CN102397078B - X-ray computerized tomography system and method - Google Patents

Abstract

The invention discloses an X-ray computed tomography system, which is used for partial scanning of an object to be inspected. The system includes an intermediate angle calculation module, a reconstruction angle calculation module and a scanner. The size and center coordinates of the cross-section of the field of view to calculate the intermediate angle, and transmit the intermediate angle to the reconstruction angle calculation module; the reconstruction angle calculation module is used to add 180 degrees to the intermediate angle to obtain the reconstruction angle, and transmit the reconstructed angle to the scanner; the scanner is used to partially scan the object to be inspected according to the reconstructed angle. The invention also discloses an X-ray computed tomography scanning method. By adopting the system and method of the invention, the scanning time can be shortened, the time resolution can be improved, and the radiation dose received by patients can be reduced.

Description

An X-ray computed tomography system and method

technical field

The invention relates to the field of medical imaging, in particular to an X-ray computed tomography system and method.

Background technique

In X-ray computed tomography (Computed Tomography, CT), in order to obtain high temporal resolution, dual-source CT and partial scanning are often used. Partial scans are between half scans and full scans, and are advantageous when scanning organs or tissues in motion (such as the heart), because the shorter the scan time, the less likely the object to be examined is to move during the imaging process, thereby reducing The impact of motion artifacts on image quality was investigated.

其中T为X射线管1旋转一圈，即360°所需的时间。这种固定的重建角度会导致对较小的待检对象进行断层扫描时，探测器(如附图标记6所示)实际获取的投影数据量多于重建图像所需的最少投影数据量，这就增加了不必要的投影数据，还增加了扫描时间，降低了时间分辨率。Part of the scan has a rotational scan angle of less than 360°. At present, in the partial scan of the CT system, the scan time is usually determined according to a fixed reconstruction angle, as shown in FIG. 1 , which is a schematic diagram of scanning the Field of Measurement (FOM) with a fixed reconstruction angle in the partial CT scan. FOM is defined as the cross-sectional area where the object to be inspected is fully irradiated when the X-ray tube rotates 360 degrees, which determines the scanning dose directly applied to the object to be inspected and the size of the X-ray irradiation area. In the figure, the X-ray tube 1 rotates clockwise from the initial position 7 to the end position 5. During this process, the rotation angle γ of the X-ray tube 1 is defined as the reconstruction angle 3, and the angle β of the X-ray fan beam emitted by the X-ray tube 1 is defined as The exposure angle 2 is usually a fixed angle between 30 degrees and 60 degrees, and the circular area 4 is the FOM where the object to be inspected is located. During the clockwise rotation of the X-ray tube 1 from the initial position 7 to the end position 5, the X-ray tube 1 only rotates by an angle γ, and the projection data within the angle range [0, γ] is required for image reconstruction in partial scans The minimum amount of data, the missing projection data within the angle range of [γ, 360°] can be compensated by adding a higher weight of the projection data. There are existing compensation methods in the prior art, which will not be repeated here. In a conventional partial scan, one of the boundary radii of the X-ray fan beam with a central angle of β at position 7 must coincide with one of the boundary radii of the X-ray fan beam with a central angle of β at position 5, as shown in the figure The coincidence of solid and dashed lines is shown. The reconstruction angle γ is usually defined as the sum of the half-rotation angle 180 degrees and the exposure angle β, that is, γ=180°+β; part of the scanning time

Where T is the time required for the X-ray tube 1 to rotate one circle, that is, 360°. This fixed reconstruction angle will lead to the fact that when a smaller object to be inspected is tomographically scanned, the amount of projection data actually acquired by the detector (as shown in reference numeral 6) is more than the minimum amount of projection data required for image reconstruction, which results in This increases unnecessary projection data, increases scan time, and reduces time resolution.

Therefore, in order to shorten the scan time and achieve clear imaging of moving organs or tissues, the following methods are often used to improve time resolution: First, further shorten the rotation scan time on the basis of existing technologies, such as improving the algorithm of the CT system etc. The second is to develop dual-source CT. The former usually needs to greatly change the existing algorithm of the CT system, and the latter needs to change the hardware equipment of the CT system. Both are difficult to implement and costly.

