CN110335671B

CN110335671B - Modulated data compression and acquisition method for CT detector

Info

Publication number: CN110335671B
Application number: CN201910627523.1A
Authority: CN
Inventors: 王斌; 王瑶法; 徐亦飞; 黄俊杰; 刘骅
Original assignee: Sichuan Mingfeng Medical Technology Co ltd
Current assignee: Sichuan Mingfeng Medical Technology Co ltd
Priority date: 2019-07-12
Filing date: 2019-07-12
Publication date: 2023-03-24
Anticipated expiration: 2039-07-12
Also published as: CN110335671A

Abstract

The invention provides a data compression and acquisition mode of a modulatable CT detector, which relates to the technical field of medical images and comprises the steps of scanning a patient positioning sheet; the multiple scan regions are dynamically partitioned according to gantry rotation: the plurality of scanning areas comprise an area I, an area II and an area III; the area range formed by the intersection of the tangent of the focus and the heart scanning area on the detector is a second area, the intersection of the tangent of the focus and the heart scanning area on the detector and the intersection of the tangent of the focus and the scanning visual field boundary on the detector are a first area and a third area; as the gantry rotates, the sizes of the three regions dynamically change; and dynamically compressing the data of the first region and the third region, wherein the compression process is completed on a data acquisition board of a rotor part of the CT machine. The data compression acquisition mode of the invention can reduce the data bandwidth, control the data volume and reduce the requirement of the data transmission bandwidth of the slip ring.

Description

Modulated data compression and acquisition method for CT detector

Technical Field

The invention relates to the technical field of medical equipment, in particular to a data compression and acquisition method of a CT detector capable of being modulated.

Background

The main components of the third generation CT system include Tube, collimator, and Detector. The X-ray bulb tube emits X-rays, and a cone-shaped light beam is formed by the limitation of the beam limiter. The cone beam irradiates on the detector, is converted into an electric signal through the detector, is converted into digital information through the data acquisition and conversion unit and is stored in the image processing system. The image processing system generates images through a series of correction algorithms and image reconstruction algorithms for display on the display. For cost and technical maturity, the mainstream detector employs a large number of detector modules arranged on an arc or polygon surface to form the whole detector. And a matrix formed by detector units is regularly arranged in each detector module.

In order to scan the heart, the CT gantry rotor must be rotated at very high speeds for the purpose of "freezing" the heart motion. The fastest CT rotational speeds have now reached 0.23s and 0.25s per revolution. At the same time, the width of the detector is also such that it covers 256 or 320 rows of detectors for a scan length of 16 cm. The number of pixels of each row of the detector is generally about 900, and the data of each pixel is generally 16-bit or 24-bit binary data, so that the data transmission bandwidth is very large.

In the prior art, an expensive slip ring is adopted, or focal position modulation in the X direction or the Z direction is adopted, or a high-low kV switching energy spectrum imaging mode, a focal position modulation technology in the X direction or the Z direction, and a high-low kV switching energy spectrum imaging mode are adopted to further increase the demand for high transmission bandwidth. To accommodate either the flying focus scan mode or the high and low kV scan mode, the sampling rate of one turn is usually about 4096. Therefore, in the flying focus mode, the required transmission bandwidth of the slip ring is at least 320 × 900 × 24 × 4096/0.23/(1024 × 1024) =114.6Gbps. This is not achievable with current slip ring designs. Even with 16bit encoding, 256 rows of detectors, a slip ring bandwidth of 28.1Gbps is required at 2048 sample rate per turn. Some manufacturers have used a dual bulb dual detector design, with one detector covering a larger scan field of view and the other detector covering a smaller scan field of view, which further increases the amount of data. Therefore, fast scan and flying focus switching and kV switching are difficult to do on cardiac scans simultaneously, subject to slip ring bandwidth limitations. In the prior art, multiple channels are usually coupled into one channel to reduce the data bandwidth, but the area division is fixed, and the multiple channels will reduce the resolution of the whole scanning area. In the prior art, the sampling rate in the angle direction is increased to reduce aliasing artifacts caused by a large sampling distance in an off-center region, and the technique further brings larger occupation of data bandwidth.

Based on this, the present case has been made.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides a data compression and acquisition method for a modulatable CT detector, which can reduce data bandwidth and control data volume.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for data compression acquisition of a modulatable CT detector comprises the following steps:

(1) Scanning a patient positioning sheet;

(2) The plurality of scan regions are dynamically partitioned according to gantry rotation: the plurality of scanning areas comprise an area I, an area II and an area III; the area range formed by the intersection of the tangent of the focus and the heart scanning area on the detector is a second area, the intersection of the tangent of the focus and the heart scanning area on the detector and the intersection of the tangent of the focus and the scanning visual field boundary on the detector are a first area and a third area; as the gantry rotates, the sizes of the three regions dynamically change;

(3) And dynamically compressing the data of the first region and the third region, wherein the compression process is completed on a data acquisition board of a rotor part of the CT machine.

