CN107024670A - The bearing calibration of magnetic resonance system and device - Google Patents
The bearing calibration of magnetic resonance system and device Download PDFInfo
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- CN107024670A CN107024670A CN201610065839.2A CN201610065839A CN107024670A CN 107024670 A CN107024670 A CN 107024670A CN 201610065839 A CN201610065839 A CN 201610065839A CN 107024670 A CN107024670 A CN 107024670A
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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
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
Abstract
The invention discloses a kind of bearing calibration of magnetic resonance system, the magnetic resonance system includes radiofrequency emitting module, gradient modules and Receiver Module, specifically included：The first pulse train is performed, first group of echo-signal is gathered and obtains the frequency domain phase of first group of echo-signal, first pulse train is spin-echo sequence；The second pulse train is performed, second group of echo-signal is gathered and obtains the frequency domain phase of second group of echo-signal, second pulse train selects layer spin-echo sequence to be non-；System relative time delay is obtained according to the frequency domain phase of first group of echo-signal and second group of echo-signal, the system relative time delay includes radiofrequency emitting module and the relative time delay and Receiver Module and the relative time delay of gradient modules of gradient modules；Correction is compensated to the magnetic resonance system according to the system relative time delay.The present invention can accurately obtain the relative time delay of magnetic resonance system by the phase operation to echo-signal.In addition, the present invention also provides a kind of means for correcting of magnetic resonance system.
Description
【Technical field】
The present invention relates to mr imaging technique field, more particularly to a kind of magnetic resonance system bearing calibration and
Device.
【Background technology】
Magnetic resonance imaging (Magnetic Resonance Imaging, MRI) is mainly used in tissue
Certain nuclear nmr phenomena, the radiofrequency signal of gained is handled by electronic computer, reconstructed
A kind of new Medical Imaging Technology of a certain layer images of human body, due to its without ionising radiation, multisequencing,
Multi-parameter, multiple plane imaging and higher soft tissue resolving power, and it is widely used in the diagnosis of disease.
Magnetic resonance signal intensity is generally influenceed by many factors such as the proton densities, T1 values, T2 values organized, is led to
Image quality can be improved by crossing the imaging parameters such as adjustment radio-frequency pulse, gradient fields and signal acquisition moment.And lead to
The setting of the relevant parameters such as normal radio-frequency pulse, gradient fields and signal acquisition moment and its arrangement system in sequential
Referred to as MRI pulse trains, distinguish radiofrequency emitting module, gradient modules and the radio frequency receiving of correspondence system
Block.
In order to obtain accurate Scan Architecture, it is necessary to being accurately controlled to modules.However,
In actual hardware system, the release of radio-frequency module, gradient modules and receiving module is deposited in MR imaging sequences
In different delayed time, so as to cause the physics sequential actually occurred in MR imaging sequences to exist with preferable sequential
Time difference, the filter circuit or amplifying circuit and transmission channel that such as each module is present can cause gradient modules
Produce gradient link delay, radiofrequency emitting module and produce transmitting chain delay, Receiver Module produces reception
Link delay, influences the accuracy of MR imaging sequences sequential, and then influence signal to noise ratio and the contrast of image
Degree, or even bring various artifacts.Therefore, it is necessary to which the delay of calibration system modules is so as to improve MRI
Picture quality.
In the prior art most direct mode be measurement subsystems (radiofrequency emitting module, gradient modules and
Receiver Module) delay, each link instructions are measured using ancillary equipment and issued and actual electromagnetic
The time delayses that field is produced, are then compensated by the delay to each submodule and enabled a system on time together
Walk work.However, this method operating process is complicated, cost is higher and is extremely readily incorporated measurement system error.
Another delay compensation method calculates the relative of subsystems by using the magnetic resonance signal of collection
It is delayed, detailed process is：Echo is obtained using spin echo (SE) or gtadient echo (GRE) sequence
Signal, then the Fitting Calculation go out the real time point at echo center, by the real time point and theoretical time
Point can obtain the amount of delay of gradient fields in system after subtracting each other.However, the signal gathered using this method is accurate
Property is easily influenceed by undesirable factor, such as it is uneven at B0 in the case of, GRE sequences and SE
The result of sequence can be a greater impact；In gathered data, ADC sampling interval is not infinitely small, leads to
Cross calculate maximum value position mode can only precision controlling in the level in sampling interval, accuracy need into
One step is improved.By above-mentioned analysis, the absolute delay of accurate measurement subsystems link be it is extremely difficult,
It is improved it is therefore desirable to the measurement or compensation method being delayed to existing magnetic resonance system.