Contents of the invention

In view of this, the present invention proposes an X-ray computed tomography scanning system and method to shorten scanning time and improve time resolution.

The present invention provides an X-ray computed tomography system, which is used for partial scanning of an object to be inspected. The system includes: an intermediate angle calculation component, a reconstruction angle calculation component, and a scanner, wherein the intermediate angle calculation component is used for The size and center coordinates of the visual field cross-section of the object to be checked are used to calculate the intermediate angle, and the intermediate angle is transmitted to the reconstruction angle calculation component; the reconstruction angle calculation component is used to add 180 degrees to the intermediate angle The reconstruction angle is obtained, and the reconstruction angle is transmitted to the scanner; the scanner is configured to partially scan the object to be inspected according to the reconstruction angle.

The intermediate angle calculation component includes: a field of view cross-section acquisition module, a measurement field radius calculation module, and an intermediate angle calculation module. The field of view can be determined according to the front and rear positioning images and the lateral positioning images, and then the size and center coordinates of any cross-section of the field of view can be obtained; The size and center coordinates of the cross-section; and the size and center coordinates are sent to the measurement domain radius calculation module; the measurement domain radius calculation module is used to calculate the size and center coordinates of any visual field cross-section Calculate a measurement field radius; or calculate a plurality of measurement field radii according to the size and center coordinates of each visual field cross-section; and transmit the measurement field radius to the intermediate angle calculation module; the intermediate angle calculation A module for calculating the intermediate angle according to the radius of the one measurement field when the frame is not tilted; or obtaining a plurality of secondary intermediate angles according to the plurality of radiuses of the measurement field when the frame is tilted, and taking the The maximum value of the second intermediate angles is used as the intermediate angle; and the intermediate angle is sent to the reconstruction angle calculation component.

The visual field cross-section acquisition module is further configured to perform eccentric reconstruction on any or each visual field cross-section before acquiring the central coordinates.

Further, the system also includes an exposure angle control component, configured to receive the intermediate angle from the intermediate angle calculation component, and control the exposure angle to the intermediate angle so as to control the exposure angle to the intermediate angle for the object to be inspected Do a partial scan.

The present invention also provides an X-ray computed tomography method, comprising the following steps: calculating an intermediate angle according to the size of the cross-section of the field of view of the object to be inspected and the central coordinates; adding 180 degrees to the intermediate angle to obtain the reconstruction angle; A partial scan is performed on the object to be inspected according to the reconstruction angle.

According to one aspect of the present invention, the calculation of the intermediate angle includes: when the rack is not tilted, determine the field of view according to the anteroposterior and lateral positioning images of the object to be inspected, and then obtain the size and center of any visual field cross-section coordinates, and according to the size and center coordinates, calculate a measurement field radius of any field of view cross-section, and then calculate the intermediate angle according to the measurement field radius.

According to another aspect of the present invention, the calculation of the intermediate angle includes: when the rack is tilted, the field of view is determined according to the anteroposterior and lateral positioning images of the object to be inspected, and then the size and center coordinates of each visual field cross-section are obtained , and according to the size and center coordinates, calculate the plurality of measurement domain radii of the cross-sections of the field of view, and then calculate the complex number of secondary intermediate angles according to the measurement domain radius, and take the maximum value of the secondary intermediate angles as the intermediate angle.

The obtaining the central coordinates of the cross-section of the field of view further includes: performing eccentric reconstruction on the cross-section of the field of view before obtaining the central coordinates.

The measurement field radius is calculated according to the following formula:

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout></span><figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \{</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span>$

Where r is the radius of the measurement field, L _FOV is the larger of the width and length of the field of view cross-section, max is a function for finding the maximum value, x_0 is the abscissa of the center of the field of view cross-section, and y_0 is the center of the field of view cross-section ordinate.

Calculate the intermediate angle according to the following formula:

$\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; dis</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; FC</span>}}<span\; class="notranslate">\; )</span>$

Wherein, α is the intermediate angle, dis_FC is the distance from the focal point of the X-ray tube to the center of the CT gantry, and r is the radius of the measurement field.