Further, in the step (2), the plurality of scanning areas further include a defined scanning field of view, the defined scanning field of view is centered on the rotation center of the gantry, and the defined radius of the scanning field of view is R; the area range formed by the intersection of the focal point and the tangent line defining the scanning visual field on the detector is an area four; the area four includes the entire area two, and includes a part of the area one and/or the area three.

Further, the data of the remaining area except the area two in the area four is dynamically compressed.

Furthermore, the dynamic compressed data is compressed in a mode that a plurality of detector pixel units are combined into one unit.

Further, the data compression degree of the remaining area except the area two in the area four is smaller than the data compression degree of the remaining area except the area four in the area one and the area three.

The working principle of the invention is as follows: in the heart scanning imaging process, the volume of the whole scanning plane occupied by the heart is small, and the image quality requirement outside the heart is not high. The position and number of detector channels that need to be covered to the heart vary from gantry rotation angle to gantry rotation angle. The method provided by the invention is that when the frame rotates at different angles, the compression is not adopted for the pixel data of the detector covering the heart area, and the compression is carried out for the pixel data of the area outside the heart.

The invention can realize the following technical effects:

(1) The invention provides a method for dynamically compressing data of a detector, namely a method for dynamically dividing the detector into a plurality of regions according to a scanning interested region, wherein each region adopts a compression mode with different ratios to reduce the data amount, thereby enabling a scanning mode with high sampling rate. And the compression process of the invention is completed on a data acquisition board of a rotor part of the CT machine, thereby greatly reducing the requirement of slip ring data transmission bandwidth.

(2) According to the invention, during cardiac scanning, the slip ring bandwidth occupation is reduced by dynamically changing a data compression mode of the detector, so that the eccentric scanning can greatly reduce the slip ring bandwidth requirements of the cardiac scanning and the flying focus and the simultaneous use of high and low kV switching technologies in a high sampling rate mode (such as a flying focus mode, rapid kV switching and high rotation speed scanning), and the cardiac scanning can use the flying focus and high and low kV switching technologies.

Drawings

FIG. 1 is a schematic representation of the relative position of the heart and the center of rotation of the gantry in accordance with the present invention;

FIG. 2-1 is a first schematic view of the area division (at a certain rotation angle of the frame) in example 1;

FIG. 2-2 is a schematic view of the area division of embodiment 1 (at another rotation angle of the gantry);

FIG. 3-1 is a first schematic view of the area division (at a certain rotation angle of the frame) in example 2;

fig. 3-2 is a schematic diagram of the area division of embodiment 2 (at another rotation angle of the gantry).

Detailed Description

In order to make the technical means of the present invention and the technical effects achieved by the technical means more clear and more complete, 2 embodiments are provided, and the following detailed description is made with reference to the accompanying drawings, and it is stated that in the following description, a region i.e. a region 1, a region ii i.e. a region 2, and a region iii i.e. a region 3.

Example 1

The method for compressing and acquiring the data of the modulated CT detector comprises the following steps:

(1) Scanning a patient positioning sheet; the patient's prone position and spacer images on the scanning bed are acquired for subsequent calculations. The CT system estimates the area of the heart according to the positioning sheet and the prone position of the patient on the scanning bed.

(2) The multiple scan regions are dynamically partitioned according to gantry rotation: the plurality of scanning areas comprise an area I, an area II and an area III; the area range formed by the intersection of the tangent of the focus and the heart scanning area on the detector is a second area, the intersection of the tangent of the focus and the heart scanning area on the detector and the intersection of the tangent of the focus and the scanning visual field boundary on the detector are a first area and a third area; as the gantry rotates, the sizes of the three regions dynamically change;

(3) And dynamically compressing the data of the first region and the third region, wherein the compression process is completed on a data acquisition board of a rotor part of the CT machine. The dynamic compression data is compressed in a mode that a plurality of detector pixel units are combined into one unit.

In embodiment 1, as shown in fig. 2-1 and 2-2, when the gantry rotates to different angles, the tangents of the focal point and the cardiac scanning area and the detector intersect at two points B and C. Region 1 consists of detector arc FAB, region 2 consists of detector arc FBC, and region 3 consists of detector arc FCD. The size of the three zones changes dynamically as the gantry rotates to different angles. Since region 2 is the region of significant interest in scanning the heart, while regions 1 and 3 are not the point of interest, the present embodiment proposes to use different compression ratios in the three regions. The area 2 does not undergo any compression to change the original scanning data, and the data is compressed in the area 1 and the area 3 in a mode that a plurality of detector pixel units are combined into one unit. For example, two detector pixel units are combined to form one data output, so that the data rate of the area 1 and the area 3 can be reduced by half. The data rate of the area 1 and the area 3 can be reduced to one third of the uncompressed mode by adopting a mode that three detector pixel units are combined into one data output.

