WO2024060869A1

WO2024060869A1 - Method for determining position of collimator slot of ct machine, collimator, and ct machine

Info

Publication number: WO2024060869A1
Application number: PCT/CN2023/112282
Authority: WO
Inventors: Wei Zhou; Yi TIAN; Yang Wang; Chang Qing Teng
Original assignee: Siemens Shanghai Medical Equipment Ltd.
Priority date: 2022-09-20
Filing date: 2023-08-10
Publication date: 2024-03-28
Also published as: CN115813415A

Abstract

The present invention provides a method for determining a position of a collimator slot of a CT machine. The method includes: emitting, by an X-ray source, an X-ray, where the X-ray passes through a hole and forms a plurality of projections on a channel array of a detector; obtaining a first center-of-gravity position G (n,m) of each of the projections in a direction of rows of the channel array; obtaining a second center-of-gravity position G according to the first center-of-gravity positions G(n,m) of all the projections; obtaining a first deviation ΔZ according to a difference between the second center-of-gravity position G and a target position Ztar get, where ΔZ＝G-Ztar get;and determining a position Zoptimal of the collimator slot according to the first deviation ΔZ.The present invention can quickly and precisely determine the position of the collimator slot.

Description

METHOD FOR DETERMINING POSITION OF COLLIMATOR SLOT OF CT MACHINE, COLLIMATOR, AND CT MACHINE

TECHNICAL FIELD

The present invention relates to a method for determining a position of a collimator slot of a CT machine, and in particular, to a method for determining a position of a collimator slot of a CT machine, a collimator, and a CT machine in the field of imaging medicine.

BACKGROUND

In a computer tomography system (a CT machine) , a tube, a collimator, and a detector are arranged on an X-ray path, and an X-ray focus in the tube emits an X-ray that hits the detector through the collimator. To ensure the precision, the tube, the collimator, and the detector need to be in a scan plane perpendicular to a movement direction of bed (a direction Z in FIG. 3) . However, due to the errors in manufacturing and assembly of components, it is very difficult to realize precise positioning. What's more, when a scan mode changes (for example, a voltage and a revolving speed change) or an anode temperature increases, the focus of the tube will move during the scan, causing the collimator to further deviate from a preset target position. Many researchers have been trying to find solutions to the above problem to reduce and avoid the impact on image quality.

Some existing methods aim at the stability of the focus, in which a closed control loop is added to control the focus and stabilize a position of the focus during the scan. This solution inevitably increases the complexity of the system and the costs for development and maintenance.

A more widely used method is to adjust a position of the collimator. A collimator slot is adjusted to an optimal position to ensure that the detector is always symmetrically irradiated by the X-ray from the focus of the tube. However, to find an optimal position of the slot, the collimator needs to move under a plurality of exposures, and some iterative calculations are required. This method is time-consuming and has unstable results.

SUMMARY

The present invention is intended to provide a method for determining a position of a collimator slot of a CT machine, which can quickly and precisely determine the position of the collimator slot.

The present invention provides a method for determining a position of a collimator slot of a CT machine. The CT machine includes an X-ray source configured to emit an X-ray, a collimator, and a detector. The collimator includes a collimator slotted plate. The collimator slotted plate has a collimator slot and a hole. The detector is composed of a channel array having q rows and m columns, and has a preset target position Z_target that needs to be irradiated by the X-ray. The method for determining a position of a collimator slot of a CT machine includes: emitting, by an X-ray source, an X-ray, where the X-ray passes through a hole and forms a plurality of projections on a channel array of a detector; obtaining a first center-of-gravity position G (n, m) of each of the projections in a direction of rows of the channel array; obtaining a second center-of-gravity position G according to the first center-of-gravity positions G (n, m) of all the projections; obtaining a first deviation ΔZ according to a difference between the second center-of-gravity position G and the target position Z_target, where, ΔZ=G -Z_target; and determining a position Z_optimal of the collimator slot according to the first deviation ΔZ.

