CN104490393B - Brain blood oxygen level measuring method based on magnetic resonance - Google Patents
Brain blood oxygen level measuring method based on magnetic resonance Download PDFInfo
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
- A61B5/14542—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue for measuring blood gases
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
Abstract
The invention provides a brain blood oxygen level measuring method based on magnetic resonance. The measuring method includes acquiring an amplitude diagram and a phase diagram of brain tissues; standardizing the amplitude diagram into a noise SD diagram, and acquiring a standardized diagram Ic according to linear fitting of the noise SD diagram; unwrapping the phase diagram to acquire a standard field diagram; putting the standard field diagram and the standardized diagram Ic into a regularization constraint rule to acquire a magnetism sensitiveness matrix without an ambient field; acquiring a vein oxygen saturation value and an oxygen metabolism parameter according to the magnetism sensitiveness matrix. The brain blood oxygen level measuring method has the advantages that magnetic field phase changes generated by air tissues are removed, so that magnetism sensitiveness values of the tissues are regained better, and venous blood oxygen saturation Yv and residual saturation of hemoglobin in venous blood, namely an oxygen extraction fraction (OEF), are acquired.
Description
Technical field
The present invention relates to magnetic resonance image (MRI) process field, espespecially a kind of magnetic resonance brain blood oxygen level measuring method.
Background technology
Oxygen saturation refers to that hemoglobin is combined the percent for reaching degree of saturation with oxygen, and it is measure blood oxygen level one
Individual critically important parameter, arterial oxygen saturation (Ya) normal value is 97%, and vein oxygen saturation value is generally 50%-75%, here,
It is main measuring vein oxygen saturation value.The functional mri (fMRI) of vein oxygen mark Yv and Blood oxygen level dependence (BOLD)
Signal has direct relation, it is well known that BOLD fMRI signals are suffered from very with the oxygen consumption of blood oxygen, blood flow and brain
Complicated relation, therefore evaluation measurement Yv can be better understood from BOLD signaling mechanisms, and can be also used for evaluating other lifes
Reason parameter such as oxygen intake fraction (oxygen extraction fraction：OEF) and brain oxygen metabolism rate (cerebral
metabolic rate of oxygen：CMRO2).Diagnosis of these parameters to some early stage diseases, the detection after later stage healing
Etc. playing critically important effect.Existing Positron Emission Tomography visualization (PET), although the method is most can accurately to survey at present
Amount OEF (oxygen is penetrated and takes fraction), vein oxygen saturation (Yv), the isoparametric method of oxygen metabolism rate of brain, but due to using radiation
Property material, while in operation, it is possible to create the complicated procedures of forming such as multiple injection, Preparatory work of experiment, and also needs to special dress
Standby and corresponding expensive experiment reagent, often produces further impact and cannot function as on experimenter's psychology and health
Conventional routine inspection, checks repeatedly Ru postoperative, and non-acute patient checks etc..
Existing PET technologies are injected by interior neck17The oxygen or arteriovenous oxygen of O (for magnetic resonance measurement) labelling
Difference measuring OEF, vein oxygen saturation etc..The method has been another the cerebral function imaging tomography skill since CT technologies occur
Art, due to injection is a kind of radionuclide, and generation harmful effect and radiation etc. are known from experience to people, and other endanger.Also in addition
One kind near infrared spectroscopy (Near infrared spectroscopy：NIRS), oxygen-containing in venous blood of NIRS and
Deoxyhemoglobin absorbs the near infrared light of different wave length obtaining their value, so as to can also further measure theirs
Relative concentration is measuring OEF, but the method can be produced organizes draining outside skull, cerebrospinal fluid, Sui Shao, ambient light and cranium
Deng untoward reaction.It is radiationless for this, it would be desirable to search out one kind without intrusion, without the need for the measurement of any exogenous material
Method is measuring.
