CN101793950B - Method for maintaining phase coherence of transmitter and a plurality of receivers - Google Patents
Method for maintaining phase coherence of transmitter and a plurality of receivers Download PDFInfo
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- CN101793950B CN101793950B CN201010134678A CN201010134678A CN101793950B CN 101793950 B CN101793950 B CN 101793950B CN 201010134678 A CN201010134678 A CN 201010134678A CN 201010134678 A CN201010134678 A CN 201010134678A CN 101793950 B CN101793950 B CN 101793950B
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Abstract
The invention discloses a method for maintaining the phase coherence of a transmitter and a plurality of receivers, which is characterized by comprising the following steps: adding a compensation stage in a pulse sequence; switching frequencies of all receivers to an excitation frequency at an excitation stage of the pulse sequence; switching the frequencies of all the receivers to respective sampling frequency at a data sampling stage; and switching the frequencies of all the receivers to sampling frequencies of other receivers sequentially at the compensation stage. The frequencies of all the receivers are identical at other stages of the pulse sequence; and a frequency of the transmitter is always identical with that of one of the receivers in an implementation period of the pulse sequence. The method can ensure the phase coherence of the transmitter and the plurality of receivers simultaneously; moreover, the influence of rounding errors of the frequencies of the transmitter and the receivers on phases are identical, so the phase coherence cannot be influenced.
Description
Technical field
The present invention relates to nuclear magnetic resonance technique, particularly is a kind of transmitter and relevant method of a plurality of receiver phase of keeping.
Background technology
Transmitter and receiver is two important component parts of nuclear magnetic resonance spectrometer.Wherein, transmitter is used to launch radio-frequency pulse, and receiver is used to receive NMR signal.The general kernel nuclear magnetic resonance spectrometer respectively uses a frequency source on transmitter and receiver, the phase place of the NMR signal that finally receives will be by the phase place (hereinafter to be referred as transmitter phase) in transmitter frequency source and the common decision of phase place (hereinafter to be referred as receiver phase) of receiver frequency source.
In nuclear magnetic resonance technique, call pulse train to the setting of correlation parameters such as radio-frequency pulse, gradient pulse and signals collecting and the arrangement on sequential thereof.Generally, magnetic resonance imaging need add up and the gradient phase encoding, and this just means that pulse train need repeatedly be repeated.In order can normally to add up and the gradient phase encoding, in the process that pulse train repeats, need to guarantee transmitter and receiver phase coherence.Transmitter and receiver phase coherence is meant, when pulse train repeats, and the pairing transmitter phase of each time point in the sequence and the poor ΔΦ of receiver phase
i j(hereinafter to be referred as the phase differential of transmitter with receiver) all is identical each time.This condition can use equality (1) to describe:
Wherein, ΔΦ
i jRepresent when repeating pulse train the j time the phase differential of i pairing transmitter of time point and receiver in the sequence.
For general pulse train, the term of execution of sequence, do not need switching frequency.As shown in Figure 1, because the phase differential of transmitter and receiver do not change all the time, so transmitter and receiver can keep phase coherence.But the pulse train for stage construction scanning has two periods respectively the frequency of transmitter and receiver to be had particular requirement in the sequence.Wherein, in excitation phase, need repeatedly switch the frequency of transmitter; In data acquisition phase, the frequency of receiver need switch on the resonant frequency.Be example with the transmitter switching frequency among Fig. 2, explain that their phase differential can change when both had only a switching frequency when transmitter and receiver.Like this, after pulse train was carried out, the change meeting of phase differential was added up.When pulse train is carried out next time, the phase differential in the sequence on the corresponding time point and preceding once unequal, equality (1) is false, so transmitter and receiver can not keep phase coherence, and then causes normally adding up and the gradient phase encoding.
