JPH0573416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tomographic examination apparatus that performs tomographic imaging of a subject using radiation or the like.

[Technical background of the invention and its problems] Computer tomography scanners are used as devices that can non-destructively and non-invasively inspect lesions, compositions, internal defects and structures of objects, etc. inside a subject, and can measure them with high accuracy. There is a tomographic inspection device called a CT scanner (hereinafter referred to as a CT scanner).

For example, this device is arranged to face a radiation source that emits Fan beam X-rays that spread in a flat fan shape as a radiation source, and to face this radiation source through a subject, and a plurality of The radiation source and the detector are sequentially rotated and scanned in the same direction, for example, from 180 to 360 degrees in one-degree increments, with the subject as the center. After collecting X-ray transmission data, that is, X-ray absorption data, from multiple directions of the tomographic plane to be imaged, a computer etc. performs image reconstruction processing to reconstruct the tomographic image. Since images can be reconstructed in as many as 2,000 stages depending on the composition for each position on the surface, the condition of the tomographic plane of the subject can be known in detail.

An example of such a CT scanner is shown in FIG.

In the figure, 1 is a scanner body, and 2 is an X-ray source that emits a fan beam X-ray FB having a predetermined spread width. Reference numeral 3 denotes a radiation detector provided facing the X-ray source 2. This radiation detector 3 has a large number of minute radiation detection elements arranged in parallel in the direction of spread of the Fan beam X-ray FB. With the resolution, the intensity of the X-rays from the X-ray source 2 can be detected. Here, the X-ray path connecting the X-ray source 2 and each radiation detection element is called an X-ray path, and each radiation detection element outputs a signal according to the intensity of radiation on this X-ray path. The scanner main body 1 also has a rotating mount that holds the X-ray source 2 and the radiation detector 3 facing each other with the imaging area as the center, and rotates and scans them sequentially in one direction at predetermined angle increments. There is. Reference numeral 4 designates a subject disposed in the imaging area of this rotary mount, and reference numeral 5 designates an X-ray controller that controls the tube current, tube voltage, and X-ray exposure of the X-ray source 2. Reference numeral 6 denotes a scanner controller, which controls the rotation of the rotating pedestal of the scanner main body 1. A system controller 7 controls the entire system. Reference numeral 8 denotes a console, through which an operator can give various commands to the system, and can input various operational commands and data to the system. Reference numeral 9 denotes a data acquisition device which receives output signals from each radiation detection element of the radiation detector 3, performs A/D conversion (analog/digital conversion), and outputs the resultant signals as X-ray absorption data. 10
is a preprocessing device that receives the X-ray absorption data for each projection (projection direction) collected by the data collection device 9 and performs preprocessing such as logarithmic transformation, gain correction, offset correction, etc. It is. 11 is a convolver, and the pretreatment device 1
The preprocessed data output by 0 is convolved.

12 is a back projector; 13 is an image memory for storing image data composed of a predetermined number of pixels; the back projector 12 transfers the convolved data to the image memory 13;
On the other hand, a tomographic image is reconstructed by back projecting the data in a direction corresponding to the projection direction at the time of data collection and accumulating (superimposing) the data. 14 is a CT of a desired range among the data stored in the image memory 13.
This is an image converter that outputs a value (data as a value corresponding to the level of radiation absorption) as a black and white grayscale image. A CRT display 15 receives the output of the image converter 14 and displays it as an image.

In such a configuration, first, the operator operates the console 8 to start up the system and start scanning (starting photographing). Then, the system controller 7 controls the scanner controller 6 to control the rotation of the rotary mount in the scanner main body 1 in predetermined angle increments, and also controls the X-ray controller 5 to perform rotation in the predetermined angle increments. Each time, a predetermined tube current and tube voltage are applied to the X-ray source 2 for a predetermined time width. As a result, the X-ray source 2 sequentially emits fan beam X-rays FB in a pulsed manner. A subject 4 is placed at the center of rotation (imaging area) of the rotating mount, and an X-ray source 2 and a detector 3 are mounted on the rotating mount so as to face each other across the center of rotation. Therefore, the X-ray source 2 is
The Fan beam X-rays FB are irradiated on a predetermined cross section of the plane while changing the direction sequentially.
The radiation transmission value of each X-ray pass in this fan beam X-ray FB is detected by each radiation output element of the radiation detector 3 and converted into an electrical signal.

