CN105785457B - The measuring method of ground nuclear magnetic resonance T2 based on bipolar pulse - Google Patents
The measuring method of ground nuclear magnetic resonance T2 based on bipolar pulse Download PDFInfo
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- CN105785457B CN105785457B CN201610318060.7A CN201610318060A CN105785457B CN 105785457 B CN105785457 B CN 105785457B CN 201610318060 A CN201610318060 A CN 201610318060A CN 105785457 B CN105785457 B CN 105785457B
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- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/14—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electron or nuclear magnetic resonance
Abstract
The present invention relates to the fields of measurement of nuclear magnetic resonance T2, and in particular to the measuring method of the ground nuclear magnetic resonance T2 based on bipolar pulse, using bipolarity spin echo to T2 T2Measure, by launching the 90 ° of pulses of No. 1 positive polarity and 180 ° of measured signals of pulse collection first of No. 1 positive polarity and the second measured signal, launch the 90 ° of pulses of No. 2 negative polarity and 180 ° of measured signals of pulse collection the 3rd of No. 2 positive polarity and the 4th measured signal again, second measured signal and the 4th measured signal are overlapped, you can obtain the spin echo signal without free induction decay signal interference.By changing the time interval τ between 90 ° of pulses and 180 ° of pulses, multiplicating measurement is carried out, multiple spin echo signals can be obtained.The present invention improves ground nuclear magnetic resonance T2 T2Measurement accuracy, avoid T2When smaller, the spin echo signal number of CPMG sequence collection is few, the problem of measurement accuracy is limited.
Description
Technical field
The present invention relates to the fields of measurement of nuclear magnetic resonance T2, and in particular to based on bipolarity spin echo
A kind of measuring method of ground nuclear magnetic resonance T2.
Background technology
The characteristic parameter transverse relaxation of ground nuclear magnetic resonance (Magnetic Resonnance Sounding, MRS) signal
Time T2Distribution includes the formation information of very abundant, directly reflects media particle and pore size, is determined for hole
The hydrogeological parameter such as porosity, irreducible water saturation, permeability, pore-size distribution and fluid behaviour and water content.But mesh
Preceding ground nuclear magnetic resonance water explorer commercialized in the world typically obtains free induction decay FID letters using single pulse train
Number, therefore T2 T can only be obtained2Approximation-mean time of relaxation T2 *, in the case of outer Magnetic field inhomogeneity,
The mean time of relaxation T of large aperture2 *Respectively less than T2 T2, thus can not accurately calculate porosity, constraint water saturation
The formation informations such as degree, permeability and pore-size distribution, ground nuclear magnetic resonance technology is seriously constrained in necks such as groundwater resources prospectings
The development and application in domain.
At present, in nuclear magnetic resonance detection process, T2 T is measured2Method mainly have spin echo SE sequences
Two methods of row and CPMG sequence.Nuclear Magnetic Resonance Measurement scheme based on spin-echo sequence is on the basis that pulse excites
On, increase by 180 ° of pulses and be used to observe spin echo signal SE signals, so as to measure T2 T2.This method is easy to real
It is existing, but following shortcomings be present, launch 90o one FID signal of pulses generation, 180 ° of pulses of transmitting not only produce spin echo SE
Signal, while second FID signal can be also produced, second FID signal can disturb spin echo SE signals, and measured signal is
The superposed signal of FID signal and spin echo SE signals, the amplitude and shape of real spin echo SE signals will be covered.Together
When, spin echo SE sequences only obtain a spin echo SE signal, and T2 T2 measurement accuracy is low.CPMG sequence
It is on the basis of spin echo SE sequences, repeatedly applies 180 ° of pulsus durus punchings, so as to obtain multiple spin echo signals.But deposit
In following shortcomings, CPMG sequence needs repeatedly 180 ° of pulses of transmitting, it is necessary to consume the substantial amounts of time；In T2When smaller, cpmg sequence
It is less to arrange the spin echo signal of collection, so as to cause T2Measurement accuracy is low.180 ° of pulses generation FID signals be present simultaneously, do
The problem of disturbing true spin echo signal.
