CN102846331B - X-ray computed tomography scanning system and method - Google Patents

Abstract

The invention relates to an X-ray computed tomography scanning system and a method. The X-ray computed tomography scanning system comprises a profile scanning parameter determining unit, a control curve determining unit and a scanner, wherein the profile scanning parameter determining unit is used for determining each optimal radiation starting angle alpha<0>opt and each minimum reconstruction angle gamma min which are required for scanning regions of interest in each two-dimensional profile; the control curve determining unit is used for determining control curves which are used for controlling scanning of three-dimensional regions of interest along the direction that a bedstead goes into or out of a gantry according to the obtained optimal radiation starting angles alpha<0>opt and the obtained minimum reconstruction angles gamma min; and the scanner is used for scanning the three-dimensional regions of interest according to the control curves. By means of the X-ray computed tomography scanning system and the method, image reconstruction of the three-dimensional regions of interest can be achieved by using few total radiation doses, energy consumption is saved, temporal resolution of image reconstruction is improved, and service life of X-ray tubes is prolonged.

Description

A kind of X-ray computerized tomography system and method

Technical field

The present invention relates to medical imaging field, especially a kind of X-ray computerized tomography system and method.

Background technology

Carrying out X ray computer tomoscan (Computed Tomography, CT) in process, usually the organ or the tissue that need object to be checked to carry out quality image reconstruction are called region-of-interest (region of interest, ROI), this ROI is 3 D stereo region.Based on prior art, to scan regardless of hope and the ROI rebuild is positioned at which position or its size of object to be checked, the fixing reconstruction angle that all will determine according to fixing collimator (phi-collimator) degree of opening, fixing exit dose and certain scan method, carries out the radioscanning of tomography (slide) one by one to patient.

In traditional complete scanning method, to carry out rebuilding the scanning completely that angle (irradiation duration) γ is 360 ° to each tomography.In part scanning method, certain fixing angle γ of reconstruction (such as 240 °) is adopted to come measurement field (the Field of Measurement in this section, FOM) scan, FOM determines the size of radiological dose and the x-ray irradiation area directly applied object to be checked.And in the part scanning method improved (see patent documentation 1), to reconstruction angle be carried out in this section radioscanning, wherein by the determined angle value of the size of object to be checked.

As can be seen here, according to existing CT scan technology, even if three-dimensional ROI is only a very little organ of object to be checked or tissue, total radiological dose can not reduce.

Patent documentation 1: SSME is in December in 2010 application on the 19th, and application number is 201010286350.0, and denomination of invention is the application for a patent for invention of " a kind of X-ray computerized tomography system and method ".

Summary of the invention

In view of this, the present invention proposes a kind of system and method carrying out X ray computer tomoscan, in order to reduce the reconstruction angle of each section under the prerequisite of reconstructed image quality ensureing three-dimensional ROI significantly, thus effectively reduce total radiological dose of X-ray.

According to an aspect of the present invention, a kind of X-ray computerized tomography system is provided.This X-ray computerized tomography system comprises: profile scanning parameter determination unit, for each optimum radiation initial angle α needed for determining to scan the region-of-interest in each two-dimensional cross-section ₀opt and each minimum reconstruction angle γ min; Controlling curve determining unit, for radiating initial angle α according to obtained each optimum ₀opt and each minimum reconstruction angle γ min, the direction along bedstead turnover frame determines the controlling curve controlling three dimensional region of interest scanning; And scanning device, for scanning three dimensional region of interest according to described controlling curve.

Preferably, described profile scanning parameter determination unit comprises: relation curve computing unit, for according to the described region-of-interest in two-dimensional cross-section, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation; Optimum radiation initial angle determining unit, for according to obtained described relation curve, determines the optimum radiation initial angle α in this two-dimensional cross-section ₀opt; Minimum radiation adds angle determining unit, for according to obtained described relation curve, determines that the minimum radiation in this two-dimensional cross-section adds angle δ min; And minimum reconstruction angle calculation unit, calculate minimum reconstruction angle γ min in this two-dimensional cross-section for adding angle δ min according to determined minimum radiation.

Preferably, described relation curve computing unit obtains given radiation initial angle α on described relation curve as follows one by one ₀corresponding radiation adds angle δ, thus draws described relation curve: from this two-dimensional cross-section, bulb runs circular path upper angle is given radiation initial angle α ₀starting point draw two outer tangent lines to the described region-of-interest in two-dimensional scan plane, and run circular path with described bulb and intersect at two intersection points; Using from described starting point described bulb run after when circular path rotates clockwise through intersection point as end point; Calculate the difference of central angle that described starting point turns over to described end point and 180 °, be described given radiation initial angle α ₀corresponding radiation adds the value of angle δ.

Preferably, according to the described region-of-interest in this two-dimensional cross-section and given radiation initial angle α ₀, described relation curve computing unit according to the additional angle δ of following formulae discovery radiation, thus draws described relation curve:

$\mathrm{\&delta;}=2\left[\begin{array}{c}\arcsin \left(\frac{\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\sin (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)-\\ \arcsin \left(\frac{\mathrm{ROI}\_\mathrm{radius}}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)\end{array}\right]$

Wherein, ROI_radius is the radius of region-of-interest described in this two-dimensional cross-section, ROI_offset be region-of-interest described in this two-dimensional cross-section relative to the side-play amount of scanning center, ROI_angle is the position angle of region-of-interest described in this two-dimensional cross-section, R _focusit is the radius that described bulb runs circular path.

Preferably, described minimum reconstruction angle calculation unit calculates the described minimum reconstruction angle γ min in this two-dimensional cross-section according to following formula:

γmin＝180°+δmin

Wherein, δ min is that described minimum radiation in this two-dimensional cross-section adds angle.

Preferably, described X-ray computerized tomography system also comprises three dimensional region of interest determining unit, for determining described three dimensional region of interest from checked object.

Preferably, described three dimensional region of interest determining unit calculates the geometric parameter of the region-of-interest in each two-dimensional cross-section according to the topological diagram picture that prescan goes out, thus determines described three dimensional region of interest.

