CN109613462A - A kind of scaling method of CT imaging - Google Patents
A kind of scaling method of CT imaging Download PDFInfo
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- CN109613462A CN109613462A CN201811388986.9A CN201811388986A CN109613462A CN 109613462 A CN109613462 A CN 109613462A CN 201811388986 A CN201811388986 A CN 201811388986A CN 109613462 A CN109613462 A CN 109613462A
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/58—Calibration of imaging systems, e.g. using test probes, Phantoms; Calibration objects or fiducial markers such as active or passive RF coils surrounding an MR active material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
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- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
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Abstract
The invention discloses a kind of scaling methods of CT imaging, determine the transmission model of CT imaging system according to known transmission medium and the transmission data being collected into first.The transmission parameters of unknown medium are determined using Radon integral transformation and inverse transformation on the basis of this model.In view of ray may be subjected to the influence of external interference and rotary motion in CT system, transmission data carries out adaptive smooth denoising.Through transmission parameters after transformation template compared with the accuracy of original template transmission parameters, the template of CT system is improved to new template.
Description
Technical field
The present invention is to be related to a kind of parameter calibration method of CT imaging, concretely relates to a kind of CT system parameter really
Fixed and image reconstruction algorithm.
Background technique
CT system is made of transmitter, detector and square pallet, what entire emitting-receiving system can be fixed around certain
Rotation center rotation.Because CT image reconstruction algorithm is all built upon in ideal system parameter, need to make system parameter
As far as possible accurately, can just make image reconstruction closer to actual conditions.The calibration technique of existing CT imaging is by imaging object
The influence of movement and metal, it is difficult to the true shape of Accurate Determining object.Electromagnetic radiation in CT system also can to imaging effect
It has an impact.
Summary of the invention
The purpose of the present invention is overcoming deficiency in the prior art, a kind of parameter calibration of novel CT imaging is proposed
Method.Being imaged for known media is first used to absorb the rotation center that data scaling goes out CT system, the parameters such as detector distance, then
The imaging transmissivity of unknown medium is demarcated using Radon transformation algorithm in the imaging system of known parameters, and is proposed
A kind of new template, for establishing corresponding peg model, to improve stated accuracy and stability.
The present invention is achieved through the following technical solutions:
A kind of parameter calibration method of CT imaging, comprising the following steps:
The first step will typically be justified using the center of CT system square templates as establishment of coordinate system cartesian cartesian coordinate system
The discrete point of shape and the absorption data of an elliptical absorbing medium is converted into continuous figure, sets out rotation center coordinate, visits
The slope of survey device cell spacing and 180 directions, the functional relation across uniform dielectric damping capacity and after gain process,
Simultaneous ellipse and equation of a circle, it can be deduced that the calculated value of the data after absorption is compared with the actual value being collected into；
Second step, calculated value and the actual value for choosing corresponding to some detector cells 180 data are equal, can solve 180
A slope is scaled the angle degree of directions of rays and positive direction of the x-axis；
Third step, then several detectors are chosen, the angle degree solved is averaged, 180 angle degrees can be exported.
For square templates, image reconstruction is carried out using Radon image reconstruction model, is adopted before using Radon function
It is filtered with cubic spline principle, the anti-Integral Processing of Radon is carried out to filtered data, the shape of correspondence image can be obtained；
The shape being fitted according to image can obtain relative position of the ellipse in emission system, obtain depending on the relative position and be
The relative position of the rotation center of system in the picture；According to obtained conclusion, the geometric center of square rotation plate face with
The relative different of the system rotation center is it is known that demarcate square templates center according to rotation center, and in conjunction with the ellipse, institute is in place
Set the position that can obtain the ellipse relative square template.
The measurement data of unknown medium is used into the matrix and known Jie of the anti-integral transformation of Radon and boil down to 256*256
The matrix of prime number evidence compares, and the numerical value of same position is subtracted each other to take absolute value obtains error rate in the position divided by standard value 1,
Then the average value for calculating all location error rates, then obtains the precision of parameter calibration.To the roundlet center of circle and elliptical center
Distance, four parameters of elliptical major semiaxis length and semi-minor axis length carry out sensitivity analysis, combine correlation based on the analysis results
The new calibrating template of Data Design.
