JPH0824253A - X-ray ct apparatus - Google Patents

Abstract

PURPOSE:To obtain rapidly a number of sheets of CT images wherein the time for reconstitution of a sheet of an image is remarkably shortened and the time resolution is high and which are time series-like series. CONSTITUTION:A sheet of a CT image is obtd. by performing back projection of projection data of each of rotating angle ranges A, B, C and D of an X-ray tube 1 and an X-ray detector 2 after performing each initialization to each of memories 6-9 on every plane for back projection by means of a back projector 4 under a selective control of a selector 5 and adding the contents of these memories on every corresponding pixel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, X-rays that have passed through an object
The image is reconstructed by backprojecting the projection data by lines. To obtain a CT image for one slice plane, projection data for 360 ° or 180 ° for that slice plane is required. As a scan method for collecting projection data from each angle direction in these necessary angle ranges, a rotation / rotation type in which an X-ray tube and a fan-shaped X-ray detector both rotate around the subject,
Rotation / stationary type, in which the X-ray detector is fixed and only the X-ray tube rotates, with the X-ray detector arranged all around the circumference.
There is known a stationary / stationary type in which the X-ray detector is also fixed and the X-ray focus is rotated around the subject, and the X-ray detector is fixed around the entire circumference. In these, in order to obtain projection data from each angle direction, at least only the X-ray focal point needs to be rotated around the subject.

In these, at least only the X-ray focus is continuously rotated, that is, only the X-ray focus is continuously rotated in the stationary / stationary type, and the entire X-ray tube is continuously rotated in the rotation / stationary type. To rotate the X-ray focal point continuously, and in the rotation / rotation type to continuously rotate the entire X-ray tube to continuously rotate the X-ray focal point and the X-ray detector to continuously rotate the image of one slice plane. If the projection data in the angle range necessary for reconstruction is sequentially obtained in time series, it is possible to obtain a large number of images displaying a moving image that changes in time series for one slice plane. As a result, it becomes possible to display a moving image showing the movement of the contrast medium injected into the blood vessel, for example.

In this case, conventionally, one image is reconstructed by sequentially backprojecting projection data in an angle range necessary for reconstructing one image for each angle into a memory for backprojection. After construction, this memory is initialized to prepare for the next back projection.

[0005]

However, if the memory for back projection is initialized every time one image is reconstructed as in the conventional case, the processing time required to obtain one CT image is increased. There is a problem that it takes a long time.
Therefore, even if the speed of continuous rotation for collecting projection data in each angle direction is increased and the time resolution is increased, it is not possible to reconstruct a large number of CT images following it, and real-time You will not be able to display moving images. Therefore, when the continuous rotation speed is increased and the time resolution is increased in this way, projection data is temporarily stored in a memory, a magnetic disk, etc., and read out later to reconstruct an image. However, even in that case, since the time required for one CT image is long, it takes a lot of time to obtain a large number of CT images.

In view of the above, the present invention, when at least the X-ray focus is continuously rotated to continuously collect projection data in each angle direction over 360 °,
An object of the present invention is to provide an improved X-ray CT apparatus capable of shortening the time required to reconstruct a CT image for each sheet and improving the time resolution of a large number of reconstructed CT images. And

[0007]

In order to achieve the above object, in the X-ray CT apparatus according to the present invention, at least the X-ray focal point is continuously rotated to continuously project projection data in each angular direction over 360 ° or more. A means for collecting, a memory means for back projection of a plurality of planes, an angle range of projection data necessary for reconstructing one image is divided into a plurality, and the projection data of the divided angle range is A feature is that each of the memory means of a plurality of planes is provided with a means for selectively performing back projection and an adding means for adding the same pixels of the memory means of each plane.