The division mode is realized by calculating the division mode that the data of the detector is compressed in different frame rotation angles by the operating table computer according to the frame rotation angle and the frame rotation time of the initial exposure.

And the computer on the operation table sends the data of the division mode of the detector calculated in the previous step, the compression ratios of different areas and the compression method to the data acquisition control panel of the rotor part.

The data acquisition control board initializes the detector and system setting information to start exposure, dynamically compresses data according to a pre-calculated region division mode and transmits the data to the reconstruction computer in real time through a slip ring system.

The reconstruction computer reconstructs the received compressed detector data to obtain a scanned image.

Example 2

The method for compressing and acquiring the data of the CT detector capable of being modulated comprises the following steps:

(1) Scanning a patient positioning sheet; the patient's prone position on the scanning bed and the topogram images are acquired for subsequent calculations.

The CT system estimates the area of the heart according to the positioning sheet and the prone position of the patient on the scanning bed.

(2) The multiple scan regions are dynamically partitioned according to gantry rotation: the plurality of scanning areas comprise an area I, an area II and an area III; the area range formed by the intersection of the tangent of the focus and the heart scanning area on the detector is a second area, the intersection of the tangent of the focus and the heart scanning area on the detector and the intersection of the tangent of the focus and the scanning visual field boundary on the detector are a first area and a third area; as the gantry rotates, the sizes of the three regions dynamically change; the scanning areas further comprise a defined scanning visual field, the defined scanning visual field takes the rotating center of the frame as the center, and the defined scanning visual field radius is R; the area range formed by the intersection of the focal point and the tangent line defining the scanning visual field on the detector is an area four; the area four includes the entire area two, and includes a part of the area one and/or the area three.

(3) And dynamically compressing the data of the first region and the third region, wherein the compression process is completed on a data acquisition board of a rotor part of the CT machine. The dynamic compression data is compressed in a mode that a plurality of detector pixel units are combined into one unit. And dynamically compressing the data of the remaining area except the area two in the area four. The data compression degree of the remaining area except the area two in the area four is smaller than the data compression degree of the remaining area except the area four in the area one and the area three.

In embodiment 2, one scanning field of view (scanning field of view radius R) is defined on the basis of the first implementation (division in embodiment 1). And a lower compression ratio is adopted in the scanning visual field, a higher compression ratio is adopted in the visual field, and the number and the size of the regions are dynamically divided according to different angles of the bulb tube. As shown in fig. 3-1 and 3-2, the two racks may be divided into 4 zones and 5 zones at different rotation angles, respectively. The regions FAE, FCD in FIG. 3-1 and the regions FAE and FGD of FIG. 3-2 may be synthesized into one data output using 3 detector pixels. The region FEB in FIG. 3-1 and the regions FEB and FCG in FIG. 3-2 can be combined into one data output using 2 detector pixels. No probe data compression is performed in the zone FBC.

The dynamic data compression can be realized by using FPGA programming or adopting an embedded programming mode in a data acquisition system of a rotor part. The data sampled by each bulb tube at different sampling angles comprises dynamically compressed data and header information which is used for recording area division information, a compression ratio and a compression mode. Of course, the dynamic data compression method according to the present invention may also adopt other well-known data compression methods, such as run-length coding, besides the method of directly adding and merging multiple channels into one channel in the above two examples.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments of the invention, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for data compression acquisition of a modulatable CT detector is characterized by comprising the following steps:

(1) Scanning a patient positioning sheet;

(3) Dynamically compressing data of the first region and the third region, wherein the second region is not compressed, and the compression process is completed on a data acquisition board of a rotor part of the CT machine;

in the step (2), the plurality of scanning areas further include a defined scanning field, the defined scanning field is centered on the rotation center of the gantry, and the defined radius of the scanning field is R; the area range formed by the intersection of the focal point and the tangent line defining the scanning visual field on the detector is an area four; the area four comprises the whole area two and comprises part of the area one and/or the area three; dynamically compressing the data of the remaining area except the area two in the area four;

the data compression degree of the remaining area except the area two in the area four is smaller than the data compression degree of the remaining area except the area four in the area one and the area three.

2. The method of claim 1, wherein the method comprises: and the dynamic compressed data is compressed in a mode that a plurality of detector pixel units are combined into one unit.

3. A method as claimed in claim 2, wherein the modulated CT detector data compression acquisition method comprises: the dynamic compression data is realized by using an FPGA programming or embedded programming mode in a data acquisition system of a rotor part.