Calculate the secondary intermediate angle according to the following formula:

${\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; dis</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; FC</span>}}<span\; class="notranslate">\; )</span>$

Among them, i is the number of cross-sections of the field of view, α _i is the secondary intermediate angle of the cross-section of the i-th field of view, dis_FC is the distance from the focal point of the X-ray tube to the center of the CT gantry, and r _i is the cross-section of the i-th field of view The measurement domain radius of .

Further, the method includes: controlling the exposure angle to the intermediate angle to partially scan the object to be inspected.

Since the present invention proposes a reconstruction angle that is not greater than the fixed reconstruction angle γ and can be adjusted according to the size of the cross-section of the field of view, this shortens the scan time, reduces the X-ray dose received by the patient, and improves the time resolution at the same time. Suitable for scanning moving organs or tissues such as the heart. Moreover, the present invention does not change the existing hardware equipment of the CT system, and does not make a lot of improvements to the existing algorithms of the CT system. It is easy to implement based on the existing CT system and reduces the cost.

Description of drawings

FIG. 1 is a schematic diagram of scanning the FOM with a fixed reconstruction angle in a conventional partial CT scan.

FIG. 2 is a schematic diagram of scanning FOM using the system and method of the present invention in partial CT scanning.

FIG. 3 is a schematic diagram of the components of the CT scanning system of the present invention.

Fig. 4 is a schematic diagram of the composition of the intermediate angle calculation component of the present invention.

Fig. 5 is a flow chart of the CT scanning method of the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the following examples are given to further describe the present invention in detail.

In the present invention, the object to be inspected may be a certain area of the human body, or a certain organ or tissue of the human body. The scanning direction is the direction in which the examination bed enters and exits the rack in the CT system, usually the z direction.

The CT scanning system of the present invention is used to partially scan the object to be examined. As shown in FIG. 3 , it is a schematic diagram of components of the CT scanning system of the present invention, including: an intermediate angle calculation component 20, a reconstruction angle calculation component 21 and a scanner 22, wherein, The intermediate angle calculation component 20 is used to calculate the intermediate angle according to the size and center coordinates of the field of view (Field of View, FOV) cross section of the object to be checked, and transmit the intermediate angle to the reconstruction angle calculation component 21; reconstruction angle calculation The component 21 is configured to add 180 degrees to the intermediate angle to obtain the reconstruction angle, and transmit the reconstruction angle to the scanner 22; the scanner 22 is configured to partially scan the object to be inspected according to the reconstruction angle.

Fig. 4 is a schematic diagram of the composition of the intermediate angle calculation component of the present invention. The intermediate angle calculation component 21 in FIG. 4 includes: a field of view cross-section acquisition module 201 , a measurement field radius calculation module 202 and an intermediate angle calculation module 203 . in:

The field of view cross-section acquisition module 201 is used to determine the field of view according to the anteroposterior and lateral positioning images of the object to be inspected when the rack is not tilted, and then obtain the size and center coordinates of any visual field cross-section; or When the frame is tilted, the field of view is determined according to the anteroposterior positioning image and the lateral positioning image of the object to be inspected, and then the size and center coordinates of each field of view cross-section are obtained; and the size and center coordinates are transmitted to the measurement field radius calculation module 202.

