and if the value is other than the value λ, the value stored in the second image memory unit 105 as it is is used as the value of that pixel. As a result, the data supplied from the enlargement processing unit 97 and the data stored in the second image memory unit 105 are combined. The synthesized data is stored in the composite image memory unit 21.

【0119】

After that, the data synthesized by the image synthesizing unit 107 is displayed on the display of the display unit 25 by operating in the same manner as the image reconstructing device 70 of the fourth embodiment.

【0120】

As described above, in the image reconstruction apparatus 90 of the fifth embodiment, a predetermined region is extracted from the data obtained by subtracting the latest reconstruction data and the reconstruction data one frame before, and the predetermined region is obtained. All pixels are reconstructed based on the projection data that is not reduced, and 2 × 2 pixels are reconstructed as one pixel based on the reduced projection data except for the area. Therefore, the image quality of the area should be deteriorated. Therefore, the time required for the reconstruction process can be shortened. In particular, in the image reconstruction apparatus 90 of the fifth embodiment, a predetermined region is extracted from the data obtained by subtracting the latest reconstruction data and the reconstruction data one frame before, so that an arbitrary fault is continuously scanned. However, by reconstructing the cross section at high speed, it is highly effective in tracking the tip of the catheter and observing changes in the inflow and outflow of the contrast medium.

【0121】

Next, a sixth embodiment of the image reconstruction apparatus according to the present invention will be described with reference to FIG. In FIG. 17, the same ones shown in FIG. 15 are given the same symbols and detailed explanations are omitted.

【0122】

As shown in FIG. 17, the image reconstruction apparatus 110 of the sixth embodiment includes a detector 3, an A / D conversion unit 5, a first reconstruction processing unit 71 as a first reconstruction means, and a first. An image memory unit 111, an interpolation processing unit 75, a subtractor 77 as a subtraction means, an area extraction unit 79 as an area extraction means, a second reconstruction processing unit 81 as a second reconstruction means, and a second (Ii) It has an image memory unit 83, an image composition unit 85 as a composition means, a composition image memory unit 21, a D / A conversion unit 23, and a display unit 25.

【0123】

As shown in FIG. 17, the first image memory unit 111 is composed of four memories 111a to 111d, and stores each 2 × 2 pixels according to the pixel position. For example, in FIG. 18, the reconstruction data of each pixel indicated by the number 1 is stored in 111a, the reconstruction data of each pixel indicated by the number 2 is stored in 111b, and the reconstruction data of each pixel indicated by the number 3 is stored. It is stored in 111c, and the reconstruction data of each pixel indicated by the number 4 is stored in 111d.

【0124】

The first reconstruction processing unit 71 of the image reconstruction device 110 of the sixth embodiment changes the pixels to be reconstructed for each frame. For example, as shown in FIG. 18, the pixel of the number 1 is reconstructed in the first frame, the pixel of the number 2 is reconstructed in the second frame, the pixel of the number 3 is reconstructed in the third frame, and the pixel of the number 3 is reconstructed in the fourth frame. Then, the pixel of the number 4 is reconstructed, and this is repeated thereafter. The order of reconstruction is not limited to this, and reconstruction may be performed in another order.

【0125】

Then, the subtractor 77 subtracts the previous reconstruction data at the same position as the reconstruction data supplied from the first reconstruction processing unit 71 and supplies the data to the region extraction unit 79. Here, the reconstruction data supplied from the first reconstruction processing unit 71 and the reconstruction data immediately before the same position are subtracted, but not limited to this, the pixel positions are slightly shifted. , The reconstruction data supplied from the first reconstruction processing unit 71 and the reconstruction data one frame before (when the pixel of the number 2 is reconstructed by the first reconstruction processing unit 71, each pixel of the number 1). (Reconstruction data of) and may be subtracted.

【0126】

Also, both the result of subtracting the data at the same position and the result of subtracting the reconstructed data one frame before are sent to the area extraction process. For example, if either result is within a certain value range, it is reconstructed. The extraction area may be determined by combining the two results, such as by extracting as an area.

【0127】

After that, it operates in the same manner as the image reconstructing device 70 of the fourth embodiment, and the data supplied from the first image memory unit 111 by the image synthesizing unit 85 and the data stored in the second image memory unit 83 are combined. Is displayed on the display of the display unit 25.