In the method for determining a position of a collimator slot of a CT machine provided in the present invention, the X-ray is caused to pass through the hole in the collimator slotted plate to form the plurality of projections on the detector, and the first center-of-gravity position of each of the projections in the direction of the rows of the channel array of the detector is determined according to intensity signals of the projections received on the detector, and then the second center-of-gravity position is obtained by averaging all the first center-of-gravity positions, that is, deviations between all the projections and the preset target position may be determined. The position of the collimator slot may be quickly and precisely determined by using the deviations. Then, the collimator slotted plate may be moved according to the position of the collimator slot to adjust the collimator to an optimal position, which effectively compensates for the deviations a focus position in a direction Z in various scanning conditions.

In an exemplary implementation of the method for determining a position of a collimator slot of a CT machine, in the step of obtaining the first center-of-gravity position G (n, m) of each of the projections in the direction of the rows of the channel array, the first center-of-gravity position G (n, m) is obtained through the following formula: where n is the number of the projections formed on the channel array by the X-ray passing through the hole and hitting the detector, s1 is background noise of a detector signal in a current scanning condition, and p_m, q (n) is light intensity of the X-ray received by the detector.

In an exemplary implementation of the method for determining a position of a collimator slot of a CT machine, in the step of obtaining the second center-of-gravity position G according to the first center-of-gravity positions G (n, m) of all the projections, the second center-of-gravity position is obtained through the following formula: G=∑_n (∑_mG (n, m) /m) /n. The second center-of-gravity position G is an average of all the first center-of-gravity positions G (n, m) .

In an exemplary implementation of the method for determining a position of a collimator slot of a CT machine, in the step of determining the position Z_optimal of the collimator slot according to the first deviation ΔZ, a hole position deviation ΔP is first determined according to the first deviation ΔZ, and then the position Z_optimal of the collimator slot is determined according to the hole position deviation ΔP. The hole position deviation ΔP is obtained through the following formula: where d_FC is a distance from the X-ray source to the slotted plate, d_FD is a distance from the X-ray source to the detector, and z_pitch is a distance between adjacent channels of the detector in the direction in which the rows of are arranged. The hole position deviation may be determined according to the obtained deviation between the center-of-gravity position of the projection on the detector and the target position, that is, the first deviation ΔZ, as well as a geometric relationship among the tube, the collimator, and the detector, and then a deviation of the collimator slot may be determined.

In an exemplary implementation of the method for determining a position of a collimator slot of a CT machine, in the step of determining the position Z_optimal of the collimator slot according to the hole position deviation ΔP, the position Z_optimal of the collimator slot is determined according to the hole position deviation ΔP through the following formula: Z_optimal=Z_initial+ΔP+D, where Z_initial is an initial position of the collimator slot, and D is a distance between a center of the hole and a centerline of the collimator slot. The position of the collimator slot, that is, the optimal position of the collimator in the current scanning condition may be determined according to the deviation of the collimator slot, an original position of the collimator, and a geometric relationship between the center of the hole and the collimator slot.

The present invention is further intended to provide a collimator for a CT machine. The collimator includes a collimator slotted plate. The collimator slotted plate has a collimator slot and a hole. The above hole-based scanning method is used to determine the optimal position of the slot, and the collimator slot allows the X-ray to pass through during scan of a patient on the CT machine.

The present invention further provides a CT machine. The CT machine includes an X-ray source configured to emit an X-ray, the above collimator, and a detector. The detector is composed of a channel array having m columns and q rows, and has a preset target position Z_target that needs to be irradiated by the X-ray through the collimator. According to the CT machine provided in the present invention, the position of the collimator slot is quickly and precisely determined, which effectively compensates for the deviation of a focus in various scanning conditions, thereby ensuring the image quality to the largest extent.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely exemplary descriptions and explanations and do not limit the scope of the present invention.

FIG. 1 is a schematic diagram of an exemplary implementation of a CT machine according to the present invention.

FIG. 2 is a schematic flowchart of a method for determining a position of a collimator slot of a CT machine according to an exemplary implementation of the present invention.

FIG. 3 is a schematic diagram of a collimator slotted plate in a plane formed by directions X and Z of a coordinate system shown in FIG. 1.

Reference numerals:

10 X-ray source

30 Detector

24 Collimator slot

26 Hole

DETAILED DESCRIPTION

For clearer understanding of the technical features, objectives, and effects of the present invention, specific implementations of the present invention are described with reference to the drawings. The same labels in the figures represent components with the same structure or similar structures but the same function.

Herein, "exemplary" means "being used as an instance, example, or description" , and any illustration or implementation described as "exemplary" herein should not be interpreted as a more preferred or advantageous technical solution.

