CN101396270B - Method for reducing the influence of examining bed on CT image - Google Patents
Method for reducing the influence of examining bed on CT image Download PDFInfo
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- CN101396270B CN101396270B CN200710153225.0A CN200710153225A CN101396270B CN 101396270 B CN101396270 B CN 101396270B CN 200710153225 A CN200710153225 A CN 200710153225A CN 101396270 B CN101396270 B CN 101396270B
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Abstract
The invention provides a method for reducing the effect of an examination couch on a CT image. The method comprises the following steps: (1) under the condition that the examination couch is empty, an X-ray is used for scanning the examination couch, and after the X-ray passes the examination couch, the function of the extinguishment of the X-ray, the angle of the X-ray, and the position of the examination couch is obtained; (2) under the condition that a person to be examined lies on the examination couch, the X-ray is used for scanning the person to be examined and the examination couch under different angles, the extinguishment of the X-ray after the X-ray passes the person to be examined and the examination couch is obtained by measuring under different angles; (3) the extinguishment of the X-ray after the X-ray passes the person to be examined is obtained by calculating under different angles; (4) a convolution backprojection algorithm is used for reconstructing CT images on the extinguishing after passing the person to be examined.
Description
Technical field
The present invention relates to a kind of method of improving picture quality, the especially a kind of method of examinating couch that in computed tomography (Computed Tomography is hereinafter to be referred as CT) process, reduce to the influence of CT image.
Background technology
The computer tomography scanning means mainly is made up of frame (gantry) examinating couch (table), is provided with high tension generator (generator), bulb (tube), detector (detector) and data collecting system (dataacquisition system) in the frame.The high pressure that high tension generator produces uses for bulb, and bulb and detector then are installed in the both sides that are scanned tissue respectively, and direction is relative.Bulb generates X ray, and detector receives the projection of X ray behind human body.CT utilizes the X wire harness the certain thickness aspect in human body a part to be scanned the projection (projection) that obtains different angles, and utilization convolution backprojection algorithm (convolutedbackprojection, also cry filtered back projection, filtered backprojection) rebuild the cross-sectional image that (reconstruction) goes out this position tissue.
Present examinating couch, the examinating couch bed board that especially carries the patient are normally made by special steel material.The characteristics of this steel material are lightweights, and are less to the absorption of X ray.But, however, because this special material can absorb a spot of X ray, and the X ray amount through behind human body and the examinating couch that the image quality of CT image and detector receive is directly proportional, so the examinating couch that this special material is made still can cause adverse influence to last image.
Because material is special, the expense that is used to make examinating couch at present is relatively more expensive, and this has increased the production cost of CT device.
Summary of the invention
Main purpose of the present invention provides a kind of method of the CT of improvement image quality, can eliminate the influence that the existence of examinating couch in the scanning process causes the CT scan image by this method.Owing to eliminated this influence, made the material of making examinating couch to replace with common material, thereby can reduce production cost from present relatively more expensive special steel material.
For achieving the above object, technical scheme of the present invention specifically is achieved in that a kind of method that reduces examinating couch to the influence of CT image, said method comprising the steps of:
(1) is under the situation of empty bed at described examinating couch, uses X ray that described examinating couch is scanned, obtain the function of described X ray through the position of the decay behind the described examinating couch and the angle of described X ray, described examinating couch;
(2) under examine person is positioned at situation on the described examinating couch, use X ray under different angles, described examine person and examinating couch to be scanned, record the decay after described X ray under the described different angles is through examine person and examinating couch;
(3) calculate decay after described X ray under the described different angles only passes through examine person; And
(4) use the convolution backprojection algorithm only to carry out the CT image reconstruction through the decay behind the examine person to described.
According to an aspect of the present invention, in step (1), the position of described examinating couch comprises that hat to, arrowhead and axially.
According to another aspect of the present invention, if the material of described examinating couch described be uniform distribution axially, then the position of described examinating couch comprise hat to and arrowhead.
According to a further aspect of the invention, in described step (1), examinating couch for unlike material, be under the situation of empty bed at described examinating couch respectively, X ray is scanned described examinating couch in different angles, obtain the function of the described X ray of the examinating couch of unlike material through the position of the decay behind the described examinating couch and described angle, described examinating couch.
According to a further aspect of the invention, described examinating couch is the steel examinating couch.