The content of the invention
To solve the above problems, present invention aim at one kind is provided without intrusion, it is radiationless, without the need for any exogenous material
Measuring method to measure brain in vein oxygen saturation value and oxygen metabolism parameter.
It is up to above-mentioned purpose.The present invention is based on the vein oxygen saturation value in quantitative magnetic responsivity imaging technique measurement brain
With oxygen metabolism parameter, the measuring method is specific as follows：
The present invention provides a kind of magnetic resonance brain blood oxygen level measuring method, and the measuring method is included：Obtain cerebral tissue
Amplitude figure and phase diagram；The amplitude figure standardization is processed as into noise SD figures, according to the linear fit of the noise SD figures,
Standardization figure Ic is obtained, is solved by the standardization figure Ic and is obtained weight matrix W；By carrying out uncoiling to the phase diagram
Around, pattern field figure is obtained, removing background magnetic field in the pattern field figure affects to obtain local field figure；By by the local field figure
Bring in regularization constraint method with the weight matrix W, obtain the magnetic responsivity matrix of cerebral tissue；According to the magnetic responsivity
Matrix, obtains vein oxygen saturation value and oxygen metabolism parameter.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, described solution by the standardization figure Ic obtains weight
Matrix W is included：Weight matrix W is obtained by the product of the pattern field figure Ic and Mask matrixes.
It is described to remove background magnetic field impact in the pattern field figure in above-mentioned magnetic resonance brain blood oxygen level measuring method
Obtain local field figure to include：Background is got rid of using the method or dipole sciagraphy of low-pass filtering to the pattern field figure
The impact in magnetic field obtains final local field figure.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：Solution winding is carried out to the phase diagram, is obtained
Phase change value of the cerebral tissue in magnetic field；Phase change value by cerebral tissue in magnetic field is brought in following equation, is obtained
Obtain the pattern field figure；
In above formula, B0For main field；γ is gyromagnetic ratio；The phase change value for being cerebral tissue in magnetic field；TE is back
The ripple time；δ is pattern field figure.
It is described to remove background magnetic field impact in the pattern field figure in above-mentioned magnetic resonance brain blood oxygen level measuring method
Obtain local field figure to include：By following equation, removing background magnetic field in the pattern field figure affects to obtain local field figure；
In above formula, α is a regularization parameter, and W is weight matrix, and M is Mask matrixes, and D is character matrix, and F is unit
Matrix；χ is magnetic responsivity matrix, and δ is pattern field figure Ic,To remove the local field figure of background magnetic field impact.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：It is described by by the local field figure and institute
State weight matrix W to bring in regularization constraint method, the magnetic responsivity matrix for obtaining cerebral tissue is included：By the local field figure with
The weight matrix W is brought in following equation, obtains the magnetic responsivity matrix of cerebral tissue；
In above formula, W is weight matrix；M is Mask matrixes；G is a First-order Gradient operator；To remove background magnetic field shadow
Loud local field figure；D is character matrix；α, λ are a regularization parameters；F is unit matrix；χ is magnetic responsivity matrix.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：The magnetic responsivity matrix is brought into following
In formula, vein oxygen saturation value is obtained；
χ=Δ χ0·Hct·(1-Yv)；
In above formula：Hct is fraction specific volume, is worth for 0.4；Δχ0Be every unit hematocrit in all of deoxygenated blood and
The magnetic responsivity change of Oxygenated blood, is worth for 0.18ppm/per unit Hct；χ is magnetic responsivity matrix；Yv is vein oxygen saturation
Value.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：Absorb comprising oxygen in the oxygen metabolism parameter
Fraction and oxygen metabolism rate, wherein oxygen intake fraction and the oxygen metabolism rate are obtained by below equation：
OEF=1-Yv, CMRO2=CBFOEFCa；
In above formula：OEF is that oxygen absorbs fraction；Yv is vein oxygen saturation value；CBF is cerebral blood flow；Ca is constant value, Ca=
833.7umol O2/ 100ml blood.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：The many echo GRE sequences compensated by flow velocity
Obtain the amplitude figure and phase diagram of cerebral tissue.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：In many echoes compensated by flow velocity
Parallel acquisition process is also carried out in the amplitude structure chart and phase diagram of GRE sequences acquisition brain.