Then, this converted signal is collected by the data collection device 9, and one projection (imaging direction;
The preprocessing device 10 performs logarithmic transformation, gain correction, offset correction, etc. for each photographing direction. This processed data (X-ray absorption data in each X-ray pass for each projection direction) is convolved in a convolver 11, back-projected onto an image memory 13 in a next back projector 12, and superimposed. CT of each pixel position is added onto the image memory 13 in the form of
The CT value is calculated, and a tomographic image is reconstructed based on this CT value. The reconstructed image is stored in a large capacity memory (not shown). Then, by giving a command from the console 8, this saved reconstructed image or the reconstructed image from the image memory 13 is read out as needed, and the image converter 14 converts the CT value in a desired range into a CT value. It is displayed on the CRT display 15 after converting it into a gradation level corresponding to the gradation level. As a result, the reconstructed image is displayed as a black and white grayscale image.

This type of CT scanner is of the so-called 3rd generation system, and also has an X-ray source that generates pencil beam X-rays and a detector with a single radiation detection element placed facing each other across the subject. X
The first generation uses a radiation source and detector that alternately repeats traverse scan and rotational scanning of the subject, and a large number of detection elements are placed around the subject around the subject. fan beam x
There are various types, such as the fourth generation, in which only the X-ray source that emits radiation is rotated around the subject.

By the way, the number of data for each projection direction is the number of detector elements (number of channels) in the 3rd and 4th generation, etc.
In addition, in the first generation, if the number of data is N, which corresponds to the number of repetitions of traverse scan in one projection direction, and if X-rays are irradiated M times in 360°, the number of projections is M. become. Here 1
The above-mentioned N data group obtained by multiple projections is called a view, and the N pieces of individual data are called a ray (RAY).

Normally, N output from the detector by one view
The ray data are converted into digital values by an AD converter, convolved by a convolver, and back-projected onto an image memory by a back projector in a direction corresponding to the projection direction at the time of X-ray projection. Do this for all views,
Superimpose it on the memory (that is, add the ray data for each view to the memory of that pixel as the data of the pixel located in that view direction)
By accumulating data, an image based on radiation absorption is reconstructed on the memory.

In this way, reconstruction processing involves performing prescribed processing (convolution, etc.) on the data of one view and adding this to the image memory.
This calculation is performed for all views. Therefore, if the number of views and rays is large, the time required for reconstruction processing becomes longer.Especially in recent years, in order to improve image quality, the number of pixels has been increased from the conventional 256 x 256 to 512.
When increasing to x512, 1024 x 1024,
The time required to complete the reconfiguration also becomes very long.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide a tomographic examination apparatus that can perform reconstruction processing at high speed even when the number of pixels increases. It's about doing.

[Summary of the invention] That is, in order to achieve the above object, the present invention has the following features:
Transmission data from a radiation or material-transmitting beam is collected from each direction of a specific cross section of the object with two-dimensional resolution, and image reconstruction processing is performed on the collected transmission data for each direction. In a tomographic examination apparatus configured to obtain a reconstructed image of a specific cross section of a subject, at least two systems are provided for the reconstruction processing section that performs the reconstruction processing, and each of the reconstruction processing sections is sequentially provided with the reconstruction processing section. The collected transmission data for each direction is divided into the above-mentioned systems for each direction, and the reconfiguration process is performed to complete the reconstruction process within the range of the collected transmission data given to the own system. After the reconstruction processing is completed for the collected transmission data, a control means is provided for adding the reconstruction processing results obtained in each system to complete the reconstructed image. In other words, two systems of reconstruction processing units are provided, one for processing odd-numbered view data and one for processing even-numbered view data, and when odd-numbered view data is taken in, the processing unit for processing odd-numbered view data Data is reconstructed using only odd views in the pipeline, and when even view data is captured, the data is reconstructed using only even views in the pipeline in the even view data processing arithmetic processing unit. By performing reconstruction processing, thereby completing image reconstruction using only even views and only odd views, and finally adding both reconstructed images to complete the reconstructed image, To reduce the computational burden of reconstruction processing and to speed up each calculation as much as possible, so that reconstruction processing can be performed at high speed even for high-density images.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main structure of the present device, centering on the reconfiguration arithmetic processing section.