Before the CT equipment starts serial scanning or helical scanning, it is usually necessary to scan one or two positioning images of the patient to determine the position and size of the object to be inspected, so as to obtain the range of the CT scan. The anterior-posterior positioning image and lateral positioning image of the object to be inspected can be obtained in the following way: when the human body is lying flat, the X-ray tube is irradiated at 90 degrees or 270 degrees (that is, the vertical direction) to obtain the anteroposterior positioning image , the X-ray tube irradiates the object to be inspected at 0 degrees or 180 degrees (ie, the horizontal direction) to obtain a lateral positioning image. Based on the two positioning images, the doctor determines the field of view surrounding the object to be inspected (ie, the aforementioned FOV), which is usually a rectangular area whose size can be set according to the doctor's experience. Doctors generally set the FOV relatively large so as to completely cover the object to be inspected, but this increases the X-ray irradiation received by the area around the object to be inspected to a certain extent. Although the X-ray dose received by the human body is still within the safe dose range in this case, we always hope to further reduce the X-ray dose received by the area around the object to be inspected without affecting the image quality. Therefore, it is hoped that the doctor can adjust the FOV according to the different sizes of the objects to be inspected, such as using the contour recognition technology of the CT system to obtain the size of the object to be inspected, and use it as the size of the FOV, which reduces the X received by the area around the object to be inspected. radiation exposure. In addition, the cross-section of FOV in the present invention is a rectangle, and the circumscribed circle of the rectangle is FOM, so FOV<FOM, this is because in principle the object to be inspected must be measured by each slice reading included in the reconstruction area, so only Correct reconstruction can only be performed when the object to be inspected is within the FOM.

After obtaining the cross-section of the field of view, the size and center coordinates of the cross-section of the field of view can be obtained. Further, the field of view cross-section acquisition module 201 of the present invention is further configured to perform off-center reconstruction on any or each field of view cross-section before acquiring the central coordinates.

Due to the different body shapes of different patients, the positions and sizes of different organs or tissues of the same patient are different. When performing image reconstruction on the subject to be examined, if the patient is large in size and/or the lesion is on one side of the patient's body, the hospital bed will be in the vertical direction. If the center of the object to be inspected cannot be reached after lifting and/or translating in the horizontal direction, eccentric reconstruction is required to obtain the distance x_0 of the abscissa of the center of the FOV cross-section from the center of the rack and the distance y_0 of the vertical coordinate from the center of the rack . The vertical lifting direction of the hospital bed is the y direction, the horizontal direction of the hospital bed entering and exiting the frame is the z direction, the z direction is perpendicular to the y direction, and the direction orthogonal to both the y direction and the z direction is the x direction.

According to the first embodiment of the present invention, when the gantry is not tilted during the entire scanning process, the size of each FOV cross-section and the center coordinates (x_0, y_0) after eccentric reconstruction are the same, and only any cross-section is required The size and eccentric reconstruction coordinates (x_0, y_0) are enough.

According to the second embodiment of the present invention, if the frame is tilted according to the needs of the scanning area during the scanning process, for example, when scanning the head, it is necessary to tilt the frame to avoid scanning eyes, then the FOV is no longer a rectangle but Parallelogram or rhombus, so for different FOV cross-sections, the distance of the abscissa of each cross-section center from the center of the frame and the distance of the ordinate from the center of the frame are no longer fixed, but according to each FOV cross-section Change, set it to ( _xi _0, y _i _0), where i is the number of FOV cross-sections.

The measurement field radius calculation module 202 is used to calculate a measurement field radius according to the size and central coordinates of any of the visual field cross sections; or to calculate a plurality of measurement fields according to the size and central coordinates of each visual field cross section Radius; and transmit the measurement domain radius to the intermediate angle calculation module 203.

According to the first embodiment of the present invention, when the gantry is not tilted during the whole scanning process, the FOM radius r where any FOV cross section is located can be calculated according to formula (1).

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout></span><figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \{</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Wherein max is a function for finding the maximum value, r is the radius 13 of FOM (as shown in the circular area 9 in Figure 2), and L _FOV is the larger one in the width and length of the FOV cross section, and the FOM of the present invention can Completely cover the object to be inspected.

According to the second embodiment of the present invention, if the gantry is tilted according to the needs of the scanning area during the scanning process, the radius r _i of the FOM where each FOV cross-section is located is calculated according to formula (2).

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout></span><figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \{</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, i is the number of FOV cross-sections, x _{i_0} is the distance from the abscissa of each cross-section center of FOV after eccentric reconstruction to the frame center, and y _{i_0} is the ordinate of each cross-section center of FOV after eccentric reconstruction The distance from the center of the rack.

The intermediate angle calculation module 203 is used to calculate the intermediate angle α according to the radius r of the measurement field when the frame is not tilted; or to obtain a complex number according to the plurality of radius r _i of the measurement field when the frame is tilted. secondary intermediate angles α _i , and take the maximum value of the secondary intermediate angles as the intermediate angle α, and transmit the intermediate angles to the reconstruction angle calculation component 21.