【The content of the invention】
The technical problems to be solved by the invention are bearing calibration and the device for proposing a kind of magnetic resonance system, energy
Relative time delay between enough accurate correction each modules of system, improves image quality.
The present invention solve the technical scheme that is used of above-mentioned technical problem for：A kind of correction side of magnetic resonance system
Method, the magnetic resonance system includes radiofrequency emitting module, gradient modules and Receiver Module, specifically includes
Following steps：
The first pulse train is performed, first group of echo-signal is gathered and obtains the frequency of first group of echo-signal
Domain phase, first pulse train is spin-echo sequence；
The second pulse train is performed, second group of echo-signal is gathered and obtains the frequency of second group of echo-signal
Domain phase, second pulse train selects layer spin-echo sequence to be non-；
System is obtained according to the frequency domain phase of first group of echo-signal and second group of echo-signal relatively to prolong
When, the system relative time delay includes radiofrequency emitting module and the relative time delay and radio frequency reception of gradient modules
The relative time delay of module and gradient modules；
Correction is compensated to the magnetic resonance system according to the system relative time delay.
Further, first pulse train comprising 90 °, 180 °, 180 ° of three radio-frequency pulses,
Two slice selective gradients, two readout gradients and one read pre- dephasing gradient, and second pulse train is included
90 °, 180 °, 180 ° of three radio-frequency pulses, two readout gradients and one read pre- dephasing gradient.
Further, the radiofrequency emitting module and the relative time delay of the gradient modules are proportional to described first
The difference of the slope of the frequency domain phase of group echo-signal and second group of echo-signal, the Receiver Module and institute
State gradient modules relative time delay be proportional to second group of echo-signal frequency domain phase slope, described time
The slope of the frequency domain phase of ripple signal is echo-signal frequency domain phase on being imaged the one of voxel partial center distance
Order derivative.
Further, the gradient fields in first pulse train or the second pulse train are positive along X-axis.
Further, the specific of correction is compensated to the magnetic resonance system according to the system relative time delay
Process is：It is reference to select the gradient modules, and the radio frequency is corrected respectively according to the system relative time delay
The delay of transmitter module and Receiver Module relative to gradient modules.
Further, the specific of correction is compensated to the magnetic resonance system according to the system relative time delay
Process is：According to the system relative time delay, the radiofrequency emitting module and the Receiver Module are obtained
Relative time delay, and using the Receiver Module as reference, the radiofrequency emitting module and ladder are corrected respectively
Spend delay of the module relative to Receiver Module.
Further, first group of echo-signal and/or second group of echo-signal decline not comprising free induction
Cut signal.
Further, when calculating gradient fields along X-axis, Y-axis and Z axis respectively, the radio frequency receiving
Block prolongs with the relative time delay or the radiofrequency emitting module of the gradient modules with the relative of the gradient modules
When, the gradient fields of the gradient modules are obtained along relative time delay when X-axis, Y-axis and Z axis, and root
The gradient modules are corrected according to the relative time delay.
Further, the specific of correction is compensated to the magnetic resonance system according to the system relative time delay
Process is：
Obtain the corresponding gradient link delay of gradient modules；Prolonged according to the system relative time delay and gradient link
When, the corresponding transmitting chain delay of radiofrequency emitting module reception chain corresponding with Receiver Module is obtained respectively
Road is delayed；And be delayed according to the gradient link delay, transmitting chain delay and receives link, it is right
The magnetic resonance system compensates correction.
The present invention also provides a kind of means for correcting of magnetic resonance system, including：
Detection unit, for performing scanning sequence and obtaining echo-signal, the scanning sequence includes the first arteries and veins
Sequence and the second pulse train are rushed, first pulse train is spin-echo sequence, for producing first group
Echo-signal, second pulse train selects layer spin-echo sequence to be non-, for producing second group of echo letter
Number；
Relative time delay acquiring unit, for being obtained according to first group of echo-signal and second group of echo-signal
The slope of the frequency domain phase of echo-signal, and according to being obtained the slope of the frequency domain phase of the echo-signal
The relative time delay and Receiver Module and gradient-norm of magnetic resonance system radiofrequency emitting module and gradient modules
The relative time delay of block；
Link delay acquiring unit, for obtaining the corresponding gradient link delay of gradient modules, and according to described
Relative time delay and gradient link delay, obtain the corresponding transmitting chain delay of radiofrequency emitting module and radio frequency connects
Receive the corresponding receives link delay of module；
Correction module, it is common to magnetic according to the gradient link delay, transmitting chain delay or receives link delay
Vibrating system sweep parameter compensates correction.
