CN100401089C - Method for realizing multilayer sanning sequence phase coherent - Google Patents
Method for realizing multilayer sanning sequence phase coherent Download PDFInfo
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- CN100401089C CN100401089C CNB2004100531539A CN200410053153A CN100401089C CN 100401089 C CN100401089 C CN 100401089C CN B2004100531539 A CNB2004100531539 A CN B2004100531539A CN 200410053153 A CN200410053153 A CN 200410053153A CN 100401089 C CN100401089 C CN 100401089C
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- frequency
- transmitter
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- source
- phase coherence
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Abstract
The present invention relates to an NMR imaging technology particularly to a method for realizing the phase coherence of multilayered scanning sequences. The method is characterized in that before the excitation pulses of a selected layer, the frequency of a transmitter and a receiver is simultaneously switched to the excitation frequency of the layer; before sampling, the frequency of the frequency sources of the transmitter and the receiver is simultaneously switched to receiving frequency. The present invention has the advantages that under the condition of changing excitation frequency to realize chip selection, the problem of the phase coherence of the transmitter and the receiver; the excitation frequency is changed so as to realize the chip selection, which is simpler than the method for realizing the chip selection by changing the magnitude of a main magnetic field B0, and the complicacy of instruments is greatly reduced.
Description
Technical field
The present invention relates to nmr imaging technique, is a kind of method that realizes the phase coherence of stage construction scanning sequence concretely.
Background technology
In Magnetic resonance imaging, the choosing layer is realized in conjunction with the chip select gradient by soft pulse.According to chip select position formula Z=(ω
i-γ B
0)/γ G
zAs can be known, the position that change chip select can change excitation frequency omega
i, main field B
0Or chip select gradient G
zIn clinical sequences, generally seldom realize chip select by changing the chip select gradient magnitude, main usually by changing main field B
0Or change excitation frequency omega
iRealize chip select.By changing main field B
0Realize that chip select needs one group of B
0Coil and corresponding DA control module, so structure more complicated, cost are big.Because the development of direct digital frequency synthesis technology (DDS) at present, the frequency source chip of many employing DDS technology is switching frequency apace, therefore can be by changing excitation frequency omega
iRealize the choosing layer, adopt this scheme complicacy and the cost of lowering apparatus greatly.
Transmitter and receiver is two elements of nuclear magnetic resonance spectrometer, and transmitter is used to launch radio-frequency pulse, and receiver is used to receive the FID signal.The general kernel nuclear magnetic resonance spectrometer respectively uses a frequency source on transmitter and receiver, the phase place of the FID signal that finally receives will be determined jointly by the phase place in transmitter frequency source and the phase place of receiver frequency source.The term of execution that just requiring nuclear magnetic resonance pulse sequence, this to guarantee the phase coherence of transmitter and receiver.The phase coherence of transmitter and receiver is meant that mainly the phase place in transmitter frequency source and the phase place of receiver frequency source will keep a fixing phase differential term of execution of pulse train.Phase coherence is to add up and the basis of gradient phase encoding.For general pulse train, the frequency of the frequency of transmitter and receiver is identical term of execution of pulse train, therefore can remain relevant.As can be seen from Figure 1, do not have at transmitter under the situation of switching frequency, therefore transmitter and receiver can remain phase coherence with one start of a race of identical frequency.In Fig. 2, transmitter has switched twice frequency, has switched a lower frequency at 1 place, switches back to original frequency again at 2 places, and after 1 switching frequency, transmitter and receiver just can not keep phase coherence.