A kind of method that addresses this problem is to adopt the technology of unrolling.In this method, after the excitation phase of pulse train, increase by one and unroll the stage.The term of execution of sequence, the fixed-frequency of receiver is on resonant frequency.Other periods of sequence (except excitation phase with unroll the stage), transmitter is identical with the frequency of receiver.In its frequency in the stage of unrolling of the frequency of excitation phase adjustment, the phase differential that makes transmitter and receiver is in the change of excitation phase and cancel out each other in the change in the stage of unrolling according to transmitter.Like this, when pulse train was carried out next time, the phase differential in the sequence on the corresponding time point equated with last time, makes equality (1) set up, and transmitter and receiver keeps phase coherence.Yet the frequency accuracy of transmitter and receiver all is limited, and generally, the frequency values that unroll stage and excitation phase are got is inequality, owing to there is round-off error, transmitter and receiver can not keep phase coherence well.
In order to overcome the influence of frequency round-off error to the coherence, granted patent ZL 200410053153.9 discloses another kind of method and has guaranteed transmitter and receiver phase coherence.As shown in Figure 3, the Frequency Synchronization of transmitter and receiver is switched in this method.That is, in excitation phase, the Frequency Synchronization of receiver and transmitter switches on the stimulating frequency; In other periods of sequence (except excitation phase), the frequency of transmitter and receiver all switches on the resonant frequency.Like this, the frequency of transmitter and receiver is identical all the time, and their phase differential does not change, so transmitter and receiver can keep phase coherence.And the frequency round-off error also is identical to their influences that phase place produced separately, so round-off error can not exert an influence to phase coherence.
Along with the development of technology, a plurality of receivers are widely used in magnetic resonance imaging, so that accelerate image taking speed and improve imaging sensitivity.Under a kind of simple relatively situation, a plurality of receivers carry out data acquisition with identical rf frequency, that is, a plurality of receivers are identical in the frequency of data acquisition phase, and at this moment a plurality of receivers are called as multichannel receiver.For the phase coherence problem of transmitter and multichannel receiver, still can adopt the method for patent ZL 200410053153.9 to solve.
Yet when a plurality of receivers carried out data acquisition with different separately rf frequencies, promptly the frequency at a plurality of receivers of data acquisition phase of pulse train was different, and above-mentioned two kinds of methods all can't guarantee the phase coherence of transmitter and a plurality of receivers.Its reason: (1), owing to receive the restriction of transmitter and receiver frequency accuracy, " technology of unrolling " can't be eliminated the influence of frequency round-off error to phase coherence.Identical two kinds of situation with single receiver and a plurality of receiver frequency are compared, and when a plurality of operation of receiver during at different frequency, round-off error can produce bigger influence to phase coherence.Therefore " technology of unrolling " can not guarantee well that transmitter and a plurality of receiver phase are concerned with.(2), the method for patent ZL 200410053153.9 can only guarantee in a plurality of receivers that a receiver and transmitter phase are relevant, and other receiver and transmitter phase are irrelevant.For brevity, Fig. 4 has provided the example of two receivers.At receiver data acquisition period (among Fig. 41 and 2 between), in order to satisfy the requirement of pulse train, the frequency of receiver 1 and receiver 2 can not be identical.Therefore, the frequency of transmitter can only switch on the frequency of one of them receiver.In the example of Fig. 4, in data acquisition period, transmitter frequency switches on the frequency of receiver 1.In the each process of carrying out of pulse train, the phase differential of transmitter and receiver 1 does not change, and therefore, satisfies the requirement of equality (1), transmitter and receiver 1 phase coherence.And change has taken place in the phase differential of transmitter and receiver 2, therefore, does not satisfy the requirement of equality (1), and transmitter and receiver 2 phase places are irrelevant.
Summary of the invention
The objective of the invention is weak point, proposed a kind of transmitter and relevant method of a plurality of receiver phase of keeping to above-mentioned prior art.This method can guarantee simultaneously that transmitter and a plurality of receiver phase are concerned with.And; Because having experienced identical frequency with each receiver, transmitter switches and the retention time; The frequency round-off error is identical to their the accumulative total effect that phase place produced; Therefore round-off error can not influence phase coherence to the not contribution of phase differential of transmitter and each receiver.