Compared with prior art, the advantage of the invention is that：According to the radio-frequency module and gradient of magnetic resonance system
There is relative time delay between module and receiving module and gradient modules, and the relative time delay meeting between each module
Echo-signal is caused to there is the phase offset linear with relative time delay, and then collecting magnetic resonance signal is simultaneously
Phase of the signal in domain space is obtained, is directly obtained between each module by the phase operation of echo-signal
Relative time delay, can be prevented effectively from due to detection error caused by the sampling interval, measurement result is more accurate, and not
Easily influenceed by factors such as B0 heterogeneities.
【Brief description of the drawings】
Fig. 1 is magnetic resonance system structural representation；
Fig. 2 is the bearing calibration flow chart of magnetic resonance system of the present invention；
Fig. 3 is the first pulse train structural representation in one embodiment of the invention；
Fig. 4 is the second pulse train structural representation in one embodiment of the invention；
Fig. 5 is the echo-signal phase schematic diagram obtained according to the scanning sequence of different delayed time；
Fig. 6 is the slope and corresponding delay function relation schematic diagram according to Fig. 5 echo-signal phases obtained.
【Embodiment】
It is understandable to enable the above objects, features and advantages of the present invention to become apparent, below in conjunction with the accompanying drawings and
Embodiment is described in detail to the embodiment of the present invention.
As shown in figure 1, magnetic resonance system hardware mainly includes：Magnetic body module 100, gradient modules 200,
Other accessory systems such as radio-frequency module 300, spectrometer system 400 and computer system 500, wherein, magnetic
Module 100 is used to produce main field, gradient modules 200 mainly comprising gradient current amplifier (AMP),
Gradient coil；Radio-frequency module 300 mainly includes radiofrequency emitting module and Receiver Module；Spectrometer system
400 mainly include pulse-series generator, gradient waveform generator, transmitter and receiver etc., and calculate
Machine system 500 is used for control system and runs and be ultimately imaged, and its general procedure being imaged is：Computer system
500 storages and the instruction for sending the scanning sequence (scan sequence) for needing to perform, pulse train occur
Device is controlled according to scanning sequence instruction to gradient waveform generator and emitter, and gradient waveform generator is defeated
Go out the gradient pulse signal with scheduled timing and waveform, the signal passes through Gx, Gy and Gz gradient current
Amplifier, then pass through three autonomous channels Gx, Gy, Gz in gradient modules 200, each gradient amplification
Device excites a corresponding gradient coil in gradient coil set, produces for generating additional space encoded signal
Gradient fields, to carry out space orientation to magnetic resonance signal；Pulse-series generator in spectrometer system 400 is also
Perform scanning sequence, output include the data such as timing, intensity, the shape of radio-frequency pulse of radio-frequency transmissions and
The timing of radio frequency reception and the length of data acquisition window are to emitter, while emitter is by respective radio-frequency pulse
Send body transmitting coil into radio-frequency module 300 and produce B1, under B1 field actions in patient body by
The signal that the atomic nucleus excited is sent is perceived by the receiving coil in radio-frequency module 300, then by sending
/ receive switch and be transferred to preamplifier, the magnetic resonance signal of amplification is demodulated, filtering, AD conversion etc.
Digitized processing, is then communicated to the storage module of computer system 500.When storage module obtains one group of original
After the k- spatial datas of beginning, the end of scan.Original k- spatial datas are rearranged into will be weighed with each
The corresponding single k- space data sets of image built, each k- space data sets are input into array processor,
Carry out combining magnetic resonance signal after image reconstruction, form one group of view data.In above-mentioned imaging process, penetrate
Frequency pulse, the setting of gradient fields each parameter related to the signal acquisition moment etc. and its being arranged as in sequential
MRI pulse trains.In order to improve electric property, it would generally be adopted in the design of waveform generator or amplifier
With wave filter, but the use of wave filter can inevitably cause the waveform signal in transmission channel to be delayed,
In addition, the self-induction from cable or miscellaneous part can also cause certain system delay.Therefore, in reality
In the hardware system of border, gradient modules 200 can have certain gradient link delay, and radiofrequency emitting module can be deposited
It is delayed in certain transmitting chain, Receiver Module or signal acquisition module can also have certain reception chain
Road is delayed, and the link delay of above-mentioned modules finally causes the physics sequential of imaging sequence inaccurate or system
Delay.
