CN105572612A - Method of improving multichannel radio frequency coil performances - Google Patents
Method of improving multichannel radio frequency coil performances Download PDFInfo
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- CN105572612A CN105572612A CN201511027258.1A CN201511027258A CN105572612A CN 105572612 A CN105572612 A CN 105572612A CN 201511027258 A CN201511027258 A CN 201511027258A CN 105572612 A CN105572612 A CN 105572612A
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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
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
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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]
- G01R33/48—NMR imaging systems
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F5/00—Coils
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Abstract
Provided is a method of improving multichannel radio frequency coil performances, comprising the steps of: before magnetic resonance scanning, adding a magnetic meta-material into a multichannel radio frequency coil; under the condition of no radio frequency emission power, collecting the noise of each channel in the multichannel radio frequency coil; calculating the noise coupling matrix of the multichannel radio frequency coil after adding the magnetic meta-material; and in an image reconstruction process, employing the noise coupling matrix to compensate for the coupling of the multichannel radio frequency coil. The method collects the noise of each channel of the multichannel radio frequency coil, calculates the noise coupling matrix thereof, and employs the noise coupling matrix to compensate for the coupling deterioration of the multichannel radio frequency coil in image reconstruction, thereby improving multichannel radio frequency coil performances when the magnetic meta-material is added into the multichannel radio frequency coil, increasing an image signal to noise ratio and a resolution ratio, and improving image quality.
Description
Technical field
The present invention relates to magnetic resonance imaging, particularly relate to a kind of method improving Multi-channel radio-frequency coil performance.
Background technology
Meta Materials performance describes mainly through electromagnetic parameters such as specific inductive capacity, magnetic permeability and refractive indexes.And the Meta Materials of magnetic Meta Materials to be microstructure to electromagnetic field produce magnetic response, it has can the feature of manual control magnetic permeability.Magnetic Meta Materials realizes the adjustment to equivalent permeability by magnetic resonance structure (as split ring resonator) and its distressed structure.When electromagnetic wave incident, split ring resonator can form the LC resonant tank of equivalence in the structure, thus realizes electromagnetic control and constraint by magnetic resonance, realizes strengthening effect to electromagnetic field.
At present, magnetic Meta Materials is used widely in RF application, especially application in magnetic resonance imaging (MagneticResonanceImaging, MRI).Those skilled in the art adopt magnetic Meta Materials to devise the microstructure being applied to magnetic resonance imaging, this kind of microstructure is the multilayer right cylinder that aluminium foil is rolled into, wherein, the thickness of aluminium foil is 50 μm, the cylindrical diameter 10mm of multilayer, length 200mm, this multilayer right cylinder rearranges into a hexagonal structure in the mode that every limit is 10.Should be 21.3MHz based on the resonant frequency of the microstructure of magnetic Meta Materials, and be applied to the MRI equipment of 0.5T type, this microstructure is positioned between imaging thing and radio-frequency coil, the effect of direct magnetic flux can be realized, improve image quality.In addition, those skilled in the art have also been devised a kind of split ring resonator of three-dimensional structure, and all external high precision (± 1%) electric capacity of each split ring resonator, reaches the object of required frequency.This split ring resonator is made up of micro structure array, and diameter is 15mm, and resonant frequency is 63.28Mhz, is applied to the MRI equipment of 1.5T type.
Although, show magnetic Meta Materials in an experiment and can improve resonance image quality and resolution.But, in clinical practice, when split ring resonator is inserted into Multi-channel radio-frequency coil, the mutual inductance caused between each unit coil is changed, its main cause is: unit coil carries out Decoupling design under not having to consider to add the condition of magnetic Meta Materials, to such an extent as to the decoupling effect after adding magnetic Meta Materials between coil unit declines, and causes the hydraulic performance decline of Multi-channel radio-frequency coil, can not play the effect promoting picture quality.
Summary of the invention
The present invention solves the technical matters existed in prior art, a kind of method improving Multi-channel radio-frequency coil performance is provided, reduce the coupling between multi-channel coil, solve the problem of the Multi-channel radio-frequency coil hydraulic performance decline adopting magnetic Meta Materials, thus improve resonance image quality and resolution.
