JPH0471536B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to CT (CT) using the Filtered Back Projection method, which is used for image reconstruction in X-ray CT equipment, emission CT equipment, NMR-CT equipment, etc. This invention relates to improvements in image reconstruction devices (computer tomography).

(b) Prior art Traditionally, as a CT image reconstruction method, projection data is filtered and then back-projected.
The Filtered Back Projection method is generally used, but since the reconstruction area is fixed to a large circle or ellipse so that it can sufficiently cover the subject, unnecessary parts other than the subject are back projected and the reconstruction takes time. There was a drawback that it took a while.

In particular, when a large number of slice planes are scanned continuously to obtain images of a large number of slice planes, additional wasted time is multiplied by the number of slice planes. This was a problem as it caused a decrease in processing capacity.

(c) Purpose This invention aims to shorten image reconstruction time.
The purpose is to provide a CT image reconstruction device.

(D) Configuration In the CT image reconstruction device according to the present invention, projection data collected for each of a plurality of adjacent slice planes of an object is filtered, and then projection data for each filtered slice is reconstructed. When sequentially back-projecting onto memory to obtain reconstructed images for each slice plane, we focused on the fact that the external shape does not change much between adjacent slice planes of the same subject. Delineate its outline from the reconstructed image,
Based on the contour of the reconstructed image for a certain slice plane obtained earlier, a back projection area on the reconstruction memory for the next adjacent slice plane is determined in advance, and only within this area , is characterized in that the projection data for the slice plane is back-projected.

(E) Embodiment FIG. 1 shows an embodiment in which the present invention is applied to an X-ray CT apparatus.
A fan beam of X-rays is irradiated toward the object 2 from the object 2, and the X-rays are detected by the X-ray detector 3, which has a large number of small detection elements arranged. projection data is obtained. The X-ray tube 1 and X-ray detector 3 rotate around the subject 2, and projection data from multiple directions can be obtained. Such projection data is collected by a data collection device 4 that includes a preamplifier, an A/D converter, a memory, and the like. The projection data thus collected is first subjected to convolution integration by the convolver 5. This convolution is a type of filtering. The projection data thus superimposed and integrated is sent to the back projection device 6 and back projected onto the reconstruction memory 61. At this time, this backprojection is performed only within the backprojection area 92 defined by the mask memory 62. The image reconstructed on the memory 61 by back projection in this manner is sent via the CPU 7 to a display device 8 such as a CRT device and displayed.

Here, a case will be described in which adjacent slice planes 11 and 12 of the subject 2 are successively scanned as shown in FIG. 2, data is obtained, and images of these slice planes 11 and 12 are reconstructed. FIG. 3 is a schematic diagram showing the memory area in the reconstruction memory 61. Since the outline of the subject 2 is unknown in the first scan, the mask memory 62 is
A back projection area 91 of the largest circle is defined. Therefore, the projection data obtained from the first scan is
The image 21 of the slice plane 11 is reconstructed by being projected into this back projection area 91 on the reconstruction memory 61. When the image reconstruction is completed in this manner, the CPU 7 draws a contour from the obtained image 21, a back projection area 92 is determined from this contour with a little margin, and this area 21 is set in the mask memory 62. In the next second scan, projection data regarding the slice plane 12 is collected, and this data is back-projected only to the back-projection area 92 of the reconstruction memory 61. In other words, slice plane 1 of subject 2
Since the back projection is performed only on the area 92 that has approximately the same shape as 2, there is no need to perform unnecessary back projection, and a significant time reduction can be achieved. Here, the outline of the human body is determined even if the slice plane is shifted in the body axis direction.
If the shifted distance is small, it will not change so rapidly, and when trying to obtain images by continuously scanning a large number of adjacent slice planes 11, 12,... Focusing on the fact that the image of the slice plane should not be much different in size from the image of the adjacent slice plane obtained in the previous scan, the reconstruction area of the second image is as shown in Figure 3. It is not necessary to set the size to the circle 91 shown in FIG. 2, and it is sufficient to set the size to a region 92 that is slightly larger than the outline of the previous image 21. By performing backprojection by limiting the backprojection area in this way, for example, if the maximum image reconstruction area in real space is a circular area with a diameter of 256 mm,
The memory area 9 of the reconstruction memory 61 is determined so that a circular back projection area 91 corresponding to this can be obtained, but the average size of the actual human head is
Since it is approximately 180 mm, the back projection area for head photography is approximately halved, and the back projection time can be reduced by approximately 50%.

In addition, in the above case, when successively scanning a large number of adjacent slice planes and trying to obtain those images one after another, the CPU 7 draws the outline of the previous image.
Based on this contour, the CPU 7 is configured to automatically set the reconstruction area of the next image for adjacent slices, but the automatically set back projection area is limited to only circular, elliptical, or similar shapes. Instead, the ring-shaped band is used as the back projection area (this is an industrial X
(This is effective for observing the cross-sectional state of pipes using a line CT device.) Any shape can be set.

(F) Effect According to the CT image reconstruction device of the present invention, when obtaining an image by sequentially back projecting data for each of a plurality of adjacent slice planes of a subject, the outline of the previously obtained image is drawn. As a result, the back projection area for the next adjacent slice plane is automatically set, and the data for the adjacent slice plane is back projected only in that set area, which reduces image re-projection. The time required for configuration processing can be reduced. In other words, in view of the empirical fact that the outline of the same subject does not change significantly between multiple adjacent slice planes, this can be used to find the outline of an image obtained from a certain slice plane. , the outline of the next adjacent slice plane is predicted based on the contour, and the back projection area for the adjacent slice plane is determined based on the prediction. As a result, the back projection area can be automatically limited without any practical problems, and the time required for image reconstruction processing can be shortened. With current general CT image reconstruction equipment,
Since the image reconstruction time is mainly determined by the back projection time, the time reduction effect is significant even when viewed as the overall processing time during which images are obtained.
In particular, when images of multiple slice planes are sequentially obtained by successive scans of adjacent multiple slice planes, the processing time reduction effect is extremely significant, and a marked improvement in patient throughput can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining a slice plane during continuous scanning, and FIG. 3 is a schematic diagram for explaining a memory area in a reconstruction memory. be. 1... X-ray tube, 2... Subject, 3... X-ray detector, 4... Data acquisition device, 5... Convolver,
6...Back projection device, 7...CPU, 8...Display device, 61...Reconstruction memory, 62...Mask memory.

Claims (1)

[Claims] 1. A means for filtering projection data collected for each of a plurality of adjacent slice planes of a subject, and a means for sequentially back-projecting the projection data for each filtered slice onto a reconstruction memory to obtain information for each slice plane. a back projection means for sequentially obtaining reconstructed images; a means for delineating the contour from the reconstructed image obtained by back projection; and an adjacent slice plane to be performed next based on the contour of the previously obtained reconstructed image. , mask means for predetermining a back projection area on the reconstruction memory and performing back projection of projection data for the slice plane only within this area.
Image reconstruction device.