The radius of the roundlet of periphery is smaller, and corresponding accuracy is higher, but simultaneously as image is that have 256*256 a discrete
Point composition, therefore when the radius of roundlet is smaller, error is also bigger, and radius shortens 1 ㎜, the change 0.02% of accuracy, phase
To smaller.And elliptical long axis with short axle when equally shortening similar ratio, knots modification is significantly greater.But based on the steady of image
Qualitative, area shared by the medium for needing to demarcate cannot be too small, otherwise can serious distortion.
It is directed to the biggish absorption image of noise content in the first step, needs to be gone on the basis of above-mentioned Radon model
Noise processed, specifically: adaptive smooth denoising model only is established to statistical noise and is restored, the model is to planar medium
Each point and its neighborhood are analyzed, and the statistic of corresponding neighborhood is obtained, and separate statistical noise by statistic and the point absorbs
True value embodies the effect of reduction true value using the smoothness of neighborhood where the point as index.
Internal system noise mainly includes the noise of electronic circuit and due to ray emission process and ray and substance phase
The randomness of interaction process and the statistic fluctuation noise for causing detector to export, i.e. circuit noise and statistical noise, they are
The main source of system noise.Influence of the noise of electronic circuit to system can be ignored substantially, so can be to the system
Statistical noise analyzed.The anti-integral transformation of Radon can be carried out to the transmission data being collected into, gained distribution map is inputted
The numerical value of each point is exported because directly anti-integral gained planar graph is noisy acoustic model, exports number by above-mentioned algorithm
Value is made of above-mentioned statistical noise, absorptivity mean value, variations in detail value.
It, will be typical round first using the center of CT system square pallet as establishment of coordinate system cartesian cartesian coordinate system
It is converted into continuous figure with the discrete point of the absorption data of an elliptical absorbing medium, sets out rotation center coordinate, is detected
The slope of device cell spacing and 180 directions, the functional relation across uniform dielectric damping capacity and after gain process, connection
Vertical oval and equation of a circle, it can be deduced that the calculated value of the data after absorption is compared with the actual value being collected into, makes overall error
It is minimum.Ray is obtained perpendicular to long axis by the RGB rendering figure that analysis data and the data by being collected into are drawn in practical operation
With two special circumstances of short axle, the spacing of detector cells can be first found out, the coordinate of rotation center declines with uniform dielectric is crossed
Subtract energy and the functional relation after gain process.Then, the calculating of 180 data corresponding to some detector cells is chosen
Value is equal with actual value, can solve 180 slopes, be scaled the angle degree of directions of rays and positive direction of the x-axis.It is missed to reduce
Difference similarly, then chooses several detectors, and the angle degree solved is averaged, and can export 180 angle degrees.
The problem of unknown dielectric distribution in the square templates, can not assume its decaying because it is unknown to be related to medium
Amount is directly proportional to light penetration length, therefore introduces Radon image reconstruction model and carry out image reconstruction.Because of the CT imaging generally used
Technology is first generation Plane Rotation technology, and there are Divergent Phenomenons for transmitted light, can not accurately reflect the shape of institute's transmission goal, therefore
Using using cubic spline principle to be filtered before Radon function, the anti-Integral Processing of Radon is carried out to filtered data,
The shape of correspondence image can be obtained.The shape being fitted according to image can obtain relative position of the ellipse in emission system, can root
The relative position of the rotation center of this system in the picture is obtained according to the relative position.According to obtained conclusion, square
The geometric center of plate face and the relative different of the system rotation center are rotated it is known that therefore square wood can be demarcated according to rotation center
Plate center can obtain the position of the ellipse relative square plank in conjunction with the ellipse position.
For the biggish absorption image of noise content, need to carry out Denoising disposal on the basis of above-mentioned Radon model.
Meet the statistical noise influence on RT of rule in CT system much larger than other external world's influences and internal influence, so only
Adaptive smooth denoising model is established to statistical noise to restore.
Aiming at the problem that parameter calibration template, the measurement data of unknown medium can be used into the anti-integral transformation of Radon simultaneously
The matrix of boil down to 256*256 compared with the matrix of known media data, the numerical value of same position is subtracted each other take absolute value divided by
Standard value 1 obtains error rate in the position, then calculates the average value of all location error rates, then obtains parameter calibration
Precision.To the distance in the roundlet center of circle and elliptical center, four parameters of elliptical major semiaxis length and semi-minor axis length carry out sensitive
Degree analysis, combines related data to design new calibrating template based on the analysis results.