[0008]

For example, projection data in the 360 ° angle range is used to reconstruct one image, and the 360 ° angle range is divided into four equal parts. Then, the memory means has four planes. Since the projection data in each angle direction is continuously collected over 360 ° or more, the data of 0 ° to 90 ° for each rotation is on the first plane, the data of 90 ° to 180 ° is on the second plane, and the data of 90 ° to 180 ° is 180 °. The data from ゜ to 270 ゜ is 2 on the 3rd plane.
Data of 70 ° to 360 ° are back-projected to the fourth plane. At the end of one rotation (360 °), if the same pixels of the first to fourth planes are added, one image reconstructed by the back projection data of 0 ° to 360 ° can be obtained. . At the end of 1 (1/4) rotation, the same pixels in the first to fourth planes are added to each other to obtain a single image reconstructed by the back projection data of 90 ° to 450 °. Therefore, a large number of images having a time resolution for each quarter rotation are sequentially obtained. Further, since initialization of each plane at the time of rewriting is performed only for that plane, rewriting does not take time, and the other three planes can be used as they are without being rewritten. Therefore, the time required to obtain one image for each quarter rotation is extremely short. Therefore, it is possible to reconstruct a large number of images in real time.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied to a rotation / rotation type X-ray CT apparatus. In FIG. 1, X
The X-ray tube 1 and the X-ray detector 2 are arranged so as to face each other, and the subject 21 can be arranged between them.
The X-ray detector 2 and the X-ray detector 2 are integrally rotated by a rotating mechanism (not shown) around the subject 21.

The X-rays transmitted through the subject 21 are detected by the X-ray detector 2.
And a signal representing the transmitted X-ray intensity is obtained. As a result, data indicating the X-ray absorption in the subject 21 is obtained. The X-ray detector 2 is formed in a fan shape, and a large number of detection elements are arranged in an arc direction. So X
The data obtained from the X-ray detector 2 is profile data indicating the X-ray absorption by the X-rays emitted from the X-ray tube 1 in a fan shape.

This profile data is sent to the projection data creating apparatus 3 and converted into projection data for back projection. When the X-ray tube 1 and the X-ray detector 2 rotate from the reference position (angle of 0 °), projection data for each angle is sequentially obtained, and this is designated by the selector 5 by the back projector 4. Memory 6, 7, 8,
Back projection to any of the nine. The four memories 6, 7, 8 and 9 are memories for back projection and each are one plane. That is, each of the four memories 6, 7, 8 and 9 has an address of 256 × 256 corresponding to the pixel if the reconstructed image has a pixel represented by a 256 × 256 matrix. There is.

Here, when the X-ray tube 1 and the X-ray detector 2 rotate continuously, the angle range of 0 ° to 90 ° is range A and the angle range of 90 ° to 180 ° is range as shown in the figure. B,
The angle range of 180 ° to 270 ° is range C, 270 ° to 3
The angle range of 60 ° is referred to as range D. As shown in FIG. 2, the projection data accompanying the continuous rotation includes the ranges A, B, C, D for the first rotation and the ranges A, B, C, D for the second rotation.
…, And so on. When the projection data of the range A is obtained, the selector 5 designates the memory 6 so that the back projection of the projection data of the range A is performed in the memory 6, and the memory is selected in the ranges B, C, and D. 7, 8 and 9 are designated respectively, and the back projection of the projection data of each of the ranges B, C and D is performed on them.

When the first rotation is completed, the projection data of 90 ° is back-projected to each of the memories 6, 7, 8 and 9, and the total projection amount is 36.
Since the back projection of 0 ° projection data is performed, if the corresponding pixels of 6, 7, 8, and 9 are added by the adder 10, 0 is obtained.
This means that the first image # 1 is obtained by the projection data of 360 ° for 360 ° to 360 ° (see FIG. 2). This is a process called back projection
This is because the projection data is added to the pixels on the projection line.

Next, the first rotation is completed and the subsequent 1
At the / 4th rotation, after the memory 6 is initialized, the projection data in the range A is backprojected to the memory 6. 1 counting from the beginning
When the (1/4) rotation is completed, if the same pixels in the memories 6, 7, 8, and 9 are added by the adder 10,
As shown in FIG. 2, the second image # 2 is obtained by the projection data for 360 ° of 90 ° to 450 °.

In this case, the initialization of the back-projection memory and the rewriting to the back-projection memory may be performed only for the memory 6 corresponding to 1/4 of the entire memory for 360 °, and for the other 3/4. No operation is performed on the memories 7, 8 and 9, and the contents stored up to that time may be simply read out and added by the adder 10. In other words, since the back projection operation only needs to correspond to ¼ of the whole, the time required to obtain the second image # 2 after obtaining the first image # 1 is extremely short.

