DATA PROCESSOR FOR IMAGE RECONSTRUCTION

Abstract: A single inverse projection unit (BPU) is connected to a number of high speed arithmetic units (FPU) which operate in parallel. The BPU has a number of inverse projection execution units provided corresp. to the number of FPU's and a single pixel memory onto which will be inversely projected the sum of output data of these execution units.

Description: (Technical Field) The present invention relates to an image reconstruction data processing unit for a X-ray tomographic apparatus and the like, which is adapted to process data for reconstructing a tomographic image of an object on the basis of data on the object from various directions. (Background Technology) As is well known, the X-ray tomographic apparatus is used for forming a tomographic image of an object in such a manner that a number of projection data are collected by applying X-rays at various angles and the collected data are processed for image reconstruction. The data processing by such X-ray tomographic apparatus basically comprises the steps of preprocessing, reconstruction and postprocessing. In the preprocessing step, logarithmic conversions, predetermined corrections including X-ray intensity correction, beam quality hardening correction, scattering correction etc., and filtering are performed and in the reconstruction step,the operation of back projections is performed by using the preprocessed projection data thereby forming image data indicative of a tomographic image of an object. The image data thus obtained are corrected by the postprocessing step to a form suitable for them to be stored in a recording medium. As an appratus for performing the above data processing steps at high speeds, there is employed a data processing unit comprising a combination of a fast processing unit (hereinafter referred to as "FPU") and one or a plurality of back projection units (hereinafter referred to as "BPU"). The FPU is provided with a main memory for storing projection data and an operation part for preprocessing the projection data, and the BPU is provided with a computing element and an image memory having addresses each corresponding to each of pixels of a reconstruction image. To increase the image reconstruction speed, it is considered to operate a plurality of such data processing units in parallel relationships with one another but in that case, the following problems arise. That is, the data on the reconstruction image must be a total sum of back projection data obtained by each BPU and further, the reconstruction image data must be postprocessed by a desired FPU so that buses for reception and transmission of the back projection data between the BPUs and between the FPUs and BPUs are required. Consequently, the structure of the data processing unit becomes complicated. Prior art document EP-A-0 182 186 discloses a back projection image reconstruction apparatus wherein image reconstruction time in a CT scanner is enhanced by using a pipeline structure and interpolation techniques to identify each detector for use in back projection of radiation absorption measurements through each pixel in each view of the scanner. Detectors are identified by calculation for a pixel in every third view with detectors for intermediate views obtained by interpolation of the calculated detectors. Similarly, detectors are identified for every other pixel in a view with the detector for the intermediate pixel identified by interpolation. Further, prior art document EP-A-0 052 342 discloses a data processing device applied to a computed tomography system which examines a living body utilizing radiation of X-rays. The X-rays which have penetrated the living body are converted into electric signals in a detecting section. The electric signals are acquired and converted from an analog form into a digital form in a data acquisition section, and then supplied to a matrix data-generating section included in the data processing device. By this matrix data-generation section are generated matrix data which correspond to a plurality of projection data. These matrix data are supplied to a partial sum-producing section. The partial sums respectively corresponding to groups of the matrix data are calculated in this partial sum-producing section and then supplied to an accumulation section. In this accumulation section, the final value corresponding to the total sum of the matrix data is calculated, whereby the calculation for image reconstruction is performed. (Disclosure of the Invention) The object of the present invention is to provide an image reconstruction data processing unit which though simple in structure, can perform a fast data processing by parallel operations of a plurality of FPUs. To solve this object the present invention provides an image reconstruction data processing unit as specified in the claim. The data processing unit of the present invention comprises a plurality of FPUs and a single BPU connected to the formers. The BPU is characterized by the provision of a plurality of back projection execution parts and a single pixel memory in which a total sum of output data from the formers is stored in a back-projected state. (Brief Description of the Drawings) Fig.1 is a block diagram of one embodiment of the present invention; Figs.2A and 2B are views illustrating projection data on an object in two directions, respectively; and Figs.3 and 4 are block diagrams of other embodiments of the present invention. (Best Status for Working the Invention) The present invention will now be described in detail with reference to the accompanying drawings. In Fig.1, a single BPU 11 is connected to two FPUs 12 and 13 through general purpose buses 16 and 19. The structure of the BPU is as follows: Two back projection execution parts 14 and 15 are provided so as to correspond to the FPUs 12 and 13. The back projection execution part 14 is provided with an address generating part 17and a data memory 18 connected to the FPU 12 through the general purpose bus 16, and the back projection execution part 15 is provided with an address generating part 20 and a data memory 21 connected to the FPU 13 through the general purpose bus 19. Further, two registers 22 and 23 are provided in correspondence to the two FPUs, respectively, so as to hold control data from each of the FPUs and transmit the control data to a control part 24. The control data is deemed effective when it comes from the register connected to the FPU selected by a switch 25. The switch 25 is adapted to select either the FPU 12 or 13 which is to become a master control unit and turned on and off manually or automatically in compliance with such FPU as is worthy of the master control unit. Further, it may be a software switch. The control part 24 generates a control signal to the back projection execution parts 14, 15 and buffers 27, 28. An adder 26 has an input port through which data read from the data memories 18 and 21 and output data from the buffers 27 and 28 are inputted thereinto and a result of addition of these data is inputted to an adder 30. The buffers 27 and 28 are controlled to become effective or ineffective of their operations and when held effective, generate a data "0" signal. The adder 30 adds data inputted from the adder 26 and data read out from one of addresses of a pixel memory 29 and the result of such addition is stored at the same address. The pixel memory 29 is of the type that stores data on a reconstruction image and has addresses corresponding to those of the pixel memory 29, respectively. Further, the pixel memory 29 has ports connected to the general purpose buses 16 and 19 through which ports accesses from the FPUs 12 and 13 to the pixel memory 29 are made possible. With the above structure, a case in which image reconstruction is performed by the parallel operations of the two FPUs will be described. Now, assuming that the switch 25 be turned to the FPU 12, the control part 24 will control the computation of back projections on the basis of the content of the register 22 with the FPU 12 acting as a master control unit. As the control data from the control part 24 is now indicative of image reconstruction by parallel operations of the two FPUs, the operations of the buffers 27 and 28 are held ineffective so that the adder 26 is in a state in which it is ready to add the output data of the back projection execution part 14 and that of the back projection execution part 15 and generate an output. In this case, if, for example, it is assumed that the FPU 12 writes in the data memory 18 preprocessed projection data corresponding to an i-view shown in Fig.2, through the general purpose bus 16 and the FPU 13 writes in the data memory 21 preprocessed projection data corresponding to a j-view shown in Fig.2B, through the general purpose bus 19, then the back projection execution parts 14 and 15 will execute back projections while marking a pixel 31 representing the same portion of the object. That is, the address generating parts 17 and 20 designate to the data memories 18 and 21 addresses at which the projection data on the common pixel of interest in the i-view and j-view are stored and read the projection data corresponding thereto. Then the two kinds of data thus read are added by the adder 26 and after that, the added data are further added to the image data read out from the address in the pixel memory 29 corresponding to the pixel 31 of interest so as to be rewritten again at the same address, so that the back projection of the pixel 31 is simultaneously performed by the use of the projection data corresponding to the i- and j-views. The above operation is performed throughout all views in sequence with respect to all pixels. That is, the image reconstruction by parallel operations of the two FPUs is performed. In this case, as the back projections are performed with respect to the common pixel memory 29, a reconstructed image is complete in the single pixel memory 29. This means that an image reconstruction data processing unit having a structure simpler than that of the conventional one can be realized by parallel operations of two FPUs. After completing the back projections, the FPUs 12 and 13 are operated parallelly according to necessity so as to perform a postprocessing step by getting access to the common pixel memory 29 through their ports. As the pixel memory 29 is common to the FPUs, even when either one of the two FPUs is out of order or disconnected, the image reconstruction process can be performed by the remaining one. Now, assume that the FPU 13 be out of order or disconnected from the beginning. Then the switch 25 may be turned to select the FPU 12 and the control operation of the control part 24 may be regulated according to the content of the register 22. In this case, the control information in the register 22 includes information indicative of an independent mode of the FPU 12 so that the output operation of the buffer 28 is held effective through a control based on this information and the buffer 28 generates a "0" signal thereby forcing the leftside input of the adder 26 to become zero. Consequently, the output of the adder 26 becomes identical with that of the back projection execution part 14 and is added to the pixel data stored in the pixel memory 29 by the adder 30, thereby enabling back projections to be performed by the single operation of the FPU 12. Further, where a master FPU is determined in advance, the structure of the data processing unit may be simplified as shown in Fig.3 wherein the FPU 12 is determined as a master unit. However, the image reconstruction by parallel operations of the FPUs 12 and 13 and that by the single operation of the FPU 12 are performed in the same manner as in the case of Fig.1. Although, in the above embodiment, a case using two FPUs has been described, if a data processing unit provided with still more FPUs is desired, the BPU may be constructed as shown in Fig.4 in which the BPU is provided with n-numbered back projection execution parts 32 1 , 32 2 , ..., 32 n corresponding to n-numbered FPUs and an adder 33 having n-numbered input ports.

