CN102521809A - Regularization correction method of magnetic resonance phase array coil image uniformity - Google Patents
Regularization correction method of magnetic resonance phase array coil image uniformity Download PDFInfo
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Abstract
Based on a theory that a reconstructed image in magnetic resonance is modulated by a phased array coil unit sensitivity, the invention provides a regularization correction method of a magnetic resonance phase array coil image uniformity. According to the method of the invention, a general coil with the uniform sensitivity in the superconductive magnetic resonance and each phased array imaging coil channel are used to carry out pre-scan so as to obtain the coil sensitivity. Through introducing a regular function, noise of the reconstructed image can be inhibited. Simultaneously, in the superconductive resonance, the general-coil pre-scan image is taken as a reference image in a regularization function so that the good uniformity can be obtained. A calculating speed is very fast. The method has little influence on image reconstruction time.
Description
Technical field:
The present invention relates generally to the inhomogeneity regularization bearing calibration of a kind of magnetic resonance phased-array coil image, belongs to the mr imaging technique field.
Background technology:
Magnetic resonance imaging (MRI) is because it radiationless, and resolution is high, and advantages such as multi-faceted, multiparameter are used widely at present clinically.The image homogeneity is to weigh the key index of MRI imaging system.The inhomogeneous accuracy that not only can directly influence diagnosis of image, the use to post processing of image such as Image Automatic Segmentation technology simultaneously also can produce harmful effect.
The inhomogeneous different regional areas that are meant homologue in image of image, the average of image pixel gray-scale value or other picture characteristics, variance have very large deviation.The homogeneity of MRI image can receive the influence of several factors usually, such as the homogeneity of main field, and the homogeneity of radio-frequency transmissions field, the homogeneity of gradient fields, and the susceptibility of receiving coil etc.In numerous factors, it is a principal element that the receiving coil susceptibility relevant with phased-array coil distributes.Phased-array coil is exactly that a plurality of linear polarization coils or quadrature coil are formed a phased array, and each component is called coil unit.At present, phased-array coil has been widely used in the MRI equipment, because it can provide bigger scan vision, and higher signal to noise ratio (S/N ratio).Particularly use the parallel imaging technique of phased-array coil significantly to shorten sweep time, in dynamic imaging, can effectively suppress pseudo-shadow.
The most frequently used image reconstruction, the composition algorithm of phased-array coil is the SOS algorithm, and the SOS algorithm is as last reconstructed image with the image behind the quadratic sum evolution of all coils cell picture.Yet, itself be uneven owing to form the susceptibility distribution of the coil unit of phased-array coil, generally strong at regional signal near coil; Along with the increase of the distance of off-line circle, signal constantly reduces.Therefore composograph can receive the modulation with the locus coherent signal, inequality property occurs.At present, big metering method can be used for the nonuniformity correction of phased-array coil image, mainly contains based on the correcting algorithm of post processing and filtering with based on the responsive method of scheming of coil.Method based on post processing and filtering; Suppose to cause that the uneven deviation field signal of image is the low frequency signal with spatial variations, so when deviation field signal change of frequency was very fast, this method tended to lose efficacy; Particularly for baroque human body image, this class methods calibration result is less better; And tradition at first need obtain the sensitivity figure of coil according to reconstructed image based on the method for the responsive figure of coil, carries out some complicated aftertreatments again, makes the image reconstruction time extend.
Summary of the invention:
Goal of the invention:
The present invention provides a kind of magnetic resonance phased-array coil image inhomogeneity regularization bearing calibration; Its purpose is to solve when using phased-array coil as receiving coil in the magnetic resonance owing to receive the modulation that signal receives the coil unit susceptibility relevant with the position; Reconstructed image occurs inhomogeneous, thereby influences diagnosis and problems such as later image is cut apart automatically, registration.