A third image # 3 is obtained when the next ¼ rotation is completed, and a fourth image is obtained when the next ¼ rotation is completed. Then, an image based on projection data for 360 ° is obtained one after another. These images are sequentially sent to the display device 12 via the image memory 11 and displayed.
Therefore, on the display screen, as the imaging system of the X-ray tube 1 and the X-ray detector 2 is continuously rotated, a large number of time-series images are sequentially displayed in real time every ¼ rotation of the rotation. It will be.

In this example, the adder 10 has memories 6, 7,
Although the same pixels of 8 and 9 are added to each other, the memories 6, 7, 8 and 9 can be selectively added by the adder 10. For example, if the same pixels in only the memories (that is, two memories) for which the back projection for the preceding 1/4 rotation and the preceding 1/4 rotation from the current time are performed are performed, FIG. As shown, when the half rotation is completed from the beginning, the addition of the memories 6 and 7 is performed, and when the next quarter rotation (3/4 rotation from the beginning) is completed, the memories 7 and 8 are completed.
Is added, and the next 1/4 rotation (from the beginning 4
/ 4 rotation) is completed, the memories 8 and 9 are added, and when the next ¼ rotation (5/4 rotation from the beginning) is completed, the memories 9 and 6 are added. , Images # 1, # 2, # by back projection of projection data for 180 ° respectively
.. can be sequentially obtained for every 1/4 rotation.

In this case, since it is sufficient for the memory to have a back projection for 180 °, only two of the four memories 6, 7, 8 and 9 are required. If four memories 6, 7, 8 and 9 are provided, a CT image with 360 ° projection data as in the first example above and a CT image with 180 ° projection data as in this example It is also possible to get both with the statue.

It should be noted that the back projection memory is an independent memory 6 of one plane each.
Although 7, 8, and 9 are used, it is needless to say that the area of each plane can be provided in one memory by managing the address.

Further, if the number of planes of the back projection memory is further increased to, for example, 8 planes, back projection of projection data for 1/8 rotation (45 °) can be performed on each of the planes. It is possible to sequentially obtain images of projection data for 360 ° or 180 ° for every / 8 rotation. In this way, by increasing the number of planes of the back projection memory, it is possible to arbitrarily increase the time resolution of a large number of images obtained in time series. Moreover, even with such a configuration that enhances the temporal resolution, by controlling the addition timing and the selection of the memory to be added by the adder 10, one rotation is performed as in the normal CT image reconstruction method. It is also possible to lower the time resolution by, for example, sequentially obtaining one image for each rotation or one image for every 1/2 rotation. Further, although the present invention is applied to the rotation / rotation type X-ray CT apparatus in the above-mentioned embodiment, it can be applied to other rotation / stationary type or stationery / stationary type X-ray CT apparatuses. It goes without saying that the present invention can be applied.

[0021]

As described in the above embodiments, according to the X-ray CT apparatus of the present invention, the time for reconstructing one image is greatly shortened and a large number of time-sequential CT images can be processed at high speed. In addition to being able to obtain the CT images, it is possible to arbitrarily enhance the time resolution of the CT images.

[Brief description of drawings]

FIG. 1 is a block diagram of an X-ray CT apparatus according to an embodiment of the present invention.

FIG. 2 is a view for explaining an operation example in the same embodiment.

FIG. 3 is a diagram for explaining another operation example in the embodiment.

[Explanation of symbols]

1 X-ray tube 2 X-ray detector 3 Projection data creation device 4 Back projector 5 Selector 6, 7, 8, 9 Memory 10 Adder 11 Image memory 12 Display device 21 Subject

Claims (1)

[Claims] 1. A means for continuously rotating at least an X-ray focal point to continuously collect projection data in each angular direction over 360 °, a memory means for back projection of a plurality of planes, and a single image reconstructed. A means for dividing the angle range of the projection data necessary for constructing into a plurality and selectively back-projecting the projection data of the divided angle range to each of the memory means for the plurality of planes, and a memory means for each plane. X-ray CT apparatus, comprising: an addition unit that adds the same pixels of