CN102397078A - 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 computer tomographic system and method

Technical field

The present invention relates to the medical imaging field, especially a kind of X ray computer tomographic system and method.

Background technology

The X ray computer tomoscan (Computed Tomography, CT) in, in order to obtain high time resolution, often adopt double source CT and part scanning.Part scanning is between half scanning with fully between the scanning; When organ or tissue's (like heart) of scanning motion, have superiority; Because sweep time is short more, the probability of object motion to be checked is just more little in imaging process, thereby has reduced the influence of motion artifacts to image quality.

The rotation sweep angle of part scanning is less than 360 °.In the CT components of system as directed scanning at present, confirm sweep time according to fixed reconstruction angle usually, as shown in Figure 1, for CT adopts fixed reconstruction angle to measurement territory (Field ofMeasurement, the sketch map that FOM) scans in partly scanning.FOM is defined as at X-ray tube and revolves the transverse cross-sectional area that object to be checked in the process of three-sixth turn obtains total radiation, the scanning dose that it has determined directly object to be checked is applied and the size of x-ray irradiation area.X-ray tube 1 is rotated clockwise to end position 5 from initial position 7 among the figure; The angle γ of X-ray tube 1 rotation is defined as and rebuilds angle 3 in this process; The X ray fan beam angle β that X-ray tube 1 sends is defined as exposure angle 2; Be generally 30 and spend to the fixed angle between 60 degree, border circular areas 4 is the FOM at object to be checked place.Be rotated clockwise to the process of end position 5 from initial position 7 at X-ray tube 1; 1 of X-ray tube has rotated angle γ, and the data for projection in [0, γ] angular range is the required minimal data amount of image reconstruction in the part scanning; At [γ; 360 °] data for projection of disappearance can compensate through the higher weight of replenishing data for projection in the angular range, and existing compensation method is repeated no more here in the prior art.In the scanning of the part of routine, being in the X ray fladellum border radius of β one at position 7 place's central angles must be a coincidence in the X ray fladellum border radius of β with position 5 place's central angles, like overlapping of solid line shown in scheming and dotted line.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 fixed reconstruction angle can cause that less object to be checked carried out tomoscan; The actual data for projection amount of obtaining of detector (shown in Reference numeral 6) is more than the required minimum data for projection amount of reconstructed 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, the following method of normal at present employing improves 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, the development double source CT.The former need greatly change CT system existing algorithm usually, and the latter then need change the hardware device of CT system, and the two all compares difficulty on implementation, and the cost cost is higher.

Summary of the invention

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

The present invention provides a kind of X ray computer tomographic system; Be used for object to be checked is carried out part scanning; This system comprises: intermediate angle computation module, reconstruction angle calculation assembly and scanning device, wherein, said intermediate angle computation module; Be used for calculating intermediate angle, and send said intermediate angle to said reconstruction angle calculation assembly according to the size and the centre coordinate of the visual field cross section of object to be checked; Said reconstruction angle calculation assembly is used for said intermediate angle is added that 180 degree obtain said reconstruction angle, and sends said reconstruction angle to said scanning device; Said scanning device is used for according to said reconstruction angle object to be checked being carried out part scanning.

Said intermediate angle computation module comprises: visual field cross section acquisition module, measurement territory radius calculation module and intermediate angle computing module; Said visual field cross section acquisition module; Be used for when frame does not tilt; Anteroposterior position location picture and side locating image according to object to be checked are confirmed the visual field, and then obtain the size and the centre coordinate of arbitrary visual field cross section; Perhaps when rack inclining, confirm the visual field according to the anteroposterior position location picture and the side locating image of object to be checked, and then obtain the size and the centre coordinate of each visual field cross section; And send said size and centre coordinate to said measurement territory radius calculation module; Said measurement territory radius calculation module is used for calculating a measurement territory radius according to the size and the centre coordinate of said arbitrary visual field cross section; Perhaps size and the centre coordinate according to said each visual field cross section calculates a plurality of measurements territory radius; And send said measurement territory radius to said intermediate angle computing module; Said intermediate angle computing module is used for when frame does not tilt, and measures the territory radius according to said one and calculates said intermediate angle; Perhaps when rack inclining, obtain intermediate angle a plurality of times, and the maximum of getting said intermediate angle is as said intermediate angle according to said a plurality of measurements territory radius; And send said intermediate angle to said reconstruction angle calculation assembly.

Said visual field cross section acquisition module was further used for before obtaining said centre coordinate, and said arbitrary visual field cross section or each visual field cross section are carried out the off-centre reconstruction.

Further; Said system also comprises exposure angle Control Component; Be used to receive the said intermediate angle from said intermediate angle computation module, the angle of will making public is controlled to be the said intermediate angle angle of will making public and is controlled to be said intermediate angle object to be checked is carried out part scanning.