The objective of the invention is to realize like this:
A kind of transmitter and relevant method of a plurality of receiver phase of keeping, this method is in pulse train, to increase compensated stage.Switch on the stimulating frequency in the excitation phase of pulse train frequency all receivers; Switch on the SF separately in the frequency of data acquisition phase all receivers; All switch to successively on the SF of other receivers in the frequency of compensated stage all receivers.In other stages of pulse train, the frequency of all receivers is identical.The term of execution of pulse train, the frequency of the transmitter frequency with one of them receiver all the time is identical.
Because ΔΦ
i jBe to produce by the operation on the corresponding time point in the pulse train (like radio-frequency pulse, gradient pulse and signals collecting); Therefore; After the each execution of pulse train; As long as the accumulative total of the phase differential of transmitter and receiver is changed to 0, when then repeating sequence, the change procedure of phase differential and last time are identical next time.Like this, just can guarantee transmitter and receiver phase coherence so that equality (1) is set up.
All equal 0 for the accumulative total of the phase differential that makes transmitter and a plurality of receivers changes, the present invention increases compensated stage after the data acquisition phase of pulse train.Suppose to have N receiver, when pulse train was carried out, in excitation phase, the frequency of transmitter and all receivers all switched on the stimulating frequency Ft.In data acquisition phase, receiver switches to SF Fr separately
1, Fr
2Fr
NOn, the frequency of transmitter switches to that (hypothesis is Fr on the frequency of one of them receiver here
1).Compensated stage is divided into N-1 unit, and the time of each unit is equal to data acquisition time.At the 1st unit, the frequency of transmitter and receiver 1 is Fr
2, the frequency of receiver 2 is Fr
3... The frequency of receiver N is Fr
1At the 2nd unit, the frequency of transmitter and receiver 1 is Fr
3, the frequency of receiver 2 is Fr
4... The frequency of receiver N is Fr
2The rest may be inferred, and at N-1 unit, the frequency of transmitter and receiver 1 is Fr
N, the frequency of receiver 2 is Fr
1... The frequency of receiver N is Fr
(N-1)In other stages, the frequency of transmitter and all receivers identical (for example, all switching on the Ft).
The invention has the advantages that and to guarantee simultaneously that transmitter and a plurality of receiver phase are concerned with.And; Because having experienced identical frequency with each receiver, transmitter switches and the retention time; The frequency round-off error is identical to their the accumulative total effect that phase place produced; Therefore round-off error can not influence phase coherence to the not contribution of phase differential of transmitter and each receiver.
Description of drawings
Phase coherence synoptic diagram when Fig. 1 does not have switching frequency for transmitter
The irrelevant synoptic diagram of phase place when Fig. 2 is the transmitter switching frequency
Fig. 3 keeps the phase coherence synoptic diagram for the frequency of switching transmitter and receiver simultaneously;
Fig. 4 can only keep transmitter and the synoptic diagram that receiver phase is relevant for the while switching frequency
Fig. 5 keeps transmitter and the relevant synoptic diagram of a plurality of receiver phase for the present invention
Embodiment
Below in conjunction with accompanying drawing the present invention is done further explain, so that technician's of the same trade understanding:
Consult Fig. 5; To adopt the present invention to keep transmitter and two receiver phases to be concerned with is example; (be N=2 among Fig. 5, and 3 ' overlap with 3) switches to the frequency of transmitter and two receivers in excitation phase that to excite frequently be the synoptic diagram that adopt the present invention to keep transmitter and two receiver phases to be concerned with simultaneously; As shown in the figure, switch to the frequency of transmitter and two receivers simultaneously on the stimulating frequency Ft in excitation phase.At data acquisition phase (among Fig. 5 between 1 to 2), two receivers need be with different frequency Fr
1And Fr
2Image data), and with the frequency of transmitter switch to Fr
