CN1959427B - Method for guaranteeing coherence between radio transmitting and receiving signals in magnetic resonance imaging spectrometer - Google Patents
Method for guaranteeing coherence between radio transmitting and receiving signals in magnetic resonance imaging spectrometer Download PDFInfo
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- CN1959427B CN1959427B CN200610116891A CN200610116891A CN1959427B CN 1959427 B CN1959427 B CN 1959427B CN 200610116891 A CN200610116891 A CN 200610116891A CN 200610116891 A CN200610116891 A CN 200610116891A CN 1959427 B CN1959427 B CN 1959427B
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- frequency
- receiver
- transmitter
- magnetic resonance
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Abstract
A method for ensuring coherence of radio frequency emission with receiving signal in magnetic resonant imaging spectrometer switches emitting and receiving frequency over to be initial frequency valueof pulse sequence for realizing coherence of emission with receiving signal after data sampling is finished.
Description
Technical field
The present invention relates to the mr imaging technique class, be specifically related to the core component in the magnetic resonance tool equipment---spectrometer, more particularly relate to guarantee in a kind of Magnetic resonance imaging spectrometer the method for radiofrequency signal phase coherence between radio-frequency transmissions passage and the receiving cable.
Background technology
In magnetic resonance imaging (MRI), the three-dimensional body image adopts the two dimensional image of multilayer to represent usually, and this just needs so-called " choosing layer " technology.The choosing layer normally relies on gradient magnetic and radio frequency soft pulse (SINC) to combine, and acts on tissue, excites the aspect of the imaging of wanting.Suppose that main field strength is B
0, the centre frequency of SINC soft pulse is ω
i, exciting bandwidth is Δ ω
i, the gradient fields intensity that applies in the Z direction is G
z, so, according to formula ω
i=γ (B
0+ zG
z) can obtain: choosing layer position is z=(ω
i-γ B
0)/γ G
zBed thickness is Δ z=Δ ω
i/ γ G
zAccording to above formula, the position of choosing layer can be by changing B
0Perhaps switch rf frequency ω
iRealize, and the control of bed thickness is generally by changing gradient G
zSize realize.
In traditional simulation nuclear magnetic resonance spectrometer, the frequency that the radio-frequency channel transmits and receives is not easy at random to change.Therefore, the choosing layer can pass through at main field B
0Go up additional Δ B
0Realize.This just needs one group of extra coil (to be called B
0Coil), thereby the cost of equipment is risen, the eddy current that causes because of the change of magnetic field intensity will make the quality of image descend simultaneously.In the middle of the digital nuclear magnetic resonance spectrometer of modernization, transmission channel (frequency source) and receiving cable (receiver) have all adopted digitizing technique.Frequency source adopts Direct Digital frequency synthesis (DDS, Direct Frequency Synthesizer) technology, switching frequency, amplitude and phase place apace.Therefore, can be by changing excitation frequency omega
iRealize the choosing layer.This method not only makes the structure of whole instrument simplify greatly, has also reduced cost simultaneously.
Magnetic resonance signal (FID) is a complex signal, and it has also comprised phase information except amplitude information is provided.The phase place of the FID signal that is finally obtained by receiver is by the common decision of phase place of the phase place of transmission channel (frequency source) and receiving cable (receiver).Therefore, in the whole process that magnetic resonance imaging pulse train is carried out, all must guarantee the radiofrequency signal phase coherence of transmission channel and receiving cable, that is to say the phase differential that in scanning process, requires transmitter frequency source and receiver frequency source to be maintained fixed.Just can carry out effective signal on this basis adds up and phase encoding.
If the frequency of transmitter and receiver all not working frequency switch, and they are operated on the identical frequency, their phase place can keep relevant always so.The mode of operation of this conventional just nuclear magnetic resonance spectrometer device.Yet for MR imaging apparatus, as mentioned above, in order to reach " choosing layer " purpose, the frequency of transmitter must be carried out frequency and be switched.Therefore, their phase coherence of assurance needs the particular processing method under this condition.
In existing technology, for guaranteeing the phase coherence of transmitter and receiver, what adopt usually is phase place " (rewind) unrolls " technology, as shown in Figure 1.Among the figure, the frequency of receiving cable Rx keeps ω from start to finish
0Constant. transmission channel Tx begins moment at T1 frequency is switched, it has run δ ω fast than receiver, when T1 finishes, a phase place Φ of receiver 1=δ ω * T1. allows transmitter switch on the low frequency in the T2 time if transmitter is leading, allow it pull up lame than receiver, so, having arrived T3 begins, receiver just might catch up with transmitter. when the δ ω that satisfies condition * T1=δ ω ' * T2, transmitter and receiver has been got back to coherency states again. usually be called " rewind time-delay " during the T2. although the rewind method is effective, also be widely adopted simultaneously, but it needs the extra time-delay of inserting, when pulse train is write, add trouble more or less, and increased time (as the echo time TE) length of pulse train.