According to above-mentioned algorithm of the present invention, can further reduce even eliminate the influence that the existence of examinating couch in the scanning process causes the CT scan image.Owing to eliminated this influence, made the material of making examinating couch to replace with common material, thereby can reduce production cost from present relatively more expensive special steel material.
Description of drawings
Below in conjunction with accompanying drawing the specific embodiment of the present invention is described in further detail, wherein:
Fig. 1 is the method flow diagram of reduction examinating couch of the invention process to the influence of CT image.
The specific embodiment
Common CT scan process is that at first, examine person lies on the CT examination bed; Then, the health for the treatment of the examiner at different angles emission X ray by the CT bulb scans, the detector that is positioned at bulb offside on the frame records the attenuation through X ray behind examine person's the health, because this moment, examine person was positioned on the examinating couch, therefore strictly speaking, this moment, detector recorded is attenuation through X ray behind examine person's health and the examinating couch bed board; At last, according to the measurement result of detector, utilization convolution backprojection algorithm is carried out image reconstruction, and generating finally can be for the CT reconstructed image of diagnosis use.
In said process, the examinating couch bed board can absorb a part of X ray inevitably.Although present bed board by adopting relatively more expensive special material such as special steel to make examinating couch in the prior art, to reduce of the absorption of examinating couch bed board as far as possible to X ray, but this absorption exists all the time, that is to say, the detector actual detection to X ray be the X ray of the X ray that sends of bulb after through the decay of further passing through examinating couch behind examine person's the health again, and in fact wish to be used to generate the CT reconstructed image only be the X ray that sends of bulb through the X ray amount behind examine person's the health, the two difference must be brought adverse effect to the CT quality of reconstructed images.
Adopt the inventive method then can further reduce even eliminate the influence of examinating couch for the CT image.Fig. 1 is the method flow diagram of reduction examinating couch of the invention process to the influence of CT image.According to this embodiment, the present invention can adopt following steps:
The first step for the examinating couch of unlike material bed board, is under the situation of empty bed at examinating couch respectively, and the X ray that uses the CT bulb to send scans examinating couch.This scanning is that the different angles in X ray emission, the diverse location of examinating couch carry out, thereby the X ray that obtains is to be a function of variable with the angle of X ray emission, the position of examinating couch through the decay behind the examinating couch.This function r
i(wherein i represents unlike material for p, θ) expression, and p represents the position of examinating couch, and θ represents the angle of X ray emission.
The position of examinating couch comprises X, Y, three directions of Z, and promptly usually said hat to, arrowhead and axially.Therefore the function above can further be expressed as r
i(x, y, z, θ), and x wherein, y, z represent X, Y, the Z shaft position of examinating couch respectively.
Second step, under examine person is positioned at situation on the examinating couch, use X ray under different angles, to treat the examiner and examinating couch scans, record the decay after through examine person and examinating couch of under different angles X ray.
Scanning process and scanning process of the prior art in second step are basic identical, just record the decay of X ray behind process examine person and examinating couch bed board under the different angles with detector, with μ 1 (x, y) expression.
In the 3rd step, calculate the decay behind the X ray process examine person under the different angles.Owing in the first step, passed through r
i(p, θ) set up X ray, therefore just can calculate decay after X ray only passes through examine person by the decay behind X ray process examine person and examinating couch under the different angles that records in second step only through the synopsis of the position of the angle of the decay behind the NULLCHECK bed and X ray emission, examinating couch.
By said process as can be known, decaying to behind X ray process examine person and the examinating couch bed board:
μ 1 (x, y)=μ (x, y) r
i(x, y, z, θ) (formula 1)
Wherein, (x y) is decay after X ray that the CT bulb sends only passes through examine person's health, r to μ
i(z θ) is the attenuation quotient of the examinating couch of unlike material bed board for x, y, and i represents unlike material, and x, y, z represent X, Y, the Z shaft position of examinating couch respectively, and θ represents the angle of X ray emission, between 0 ° to 360 °.
If to being uniform distribution, then X, Y both direction only need be considered in the position of examinating couch to the material of examinating couch at Z, above-mentioned formula 1 can be reduced to:
μ 1 (x, y)=μ (x, y) r
i(x, y, θ) (formula 2)
Symbol implication wherein is with formula 1.
Therefore can obtain:
μ (x, y)=μ 1 (x, y)/r
i(x, y, z, θ) (formula 3)
Symbol implication wherein is with formula 1.