For general pulse train, owing to the term of execution of pulse train, do not need switching frequency.Therefore these sequences the term of execution can keep phase coherence all the time.But for the pulse train of using stage construction scanning, these sequences need repeatedly be switched the stimulating frequency (being used to select different aspects) in transmitter frequency source term of execution of pulse train, so just caused transmitter frequency source and receiver frequency source phase place irrelevant, can be to the influence that adds up and the generation of gradient phase encoding is certain.Here be the example explanation with the stage construction fast acquisition interleaved spin echo, its pulse sequence diagram as shown in Figure 5.The stage construction fast acquisition interleaved spin echo needs to excite a plurality of aspects during a TR, and each aspect is carried out repeatedly phase encoding gather a plurality of echoes.Because this sequence need excite a plurality of aspects, therefore need to switch transmitter frequency and select different aspects, will cause phase place irrelevant like this, can't carry out phase encoding (, also having produced different phase shifts between each echo) even do not add phase encoding gradient.General solution is not add earlier sequence of phase encoding gradient scanning, each echo is carried out phase correction, note the phase correction coefficient of each echo, add that then gradient carries out phase encoding, and each echo is multiplied by the respective phase correction coefficient.Adopt this method more complicated, and be not very accurate, also depend on very much signal to noise ratio (S/N ratio).
Summary of the invention
The objective of the invention is according to above-mentioned the deficiencies in the prior art part, a kind of method that realizes the phase coherence of stage construction scanning sequence is provided, this method is when exciting and sample, all transmitter and receiver is switched to same frequency and remain phase coherence the pulse train term of execution, also just guaranteed the phase coherence of stage construction scanning sequence to realize transmitter and receiver.
The object of the invention realizes being finished by following technical scheme:
When doing stage construction pulse train, select different aspects by different stimulating frequencies is set, and receive frequency should remain on the fixing receive frequency when receiving the signal of different aspects, so stimulating frequency and receive frequency are inconsistent.According to conventional way, single switch transmitter frequency and do not switch the receiver frequency and can not allow transmitter and receiver keep phase coherence.Therefore thinking of the present invention is simultaneously the frequency of transmitter and receiver frequency source to be switched on the same frequency, allows transmitter and receiver keep phase coherence.
The solution of the present invention is: before the excitation pulse of choosing layer, simultaneously the frequency of transmitter and receiver frequency source is switched on the stimulating frequency of this layer, and the frequency of transmitter and receiver frequency source was switched on the receive frequency simultaneously before sampling again.So repeatedly, just can allow transmitter and receiver keep phase coherence all the time.
Because at duration of exciting, receiver is idle simultaneously, and at reception period, transmitter is idle, can not cause that any bad problem takes place instrument so above-mentioned frequency is switched.
Fig. 3 is the synoptic diagram that frequency is switched when exciting two aspects, the frequency of transmitter and receiver frequency source is switched to simultaneously on the stimulating frequency that excites first aspect at the pulse train section start, (1 place among Fig. 3) switches to the frequency of transmitter and receiver frequency source on the receive frequency simultaneously before first aspect of reception.Then excite second aspect, (2 places among Fig. 3) switch to the frequency of transmitter and receiver frequency source on the frequency that excites second aspect simultaneously before exciting second aspect, and (3 places among Fig. 3) switch to the frequency of transmitter and receiver frequency source on the receive frequency more simultaneously before receiving second aspect.As can be seen from Figure 3, transmitter and receiver remains phase coherence.
Advantage of the present invention is to adopt the change stimulating frequency to realize having solved the phase coherence problem of transmitter and receiver under the condition of chip select, and adopts the change stimulating frequency to realize chip select than passing through to change main field B
0Size realizes that chip select is simpler, greatly reduces the complicacy of instrument.
Summary of drawings
Phase coherence synoptic diagram when accompanying drawing 1 does not have switching frequency for transmitter;
The irrelevant synoptic diagram of phase place when accompanying drawing 2 is the transmitter switching frequency;
Accompanying drawing 3 keeps the phase coherence synoptic diagram for the frequency of switching transmitter and receiver simultaneously;
Accompanying drawing 4 is the structured flowchart of transmitter and receiver frequency source;
Accompanying drawing 5 is a stage construction fast acquisition interleaved spin echo sequential chart.
Concrete technical scheme
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:
To switch the frequency of transmitter and receiver in the present embodiment simultaneously, need to be realized from hardware and software two aspects.
On hardware, be provided with two fully independently transmitter and receiver frequency sources, an internal memory is arranged, all frequency data that need switch during can the storage pulse sequence on the internal memory on the every frequency source.Frequency source is provided with an external trigger source, and a trigger pip is arranged on the external trigger source, and frequency source goes to the renewal frequency source from the current frequency values of employing in the internal memory.