The present invention Advantageous Effects be：The present invention is radiationless using magnetic resonance, the imaging of multi-faceted and multiparameter
The advantages of, the different characteristic showed in magnetic resonance according to venous oxygen composition, using quantitative magnetic responsivity imaging technique,
The ambient field removing method that regularization constraint and a robustness are introduced on original magnetic responsivity imaging technique removes sky
The magnetic phase change that gas tissue is produced, rather than the phase place change produced by the magnetic responsivity characteristic of vein oxygen, so as to more preferable
Recovery organization magnetic susceptibility angle value, so as to obtain the remaining saturation of venous oxygen saturation Yv and vein blood hemoglobin,
That is oxygen intake fraction OEF.
Description of the drawings
Accompanying drawing described herein is used for providing a further understanding of the present invention, constitutes the part of the application, not
Constitute limitation of the invention.In the accompanying drawings：
Fig. 1 is the flow chart of magnetic resonance brain blood oxygen level measuring method provided by the present invention；
Fig. 2A is the design sketch that existing measuring method is obtained；
Fig. 2 B are the design sketch that measuring method provided by the present invention is obtained.
Specific embodiment
Purpose, technical scheme and advantage to make the embodiment of the present invention becomes more apparent, with reference to embodiment and attached
Figure, is described in further details to the present invention.Here, the schematic description and description of the present invention is used to explain the present invention,
But it is not as a limitation of the invention.
Quantitative magnetic responsivity imaging technique (Quantitative Susceptibility Mapping:QSM) it is foundation
In vein blood vessel, the paramagnetism feature of deoxyhemoglobin can produce the inhomogeneities of local magnetic field in magnetic resonance, and show
Quick this feature of dephasing position for going out, the magnetic responsivity of cerebral tissue is measured by its phase place change, so as to according to magnetic susceptibility
Effectively measuring the measuring method of the vein oxygen saturation value of brain, measuring method QSM has successfully applied to measurement to angle value
Cerebral hemorrhage, iron content measurement, the aspect such as brain and bodily tissue calcification.
The present invention is radiationless using magnetic resonance, the advantages of multi-faceted and multiparameter is imaged, exists according to venous oxygen composition
The different characteristic showed in magnetic resonance, using quantitative magnetic responsivity imaging technique, on original magnetic responsivity imaging technique
The ambient field removing method for introducing regularization constraint and a robustness removes the magnetic phase change that air tissue is produced,
Rather than the phase place change produced by the magnetic responsivity characteristic of vein oxygen, so as to the magnetic susceptibility angle value of more preferable recovery organization, from
And the remaining saturation of venous oxygen saturation Yv and vein blood hemoglobin is obtained, namely oxygen intake fraction OEF, method detailed is such as
Shown in lower：
Refer to shown in Fig. 1, the flow chart of the magnetic resonance brain blood oxygen level measuring method that Fig. 1 is provided for the present invention；Should
Measuring method is included：
Step S101：Obtain the amplitude figure and phase diagram of cerebral tissue；
Step S102：The amplitude figure standardization is processed as into noise SD figures, according to the linear fit of the noise SD figures,
Standardization figure Ic is obtained, a weight matrix W is obtained by Ic figure solutions；
Step S103：By carrying out solution winding to the phase diagram, pattern field figure is obtained, then using the side of low-pass filtering
Method or dipole sciagraphy get rid of the impact of background magnetic field and obtain final local field figure；
Step S104：By the way that the local field figure is brought in regularization constraint method with the weight matrix W, brain is obtained
The magnetic responsivity matrix of tissue；
Step S105：According to the magnetic responsivity matrix, vein oxygen saturation value and oxygen metabolism parameter are obtained.