CN102096112A discloses a kind of nuclear magnetic resonance underground water survey meter based on array coil and field detection side
Method, this invention are made up of through the connection of control unit, transmitting coil and receiving coil Serial Port Line or network interface line computer, received
Coil is to connect and compose array coil by 25 receiving units, by the use of array coil as the antenna of receiving unit, and is each
Antenna is equipped with independent receiving unit.This invention the advantages of be：It can realize that two and three dimensions underground water is imaged, not only can be real
Existing high sensitivity collection and remote data transfer, and can be laid on complicated landform landforms, improve nuclear-magnetism
The precision of resonant probe in the horizontal plane, well location of digging a well can be efficiently and accurately determined, reduce the risk for beating dry-well.But this
The shortcomings that invention is：The transmitting pulse of the nuclear magnetic resonance underground water survey meter is conventional hard pulse sequence, can only obtain average relaxation
Henan time T2 *, in the case of outer Magnetic field inhomogeneity, cause calculating hydrogeological parameter error big, reduce water detection efficiency.
CN103852794A discloses a kind of hydrocarbon contamination shallow underground water magnetic resonance detection means and detection method, this dress
Put by transmitting logic and control unit, MCU, data acquisition card, 24V batteries, DCDC modules, signal conditioning circuit, energy storage transmitting
Unit, voltage x current collecting unit transmitting coil and receiving unit are formed.This invention the advantages of be：Non-intrusion type is realized to quantify
Observational measurement, scene quickly obtain test result, and the intensity in local earth's magnetic field is improved with permanent magnet, can be disturbed in electric power tighter
Nuclear Magnetic Resonance Measurement is implemented in the place of weight, effectively improves signal to noise ratio, nuclear magnetic resonance can not be implemented because of electric power serious interference by breaking
The constraint of detection, can be efficiently against the result inaccuracy that Magnetic field inhomogeneity is brought with spin echo pulse the shortcomings that, can
Rapidly and accurately detect hydrocarbon contamination in 5 meters of underground.But the shortcomings that this invention, is：The spin echo arteries and veins of this invention transmitting
Punching is CPMG pulses, and therefore, this invention has the shortcomings that CPMG sequence.Meanwhile the device of this invention need to be in the feelings not charged
Under condition, repeatedly 180 ° of pulses of transmitting are carried out, supply voltage declines, and transmitting pulse can be caused to be not up to 180 °, it is impossible to accurate measurement
T2 T2。
Therefore, it is necessary to which T2 T can fast and effeciently be measured by inventing one kind2Method, it is conventional single to solve
The T of impulsive measurement2 *Estimate the problem of hydrogeological parameter error is big, and the T in the case of outer Magnetic field inhomogeneity2It is effective
Measurement.
The content of the invention
The technical problems to be solved by the invention are to provide a kind of ground nuclear magnetic resonance transverse direction based on bipolar pulse
The measuring method in relaxation time, to solve in the case of outer Magnetic field inhomogeneity, conventional single-pulse measurement mean time of relaxation T2 *
Estimate the problem of hydrologic parameter error is big, and T2 T2Measure problem.
The present invention is achieved in that a kind of measurement of the ground nuclear magnetic resonance T2 based on bipolar pulse
Method,
Launch the 90 ° of pulses of No. 1 positive polarity, gather the first measured signal,
Elapsed time interval τ, launch the 180 ° of pulses of No. 1 positive polarity, gather the second measured signal；
After elapsed time recovers, launch the 90 ° of pulses of No. 2 negative polarity, gather the 3rd measured signal；
By same time interval τ, launch the 180 ° of pulses of No. 2 positive polarity, gather the 4th measured signal；
Second measured signal and the 4th measured signal are overlapped, obtains and eliminates the interference of free induction FID signal
Spin echo SE signals；
First measured signal and the 3rd measured signal are superimposed to obtain first free induction FID signal；
By changing time interval τ between 90 ° of pulses and 180 ° of pulses, repeat above-mentioned steps, in the duplicate measurements phase
Between obtain multiple spin echo SE signals；
The initial amplitude of first free induction FID signal is connected with the peak value of each spin echo SE signals, formed
One exponential decay curve, fitting obtain T2 T2.