【0128】

As described above, in the image reconstruction device 110 of the sixth embodiment, since the pixels to be reconstructed by the first reconstruction processing unit 71 are changed for each frame, the image quality is deteriorated in the above area. Therefore, the time required for the reconstruction process can be shortened.

【0129】

Next, a seventh embodiment of the image reconstruction apparatus according to the present invention will be described with reference to FIG. In FIG. 19, the same ones shown in FIG. 15 are given the same symbols and detailed explanations are omitted.

【0130】

As shown in FIG. 19, the image reconstruction apparatus 120 of the seventh embodiment subtracts the detector 3, the A / D conversion unit 5, the first projection data memory unit 121, and the second projection data memory unit 123. A subtractor 125 as a means, an area extraction unit 127 as an area extraction means, a first reconstruction processing unit 129 as a first reconstruction means, and a second reconstruction processing unit as a second reconstruction means. 131, the second image memory unit 133, the reduction processing unit 135 as the reduction means, the third reconstruction processing unit 137, the enlargement processing unit 139, the first image memory unit 141, and the image composition as the composition means. It has a unit 85, a composite image memory unit 21, a D / A conversion unit 23, and a display unit 25.

【0131】

The first projection data memory unit 121 temporarily holds the projection data converted into a digital signal by the A / D conversion unit 5. The second projection data memory unit 121 temporarily holds the projection data one frame before the projection data stored in the first projection data memory unit 121. The subtractor 125 subtracts the projection data stored in the first projection data memory unit 121 and the projection data stored in the second projection data memory unit 123.

【0132】

In the data supplied by the subtractor 125, the region extraction unit 127 sets a region corresponding to a range of values set by the operator using an input device (not shown) in advance to a target region (for example, a bone). It is extracted as an area on the detector projected by the contrast-enhanced blood vessel, etc.), and the projection data of this extracted area is set to "1", and the other areas are set to "0".

【0133】

The first configuration processing unit 129 uses the binary projection data in the 1200 direction as shown in FIG. 12 to set the region reproduced by the back projection and the logical product processing as the reconstruction region, and finely reconstructs the region. Instructs the second reconstruction processing unit 131, and at the same time, instructs the third reconstruction processing unit 137 to perform reconstruction at a coarse pitch.

【0134】

The second reconstruction processing unit 131 reconstructs the X-ray absorption coefficient distribution based on the projection data temporarily held in the first projection data memory unit 121 for the reconstruction area instructed by the first configuration processing unit 129. Reconstruct as. The second image memory unit 133 stores the reconstruction data reconstructed by the second reconstruction processing unit 131. The reduction processing unit 135 reduces the number of projection data temporarily held in the first projection data memory unit 121 from, for example, 512 to 256. The third reconstruction processing unit 137 reconstructs the X-ray absorption coefficient distribution as reconstruction data based on the projection data reduced by the reduction processing unit 135.

【0135】

The enlargement processing unit 139 expands the data reconstructed by the third reconstruction processing unit 137, and expands, for example, the reconstructed data 256 × 256 pixels to 512 × 512 pixels. At this time, as for the value of each pixel, the reconstructed 1 pixel may be regarded as 2 × 2 pixels as it is, and the values of 2 × 2 pixels may be all the same value, or the reconstructed value of the 2 × 2 pixels may be used. The value of the center position may be obtained in the same manner as the interpolation process shown in FIG. The first image memory unit 141 stores 512 × 512 pixel data enlarged by the enlargement processing unit 139.

【0136】

Next, the operation of the image reconstructing device 120 according to the seventh embodiment will be described. First, in an X-ray CT apparatus (not shown), X-rays are irradiated in a fan shape while rotating an X-ray beam source (not shown).

【0137】

When X-rays are irradiated, the detector 3 detects the irradiated X-rays and obtains projection data of 1200 patterns (for one rotation) of, for example, 0.3 degrees each. The projection data of the 1200 patterns is converted into a digital signal by the A / D conversion unit 5 and supplied to the first projection data memory unit 121.

【0138】

When the projection data is supplied from the A / D conversion unit 5, the first projection data memory unit 121 causes the second projection data memory unit 123 to hold the projection data temporarily held at the present time, and the latest projection data is stored. It is temporarily held and supplied to the subtractor 125.

【0139】

When the projection data is supplied from the first projection data memory unit 121, the subtractor 125 temporarily holds the projection data supplied from the first projection data memory unit 121 and the projection data temporarily held in the second projection data memory unit 123. The data is subtracted and supplied to the area extraction unit 127.