Compared with prior art, the beneficial effects of the present invention are:
Two kinds of mathematical models according to the present invention are applied to the neck of image restoring as the Fundamentals of Mathematics of image reconstruction
Domain.Radon integral is not only applicable in this directional light CT system with anti-integral transformation, is widely applied and is pushed CT technology from flat
Row light develops to fan beam, cone-shaped beam, but computer can not solve continuous wireless line integral, and discrete integral is used
There are problems that the stability of image and edge clear in reconstruction image；Adaptive smooth denoising model has also been widely applied
In the aspect of photo denoising, compared to median filtering method there is a possibility that the resolution ratio of image incurs loss, it is also possible to lead to peak
Value signal is suppressed, and Wavelet noise-eliminating method is only applicable to white noise and broadband noise, and impulsive noise cannot be dropped well
It makes an uproar effect, this method utmostly eliminates noise, achieve more satisfactory while guaranteeing the details such as image border jump
Effect.
Detailed description of the invention
Fig. 1 is the parameter calibration flow chart of known transmission medium；
Fig. 2 is the parameter calibration flow chart of unknown transmission medium；
Fig. 3 is the transmission schematic diagram of unknown inhomogeneous medium；
In Fig. 3,1 is the transmitted ray of CT system, 2 be in CT system through across inhomogeneous medium, 3 be transmission of radiation medium
Intensity in transmission on a projection plane afterwards；
Fig. 4 is the flow chart of modified parameters calibrating template.
Specific embodiment
In the parameter calibration process of the CT imaging of known transmission medium, need to pass through discrete image data serialization
The rotation center of CT imaging system and the rotation center of image forming medium are made in Radon transformation.
The unknown medium of CT imaging system transmission is likely to be non-uniform dielectric, and the data after transmiting there may be it is white
Noise.Therefore the white noise content of transmission data is examined first, and carries out denoising using adaptive smooth Denoising Algorithm, it reuses
The anti-integral transformation algorithm of Radon swaps out data for projection contravariant transmission medium.
When improving out new calibrating template, the measurement data of unknown medium is used into the anti-integral transformation of Radon and boil down to
The numerical value of same position is subtracted each other and is taken absolute value divided by standard value 1 compared with the matrix of known media data by the matrix of 256*256
Error rate in the position is obtained, the average value of all location error rates is then calculated, then obtains the precision of parameter calibration.It adjusts
Mould preparation plate is to improve stated accuracy.
Present invention is further described in detail with specific embodiment with reference to the accompanying drawing:
In the imaging parameters demarcation flow figure of known transmission medium shown in Fig. 1, flute card is first established with square tray center
That coordinate system, introduces rotation center coordinate, detector spacing, and the slope of straight line where 180 directions of rays and ray pass through
The functional relation of even dielectric thickness and the numerical value after gain, can establish equation with collected transmission numerical value, can be with most
Small square law solves.In actual operation, data are first analyzed, the specific position of detector plane and transverse is found out, it is approximate
Obtain cell spacing d；Reasonable assumption CT system rotation center is in the receiver on vertical line, special also according to vertically and horizontally
Position obtains the deviation of rotation center Yu square templates geometric center, and verifies rotation center in the receiver on vertical line；It adopts
The data of numerical value q after collecting multiple groups thickness h and gain, reasonable assumption gain function are that linear extendible model is fitted it, and tests
Demonstrate,prove rotation center coordinate.180 flying spot equations of a detector cells are selected to enable itself and corresponding actual value phase in a model
Deng solving 180 angles, similarly select 4 detectors again, take the average value of angle, obtain final sumbission.
In the imaging parameters demarcation flow figure of unknown transmission medium shown in Fig. 2, it is possible to which the transmission medium passed through is
It is non-uniform.When CT ray passes through non-uniform dielectric, Absorption of Medium rate need to be integrated the enterprising line of the straight line where light, that is, drawn
Enter Radon integral and anti-integral transformation.The transmission data being collected into is obtained into required unknown medium using the anti-integral transformation of Radon
Shape can find out position of the shape with respect to CT system rotation center using the unknown elliptical feature of shape of medium, then
According to the position of square templates relative rotation center, which is translated and compressed on square templates, can be found out
Position of the shape relative to square templates, such as Fig. 3.