The structured flowchart of concrete frequency source as shown in Figure 4.On each piece frequency source card, a digitization frequencies source chip (DDS) is arranged, a slice memory chip (RAM), a programmable logic device (PLD) chip (FPGA) and a PCI bridging chip (PCI 9052Bridge).Digitization frequencies source DDS can switch amplitude, frequency and phase place fast.Memory chip is used to store many group DDS data (each group DDS data is according to the sequential storage of amplitude, frequency, phase place).Fpga chip plays control, and promptly it whenever receives an outer triggering signal, and employ current internal memory pointer memory value pointed certainly and remove to upgrade DDS, and the current internal memory pointer of stepping, make it point to next memory value.PCI 9052Bridge chip is an interface chip, is mainly used between internal memory and pci bus (PCI Bus) to transmit data.
Before carrying out pulse train at first according to the requirement of pulse train by pci bus write data on the frequency source internal memory; The term of execution of pulse train, (External Trig Source) sends trigger request according to the requirement of pulse train by the external trigger source.FPGA whenever receives a trigger request, and the DDS data that current pointer in the internal memory is pointed to are sent to the DDS register and upgrade DDS automatically, simultaneously next group data of the pointed of pointing to the DDS data in the internal memory.
On software, realize switching simultaneously that the frequency of transmitter and receiver mainly realizes by pulse sequence compiler software.Independently transmitter frequency source control module and receiver frequency source control module are arranged on pulse sequence compiler software, and allow the user to upgrade the frequency of transmitter and receiver simultaneously.Each frequency source control module is all supported list of frequency, and the user can be filled in the frequency that all need switch on the list of frequency in advance according to the requirement of pulse train.
Be to keep transmitter and receiver phase coherence, transmitter and receiver frequency source control module can a shared list of frequency, and can shared one upgrades the triggering source, guarantees to upgrade simultaneously.When doing multilayer and select pulse train, can be according to ground floor stimulating frequency, receive frequency, second layer stimulating frequency, receive frequency ... order insert list of frequency successively, before carrying out pulse train, the value in the list of frequency is inserted in the internal memory of transmitter and receiver frequency source, gone to upgrade the frequency of transmitter and receiver according to the result of pulse sequence compiler compiling successively with the frequency values in the list of frequency.
Be that example is illustrated with the stage construction fast acquisition interleaved spin echo below.
Stage construction fast acquisition interleaved spin echo figure as shown in Figure 5.For the sake of simplicity, excite two aspects in the present embodiment, each aspect is gathered three echoes under the out of phase coding.As can be seen from Figure 5, whenever excite an aspect need switch 6 secondary frequencies, therefore excite two aspects need switch 12 secondary frequencies altogether.Concrete rule is before the emission radio-frequency pulse, simultaneously the frequency of transmitter and receiver is switched on the stimulating frequency of this layer, before image data, the frequency of transmitter and receiver is switched on the receive frequency simultaneously.The stimulating frequency f of first aspect
I1Expression, the stimulating frequency f of second aspect
I2Expression, receive frequency f
OcqExpression.The order of the frequency values that first aspect is switched is f
I1-f
Acq-f
I1-f
Acq-f
I1-f
Acq, the frequency values of second aspect switching is f in proper order
I2-f
Acq-f
I2-f
Acq-f
I2-f
AcqTherefore the order of filling in whole pulse train medium frequency tabulation medium frequency value is
f
i1-f
acq-f
i1-f
acq-f
i1-f
acq-f
i2-f
acq-f
i2-f
acq-f
i2-f
acq。Before pulse train is carried out, the frequency values in the list of frequency is write in the internal memory of transmitter and receiver frequency source, go to upgrade the frequency of transmitter and receiver successively with the frequency values in the list of frequency according to the result of pulse sequence compiler compiling.