Technical scheme:
The inhomogeneity regularization bearing calibration of a kind of magnetic resonance phased-array coil image, it is characterized in that: this method is carried out according to the following steps:
The calculating of a, coil sensitivities volume data:
Use is applicable to the uniformly big body coil of superconducting magnetic resonance and the low resolution multilayer prescan that imaging coil carries out the 3D sequence, in order to reduce the influence that cause image the locus, need carry out LPF to prescanned data, utilizes formula then
Try to achieve the susceptibility volume data of each coil unit, wherein<>The expression LPF, M
iBe the reconstructed image of i unit of phased array imaging coil, B is the reconstructed image of homogeneous body coil or the root mean square image of imaging coil unit;
B, according to its corresponding susceptibility image of positional information calculation of scan image to be corrected:
Since image to be corrected on the locus can not with
In image overlap fully, so must be according to the positional information and the direction parameter of image to be corrected, use the 3D linear interpolation algorithm from the susceptibility volume data
Middle interpolation goes out the responsive collection of illustrative plates s of the corresponding coil of image to be corrected
i
C, use regularization method carry out homogeneity correction to reconstructed image:
Use regularization updating formula
can carry out homogeneity correction to acquired original image R; Wherein β is a regular parameter; C is the regularization function, and W is the noise covariance matrix of receiving coil;
D, in the scan rebuilding module of MR imaging apparatus, embed this algorithm, the inhomogeneous correction of image that the susceptibility modulation that receives the phased-array coil unit is caused.
Advantage and effect:
When the present invention uses phased-array coil for solving in the magnetic resonance imaging; Image often adopts a kind of brand-new inhomogeneity regularization bearing calibration of magnetic resonance phased-array coil image owing to uneven phenomenon appears in the modulation that receives coil sensitivities, has following advantage:
Novel part of the present invention is its principle from phased-array coil reception signal, makes full use of the information that provides in the magnetic resonance imaging process.Construct a suitable cost function, minimized this cost function through least square method then, obtained reflecting the true inhomogeneity ideal image of scanning object.For the robustness that suppresses noise amplification raising algorithm is also introduced the regular function item in cost function.Distinctive big body coil can provide the extraordinary image of homogeneity these characteristics in the superconducting magnetic resonance and in the regularization function, make full use of, the homogeneity image of big body coil image as a reference.The inventive method is calculated simple, and is irrelevant with the scanning sequence type in image source.In addition, can regulate the signal to noise ratio (S/N ratio) and the homogeneity of correcting image, better obtain good homogeneity under the signal to noise ratio (S/N ratio) through regular parameter.Through in the magnetic resonance imaging equipment of reality, using polytype phased-array coil scanning water mould and human body, use method of the present invention to proofread and correct the homogeneity that has significantly improved image then.
Description of drawings:
Fig. 1 scans the inhomogeneous image that even die body obtains for using four-way phase control coil;
Fig. 2 is the intensity profile curve of image middle line among Fig. 1;
Fig. 3 is the low resolution water mould image of body coil;
Fig. 4 is the low resolution water mould image of each unit of imaging coil;
Fig. 5 is a 3D interpolation synoptic diagram;
Fig. 6 is the correcting result of the inventive method to even water mould image;
Fig. 7 is the Gray Projection curve of image middle line among Fig. 6;
Fig. 8 is the correcting result of SPM software to even water mould image;
Fig. 9 is the Gray Projection curve of image middle line among Fig. 8;
Figure 10 is the inventive method and SPM software to the correcting result of human body head scan image relatively.
Embodiment:
The present invention realizes proofreading and correct the image that causes because of phased-array coil in the magnetic resonance imaging is inhomogeneous through a kind of new method.The image homogeneity is to weigh the key index of MRI imaging system.The inhomogeneous accuracy that not only can directly influence diagnosis of image, the use to post processing of image such as Image Automatic Segmentation technology simultaneously also can produce harmful effect.At present, can be used for the method for the nonuniformity correction of phased-array coil image, mainly contain based on the correcting algorithm of post processing and filtering with based on the responsive method of scheming of coil.Method based on post processing and filtering; Suppose to cause that the uneven deviation field signal of image is the low frequency signal with spatial variations, so when deviation field signal change of frequency was very fast, this method tended to lose efficacy; Particularly for baroque human body image, this class methods calibration result is less better; And tradition at first need obtain the sensitivity figure of coil according to reconstructed image based on the method for the responsive figure of coil, carries out some complicated aftertreatments again, makes the image reconstruction time extend.