In above-mentioned steps S102, according to the linear fit of the noise SD figures, obtain standardization figure Ic and specifically include：Will
The noise SD figure lines are fitted to final amplitude figure, the final amplitude figure are converted into into standardization figure Ic, by the mark
Standardization schemes Ic and obtains a weight matrix W with the product of Mask matrixes.The noise SD figure lines are fitted to into final amplitude figure
Will several noises SD figure lines be fitted to a secondary noise SD figures, concrete grammar is known technology (Ludovic de
Rochefort.Quantitative Susceptibility Map Reconstruction from MR Phase Data
Using Bayesian Regularization:Validation and Application to Brain
Imaging.Magnetic Resonance in Medicine 63:194-206 (2010)), will not be described in detail herein.
Also include in above-mentioned steps S103：Solution winding is carried out to the phase diagram, acquisition cerebral tissue is in magnetic field
Phase change value；Phase change value by cerebral tissue in magnetic field is brought in following equation, obtains the pattern field figure；
Wherein, B0For main field；γ is gyromagnetic ratio；The phase change value for being cerebral tissue in magnetic field；TE is echo
Time；δ is pattern field figure.Then background magnetic field is got rid of according to below equation, obtains the local field figure of cerebral tissue；
Wherein, α is a regularization parameter, and W is weight matrix, and M is Mask matrixes, and D is character matrix, and F is unit square
Battle array；χ is magnetic responsivity matrix, and δ is pattern field figure Ic,To remove the local field figure of background magnetic field impact.
Also include in above-mentioned steps S104：The local field figure is brought into following public affairs with the weight matrix W for trying to achieve
In formula, magnetic responsivity matrix is obtained；
Wherein, W is weight matrix；M is Mask matrixes；G is a First-order Gradient operator；Affect to remove background magnetic field
Local field figure；D is character matrix；α, λ are a regularization parameters；F is unit matrix；χ is magnetic responsivity matrix.
In above-mentioned steps S105, also include：The magnetic responsivity matrix is brought in following equation, is obtained vein oxygen and is satisfied
And value；
χ=Δ χ0·Hct·(1-Yv)；
Wherein：Hct is fraction specific volume, is worth for 0.4；Δχ0All of deoxygenated blood and contain in the hematocrit for being every unit
The magnetic responsivity change of oxygen blood, is worth for 0.18ppm/per unit Hct；χ is magnetic responsivity matrix；Yv is vein oxygen saturation value.
In above-mentioned magnetic resonance brain blood oxygen level measuring method, also include：Absorb comprising oxygen in the oxygen metabolism parameter
Fraction and oxygen metabolism rate, wherein oxygen intake fraction and the oxygen metabolism rate are obtained by below equation：
OEF=1-Yv, CMRO2=CBFOEFCa；
Wherein：OEF is that oxygen absorbs fraction；Yv is vein oxygen saturation value；CBF is cerebral blood flow；Ca is constant value, Ca=
833.7umol O2/ 100ml blood.
In above-mentioned steps S101, also include：The many echo GRE sequences compensated by flow velocity obtain the amplitude of cerebral tissue
Figure and phase diagram.
In above-mentioned steps S101, also include：The width of brain is obtained in many echo GRE sequences compensated by flow velocity
Parallel acquisition process is also carried out in value structure chart and phase diagram.
It is as follows that the quantitative magnetic responsivity being based in the present invention is imaged (QSM) concrete principle：Iron substance in brain, with
And it is a kind of paramagnet that the deoxyhemoglobin in vein blood vessel shows in MR magnetic fields, they can cause magnetic field
Dephasing position, what is shown on amplitude figure is some stains, but as the space in tissue, there is the position of air, and certain
A little tissue calcification etc. on amplitude figure due to without signal, also still showing stain, so being weighted with conventional magnetic responsivity
Imaging method and other methods are difficult to distinguish these, and quantitative magnetic responsivity imaging will recognise that these difference, Neng Gougeng
Good diagnoses to patient.