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

According to an aspect of the present invention; Said calculating intermediate angle comprises: when frame does not tilt; Anteroposterior position location picture and side locating image according to object to be checked are confirmed the visual field, and then obtain the size and the centre coordinate of arbitrary visual field cross section, and according to said size and centre coordinate; Measure the territory radius for one that calculates said arbitrary visual field cross section, again according to the said intermediate angle of said measurement territory radius calculation.

According to a further aspect in the invention; Said calculating intermediate angle comprises: when rack inclining, confirm the visual field according to the anteroposterior position location picture and the side locating image of object to be checked, and then obtain the size and the centre coordinate of each visual field cross section; And according to said size and centre coordinate; Calculate a plurality of measurements territory radius of said each visual field cross section, calculate intermediate angle a plurality of times according to said measurement territory radiuscope again, and the maximum of getting said intermediate angle is as said intermediate angle.

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

Calculate measurement territory radius according to following formula:

$r=\sqrt{2}(\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600011.png,HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{FOV}}}{2}+\max \{|x\_0|,|y\_0|\left\}\right)$

Wherein r is the radius in said measurement territory, L _FOVBe the width of visual field cross section and the greater in the 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.

Calculate intermediate angle according to following formula:

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

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

Calculate time intermediate angle according to following formula:

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

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 the CT frame central, r _iIt is the measurement territory radius of i visual field cross section.

Further, said method comprises: the angle of will making public is controlled to be said intermediate angle object to be checked is carried out part scanning.

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; Reduced the x-ray dose that patient accepts, improved temporal resolution simultaneously, be more suitable for scanning like organ of locomotion or tissues such as hearts.And the present invention do not change the existing hardware equipment of CT system, and the existing algorithm of CT system is not improved in a large number yet, realizes easily based on existing C T system, reduced cost.

Description of drawings

Fig. 1 is the sketch map that adopts fixed reconstruction angle that FOM is scanned during conventional CT partly scans.

Fig. 2 is the sketch map that in CT partly scans, adopts system and method for the present invention that FOM is scanned.

Fig. 3 is the assembly sketch map of CT scan of the present invention system.

Fig. 4 is the composition sketch map 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 of the invention, technical scheme and advantage clearer, below lift embodiment to further explain of the present invention.

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

CT scan of the present invention system is used for object to be checked is carried out part scanning; As shown in Figure 3 is the assembly sketch map of CT scan of the present invention system, comprising: intermediate angle computation module 20, rebuild angle calculation assembly 21 and scanning device 22, wherein; Intermediate angle computation module 20; Be used for according to object to be checked the visual field (Field of View, FOV) size of cross section and centre coordinate calculate intermediate angle, and said intermediate angle sent to rebuild angle calculation assembly 21; Rebuild angle calculation assembly 21, be used for said intermediate angle is added that 180 degree obtain said reconstruction angle, and send said reconstruction angle to scanning device 22; Scanning device 22 is used for according to said reconstruction angle object to be checked being carried out part scanning.

Fig. 4 is the composition sketch map of intermediate angle computation module of the present invention.Intermediate angle computation module 21 comprises among Fig. 4: 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 is used for when frame does not tilt, and confirms the visual field according to the anteroposterior position location picture and the side locating image of object to be checked, and then obtains the size and the centre coordinate of arbitrary visual field cross section; Perhaps when rack inclining, confirm the visual field according to the anteroposterior position location picture and the side locating image of object to be checked, and then obtain the size and the centre coordinate of each visual field cross section; And send said size and centre coordinate to said measurement territory radius calculation module 202.

Before CT equipment begins series scanning or helical scanning, need scan a width of cloth or two width of cloth location picture to patient usually, confirming the position and the size of object to be checked, thereby obtain the scope of CT scan.Can obtain the anteroposterior position location picture and the side locating image of object to be checked through following mode: when human body lies low; X-ray tube shines object to be checked at 90 degree or 270 degree (being vertical direction) and promptly obtains anteroposterior position location picture, and X-ray tube shines object to be checked at 0 degree or 180 degree (being horizontal direction) and promptly obtains side locating image.The doctor confirms to surround the visual field (being aforementioned FOV) of this object to be checked according to this two width of cloth location picture, is generally the rectangular area, and its big I is provided with according to doctor's experience.The doctor generally can be provided with FOV bigger, and to cover object to be checked fully, this has but increased the x-ray irradiation that object to be checked peripheral region is accepted to a certain extent.Although still in the safe dose scope, we always hope under the prerequisite that does not influence image quality the X ray of human body acceptance, further reduce the x-ray dose that object to be checked peripheral region receives in this case.Can adjust FOV according to the different sizes of object to be checked so hope the doctor, as utilize the profile recognition technology of CT system to obtain the size of object to be checked,, so just reduce the x-ray irradiation that object to be checked peripheral region is accepted its size as FOV.In addition; The cross section of FOV is a rectangle among the present invention, and this orthogonal circumscribed circle is FOM, so FOV＜FOM; This is because object to be checked must be measured through the sheet of reading that is included in the reconstruction regions at every turn in principle, just can carry out correct reconstruction so have only when object to be checked is in FOM.