Summary of the invention
The objective of the invention is according to above-mentioned the deficiencies in the prior art part, a kind of guarantee radio-frequency transmissions and the relevant method of received signal in the magnetic resonance imaging spectrometer are provided, this method is after data sampling finishes, to transmit and receive frequency at last and switch to the initial frequency values of pulse train, realize emission and the signal coherence that receives.
The object of the invention realizes being finished by following technical scheme:
A kind ofly guarantee the relevant method of radio-frequency transmissions and received signal in the magnetic resonance imaging spectrometer, comprise main frame, pulse-series generator, transmitter and frequency source thereof and internal memory, receiver and frequency source thereof and internal memory, the pulse-series generator generation is used for that transmitter and receiver is carried out frequency and upgrades needed trigger pulse, the step that it is characterized in that this method is: sampling is initial, before pulse train begins, write all frequency updating value to the internal memory of transmitter and the internal memory of receiver by main frame; Secondly the term of execution of pulse train, when the transmitter renewal frequency, the while is the new receiver frequency more, and afterwards, the address pointer in the internal memory moves one backward, points to next frequency values; After the data sampling of all layers finishes, just transmit and receive frequency at last and switch to the initial frequency values of pulse train.
The frequency source of described transmitter and receiver adopts same reference clock.
Advantage of the present invention is, need not to add extra " rewind time-delay ", thereby make that writing of pulse train obtains simplifying, and this method not relying on the concrete structure of nuclear magnetic resonance spectrometer transmitter and receiver hardware components, is a kind of general method that is applicable to Digital Spectrometer.
Description of drawings
Accompanying drawing 1 for prior art adopt " (rewind) unrolls " technology keep phase coherence synoptic diagram;
Accompanying drawing 2 switches the synoptic diagram of the frequency maintenance phase coherence of transmitter and receiver simultaneously for the present invention;
The synoptic diagram of card phase coherence method when accompanying drawing 3 is switching frequency of the present invention;
Accompanying drawing 4 is the present invention's synoptic diagram of card phase coherence method during switching frequency repeatedly;
Accompanying drawing 5 is the synoptic diagram of embodiment of the invention multilayer spin echo;
Embodiment
Feature of the present invention and other correlated characteristic are described in further detail by embodiment below in conjunction with accompanying drawing, so that technician's of the same trade understanding:
In nuclear magnetic resonance spectrometer, the pulse-series generator generation is used for that transmitter and receiver is carried out frequency and upgrades needed trigger pulse.Transmitter and receiver also needs an internal memory except comprising separately frequency source, being used to deposit needs all frequency informations of switching in the middle of the whole pulse.Before pulse train begins, at first write all frequency updating value to the internal memory of transmitter and receiver by main frame.The term of execution of pulse train,, just send into frequency source separately, renewal frequency immediately with the frequency values in the current internal memory whenever transmitter and receiver is received the trigger pulse that pulse-series generator produces; Simultaneously, the address pointer in the internal memory moves one backward, points to next frequency values.
Be example with the multilayer spin echo below, describe the pulse train implementation in detail and how to carry out the frequency switching, and guarantee the phase coherence of transmitter receiver.
As shown in Figure 5, the frequency source that Tx_update and Rx_update correspond respectively to transmitter and receiver upgrades. in 90 ° of radio-frequency pulses, the frequency of transmitter and receiver is all switched on the resonant frequency of selected layer, and the frequency source of transmitter and receiver adopts same reference clock. before to the echoed signal sampling, frequency is switched back on the frequency values of acquiescence, so that image data. after the data sampling of all layers finishes, at last frequency is switched to the initial frequency values of pulse train. like this, just can guarantee the phase coherence of transmitter and receiver.
The theoretical analysis of present embodiment method is as follows: in the middle of multilayer pulse train, in order to guarantee the phase coherence of transmitter and receiver, can take the transmitter and receiver method of switching frequency simultaneously, as Fig. 2.Like this, at any time transmitter and receiver all run equally fast, phase differential is fixed, and has guaranteed phase coherence.
Yet the requirement that will satisfy " transmitter and receiver can simultaneously renewal frequency " in the ordinary course of things and be not easy.At first, when the frequency source of transmitter and receiver adopted device inequality, their frequency renewal speed just had difference.Secondly, even they adopt identical device, also can there be certain otherness in two devices.Still more because the physical location difference of two passages, and the control signal that frequency is upgraded is produced by pulse-series generator, so the frequency update signal reaches the time that transmits and receives passage and has minute differences.This mistiming also can be subjected to the influence of environment (for example temperature), thereby causes the incomplete while of renewal of two channel frequences.
The method that present embodiment proposes is used to transmit and receive that the frequency of passage is not strict when upgrading simultaneously, and the coherence who guarantees them is very important.