In the figure, 21 is a CPU, 22 is a magnetic disk, 23, 23' are controllers, 24, 24' are preprocessing devices, 25, 25' are convolvers, 26,
26' is a back projector, 27 and 27' are image memories, and 28 is a DMA (direct memory access) bus.

The preprocessing devices 24 and 24' receive absorption data for each projection collected by a data collecting device (not shown) and perform preprocessing such as logarithmic transformation, gain correction, and offset correction on the absorption data. . Convolvers 25, 25' convolve the preprocessed data output from the preprocessing devices 24, 24'.

Furthermore, the back projectors 26, 26' store the convolved data by back projecting it onto the image memories 27, 27' in a direction corresponding to the projection direction at the time of data acquisition, and reconstruct the tomographic image. This is a back projector to configure. The image memories 27, 27' are, for example, 512×512,
This is a memory for storing images that has a number of pixels of approximately 1024×1024.

The CPU 21 controls the entire system of the CT scanner. Further, the magnetic disk device 22 is a large-capacity external storage device for storing preprocessed collected data and reconstructed image data. The controllers 23, 23' are connected to the pre-processing devices 24, 2.
4', convolvers 25, 25', back projectors 26, 26', and image memories 27, 27'.

This device includes a controller 23, a preprocessing device 24,
Odd-numbered view data is processed by the convolver 25, back projector 26, and image memory 27, and even-numbered view data is processed by the controller 23', preprocessor 24', convolver 25', back projector 26, and image memory 27'. The configuration is such that the view data is processed.
Then, the reconstructed images based on the odd number view data and even number view data in the image memories 27, 27' processed by these reconstruction arithmetic processing units are added by an adder ADD provided in the controller 23' to complete the image. It is stored in the magnetic disk device 22 as a reconstructed image, or
This is what is displayed on a CRT display device.

In this apparatus having such a configuration, an operator first operates the console to start up the system and start scanning (starting projection). This results in
A ray beam is emitted, and the radiation transmission value of each X-ray pass for a predetermined cross section of the subject is detected by each radiation output element of the radiation detector and converted into an electrical signal. This converted signal is then collected by a data acquisition device and input to preprocessing devices 24, 24' for each projection (one projection direction).
However, the controllers 23 and 23' control the data so that odd-numbered view data is taken into the preprocessing device 24, and even-numbered view data is taken into the preprocessing device 24'. That is, in odd-numbered projections, the collected data is taken into the preprocessing device 24, and in even-numbered projections, the collected data is taken into the preprocessing device 24', where it undergoes logarithmic transformation, gain correction, and offset. Corrections etc. are made.

This processed data (X-ray absorption data in each X-ray pass for each projection direction in odd or even numbers) is transferred to the next convolver 25 or 25' after data processing for one view is completed.
It is convolved here, and is back-projected onto the image memory 27 or 27' by the next back projector 26 or 26', and is then transferred to the image memory 27 or 27' in a superimposed manner.
7', the CT value of each pixel position is determined, and a tomographic image is reconstructed based on this CT value. As a result, the image memory 27, 2
Reconstructed images of odd-numbered views and even-numbered views are obtained on 7'. These two reconstructed images are controlled by the controller 23,
23', and the magnetic disk device 22
At that time, the reconstructed images of the odd and even views are added by the controller 23' through its adder ADD, and both are output as a completed reconstructed image in which they are superimposed and stored. . This stored data or added data is read out as needed by giving commands from the console, and an image converter (not shown) converts the CT values in the desired range into gradations according to the CT values, and then displays the data on the CRT. Display it on the display. This results in
The reconstructed image is displayed as a black and white grayscale image.