Improve a method for Multi-channel radio-frequency coil performance, comprise the following steps:
(1) before magnetic resonance imaging, magnetic Meta Materials is joined in Multi-channel radio-frequency coil;
(2) when there is no radio-frequency emission power, magnetic resonance imaging system gathers the noise image m of each passage in described Multi-channel radio-frequency coil
i(), wherein 1≤i≤L, L represents the port number of multi-channel coil here.
(3) the noise coupling matrix Ψ of the described Multi-channel radio-frequency coil after adding described magnetic Meta Materials is calculated;
(4) in image reconstruction process, described noise coupling matrix is adopted to compensate described Multi-channel radio-frequency coil coupling.
Further, described in step (2), the sampled point of noise image is greater than 10,000.
Further, described in step (3), the computing formula of noise coupling matrix is:
wherein, m
i() represents the noise image of i-th channel acquisition,
represent m
jr the conjugate transpose of (), 1≤i, j≤L, L represents the port number of multi-channel coil here.
Further, described in step (4), the formula of image reconstruction is:
described I represents the rear image of reconstruction.
Further, in the formula of described image reconstruction, S is the collection image of each passage, and C is the sensitivity distribution of Multi-channel radio-frequency coil.
Further, when C equals S, the formula of reduction of image reconstruction is
described I represents the rear image of reconstruction.
Further, described magnetic Meta Materials is split ring resonator.
Beneficial effect of the present invention:
In sum, a kind of method improving Multi-channel radio-frequency coil performance provided by the invention, by gathering each channel noise of Multi-channel radio-frequency coil and calculating its noise coupling matrix, and the coupling degrades of noise coupling matrix compensation Multi-channel radio-frequency coil is adopted when image reconstruction, thus the object promoting Multi-channel radio-frequency coil performance is realized when Multi-channel radio-frequency coil adds magnetic Meta Materials, improve signal to noise ratio (S/N ratio) and the image resolution ratio of image, promote picture quality.
Accompanying drawing explanation
Fig. 1 is the process flow diagram that the embodiment of the present invention improves the method for Multi-channel radio-frequency coil performance.
Fig. 2 is embodiment of the present invention Multi-channel radio-frequency coil experimental apparatus for capability structural representation.
Fig. 3 is embodiment of the present invention Multi-channel radio-frequency coil noise coupling matrix calculation result figure.
Fig. 4 (a) is the signal to noise ratio (S/N ratio) figure before embodiment of the present invention Multi-channel radio-frequency coil does not compensate; B () is the signal to noise ratio (S/N ratio) figure after embodiment of the present invention Multi-channel radio-frequency coil compensates.
Embodiment
In order to set forth technical characterstic of the present invention and structure better, be described in detail below in conjunction with the preferred embodiments of the present invention and accompanying drawing thereof.
Consult Fig. 1, a kind of method improving Multi-channel radio-frequency coil performance, comprises the following steps:
(S1) before magnetic resonance imaging, magnetic Meta Materials is joined in Multi-channel radio-frequency coil; Multi-channel coil is that a coil has multiple passage, carrys out Received signal strength respectively.For example: 8 channel radio frequency coils, it comprises 8 passages, and these 8 passages can be used for Received signal strength respectively.
(S2) when there is no radio-frequency emission power, magnetic resonance imaging system gathers the noise image of each passage in Multi-channel radio-frequency coil.
(S3) the noise coupling matrix of the Multi-channel radio-frequency coil after adding magnetic Meta Materials is calculated;
(S4) in image reconstruction process, noise coupling matrix is adopted to compensate Multi-channel radio-frequency coil coupling.
Particularly, implementation method in step (S2): in practical clinical, do not have the situation of radio-frequency emission power be magnetic resonance imaging before or after magnetic resonance imaging, or after the emission power for closedown Multi-channel radio-frequency coil, thus the noise of each passage in collection Multi-channel radio-frequency coil, in order to improve the accuracy of result, the sampled point of this noise is greater than 10,000.