Claims: An image reconstruction data processing unit comprising: a plurality of fast processing units (12, 13); a plurality of back projection execution parts (14, 15) provided in correspondence to the fast processing units (12, 13), respectively, and adapted to extract and generate projection data on a common pixel of interest from among projection data on different views given by said fast processing units (12, 13); a first adder (26) for obtaining a total sum of the output data from said back projection execution parts (14, 15) and generates an output indicative of said sum; a pixel memory (29) having addresses corresponding to pixels of a reconstruction image; and a second adder (30) for adding data read from an address in said pixel memory (29) corresponding to said pixel of interest to the output data from said first adder (26), characterized in that a plurality of registers (22, 23) are provided in correspondence to said plurality of fast processing units (12, 13), so as to hold control data from each of the fast processing units (12, 13) and transmit the control data to a control part (24), said control data being deemed effective when it comes from the register connected to the fast processing unit (12, 13) selected by a switch (25), and said control part(24) generates a control signal to said back projection execution parts (14, 15) and a buffer unit (27, 28) which is controlled to become effective or ineffective of its operation and, when held effective, generates a data "0" signal to said first adder (26), thereby determining the number of data providing parallel back projection execution parts (14, 15).

Inventors: SATTA YUSUKE, TAKIURA YASURO, SATTA, YUSUKE, TAKIURA, YASURO, SATTA, YUSUKE YOKOGAWA MEDICAL SYSTEMS, LTD., TAKIURA, YASURO YOKOGAWA MEDICAL SYSTEMS, LTD.
Applicants: YOKOGAWA MEDICAL SYST, GE YOKOGAWA MEDICAL SYSTEMS, LTD., YOKOGAWA MEDICAL SYSTEMS, LTD
Application year: 1988
Main classification: G06T11
IPC codes: G06T11