Further, the second measured signal and the 4th measured signal are overlapped for：By the second measured signal and the 4th
Measured signal subtracts each other divided by 2.
Further, it is specially by the first measured signal and the superposition of the 3rd measured signal：By the first measured signal and the 3rd
Measured signal subtracts each other divided by 2.
Further, launching the 90 ° of pulses of No. 1 positive polarity is：In three-dimensional cartesian coordinate system, magnetostatic field Bo is along three-dimensional right angle
In the Z-direction of coordinate system, transmitting coil is positioned on ground, the X-axis in the X/Y plane perpendicular to magnetostatic field Bo directions
Launch the 90 ° of pulses of No. 1 positive polarity to underground in direction.
Further, launching the 180 ° of pulses of No. 1 positive polarity is：In three-dimensional cartesian coordinate system, magnetostatic field Bo is along three-dimensional straight
In the Z-direction of angular coordinate system, transmitting coil is positioned on ground, launches No. 1 180 ° of positive polarity to underground in the Z-axis direction
Pulse.
Further, launching the 90 ° of pulses of No. 2 negative polarity is：In three-dimensional cartesian coordinate system, magnetostatic field Bo is along three-dimensional right angle
In the Z-direction of coordinate system, transmitting coil is positioned on ground, the negative X in the X/Y plane perpendicular to magnetostatic field Bo directions
Direction of principal axis launches the 90 ° of pulses of No. 2 negative polarity to underground.
Further, launching the 180 ° of pulses of No. 2 positive polarity is：In three-dimensional cartesian coordinate system, magnetostatic field Bo is along three-dimensional straight
In the Z-direction of angular coordinate system, transmitting coil is positioned on ground, launches the 180 ° of pulses of No. 2 positive polarity in the Z-axis direction.
Compared with prior art, beneficial effect is the present invention：Area's Distribution of Magnetic Field is surveyed generally with uneven due to actual
Property, the T surveyed2* it is less than T2 T2, therefore use T2* the ground such as irreducible water, permeability and the pore-size distribution of acquisition are calculated
Layer information and notional result error are big.And the T2 in spin echo signal will not be by the shadow of magnetic field bump
Ring, therefore can be realized to T2 T using dipulse spin-echo sequence2Measurement.It is ambipolar by launching
90 ° of pulses, interference of the FID signal of 180 ° of pulses generations to spin echo SE signals can be eliminated, so as to obtain it is real from
Cycle ripple SE signals.By changing the time interval τ between 90 ° of pulses and 180 ° of pulses, repeatedly launched, can be obtained more
Individual spin echo signal, so as to improve T2 T2Measurement accuracy.
Brief description of the drawings
Accompanying drawing is used for providing a further understanding of the present invention, and a part for constitution instruction, the reality with the present invention
Example is applied to be used to explain that the present invention is not construed as limiting the invention together.In the accompanying drawings：
Ground nuclear magnetic resonance T2 Ts of the Fig. 1 based on bipolarity spin echo2The flow chart of measuring method；
The phase diagram of FID signal and spin echo SE signals caused by Fig. 2 transmitting bipolarity spin echoes；A is to launch just
The FID signal of 180 ° of pulse collections of 90 ° of pulses of polarity and positive polarity and the phase diagram of SE signals, b are transmitting 90 ° of pulses of negative polarity
With the FID signal of 180 ° of pulse collections of positive polarity and the phase diagram of SE signals, c be superimposed by a and b the FID signal that obtains and
Spin echo SE signals.