To make the drawings concise, only parts related to the present invention are schematically shown in the figures, which do not represent the actual structure of the product.

Herein, "first" , "second" , and the like do not indicate the significance or order thereof, but indicate their differences and facilitate the description of the document.

FIG. 1 is a schematic diagram of an exemplary implementation of a CT machine according to the present invention. The CT machine uses the method for determining a position of a collimator slot of the present invention.

The CT machine includes an X-ray source 10, a collimator, and a detector 30. An X-ray may be emitted through the X-ray source 10. The collimator includes a collimator slotted plate 20.The collimator slotted plate has a collimator slot 24 and a hole 26. The detector is composed of a channel array having m columns and q rows, as shown in FIG. 1. In an exemplary implementation, the detector has q rows of channels, that is, a first row (Row (1) ) to a qth row (Row (q) ) arranged from left to right in FIG. 1. Each row has m channels. The detector 30 has a preset target position Z_target that needs to be irradiated by the X-ray. The detector 30 receives the X-ray emitted by the X-ray source 10, and the X-ray forms projections on the detector 30. Positions of these projections may be represented by light intensity of the projections received by the detector. A three-dimensional rectangular coordinate system is arranged in the CT machine. A direction Z is the direction in which rows of the channel array of the detector are arranged. As shown in the figure, the channel array includes channels arranged from the first row to the qth row in the direction Z. A direction Y is a direction in which a shortest distance exists between the X-ray source 10 and the detector 30. A direction X is perpendicular to the directions Y and Z. During scan of the CT machine, the X-ray passes through the hole and forms a plurality of projections on the channel array of the detector. Positions of these projections are represented by light intensity of the projections received by the channel array of the detector.

As shown in FIG. 2, the method for determining a position of a collimator slot of a CT machine includes the following steps:

S1: Emit an X-ray through an X-ray source, where the X-ray passes through a hole and hits a detector, and forms a plurality of projections on a channel array.

S2: Obtain a first center-of-gravity position G (n, m) of each of the projections in a direction in which rows of the channel array are arranged. In an exemplary implementation, the first center-of-gravity position G (n, m) is obtained according to a sinogram of scanning intensity of each of the projections in the direction in which the rows of the channel array are arranged through the following formula:

m is the number of columns in the channel array of the detector, q is the number of rows in the channel array of the detector, n is the number of the projections formed on the channel array by the X-ray passing through the hole and hitting the detector, and s1 is background noise of a detector signal in a current scanning condition. The first center-of-gravity position G (n, m) may be represented by position coordinates of the projection in the direction of the rows of the channel array. s1 is the background noise of the detector signal in the current scanning condition. If p_m, q (n) ≥s1, it indicates that the position of the detector array is hit by the X-ray passing through the hole. The signal data may be used for calculation. If p_m, q (n) ＜s1, it indicates that the position is not hit by the X-ray passing through the hole.

S3: Obtain a second center-of-gravity position G according to the first center-of-gravity positions G (n, m) of all the projections. In an exemplary implementation, all the first center-of-gravity positions G (n, m) are averaged to obtain G:

G=∑_n (∑_mG (n, m) /m) /n.

S4: Obtain a first deviation ΔZ according to a difference between the second center-of-gravity position G and the target position Z_target, where ΔZ=G -Z_target. In an exemplary implementation, a hole position deviation ΔP is determined according to the first deviation ΔZ. The hole position deviation ΔP is determined through the following formula:

where f_FC is a distance from the X-ray source to the slotted plate, d_FD is a distance from the X-ray source to the detector, and z_pitch is a distance between adjacent channels of the detector in the direction of the rows.

S5: Obtain the position Z_optimal of the collimator slot according to the hole position deviation ΔP. In an exemplary implementation, the position Z_optimal of the collimator slot is determined according to the hole position deviation ΔP through the following formula:

Z_optimal=Z_initial+ΔP+D, where Z_initial is an initial position of the collimator slot, and D is a distance between a center of the hole and a centerline of the collimator slot. The determined position Z_optimal of the collimator slot is the optimal collimator slot position in the current scanning mode.