Magnetic field based on Arbitrary Target can be write as the convolution of its magnetic responsivity characteristic and polarized nucleus：
Wherein
In above formula, B0For main field, γ is gyromagnetic ratio,Phase change value in be organized in magnetic field, when TE is echo
Between, χ is the magnetic responsivity matrix to be solved, and δ is pattern field figure.The B in above-mentioned formula0、γ、TE is known, therefore,
We can be in the hope of δ, i.e. pattern field figure；
Then, due in above formula, convolution and be inconvenient to calculate, therefore, above formula is changed into the product in Fourier
Solve：
Then：δ=F-1DFχ (2)
In making formula, C=F-1DF, then δ=C χ, D are a known character matrixs.But if we are direct solution χ
From formula δ=C χ, the plan of solution matrix, but Matrix C can be related at magic angle 550When be irreversible, or even in pointWhen, it is discrete.Therefore direct solution χ can cause noise to magnify.Therefore must be introduced into a regularization side
Formula constraint solving is obtaining an accurate approximate solution.
To solve the above problems, the present invention provides a kind of regularization constraint method to process magnetic responsivity imaging, specifically such as
Under：For the solution of above-mentioned plan problem, specification can be carried out by prior information.The prior information can be as a perimeter strip
Part is solving a minimization problem.It is as follows：
It is that, with spatial variations, therefore we add a weight matrix W normalized noise in MR fields in view of noise
To standard profile N, (0,1), this weight matrix W is to be normalized into standardization figure Ic by final amplitude figure to obtain, i.e.,
Magnitude image after the standardization of multiple echoes is obtained with a Mask matrix multiple, is one under incoherent noise situations
Individual diagonal matrix.M is a Mask matrix, and it is 1 in targeted tissue areas thresholding, and remaining noise region is 0, can be by dividing
Swath value figure is obtaining.G is a First-order Gradient operator, is the openness of promotion χ.MG χ are that a Riemann border solves, and M is used
In causing χ in given segment smoothing, α, λ are a regularization parameters.In view of there are some air sections in the brain, at this
The inhomogeneities in magnetic field can be produced around a little air, so as to influence whether to solve the magnetic susceptibility angle value of tissue itself.General tissue
Gap typically produce low frequency space signal, can be by high-pass filtering, fitting of a polynomial, reference target scanning and other
More complicated method is filtering this impact.Therefore, the present invention passes through above regular termsThis problem can be solved, because
Can be removed by M for ambient field, remaining field can just estimate the magnetosensitive inductance value of cerebral tissue.
Certainly minimization problem above is solved, it is difficult to direct solution, it is possible to by changing into following optimization problem,
Gradient is asked to above formula equation：
Namely：
Wherein, T is a diagonal matrix, its diagonal elementμ is a very little
Positive number, is traditionally arranged to be 10-15, formula 5 can be solved by a nonlinear conjugate gradient method, introduce μ and just be so that T is
Positive definite, therefore above formula can obtain optimal solution χ by limited number of time iteration.