Ground nuclear magnetic resonance T2 Ts of the Fig. 3 based on bipolarity spin echo2The pulse sequence of measuring method
Figure, a is that time interval is τ1First time measurement, b is that time interval is τ2Second measurement, c is that time interval is τ3
Measure three times, d is that time interval is τnN-th measurement.
Fig. 4 GPMG sequences (a) and bipolarity spin echo (b) obtain T2 T2Comparison diagram；
Fig. 5 bipolaritys spin echo eliminates the design sketch of free induction decay signal interference, and a is the first measured signal, and b is
Second measured signal, c are the 3rd measured signal, and d is the 4th measured signal, and e is FID signal, and f is spin echo SE signals.
Embodiment
In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to embodiments, to the present invention
It is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, it is not used to
Limit the present invention.
A kind of ground nuclear magnetic resonance T2 T based on bipolar pulse of the present invention2The implementation of measuring method
The block diagram of example 1 is as shown in figures 1 and 3.When survey regional magnetic field it is uneven when, it is necessary to using bipolar pulse to transverse relaxation when
Between T2Measure.Ground MRS T2 T of the present invention based on bipolar pulse2Measuring method step is as follows：
Step 10：Launch the 90 ° of pulses of No. 1 positive polarity；
In three-dimensional cartesian coordinate system, magnetostatic field BoAlong in the Z-direction of three-dimensional cartesian coordinate system, transmitting coil is placed
In on ground, perpendicular to magnetostatic field BoX-direction in the X/Y plane in direction launches the 90 ° of pulses of No. 1 positive polarity to underground, swashs
Hydrogen nuclei in underground water is encouraged, it is carried out precessional motion in earth's magnetic field, after stopping is encouraged, hydrogen nuclei produces spin and relaxed
Henan phenomenon (dephasing), the signal collected using ground receiver coil are the first measured signal 11；
Step 20：Launch the 180 ° of pulses of No. 1 positive polarity；
By step 12 time interval τ, launching the 180 ° of pulses of No. 1 positive polarity in the Z-axis direction, (firing time is 90 ° of arteries and veins
Punching twice), the hydrogen nuclei of dephasing is focused on carry out precessional motion again, when encourage stop after hydrogen nuclei be produced from again
Relaxation phenomena is revolved, the signal collected is the second measured signal 21；
Step 30：Launch the 90 ° of pulses of No. 2 negative polarity；
By step 22 time t, hydrogen nuclei restPoses, and launches No. 2 negative polarity to underground in negative X-direction
90 ° of pulses, after stopping is encouraged, the signal collected using ground receiver coil is the 3rd measured signal 31；
Step 40：Launch the 180 ° of pulses of No. 2 positive polarity；
By step 32 time interval τ (between the time between 180 ° of pulses of the 90 ° of pulses of No. 1 positive polarity and No. 1 positive polarity
It is identical every τ), launch the 180 ° of pulses of No. 2 positive polarity in the Z-axis direction, when encourage stop after, letter that ground receiver coil collects
Number it is the 4th measured signal 41.
Step 50：Superposition, which gains freedom, senses FID signal；
Referring to Fig. 2, the phase diagram of FID signal and spin echo SE signals caused by bipolarity spin echo of the present invention, root
According to nuclear magnetic resonance principle, launch first FID1 signal of 90 ° of pulses generations, launch one spin of 180 ° of pulses generations
Echo SE signals, while second FID2 signal is produced, FID2 signal interference spin echo SE signals, the collection of ground receiver coil
The measured signal arrived is the superposed signal of FID2 signals and spin echo SE signals, and this signal masks real spin echo SE
The amplitude and shape of signal.Therefore, the first measured signal and the 3rd measured signal that the present invention gathers are FID1 signals, and second is real
The superposed signal of signal and the 4th measured signal for FID2 signals and spin echo SE signals is surveyed, the second measured signal and the 4th is in fact
Survey amplitude and shape that signal masks true spin echo SE signals.