Through embodiment the present invention is further specified below:
Embodiment: the phased array head coil that uses four passages is to being filled with CuSO
4The even water mould of the F23 of solution is carried out to picture under 1.5T MRI; Scanning sequence is FSE sequence (TR/TE=3000/100, ETL=20, Matrix size=256 * 256; FOV=220mm); Fig. 1 is not for using the inhomogeneous image after the inventive method scanning, and Fig. 2 be the intensity profile curve of this image middle line, and it is bigger inhomogeneous to find out that from scheme the image that obtains for even water mould has occurred.
The inhomogeneity regularization bearing calibration of magnetic resonance phased-array coil image
The technical essential that this invention relates generally to has:
1, the calculating of coil sensitivities volume data:
Use uniformly big body coil (in the superconducting magnetic resonance) and imaging coil to carry out the low resolution multilayer prescan of 3D sequence respectively.For improving prescan speed and reducing the influence of magnetic field inequality to pre-scan images, the prescan 3D sequence use scan matrix that the present invention uses is 32 spin-echo sequence.Be in order to reduce the influence that cause image the locus, need to carry out LPF to prescanned data.The present invention uses the peaceful low-pass filter of the Chinese, because the peaceful low-pass filter of the Chinese has wideer main lobe width and littler secondary lobe amplitude, can reduce the gibbs artifact of filtering image.Utilize formula (1) then, try to achieve the susceptibility volume data of each coil unit
Wherein<>The expression LPF, M
iBe the reconstructed image of i unit of phased array imaging coil, B is the reconstructed image of homogeneous body coil.Fig. 3 is the low resolution water mould image of body coil, and Fig. 4 is the low resolution imaging coil image that the phased array head coil with four coil units obtains.
2, according to its corresponding susceptibility image of positional information calculation of scan image to be corrected:
Next prescan through low resolution need obtain the susceptibility image of this layer correspondence according to the positional information of certain tomographic image to be corrected, the positional information of susceptibility volume data after obtaining responsive figure volume data.In fact be exactly from known volume data interpolation obtain any 1 P in space (value z) so utilize 3D linear interpolation algorithm formula (7), is easy to obtain for x, y:
V
P＝V
0(1-x)(1-y)(1-z)+V
1(1-x)y(1-z)+V
2(1-x)(1-y)(1-z)+
V
3(1-x)yz+V
4x(1-y)(1-z)+V
5xy(1-z)+V
6x(1-y)z+V
7xyz
(7)
V wherein
i(i=0,1 .., 7) are the data on cubical 8 summits at P point place, and these 8 summits are positioned on the known volume data.As shown in Figure 5.
In order to improve the speed of interpolation algorithm; Obtain the space arbitrarily during any value in interpolation from volume data; The present invention is put into all calculating unifications in the coordinate system at volume data place; Promptly carry out from the spatial coordinate transformation to the volume data, belonging to coordinate system, and move to the initial point coincidence that is with physical coordinates to this coordinate origin.Suppose any 1 q among certain tomographic image I at the following coordinate of physical coordinates system (x ', y ', z '), through the direction matrix A at place layer; The center point coordinate of layer (x0, y0, z0), and this coordinate (x in layer; Y) calculate, so: (x ', y ', z ')=A (x; Y, 0)+(x0, y0, z0).And the direction matrix of the low-resolution scan tomographic image of known constituting body data is B, so (8) calculating by formula of the coordinate of q point in volume data
(x″，y″，z″)＝B
-1(x′，y′，z′)＝B
-1A(x，y，0)+B
-1(x0，y0，z0) (8)
After treating each point in the correcting image respectively and calculate through above algorithm, from the susceptibility volume data
Middle interpolation goes out the responsive collection of illustrative plates s of the corresponding coil of image to be corrected
i
3, use regularization method that reconstructed image is carried out homogeneity correction:
Suppose that in the MRI imaging process receiving coil is the phased-array coil with n coil unit, so the pixel x in the complex image of i coil unit acquisition
jValue R
i(x
j) can be expressed as
R
i(x
j)＝S
i(x
j)I(x
j)+N
i(x
j)，i＝1...n；j＝1，...，m (2)
Be the I true picture, S
iBe the plural susceptibility figure of i coil unit, N
iIt is the additive Gaussian noise in this coil unit.Can be expressed as with matrix form
R＝SI+N (3)
Wherein, R=[R
1, R
2..., R
n]
T, S=[S
1, S
2..., S
n]
T, I=[I (x
1), I (x
2) ..., I (x
m)]
T,
S
1＝[S
1(x
1)，S
1(x
2)，…，S
1(x
m)]，R
1＝[R
1(x
1)，R
1(x
2)，…，R
1(x
m)]
To formula (3); Under the situation of known R; Can utilize the method for least-squares estimation to find the solution I, promptly minimize optimal estimation
that the punishment weighted least-squares cost function Ψ (I) shown in the formula (4) obtains I promptly suc as formula (5):
Ψ(I)＝‖R-SI‖
W+βL(I)?(4)
Wherein β is a regular parameter, is used for controlling two bound terms of cost function, and L (I) is the regularization function, generally gets and makes L (I)=I
HCI, getting C among the present invention is unit matrix, W is the noise covariance matrix of receiving coil.So correcting image
can calculate by formula (6):
4, in the scan rebuilding module of MR imaging apparatus, use above-mentioned regularization bearing calibration, and select through proper parameters, can obtain the good image of homogeneity fast.