According to another aspect of the present invention, a kind of X ray computer tomography method is provided, comprises: profile scanning parameter determining step, for each optimum radiation initial angle α needed for determining to scan the region-of-interest in each two-dimensional cross-section ₀opt and each minimum reconstruction angle γ min; Controlling curve determining step, for radiating initial angle α according to obtained each optimum ₀opt and each minimum reconstruction angle γ min, the direction along bedstead turnover frame determines the controlling curve controlling three dimensional region of interest scanning; And scanning step, for scanning three dimensional region of interest according to described controlling curve.

Preferably, described profile scanning parameter determining step comprises: relation curve calculation procedure, for according to the described region-of-interest in two-dimensional cross-section, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation; Optimum radiation initial angle determining step, for according to obtained described relation curve, determines the optimum radiation initial angle α in this two-dimensional cross-section ₀opt; Minimum radiation adds angle determining step, for according to obtained described relation curve, determines that the minimum radiation in this two-dimensional cross-section adds angle δ min; And minimum reconstruction angle calculating step, calculate minimum reconstruction angle γ min in this two-dimensional cross-section for adding angle δ min according to determined minimum radiation.

Preferably, in described relation curve calculation procedure, obtain given radiation initial angle α on described relation curve as follows one by one ₀corresponding radiation adds angle δ, thus draws described relation curve: from this two-dimensional cross-section, bulb runs circular path upper angle is given radiation initial angle α ₀starting point draw two outer tangent lines to the described region-of-interest in two-dimensional scan plane, and run circular path with described bulb and intersect at two intersection points; Using from described starting point described bulb run after when circular path rotates clockwise through intersection point as end point; Calculate the difference of central angle that described starting point turns over to described end point and 180 °, be described given radiation initial angle α ₀corresponding radiation adds the value of angle δ.

Preferably, according to the described region-of-interest in this two-dimensional cross-section and given radiation initial angle α ₀, according to the additional angle δ of following formulae discovery radiation in described relation curve calculation procedure, thus draw described relation curve:

$\mathrm{\&delta;}=2\left[\begin{array}{c}\arcsin \left(\frac{\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\sin (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)-\\ \arcsin \left(\frac{\mathrm{ROI}\_\mathrm{radius}}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)\end{array}\right]$

Wherein, ROI_radius is the radius of region-of-interest described in this two-dimensional cross-section, ROI_offset be region-of-interest described in this two-dimensional cross-section relative to the side-play amount of scanning center, ROI_angle is the position angle of region-of-interest described in this two-dimensional cross-section, R _focusit is the radius that described bulb runs circular path.

Preferably, in described minimum reconstruction angle calculating step, calculate the described minimum reconstruction angle γ min in this two-dimensional cross-section according to following formula:

γmin＝180°+δmin

Wherein, δ min is that described minimum radiation in this two-dimensional cross-section adds angle.

Preferably, described X ray computer tomography method also comprises three dimensional region of interest determining step, for determining described three dimensional region of interest from checked object.

Preferably, in the determining step of described three dimensional region of interest, the topological diagram picture gone out according to prescan calculates the geometric parameter of the region-of-interest in each two-dimensional cross-section, thus determines described three dimensional region of interest.

Preferably, described X ray computer tomography method also comprises prescan step, for obtaining the topological diagram picture of checked object.

According to technique scheme, the present invention is according to the three-dimensional ROI region of difference, the radiation initial angle of the X-ray on each x-y plane of scanning motion can be adjusted and rebuild angle, like this in the whole scanning process of frame (gantry), in the reconstruction angular range that X-ray bulb is just less in each x-y plane of scanning motion, be in opening.Therefore, by technical scheme of the present invention, reconstruction angle less in each section can be utilized, namely less radiological dose realizes the image reconstruction of three dimensional region of interest, save energy consumption, improve the temporal resolution (temporal resolution) of image reconstruction, and extend the life-span of X-ray bulb.

And according to feature of the present invention, when the organ or tissue more for shifted scanning center carries out imaging, or the special medical process to the imaging of ad-hoc location high-quality is needed for interventional therapy etc., more significant effect can be obtained.

Accompanying drawing explanation

The preferred embodiments of the present invention will be described in detail by referring to accompanying drawing below, the person of ordinary skill in the art is more clear that above-mentioned and other feature and advantage of the present invention, in accompanying drawing:

Fig. 1 is the system construction drawing of the X-ray computerized tomography system in the specific embodiment of the invention.

Fig. 2 (a) and Fig. 2 (b) shows the topological diagram picture that the CT equipment prescan in the specific embodiment of the invention goes out.

Fig. 3 (a) shows the stereoscopic model of three dimensional region of interest in the specific embodiment of the invention.

Fig. 3 (b)-(e) shows the plane of scanning motion figure of four sections in the stereomodel of three dimensional region of interest in the specific embodiment of the invention.

Fig. 4 is the structure chart of the profile scanning parameter determination unit in the specific embodiment of the invention.

Fig. 5 is the radiation initial angle of the x-y plane of scanning motion in the specific embodiment of the invention and the geometrical relationship schematic diagram at the additional angle of radiation.

Fig. 6 shows geometric representation and the radiation initial angle α of ROI section in the x-y plane of scanning motion in a specific embodiment ₀with the graph of relation of the additional angle δ of radiation.

Fig. 7 shows geometric representation and the radiation initial angle α of ROI section in the x-y plane of scanning motion in a specific embodiment ₀with the graph of relation of the additional angle δ of radiation.

Fig. 8 is the flow chart of steps of the method for determination profile scanning parameter in the specific embodiment of the invention.

Fig. 9 calculates radiation initial angle α in the specific embodiment of the invention ₀and the method flow diagram of the relation curve between the additional angle δ of radiation.

Figure 10 is the curve chart that three geometric parameters of each section of three dimensional region of interest change along z-axis.

Figure 11 is that the optimum radiation initial angle of each section of three dimensional region of interest and minimum radiation add the curve chart that angle changes along z-axis.

Figure 12 is optimum radiation initial angle and the curve chart that changes along z-axis of minimum reconstruction angle of each section of three dimensional region of interest.