According to nuclear magnetic resonance principle, the phase and the phase of 90 ° of pulses of the FID1 signals collected and spin echo SE signals
Position is consistent, and the phase for the FID2 signals that 180 ° of pulse collections of transmitting arrive is consistent with the phase of 180 ° of pulses.Due to No. 1 90 ° of pulses
With the opposite polarity of No. 2 90 ° of pulses, therefore the FID1 signals of the first measured signal and the 3rd measured signal phase difference
180 °, the phases of the spin echo SE signals in the second measured signal and the 4th measured signal differs 180 °, and the second actual measurement letter
It is number identical with the phase of the FID2 signals in the 4th measured signal.Therefore, the first measured signal and the 3rd measured signal are subtracted each other
Divided by 2 i.e. can obtain FID signal 51；
Step 60：Superposition obtains spin echo SE signals；
According to the nuclear magnetic resonance principle described in step 50, FID2 signal phases in the second measured signal and the 4th measured signal
Position is identical, and SE signal phases differ 180 °, therefore the second measured signal and the 4th measured signal are subtracted each other divided by 2 can be disappeared
Except the spin echo SE signals 61 of free induction FID signal；
Step 70：Change time interval τ, transmitting is repeated several times；
Referring to ground nuclear magnetic resonance T2 Ts of the Fig. 3 based on bipolarity spin echo2During the pulse of measuring method
Sequence figure, in order to improve T2 T2Measurement accuracy, by changing time interval τ between 90 ° of pulses and 180 ° of pulses,
Repeat step 10,20,30,40,50 and 60, multiple spin echo SE signals are obtained during duplicate measurements, so as to realize
Accurate T2 T2Measurement；
Step 80：It is fitted T2 T2；
Referring to Fig. 4 (b) bipolar pulses measurement T2 T2Schematic diagram, in time domain, spin echo SE signals
Envelope approximate representation be：
When practical application, expression formula can be expressed as：
Wherein Δ t0.5The half width of spin echo SE signals, i.e. envelope shared by the half of echo-signal amplitude peak
Width.
The peak value V of spin echo SE signalsSETime domain observation signal v can be usedSEIt is fitted and is obtained by expression formula (2).By free induction
The peak value V of FID signal and each spin echo signalSEConnection, form an exponential decay curve
It is exactly T2Attenuation curve, therefore T can be fitted using this peak atenuation rule2Value.
As shown in figure 5, bipolar pulse of the present invention eliminates the design sketch of free induction decay signal interference, it is total to according to nuclear-magnetism
Shake principle, transmitting 90 ° of pulses of bipolarity can obtain opposite polarity FID1 signals and SE signals, 180 ° of polarity of transmission identical
Pulse, polarity identical FID2 signals, the spin echo for FID2 signal interferences that Signal averaging can be eliminated can be obtained
SE signals.
In summary, as shown in figure 4, GPMG sequences of the present invention and bipolar pulse obtain T2 T2Contrast
Figure, a figures are CPMG sequence collection T2 T2Schematic diagram, as the T2 T of measured zone2During very little, such as scheme
It is shown, because the interval time between the 90 ° of pulses and 180 ° of pulses of CPMG sequence is fixed, in multiple 180 ° of pulses of transmitting
In, only 180 ° of pulses of first few can collect SE signals, and spin echo SE signal numbers are less, when influenceing transverse relaxation
Between T2Measurement accuracy.B figures are the spin-echo sequence collection T2 T of dipulse changing distance2Schematic diagram, by changing
The time interval τ become between 90 ° of pulses and 180 ° of pulses, can gather multiple spin echo SE signals, it will be apparent that improve horizontal stroke
To relaxation time T2Measurement accuracy.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all essences in the present invention
All any modification, equivalent and improvement made within refreshing and principle etc., should be included in the scope of the protection.