【0140】

When the projection data subtracted from the subtractor 125 is supplied, the area extraction unit 127 is within the range of the values previously input by the input device (not shown) in the projection data subtracted by the subtractor 125. Is extracted as a region on the detector projected by the target site (for example, bone or contrasting blood vessel), and the projection data of this extracted region is set to "1" and the other projection data is set to "0". ..

【0141】

When the region extraction unit 127 determines the range in which the target portion exists, the first reconstruction processing unit 129 performs back projection and logical product processing using binary projection data in the 1200 directions as shown in FIG. The regenerated area is set as a reconstruction area, and the third reconstruction processing unit 137 is instructed to roughly reconstruct the area.

【0142】

When the reconstruction processing area 129 is instructed by the first reconstruction processing unit 129, the second reconstruction processing unit 131 is based on the projection data temporarily held in the first projection data memory unit 121 for the instructed reconstruction area. The X-ray absorption coefficient distribution is reconstructed as reconstructed data and stored in the second image memory unit 133.

【0143】

On the other hand, when the projection data is temporarily held in the first projection data memory unit 121, the reduction processing unit 135 reduces the number of projection data from, for example, 512 to 256 and supplies the projection data to the third reconstruction processing unit 137. ..

【0144】

When the reduced projection data is supplied, the third reconstruction processing unit 137 reconstructs the X-ray absorption coefficient distribution as reconstruction data based on the reduced projection data and sends it to the enlargement processing unit 139.

【0145】

The enlargement processing unit 139 expands the data reconstructed by the third reconstruction processing unit 137, and expands, for example, the reconstructed data 256 × 256 pixels to 512 × 512 pixels. At this time, as for the value of each pixel, the reconstructed 1 pixel may be regarded as 2 × 2 pixels as it is, and the values of 2 × 2 pixels may be all the same value, or the reconstructed value of the 2 × 2 pixels may be used. The value of the center position may be obtained in the same manner as the interpolation process shown in FIG.

【0146】

When the reconstruction data is stored in the first image memory unit 141 and the second image memory unit 133, the image synthesis unit 85 reconstructs the reconstruction data stored in the first image memory unit 141 and the second image memory unit 133. The data is combined and stored in the composite image memory 21.

【0147】

After that, the data synthesized by the image synthesizing unit 85 is displayed on the display of the display unit 25 by operating in the same manner as the image reconstructing device 70 of the fourth embodiment.

【0148】

In this way, the image reconstruction apparatus 120 of the seventh embodiment extracts a predetermined region from the data obtained by subtracting the latest projection data and the projection data one frame before, and does not reduce the predetermined region. Since it is reconstructed based on the projection data and the areas other than the above area are reconstructed based on the reduced projection data, the time required for the reconstruction process can be shortened for the above area without deteriorating the image quality. it can. In particular, in the image reconstruction apparatus 120 of the seventh embodiment, a predetermined region is extracted from the data obtained by subtracting the latest projection data and the projection data one frame before, so that an arbitrary tomographic image can be continuously scanned. By reconstructing the cross section at high speed, it is highly effective in tracking the tip of the catheter and observing changes in the inflow and outflow of the contrast medium.

【0149】

Although the type of the X-ray CT apparatus is not particularly described in the above-described embodiment, the present invention can be applied to any X-ray CT apparatus. In particular, the effect is high when the reconstruction process takes time, such as the helicopter scan CT and the cone beam CT.

【0150】

[Effect of the invention]

As described above, the image reconstruction apparatus according to claim 1 obtains the X-ray absorption coefficient distribution in the region of interest with a higher spatial resolution than in the regions other than the region of interest. Can shorten the time required for the reconstruction process without deteriorating the image quality.

【0151】

Further, since the image reconstructing apparatus according to claim 3 obtains the X-ray absorption coefficient in the region of interest with higher accuracy than in the other regions, the image quality is deteriorated in the region of interest. The time required for the reconstruction process can be shortened without any problem.

【0152】

Further, since the image reconstruction apparatus according to claim 7 reconstructs only the target area for all pixels, the time required for the reconstruction process is shortened without deteriorating the image quality of the target area. be able to.

【0153】

Further, the image reconstructing apparatus according to claim 8 extracts the target area after reducing the projection data, reconstructs the target area based on the entire projection data, and reduces the area other than the target area. Since the reconstruction is performed based on the projected projection data, the time required for the reconstruction processing can be shortened for the target area without deteriorating the image quality.

