CN101625402B - Method for improving nuclear magnetic resonance signal to noise ratio - Google Patents
Method for improving nuclear magnetic resonance signal to noise ratio Download PDFInfo
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- CN101625402B CN101625402B CN200910055700XA CN200910055700A CN101625402B CN 101625402 B CN101625402 B CN 101625402B CN 200910055700X A CN200910055700X A CN 200910055700XA CN 200910055700 A CN200910055700 A CN 200910055700A CN 101625402 B CN101625402 B CN 101625402B
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Abstract
The invention discloses a method for improving nuclear magnetic resonance signal to noise ratio, and the method comprises the steps of setting a gain control circuit at the front stage of a receiver, setting gain waveform and standard gain of the receiver before starting sampling, dynamically changing the gain of the receiver according to the set gain waveform during the sampling process, calculating the corresponding values of the collected data under the standard gain according to the set gain waveform after the completion of the sampling and the like. Compared with the prior art, the method reduces noise from the receiver and improves the nuclear magnetic resonance signal to noise ratio in case of equivalent signals.
Description
Technical field
The present invention relates to the nuclear magnetic resonance technique field, especially a kind of method of improving the signal to noise ratio (S/N ratio) of NMR signal through the performance that improves nmr receiver.
Background technology
Nuclear magnetic resonance technique has become in scientific research and the medical clinic applications very useful means.Obtain high-quality image and spectrogram, the signal to noise ratio (S/N ratio) that improves NMR signal is very crucial.Usually, in NMR system, a complete receiving system comprises RF receiving coil, prime amplifier and receiver, and is as shown in Figure 1.In receiving system, signal is through each level, and the noise that all can have this one-level to produce adds.Receiving coil and prime amplifier are positioned at receiving system foremost, and its noisiness is very remarkable to the signal to noise ratio (S/N ratio) influence of NMR signal.Therefore, under normal conditions, the measure that improves the receiving system noisiness mainly is to be directed against receiving coil and prime amplifier.In fact, the NMR signal that amplifies through prime amplifier remains fainter.Along with the progress of nuclear magnetic resonance technique, new experimental technique (like high-resolution imaging) is to the demands for higher performance of nuclear magnetic resonance apparatus receiving system, and the receiver that is positioned at after the prime amplifier becomes the bottleneck that improves the receiving system noisiness gradually.In addition, in some conventional application, because the characteristic (differing bigger like different components contents to be measured in the sample) of sample itself, the noisiness of receiver is also bigger to the spectrogram quality influence.
The noise of receiver mainly contains following three kinds: the first, and analogue noise.Although the NMR signal that RF receiving coil induces is through the amplification of prime amplifier, its amplitude still can't reach analog-to-digital requirement, still need in receiver, at first carry out voltage amplification.In addition, the setting that need gain according to the size of the NMR signal that sample produced of this one-level amplifier in the receiver.These analogue amplifiers and gain control mimic channel all can produce analogue noise inevitably.The second, the digital-to-analogue noise.The signal that on receiver, transmits comprises digital signal and simulating signal.Digital signal on the digital signal of receiver self and the hardware effort platform (like industrial control computer) thereof can cause interference to the simulating signal on the receiver, thereby reduce the signal to noise ratio (S/N ratio) of NMR signal through modes such as power supply coupling and space couplings.This coupling noise that is produced by digital circuit is called the digital-to-analogue noise to the noise in the receiver mimic channel.The 3rd, the quantizing noise of analog to digital converter (ADC).NMR signal need be gathered, so that in computing machine, carry out data processing.Need adopt ADC and accomplish to the collection of NMR signal.All there is quantizing noise in any ADC device, and its size depends on the digital resolution of ADC.In the high-field nuclear magnetic resonance system, perhaps when carrying out the scanning of three-dimensional high definition Magnetic resonance imaging, the signal that gets into receiver has very high signal to noise ratio (S/N ratio).At this moment, quantizing noise becomes the principal element that influences signal to noise ratio (S/N ratio) usually.
In order to reduce simulation and the digital-to-analogue noise on the receiver card, except selecting the low-noise simulation device for use, in circuit design, to adopt rigid measures, comprise analog power is carried out filtering, for analog device adds radio frequency shielded enclosure etc.Though these measures have improved the noisiness of receiver to a certain extent, increased the complicacy and the cost of manufacture of circuit design.