Here, when the data processing for one view is completed in each calculation unit (preprocessor 24, 24', convolver 25, 25', back projector 26, 26'), the reconstruction calculation processing unit transfers the data to the next calculation unit. A so-called view pipe line method is used in which data is transferred and data is simultaneously fetched from the previous processing unit, thereby enabling high-speed data processing.

Such pipeline-like operations are performed by controllers 23, 23'. In addition, the controllers 23 and 23' store preprocessed data.
It has a function to transfer to CPU21.

In this way, two systems of reconstruction processing units are provided, one for processing odd-numbered view data and one for processing even-numbered view data, and when odd-numbered view data is taken in, the processing unit for processing odd-numbered view data is used. Reconfigures the data using only odd views in the pipeline, and when even view data is captured, the arithmetic processing unit for processing even view data reconstructs the data using only even views in the pipeline. Data reconstruction processing is performed, thereby completing image reconstruction using only even-numbered views and only odd-numbered views, and finally adding both reconstructed images to complete the reconstructed image. As a result, it is possible to reduce the burden of reconstruction processing calculations on each reconstruction calculation processing unit, and the speed of individual calculations can be increased by pipe line processing.
Even with high-density images, reconstruction processing can be performed at high speed. Incidentally, in the above-mentioned example using two systems of reconfiguration calculation processing units, the number of calculations for each is halved, so the processing time is also halved.

Furthermore, since the image is divided for each imaging direction, each reconstruction arithmetic processing section has the ability to independently complete a tomographic image. Therefore, for CT systems that require higher-precision images, it is possible to simply add this reconstruction calculation processing unit for each unit and input it to the adder at the final stage, making it extremely easy to handle. It also has

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can of course be carried out by changing the gist and modifying it as appropriate within the scope.
For example, in the above embodiment, there are two systems of reconfiguration processing units, but if necessary, three or more systems may be used.
Furthermore, the present invention can be used not only for each generation of CT scanners, but also for X-ray CT scanners.
It can be widely used in devices that obtain images by performing the above-mentioned reconstruction calculation processing, such as CT scanners that utilize magnetic resonance phenomena and CT scanners that utilize ultrasound.

[Effects of the Invention] As detailed above, according to the present invention, there is provided a tomographic examination apparatus that can complete calculation processing in a short time even with high-density reconstructed images and can quickly obtain high-quality images. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram for explaining an example of the structure of a CT scanner. 1... Scanner body, 2... X-ray source, 3... Radiation detector, 4... Subject, 5... X-ray controller, 6... Scanner controller, 7... System controller, 8... Console , 9...Data collection device, 10...Preprocessing device, 14...Image converter, 15...CRT display, 21...CPU,
22... Magnetic disk, 23, 23'... Controller, 10, 24, 24'... Preprocessing device, 1
1, 25, 25'... convolver, 12, 26,
26'... Back projector, 13, 27, 2
7′...image memory, 28...DMA (direct memory access) bus.

Claims (1)

[Claims] 1. Collecting transmission data with a two-dimensional resolution from a radiation or material-penetrating beam from each direction on a specific cross section of the object, and performing image reconstruction processing on the collected transmission data for each direction. , in the tomographic examination apparatus configured to obtain a reconstructed image of a specific cross section of the subject, at least two systems of reconstruction arithmetic processing units are provided for performing the reconstruction processing, and the reconstruction arithmetic processing unit is sequentially provided with a controller that controls all the collected transmission data for each direction to be divided into the systems for each direction and inputted; and a calculation means that completes the reconstruction process within the range of the collected transmission data given to the own system. , a tomographic examination apparatus characterized by being provided with an addition means for adding the reconstruction processing results obtained in each system to complete the reconstructed image after the reconstruction processing is completed for collected transmission data for all directions. .