【0154】

Further, the image reconstructing apparatus according to claim 9 extracts a target area based on the data obtained by subtracting the latest reconstructed data and the data reconstructed before the latest data. However, since only this target area is reconstructed for all pixels, it is possible to shorten the time required for the reconstruction process without deteriorating the image quality of the target area.

【0155】

Further, the image reconstructing apparatus according to claim 10 is obtained by subtracting the latest reconstructed data and the reconstructed data before the latest data based on the reduced projection data. A target area is extracted based on the data, the target area is reconstructed based on a predetermined number of projection data, and the area other than the target area is reconstructed based on the reduced projection data. Therefore, it is possible to shorten the time required for the reconstruction process for the target area without deteriorating the image quality.

【0156】

Further, the image reconstruction apparatus according to claim 11 extracts a target area based on the projection data, and reconstructs the target area based on the projection data. The time required for the reconstruction process can be shortened without degrading the image quality.

【0157】

Further, the image reconstructing apparatus according to claim 12 extracts a target area based on the data obtained by subtracting the latest projection data and the projection data obtained before the latest projection data. The target area is reconstructed based on a predetermined number of projection data, and the area other than the target area is reconstructed based on the reduced projection data. The time required for the reconstruction process can be shortened without degrading the image quality.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram which showed the 1st Embodiment of the image reconstruction apparatus which concerns on this invention.

[Figure 2]

It is a figure which shows the arrangement of the pixel every other pixel.

[Fig. 3]

It is a figure which shows another example of the arrangement of the pixel every other pixel.

[Fig. 4]

It is a figure which shows the range to be extracted as a reconstruction area.

[Fig. 5]

It is a figure which shows another example of the range to be extracted as a reconstruction area.

[Fig. 6]

It is a figure which shows the center position of a 2 × 2 pixel.

[Fig. 7]

It is a figure for demonstrating two-dimensional linear interpolation.

[Fig. 8]

It is a block diagram which shows the structure of the 2nd Embodiment of the image reconstruction apparatus which concerns on this invention.

[Fig. 9]

It is a figure for demonstrating the case where 2 × 2 pixels are regarded as one pixel.

[Fig. 10]

It is a block diagram which shows the structure of the 3rd Embodiment of the image reconstruction apparatus which concerns on this invention.

[Fig. 11]

It is a figure which shows the structure of the region extraction part in the case of injecting a contrast medium into an extraction target.

[Fig. 12]

It is a figure which shows the reconstruction area of the projection data.

[Fig. 13]

It is a figure which shows the means in the case of expanding the area by a predetermined amount before performing reconstruction by a 2nd reconstruction processing part.

[Fig. 14]

It is a figure which showed the convolution kernel used when expanding the area by a predetermined amount.

[Fig. 15]

It is a block diagram which shows the structure of 4th Embodiment of the image reconstruction apparatus which concerns on this invention.

[Fig. 16]

It is a block diagram which shows the structure of 5th Embodiment of the image reconstruction apparatus which concerns on this invention.

[Fig. 17]

It is a block diagram which shows the structure of the 6th Embodiment of the image reconstruction apparatus which concerns on this invention.

[Fig. 18]

It is a figure for demonstrating the pixel stored in each memory of the 1st image memory part, and the order of being reconstructed by a 1st reconstruction processing part.

[Fig. 19]

It is a block diagram which shows the structure of 7th Embodiment of the image reconstruction apparatus which concerns on this invention.

[Fig. 20]

It is a figure which showed schematicly the helical scan CT.

[Fig. 21]

It is the figure which showed the cone beam CT schematicly.

[Explanation of symbols]

1,30,40,70,90,110,120 Image reconstruction device 3 detector 5 A / D converter 7,33,43,71,93,127 First reconstruction processing unit 9,75 Interpolation processing unit 11,37,73,95,111,141 First image memory section 13,79,101,127 Area extraction section 15,45,81,103,131 Second reconstruction processing unit 17,83,105,133 Second image memory section 19,85,107 Image composition section 21 Composite image memory section 23 D / A converter 25 Display 31,91,135 Reduction processing unit 35,97,139 Enlargement processing unit 47 Image memory section 77,99,125 subtractor 121 First projection data memory section 123 Second projection data memory section 137 Third reconstruction processing unit