After obtaining visual field cross section, and then just can obtain the size and the centre coordinate of visual field cross section.The further visual field of the present invention cross section acquisition module 201 also was used for before obtaining said centre coordinate, and said arbitrary visual field cross section or each visual field cross section are carried out the off-centre reconstruction.

Because different patients' build is different; The position of same patient's Different Organs or tissue with vary in size; When object to be checked is carried out image reconstruction, if patient's build is big and/or focus in a side of patient body, make sick bed vertical direction go up and down and/or translation in the horizontal direction after still can't arrive the center of object to be checked; Just need carry out off-centre and rebuild, the abscissa that obtains the FOV cross-section center departs from distance y _ 0 of departing from frame central apart from x_0 and vertical coordinate of frame central.Wherein the vertical lifting direction of sick bed is the y direction, and the horizontal direction of sick bed turnover frame is the z direction, and the z direction is vertical with the y direction, with y direction and all orthogonal direction of z direction then be the x direction.

According to the first embodiment of the present invention; When frame did not tilt in whole scanning process, (x_0 was the same y_0) to the centre coordinate after the size of each FOV cross section is rebuild with off-centre; (x_0 y_0) gets final product coordinate after the size that demand goes out arbitrary cross section and eccentric the 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; Need the inclination frame to avoid scanning eyes; At this moment FOV just no longer is rectangle but parallelogram or rhombus, so for different FOV cross sections, it is fixed no longer just with the distance that vertical coordinate departs from frame central that the abscissa of each cross-section center departs from the distance of frame central; But change according to each FOV cross section, it is set to (x _i_ 0, y _i_ 0), wherein i is the number of FOV cross section.

Measure territory radius calculation module 202, be used for calculating a measurement territory radius according to the size and the centre coordinate of said arbitrary visual field cross section; Perhaps size and the centre coordinate according to said each visual field cross section calculates a plurality of measurements territory radius; And send said measurement territory radius to said intermediate angle computing module 203.

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

$r=\sqrt{2}(\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600011.png,HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{FOV}}}{2}+\max \{|x\_0|,|y\_0|\left\}\right)---\left(1\right)$

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

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

$r_i=\sqrt{2}(\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; FOV"\; filenames="HSA00000276070600011.png,HSA00000276070600012.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{FOV}}}{2}+\max \{|x_i\_0|,|y_i\_0|\left\}\right)---\left(2\right)$

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

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

Fig. 2 is the sketch map that in CT partly scans, adopts system and method for the present invention that FOM is scanned.

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

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

As shown in Figure 2, wherein dis_FC is the distance 11 from the focus of X-ray tube 1 to the CT frame central, and α is an intermediate angle, shown in X ray fan beam angle 10 among 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 _iCalculate corresponding time intermediate angle α according to following formula (4) _i

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

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

α＝max{α _n，...，α _n+X} (5)

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

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

Rebuild angle calculation assembly 21, be used for intermediate angle α is added that 180 degree obtain rebuilding angle

and send said reconstruction angle to scanning device 22.

Calculate reconstruction angle according to intermediate angle α by following formula (6)

Only differ from 180 degree owing to rebuild angle and intermediate angle, so

also changes along with the size of FOV cross section.Here

rebuilds angle for carrying out the required minimum of image reconstruction.

Scanning device 22 is used for according to rebuilding angle

object to be checked being carried out part scanning.

Further; Said CT system also comprises exposure angle Control Component 23; Be used to receive intermediate angle α from intermediate angle computation module 20; The angle of will making public is controlled to be intermediate angle α and scans object to be checked is carried out part, thereby further reduces the irradiation of FOM peripheral region and the x-ray dose of human body reception.

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

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

Preferably, the said visual field cross-section center coordinate that obtains further comprises: before obtaining said centre coordinate, said visual field cross section is carried out off-centre and rebuild.

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

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

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

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

Step 303 when frame does not tilt, is measured the territory radius r according to said one and is calculated said intermediate angle α; Perhaps when rack inclining, according to said a plurality of measurements territory radius r _iObtain intermediate angle α a plurality of times _i, and the maximum of getting said intermediate angle is as said intermediate angle α.

