JPS59194260A - Computer tomography device - Google Patents

Abstract

PURPOSE:To perform the operation processing of reverse projection at a high speed by generating reverse projection data by addition between two groups of reverse projection data in at a different angle direction by 180 deg., and performing the operation for reconstitution extending over the angle of 180 deg. around a sample. CONSTITUTION:Fluoroscopic image data collected as a fan beam is converted into data as a parallel beam by a fan beam/parallel beam converter FPC. The data is supplied to a Fourier transforming device FFT for the Fourier transformation, and a reverse Fourier transforming device IFFT performs the reverse Fourier transformation. Data is supplied to a reverse projection controller BPC to add every two data as parallel beams whose paths (data collection path) are on the same straight line between two groups of data in different angle directions by 180 deg.. Those sum data are used by the reverse projection controller BPC to process the reverse projection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to a computer/mography apparatus used primarily in the field of electronic medical equipment. In particular, the present invention relates to an improvement in a computer tomography apparatus that reconstructs a radiation absorption coefficient distribution image regarding a cross-sectional portion of a subject using a back projection method.

[Description of prior art]

A computer tomography device is configured to generate radiation, transmit the radiation to a cross-sectional area of a subject, and collect fluoroscopic image data obtained as multiple sampling data in multiple angular directions with respect to the cross-sectional area. has been done.

This fluoroscopic image data has an angle of 0° to 36° around the subject.

By collecting data in a wide range of angular directions, when reconstructing a radiation absorption coefficient distribution image, a high-quality image with less noise and various artifacts can be obtained. For this reason, devices that are conventionally configured to rotate a radiation beam by 36 degrees around a subject and collect fluoroscopic image data are widely known.

On the other hand, fluoroscopic image data is collected by transmitting a parallel beam of radiation through a cross section of the object and scanning the parallel beam within the cross section, or by generating fan beam radiation. There is a method in which the image is transmitted through a cross-sectional area of the subject. Collecting fluoroscopic image data using parallel beams is inefficient and the energy of the radiation source is inefficient.From these points of view, a method of collecting fluoroscopic image data using a fan beam is superior.

However, in order to reconstruct a radiation absorption coefficient distribution image using the back projection method from perspective image data collected by a fan beam, the calculation process is inevitably complicated, and therefore it takes a long time to obtain the reconstructed image. become longer. In order to improve this, the inventor of the present application irradiated the subject with a fan beam to obtain fluoroscopic image data using the fan beam, converted this into data equivalent to fluoroscopic image data using a parallel beam through calculation, and inverted the data. He invented a method for performing projection processing and filed a patent application (Japanese Patent Application No. 58-44802).

In this way, it has become possible to collect perspective image data at a J rate using a fan beam, convert it into a parallel beam, and execute back projection calculation processing at high speed.

However, when the inventor performs back projection processing on perspective image data using a parallel beam, it is possible to
It was found that there was still waste in performing the calculation in the angular direction over 60 degrees, and that this could be processed efficiently.

[Purpose of the invention]

An object of the present invention is to provide a computer tomography apparatus that can perform back projection calculation processing at higher speed without losing the advantage of collecting data in angular directions ranging from 0° to 360° around the subject. purpose.

[Features of the invention]

The present invention collects data by irradiating radiation around the subject in angular directions ranging from 0° to 360°, and is a part of the reconstruction process that calculates the distribution of radiation absorption coefficients from the image data obtained by imaging. For the data group of back projection data in all angular directions obtained by applying Create back projection data by adding (or calculating proportional to the addition) for each data, and use the data obtained in this way as new data to create an angle 3 around the subject.
It is characterized by performing reconstruction calculations by back projection over an angle of 180 degrees, which is half of that angle, instead of 60 degrees.

Reconstruction by back projection according to the present invention is performed using perspective image data for parallel beams. When the perspective image data is obtained by a parallel beam, the perspective image data can be used as is.

When the perspective image data is collected by a fan beam, this data may be converted into a take of a parallel beam by calculation and supplied to a means for reconstructing by a back projection method.

Back projection processing requires a larger amount of data to be processed, and occupies a larger portion of the time for reconstruction. However, since the process of simply adding two pieces of data is simple and the amount of data is much smaller, the calculation time is negligibly short compared to the time for backprojection processing.

Therefore, the time for backprojection reconstruction is halved with the present invention.

The 1 degree 180 degree angle for which calculation processing is performed may be from 0 degree to 180 degrees, from 180 degrees to 360 degrees, or any other 180 degree portion.