Figure 13 is the method flow diagram of x-ray tomography in the specific embodiment of the invention.

Detailed description of the invention

For making the object, technical solutions and advantages of the present invention clearly, the present invention is described in more detail by the following examples.

Fig. 1 is the system construction drawing of the X-ray computerized tomography system in the specific embodiment of the invention.

As shown in Figure 1, in the specific embodiment of the present invention, X-ray computerized tomography system comprises: profile scanning parameter determination unit 10, for each optimum radiation initial angle α needed for determining to scan the region-of-interest in each two-dimensional cross-section ₀opt and each minimum reconstruction angle γ min; Controlling curve determining unit 20, for radiating initial angle α according to obtained each optimum ₀opt and each minimum reconstruction angle γ min, the direction along bedstead turnover frame determines the controlling curve controlling three dimensional region of interest scanning; And scanning device 30, for scanning three dimensional region of interest according to described controlling curve.

In a preferred embodiment, this X-ray computerized tomography system also comprises three dimensional region of interest determining unit 40, for determining described three dimensional region of interest from checked object.

Below, first we introduce in the specific embodiment of the invention about determining the technology contents of three-dimensional ROI.

determine three-dimensional ROI

In the present invention, the vertical lifting direction of definition sick bed is y direction, and the horizontal direction of sick bed turnover frame is z direction, and z direction is vertical with y direction, is then x direction with all orthogonal direction in y direction and z direction.

In the specific embodiment of the invention, suppose only to need to carry out high-quality image reconstruction for the organ corresponding to three-dimensional ROI or tissue.This ROI region can comprise partial organ or tissue, whole organ or tissue, or the set of the several organ or tissues paid close attention in medical examination.

Before CT equipment starts formal scanning, usually need the some width positioning images of object prescan to be checked, this positioning image is called as topological diagram picture (topography image).Fig. 2 shows the example of the topological diagram picture used in the specific embodiment of the invention.Usually can to the normotopia topological diagram picture of object scan to be checked as shown in Fig. 2 (a) and position, the side topological diagram picture etc. as shown in Fig. 2 (b).These topological diagram pictures in order to determine position that in object to be checked, three-dimensional ROI is general and size, thus obtain rough sweep limits.

For certain concrete medical examination application, three dimensional region of interest determining unit 40 can according to topological diagram picture, use specific image recognition algorithm to automatically identify the three-dimensional ROI region of a reference, manual adjustment can be done according to the three-dimensional ROI region of medical application to reference of reality more afterwards, thus determine paid close attention to three-dimensional ROI region.

For the ease of analyzing and understanding, three-dimensional ROI can be interpreted as the three-dimensional bodies that several sections are stacking in a z-direction by us, and wherein each section forms an x-y plane of scanning motion, can be described as again two dimensional x-y plane ROI or ROI section.Thus, the topological diagram picture that three dimensional region of interest determining unit 40 also can go out according to prescan calculates the geometric parameter of the ROI in each two-dimensional cross-section, thus determines three-dimensional ROI.

(variable z is used for each position in z-axis _irepresent), the object normotopia topological diagram picture to be checked shown in Fig. 2 (a) can be used to determine three-dimensional ROI size in the x direction and position, this size and position variables L _x(z _i) and C _x(z _i) represent, wherein L _x(z _i) and C _x(z _i) represent respectively in normotopia topological diagram picture at z _ithe length of position line section and center; Meanwhile, the image-side position to be checked topological diagram picture shown in Fig. 2 (b) can be used to determine three-dimensional ROI size in y-direction and position, this size and position variables L _y(z _i) and C _y(z _i) represent, wherein L _y(z _i) and C _y(z _i) represent in the topological diagram picture of position, side at z respectively _ithe length of position line section and center.

Conveniently analysis and calculation, the section of three-dimensional ROI region in each x-y plane all can be appointed as a circle by three dimensional region of interest determining unit 40.Like this, for each z in z-axis _iposition, about several main geometric parameters of ROI some x-y plane section just according to the variable parameter in topological diagram picture, can be calculated by following formula (1)-(4):

$\mathrm{ROI}\_\mathrm{radius}|z_i=\max \{\frac{L_x\left(z_i\right)}{2},\frac{L_y\left(z_i\right)}{2}\}\&CenterDot;\&CenterDot;\&CenterDot;\left(1\right)$

$\mathrm{ROI}\_\mathrm{offset}|z_i=\sqrt{C_x{\left(z_i\right)}^2+C_y{\left(z_i\right)}^2}\&CenterDot;\&CenterDot;\&CenterDot;\left(2\right)$

$\cos (\mathrm{ROI}\_\mathrm{angle})=\frac{C_x\left(z_i\right)}{\sqrt{C_x{\left(z_i\right)}^2+C_y{\left(z_i\right)}^2}}\&CenterDot;\&CenterDot;\&CenterDot;\left(3\right)$

$\sin (\mathrm{ROI}\_\mathrm{angle})=\frac{C_y\left(z_i\right)}{\sqrt{C_x{\left(z_i\right)}^2+C_y{\left(z_i\right)}^2}}\&CenterDot;\&CenterDot;\&CenterDot;\left(4\right)$

Wherein, ROI_radius is the radius of circle of ROI section; ROI_offset is the side-play amount of ROI section relative to the scanning center (Iso center) of corresponding x-y plane; ROI_angle is the position angle of ROI, and they are value between 0 °-360 °.Those skilled in the art are known, by the result of formula (3) and formula (4), can determine the value of ROI_angle.

Like this, according to the geometric parameter of ROI on each x-y section (value of ROI_radius, ROI_offset and ROI_angle), three dimensional region of interest determining unit 40 can construct the stereomodel of three-dimensional ROI.

Fig. 3 shows the stereoscopic model of three-dimensional ROI in the specific embodiment of the invention and the plane of scanning motion figure of wherein four sections.Wherein, Fig. 3 (a) be constructed by the stereoscopic model of three-dimensional ROI that goes out, Fig. 3 (b)-(e) is the plane of scanning motion figure that value is respectively on the x-y section of four coordinates in z-axis.