Implementation method in step (S3): according to the collection result in step (S2), calculates the noise coupling matrix of the Multi-channel radio-frequency coil after adding magnetic Meta Materials, and the computing formula of this noise coupling matrix is:
Wherein, m
i() represents the noise image of i-th channel acquisition,
represent m
jr the conjugate transpose of (), 0<i, j≤L, L represents the port number of multi-channel coil here.
Implementation method in step (S4): after magnetic resonance imaging, Multi-channel radio-frequency coil receives data, by data, image is rebuild, when image reconstruction, noise coupling matrix is brought in image reconstruction, compensate Multi-channel radio-frequency coil, reduce the Multi-channel radio-frequency coil hydraulic performance decline because coupling degrades causes, the formula of this image reconstruction is:
In formula, S is the collection image of each passage, and C is the sensitivity distribution of Multi-channel radio-frequency coil.
When C equals S, the formula of reduction of image reconstruction is:
It should be noted that, when adding that after magnetic Meta Materials, MRI equipment carries out imaging, this embodiment avoids noise coupling matrix when traditional images is rebuild and adopt the mode of unit matrix, and adopt the result of calculation of noise coupling matrix in step (S3), obtain the coupling condition of Multi-channel radio-frequency coil unit, thus Multi-channel radio-frequency coil element coupling deterioration problem is compensated by image reconstruction formula when image reconstruction, thus improve Multi-channel radio-frequency coil performance, promote picture quality.
In order to verify the validity of patent of the present invention, 1.5T magnetic resonance imaging system devises experimental provision as shown in Figure 2.As shown in Figure 2, this experimental provision comprises the metamaterial board 2 be arranged on sick bed 1, and is held on the water mould 3 in described metamaterial board 2; Volume coil 4 covers on described water mould 3 and a spine coil 5 is connected with described magnetic resonance imaging system (not shown) by wire (not shown).
The concrete assembling mode of above-mentioned experimental provision is: be first placed on sick bed 1 by metamaterial board 2, to be 150 mm dias by height be again, and the cylindrical water mould 3 of 115 millimeters is placed upside down in above metamaterial board 2, and the body coil 4 of four-way is placed on above cylindrical water mould 3 afterwards.The body coil 3 of four-way and the spine coil 5 of eight passages are directly connected on magnetic resonance imaging system by plug.Finally, magnetic resonance imaging system gathers signal and the noise of the body coil 4 of four-way and the spine coil 5 of eight passages.
In addition, the magnetic metamaterial board 2 that experimental provision is placed is split ring resonator.It should be noted that, split ring resonator is arranged in perpendicular variation magnetic field, produce induction field, split ring resonator is now equivalent to inductance, the two ends of split ring resonator are provided with electric capacity, and electric charge can gather at two ends, make split ring resonator form resonant circuit, the electric dipole moment that split ring resonator two ends produce cancels each other, thus ground improves magnetic permeability.
The present embodiment is in clinical trial, and in the enterprising line scanning of MRI equipment of 1.5T type, in the enterprising line scanning of MRI equipment of 1.5T type, the noise coupling matrix obtained as shown in Figure 3.The image utilizing this technical method to obtain with only add magnetic shake imaging after Meta Materials image compared with, as shown in Figure 4.Associative list 1 can be found out, after compensation, signal to noise ratio (S/N ratio) has lifting in water mould.Therefore, adopt this technical method to obtain the signal to noise ratio (S/N ratio) of image higher, improve image resolution ratio, promote picture quality.
Table 1 area-of-interest signal to noise ratio (S/N ratio) mean value compares.
| Area-of-interest | Do not compensate average signal-to-noise ratio | Average signal-to-noise ratio after compensating | Signal to noise ratio (S/N ratio) promotes |
| 1 | 0.52 | 0.72 | 38.4％ |
| 2 | 0.38 | 0.57 | 50％ |
| 3 | 0.73 | 0.84 | 15％ |
Remarks: described area-of-interest refers to that medical personnel wish the patient part detected.