The present invention proposes a kind of bearing calibration of magnetic resonance system, and it detects gradient modules and radiofrequency emitting module
And the relative time delay of gradient modules and Receiver Module, mainly include the following steps that as shown in Figure 2：
S10, the first pulse train of execution, gather first group of echo-signal of first group of echo-signal and acquisition
Frequency domain phase, wherein the first pulse train is spin-echo sequence.If Fig. 3 is that the first pulse train structure is shown
Be intended to, comprising 90 ° of radio-frequency pulses, two subsequent 180 ° of radio-frequency pulses, two slice selective gradient Gs,
A two readout gradient Gr and pre- dephasing gradient G r/2 of reading, the direction of each gradient fields is consistent, all applies
In same gradient axes, gradient fields (can refer to along X-axis (left side for pointing to human dissection position), Y-axis
To the front side of human dissection position) or Z axis (people's long axis of body) three in either direction, and gradient fields point
Wei not be along X-axis gradient fields (Gx), Y-axis gradient fields (Gy), Z axis gradient fields (Gz).In the present embodiment
The gradient fields used is Gx, and gradient axes are x-axis, and readout gradient can be being applied using above-mentioned pulse train
First group of echo-signal is obtained in time range, first group of echo-signal includes echo-signal 1 and 2, its
In, echo-signal 1 is produced in the range of the first readout gradient Gr, by radiofrequency emitting module and gradient-norm
The influence being delayed between block between delay and Receiver Module and gradient modules；Echo-signal 2 is second
Produced in the range of readout gradient Gr, because of the use of 180 ° of radio-frequency pulses twice, most of magnetic can be offset common
The echo-signal phase offset that vibrating system radiofrequency emitting module is produced with gradient modules because there is delay, i.e., should
Echo-signal phase offset can be neglected caused by delay.In addition, plus shadow of the pre- dephasing gradient to echo-signal
Ring, the strength S of echo-signal 1E1With the strength S of echo-signal 2E2It is represented by：
Wherein, FOV is visual field, during ρ represents that the signal density in unit volume, x are expressed as voxel partially
Heart distance, γ is gyromagnetic ratio, and t is the echo wave signal acquisition time, and Gs and Gr represent slice selective gradient and reading respectively
Go out the intensity of gradient.TD1The relative time delay of radiofrequency emitting module and gradient modules for magnetic resonance system, is returned
Exist and T along the magnetic resonance signal of each position on gradient direction of principal axis in ripple signalD1The phase of linear correlation
Offset 2Gsx γ TD1, TD2The relative time delay of Receiver Module and gradient modules for magnetic resonance system,
Exist and T along the magnetic resonance signal of each position on gradient fields direction of principal axis in echo-signalD2Linear correlation
Phase offset Grx γ TD2, Δ M is pre- dephasing gradient G r/2 integral areas deviation that may be present, then
Generation-x γ Δs M phase deviation in echo-signal 1, and in echo 2 generation+x γ Δs M phase
Position deviation.Phase of the echo-signal in frequency domain can be obtained by making Fourier transformation to first group of echo-signal.
S20, the second pulse train of execution, gather second group of echo-signal and simultaneously obtain second group of echo letter
Number frequency domain phase, wherein the second pulse train selects layer spin-echo sequence to be non-.It is illustrated in figure 4 second
Pulse train structural representation, comprising 90 ° of radio-frequency pulses, two subsequent 180 ° of radio-frequency pulses, two
A readout gradient Gr and pre- dephasing gradient G r/2 of reading, application direction and the first pulse train of gradient fields
Middle application gradient field direction is identical, and from the first pulse train unlike, the second pulse train is not comprising two
Individual slice selective gradient.Second group of echo letter is obtained in application readout gradient time range using above-mentioned pulse train
Number, second group of echo-signal equally includes echo-signal 3 and 4, wherein, echo-signal 3 is read first
Go out in the range of gradient G r and produce, echo-signal 4 is produced in the range of the second readout gradient Gr, two echoes letter
Number all by relative time delay between magnetic resonance system receiving module and gradient modules and read pre- dephasing gradient
Influence.The strength S of echo-signal 3E3With the strength S of echo-signal 4E4It is represented by：
Wherein, FOV is visual field, during ρ represents that the signal density in unit volume, x are expressed as voxel partially
Heart distance, γ is gyromagnetic ratio, and t is the echo wave signal acquisition time, and Gr represents the intensity of readout gradient.TD2
The relative time delay of receiving module and gradient modules for magnetic resonance system, Δ M integrates for pre- dephasing gradient G r/2
Area deviation that may be present.Equally, echo-signal can be obtained by making Fourier transformation to second group of echo-signal
In the phase of frequency domain.
