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

Abstract

The invention discloses an X-ray computerized tomography system, which is used for partially scanning an object to be detected. The system comprises a middle angle computing module, a rebuilding angle computing module and a scanner, wherein the middle angle computing module is used for computing a middle angle according to the size of the vision field cross section and the central coordinate of the object to be detected, and transmitting the middle angle to the rebuilding angle computing module; the rebuilding angle computing module is used for adding the middle angle to 180 degrees to obtain a rebuilding angle, and transmitting the rebuilding angle to the scanner; and the scanner is used for scanning a part of the object to be detected according to the rebuilding angle. The invention further discloses an X-ray computerized tomography method. Due to the adoption of the system and the method, the scanning time can be shortened, the time resolution can be increased, and the radiation dosage received by a patient can be reduced.

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

In X ray computer tomoscan (Computed Tomography, CT), in order to obtain high time resolution, often adopt double source CT and part scanning.Part scanning is between half scanning with completely between scanning, when organ or tissue's (as heart) of scanning motion, have superiority, because sweep time is shorter, in imaging process, the probability of object motion to be checked is just less, thereby has reduced the impact of motion artifacts on image quality.

The rotation sweep angle of part scanning is less than 360 °.In at present CT components of system as directed scanning, conventionally according to fixing reconstruction angle, determine sweep time, as shown in Figure 1, the schematic diagram that adopts fixing reconstruction angle to scan measurement territory (Field ofMeasurement, FOM) in partly scanning for CT.FOM is defined as the transverse cross-sectional area that in the process of X-ray tube rotating 360 degrees object to be checked obtains total radiation, and it has determined the scanning dose that directly object to be checked applied and the size of x-ray irradiation area.In figure, X-ray tube 1 is rotated clockwise to end position 5 from initial position 7, in this process, the angle γ of X-ray tube 1 rotation is defined as and rebuilds angle 3, the X ray fan beam angle β that X-ray tube 1 sends is defined as exposure angle 2, be generally 30 degree to the fixed angle between 60 degree, border circular areas 4 is the FOM at object to be checked place.At X-ray tube 1, from initial position 7, be rotated clockwise to the process of end position 5,1 of X-ray tube has rotated angle γ, [0, γ] data for projection in angular range is the required minimal data amount of image reconstruction in part scanning, at [γ, 360 °] data for projection of disappearance can compensate by supplementing the higher weight of data for projection in angular range, and in prior art, existing compensation method, repeats no more here.In the scanning of conventional part, in the X ray fladellum border radius that is β at position 7 place's central angles one must and position 5 place's central angles X ray fladellum border radius that is β in a coincidence, solid line and dotted line overlaps as shown in FIG..Rebuild angle γ and be normally defined half anglec of rotation 180 degree and exposure angle beta sum, be i.e. γ=180 °+β; Part sweep time

wherein T is that X-ray tube 1 revolves and turns around, i.e. 360 ° of required times.When this fixing reconstruction angle can cause less object to be checked to carry out tomoscan, the actual data for projection amount of obtaining of detector (as shown in Reference numeral 6) is more than rebuilding the required minimum data for projection amount of image, this has just increased unnecessary data for projection, also increase sweep time, reduced temporal resolution.

Therefore, in order to shorten sweep time, to realize the blur-free imaging to organ of locomotion or tissue, often adopt at present and improve with the following method temporal resolution: the one, further shorten the rotation sweep time on the basis of existing technology, as improve the algorithm etc. of CT system, and the 2nd, development double source CT.The former need to greatly change the existing algorithm of CT system conventionally, and latter need to change the hardware device of CT system, and the two is all more difficult in implementation, and cost cost is higher.

Summary of the invention

In view of this, the present invention proposes a kind of X-ray computerized tomography system and method, to shorten sweep time, improves temporal resolution.

The invention provides a kind of X-ray computerized tomography system, for object to be checked is carried out to part scanning, this system comprises: intermediate angle computation module, reconstruction 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 send described intermediate angle to described reconstruction angle calculation assembly; Described reconstruction angle calculation assembly, for described intermediate angle being added to 180 degree obtain described reconstruction 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, 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; 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.

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.

Further, described system also comprises exposure angle Control Component, for receiving the described intermediate angle from described intermediate angle computation module, it is that described intermediate angle controls exposure angle for described intermediate angle is to carry out part scanning to object to be checked that exposure angle is controlled.

The present invention also provides a kind of X ray computer tomoscan method, comprises the steps: to calculate intermediate angle according to size and the centre coordinate of the visual field cross section of object to be checked; Described intermediate angle is added to 180 degree obtain described reconstruction angle; According to described reconstruction angle, object to be checked is carried out to part scanning.