In Fig. 3 (b)-(e), z-axis coordinate value is respectively z=0mm, z=47mm, z=96mm and z=150mm.According to the three-dimensional ROI stereomodel shown in Fig. 3 (a), each in Fig. 3 (b)-(e) illustrates the size of corresponding ROI section on the plane of scanning motion and position, wherein central point represents the Iso center of corresponding section, dashed circle (1) represents that the bulb of X-ray bulb in corresponding section runs circular path, dashed circle (2) represents the measurement field FOM of corresponding section, and solid line circle (3) then represents the corresponding section of ROI in this x-y plane.

In this embodiment, first we illustrate the embodiment of the present invention in an x-y plane of scanning motion, and this embodiment expands in three-dimensional ROI by we afterwards, thus form the system and method in the specific embodiment of the invention.

the x-y plane of scanning motion

In the x-y plane of scanning motion, be different from existing part scanning method, the radiation initial angle α in this detailed description of the invention ₀carry out adaptive selection by according to the size of ROI section and position, add angle δ to obtain less radiation and rebuild angle γ.

Fig. 4 is the structure chart of the profile scanning parameter determination unit in the specific embodiment of the invention.

As shown in Figure 4, the profile scanning parameter determination unit 10 in the specific embodiment of the invention comprises: relation curve computing unit 101, for according to the ROI section in the two-dimentional x-y plane of scanning motion, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation; Optimum radiation initial angle determining unit 102, for according to obtained relation curve, determines that this x-y scans the optimum radiation initial angle α in section ₀opt; Minimum radiation adds angle determining unit 103, for according to obtained relation curve, determines that the minimum radiation in this x-y plane of scanning motion adds angle δ min; And minimum reconstruction angle calculation unit 104, calculate minimum reconstruction angle γ min in this x-y plane of scanning motion for adding angle δ min according to determined minimum radiation.

For the ROI section of specifying, this detailed description of the invention can be determined to make the minimum optimum of the required angle γ of reconstruction radiate initial angle α ₀opt and corresponding minimum reconstruction angle γ min.

Discovery is studied, when only needing to carry out high-quality image reconstruction for the section of ROI on the x-y plane of scanning motion, from suitable radiation initial angle α through inventor ₀the scanning starting necessarily to rebuild angle can obtain the minimum data amount of carrying out needed for data reconstruction to ROI, and rebuilding angle γ can calculate according to following formula (5):

γ＝180°+δ……………………(5)

Wherein δ is called the additional angle of radiation in the present invention, and it is by ROI section and radiation initial angle α ₀the angle value jointly determined.

Known by studying, due to radiate additional angle δ to be usually less than in prior art 60 ° of set fan angles or , may be even negative angle, therefore compared with prior art, the present invention can reduce to scan the reconstruction angle γ needed for each ROI section significantly, thus reduces total radiological dose.

Fig. 5 is the geometrical relationship schematic diagram radiating initial angle and the additional angle of radiation in the specific embodiment of the invention in the x-y plane of scanning motion.

As shown in Figure 5, when X-ray bulb to run from bulb position 1 on circular path (in as Fig. 5 shown in the dotted line of outer ring) as radiation starting point launch X-ray and circumferentially track rotates clockwise time, when the coordinate axes in 3 o'clock direction is pointed to as 0 ° of coordinate axes position in setting Yi Cong Iso center 4, then the corner that this position 1 is corresponding is in an x-y plane radiation initial angle α ₀.Position that determined by region-of-interest determining unit 40 in this x-y plane of scanning motion, that need to carry out the ROI section of quality image reconstruction is also show in Fig. 5.

In this embodiment, relation curve computing unit 101, first according to the ROI section determined, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation.

First, relation curve computing unit 101 can determine certain given radiation initial angle α by following geometric ways ₀corresponding radiation adds the value of angle δ.As shown in Figure 5, draw two tangent lines of the border circular areas of ROI section from position 1, and run circular path with bulb and intersect at position 2 and position 3 two point.Find through research, X-ray bulb is run the position of intersecting point met after circular path dextrorotation goes to along bulb, using this point as radiation end point, be the point of position 2 in Figure 5, the minimum data amount of carrying out needed for data reconstruction to ROI section can be obtained.As can be seen here, radiation starting point, to the difference of radiating the central angle that turns over of end point and 180 °, is given radiation initial angle α ₀corresponding radiation adds the value of angle δ.

Because in the example shown in Fig. 5, δ angle is negative value, the corner dimension therefore in Fig. 5 between the line at position 2 and Iso center 4 and the extended line of position 1 and Iso center 4 line is the order of magnitude radiating additional angle δ.As can be seen from Figure 5, X-ray bulb is from radiation starting point (position 1) to the angle that radiation end point (position 2) rotates through and rebuilds angle γ, according to formula (5), the additional angle δ of radiation has the differential seat angle of 180 ° with rebuilding angle γ, thus can by determining that radiating additional angle δ determines to rebuild angle γ.Relation is known thus, and the reconstruction angle γ in this x-y plane of scanning motion is less for δ-value less then X-ray bulb, then the radiological dose for the enforcement of this ROI section is less.

As mentioned above, relation curve computing unit 101 can determine given radiation initial angle α by geometric ways ₀corresponding radiation adds the value of angle δ.Equally, for certain given radiation initial angle α ₀, those skilled in the art also according to the mathematic parameter of ROI section determined in formula (1)-(4), can calculate given radiation initial angle α by mathematical formulae ₀corresponding radiation adds the value of angle δ.

For the ROI section determined in an x-y plane, the accurate location of this ROI can be determined by the value of determined ROI_radius, ROI_offset and ROI_angle tri-variablees in formula (1)-(4).It will be understood by those skilled in the art that according to above-mentioned three variable determined ROI positions and given radiation initial angle α ₀, the value of the additional angle δ of radiation just can be calculated according to following formula (6):

$\mathrm{\&delta;}=2\left[\begin{array}{c}\arcsin \left(\frac{\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\sin (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)-\\ \arcsin \left(\frac{\mathrm{ROI}\_\mathrm{radius}}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)\end{array}\right]\&CenterDot;\&CenterDot;\&CenterDot;\left(6\right)$

Wherein, R _focusthat bulb runs the radius of circular path, i.e. the radius of outer ring broken circle in Fig. 5.