According to above-mentioned analysis, gather and there is certain pair between the echo-signal obtained and each module relative time delay
It should be related to, in order to verify the correctness of above-mentioned hypothesis, the present invention sets a series of scanning sequence to act on magnetic
Resonator system, each scanning sequence sets the relative time delay of gradient modules and radiofrequency emitting module to distinguish in sequential
For -8 μ s, -4 μ s, 0 μ s, 4 μ s, 8 μ s, remaining every sweep parameter is all identical or all identical with preferable sequential.
A series of echo-signal can be collected in magnetic resonance system signal receiving end, echo-signal is transformed into frequency
Domain, can obtain the frequency domain phase of each echo-signal as depictedWith imaging voxel partial center apart from x pass
It is schematic diagram.As shown in figure 5, abscissa is expressed as voxel partial center apart from x (mm), ordinate table
Show phase of the echo-signal in frequency domain(°), the phase for belonging to the echo-signal of same scanning sequence is passed through with x
Fitting is linear, and the echo-signal and x of different scanning sequence (delay different) meet different linear
(different slopes are presented) in relation.Further, the oblique of echo-signal frequency domain phase can be obtained according to Fig. 5
Relation between rate and corresponding delay, with the delay (μ s) of scanning sequence for abscissa, with correspondence scanning sequence
The echo-signal of acquisition is ordinate in the phase slope (°/mm) of frequency domain, can obtain gradient modules and radio frequency
When the relative time delay of transmitter module is respectively -8 μ s, -4 μ s, 0 μ s, 4 μ s, 8 μ s, corresponding echo-signal
The scatterplot of phase slope composition, through over-fitting, the slope of echo-signal frequency domain phase as shown in Figure 6 with it is corresponding
Delay meets linear functional relation.
Therefore, the relative time delay of magnetic resonance system can be obtained in the following way：Detect any two scanning sequence
Two groups of echo-signals are obtained, the system relative time delay parameter of two scanning sequence is different and is given value；Obtain
Two groups of echo-signals frequency domain phase, and according to two groups of echo-signals frequency domain phase obtain echo-signal
The slope of frequency domain phase；System relative time delay and echo are obtained according to the slope of two groups of echo-signal frequency domain phases
The linear functional relation of the slope of signal frequency domain phase；Current Scan sequence is performed, current echo-signal is obtained,
The corresponding system delay of current echo sequence is unknown；Current echo-signal is transformed into frequency domain, current return is obtained
Slope of the ripple signal in frequency domain；According to system relative time delay and the linear letter of the slope of echo-signal frequency domain phase
Number relation and current echo-signal can accurately obtain current system relative time delay in the slope of frequency domain；Subsequent root
According to current system relative time delay, compensation time sequence parameter can be set in software end or spectrometer system.
S30, obtain according to the frequency domain phase of first group of echo-signal and second group of echo-signal that system is relative to prolong
When, system relative time delay includes radiofrequency emitting module and the relative time delay and Receiver Module of gradient modules
With the relative time delay of gradient modules.Detailed process is：According to first group of echo-signal and second group of echo-signal
In the phase of frequency domain, its frequency domain phase is obtained with being imaged functional relation of the voxel partial center apart from xWherein σ1Zeroth order biasing is represented, echo-signal 1
The slope (first derivative of the frequency domain phase on x) of frequency domain phaseFor (2GsTD1+Gr·TD2-ΔM)γ；
The frequency domain phase and x functional relation of echo-signal 2Wherein σ2
Represent zeroth order biasing, and the slope of the frequency domain phase of echo-signal 2 (frequency domain phase mediates number on the one of x)For (GrTD2+ΔM)γ.The echo-signal 3 collected and echo-signal 4 are made into Fourier transformation,
Obtain its frequency domain phase and x functional relationWherein σ3Represent zeroth order
Biasing, and the slope (first derivative of the frequency domain phase on x) of the frequency domain phase of echo-signal 3For
(Gr·TD2-ΔM)γ；The frequency domain phase and x functional relation of echo-signal 4Wherein σ4Represent zeroth order biasing, and the frequency domain phase of echo-signal 4
The slope (first derivative of the frequency domain phase on x) of positionFor (GrTD2+ΔM)γ.According to above- mentioned information,
It can obtain：Relative time delay between radiofrequency emitting module and gradient modulesPenetrate
Frequency transmitter module and the relative time delay of gradient modules are proportional to the slope of the frequency domain phase of first group of echo-signal
And the difference of the slope of the frequency domain phase of second group of echo-signal；Phase between Receiver Module and gradient modules
To delayThat is the relative time delay of Receiver Module and gradient modules is proportional to second group and returned
The slope of the frequency domain phase of ripple signal.
