阅读说明：本技术 一种ct变速扫描调节剂量方法 (Dose adjusting method for CT variable speed scanning ) 是由 陈伟 徐亦飞 王瑶法 于 2020-12-21 设计创作，主要内容包括：本发明涉及医学影像设备技术领域,尤其涉及一种CT变速扫描调节剂量方法,在电流固定的条件下,通过Gantry旋转转速(积分时间的长短)来调节剂量,当穿透比较少的地方时,用快旋转速率,当穿透比较多的地方时,用慢的旋转速率；使用高转速对低吸收的区域进行扫描时,其余区域不曝光,使用低转速对高吸收的区域进行扫描时,其余区域不曝光,本技术不会牺牲图像质量,且不需要使用大电流变化率的高成本球管。(The invention relates to the technical field of medical imaging equipment, in particular to a dose adjusting method for CT variable-speed scanning, which adjusts the dose through Gantry rotating speed (the length of integral time) under the condition of fixed current, wherein when the penetration is less, the rotating speed is high, and when the penetration is more, the rotating speed is low; when the high rotating speed is used for scanning the low-absorption area, the rest areas are not exposed, and when the low rotating speed is used for scanning the high-absorption area, the rest areas are not exposed.)

1. A dose adjusting method for CT variable speed scanning is characterized by comprising the following steps:

s1, scanning the locating plate, collecting the locating plate image, and storing the corresponding scanning parameters;

s2, calculating the dosage needed by the bulb tube at different positions according to the scanning parameters by an automatic exposure control algorithm;

s3, dividing the exposure position into several different areas according to the required dosage, and determining the tube current I needed by the exposure;

dividing the areas with the similar exposure dose into the same exposure so as to determine the required exposure times, and simultaneously calculating the average exposure dose Di required by the corresponding areas in the same exposure;

s4, calculating to obtain the rotating speed required by each exposure, wherein the rotating speed Si = Di/I;

s5, according to the determined exposure times and positions, using corresponding rotating speed to carry out exposure and data acquisition;

and S6, reconstructing data by using the acquired data.

Technical Field

The invention relates to the technical field of medical imaging equipment, in particular to a dose adjusting method for CT variable-speed scanning.

Background

In order to reduce the radiation dose while ensuring image quality, an automatic exposure control technique is used. The basic principle of this technique is to scan at different positions with different tube currents, i.e. scan at positions where the absorption intensity of X-rays is low with a smaller tube current, and vice versa with a larger tube current. The automatic milliamp modulation technology can be divided into two types according to different modulation directions, wherein one type is to modulate along the direction of a patient (Z direction); the other is modulation along the gantry rotation direction (XY direction), and both directions of modulation can also be used simultaneously.

When using the automatic exposure control technique, the tube current is often required to be varied within a relatively large range in order to achieve a good modulation effect. Taking a common spiral scan of the chest and lung as an example, a scan in the anterior-posterior direction (AP) of a patient requires a small tube current, and a scan in the left-right direction (LR) of the patient requires a large tube current. Thus, when XY direction modulation is enabled, it is necessary to have the tube current change from a small value to a large value within the time of 90 ° of gantry rotation. At present, the common rotating speed of the chest and lung spiral scanning is 0.5s, and if the ideal tube current difference required in the AP and LR directions is 400mA, the ideal tube current change rate is 400mA/(500ms/4) =3.2mA/ms, but many types of bulb tubes cannot achieve the high tube current change rate.

In order to solve this problem, a common way is to limit the variation range of the tube current not to exceed the maximum value supported by the tube current, which may cause the actually used current value to have a certain difference from the ideal value and deteriorate the final image quality; another common solution is to use better performing bulbs, which results in increased production costs.

Disclosure of Invention

In order to solve the above problems, an object of the present invention is to provide a dose adjusting method for CT variable-speed scanning, which can adjust the dose by increasing the number of scans and using different rotation speeds in a single scan to avoid the problem that the tube current cannot be changed rapidly.