[Explanation based on examples]

FIG. 1 is a block diagram of a computerized tomography apparatus according to an embodiment of the present invention. For table gantry TG,
Equipped with a ray generating section XG and an X-ray detecting section S,
(patient) is configured to lie down. Fan beam X-rays are generated from the X-ray generator XG to the subject PA by a known method and transmitted through the subject PA, and then converted into electrical signals by the X-ray detector S. This electrical signal is amplified and integrated by the data acquisition device DAS, and analog-to-digital conversion is performed to obtain perspective image data of the digital signal. This transmission image data is temporarily stored in the data storage device DS1, and is subjected to preprocessing for cross-sectional image reconstruction by the preprocessing device PPC. The data obtained as a result of the preprocessing is temporarily stored in the data storage device DS2. This data storage device D
The data stored in S2 is processed by the fan beam parallel beam converter FPC and temporarily stored in the data storage device DS3.

This data is subjected to Fourier transform processing with the Fourier transform device FFT, and the result is temporarily stored in the data storage device I)'S4. The data storage device D
Regarding the data stored in S4, the filter device FIL
Filter processing is performed by T, further inverse Fourier transform processing is performed by an inverse Fourier transform device IFFT,
It is temporarily stored in the data storage device DS5. This data is processed by the back projection control device BPC to become video data and is stored in the video data storage device IM. This video data is photographed by an image photographing device MFC and displayed on an image display device Gl)C.

A table gantry controller TGC is connected to the table gantry TG, and an X-ray generator controller XGC is connected to the X-ray generator XG.

Each is configured to control X-ray generation and irradiation.

These table/gantry control device TGC and X-ray generator control device Device S
It is configured to be controlled by CC.

In the computer tomography apparatus configured in this way, the subject PA is placed on the table/gantry TG, and the subject P is placed on the table/gantry TG.
Fluoroscopic image data obtained as a plurality of N sampling data for the cross-sectional portion of A are collected in a large number of angular directions and stored in a data storage device DSI, and after preprocessing the data, a fan beam parallel beam conversion device FPC
The perspective image data collected by the fan beam is converted into parallel beam data. The data is subjected to Fourier transform using a Fourier transform device FFT to obtain Fourier image data regarding the cross section. This data is stored in the data storage device DS4, subjected to filter processing by the filter device FILT and inverse Fourier transform processing by the inverse Fourier transform device IFFT to become data corresponding to the radiation absorption coefficient, and is back-projected by the back projection control device BPC. This results in image data that shows the distribution of radiation absorption coefficients for each part. 'Then, the image is displayed on the image display device GDC and a photograph is taken using the image photographing device MFC.

Here, the feature of the present invention is that the f data supplied to the back projection control device BPC has the same parallel beam path (data collection path) between two sets of data in angular directions different from each other by 180 degrees. Two pieces of data are added together for each piece of data on the straight line, and the backprojection control device BPC executes backprojection processing using the added data.

FIG. 2 is a flowchart showing the operating procedure of the apparatus according to the embodiment of the present invention.

The algorithm of this embodiment device will be explained. Third
The figure shows the cross section of the subject PA for parallel beams on the xy plane.
Assuming that (x, y) is the radiation absorption coefficient at the point PT (X, )') and Δt is the length between adjacent parallel lines, the algorithm for the filtered back projection method is as follows.

11Ei! The Fourier transform (FFT) algorithm is
・・・・・・・・・(1) The filtering algorithm is Q(ωヮ, θi) = P(ωtw, θi)・H(ω?t
)・・・・・・・・・(2) Inverse Fourier transform-FFT algorithm is...
......(3) The back projection algorithm is f (x, y) = CμΣq'(ti, θJ)...
・(4) This is O.

Here, the feature of the present invention is that q'(ti,
θi) = q (t i, θj) + q(tL'
, θ,′)・・・・・・(5) However, θ′−θj
→-180°ti'--1i ti=x-cosθj+)'-5inθj, the path of the parallel beam (data collection path) is on the same straight line between two sets of data with 180° angular directions different from each other. It consists in using two pieces of data that are added to each other for each piece of data.

FIG. 4 is a diagram showing the correspondence between a set of data in a certain angular direction i Vie- and a set of data 1'v'rew in a different 180 degree angular direction. PA represents the object area, and O represents the center of the object area.