As mentioned above, those skilled in the art can determine given radiation initial angle α by the geometrograph in Fig. 5 or according to the mathematic parameter of given ROI section ₀corresponding radiation adds angle δ.When radiation initial angle is at α ₀value one by one within the scope of 0 °-360 °, relation curve computing unit 101 just can obtain under the condition of given ROI section, radiation initial angle α ₀with the relation curve of the additional angle δ of radiation, as shown in Fig. 6 (a) He Fig. 7 (a).

Fig. 6 and Fig. 7 respectively illustrates geometric representation and the radiation initial angle α of ROI section in two different x-y planes of scanning motion ₀with the graph of relation of the additional angle δ of radiation.In Fig. 6 (b), Fig. 6 (c), Fig. 7 (b), Fig. 7 (c), respectively illustrate the x-y plane geometric representation for two different ROI sections, ROI section wherein in Fig. 6 is larger, and cover the Iso center of the x-y plane of scanning motion, and ROI section in Fig. 7 is less, and away from the Iso center of the x-y plane of scanning motion.Fig. 6 (a) and Fig. 7 (a), respectively for two ROI sections, shows radiation initial angle α ₀with the relation curve of the additional angle δ of radiation.Those skilled in the art with the geometrograph in Fig. 5 or the mathematic parameter according to given ROI section, can obtain the relation curve shown in Fig. 6 (a) He Fig. 7 (a) by formula (6).

Known by formula (5), the reconstruction angle γ of the additional angle δ less then X-ray bulb of radiation is less, then less for the radiological dose needed for ROI section, thus those skilled in the art need to determine in the x-y plane of scanning motion radiation is added optimum radiation initial angle α that angle δ reaches minima δ min ₀opt.

According to the relation curve that relation curve computing unit 101 calculates, radiation initial angle α when additional for radiation on relation curve angle δ can be minima by optimum radiation initial angle determining unit 102 ₀the optimum radiation initial angle α be defined as ₀opt.Meanwhile, according to the relation curve that relation curve computing unit 101 calculates, minimum radiation adds angle determining unit 103 also can determine that minimum radiation adds the value of angle δ min.And then minimum reconstruction angle calculation unit 104 can add angle δ min according to determined minimum radiation, formula (5) is utilized to try to achieve minimum reconstruction angle γ min.

Determining optimum radiation initial angle α ₀after opt and minimum reconstruction angle γ min, they can together store by CT system, using as obtaining the data of controlling curve will illustrated hereinafter.

Below, we are for Fig. 6 and Fig. 7, illustrate that X-ray computerized tomography system in this detailed description of the invention is when scanning the ROI section in the x-y plane of scanning motion, relative to the remarkable technique effect of prior art.

As shown in Figure 6, ROI section given is here comparatively large and cover the Iso center of the x-y plane of scanning motion, and its location parameter is ROI_radius=150mm, ROI_offset=50mm, ROI_angle=60 ° respectively.Now, optimum radiation initial angle α ₀minimum radiation corresponding to opt adds angle δ min=19.35 °, and namely minimum reconstruction angle γ min is now 180 °+19.35 °=199.35 °.Contrast traditional complete scanning method, reconstruction angle γ and corresponding radiological dose decrease about 44.6%, and contrast part scanning method, and reconstruction angle γ and corresponding radiological dose decrease about 17%.

As shown in Figure 7, ROI section given is here less and away from the Iso center of the x-y plane of scanning motion, its location parameter is ROI_radius=50mm, ROI_offset=200mm, ROI_angle=230 ° respectively.Now, optimum radiation initial angle α ₀minimum radiation corresponding to opt adds angle δ min=-29.2 °, and namely minimum reconstruction angle γ min is now 180 °+(-29.2 °)=154.7 °.Contrast traditional complete scanning method, reconstruction angle γ and corresponding radiological dose decrease about 57%, and contrast part scanning method, and reconstruction angle γ and corresponding radiological dose decrease about 37.2%.

As can be seen from ROI section situations different in Fig. 6 and Fig. 7, when ROI section does not cover the Iso center of the x-y plane of scanning motion time, δ min is negative value, now rebuild angle γ and can be less than 180 °, the radiological dose therefore for scanning ROI section in the x-y plane of scanning motion can be reduced significantly.Particularly, when the FOM edge of the less and close x-y plane of scanning motion of scope of ROI section time, radiological dose can obtain reduction by a larger margin.

Below, we illustrate for the given x-y plane of scanning motion, determine and store the optimum radiation initial angle α of the ROI section in this plane ₀the method of opt and minimum reconstruction angle γ min.

Fig. 8 is the flow chart of steps of the method for determination profile scanning parameter in the specific embodiment of the invention.

As shown in Figure 8, step S51 is used for according to the ROI section in this x-y plane of scanning motion, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation.As mentioned above, in step s 51, those skilled in the art can by the geometrograph in Fig. 5 or according to the mathematic parameter of given ROI section, determine given radiation initial angle α by formula (6) ₀corresponding radiation adds angle δ.When radiation initial angle is at α ₀value one by one within the scope of 0 °-360 °, just can obtain under the condition of given ROI section, radiation initial angle α ₀with the relation curve of the additional angle δ of radiation, such as, shown in Fig. 6 (a) He Fig. 7 (a).In this step S51, include step S511-S514 many steps, specifically see the method flow diagram shown in Fig. 9.

Fig. 9 calculates radiation initial angle α in this detailed description of the invention ₀and the flow chart of the relation curve between the additional angle δ of radiation.

As shown in Figure 9, first in step S511, α is set ₀=0 °, namely calculate from radiation initial angle is the position of 0 °.Flow process enters step S512.