In order to reduce the quantizing noise of receiver, generally can select the more ADC device of seniority for use.In addition, over-sampling (Over-Sampling) technology also is to reduce the effective ways of quantizing noise.But these technology all can receive the restriction of microelectric technique development.In fact, after having adopted above-mentioned technology, the number of significant digit of ADC is greatly improved, yet, still can't satisfy the growing requirement of nuclear magnetic resonance experiment.
NMR signal can be divided into two big types, free damping signal and echoed signal.Wherein, the characteristics of free damping signal are: the amplitude of signal diminishes according to negative e index variation gradually; The characteristics of echoed signal are: at echo center signal amplitude maximum (peak dot), therefrom mind-set both sides signal amplitude is according to negative e index variation.
In order to obtain correct nuclear magnetic resonance image or spectrogram, the multiple that each sampled point of NMR signal is exaggerated in receiving system must be identical.Therefore, in the prior art, in sampling process, the gain of receiver is fixed.The gain setting of its receiver is: under the prerequisite that the maximal value of NMR signal is not overflowed, and the maximal value G in the AG scope
0If the ratio of gains G of receiver
0Greatly, a part of signal that amplitude is bigger in the signal can not be by normal collection (overflowing).
Summary of the invention
The objective of the invention is to the deficiency of prior art and a kind of method that improves the nuclear magnetic resonance signal to noise ratio (S/N ratio) is provided, this method has reduced receiver noise shared ratio in the receiving system noise, thereby reaches the purpose that improves the nuclear magnetic resonance signal to noise ratio (S/N ratio).
The objective of the invention is to realize like this:
A kind of method that improves the nuclear magnetic resonance signal to noise ratio (S/N ratio), it comprises following concrete steps:
A) gain control circuit is located at the receiver prime.
B) start before the sampling, set the gain of receiver gain waveform and standard; Comprise:
I, on amplitude, the Changing Pattern of receiver gain waveform and NMR signal is opposite, that is: less value is corresponding to value bigger in this waveform in the NMR signal, value bigger in the NMR signal is corresponding to value less in this waveform;
Minimum value in ii, the gain waveform gains as standard, and note is made G
0
Iii, the waveform that will gain be saved on the receiver card or computing machine on, and first value in the waveform pointed waveform that will gain.
C) in sampling process, the gain waveform according to setting dynamically changes the gain of receiver; Comprise:
I, receive a sampling trigger signal when receiver, the current value pointed of gain waveform pointer is set to the gain of receiver;
Ii, the next value of gain waveform pointed;
If sampling number is n, receiver will be received n sampling trigger signal, and i in this step and ii repeat n time; Wherein, in the time of the n time, " next value " among the ii is null value.
D) after sampling finishes,, calculate the data note that collects and make A according to the gain waveform of setting
jPairing value under the standard gain; Comprise:
I, receiver collect n data A
j, each data A
jPairing yield value note is made G
i, calculate G
jWith the standard gain G
0Ratio g
j, i.e. g
j=G
j/ G
0, j=1 wherein, 2 ... N;
Each data A that ii, receiver collect
jG divided by correspondence
j, obtain standard gain pairing data a down
j, i.e. a
j=A
j/ g
j, j=1 wherein, 2 ... N.
Description of drawings
Fig. 1 is the structural representation of receiving system in the nuclear magnetic resonance apparatus
Fig. 2 is receiver principle figure of the present invention
Fig. 3 finishes the process flow diagram of back data processing for the present invention samples
Embodiment
The present invention is in sampling process, and the gain of receiver is dynamically to change.
Start before the sampling, set the gain of receiver gain waveform and standard.A yield value on the gain waveform is corresponding to a sampled point of NMR signal.Each gain value settings is on the gain waveform: under the prerequisite that the value of the NMR signal sampled point corresponding with this yield value is not overflowed, and the maximal value in the AG scope; That is: on amplitude, the Changing Pattern of receiver gain waveform and NMR signal is opposite, adopts the less value in the bigger gain acquired signal, adopts bigger value in the less gain acquired signal; The maximal value of NMR signal is corresponding to minimum yield value in the gain waveform, and this yield value gains as standard.