1On.From Fig. 5, can see, after data acquisition is accomplished (2 places among Fig. 5), transmitter and receiver 1 phase coherence, transmitter and receiver 2 phase places are irrelevant.After data acquisition phase, increase a compensated stage that equates with data acquisition (between 2 to 3 among Fig. 5), and the frequency of transmitter and receiver 1 is switched to Fr
2On, the frequency with receiver 2 switches to Fr simultaneously
1On.In other stages of pulse train, the frequency identical (all switching on the Ft among Fig. 5) of transmitter and two receivers.Like this, the term of execution of pulse train (among Fig. 5 1～4), the phase place that transmitter ran is:
Φt＝Ft×(T
1-T
0)+Fr
1×(T
2-T
1)+Fr
2×(T
3-T
2)+Ft×(T
4-T
3) (2)
The phase place that receiver 1 ran is:
Φr
1＝Ft×(T
1-T
0)+Fr
1×(T
2-T
1)+Fr
2×(T
3-T
2)+Ft×(T
4-T
3) (3)
The phase place that receiver 2 ran is:
Φr
2＝Ft×(T
1-T
0)+Fr
2×(T
2-T
1)+Fr
1×(T
3-T
2)+Ft×(T
4-T
3) (4)
The initial value of supposing the phase differential of transmitter and receiver 1 is a ΔΦ
1, the initial value of the phase differential of transmitter and receiver 2 is a ΔΦ
2, then pulse train complete after, the phase differential of transmitter and receiver 1 is:
ΔΦ
1′＝ΔΦ
1+(Φr
1-Φt)＝ΔΦ
1 (5)
The phase differential of transmitter and receiver 2 is:
ΔΦ
2′＝ΔΦ
2+(Φr
2-Φt) (6)
＝ΔΦ
2+(Fr
2-Fr
1)×[(T
2-T
1)-(T
3-T
2)]
Wherein, (Fr
2-Fr
1) ≠ 0, (T
2-T
1) be data acquisition phase, (T
3-T
2) be compensated stage.Can find out from (2)～(6), as (T
2-T
1)=(T
3-T
2) time, ΔΦ
1'=ΔΦ
1, ΔΦ
2'=ΔΦ
2Like this, after pulse train was complete, the phase differential of transmitter and two receivers equated that with initial phase difference the variation of phase differential accumulative total is 0.When repeating sequence, the change procedure of their phase differential and last time are identical next time.Like this, just can guarantee that transmitter and two receiver phases are relevant so that equality (1) is set up.
When a plurality of receivers carry out data acquisition with different separately frequencies, guarantee that transmitter and a plurality of receiver phase are relevant, just must after the each execution of pulse train, make the accumulative total variation of the phase differential of transmitter and a plurality of receivers all equal 0.This need realize from hardware and software two aspects.
On hardware, transmitter all needs frequency source separately with each receiver.Frequency source should be able to switch output signal frequency fast.Each frequency source all has data-interface, internal memory, trigger signal source and logic control element.Before pulse train is carried out, the whole frequency data write memories that switched with pulse train the term of execution through data-interface.The term of execution of pulse train, trigger signal source will produce trigger pip according to the requirement of sequence.Whenever trigger signal source sends a trigger pip, frequency source just under the control of logic control element with internal memory in current frequency values go to upgrade output signal frequency, and with next set of frequency data of memory pointers.
On software, realize that through the pulse train composing software frequency of transmitter and receiver is switched.In pulse sequence compiler software, the transmitter frequency source all has independently control module with each receiver frequency source, and each control module all has the independent frequency tabulation.In addition, transmitter and a plurality of reception function while switching frequency.
For simplicity, be example with situation shown in Figure 5.As shown in the figure, pulse train is carried out once need be provided with 4 secondary frequencies.Consider when pulse train repeats that the value of Ft can change according to the requirement of sequence, in order to distinguish, note is f respectively
1, f
2F
mLike this, the frequency values of transmitter is followed successively by (f
1-Fr
1-Fr
2-f
1)-(f
2-Fr
1-Fr
2-f
2) ... (f
m-Fr
1-Fr
2-f
m), the frequency values of receiver 1 is followed successively by (f
1-Fr
1-Fr
2-f
1)-(f
2-Fr
1-Fr
2-f
2) ... (f
m-Fr
1-Fr
2-f
m), the frequency values of receiver 2 is followed successively by (f
1-Fr
2-Fr
1-f
1)-(f
2-Fr
2-Fr
1-f
2) ... (f
m-Fr
2-Fr
1-f
m).Before pulse train is carried out for the first time, the said frequencies value is write respectively in the internal memory of transmitter frequency source and receiver frequency source, with the said frequencies value is write in the list of frequency corresponding in the composing software.The term of execution of pulse train,, upgrade the frequency of transmitter and receiver successively with the frequency values in the list of frequency according to the result of pulse train composing software.