If to being uniform distribution, formula 3 can be reduced to the material of examinating couch at Z:
μ (x, y)=μ 1 (x, y)/r
i(x, y, θ) (formula 4)
In the 4th step, use the convolution backprojection algorithm to carry out the CT image reconstruction.
So-called CT image reconstruction is the data after surveying according to detector, finds the solution pixel in the image array, re-constructs the process of image then; And finding the solution by computer of image array finished, and in the method for X-CT image reconstruction, at present the most frequently used is the filtered back projection's method that adopts convolution algorithm, also claims convolution back projection method.
Carry out image reconstruction according to the decay behind X ray process examine person and the examinating couch bed board in the prior art, (x y) rebuilds just to utilize above-mentioned μ 1.Through after the inventive method, (x y) carries out image reconstruction, thereby can further reduce even eliminate the influence of examinating couch bed board to the CT reconstructed image to utilize μ.
During convolution backprojection reconstruction image, first is that (x y) has carried out convolution algorithm with a filter function to μ, obtains the projection function of all directions convolution by the initial data that obtains on the detector; And then they are carried out back projection from all directions, promptly by its original route mean allocation on each matrix element, obtain the CT value of each matrix element after superposeing; Again through suitably handling the faultage image that the back just can obtain scanned object, the edge that simple back projection's generation can be eliminated by convolution back projection loses sharp effect, radio-frequency component in the compensation projection and reduction projection centre density, and guarantee that reconstructed image edge clear and inside are evenly distributed.
Claims (5)
1. one kind is reduced examinating couch to the method that the CT image influences, and it is characterized in that said method comprising the steps of:
(1) is under the situation of empty bed at described examinating couch, uses X ray that described examinating couch is scanned, obtain the function of described X ray through the position of the decay behind the described examinating couch and the angle of described X ray, described examinating couch;
(2) under examine person is positioned at situation on the described examinating couch, use X ray under different angles, described examine person and examinating couch to be scanned, record the decay after described X ray under the described different angles is through examine person and examinating couch;
(3) calculate decay after described X ray under the described different angles only passes through examine person; And
(4) use the convolution backprojection algorithm only to carry out the CT image reconstruction through the decay behind the examine person to described.
2. reduction examinating couch according to claim 1 is characterized in that the method for CT image influence, and in step (1), the position of described examinating couch comprises that hat to, arrowhead and axially.
3. reduction examinating couch according to claim 2 is characterized in that the method for CT image influence, if the material of described examinating couch described be uniform distribution axially, then the position of described examinating couch comprise hat to and arrowhead.
4. reduction examinating couch according to claim 2 is to the method for CT image influence, it is characterized in that, in described step (1), examinating couch for unlike material, be under the situation of empty bed at described examinating couch respectively, X ray is scanned described examinating couch in different angles, obtain the function of the described X ray of the examinating couch of unlike material through the position of the decay behind the described examinating couch and described angle, described examinating couch.
5. reduction examinating couch according to claim 1 is characterized in that to the method for CT image influence described examinating couch is the steel examinating couch.
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| CN102551774B (en) * | 2010-12-20 | 2016-05-11 | Ge医疗系统环球技术有限公司 | Belt-type bed and CT equipment and for the acquisition methods of CT equipment Alignment data |
| CN105806858B (en) * | 2014-12-31 | 2019-05-17 | 北京固鸿科技有限公司 | CT detection method and CT equipment |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5117829A (en) * | 1989-03-31 | 1992-06-02 | Loma Linda University Medical Center | Patient alignment system and procedure for radiation treatment |
| US5872829A (en) * | 1996-04-19 | 1999-02-16 | U.S. Philips Corporation | Method for the detection and correction of image distortions in medical imaging |
| CN1792331A (en) * | 2004-12-21 | 2006-06-28 | 西门子公司 | Method of imaging medical equipment |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5117829A (en) * | 1989-03-31 | 1992-06-02 | Loma Linda University Medical Center | Patient alignment system and procedure for radiation treatment |
| US5872829A (en) * | 1996-04-19 | 1999-02-16 | U.S. Philips Corporation | Method for the detection and correction of image distortions in medical imaging |
| CN1792331A (en) * | 2004-12-21 | 2006-06-28 | 西门子公司 | Method of imaging medical equipment |
Non-Patent Citations (1)
| Title |
|---|
| JP特开2007-209746A 2007.08.23 |
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