Above-mentioned optimal solution χ is being obtained, i.e., after magnetic responsivity matrix, then vein oxygen saturation value can obtained by the optimal solution
, comprise the following steps that：
Because the deoxyhemoglobin in vein blood vessel and surrounding tissue have magnetic responsivity difference, local can be produced
Magnetic field Δ B, the magnetic field Δ B of local determine the space phase change of organization internal and outside, the change of this field can cause with
Lower two kinds of reactions：(1)Shorten；(2) there is measurable phase change value.QSM is exactly to obtain quiet by this phase place change
The sensitivity differences of arteries and veins oxygen and surrounding tissue, thus QSM methods can by phase diagram, use it is proposed that regularization constraint method
It is used directly to measure vein oxygen saturation.For given vascular space position x, its phase change value with surrounding tissue
χ in formula 6, is solved by formula 5 and is obtained, and wherein γ is gyromagnetic ratio (H protons：2.678×108Rad/s/T),
B0It is main field, TE is the echo time, it is assumed that blood vessel is a limited cylinder, then the magnetic between blood vessel and surrounding tissue
Sensitivity χ can be expressed as follows with vein oxygen saturation value Y：
Hct is fraction specific volume (percentage ratio of erythrocyte in given cerebral tissue), and value is generally 0.4, Δ χ0It is every
The magnetic responsivity change of all of deoxygenated blood and Oxygenated blood, generally 0.18ppm/per unit in the hematocrit of unit
Hct.Thus we can be in the hope of the oxygen saturation value Yv of each moment blood vessel medium-sized vein oxygen, and other physiological parameters such as oxygen is absorbed
Fraction (oxygen extraction fraction：OEF=Ya-Yv=1-Yv) and brain oxygen metabolism rate (cerebral
metabolic rate of oxygen：CMRO2), CMRO2=CBFOEFCa, CBF are cerebral blood flow, and Ca is a constant value,
Ca=833.7umol O2/ 100ml blood.
Relative oxygen saturation changes delta Y for changing over time can certainly be tried to achieve：
Small tenon 1 and 0 is represented in MRI scan not in the same time, this Δ φ1With Δ φ0Come from two phases not in the same time
With blood vessel and the phase contrast of surrounding tissue, the oxygen saturation change relative by solving cerebral blood vessel, obtain with not big in the same time
The oxygen saturation and metabolic condition of brain is analyzing brain function recovery extent and extent of damage etc..
The present invention is radiationless using magnetic resonance, the advantages of multi-faceted and multiparameter is imaged, exists according to venous oxygen composition
The different characteristic showed in magnetic resonance, using quantitative magnetic responsivity imaging technique, on original magnetic responsivity imaging technique
The ambient field removing method for introducing regularization constraint and a robustness removes the magnetic phase change that air tissue is produced,
Rather than the phase place change produced by the magnetic responsivity characteristic of vein oxygen, so as to the magnetic susceptibility angle value of more preferable recovery organization, from
And the remaining saturation of venous oxygen saturation Yv and vein blood hemoglobin is obtained, namely oxygen intake fraction OEF.
Fig. 2A and Fig. 2 B are the effect contrast figure of prior art and measuring method provided by the present invention, by can be seen that in figure
Measuring method provided by the present invention is relatively sharp to be understood.
Particular embodiments described above, has been carried out further in detail to the purpose of the present invention, technical scheme and beneficial effect
Describe in detail it is bright, should be understood that the foregoing is only the present invention specific embodiment, the guarantor being not intended to limit the present invention
Shield scope, all any modification, equivalent substitution and improvements within the spirit and principles in the present invention, done etc., should be included in this
Within the protection domain of invention.
Claims (10)
1. a kind of magnetic resonance brain blood oxygen level measuring method, it is characterised in that the measuring method is included：
Obtain the amplitude figure and phase diagram of cerebral tissue；
The amplitude figure standardization is processed as into noise SD figures, according to the linear fit of the noise SD figures, standardization figure is obtained
Ic, is solved by the standardization figure Ic and obtains weight matrix W；
By carrying out solution winding to the phase diagram, pattern field figure is obtained, removing background magnetic field in the pattern field figure affects to obtain
Obtain local field figure；
By the way that the local field figure is brought in regularization constraint method with the weight matrix W, the magnetic susceptibility of cerebral tissue is obtained
Degree matrix；
According to the magnetic responsivity matrix, vein oxygen saturation value and oxygen metabolism parameter are obtained.