According to an aspect of the present invention, 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.

According to a further aspect in the invention, 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, then calculate intermediate angle a plurality of times according to described measurement territory radiuscope, and the maximum of getting described intermediate angle is as described intermediate angle.

The described visual field cross-section center coordinate that obtains further comprises: before obtaining described centre coordinate, described visual field cross section is carried out to bias and rebuild.

According to following formula, carry out computation and measurement territory radius:

$r=\sqrt{2}(\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{FOV}}}{2}+\max \{|x\_0|,|y\_0|\left\}\right)$

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.

According to following formula, calculate 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.

According to following formula, calculate 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.

Further, described method comprises: exposure angle is controlled as described intermediate angle is to carry out part scanning to object to be checked.

Because the present invention proposes a kind of reconstruction angle that is not more than the fixing angle γ of reconstruction and can adjusts according to the size of visual field cross section, this has just shortened sweep time, reduce the x-ray dose that patient accepts, improved temporal resolution simultaneously, be more suitable for scanning as the organ of locomotion such as heart or tissue.And the present invention do not change the existing hardware equipment of CT system, the existing algorithm of CT system is not improved in a large number yet, based on existing CT system, easily realize, reduced cost.

Accompanying drawing explanation

Fig. 1 is the schematic diagram that adopts fixing reconstruction angle to scan FOM during conventional CT partly scans.

Fig. 2 is the schematic diagram that adopts system and method for the present invention to scan FOM in CT partly scans.

Fig. 3 is the assembly schematic diagram of CT scan system of the present invention.

Fig. 4 is the composition schematic diagram of intermediate angle computation module of the present invention.

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

The specific embodiment

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

In the present invention, object to be checked can be certain region of human body, can be also certain organ or tissue of human body.Scanning direction is the direction of examinating couch turnover frame in CT system, is generally z direction.

CT scan system of the present invention is for carrying out part scanning to object to be checked, the assembly schematic diagram of CT scan system of the present invention as shown in Figure 3, comprise: intermediate angle computation module 20, reconstruction angle calculation assembly 21 and scanning device 22, wherein, intermediate angle computation module 20, for calculating intermediate angle according to size and the centre coordinate of the visual field of object to be checked (Field of View, FOV) cross section, and described intermediate angle is sent to and rebuilds angle calculation assembly 21; Rebuild angle calculation assembly 21, for described intermediate angle being added to 180 degree obtain described reconstruction angle, and send described reconstruction angle to scanning device 22; Scanning device 22, for carrying out part scanning according to described reconstruction angle to object to be checked.

Fig. 4 is the composition schematic diagram of intermediate angle computation module of the present invention.In Fig. 4, intermediate angle computation module 21 comprises: visual field cross section acquisition module 201, measurement territory radius calculation module 202 and intermediate angle computing module 203.Wherein:

Visual field cross section acquisition module 201, 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 202.

Before CT equipment starts series scanning or helical scanning, conventionally need to scan a width or two width location picture to patient, to determine position and the size of object to be checked, thereby obtain the scope of CT scan.Can obtain in the following way anteroposterior position location picture and the side locating image of object to be checked: when human body lies low, X-ray tube irradiates and obtains anteroposterior position location picture object to be checked at 90 degree or 270 degree (being vertical direction), and X-ray tube irradiates and obtains side locating image object to be checked at 0 degree or 180 degree (being horizontal direction).Doctor, according to this two width location picture, determines the visual field (being aforementioned FOV) that surrounds this object to be checked, is generally rectangular area, and its large I arranges according to doctor's experience.Doctor generally can arrange greatlyr by FOV, and to cover object to be checked completely, this has but increased the x-ray irradiation that object to be checked peripheral region is accepted to a certain extent.Although the X ray that human body is accepted is in this case still within the scope of safe dose, we always wish do not affecting under the prerequisite of image quality, further reduce the x-ray dose that object to be checked peripheral region receives.So wish that doctor can adjust FOV according to the difference size of object to be checked, as utilize the profile recognition technology of CT system to obtain the size of object to be checked, the size using it as FOV, has so just reduced the x-ray irradiation that object to be checked peripheral region is accepted.In addition, in the present invention, the cross section of FOV is rectangle, the circumscribed circle of this rectangle is FOM, so FOV < FOM, this is because object to be checked must be measured by the each read tablet being included in reconstruction regions in principle, so only have when object to be checked is in FOM, just can carry out correct reconstruction.