In step S512, utilize the geometric parameter of ROI section (ROI_radius, ROI_offset, ROI_angle) and given α ₀value, calculate the value of the additional angle δ of radiation according to formula (6).Flow process enters step S513.

In step S513, judge radiation initial angle α ₀whether be less than 360 °, namely judge whether circumferentially all radiation initial angle α ₀all calculate.If be judged as α ₀be less than 360 °, then flow process enters step S514, if α ₀be not less than 360 °, then to circumferentially all radiation initial angle α ₀all calculate, namely determined in ROI section and radiated initial angle α ₀and the relation curve between the additional angle δ of radiation, flow process enters step S52 and step S53 simultaneously.

In step S514, α is set ₀=α ₀after+Δ α, flow process gets back to step S512.That is, initial angle α will be radiated ₀value add an increment Delta α after again calculate corresponding to radiation add the value of angle δ.This increment Delta α can be arranged by operator voluntarily according to precision needed for operator.

Turn back to the method flow diagram shown in Fig. 8.In step S52, according to obtained relation curve, determine optimum radiation initial angle α ₀opt.Flow process enters step S55.

In step S53, according to obtained relation curve, determine that minimum radiation adds angle δ min.Flow process enters step S54.

In step S54, add angle δ min and formula (5) according to determined minimum radiation, calculate minimum reconstruction angle γ min=180 ° of+δ min.Flow process enters step S5.

In step S55, determining the optimum radiation initial angle α of the x-y plane of scanning motion ₀after opt and minimum reconstruction angle γ min, they are stored together.

the scan control curve of the three-dimensional ROI of x-y-z

As explained above, as long as determine the geometric parameter (value of ROI_radius, ROI_offset and ROI_angle) of ROI section in certain x-y plane of scanning motion, the optimum radiation initial angle α corresponding to this x-y plane of scanning motion just can be calculated ₀opt and minimum reconstruction angle γ min.For the z of z-axis _iposition, the ROI region on the x-y plane of scanning motion corresponds to whole three-dimensional ROI at z _isection on position.Below, the above-mentioned analysis and calculation for the x-y plane of scanning motion expands in x-y-z three dimensions by we, thus obtains in the specific embodiment of the invention controlling curve needed for scanning whole three-dimensional ROI.

Figure 10 to Figure 12 shows and progressively obtains the process of X-ray bulb to the controlling curve that three-dimensional ROI scans by determined three-dimensional ROI.Figure 10 is the curve chart that three geometric parameters of each section of three-dimensional ROI model shown in Fig. 3 change along z-axis.Figure 11 is the optimum radiation initial angle α of each ROI section ₀opt and minimum radiation add the curve chart that angle δ min changes along z-axis.Figure 12 is the optimum radiation initial angle α of each ROI section ₀the curve chart that opt and minimum reconstruction angle γ min changes along z-axis.

As analyzed above, for three-dimensional ROI, three geometric parameters along the ROI section of each x-y plane of scanning motion of z-axis just based on the normotopia topological diagram picture shown in Fig. 2 and position, side topological diagram picture, can be determined by formula (1)-(4).Along with coordinate z _ichange, we just can obtain the radius (ROI_radius) of ROI section, ROI section respectively relative to the position angle (ROI_angle) of the side-play amount (ROI_offset) at Iso center, ROI section respectively along the curve that z-axis is formed, as shown in Figure 10.

As explained above, for the x-y plane of scanning motion, we can determine the optimum radiation initial angle α of this plane of scanning motion ₀opt and minimum radiation add angle δ min.Along with coordinate z _ichange, we can obtain the optimum radiation initial angle α of the plane of scanning motion ₀opt and minimum radiation add angle δ min respectively along the curve that z-axis is formed, as shown in figure 11.And then according to formula (5), we can obtain the optimum radiation initial angle α of the plane of scanning motion ₀opt and minimum reconstruction angle γ min respectively along the curve that z-axis is formed, as shown in figure 12.

For three-dimensional ROI, the optimum radiation initial angle α that we can will obtain ₀the controlling curve that the curve that opt and minimum reconstruction angle γ min is formed along z-axis scans ROI as control X-ray bulb, carries out the scan control of CT system according to this curve.Like this, achieve minimizing of radiological dose at each x-y plane of scanning motion, thus finally decrease total radiological dose of whole 3-D scanning.

With in this detailed description of the invention, for the three-dimensional ROI model shown in Fig. 3, the average reconstruction angle of each plane of scanning motion in z-axis is 180.56 °, compared to rebuilding the part scanning method that angle is 240 °, total radiological dose decreases 24.8%, if compared with the complete scanning method that traditional reconstruction angle is 360 °, total radiological dose is more the reduction of 49.8%.

Figure 13 is the entire flow figure of x-ray tomography method in the specific embodiment of the invention.Wherein, 0 and Zmax represent respectively three-dimensional ROI sick bed turnover frame z direction on two extreme value places.

In step sl, before CT equipment starts scanning, first carry out the prescan of topological diagram picture, the normotopia topological diagram picture shown in Fig. 2 and position, side topological diagram picture can be comprised.Flow process enters step S2.

In step s 2, determine position that in object to be checked, three-dimensional ROI is general and size, thus obtain rough sweep limits.Particularly, specific image recognition algorithm can be used to automatically identify the three-dimensional ROI region of a reference to topological diagram picture, do manual adjustment according to the three-dimensional ROI region of medical application to reference of reality afterwards, thus determine paid close attention to three-dimensional ROI region.

If in order to accurate calculating, formula (1)-(4) can also be utilized in step s 2 to calculate the geometric parameter (ROI_radius of ROI section in each x-y plane of scanning motion, the value of ROI_offset and ROI_angle), thus construct the stereoscopic model of three-dimensional ROI, as shown in Figure 3.Certainly, for the geometric parameter on each ROI section, also can calculate in the step S4 of follow-up introduction.Flow process enters step S3.

Flow process from step S3 to step S8, we will calculate the optimum radiation initial angle α in each x-y plane of scanning motion ₀opt and minimum reconstruction angle γ min, and obtain the controlling curve for controlling X-ray bulb three-dimensional ROI being carried out to radioscanning.