In sum, a kind of method improving Multi-channel radio-frequency coil performance provided by the invention, by gathering each channel noise of Multi-channel radio-frequency coil and calculating its noise coupling matrix, and the coupling degrades of noise coupling matrix compensation Multi-channel radio-frequency coil is adopted when image reconstruction, thus the object promoting Multi-channel radio-frequency coil performance is realized when Multi-channel radio-frequency coil adds magnetic Meta Materials, improve signal to noise ratio (S/N ratio) and the image resolution ratio of image, promote picture quality.
The above embodiment of the present invention is only for example of the present invention is clearly described, and is not the restriction to embodiments of the present invention.For those of ordinary skill in the field, other multi-form change or variations can also be made on the basis of the above description.Here exhaustive without the need to also giving all embodiments.All any amendments done within the spirit and principles in the present invention, equivalent to replace and improvement etc., within the protection domain that all should be included in the claims in the present invention.
Claims (7)
1. improve a method for Multi-channel radio-frequency coil performance, it is characterized in that, comprise the following steps:
(1) before magnetic resonance imaging, magnetic Meta Materials is joined in Multi-channel radio-frequency coil;
(2) when there is no radio-frequency emission power, magnetic resonance imaging system gathers the noise image of each passage in described Multi-channel radio-frequency coil;
(3) the noise coupling matrix of the described Multi-channel radio-frequency coil after adding described magnetic Meta Materials is calculated;
(4) in image reconstruction process, described noise coupling matrix is adopted to compensate described Multi-channel radio-frequency coil coupled matrix.
2. the method for raising Multi-channel radio-frequency coil performance according to claim 1, is characterized in that, described in step (2), the sampled point of noise image is greater than 10,000.
3. the method for raising Multi-channel radio-frequency coil performance according to claim 1, is characterized in that, described in step (3), the computing formula of noise coupling matrix Ψ is:
wherein, m
i() represents the noise image of i-th channel acquisition,
represent m
jr the conjugate transpose of (), 0<i, j≤L, L represents the port number of multi-channel coil here.
4. the method for raising Multi-channel radio-frequency coil performance according to claim 1, is characterized in that, described in step (4), the formula of image reconstruction is:
wherein I represents that r place, position finally rebuilds image, Ψ
-1represent noise coupling matrix inversion.Utilize this reconstruction formula just can compensate the interchannel coupling of Multi-channel radio-frequency coil.
5. the method for raising Multi-channel radio-frequency coil performance according to claim 4, is characterized in that, in the formula of described image reconstruction, S is the collection image of each passage, and C is the sensitivity distribution of Multi-channel radio-frequency coil.
6. the method for raising Multi-channel radio-frequency coil performance according to claim 5, is characterized in that, when C equals S, the formula of reduction of image reconstruction is
7., according to the method for described raising Multi-channel radio-frequency coil performance arbitrary in claim 1 to 6, it is characterized in that, described magnetic Meta Materials is split ring resonator.
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| CN106125029A (en) * | 2016-06-21 | 2016-11-16 | 中国科学院深圳先进技术研究院 | Multi-channel magnetic resonance radio-frequency coil performance estimating method and device thereof |
| CN107356892A (en) * | 2017-07-05 | 2017-11-17 | 上海联影医疗科技有限公司 | A kind of magnetic resonance radio frequency coil adjusting method, magnetic resonance scanning system and medium |
| CN110638453A (en) * | 2019-09-19 | 2020-01-03 | 清华大学 | Tunable cylindrical super-structure surface device for nuclear magnetic resonance imaging and preparation method thereof |
| CN113017598A (en) * | 2021-03-11 | 2021-06-25 | 中国科学院深圳先进技术研究院 | Method, device, equipment and medium for predicting and monitoring radio frequency energy deposition |
| US20210215778A1 (en) * | 2016-09-29 | 2021-07-15 | Hyperfine Research, Inc. | Radio frequency coil tuning methods and apparatus |
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| CN113017598A (en) * | 2021-03-11 | 2021-06-25 | 中国科学院深圳先进技术研究院 | Method, device, equipment and medium for predicting and monitoring radio frequency energy deposition |
| CN113017598B (en) * | 2021-03-11 | 2023-11-21 | 中国科学院深圳先进技术研究院 | Radio frequency energy deposition prediction and monitoring method, device, equipment and medium |
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