After obtaining visual field cross section, and then just can obtain size and the centre coordinate of visual field cross section.The further visual field of the present invention cross section acquisition module 201, also for before obtaining described centre coordinate, carries out bias reconstruction to described arbitrary visual field cross section or each visual field cross section.

Because different patients' build is different, the position of same patient's Different Organs or tissue and varying in size, when object to be checked is carried out to image reconstruction, if patient's build is large and/or focus in a side of patient body, make sick bed still cannot arrive the center of object to be checked after vertical direction lifting and/or translation in the horizontal direction, just need to carry out bias and rebuild, the abscissa that obtains FOV cross-section center departs from the distance x_0 of frame central and distance y _ 0 that vertical coordinate departs from frame central.Wherein the vertical lifting direction of 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, with y direction and z direction all the direction of quadrature be x direction.

According to the first embodiment of the present invention, when frame does not tilt in whole scanning process, centre coordinate (x_0 after the size of each FOV cross section and eccentric reconstruction, y_0) be all the same, demand goes out the size of arbitrary cross section and the coordinate (x_0, y_0) after eccentric reconstruction.

According to a second embodiment of the present invention, if frame needs according to scanning area in scanning process tilt, during such as scanning head, the frame that need to tilt is to avoid scanning eyes, at this moment FOV is no longer just rectangle but parallelogram or rhombus, so for different FOV cross sections, the abscissa of each cross-section center departs from the distance of frame central and distance that vertical coordinate departs from frame central is just no longer fixed, but change according to each FOV cross section, be set to (x _i_ 0, y _i_ 0), wherein i is the number of FOV cross section.

Measure territory radius calculation module 202, 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 203.

According to the first embodiment of the present invention, when frame does not tilt in whole scanning process, by following formula (1), calculate arbitrary FOV cross section place FOM radius r.

$r=\sqrt{2}(\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{FOV}}}{2}+\max \{|x\_0|,|y\_0|\left\}\right)---\left(1\right)$

Wherein max is the function of maximizing, and r is the radius 13 of FOM (as shown in the border circular areas 9 in Fig. 2), L _fOVbe the width of FOV cross section and the greater in length, FOM of the present invention can cover object to be checked completely.

According to a second embodiment of the present invention, if frame needs according to scanning area in scanning process tilt, by following formula (2), calculate the radius r of each FOV cross section place FOM _i.

$r_i=\sqrt{2}(\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{FOV}}}{2}+\max \{|x_i\_0|,|y_i\_0|\left\}\right)---\left(2\right)$

Wherein, i is the number of FOV cross section, x _ithe _ 0th, after bias is rebuild, the abscissa of each cross-section center of FOV departs from the distance of frame central, y _ithe _ 0th, after bias is rebuild, the vertical coordinate of each cross-section center of FOV departs from the distance of frame central.

Intermediate angle computing module 203, for when frame does not tilt, measures territory radius r according to described one and calculates described intermediate angle α; Or when rack inclining, according to described a plurality of measurements territory radius r _iobtain intermediate angle α a plurality of times _i, and the maximum of getting described intermediate angle is as described intermediate angle α, and described intermediate angle is sent to and rebuilds angle calculation assembly 21.

Fig. 2 is the schematic diagram that adopts system and method for the present invention to scan FOM in CT partly scans.

According to the first embodiment of the present invention, if frame does not tilt in whole scanning process, according to the radius r of any FOM, by following formula (3), calculate intermediate angle α.

$\mathrm{\&alpha;}=2\&times;\arcsin \left(\frac{r}{\mathrm{dis}\_\mathrm{FC}}\right)---\left(3\right)$

As shown in Figure 2, wherein dis_FC is the distance 11 from the focus of X-ray tube 1 to CT frame central, and α is intermediate angle, as shown in X ray fan beam angle 10 in Fig. 2.

According to a second embodiment of the present invention, if frame needs according to scanning area in scanning process tilt, according to the radius r of each FOV cross section place FOM _iaccording to following formula (4), calculate corresponding time intermediate angle α _i.

${\mathrm{\&alpha;}}_i=2\&times;\arcsin \left(\frac{r_i}{\mathrm{dis}\_\mathrm{FC}}\right)---\left(4\right)$

Then, according to α _iby following formula (5), calculate intermediate angle α with the bed thickness (Slicethickness, SL) of CT system.

α＝max{α _n，...，α _n+X} (5)

Wherein, n is the coordinate figure in z direction, and unit is mm, and positive integer X meets n≤SL < n+X, and the center (Slice Position, SP) of layer meets n≤SP-0.5 * SL < n+1.