Radiofrequency emitting module and gradient fields can be obtained respectively along X using said process in embodiments of the present invention
Delay and Receiver Module and gradient fields between the gradient modules of axle is along between the gradient modules of X-axis
Delay, in theory can preferentially correction gradient along the phase between the gradient modules and radiofrequency emitting module of X-axis
To amount of delay, subsequent correction gradient is along the relative time delay between the gradient modules and Receiver Module of X-axis
Amount.It is similar with said process, it also can respectively obtain and be penetrated in magnetic resonance system of the gradient fields along Y-axis or Z axis
Relative time delay between frequency transmitter module, Receiver Module and corresponding gradient modules.In addition, according to above-mentioned
Structure can also obtain the relative time delay of the gradient modules along three different gradient field directions, and according to relative time delay
Correction gradient module.
In another embodiment, selection Receiver Module is reference, according to Receiver Module and gradient-norm
Relative time delay T between blockD2, the gradient field direction edge of the sequential of regulating gradient module, wherein gradient modules
X-axis, Y-axis or Z axis.In addition, according to radiofrequency emitting module and gradient in previous embodiment magnetic resonance system
Relative time delay T between moduleD1And the relative time delay T between Receiver Module and gradient modulesD2,
The relative time delay T between radiofrequency emitting module and Receiver Module can be obtainedD3=TD1-TD2, and then with
Receiver Module is reference, the corresponding parameter of regulation radiofrequency emitting module.
After radio-frequency pulse is excited, the magnetization vector M0 of thermal equilbrium state is partly or entirely turned to perpendicular magnetic
On the transverse plane of field, due to factors such as local magnetic field is uneven, chemical shifts so that spin is not exclusively place
It is over time, this from covibration horizontal magnetic vector no longer to be located on the resonant frequency of anticipation
In the same direction so that the vector sum of horizontal magnetic vector diminishes, and causes signal intensity to diminish, therefore gathers
The spin echo signal arrived is easily by the influence of free induction decay (FID) signal, and the present invention uses phase
The method of position circulation or Crush gradients reduces the interference of FID signal.
In an alternative embodiment of the invention, it is reduction GsThe uncertainty of size is to system delay measurement result
Influence, system delay is the average of system delay measured on positive and negative gradient direction.Specially：Adopt
First group of echo-signal and second group of echo-signal are obtained respectively with the first pulse train and the second pulse train,
Wherein, the first pulse train includes 90 °, 180 °, 180 ° of three radio-frequency pulses, two slice selective gradients
Gs, two readout gradient Gr and one stay alone pre- dephasing gradient G r/2, the second pulse train comprising 90 °,
180 °, 180 ° of three radio-frequency pulses, two readout gradient Gr and one read pre- dephasing gradient G r/2,
The direction of all gradients is positive direction, and the magnetic resonance system under positive gradient direction can be obtained according to preceding method
Delay；Additionally include three-pulse sequence and the 4th pulse train, wherein 90 ° of three-pulse sequence,
180 °, 180 ° of three radio-frequency pulses, two slice selective gradient Gs, two readout gradient Gr and a reading
Pre- dephasing gradient G r/2, the 4th pulse train includes 90 °, 180 °, 180 ° of three radio-frequency pulses, two
Individual readout gradient Gr and one read in pre- dephasing gradient G r/2, three-pulse sequence the direction of gradient and the
Gradient is in opposite direction in one sequence, i.e. negative sense gradient direction；Wherein three-pulse sequence produces the 3rd group and returned
Ripple signal, the 4th group pulse sequence can produce the 4th group of echo-signal, can be obtained also according to preceding method
The system delay measured when gradient fields are along X-axis negative sense；Further, take and measured under positive and negative gradient field direction
The average of system delay be used as final measurement.Main field is effectively reduced using the above method uneven
Deng interference of the non-ideal factor to measurement result.