In step s3, z-axis position coordinates z=0 is set, namely from three-dimensional ROI sick bed turnover frame z direction on minimum extreme value place calculate.Flow process enters step S4.

In step s 4 which, according to given z-axis position, formula (1)-(4) are utilized to calculate the geometric parameter ROI_radius of the corresponding ROI section in the x-y plane of scanning motion, the value of ROI_offset and ROI_angle.Flow process enters step S5.

Include step S51-S55 many steps in step S5, for for the given x-y plane of scanning motion, determine and store the optimum radiation initial angle α of the ROI section in this plane ₀opt and minimum reconstruction angle γ min, as shown in Figure 8.

Step S51 is used for according to ROI section, calculates the radiation initial angle α in this x-y plane of scanning motion ₀and the relation curve between the additional angle δ of radiation, that includes step S511-S514 many steps, as shown in Figure 9.

First, in the step S511 of step S51, α is set ₀=0 °, namely calculate from radiation initial angle is the position of 0 °.Flow process enters step S512.

In step S512, utilize the geometric parameter of the ROI section calculated in step S2 or step S4 (ROI_radius, ROI_offset, ROI_angle) and given α ₀value, calculate the value of the additional angle δ of radiation according to formula (6).Flow process enters step S513.

In step S513, judge radiation initial angle α ₀whether be less than 360 °, namely judge whether circumferentially all radiation initial angle α ₀all calculate.If be judged as α ₀be less than 360 °, then flow process enters step S514, if α ₀be not less than 360 °, then to circumferentially all radiation initial angle α ₀all calculate, namely determined in ROI section and radiated initial angle α ₀and the relation curve between the additional angle δ of radiation, flow process enters step S52 and step S53.

In step S514, α is set ₀=α ₀after+Δ α, flow process gets back to step S512.That is, initial angle α will be radiated ₀value add an increment Delta α after again calculate corresponding to radiation add the value of angle δ.This increment Delta α can be arranged by operator voluntarily according to precision needed for operator.

In step S52, according to obtained relation curve, determine the optimum radiation initial angle α in this x-y plane of scanning motion ₀opt.Flow process enters step S55.

In step S53, according to obtained relation curve, add the δ of angle from obtained all radiation the minimum radiation determined in this x-y plane of scanning motion and add angle δ min.Flow process enters step S54.

In step S54, add angle δ min and formula (5) according to minimum radiation determined in step S53, calculate the minimum reconstruction angle γ min=180 ° of+δ min in this x-y plane of scanning motion.Flow process enters step S55.

In step S55, by the optimum radiation initial angle α determined in step S52 ₀opt and the optimum radiation initial angle α determined in step S54 ₀opt stores together.

So far, we are for the given x-y plane of scanning motion, determine and store the optimum radiation initial angle α of the ROI section in this plane ₀opt and minimum reconstruction angle γ min.Flow process enters step S6.

In step s 6, judge whether z-axis coordinate is less than Zmax, namely judge whether all to calculate all sections of whole three-dimensional ROI.If be judged as that z is less than Zmax, then flow process enters step S7, if z is not less than Zmax, then illustrate and all calculate all sections of whole three-dimensional ROI, flow process enters step S8.

In the step s 7, after arranging z=z+ Δ z, flow process gets back to step S4.That is, z-axis is sat the geometric parameter ROI_radius again calculating the corresponding ROI section in the x-y plane of scanning motion after target value adds an increment Delta z, the value of ROI_offset and ROI_angle.This increment Delta z can be arranged by operator voluntarily according to precision needed for operator.

In step s 8, according to calculate one by one along z-axis and store, for the result of three-dimensional ROI cross sections to (minimum reconstruction angle γ min and optimum radiation initial angle α ₀opt), controlling curve determining unit 20 determines the controlling curve carrying out three-dimensional ROI scanning for controlling X-ray bulb, as shown in figure 12.Flow process enters step S9.

In step s 9, the scanning device 30 in CT system carries out radioscanning according to controlling curve determined in step S8 to three-dimensional ROI.

Show according to analysis and calculation, the present invention can reduce the total radiological dose of X bulb for ROI significantly.At ROI less and also close to FOM edge, compared to rebuilding the part scanning method that angle is 240 °, total radiological dose can reduce 40% at most, and is the complete scanning method of 360 ° compared with traditional reconstruction angle, and total radiological dose can reduce 60% at most.

Relative to complete scanning method of the prior art or part scanning method, the present invention significantly reduces the reconstruction angle of each plane of scanning motion when ensureing original ROI region picture quality, thus decreases total radiological dose.Due to the minimizing of X-ray exit dose, the energy consumed is corresponding minimizing also, improves temporal resolution, and extends the life-span of X-ray bulb.

And according to feature of the present invention, when the organ more for shifted scanning center carries out imaging, or the special medical process to the imaging of ad-hoc location high-quality is needed for interventional therapy etc., then can obtain more significant effect.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (12)

1. an X-ray computerized tomography system, comprising:

Profile scanning parameter determination unit (10), for each optimum radiation initial angle α needed for determining to scan the region-of-interest in each two-dimensional cross-section ₀opt and each minimum reconstruction angle γ min;

Controlling curve determining unit (20), for radiating initial angle α according to obtained each optimum ₀opt and each minimum reconstruction angle γ min, the direction along bedstead turnover frame determines the controlling curve controlling three dimensional region of interest scanning; And

Scanning device (30), for scanning three dimensional region of interest according to described controlling curve.

2. X-ray computerized tomography system according to claim 1, is characterized in that, described profile scanning parameter determination unit (10) comprising:

Relation curve computing unit (101), for according to the described region-of-interest in two-dimensional cross-section, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation;

Optimum radiation initial angle determining unit (102), for according to obtained described relation curve, determines the optimum radiation initial angle α in this two-dimensional cross-section ₀opt;

Minimum radiation adds angle determining unit (103), for according to obtained described relation curve, determines that the minimum radiation in this two-dimensional cross-section adds angle δ min; And

Minimum reconstruction angle calculation unit (104), calculates minimum reconstruction angle γ min in this two-dimensional cross-section for adding angle δ min according to determined minimum radiation.