FIG. 2 is a schematic diagram of scanning FOM using the system and method of the present invention in partial CT scanning.

According to the first embodiment of the present invention, if the gantry does not tilt during the whole scanning process, the intermediate angle α is calculated according to the formula (3) according to the radius r of any FOM.

$\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; dis</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; FC</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

As shown in FIG. 2 , dis_FC is the distance 11 from the focal point of the X-ray tube 1 to the center of the CT gantry, and α is an intermediate angle, as shown in the X-ray fan beam angle 10 in FIG. 2 .

According to the second embodiment of the present invention, if the gantry is tilted according to the needs of the scanning area during the scanning process, the corresponding secondary intermediate angle α _i is calculated according to the following formula (4) according to the radius r _i of the FOM where each FOV cross section is located .

${\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; dis</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; FC</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Next, according to α _i and the slice thickness (Slicethickness, SL) of the CT system, the intermediate angle α is calculated according to the following formula (5).

α=max{α _n ,...,α _n+X } (5)

Among them, n is the coordinate value in the z direction, the unit is mm, the positive integer X satisfies n≤SL<n+X, and the center position of the layer (Slice Position, SP) satisfies n≤SP-0.5×SL<n+1.

According to formula (5), it can be concluded that if the layer thickness is the entire FOV, the maximum value of the secondary intermediate angles of all cross-sections of the FOV is taken as the intermediate angle of the entire FOV; The maximum value of the secondary intermediate angles of each cross-section is used as the intermediate angle of this part of the FOV area.

The reconstruction angle calculation component 21 is used to add 180 degrees to the intermediate angle α to obtain the reconstruction angle And transmit the reconstruction angle to the scanner 22 .

According to the intermediate angle α, the reconstruction angle is calculated according to formula (6)

也随着FOV横截面的大小而变化。这里的

为进行图像重建所需的最小重建角度。Since the reconstruction angle differs only by 180 degrees from the intermediate angle, the

Also varies with the size of the FOV cross section. here

Minimum reconstruction angle required for image reconstruction.

对待检对象进行部分扫描。Scanner 22 for reconstructing angles according to

Partially scan the object to be inspected.

Further, the CT system also includes an exposure angle control component 23, which is used to receive the intermediate angle α from the intermediate angle calculation component 20, and control the exposure angle to the intermediate angle α to partially scan the object to be inspected, thereby further reducing the exposure around the FOM. The irradiation of the area and the X-ray dose received by the human body.

In addition, the present invention also provides an X-ray computed tomography method, as shown in Figure 5, comprising the following steps:

Step 301, determine the field of view according to the anteroposterior and lateral positioning images of the object to be inspected, and obtain the size and center coordinates of any visual field cross-section when the rack is not tilted; or obtain each visual field when the rack is tilted The size and center coordinates of the cross section.

Preferably, said obtaining the central coordinates of the visual field cross-section further comprises: performing eccentric reconstruction on the visual field cross-section before obtaining the central coordinates.

This has been specifically described in the field of view cross-section acquisition module 201, and will not be repeated here.

Step 302, when the rack is tilted, calculate a measurement field radius according to the size and center coordinates of any cross-section of the field of view; Computes the complex number of measurement domain radii.

According to the first embodiment of the present invention, when the gantry is not tilted during the whole scanning process, the radius r of the FOM where any FOV cross-section is located is calculated according to formula (1).

According to the second embodiment of the present invention, if the gantry is tilted according to the needs of the scanning area during the scanning process, the radius r _i of the FOM where each FOV cross-section is located is calculated according to formula (2).

Step 303, when the rack is not tilted, calculate the intermediate angle α according to the one measurement domain radius r; or when the rack is tilted, obtain a plurality of secondary intermediate angles α according to the plurality of measurement domain radii r _{i i} , and take the maximum value of the secondary intermediate angle as the intermediate angle α.