If there are more apparent fluctuations at zero for collected data, i.e. white noise is more apparent, and the noise of CT system is big
The mostly statistical noise of internal system guarantees that image edge clear is complete in order to effectively remove statistical noise again, proposes adaptive
Smoothing denoising model is answered, as shown in Figure 2.The model introduces the transformation constant k of image to describe in the processing before denoising
Variation of the statistical noise relative to mean value signal proposes and describes the detail on image in neighbourhood of a point with detail signal
Matter analyzes the estimation method of its model parameter in actual image processing system.Use gained image after this method denoising
More visible accurate, effect is obvious.
In the imaging parameters demarcation flow figure of known transmission medium shown in Fig. 4, carry out that Radon is counter to be accumulated to peg model
Divide the matrix of transformation and boil down to 256*256 compared with the matrix that standard gives, calculates relative error, then obtain parameter calibration
Precision.To the distance in the roundlet center of circle and elliptical center, four parameters of elliptical major semiaxis length and semi-minor axis length carry out spirit
Basis of sensitivity analysis, when adjusting single parameter, the radius of roundlet, when elliptical major semiaxis and semi-minor axis shorten, precision increases；It is small round
The distance of the heart and elliptical center does not influence precision.In conjunction with the analysis to existing template and consults in related data and actual conditions and be
Discrete point, length is too small to cause large error, obtain new design template.
Undeclared part involved in the present invention is same as the prior art or is realized using the prior art.
Claims (5)
1. a kind of scaling method of CT imaging, it is characterized in that: the following steps are included:
The first step will typically be justified using the center of CT system square templates as establishment of coordinate system cartesian cartesian coordinate system
The discrete point of shape and the absorption data of an elliptical absorbing medium is converted into continuous figure, sets out rotation center coordinate, visits
The slope of survey device cell spacing and 180 directions, the functional relation across uniform dielectric damping capacity and after gain process,
Simultaneous ellipse and equation of a circle, it can be deduced that the calculated value of the data after absorption is compared with the actual value being collected into；
Second step, calculated value and the actual value for choosing corresponding to some detector cells 180 data are equal, can solve 180
A slope is scaled the angle degree of directions of rays and positive direction of the x-axis；
Third step, then several detectors are chosen, the angle degree solved is averaged, 180 angle degrees can be exported.
2. the scaling method of CT imaging according to claim 1, it is characterized in that:
For square templates, image reconstruction is carried out using Radon image reconstruction model, uses three before using Radon function
Secondary batten principle is filtered, and is carried out the anti-Integral Processing of Radon to filtered data, can be obtained the shape of correspondence image；According to
The shape that image is fitted can obtain relative position of the ellipse in emission system, obtain this system depending on the relative position
The relative position of rotation center in the picture；According to obtained conclusion, the geometric center of square rotation plate face is with this
Unite rotation center relative different it is known that according to rotation center demarcate square templates center, can in conjunction with the ellipse position
Obtain the position of the ellipse relative square template.
3. the scaling method of CT imaging according to claim 2, it is characterized in that: the measurement data of unknown medium is used
The matrix of the anti-integral transformation of Radon and boil down to 256*256 are compared with the matrix of known media data, by the numerical value of same position
Subtract each other to take absolute value and obtain error rate in the position divided by standard value 1, then calculates the average value of all location error rates, so
The precision for obtaining parameter calibration afterwards, to the distance in the roundlet center of circle and elliptical center, elliptical major semiaxis length and semi-minor axis length
Four parameters carry out sensitivity analysis, combine related data to design new calibrating template based on the analysis results.
4. the scaling method of CT imaging according to claim 1, it is characterized in that: biggish for noise content in the first step
Absorption image needs to carry out Denoising disposal on the basis of above-mentioned Radon model, specifically: only statistical noise is established certainly
Adaptive smoothing denoising model is restored, which analyzes each point and its neighborhood of planar medium, obtains corresponding neighbour
The statistic in domain separates statistical noise by statistic and the point absorbs true value, using the smoothness of neighborhood where the point as index
Embody the effect of reduction true value.
5. the scaling method of CT imaging according to claim 1, it is characterized in that: passing through analysis data and the number by being collected into
Ray is obtained perpendicular to two special circumstances of long axis and short axle according to the RGB rendering figure being drawn in, and can first find out detector cells
Spacing, the coordinate of rotation center and cross uniform dielectric damping capacity and the functional relation after gain process.
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