The minimum value of gain in the waveform among the present invention, i.e. standard gain, the current gain value that is adopted with prior art equates, is under the prerequisite that the maximal value of NMR signal do not overflow the maximal value G in the AG scope
0
Consult Fig. 2, the present invention is in sampling process, and the gain of receiver is dynamically to change according to the gain waveform of setting.If the input signal of receiver is S
j, noise is N
jN wherein
jComprised noise from sample, receiving coil and prime amplifier.The first order of receiver is low noise variable gain amplifier (VGA), and the equivalent output noise of establishing VGA is N
VGAIf the noise that (comprising ADC etc.) at different levels are produced after the VGA on the receiver is N
ADCThe signal that collects is (S
j* G
j), noise is (N
j* G
j)+(N
VGA+ N
ADC).
Consult Fig. 3, in the present invention, data A
jUnder different gains, collect.In order to obtain correct image or spectrogram, need obtain standard gain pairing data a down
jAt first calculate the ratio g of pairing yield value of each data and standard gain
j=G
j/ G
0Then with the data A that collects
jDivided by the ratio of correspondence, obtain the data a under the standard gain
jWherein, the signal under the standard gain is S '
j=(S
j* G
j) * g
j=(S
j* G
0), noise is N '
j=(N
j* G
j) * g
j+ (N
VGA+ N
ADC) * g
j=(N
j* G
0)+(N
VGA+ N
ADC)/g
j
Below through embodiment the present invention is done further elaboration.
Embodiment 1
When NMR signal is the free damping signal, the present invention includes following steps:
A) gain control circuit is located at the receiver prime;
B) start before the sampling, set the gain of receiver gain waveform and standard;
C) in sampling process, the gain waveform according to setting dynamically changes receiver gain;
D) after sampling finishes,, calculate the data note that collects and make A according to the gain waveform of setting
jPairing value under the standard gain.
Wherein:
The process of said " setting the gain of receiver gain waveform and standard " may further comprise the steps:
I, on amplitude, the Changing Pattern of receiver gain waveform and free damping signal is opposite; Because the amplitude of free damping signal is according to negative e index variation, so the receiver gain waveform is according to positive e index variation;
First yield value in ii, the gain waveform is as the standard gain G
0
Iii, the waveform that will gain be saved on the receiver card or computing machine on, and first value in the waveform pointed waveform that will gain.
The process of said " the gain waveform according to setting dynamically changes receiver gain " may further comprise the steps:
I, receive a sampling trigger signal when receiver, the current value pointed of gain waveform pointer is used to be provided with the gain of receiver;
Ii, the next value of gain waveform pointed.
If sampling number is n, receiver will be received n sampling trigger signal, and step I and ii repeat n time.Wherein, in the time of the n time, " next value " among the step I i is null value.
It is said that " according to the gain waveform of setting, the data note that calculating collects is made A
jPairing value under standard gain " process may further comprise the steps:
I, receiver collect n data A
j, each data A
jPairing yield value is G
iCalculate G
jWith the standard gain G
0Ratio g
j, i.e. g
j=G
j/ G
0, j=1 wherein, 2 ... N;
Each data A that ii, receiver collect
jG divided by correspondence
j, obtain standard gain pairing data a down
j, i.e. a
j=A
j/ g
j, j=1 wherein, 2 ... N.
Embodiment 2
When NMR signal is echoed signal, the present invention includes following steps:
A) gain control circuit is located at the receiver prime;
B) start before the sampling, set the gain of receiver gain waveform and standard;
C) in sampling process, the gain waveform according to setting dynamically changes receiver gain;
D) after sampling finishes,, calculate the data note that collects and make A according to the gain waveform of setting
jPairing value under the standard gain.
Wherein:
The process of described " setting the gain of receiver gain waveform and standard " may further comprise the steps:
I, on amplitude, the Changing Pattern of receiver gain waveform and echoed signal is opposite.Echoed signal has following characteristics: at the echo center, and signal amplitude maximum (peak dot); Mind-set both sides therefrom, signal amplitude is according to negative e index variation.Therefore, the receiver gain waveform has following characteristics: at the echo center, gain is minimum; Mind-set echo both sides from echo, gain is according to positive e index variation;
The pairing yield value of the peak dot of ii, echoed signal is as the standard gain G
0
Iii, the waveform that will gain be saved on the receiver card or computing machine on, and first value in the waveform pointed waveform that will gain.