According to the first embodiment of the present invention, when the gantry is not tilted during the whole scanning process, the intermediate angle α is calculated according to formula (3).

According to the second embodiment of the present invention, if the gantry is tilted according to the needs of the scanning area during the scanning process, the intermediate angle α is calculated according to equations (4)-(5).

Step 304, adding 180 degrees to the intermediate angle to obtain the reconstruction angle.

The reconstruction angle can be calculated according to formula (6).

Step 305, according to the reconstruction angle Partially scan the object to be inspected.

Further, the CT scanning method of the present invention further includes step 306, controlling the exposure angle to the intermediate angle to perform partial scanning of the object to be inspected. This point has been specifically described in the exposure angle control component 23, and will not be repeated here.

所以缩短了扫描时间。举例而言，若固定重建角度γ为240°，X射线管焦点到机架旋转中心的距离dis_FC是535mm，X射线管焦点到探测器的距离约是940mm，X射线管旋转一周360°的最短时间是0.5s，则根据固定重建角度得到的部分扫描时间约是0.33s。而根据本发明的系统和方法，若L_FOV为250mm，机架不倾斜时FOV横截面的中心坐标是(0，-5)，则重建角度

约为220°，这样部分扫描的时间仅为0.3s，比固定重建角度的扫描时间0.33s减少了8.3％，这就更加有利于扫描心脏等运动器官或组织。Using the CT scanning system and method of the present invention to partially scan the object to be inspected can shorten the scanning time, improve the time resolution, and reduce the X-ray dose received by the patient. As shown in Figure 2, although the irradiating FOM 9 is still at a fixed exposure angle β, the X-ray tube 1 only needs to rotate clockwise from position 7 by the angle It is enough to reach position 8 instead of rotating to position 5 as in Figure 1, since the reconstruction angle is reduced

Therefore, the scanning time is shortened. For example, if the fixed reconstruction angle γ is 240°, the distance dis_FC from the X-ray tube focus to the gantry rotation center is 535mm, the distance from the X-ray tube focus to the detector is about 940mm, and the shortest time for the X-ray tube to rotate 360° once is The time is 0.5s, and the partial scan time obtained based on the fixed reconstruction angle is about 0.33s. And according to the system and method of the present invention, if the L _FOV is 250mm, and the center coordinate of the FOV cross section is (0,-5) when the rack is not tilted, then the reconstruction angle

It is about 220°, so the partial scan time is only 0.3s, which is 8.3% less than the 0.33s scan time with a fixed reconstruction angle, which is more conducive to scanning moving organs or tissues such as the heart.

In addition, in Fig. 2, the two boundary radii of the X-ray fan beam at position 7 and the two boundary radii of the X-ray fan beam at position 8 all cross, as shown in the intersection of dotted line and solid line, and It is not necessary to have a line of boundary radii coincident as required by conventional partial scanning in FIG. 1 .

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. an X-ray computerized tomography system, for object to be checked is carried out to part scanning, this system comprises: intermediate angle computation module, rebuild angle calculation assembly and scanning device, wherein,

Described intermediate angle computation module, for calculating intermediate angle according to size and the centre coordinate of the visual field cross section of object to be checked, and sends described intermediate angle to described reconstruction angle calculation assembly;

Described reconstruction angle calculation assembly, for described intermediate angle being added to 180 degree obtain rebuilding angle, and sends described reconstruction angle to described scanning device;

Described scanning device, for carrying out part scanning according to described reconstruction angle to object to be checked;

Described intermediate angle computation module comprises: visual field cross section acquisition module, measurement territory radius calculation module and intermediate angle computing module,

Described visual field cross section acquisition module, for when frame does not tilt, determines the visual field according to anteroposterior position location picture and the side locating image of object to be checked, and then obtains size and the centre coordinate of arbitrary visual field cross section; Or when rack inclining, according to anteroposterior position location picture and the side locating image of object to be checked, determine the visual field, and then obtain size and the centre coordinate of each visual field cross section; And send described size and centre coordinate to described measurement territory radius calculation module;

Described measurement territory radius calculation module, for calculating a measurement territory radius according to the size of described arbitrary visual field cross section and centre coordinate; Or calculate a plurality of measurements territory radius according to the size of described each visual field cross section and centre coordinate; And send described measurement territory radius to described intermediate angle computing module;

Described intermediate angle computing module, for when frame does not tilt, measures territory radius according to described one and calculates described intermediate angle; Or when rack inclining, according to described a plurality of measurements territory radius, obtain intermediate angle a plurality of times, and the maximum of getting described intermediate angle is as described intermediate angle; And send described intermediate angle to described reconstruction angle calculation assembly.