Claims (5)
1. method that realizes the phase coherence of stage construction scanning sequence, be used for Magnetic resonance imaging, it is characterized in that this method is before the excitation pulse of choosing layer, simultaneously the frequency of transmitter and receiver frequency source is switched on the stimulating frequency of this layer, and before sampling, again the frequency of transmitter and receiver frequency source is switched on the receive frequency simultaneously.
2. a kind of method that realizes the phase coherence of stage construction scanning sequence according to claim 1, the frequency source that it is characterized in that described transmitter and receiver is by programmable logic chip FPGA, digitization frequencies source DDS, the PCI bridging chip, the external trigger source, memory chip RAM constitutes, wherein the PCI bridging chip be used for and computer PCI bus between interface, fpga chip major control DDS and RAM, when FPGA whenever receives an outer triggering signal, remove to upgrade DDS from employing current internal memory pointer memory value pointed, and the current internal memory pointer of stepping, make it point to next memory value.
3. a kind of method that realizes the phase coherence of stage construction scanning sequence according to claim 2 is characterized in that the external trigger source in described transmitter frequency source and the external trigger source of receiver frequency source are a common external trigger source of using.
4. a kind of method that realizes the phase coherence of stage construction scanning sequence according to claim 1 is characterized in that being filled with list of frequency in the internal memory of described transmitter and receiver frequency source.
5. a kind of method that realizes the phase coherence of stage construction scanning sequence according to claim 1, it is characterized in that the described frequency of switching transmitter and receiver simultaneously mainly realizes by pulse sequence compiler software, independently transmitter frequency source control module and receiver frequency source control module are arranged on pulse sequence compiler software, and allowing the user to upgrade the frequency of transmitter and receiver simultaneously, each frequency source control module is all supported list of frequency.
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| CNB2004100531539A CN100401089C (en) | 2004-07-23 | 2004-07-23 | Method for realizing multilayer sanning sequence phase coherent |
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| CNB2004100531539A CN100401089C (en) | 2004-07-23 | 2004-07-23 | Method for realizing multilayer sanning sequence phase coherent |
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| CN100401089C true CN100401089C (en) | 2008-07-09 |
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Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| 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 |
| 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 |
| CN105676193A (en) * | 2014-11-20 | 2016-06-15 | 中国航空工业集团公司雷华电子技术研究所 | Multi-frequency signal generation method based on DDS chip |
| 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)
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|---|---|---|---|---|
| US4908578A (en) * | 1987-12-24 | 1990-03-13 | U.S. Philips Corporation | Method of and device for generating interleaved multiple-slice multiple-echo pulse sequences for MRI |
| CN1317901A (en) * | 2000-04-11 | 2001-10-17 | 中南工业大学 | Co-clock timing method for signal interference detection |
| US6313910B1 (en) * | 1998-09-11 | 2001-11-06 | Dataray, Inc. | Apparatus for measurement of optical beams |
| US6549801B1 (en) * | 1998-06-11 | 2003-04-15 | The Regents Of The University Of California | Phase-resolved optical coherence tomography and optical doppler tomography for imaging fluid flow in tissue with fast scanning speed and high velocity sensitivity |
-
2004
- 2004-07-23 CN CNB2004100531539A patent/CN100401089C/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4908578A (en) * | 1987-12-24 | 1990-03-13 | U.S. Philips Corporation | Method of and device for generating interleaved multiple-slice multiple-echo pulse sequences for MRI |
| US6549801B1 (en) * | 1998-06-11 | 2003-04-15 | The Regents Of The University Of California | Phase-resolved optical coherence tomography and optical doppler tomography for imaging fluid flow in tissue with fast scanning speed and high velocity sensitivity |
| US6313910B1 (en) * | 1998-09-11 | 2001-11-06 | Dataray, Inc. | Apparatus for measurement of optical beams |
| CN1317901A (en) * | 2000-04-11 | 2001-10-17 | 中南工业大学 | Co-clock timing method for signal interference detection |
Non-Patent Citations (2)
| Title |
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| 用于核磁共振的直接数字合成频率源. 蒋瑜等.波谱学杂志，第18卷第4期. 2001 |
| 用于核磁共振的直接数字合成频率源. 蒋瑜等.波谱学杂志，第18卷第4期. 2001 * |
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