JPS62100875A - Method for compressing raw data of ct device - Google Patents

Abstract

PURPOSE:To attain the compression of raw data by storing the difference between the values before and after view data collected by a CT device with the constitution of a small number of bits. CONSTITUTION:The view data is detected by an array of detectors at each angle position of an X-ray tube 1. The difference between the i-th and (i+1)-th data is calculated in a certain channel (j) for the view data on the view points 1-n respectively. This calculation is carried out with all channels and stored in a range of a fixed number of bits for compression of data. In such a way, the raw data are compressed for a CT device.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention is used in the field of CT equipment and digital data compression processing.

The present invention provides a CT stretching device or a computer-controlled M! This invention relates to a method for compressing raw data in a shadow device.

(b) Prior art CT stretching devices require a huge amount of raw data and reconstructed image data in the data collection process by the scanner, so they are recorded using an external storage device or the like.

Although some methods have been used to compress images, there is no effective compression method for raw data.

(c) Regarding the compression of M-Katsu raw data, which the invention is trying to solve, there is a problem with the processing speed of 7'T encoding and decoding, and no other suitable method has been found.
The reality is that it has not been implemented.

In addition to this, with the improvement in the performance of CT equipment itself,
As the amount of raw data per scan is increasing, it is becoming increasingly difficult to store this amount of raw data.

An object of the present invention is to provide a pressure line method for raw data in a CT apparatus that can perform shoulder-speed processing in view of the above M point.

(d) Means for solving the problem The above purpose is to store projection data collected at a certain rotation angle V of the scanner as reference view data for all channels, and then to sequentially rotate the scanner for each unit angle. This can be achieved by calculating the difference 9j value from the previous view data for all channels for the projection data collected by , and storing this in a fixed number of bit ranges to compress the data.

(E) The raw data collected at a certain rotation angle or initial rotation angle of the working scanner is stored as is as basic view data,
For view data that is collected continuously after that,
Compression is performed by storing the difference value between the two view data in a small bit configuration, taking advantage of the characteristic that there is no large change in data between the view data before and after the view data.

A preferred embodiment of the invention will be explained based on the drawings.

FIG. 1 is a flowchart showing one example of this,
FIG. 2 shows a third generation Pear X-ray CT device as an example to which the method of the present invention is applied! ! It is a schematic block diagram.

In FIG. 2, the X-ray tube 1 and the detector array 2 constituting the scanner are rotated in the direction of arrow A and rotated to eight angular positions p1. p2. ,,, , p n, p n
+1. , , and collect data at slightly different angles.

View data #1 of the subject 3 at this time is shown at the top of FIG. View #1 is
This is data collected at line tube 1 or angle P1, and V'iew
12 is the angle P2, and similarly, View #n is the respective data at the angle ffpn.

Note that the data shown in FIG.
Although shown as M, it is actually discrete data obtained from the detector array 2, and is shown by connecting these data with a curve.

Usually, these data are expressed by a relatively wide dynamic range α, as shown in FIG.

However, in a CT apparatus, a difference value between adjacent view data can be expressed in a small dynamic range. For example, the difference value between View4$1 and v1ew#2 and the difference value between View#n and Viewin+l are shown on the right side of FIG. 3, respectively.

If the difference value between two consecutive views is used as compressed data in this way, the dynamic range can be significantly reduced and compressed as β as shown in the figure, significantly reducing the number of bits required to represent one piece of data. . I can do something like two.

Therefore, if there is one row, the first View data 1 data is written as it is in the storage means as reference data, and henceforth Vi
e w# 2 and later VIa view data can be created by writing the difference value from the previous view data as data.
It can be used as a pressure yarn anchor.

The structure of this method is shown in flowchart form in FIG. Here, 1 is the reference number of consecutive views, J
indicates each channel.

As an exception to the above general rule, if the difference value exceeds the dynamic range β that can be expressed in compressed data, a specific value etc. should be recorded as a flag, and at the same time the difference value should be written with data with expanded bit length. Therefore, it can be applied to data with even less variation.

In addition, as for the compression ratio, the original data is m bits, and the compressed data is m n hira F (m> n, m, n
is an integer), it is possible to compress the raw data to approximately (m-p, ),/m.

The raw data or view data may be data collected by a detector array in the illustrated embodiments, data before conversion to parallel beam data, projection data (profile data) after conversion to parallel data, or even logarithmic data. The present invention applies to data before or after processing by a converter, etc. According to the present invention, data l per frame of raw data can be reduced.
The capacity of the external storage device can be reduced to a limit of M, and with current X-ray CT equipment, it is possible to collect more and more view data as the X-ray exposure pulse rate continues to increase. In this case, a smaller dynamic range can be applied, and the data compression effect will be synergistically improved.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing one embodiment of the present invention, and FIG.
The figure is a diagram illustrating the configuration of a CT apparatus to which the present invention is applied, and FIG. 3 is a characteristic diagram of raw data in the CT apparatus. 1 is an X-ray tube, 2 is a detector Y-ray, 4 is a data processing section, 5
1 is a data processing section, 6 is an external storage device, and 7 is an image display section.

Claims (2)

[Claims] (1) Projection data collected at a certain rotation angle of the scanner is stored as reference view data for all channels,
For the projection data collected by successive rotations of the scanner per unit angle, the difference values from the previous view data are calculated for all channels, and this is stored in a fixed number of bit ranges to compress the data. A raw data compression method for a CT device, characterized by: (2) If the difference value exceeds a certain number of bits,
The bit configuration is such that the difference value is expressed using a specific bit arrangement as a flag.
A method for compressing raw data in a CT apparatus according to claim 1.