S40, according to system relative time delay magnetic resonance imaging system is accordingly compensated.According to above-mentioned detection
As a result, the relative pre-set time for logically presetting three modules can compensate for the delay of magnetic resonance system, real one
Apply in example, can according to the relative time delay between gradient modules and radiofrequency emitting module, using gradient modules as reference,
Delay of the radiofrequency emitting module relative to gradient modules is corrected, then according to gradient modules and Receiver Module
Between mutual delay, equally using gradient modules as reference, correction Receiver Module relative to gradient modules
Delay.The accuracy of magnetic resonance signal, is carried produced by can effectively ensure that magnetic resonance system by aforesaid operations
High s/n ratio simultaneously effectively eliminates the artifact that phase of echo fluctuation is caused.Ladder can be selected respectively in another embodiment
Field is spent along X-axis, three directions of Y-axis or Z axis, obtains the system relative time delay in three directions, and pass through
The relative of the relative time delay and Receiver Module and gradient modules of radiofrequency emitting module and gradient modules is prolonged
When, the relative time delay of radiofrequency emitting module and Receiver Module is obtained, and using Receiver Module as reference,
Respectively correct three kinds of gradient field directions under gradient modules relative to Receiver Module delay parameter and penetrate
Delay parameter of the frequency receiving module relative to Receiver Module.It should be noted that the correction of delay parameter
The sequential that scanning sequence can specifically be generated in spectrometer system by adjusting is completed.
In still another embodiment of the process, following mistake can be passed through by correcting magnetic resonance system according to system relative time delay
Cheng Shixian：
The corresponding gradient link delay of gradient modules is obtained, wherein gradient link delay specifically can be according to gradient width
The corresponding relation of degree and gradient delay is obtained, and the time that can be also occurred according to echo-signal peak point obtains；
According to system relative time delay and gradient link delay, the corresponding transmitting of radiofrequency emitting module can be obtained respectively
Link delay and the corresponding receives link delay of Receiver Module；
It is common to the magnetic according to the gradient link delay, transmitting chain delay and receives link delay
Vibrating system compensates correction, and transmitting sequential, the gradient of radio-frequency pulse in spectrometer system can be specifically adjusted respectively
The sweep parameter such as the transmitting sequential of pulse and the time of reception signal is realized.
The present invention also provides a kind of means for correcting of magnetic resonance system, including：
Detection unit 100, for performing scanning sequence and obtaining echo-signal, wherein scanning sequence includes the
One pulse train and the second pulse train, the first pulse train are spin-echo sequence, for producing first group
Echo-signal；Second pulse train selects layer spin-echo sequence to be non-, for producing second group of echo-signal；
Relative time delay acquiring unit 200, is connected with detection unit 100, for according to first group of echo-signal
The slope of the frequency domain phase of echo-signal is obtained with second group of echo-signal, and according to the frequency domain phase of echo-signal
The slope of position obtains magnetic resonance system radiofrequency emitting module and the relative time delay and radio frequency reception of gradient modules
The relative time delay of module and gradient modules；
Link delay acquiring unit 300, is connected with relative time delay acquiring unit 200, for obtaining gradient-norm
The corresponding gradient link delay of block, and the corresponding transmitting of radiofrequency emitting module is obtained according to the relative time delay
Link delay and the corresponding receives link delay of Receiver Module
Correct unit 400, be connected with link delay acquiring unit 300, for according to gradient link delay,
Transmitting chain is delayed or receives link delay, and correction is compensated to magnetic resonance system sweep parameter.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all in this hair
Within bright spirit and principle, any modification, equivalent substitution and improvements done etc. should be included in this hair
Within bright protection domain.
Claims (10)
1. a kind of bearing calibration of magnetic resonance system, the magnetic resonance system includes radiofrequency emitting module, ladder
Module and Receiver Module are spent, following steps are specifically included：
The first pulse train is performed, first group of echo-signal is gathered and obtains the frequency of first group of echo-signal
Domain phase, first pulse train is spin-echo sequence；
The second pulse train is performed, second group of echo-signal is gathered and obtains the frequency of second group of echo-signal
Domain phase, second pulse train selects layer spin-echo sequence to be non-；
System is obtained according to the frequency domain phase of first group of echo-signal and second group of echo-signal relatively to prolong
When, the system relative time delay includes radiofrequency emitting module and the relative time delay and radio frequency reception of gradient modules
The relative time delay of module and gradient modules；
Correction is compensated to the magnetic resonance system according to the system relative time delay.