FIG. 3 is a schematic diagram of a collimator slotted plate in a plane formed by directions X and Z of a coordinate system shown in FIG. 1. The collimator slotted plate 20 has a collimator slot 24 and a hole 26, and a distance D exists between a center of the hole 26 and a centerline of the collimator slot 24.

According to the method for determining a position of a collimator slot of a CT machine provided in the present invention, the collimator may be adjusted to an optimal position, which effectively compensates for the movement of a focus in the direction Z in various scanning conditions, thereby ensuring the image quality to a larger extent.

It should be understood that although the description is illustrated according to each embodiment, each embodiment does not necessarily include an independent technical solution. The illustration of the specification is merely for clarity. A person skilled in the art should consider the description as a whole, and the technical solutions in the embodiments may be properly combined to form other implementations that a person skilled in the art can understand.

The series of detailed descriptions listed above are merely specific illustrations of the feasible embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent implementations or changes made without departing from the spirit of the present invention, such as the combination, segmentation, or repetition of features, should be included in the protection scope of the present invention.

Claims

A method for determining a position of a collimator slot of a CT machine, wherein the CT machine comprises an X-ray source configured to emit an X-ray, a collimator, and a detector, the collimator comprises a collimator slotted plate, the collimator slotted plate has a collimator slot and a hole, and the detector is composed of a channel array having q rows and m columns, and has a preset target position Z_target; that needs to be irradiated by the X-ray, the method for determining a position of a collimator slot of a CT machine comprising:

emitting, by the X-ray source, an X-ray, wherein the X-ray passes through the hole and hits the detector, and forms a plurality of projections on the channel array;

obtaining a first center-of-gravity position G (n, m) of each of the projections in a direction in which rows of the channel array are arranged;

obtaining a second center-of-gravity position G according to the first center-of-gravity positions G (n, m) of all the projections;

obtaining a first deviation ΔZ according to a difference between the second center-of-gravity position G and the target position Z_target, wherein ΔZ=G-Z_target; and

determining a position Z_optimal of the collimator slot according to the first deviation ΔZ.
The method for determining a position of a collimator slot of a CT machine according to claim 1, wherein in the step of obtaining the first center-of-gravity position G (n, m) of each of the projections in the direction in which the rows of the channel array are arranged, the first center-of-gravity position G (n, m) is obtained through the following formula:

wherein n is the number of the projections formed on the channel array by the X-ray passing through the hole and hitting the detector, s1 is background noise of a detector signal in a current scanning condition, and p_m, q (n) is light intensity of the X-ray received by the detector.
The method for determining a position of a collimator slot of a CT machine according to claim 1, wherein in the step of obtaining the second center-of-gravity position G according to the first center-of-gravity positions G (n, m) of all the projections, the second center-of-gravity position is obtained through the following formula: G=∑_n (∑_mG (n, m) /m) /n.
The method for determining a position of a collimator slot of a CT machine according to claim 1, wherein in the step of determining the position Z_optimal of the collimator slot according to the first deviation ΔZ, a hole position deviation ΔP is first determined according to the first deviation ΔZ, and the hole position deviation ΔP is obtained through the following formula:

wherein d_FC is a distance from the X-ray source to the slotted plate, d_FD is a distance from the X-ray source to the detector, and z_pitch is a distance between adjacent channels of the detector in the direction in which the rows of the channel array are arranged; and

then the position Z_optimal of the collimator slot is determined according to the hole position deviation ΔP.
The method for determining a position of a collimator slot of a CT machine according to claim 4, wherein in the step of determining the position Z_optimal of the collimator slot according to the hole position deviation ΔP, the position Z_optimal of the collimator slot is determined according to the hole position deviation ΔP through the following formula:

Z_optimal=Z_initial+ΔP+D, wherein Z_initial is an initial position of the collimator slot, and D is a distance between a center of the hole and a centerline of the collimator slot.
A collimator for a CT machine, wherein the collimator comprises a collimator slotted plate, and the collimator slotted plate comprises:

a collimator slot, allowing an X-ray to pass through during scan of the CT machine, and

a hole, configured to determine a position of the collimator slot by using the method according to any of claims 1 to 5.
A CT machine, comprising:

an X-ray source configured to emit an X-ray;

the collimator according to claim 6; and

a detector, composed of a channel array having m columns and q rows, and having a preset target position Z_target that needs to be irradiated by the X-ray through the collimator.