Claims (7)
- A kind of 1. measuring method of the ground nuclear magnetic resonance T2 based on bipolar pulse, it is characterised in that including：Launch the 90 ° of pulses of No. 1 positive polarity, gather the first measured signal,Elapsed time interval τ, launch the 180 ° of pulses of No. 1 positive polarity, gather the second measured signal；After elapsed time recovers, launch the 90 ° of pulses of No. 2 negative polarity, gather the 3rd measured signal；By same time interval τ, launch the 180 ° of pulses of No. 2 positive polarity, gather the 4th measured signal；Second measured signal and the 4th measured signal are overlapped, obtain the spin for eliminating the interference of free induction FID signal Echo SE signals；First measured signal and the 3rd measured signal are superimposed to obtain first free induction FID signal；By changing time interval τ between 90 ° of pulses and 180 ° of pulses, repeat above-mentioned steps, obtained during duplicate measurements Obtain multiple spin echo SE signals；The initial amplitude of first free induction FID signal is connected with the peak value of each spin echo SE signals, forms one Exponential decay curve, fitting obtain T2 T2.
- 2. measuring method according to claim 1, it is characterised in that carried out to the second measured signal and the 4th measured signal Superposition is specially：Second measured signal and the 4th measured signal are subtracted each other divided by 2.
- 3. measuring method according to claim 1, it is characterised in that be superimposed the first measured signal and the 3rd measured signal Specially：First measured signal and the 3rd measured signal are subtracted each other divided by 2.
- 4. measuring method according to claim 1, it is characterised in that launching the 90 ° of pulses of No. 1 positive polarity is specially：Three To tie up in rectangular coordinate system, transmitting coil is positioned on ground by magnetostatic field Bo along in the Z-direction of three-dimensional cartesian coordinate system, X-direction in the X/Y plane in magnetostatic field Bo directions launches the 90 ° of pulses of No. 1 positive polarity to underground.
- 5. measuring method according to claim 1, it is characterised in that launching the 180 ° of pulses of No. 1 positive polarity is specially：Three Tie up in rectangular coordinate system, transmitting coil is positioned on ground by magnetostatic field Bo along in the Z-direction of three-dimensional cartesian coordinate system, in Z Launch the 180 ° of pulses of No. 1 positive polarity to underground on direction of principal axis.
- 6. measuring method according to claim 1, it is characterised in that launching the 90 ° of pulses of No. 2 negative polarity is specially：Three To tie up in rectangular coordinate system, transmitting coil is positioned on ground by magnetostatic field Bo along in the Z-direction of three-dimensional cartesian coordinate system, Negative X-direction in the X/Y plane in magnetostatic field Bo directions launches the 90 ° of pulses of No. 2 negative polarity to underground.
- 7. measuring method according to claim 1, it is characterised in that launching the 180 ° of pulses of No. 2 positive polarity is specially：Three Tie up in rectangular coordinate system, transmitting coil is positioned on ground by magnetostatic field Bo along in the Z-direction of three-dimensional cartesian coordinate system, in Z Launch the 180 ° of pulses of No. 2 positive polarity on direction of principal axis.
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| CN114325523B (en) * | 2020-09-27 | 2023-10-03 | 上海联影医疗科技股份有限公司 | T1 value determining method, device, electronic equipment and storage medium |
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| CN1006578B (en) * | 1985-04-01 | 1990-01-24 | 菲利普光灯制造公司 | Method of reducing artefacts in images formed by means of fourier zeugmatography |
| US6972564B2 (en) * | 2001-11-06 | 2005-12-06 | Baker Hughes Incorporated | Objective oriented methods for NMR log acquisitions for estimating earth formation and fluid properties |
| US6703832B2 (en) * | 2002-08-12 | 2004-03-09 | Schlumberger Technology Corporation | Method for detecting hydrocarbons by comparing NMR response at different depths of investigation |
| US7126333B2 (en) * | 2004-04-19 | 2006-10-24 | Baker Hughes Incorporated | Method and apparatus for correcting ringing in NMR signals |
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