JP3419116B2 - X-ray CT system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus. 2. Description of the Related Art In an X-ray CT apparatus, an X-ray
An image is reconstructed by back-projecting the line projection data. Since the X-ray data is actually obtained as analog data at first, it is converted into digital data and then obtained in the pre-processing such as offset processing, logarithmic conversion, calibration, and convolution, and in the direction of a sector. If the data is parallel, parallel data is collected and preprocessed as parallel data, and then subjected to projection. [0003] If projection parameters are set so as to limit the projection area to a part, and backprojection is performed, an image of only that area is reconstructed. By backprojecting the same projection data by designating a plurality of regions, the image of each region can be reconstructed. In this case, conventionally, projection data is created by performing the above-described preprocessing for each back-projection of each area. [0004] However, if the process is started again from the preprocessing stage, it takes time to obtain a reconstructed image of each area. Therefore, if a memory for storing the once created projection data is prepared, the same projection data can be used immediately and the reconstruction time can be saved.
However, also in this case, it is necessary to repeat the operation of reading data from the memory for projection of each area and writing the data to the projection memory for each projection of each area, so that reading from the memory and Only the time required for writing to the projection memory is required for each image reconstruction of each area. SUMMARY OF THE INVENTION In view of the above, the present invention provides a method for simultaneously projecting the same projection data once created by changing the parameters and projecting a plurality of times to reconstruct a plurality of images. X-ray C, which has been improved so that the time required for the entire reconstruction of a plurality of images can be significantly reduced
It is intended to provide a T device. [0006] In order to achieve the above object, an X-ray CT apparatus according to the present invention comprises a means for collecting X-ray transmission data on a subject from various directions,
Means for creating data for back projection from the collected X-ray transmission data, input means for inputting at least two arbitrary areas, and at least two types of back projection parameters for specifying each of the areas. Creating means, at least two back-projection storage means, and means for writing the back-projection data in parallel to each of the storage means in accordance with each of the above-described parameters to perform back-projection. It is characteristic. The back projection using the same back projection data according to different parameters can be performed in parallel in two or more storage means. Therefore, when two or more arbitrary regions are input, at least two types of back-projection parameters for designating each of the regions are created and reconstructed according to different parameters corresponding to each of the regions. Two or more images to be obtained will be obtained concurrently. It is possible to greatly reduce the entire reconstruction time of the images of the two or more regions. A preferred embodiment of the present invention will be described below 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 to face each other, and the subject 21 can be arranged therebetween.
The X-ray detector 2 is integrally rotated around the subject 21 by a rotation mechanism (not shown). The X-ray transmitted through the subject 21 is transmitted to the X-ray detector 2
And a signal representing the transmitted X-ray intensity is obtained, and this signal is converted into digital data by an A / D converter (not shown). 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 number of detection elements are arranged in an arc direction. Therefore, the data obtained from the X-ray detector 2 is X
This is profile data indicating X-ray absorption due to X-rays emitted in a fan shape from the tube 1. [0010] The profile data is sent to the projection data creation device 3 and converted into projection data for back projection. That is, the profile data input to the projection data generating device 3 undergoes pre-processing such as offset processing, logarithmic conversion, calibration, and convolution, and further collects parallel data from data obtained in the fan-shaped direction. Processing such as parallel data is performed. For example, assuming that profile data (equiangular data) of 400 views is acquired for one slice by one rotation of the X-ray tube 1 and the X-ray detector 2, parallel data in 400 directions is created from this, and this is back projection. Data. [0011] The back projection data thus obtained is sent to the back projector 4. The back projector 4 is controlled by the control device 13 to back-project the above data in the memories 7 and 8. That is, the operation of sequentially writing the above data in each pixel area of the memories 7 and 8 through which the projection line passes is repeated for each back projection data, that is, for each projection direction (view). Images are reconstructed on the memories 7 and 8. Here, assuming that two arbitrary regions to be reconstructed are input to the control device 13 by an input device or the like (not shown), the parameter creating device 5 specifies each region accordingly. Create parameters for
This is sent to the back projector 4. When the profile data of the first view is collected and the parameter creation device 5 creates the profile data and sends the profile data to the back projector 4, the parameter creation device 5 creates the back projection parameters of the first view in one area. To the back projector 4 to instruct a back projection operation according to the parameter. At this time, the selector 6 selects one of the memories 7 under the control of the control device 13, and the above-described back projection is performed in the selected memory 7. Next, the parameter creation device 5 sends back projection parameters of the first view of the other area to the back projector 4, and performs back projection on the memory 8 selected by the selector 6 at this time according to the parameters. Such a simultaneous back projection operation to the memories 7 and 8 is repeated every time 400 views of profile data are collected. Thereby, when the X-ray tube 1 and the detector 2 make one rotation and the collection of profile data for one screen is completed, images of two regions with different parameters are simultaneously reconstructed. Next, the reconstructed images formed in the memories 7 and 8 are read out one by one by the selector 9 and the reference CT values (water = 0,
(Air = -1000). The image data of the two reconstructed images after the conversion are sequentially transferred to the image memory 11 and simultaneously displayed on the display device 12, for example, in each of a plurality of sections of one screen. The selector 9 and the CT value converter 10 are connected to a controller 13
Is controlled by That is, as described above, the control device 13 sets the projection data creation device 3
In addition to controlling the parameter generation device 5 and the back projector 4, the CT value conversion operation after the back projection of all the views is completed is controlled to display images in two regions. In this embodiment, two memories 7 and 8 are used to reconstruct two images. However, if a single memory has a large capacity, two memories are used by address management. It can be used by dividing it into image reconstruction sections. If not only the two memories 7 and 8 (or two memory sections) but also (the capacity of) the memory is increased, it is possible to reconstruct more and more images simultaneously and in parallel. Further, in the above embodiment, the present invention is applied to a rotation / rotation type X-ray CT apparatus. However, the present invention is 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. As described above, according to the X-ray CT apparatus of the present invention, it is possible to simultaneously and concurrently reconstruct images of a plurality of regions from the same acquired data. Therefore, it is possible to greatly reduce the time required for reconstructing the entire image of the plurality of regions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an X-ray CT apparatus according to one embodiment of the present invention. [Description of Signs] 1 X-ray tube 2 X-ray detector 3 Projection data creation device 4 Back projector 5 Parameter creation device 6, 9 Selector 7, 8 Back projection memory 10 CT value conversion device 11 Image memory 12 Display device 13 Control Apparatus 21 subject

Claims (1)

(57) [Claims] [Claim 1] A means for collecting X-ray transmission data of a subject from various directions, a means for creating data for back projection from the collected X-ray transmission data,
Input means for inputting at least two arbitrary areas, means for creating at least two types of back projection parameters for specifying each of the areas,
X comprising: at least two storage means for back projection; and means for performing back projection by writing the back projection data in parallel to each storage means in accordance with each of the parameters. Line CT device.