3. X-ray computerized tomography system according to claim 2, is characterized in that, described relation curve computing unit (101) obtains given radiation initial angle α on described relation curve as follows one by one ₀corresponding radiation adds angle δ, thus draws described relation curve:

From this two-dimensional cross-section, bulb runs circular path upper angle is given radiation initial angle α ₀starting point draw two outer tangent lines to the described region-of-interest in two-dimensional scan plane, and run circular path with described bulb and intersect at two intersection points;

Using from described starting point described bulb run after when circular path rotates clockwise through intersection point as end point;

Calculate the difference of central angle that described starting point turns over to described end point and 180 °, be described given radiation initial angle α ₀corresponding radiation adds the value of angle δ.

4. X-ray computerized tomography system according to claim 3, is characterized in that, according to the described region-of-interest in this two-dimensional cross-section and given radiation initial angle α ₀, described relation curve computing unit (101) according to the additional angle δ of following formulae discovery radiation, thus draws described relation curve:

$\mathrm{\&delta;}=2\left[\begin{array}{c}\arcsin \left(\frac{\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\sin (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)-\\ \arcsin \left(\frac{\mathrm{ROI}\_\mathrm{radius}}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-{2R}_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)\end{array}\right]$

Wherein, ROI_radius is the radius of region-of-interest described in this two-dimensional cross-section, ROI_offset be region-of-interest described in this two-dimensional cross-section relative to the side-play amount of scanning center, ROI_angle is the position angle of region-of-interest described in this two-dimensional cross-section, R _focusit is the radius that described bulb runs circular path.

5. X-ray computerized tomography system according to claim 2, is characterized in that, described minimum reconstruction angle calculation unit (104) calculates the described minimum reconstruction angle γ min in this two-dimensional cross-section according to following formula:

γmin＝180°+δmin

Wherein, δ min is that described minimum radiation in this two-dimensional cross-section adds angle.

6., according to the X-ray computerized tomography system in claim 1-5 described in any one, it is characterized in that,

Also comprise three dimensional region of interest determining unit (40), the topological diagram picture for going out according to prescan calculates the geometric parameter of the region-of-interest in each two-dimensional cross-section, thus determines described three dimensional region of interest.

7. an X ray computer tomography method, comprising:

Profile scanning parameter determining step, for each optimum radiation initial angle α needed for determining to scan the region-of-interest in each two-dimensional cross-section ₀opt and each minimum reconstruction angle γ min;

Controlling curve determining step, for radiating initial angle α according to obtained each optimum ₀opt and each minimum reconstruction angle γ min, the direction along bedstead turnover frame determines the controlling curve controlling three dimensional region of interest scanning; And

Scanning step, for scanning three dimensional region of interest according to described controlling curve.

8. X ray computer tomography method according to claim 7, is characterized in that, described profile scanning parameter determining step comprises:

Relation curve calculation procedure, for according to the described region-of-interest in two-dimensional cross-section, calculates radiation initial angle α ₀and the relation curve between the additional angle δ of radiation;

Optimum radiation initial angle determining step, for according to obtained described relation curve, determines the optimum radiation initial angle α in this two-dimensional cross-section ₀opt;

Minimum radiation adds angle determining step, for according to obtained described relation curve, determines that the minimum radiation in this two-dimensional cross-section adds angle δ min; And

Minimum reconstruction angle calculating step, calculates minimum reconstruction angle γ min in this two-dimensional cross-section for adding angle δ min according to determined minimum radiation.

9. X ray computer tomography method according to claim 8, is characterized in that, in described relation curve calculation procedure, obtains given radiation initial angle α on described relation curve as follows one by one ₀corresponding radiation adds angle δ, thus draws described relation curve:

From this two-dimensional cross-section, bulb runs circular path upper angle is given radiation initial angle α ₀starting point draw two outer tangent lines to the described region-of-interest in two-dimensional scan plane, and run circular path with described bulb and intersect at two intersection points;

Using from described starting point described bulb run after when circular path rotates clockwise through intersection point as end point;

Calculate the difference of central angle that described starting point turns over to described end point and 180 °, be described given radiation initial angle α ₀corresponding radiation adds the value of angle δ.

10. X ray computer tomography method according to claim 9, is characterized in that, according to the described region-of-interest in this two-dimensional cross-section and given radiation initial angle α ₀, according to the additional angle δ of following formulae discovery radiation in described relation curve calculation procedure, thus draw described relation curve:

$\mathrm{\&delta;}=2\left[\begin{array}{c}\arcsin \left(\frac{\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\sin (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-2R_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)-\\ \arcsin \left(\frac{\mathrm{ROI}\_\mathrm{radius}}{\sqrt{{R_{\mathrm{focus}}}^2+\mathrm{ROI}\_{\mathrm{offset}}^2-{2R}_{\mathrm{focus}}\&CenterDot;\mathrm{ROI}\_\mathrm{offset}\&CenterDot;\cos (\mathrm{ROI}\_\mathrm{angle}-{\mathrm{\&alpha;}}_0)}}\right)\end{array}\right]$

Wherein, ROI_radius is the radius of region-of-interest described in this two-dimensional cross-section, ROI_offset be region-of-interest described in this two-dimensional cross-section relative to the side-play amount of scanning center, ROI_angle is the position angle of region-of-interest described in this two-dimensional cross-section, R _focusit is the radius that described bulb runs circular path.

11. X ray computer tomography method according to claim 8, is characterized in that, in described minimum reconstruction angle calculating step, calculate the described minimum reconstruction angle γ min in this two-dimensional cross-section according to following formula:

γmin＝180°+δmin

Wherein, δ min is that described minimum radiation in this two-dimensional cross-section adds angle.

12., according to the X ray computer tomography method in claim 7-11 described in any one, is characterized in that,

Also comprise three dimensional region of interest determining step, the topological diagram picture for going out according to prescan calculates the geometric parameter of the region-of-interest in each two-dimensional cross-section, thus determines described three dimensional region of interest.