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

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

Step 304 adds that with said intermediate angle 180 degree obtain said reconstruction angle.

Can calculate the reconstruction angle by formula (6).

Step 305 is carried out part scanning according to rebuilding angle

to object to be checked.

Further, CT scan method of the present invention also comprises step 306, and the angle of will making public is controlled to be said intermediate angle object to be checked is carried out part scanning.This point is existing specifying in exposure angle Control Component 23, repeats no more here.

Adopt CT scan system and method for the present invention that object to be checked is carried out part scanning, can shorten sweep time, also just improved temporal resolution, reduced the x-ray dose that patient accepts simultaneously.As shown in Figure 2; Though the exposure angle beta is fixed in remaining of irradiation FOM 9; 7 dextrorotation gyrations

in-position 8 gets final product but 1 needs of X-ray tube are from the position; And needn't image pattern 1 that kind rotate to position 5, reduced

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

Be about 220 °, the time of part scanning is merely 0.3s like this, has reduced 8.3% than fixing 0.33s sweep time that rebuilds angle, and this just helps scanning organ of locomotion or tissues such as heart more.

In addition; In two border radiuses of two border radiuses of the X ray fladellum at 7 places, position and the X ray fladellum at 8 places, position, all taken place to intersect among Fig. 2; Like the intersection of dotted line and solid line among the figure, and that kind that conventional part scanning requires in needn't image pattern 1 must have a border radius coincidence.

The above is merely preferred embodiment of the present invention, and is in order to restriction the present invention, not all within spirit of the present invention and principle, any modification of being done, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (12)

1. an X ray computer tomographic system is used for object to be checked is carried out part scanning, and this system comprises: intermediate angle computation module, reconstruction angle calculation assembly and scanning device, wherein,

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

Said reconstruction angle calculation assembly is used for said intermediate angle is added that 180 degree obtain said reconstruction angle, and sends said reconstruction angle to said scanning device;

Said scanning device is used for according to said reconstruction angle object to be checked being carried out part scanning.

2. system according to claim 1 is characterized in that, said intermediate angle computation module comprises: visual field cross section acquisition module, measurement territory radius calculation module and intermediate angle computing module,

Said visual field cross section acquisition module is used for when frame does not tilt, and confirms the visual field according to the anteroposterior position location picture and the side locating image of object to be checked, and then obtains the size and the centre coordinate of arbitrary visual field cross section; Perhaps when rack inclining, confirm the visual field according to the anteroposterior position location picture and the side locating image of object to be checked, and then obtain the size and the centre coordinate of each visual field cross section; And send said size and centre coordinate to said measurement territory radius calculation module;

Said measurement territory radius calculation module is used for calculating a measurement territory radius according to the size and the centre coordinate of said arbitrary visual field cross section; Perhaps size and the centre coordinate according to said each visual field cross section calculates a plurality of measurements territory radius; And send said measurement territory radius to said intermediate angle computing module;

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

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

4. system according to claim 1; It is characterized in that; Said system further comprises: exposure angle Control Component, be used to receive the said intermediate angle of said intermediate angle computing module, and the angle of will make public is controlled to be said intermediate angle and scans object to be checked is carried out part.

5. an X ray computer tomoscan method comprises the steps:

Size and centre coordinate according to the visual field cross section of object to be checked calculate intermediate angle;

Said intermediate angle is added that 180 degree obtain said reconstruction angle;

According to said reconstruction angle object to be checked is carried out part scanning.

6. method according to claim 5 is characterized in that, said calculating intermediate angle comprises:

When frame does not tilt; Anteroposterior position location picture and side locating image according to object to be checked are confirmed the visual field; And then obtain the size and the centre coordinate of arbitrary visual field cross section; And, measure the territory radius for one that calculates said arbitrary visual field cross section, again according to the said intermediate angle of said measurement territory radius calculation according to said size and centre coordinate.

7. method according to claim 5 is characterized in that, said calculating intermediate angle comprises:

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

8. according to claim 6 or 7 described methods, it is characterized in that the said visual field cross-section center coordinate that obtains further comprises: before obtaining said centre coordinate, said visual field cross section is carried out off-centre rebuild.

9. according to claim 6 or 7 described methods, it is characterized in that, calculate according to following formula and measure the territory radius:

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

Wherein r is the radius in said measurement territory, L _FOVBe the width of visual field cross section and the greater in the 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. method according to claim 6 is characterized in that, calculates intermediate angle according to following formula:

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

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

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

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

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 the CT frame central, r _iIt is the measurement territory radius of i visual field cross section.

12. method according to claim 5 is characterized in that, said method further comprises: the angle of will making public is controlled to be said intermediate angle object to be checked is carried out part scanning.

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