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

a method for adjusting dosage in CT variable speed scanning, comprising the steps of:

s1, scanning the locating plate, collecting the locating plate image, and storing the corresponding scanning parameters;

s2, calculating the dosage needed by the bulb tube at different positions according to the scanning parameters by an automatic exposure control algorithm;

s3, dividing the exposure position into several different areas according to the required dosage, and determining the tube current I needed by the exposure;

dividing the areas with the similar exposure dose into the same exposure so as to determine the required exposure times, and simultaneously calculating the average exposure dose Di required by the corresponding areas in the same exposure;

s4, calculating to obtain the rotating speed required by each exposure, wherein the rotating speed Si = Di/I;

s5, according to the determined exposure times and positions, using corresponding rotating speed to carry out exposure and data acquisition;

and S6, reconstructing data by using the acquired data.

The invention has the advantages that: under the condition of fixed current, the dosage is regulated through Gantry rotation speed (the length of integration time), when the penetration is less, the rotation speed is fast, when the penetration is more, the rotation speed is slow; when the high rotating speed is used for scanning the low-absorption area, the rest areas are not exposed, and when the low rotating speed is used for scanning the high-absorption area, the rest areas are not exposed.

Drawings

FIG. 1 is a schematic view of an embodiment in which an exposure position is divided into four regions;

fig. 2 is a schematic diagram of dividing the exposure position into eight regions in the embodiment.

Detailed Description

The present invention will be described in further detail with reference to examples.

Using automatic exposure control techniques requires calculating when the tube is in various positions before exposure (includingOrientation position and angular position). For a typical chest lung clinical scan, a smaller dose is required for an anterior-posterior (AP) scan and a larger dose is required for a left-right (LR) scan. For convenience, the dosage is in milliamps per second (mAs).

The dose adjusting method for CT variable-speed scanning comprises the following steps:

s1, scanning the locating plate, collecting the locating plate image, and storing the corresponding scanning parameters;

s2, calculating the dosage needed by the bulb tube at different positions according to the scanning parameters by an automatic exposure control algorithm;

and S3, dividing the exposure position into a plurality of different areas according to the required dose size, dividing the areas with the approximate required dose into the same exposure, thereby determining the required exposure times, and simultaneously calculating the average exposure dose Di required by the corresponding areas in the same exposure. As shown in fig. 1, the exposure area is divided into 4 parts, generally, the doses required for the areas 1 and 3 are close and both small, and the doses required for the areas 2 and 4 are close and both large, and the number of exposures actually required in this division mode is 2, i.e., the first exposure area is 1 or 3, the first exposure dose is the average value of the areas 1 and 3, the second exposure area is 2 or 4, and the second exposure dose is the average value of the areas 2 and 4. To make the dose variation used smoother between different regions, more regions may be divided, as shown in fig. 2. The tube current I required by exposure is determined while the exposure times are determined, the tube current I required by exposure can be determined by a user or determined by algorithm calculation according to the rotating speed range supported by the current CT system, and only the rotating speed system required by each region is required to support;

s4, calculating to obtain the rotating speed needed by each exposure, wherein the rotating speed Si = Di/I, taking fig. 1 as an example, defining the rotating speed of the first exposure as S1 and the rotating speed of the second exposure as S2;

and S5, according to the determined exposure times and positions, carrying out exposure and data acquisition by using corresponding rotating speeds. Taking fig. 1 as an example, the actual exposure process is: during the 1 st scanning, the rotating speed of the rack is S1, when the ball tube is positioned in the area 1 or 3, the exposure is carried out, and when the ball hall is positioned at other positions, the exposure is not carried out; at scan 2, the frame speed isWhen the ball tube is positioned in the area 2 or 4, the exposure is carried out, and when the ball hall is positioned at other positions, the exposure is not carried out;

and S6, reconstructing data by using the acquired data.

The above-mentioned embodiments are merely illustrative of the inventive concept and are not intended to limit the scope of the invention, which is defined by the claims and the insubstantial modifications of the inventive concept can be made without departing from the scope of the invention.