Keep the relevant extra time-delay that needs owing to making with the rewind method transmitting and receiving, guarantee the relevant simple advantage that has so select to transmit and receive switching simultaneously.But when the frequency that transmit and receive passage was upgraded not strict while, the frequency switching can cause transmitting and receiving and produces a phase differential between the passage.The frequency switch speed of supposing transmission channel is faster than receiving cable, as Fig. 3.At first, Tx and Rx are all with frequencies omega
0Run, at t1 constantly, the frequency of Tx switches to ω
1On, but the frequency switch speed of Rx is slower than Tx, and at this moment Rx still keeps original frequencies omega
0, up to having crossed δ
tAfter time, Rx just finishes frequency and upgrades.Therefore in this secondary frequencies handoff procedure, Tx is than the super previous phase place of Rx: Φ
1=(ω
1-ω
0) * δ
tIf after this Tx and Rx no longer carry out the frequency renewal, then Tx keeps the super previous phase place Φ 1 than Rx always.But, if at t2 constantly with their frequency again from ω
1Switch back ω
0, owing to the Rx passage switches still than the slow δ t time of Tx in t2 frequency constantly, so this secondary frequencies switches Tx than the super again previous phase place of Rx: Φ
2=(ω
0-ω
1) * δ
tTherefore, switch through twice frequency, Tx total phase place more leading than Rx is: Φ
1=Φ
1+ Φ
2=0.
Be the situation of only switching a secondary frequencies in the pulse train above, in fact for repeatedly frequency switching, as long as after image data is finished, frequency switched again get back to original frequency, still can guarantee the phase coherence of Tx and Rx, prove as follows: as Fig. 4, Tx and Rx have carried out the n secondary frequencies and have switched, and wherein last the switching gets back to initial frequencies omega
0On.After n switching finished, the Tx total phase place more leading than Rx was:
Φ＝Φ
1+Φ
2+ΛΦ
n
＝(ω
1-ω
0)×δ
t+(ω
2-ω
1)×δ
t+Λ
+(ω
n-ω
n-1)×δ
t+(ω
0-ω
n)×δ
t
＝0
As seen, after image data was finished, intermediate frequency and changed how many times no matter was as long as switch back original frequency (ω with the frequency that transmits and receives
0), just can guarantee their phase coherence.
Claims (2)
1. one kind guarantees radio-frequency transmissions and the relevant method of received signal in the magnetic resonance imaging spectrometer, described magnetic resonance imaging spectrometer comprises main frame, pulse-series generator, transmitter and frequency source thereof and internal memory, receiver and frequency source thereof and internal memory, the pulse-series generator generation is used for that transmitter and receiver is carried out frequency and upgrades needed trigger pulse, the step that it is characterized in that this method is: at first sampling is initial, before pulse train begins, write all frequency updating value to the internal memory of transmitter and the internal memory of receiver by main frame; Secondly the term of execution of pulse train, when the transmitter renewal frequency, the while is the new receiver frequency more, and afterwards, the address pointer in the internal memory moves one backward, points to next frequency values; After the data sampling of all layers finishes, will transmit and receive frequency at last and switch to the initial frequency values of pulse train.
2. a kind of guarantee radio-frequency transmissions and the relevant method of received signal in the magnetic resonance imaging spectrometer according to claim 1 is characterized in that the frequency source of described transmitter and receiver adopts same reference clock.
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| CN1959427B true CN1959427B (en) | 2010-05-12 |
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Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101345534B (en) * | 2008-06-30 | 2012-06-27 | 东软飞利浦医疗设备系统有限责任公司 | Generation, transmission device and method for MRI radio frequency signal |
| CN101339232B (en) * | 2008-08-13 | 2012-05-23 | 宁波鑫高益磁材有限公司 | Radio-frequency pulse synthesis method in magnetic resonance image-forming system |
| CN101793950B (en) * | 2010-03-30 | 2012-10-10 | 华东师范大学 | Method for maintaining phase coherence of transmitter and a plurality of receivers |
| CN113466280B (en) * | 2018-02-27 | 2022-07-26 | 华东师范大学 | Simulated nuclear magnetic resonance spectrum analysis method and system convenient for expanding molecular information base and application thereof |
| 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 |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5529068A (en) * | 1994-06-16 | 1996-06-25 | The Regents Of The University Of California | Synchronized digital signal processor for MRI reception |
| US5689186A (en) * | 1995-12-26 | 1997-11-18 | General Electric Company | Method for producing an off-center image using an EPI pulse sequence |
| CN1317901A (en) * | 2000-04-11 | 2001-10-17 | 中南工业大学 | Co-clock timing method for signal interference detection |
| CN1588112A (en) * | 2004-07-23 | 2005-03-02 | 华东师范大学 | Method for realizing multilayer sanning sequence phase coherent |
-
2006
- 2006-09-30 CN CN200610116891A patent/CN1959427B/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5529068A (en) * | 1994-06-16 | 1996-06-25 | The Regents Of The University Of California | Synchronized digital signal processor for MRI reception |
| US5689186A (en) * | 1995-12-26 | 1997-11-18 | General Electric Company | Method for producing an off-center image using an EPI pulse sequence |
| CN1317901A (en) * | 2000-04-11 | 2001-10-17 | 中南工业大学 | Co-clock timing method for signal interference detection |
| CN1588112A (en) * | 2004-07-23 | 2005-03-02 | 华东师范大学 | Method for realizing multilayer sanning sequence phase coherent |
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