2. the bearing calibration of magnetic resonance system according to claim 1, it is characterised in that described
One pulse train includes 90 °, 180 °, 180 ° of three radio-frequency pulses, two slice selective gradients, two readings
Go out gradient and one reads pre- dephasing gradient, second pulse train includes 90 °, 180 °, 180 °
Three radio-frequency pulses, two readout gradients and one read pre- dephasing gradient.
3. the bearing calibration of magnetic resonance system according to claim 2, it is characterised in that described to penetrate
Frequency transmitter module and the relative time delay of the gradient modules are proportional to first group of echo-signal and second group
The difference of the slope of the frequency domain phase of echo-signal, the Receiver Module is relative with the gradient modules to be prolonged
When be proportional to second group of echo-signal frequency domain phase slope, the frequency domain phase of the echo-signal
Slope is first derivative of the echo-signal frequency domain phase on being imaged voxel partial center distance.
4. the bearing calibration of magnetic resonance system according to claim 2, it is characterised in that described
Gradient fields in one pulse train or the second pulse train are positive along X-axis.
5. the bearing calibration of magnetic resonance system according to claim 1, it is characterised in that according to institute
Stating the detailed process that system relative time delay compensates correction to the magnetic resonance system is：Select the gradient
Module is reference, and the radiofrequency emitting module and radio frequency receiving are corrected respectively according to the system relative time delay
Delay of the block relative to gradient modules.
6. the bearing calibration of magnetic resonance system according to claim 1, it is characterised in that according to institute
Stating the detailed process that system relative time delay compensates correction to the magnetic resonance system is：According to the system
Relative time delay, obtains the relative time delay of the radiofrequency emitting module and the Receiver Module, and with described
Receiver Module is reference, and the radiofrequency emitting module and gradient modules are corrected respectively relative to radio frequency reception
The delay of module.
7. the bearing calibration of magnetic resonance system according to claim 1, it is characterised in that described
One group of echo-signal and/or second group of echo-signal do not include free induction decay signal.
8. the bearing calibration of magnetic resonance system according to claim 1, it is characterised in that count respectively
When calculating gradient fields along X-axis, Y-axis and Z axis, the Receiver Module and the phase of the gradient modules
To delay or the radiofrequency emitting module and the relative time delay of the gradient modules, the gradient modules are obtained
Gradient fields along relative time delay when X-axis, Y-axis and Z axis, and according to the relative time delay correction described in
Gradient modules.
9. the bearing calibration of the magnetic resonance system according to claim 1, it is characterised in that according to institute
Stating the detailed process that system relative time delay compensates correction to the magnetic resonance system is：
Obtain the corresponding gradient link delay of gradient modules；Prolonged according to the system relative time delay and gradient link
When, the corresponding transmitting chain delay of radiofrequency emitting module reception chain corresponding with Receiver Module is obtained respectively
Road is delayed；And be delayed according to the gradient link delay, transmitting chain delay and receives link, it is right
The magnetic resonance system compensates correction.
10. a kind of means for correcting of magnetic resonance system, including：
Detection unit, for performing scanning sequence and obtaining echo-signal, the scanning sequence includes the first arteries and veins
Sequence and the second pulse train are rushed, first pulse train is spin-echo sequence, for producing first group
Echo-signal, second pulse train selects layer spin-echo sequence to be non-, for producing second group of echo letter
Number；
Relative time delay acquiring unit, for being obtained according to first group of echo-signal and second group of echo-signal
The slope of the frequency domain phase of echo-signal, and according to being obtained the slope of the frequency domain phase of the echo-signal
The relative time delay and Receiver Module and gradient-norm of magnetic resonance system radiofrequency emitting module and gradient modules
The relative time delay of block；
Link delay acquiring unit, for obtaining the corresponding gradient link delay of gradient modules, and according to described
Relative time delay and gradient link delay, obtain the corresponding transmitting chain delay of radiofrequency emitting module and radio frequency connects
Receive the corresponding receives link delay of module；
Correction module, it is common to magnetic according to the gradient link delay, transmitting chain delay or receives link delay
Vibrating system sweep parameter compensates correction.
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