Figure 5 shows the data of a certain angular direction i View and 1
FIG. 6 is a diagram showing a correspondence relationship between data of i' Views in different 80-degree angular directions whose collection paths (parallel beam paths) are on the same straight line and undergo synthesis.

By performing such processing, fluoroscopic image data is collected in angular directions ranging from 0° to 360° around the subject, increasing the amount of data and producing high-quality images with less noise and various artifacts. can be reconfigured in half the processing time.

The fan beam parallel beam conversion (FPC) algorithm is as follows: i is the parallel beam perspective image data set (VIEW) number, j is the parallel beam beam number (detector channel number), and i7 is the fan Beam perspective image data set (VIEI4
) number, and j′ is the fan beam beam number (detector channel number). Here, Cμ is a constant, H(ωn) is filter-related Δθ: angle between two adjacent perspective image data sets (between two adjacent views), (when scanning is performed at constant angular intervals) Cc : Center beam number (center channel number of the detector) Δψ: Angle between two adjacent channels (two beams) of the fan beam (when the detector array is arranged at equal angular intervals when viewed from the X-ray source) ) I2: Distance between X-ray source and reconstruction center Δt: Spacing between adjacent parallel beams (detector channels).

Each of the algorithms shown in the above examples is just an example, and the present invention can be implemented by applying any other algorithm as long as it performs back projection on data using parallel beams. can.

In the above example, it was explained that the addition of data having different angular directions is executed in the back projection control device BP'C immediately before the back projection, but it can be executed at a stage before being input to the back projection control device BPC. The present invention can be practiced even if

Furthermore, the device of the present invention can be equipped with a processing device such as a dedicated high-speed processor (array processor, etc.), CP'U, microprocessor, etc., or can be connected with a storage device such as a magnetic disk, floppy disk, or magnetic tape. It can also be configured by adding a display and operation device such as an operator console. Alternatively, it can be configured by omitting unnecessary devices. Also, in the above embodiment, the configuration can be configured by sharing multiple data storage devices. It is also possible to configure a plurality of processing devices by combining them, or by separating them.

[Explanation of effects]

As described above, according to the present invention, it is possible to collect fluoroscopic image data over a range of 0° to 360° around a subject and reconstruct a high-quality image with less noise and various artifacts. In addition, it has the excellent effect of halving the time required for arithmetic processing by backprojection.

[Brief explanation of drawings]

FIG. 3 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing the control procedure of the apparatus according to the embodiment of the present invention. FIG. 3 is a diagram showing coordinates of an X-ray fluoroscopic cross section for a parallel beam. FIG. 4 is a diagram showing the correspondence between a data set in a certain angular direction i View and a data set in 5'v1eiv in a different angular direction by 180 degrees. Figure 5 shows the data of a certain angular direction i View and 1
FIG. 3 is a diagram showing the relationship between data of t' views in different 80-degree angular directions and subjected to synthesis in which the collection paths (parallel beam paths) are on the same straight line; Patent applicant: Yokogawa Medical System Co., Ltd. Representative patent attorney: Naotaka Ide'

Claims (3)

[Claims] (1) Generate radiation, transmit this radiation to a cross-sectional area of the subject, and obtain fluoroscopic image data as multiple sampling data for each cross-sectional area at multiple angles ranging from 0° to 360° around the subject. a first means for obtaining back projection data of a parallel heath by collecting data regarding the direction and subjecting the fluoroscopic image data to a part of reconstruction processing for determining the distribution of radiation absorption coefficients regarding the cross-sectional portion; and a second means for reconstructing a radiation absorption coefficient distribution image regarding the cross-sectional portion from the obtained back projection data by a back projection method, Regarding the back projection data group, which is a collection of back projection data in all angular directions, for each set of back projection data in angular directions that are 180 degrees different from each other, for each data on a straight line with the same collection path. a third means for supplying data obtained by addition of two data or a calculation proportional to the addition to the second means, and the second means supplies data obtained by the addition or an operation proportional to the addition. about angular direction 1
A computer tomography apparatus characterized in that it is configured to perform reconstruction processing over 80 degrees. (2) The computer tomography apparatus according to claim 1 (1), wherein the first means is configured to generate parallel beam radiation and collect parallel beam perspective image data. (3) The first means is a means for generating fan beam radiation, and a part of reconstruction processing of the perspective image data obtained by the fan beam radiation into parallel beam perspective image data or that data. 2. A computer tomography apparatus according to claim 1, further comprising means for computationally converting the obtained data into parallel beam data.