Fig. 6 and Fig. 7 are respectively the image and the Gray Projection curve of middle line that uses after the inventive method is proofreaied and correct even water mould, and Fig. 8 and Fig. 9 are respectively image and the Gray Projection curve of middle line of the external SPM software approach of use after to even water mould correction.From figure, find out that image is very even, the entire image gray scale is consistent.And SPM software has been raised the gray scale of image border.Use the phased array head coil of four passages that volunteer's head is carried out transverse scan.Use the inventive method to proofread and correct the back and find that the gray scale between same tissue reaches consistent basically in the head image.Figure 10 (a) and (b) with (c) be respectively the image that do not carry out proofreading and correct, use the image after the inventive method is proofreaied and correct and use the image after the SPM software approach is proofreaied and correct, the rectangle among the figure is two ROI that are used to measure average.Gray average in two selected ROI is respectively 84.9 and 85.8, and is respectively 73.2 and 83.6 before proofreading and correct.The entropy of image is respectively 5.5462 and 4.8420 before and after proofreading and correct.Use the image homogeneity after the SPM method is proofreaied and correct also to be increased, the gray average in the rectangle ROI is 72.8 and 74.3, and the image entropy after the correction is 5.0245.But after being to use this method, the unevenness that causes does not obtain proofreading and correct position shown in the arrow of Figure 10 (c) because coil unit distributes in the image border.By contrast, the method for the present invention's proposition is extremely successful to the nonuniformity correction at these positions.
Conclusion:
The present invention relates to a kind of through of inhomogeneous correction of above-mentioned easy, fast algorithm to magnetic resonance phased-array coil images acquired; After in the scan rebuilding module that this algorithm is integrated into MR imaging apparatus; Eliminated the influence of the phased-array coil unit susceptibility factor pair receiving signal system relevant, obtained uniform image with the position.The present invention adopts the method for punishment weighting regularization that inhomogeneous image is proofreaied and correct.Can between the homogeneity of correction chart and signal to noise ratio (S/N ratio), compromise through regularization parameter.And in the regularization function, introduce uniformly big volume image image as a reference, and make algorithm more be prone to convergence, also suppressed the amplification of noise.When calculating the susceptibility image, belong to coordinate system to responsive figure volume data, and, simplified coordinate Calculation through the relation between each coordinate system in order to accelerate the computing velocity unified coordinate system.The inventive method is calculated simple, and is irrelevant with the scanning sequence type in image source.Through big water gaging mould and the somatic data test of in the magnetic resonance imaging equipment of reality, using the scanning of polytype phased-array coil, adopt the inventive method can significantly improve the homogeneity of image.