2. magnetic resonance brain blood oxygen level measuring method according to claim 1, it is characterised in that described by the mark
Quasi-ization figure Ic solutions obtain weight matrix W and include：Weight matrix is obtained by the product of the standardization figure Ic and Mask matrixes
W。
3. magnetic resonance brain blood oxygen level measuring method according to claim 1, it is characterised in that described to remove the mark
Background magnetic field affects acquisition local field figure to include in quasi- field figure：The method or idol of low-pass filtering are adopted to the pattern field figure
Extremely sub- sciagraphy gets rid of the impact of background magnetic field and obtains final local field figure.
4. magnetic resonance brain blood oxygen level measuring method according to claim 2, it is characterised in that described by described
Phase diagram carries out solution winding, obtains pattern field figure and includes：
Solution winding is carried out to the phase diagram, phase change value of the cerebral tissue in magnetic field is obtained；
Phase change value by cerebral tissue in magnetic field is brought in following equation, obtains the pattern field figure；
In above formula, B0For main field；γ is gyromagnetic ratio；The phase change value for being cerebral tissue in magnetic field；When TE is echo
Between；δ is pattern field figure.
5. magnetic resonance brain blood oxygen level measuring method according to claim 4, it is characterised in that described to remove the mark
Background magnetic field affects acquisition local field figure to include in quasi- field figure：By following equation, remove background magnetic field in the pattern field figure
Affect to obtain local field figure；
C=F-1DF；
In above formula, α is a regularization parameter, and W is weight matrix, and M is Mask matrixes, and D is character matrix, and F is unit matrix；
χ is magnetic responsivity matrix, and δ is pattern field figure,To remove the local field figure of background magnetic field impact.
6. magnetic resonance brain blood oxygen level measuring method according to claim 1, it is characterised in that described by will be described
Local field figure is brought in regularization constraint method with the weight matrix W, and the magnetic responsivity matrix for obtaining cerebral tissue is included：
The local field figure is brought in following equation with the weight matrix W, the magnetic responsivity matrix of cerebral tissue is obtained；
C=F-1DF；
In above formula, W is weight matrix；M is Mask matrixes；G is a First-order Gradient operator；To remove background magnetic field impact
Local field figure；D is character matrix；α, λ are a regularization parameters；F is unit matrix；χ is magnetic responsivity matrix；H is matrix
Conjugate transpose.
7. magnetic resonance brain blood oxygen level measuring method according to claim 6, it is characterised in that described according to the magnetic
Sensitivity matrix, obtains vein oxygen saturation value and includes：
The magnetic responsivity matrix is brought in following equation, vein oxygen saturation value is obtained；
χ=△ χ0·Hct·(1-Yv)；
In above formula：Hct is fraction specific volume, is worth for 0.4；△χ0Be every unit hematocrit in all of deoxygenated blood and oxygen-containing
The magnetic responsivity change of blood, is worth for 0.18ppm/per unit Hct；χ is magnetic responsivity matrix；Yv is vein oxygen saturation value.
8. magnetic resonance brain blood oxygen level measuring method according to claim 7, it is characterised in that described according to the magnetic
Sensitivity matrix, obtains oxygen metabolism parameter and includes：
Fraction and oxygen metabolism rate are absorbed comprising oxygen in the oxygen metabolism parameter, wherein oxygen intake fraction and the oxygen metabolism rate
Obtained by below equation：
OEF=1-Yv, CMRO2=CBFOEFCa；
In above formula：OEF is that oxygen absorbs fraction；Yv is vein oxygen saturation value；CBF is cerebral blood flow；Ca is constant value, Ca=
833.7umol O2/ 100ml blood.
9. magnetic resonance brain blood oxygen level measuring method according to claim 1, it is characterised in that the acquisition brain group
The amplitude figure knitted and phase diagram are included：The many echo GRE sequences compensated by flow velocity obtain the amplitude figure and phase place of cerebral tissue
Figure.
10. magnetic resonance brain blood oxygen level measuring method according to claim 9, it is characterised in that described by stream
Parallel acquisition process is also carried out in the amplitude figure and phase diagram of many echo GRE sequences acquisition brain of speed compensation.
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