The process of said " the gain waveform according to setting dynamically changes receiver gain " may further comprise the steps:
I, receive a sampling trigger signal when receiver, the current value pointed of gain waveform pointer is used to be provided with the gain of receiver;
Ii, the next value of gain waveform pointed.
If sampling number is n, receiver will be received n sampling trigger signal, and above-mentioned steps i and ii repeat n time.Wherein, in the time of the n time, " next value " among the step I i is null value.
It is said that " according to the gain waveform of setting, the data note that calculating collects is made A
jPairing value under standard gain " process may further comprise the steps:
I, receiver collect n data A
j, each data A
jPairing yield value is G
iCalculate G
jWith the standard gain G
0Ratio g
j, i.e. g
j=G
j/ G
0, j=1 wherein, 2 ... N;
Each data A that ii, receiver collect
jG divided by correspondence
j, obtain standard gain pairing data a down
jBe a
j=A
j/ g
j, j=1 wherein, 2 ... N.
Compare the data that the present invention and prior art collect, wherein signal (S
j* G
0) equate, from the noise (N of sample, receiving coil and prime amplifier
j* G
0) also equate.Adopting prior art, is (N from the noise of receiver
VGA+ N
ADC); And employing the present invention, because G
0Be minimum yield value in the gain waveform, so g
j=G
j/ G
0>=1 (G
jIn have only a value to equal G
0, corresponding ratio equals 1, and other ratio is all greater than 1), can the noise from receiver be reduced to (N
VGA+ N
ADC)/g
jCompared with prior art, under the situation that signal equates, the present invention has reduced the noise from receiver, has improved the nuclear magnetic resonance signal to noise ratio (S/N ratio).
Claims (1)
1. method that improves the nuclear magnetic resonance signal to noise ratio (S/N ratio) is characterized in that this method comprises following concrete steps:
A) gain control circuit is located at the receiver prime;
B) start before the sampling, set the gain of receiver gain waveform and standard; Comprise:
I, on amplitude, the Changing Pattern of receiver gain waveform and NMR signal is opposite, that is: less value is corresponding to value bigger in this waveform in the NMR signal, value bigger in the NMR signal is corresponding to value less in this waveform;
Minimum value in ii, the gain waveform gains as standard, and note is made G
0
Iii, the waveform that will gain be saved on the receiver card or computing machine on, and first value in the waveform pointed waveform that will gain;
C) in sampling process, the gain waveform according to setting dynamically changes the gain of receiver; Comprise:
I, receive a sampling trigger signal when receiver, the current value pointed of gain waveform pointer is set to the gain of receiver;
Ii, the next value of gain waveform pointed;
D) after sampling finishes,, calculate the data note that collects and make A according to the gain waveform of setting
jPairing value under the standard gain; Comprise:
I, receiver collect n data A
j, each data A
jPairing yield value note is made G
j, calculate G
jWith the standard gain G
0Ratio g
j, i.e. g
j=G
j/ G
0, j=1 wherein, 2 ... N;
Each data A that ii, receiver collect
jG divided by correspondence
j, obtain standard gain pairing data a down
j, i.e. a
j=A
j/ g
j, j=1 wherein, 2 ... N.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200910055700XA CN101625402B (en) | 2009-07-31 | 2009-07-31 | Method for improving nuclear magnetic resonance signal to noise ratio |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200910055700XA CN101625402B (en) | 2009-07-31 | 2009-07-31 | Method for improving nuclear magnetic resonance signal to noise ratio |
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| Publication Number | Publication Date |
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| CN101625402A CN101625402A (en) | 2010-01-13 |
| CN101625402B true CN101625402B (en) | 2012-07-18 |
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Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1829922A (en) * | 2003-07-30 | 2006-09-06 | 皇家飞利浦电子股份有限公司 | On-chip magnetic particle sensor with improved SNR |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1829922A (en) * | 2003-07-30 | 2006-09-06 | 皇家飞利浦电子股份有限公司 | On-chip magnetic particle sensor with improved SNR |
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| CN101625402A (en) | 2010-01-13 |
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|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| ASS | Succession or assignment of patent right |
Owner name: KALEFU MAGNETIC RESONANCE TECH CO., LTD., SHANGHAI Effective date: 20120605 |
|
| C41 | Transfer of patent application or patent right or utility model | ||
| 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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| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20120718 Termination date: 20180731 |