According to formula (5), can draw: if bed thickness is whole FOV, get the maximum of inferior intermediate angle of all cross sections of FOV as the intermediate angle of whole FOV; If bed thickness is part FOV, get the maximum of the inferior intermediate angle of each cross section in this part FOV region as the intermediate angle in this part FOV region.

Rebuild angle calculation assembly 21, for intermediate angle α being added to 180 degree obtain rebuilding angle and send described reconstruction angle to scanning device 22.

According to intermediate angle α, by following formula (6), calculate reconstruction angle

Owing to rebuilding angle and intermediate angle, only differ from 180 degree, so

also along with the size of FOV cross section, change.Here

for carrying out the required minimum of image reconstruction, rebuild angle.

Scanning device 22, for according to rebuilding angle

object to be checked is carried out to part scanning.

Further, described CT system also comprises exposure angle Control Component 23, for receiving the intermediate angle α from intermediate angle computation module 20, exposure angle is controlled as intermediate angle α is object to be checked is carried out to part scanning, thereby further reduced the x-ray dose to the irradiation of FOM peripheral region and human body reception.

In addition, the present invention also provides a kind of X ray computer tomoscan method, as shown in Figure 5, comprises the steps:

Step 301, determines the visual field according to anteroposterior position location picture and the side locating image of object to be checked, when frame does not tilt, obtains size and the centre coordinate of arbitrary visual field cross section; Or when rack inclining, obtain size and the centre coordinate of each visual field cross section.

Preferably, described in, obtaining visual field cross-section center coordinate further comprises: before obtaining described centre coordinate, described visual field cross section is carried out to bias and rebuild.

In visual field cross section acquisition module 201, this is illustrated, repeat no more here.

Step 302, when rack inclining, calculates a measurement territory radius according to the size of described arbitrary visual field cross section and centre coordinate; Or when rack inclining, according to the size of described each visual field cross section and centre coordinate, calculate a plurality of measurements territory radius.

According to the first embodiment of the present invention, when frame does not tilt in whole scanning process, by formula (1), calculate the radius r of arbitrary FOV cross section place FOM.

According to a second embodiment of the present invention, if frame needs according to scanning area in scanning process tilt, by formula (2), calculate the radius r of each FOV cross section place FOM _i.

Step 303, when frame does not tilt, measures territory radius r according to described one and calculates described intermediate angle α; Or when rack inclining, according to described a plurality of measurements territory radius r _iobtain intermediate angle α a plurality of times _i, and the maximum of getting described intermediate angle is as described intermediate angle α.

According to the first embodiment of the present invention, when frame does not tilt in whole scanning process, by formula (3), calculate intermediate angle α.

According to a second embodiment of the present invention, if frame needs according to scanning area in scanning process tilt, by formula (4)-(5), calculate intermediate angle α.

Step 304, adds that by described intermediate angle 180 degree obtain described reconstruction angle.

Can calculate reconstruction angle by formula (6).

Step 305, according to rebuilding angle object to be checked is carried out to part scanning.

Further, CT scan method of the present invention also comprises step 306, and exposure angle is controlled as described intermediate angle is to carry out part scanning to object to be checked.This point is existing illustrating in exposure angle Control Component 23, repeats no more here.

Adopt CT scan system and method for the present invention to carry out part scanning to object to be checked, can shorten sweep time, also just improved temporal resolution, reduced the x-ray dose that patient accepts simultaneously.As shown in Figure 2, although irradiate the fixing exposure angle beta of remaining of FOM 9,1 needs of X-ray tube are 7 dextrorotation gyrations from position in-position 8, and needn't as Fig. 1, rotate to position 5, owing to rebuilding angle, reduced

so shortened sweep time.For example, if fixing, rebuilding angle γ is 240 °, X-ray tube focus is 535mm to the distance dis_FC of frame center of rotation, X-ray tube focus is approximately 940mm to the distance of detector, rotate a circle shortest time of 360 ° of X-ray tube is 0.5s, according to fixing part sweep time of rebuilding that angle obtains, is approximately 0.33s.And system and a method according to the invention, if L _fOVfor 250mm, when frame does not tilt, the centre coordinate of FOV cross section is not (0 ,-5), rebuilds angle

be about 220 °, the time of part scanning is only 0.3s like this, than fixing 0.33s sweep time that rebuilds angle, has reduced 8.3%, and this is just conducive to scan the organ of locomotion such as heart or tissue more.

In addition, in Fig. 2, in two border radiuses of the X ray fladellum at 7 places, position and two border radiuses of the X ray fladellum at 8 places, position, all occurred to intersect, as the intersection of dotted line in figure and solid line, and needn't as conventional part scanning requirement in Fig. 1, must there is a border radius to overlap.

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

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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