Claims (1)
1. inhomogeneity regularization bearing calibration of magnetic resonance phased-array coil image, it is characterized in that: this method is carried out according to the following steps:
The calculating of a, coil sensitivities volume data:
Use is applicable to the uniformly big body coil of superconducting magnetic resonance and the low resolution multilayer prescan that imaging coil carries out the 3D sequence, in order to reduce the influence that cause image the locus, need carry out LPF to prescanned data, utilizes formula then
Try to achieve the susceptibility volume data of each coil unit, wherein<>The expression LPF, M
iBe the reconstructed image of i unit of phased array imaging coil, B is the reconstructed image of homogeneous body coil or the root mean square image of imaging coil unit;
B, according to its corresponding susceptibility image of positional information calculation of scan image to be corrected:
Since image to be corrected on the locus can not with
In image overlap fully, so must be according to the positional information and the direction parameter of image to be corrected, use the 3D linear interpolation algorithm from the susceptibility volume data
Middle interpolation goes out the responsive collection of illustrative plates s of the corresponding coil of image to be corrected
i
C, use regularization method carry out homogeneity correction to reconstructed image:
Use regularization updating formula
can carry out homogeneity correction to acquired original image R; Wherein β is a regular parameter; C is the regularization function, and W is the noise covariance matrix of receiving coil;
D, in the scan rebuilding module of MR imaging apparatus, embed this algorithm, the inhomogeneous correction of image that the susceptibility modulation that receives the phased-array coil unit is caused.
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| CN103018689A (en) * | 2012-08-27 | 2013-04-03 | 嘉恒医疗科技有限公司 | Design method for magnetic resonance radio-frequency coil based on stream function |
| CN103091656A (en) * | 2012-12-25 | 2013-05-08 | 深圳先进技术研究院 | Calculating method based on regularization constrain polynomial fitting magnetic resonance coil sensitivity |
| CN109146802A (en) * | 2017-07-31 | 2019-01-04 | 上海东软医疗科技有限公司 | A kind of uniformity correcting method and device of magnetic resonance image |
| CN109188326A (en) * | 2018-09-29 | 2019-01-11 | 上海联影医疗科技有限公司 | MR imaging method and magnetic resonance system |
| CN110687490A (en) * | 2019-10-10 | 2020-01-14 | 上海东软医疗科技有限公司 | Parallel imaging method and device, storage medium and medical equipment |
| CN111445412A (en) * | 2020-03-26 | 2020-07-24 | 北京易康医疗科技有限公司 | Two-dimensional geometric correction method for magnetic resonance image |
| CN115905817A (en) * | 2022-12-20 | 2023-04-04 | 无锡鸣石峻致医疗科技有限公司 | Multi-channel inhomogeneous field signal noise reduction method and device and storage medium |
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| CN103018689A (en) * | 2012-08-27 | 2013-04-03 | 嘉恒医疗科技有限公司 | Design method for magnetic resonance radio-frequency coil based on stream function |
| CN103018689B (en) * | 2012-08-27 | 2015-08-05 | 嘉恒医疗科技有限公司 | Based on the magnetic resonance radio frequency coil method for designing of stream function |
| CN103091656A (en) * | 2012-12-25 | 2013-05-08 | 深圳先进技术研究院 | Calculating method based on regularization constrain polynomial fitting magnetic resonance coil sensitivity |
| CN109146802A (en) * | 2017-07-31 | 2019-01-04 | 上海东软医疗科技有限公司 | A kind of uniformity correcting method and device of magnetic resonance image |
| US10852380B2 (en) | 2017-07-31 | 2020-12-01 | Shanghai Neusoft Medical Technology Co., Ltd. | Magnetic resonance image reconstruction |
| CN109188326A (en) * | 2018-09-29 | 2019-01-11 | 上海联影医疗科技有限公司 | MR imaging method and magnetic resonance system |
| CN109188326B (en) * | 2018-09-29 | 2021-04-06 | 上海联影医疗科技股份有限公司 | Magnetic resonance imaging method and magnetic resonance system |
| CN110687490A (en) * | 2019-10-10 | 2020-01-14 | 上海东软医疗科技有限公司 | Parallel imaging method and device, storage medium and medical equipment |
| CN110687490B (en) * | 2019-10-10 | 2021-12-31 | 上海东软医疗科技有限公司 | Parallel imaging method and device, storage medium and medical equipment |
| CN111445412A (en) * | 2020-03-26 | 2020-07-24 | 北京易康医疗科技有限公司 | Two-dimensional geometric correction method for magnetic resonance image |
| CN115905817A (en) * | 2022-12-20 | 2023-04-04 | 无锡鸣石峻致医疗科技有限公司 | Multi-channel inhomogeneous field signal noise reduction method and device and storage medium |
| CN115905817B (en) * | 2022-12-20 | 2023-11-03 | 无锡鸣石峻致医疗科技有限公司 | Multi-channel non-uniform field signal noise reduction method, device and storage medium |
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Application publication date: 20120627 |