Claims (1)
1. one kind keeps transmitter and the relevant method of a plurality of receiver phase, it is characterized in that: in pulse train, increase compensated stage; Switch on the stimulating frequency in the excitation phase of pulse train frequency all receivers; Switch on the SF separately in the frequency of data acquisition phase all receivers; All switch to the frequency of all receivers on the SF of other receivers successively at compensated stage; In other stages of pulse train, the frequency of all receivers is identical; The term of execution of pulse train, the frequency of the transmitter frequency with one of them receiver all the time is identical; Wherein:
Said compensated stage is that it is divided into N-1 unit, and the time of each unit is equal to data acquisition time; At the 1st unit, the frequency of transmitter and receiver 1 is Fr
2, the frequency of receiver 2 is Fr
3... The frequency of receiver N is Fr
1At the 2nd unit, the frequency of transmitter and receiver 1 is Fr
3, the frequency of receiver 2 is Fr
4... The frequency of receiver N is Fr
2The rest may be inferred, and at N-1 unit, the frequency of transmitter and receiver 1 is Fr
N, the frequency of receiver 2 is Fr
1... The frequency of receiver N is Fr
(N-1)
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201010134678A CN101793950B (en) | 2010-03-30 | 2010-03-30 | Method for maintaining phase coherence of transmitter and a plurality of receivers |
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|---|---|---|---|
| CN201010134678A CN101793950B (en) | 2010-03-30 | 2010-03-30 | Method for maintaining phase coherence of transmitter and a plurality of receivers |
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| Publication Number | Publication Date |
|---|---|
| CN101793950A CN101793950A (en) | 2010-08-04 |
| CN101793950B true CN101793950B (en) | 2012-10-10 |
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| CN111505550B (en) * | 2020-05-06 | 2021-02-02 | 电子科技大学 | Frequency switching method for frequency source of radio frequency excitation pulse generator and spectrometer receiver |
| CN112083366B (en) * | 2020-07-22 | 2021-12-24 | 华东师范大学 | Device and method for keeping phase coherence of transmitting/receiving channel |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8528357D0 (en) * | 1985-11-18 | 1985-12-24 | Picker Int Ltd | Nuclear magnetic resonance imaging |
| CN100401089C (en) * | 2004-07-23 | 2008-07-09 | 华东师范大学 | Method for realizing multilayer sanning sequence phase coherent |
| CN1959427B (en) * | 2006-09-30 | 2010-05-12 | 上海卡勒幅磁共振技术有限公司 | Method for guaranteeing coherence between radio transmitting and receiving signals in magnetic resonance imaging spectrometer |
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Non-Patent Citations (1)
| Title |
|---|
| 宁瑞鹏等.磁共振成像数字谱仪的射频发射/接收通道相位相干性的研究.《波谱学杂志》.2007,第24卷(第04期),全文. * |
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| ASS | Succession or assignment of patent right |
Owner name: KALEFU MAGNETIC RESONANCE TECH CO., LTD., SHANGHAI Effective date: 20120605 |
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| TA01 | Transfer of patent application right |
Effective date of registration: 20120605 Address after: 200241 Dongchuan Road, Shanghai, No. 500, No. Applicant after: East China Normal University Co-applicant after: Kalefu Magnetic Resonance Tech Co., Ltd., Shanghai Address before: 200241 Dongchuan Road, Shanghai, No. 500, No. Applicant before: East China Normal University |
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