2. system according to claim 1, is characterized in that, described visual field cross section acquisition module was further used for before obtaining described centre coordinate, and described arbitrary visual field cross section or each visual field cross section are carried out to bias reconstruction.

3. system according to claim 1, it is characterized in that, described system further comprises: exposure angle Control Component, for receiving the described intermediate angle of described intermediate angle computing module, exposure angle is controlled as described intermediate angle is to carry out part scanning to object to be checked.

4. an X ray computer tomoscan method, comprises the steps:

According to size and the centre coordinate of the visual field cross section of object to be checked, calculate intermediate angle;

Described intermediate angle is added to 180 degree obtain rebuilding angle;

According to described reconstruction angle, object to be checked is carried out to part scanning;

Described calculating intermediate angle comprises:

When frame does not tilt, according to anteroposterior position location picture and the side locating image of object to be checked, determine the visual field, and then obtain size and the centre coordinate of arbitrary visual field cross section, and according to described size and centre coordinate, measure territory radius for one that calculates described arbitrary visual field cross section, then according to intermediate angle described in the radius calculation of described measurement territory.

5. method according to claim 4, is characterized in that, according to following formula, calculates intermediate angle:

$\mathrm{\&alpha;}=2\&times;\arcsin \left(\frac{r}{\mathrm{dis}\_\mathrm{FC}}\right)$

Wherein, α is described intermediate angle, and dis_FC is the distance from the focus of X-ray tube to CT frame central, and r is the radius in described measurement territory.

6. an X ray computer tomoscan method, comprises the steps:

According to size and the centre coordinate of the visual field cross section of object to be checked, calculate intermediate angle;

Described intermediate angle is added to 180 degree obtain rebuilding angle;

According to described reconstruction angle, object to be checked is carried out to part scanning;

Described calculating intermediate angle comprises:

When rack inclining, according to anteroposterior position location picture and the side locating image of object to be checked, determine the visual field, and then obtain size and the centre coordinate of each visual field cross section, and according to described size and centre coordinate, calculate a plurality of measurements territory radius of described each visual field cross section, according to described measurement territory radiuscope, calculate intermediate angle a plurality of times again, and the maximum of getting described intermediate angle is as described intermediate angle.

7. method according to claim 6, is characterized in that, according to following formula, calculates time intermediate angle:

${\mathrm{\&alpha;}}_i=2\&times;\arcsin \left(\frac{r_i}{\mathrm{dis}\_\mathrm{FC}}\right)$

Wherein, i is the number of visual field cross section, α _ibe the inferior intermediate angle of i visual field cross section, dis_FC is the distance from the focus of X-ray tube to CT frame central, r _iit is the measurement territory radius of i visual field cross section.

8. according to the method described in claim 4 or 6, it is characterized in that, described in obtain visual field cross-section center coordinate and further comprise: before obtaining described centre coordinate, described visual field cross section is carried out to bias and rebuilds.

9. according to the method described in claim 4 or 6, it is characterized in that, according to following formula, carry out computation and measurement territory radius:

$r=\sqrt{2}(\frac{L_{\mathrm{FOV}}}{2}+\max \{|x\_0|,|y\_0|\left\}\right)$

Wherein r is the radius in described measurement territory, L _fOVbe the width of visual field cross section and the greater in length, max is the function of maximizing, and x_0 is the abscissa of visual field cross-section center, and y_0 is the vertical coordinate of visual field cross-section center.

10. according to the method described in claim 4 or 6, it is characterized in that, described method further comprises: exposure angle is controlled as described intermediate angle is to carry out part scanning to object to be checked.

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