CN102116856B - Transverse relaxation time measuring method and system - Google Patents
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Abstract
The invention provides a transverse relaxation time measuring method. The method comprises the following steps of: acquiring an echo signal; fitting the echo signal to acquire a prior estimate value of the relaxation time; and calculating echo time interval according to the prior estimate value, and feeding the echo time interval to the fitting calculation to acquire a measurement value of the relaxation time. Through rough estimation on the relaxation by the fitting calculation, the transverse relaxation time measuring method and system realize optimization on the signal to noise ratio of the relaxation time in the echo signal, so that the accuracy of relaxation time measurement is effectively improved.
Description
[technical field]
The present invention relates to biomedical technology, particularly relate to a kind of transverse relaxation time measuring method and system.
[background technology]
MRI(Magnetic Resonance Imaging, magnetic resonance imaging) technology because have very high resolution, to the measurement of human body many kinds of parameters and can utilize the relaxation time weighting that tumour is carried out early diagnosis, evaluation and approved widely and use.Relaxation time is the most basic contrast mechanisms of magnetic resonance imaging.Utilize the feature in relaxation time to distinguish, to cut apart and to classify tissue, thereby improve detection and the supervision level of disease.
In the clinical practice of reality, common direct various weighted images of collection, relaxation time weighted image for example, and carry out the diagnosis of various diseases according to the relaxation time weighted image, still, this diagnostic mode needs to depend on doctor's experience to a great extent.In generating the process of weighted image, because the weighted of parameters weighting, and weight can change along with factors, even obtains weighted image by mixed weighting, even therefore veteran doctor also unavoidably misidentification can occur.
[summary of the invention]
Based on this, be necessary to provide a kind of transverse relaxation time measuring method that improves accuracy.
In addition, also be necessary to provide a kind of T2 measuring system that improves accuracy.
A kind of transverse relaxation time measuring method may further comprise the steps: obtain echoed signal; Described echoed signal is carried out the priori valuation that the Fitting Calculation obtains T2; Calculate the echo time interval and feed back to the measured value that obtains T2 in the Fitting Calculation according to described priori valuation.
Preferably, the described step of obtaining echoed signal is: obtain echoed signal by magnetic resonance pulse sequence.
Preferably, describedly described echoed signal is carried out the step that the Fitting Calculation obtains the priori valuation of T2 be: by least square method described echoed signal is carried out the priori valuation that linear fit obtains T2.
Preferably, described step of echoed signal being carried out linear fit by least square method is that front at least 3 echoed signals in the echoed signal are carried out least-squares algorithm linear fitting.
Preferably, the described step that calculates the echo time interval and feed back to the measured value that obtains T2 in the Fitting Calculation according to described priori valuation is: calculate the echo time interval according to described priori valuation; Described echo time interval is fed back to the measured value that obtains T2 in the linear fit of least square method.
A kind of T2 measuring system comprises at least: acquisition module is used for obtaining echoed signal; Fitting module is used for described echoed signal is carried out the priori valuation that the Fitting Calculation obtains T2, and obtains the measured value of T2 by the Fitting Calculation according to the echo time interval of computing module feedback; Computing module is used for calculating described echo time interval and feeding back to fitting module according to described priori valuation.
Preferably, described acquisition module is used for obtaining echoed signal by magnetic resonance pulse sequence.
Preferably, described fitting module is used for by least square method described echoed signal being carried out the priori valuation that linear fit obtains T2.
Preferably, described fitting module is used for front at least 3 echoed signals of echoed signal are carried out least-squares algorithm linear fitting.
Preferably, described fitting module is further used for the echo time interval of feedback is obtained by the linear fit of least square method the measured value of T2.
Above-mentioned transverse relaxation time measuring method and system carry out the guestimate in relaxation time by the Fitting Calculation, and then have realized the optimization to relaxation time signal to noise ratio (S/N ratio) in the echoed signal, have effectively improved the accuracy of relaxation time measurement.
[description of drawings]
Fig. 1 is the process flow diagram of transverse relaxation time measuring method among the embodiment;
Fig. 2 is echo time interval and the graph of a relation in relaxation time among the embodiment;
Fig. 3 is the schematic diagram of T2 measuring system among the embodiment;
Fig. 4 be the conventional relaxed Method Of Time Measurement of SNR=50 in the computer simulation emulation and transverse relaxation time measuring method Performance Ratio;
Fig. 5 for for the Performance Ratio of the conventional relaxed Method Of Time Measurement of SNR=10 in the computer simulation emulation and transverse relaxation time measuring method;
Fig. 6 is the phantom relaxation time collection of illustrative plates of transverse relaxation time measuring method in the phantom measurement;
Fig. 7 is the phantom relaxation time collection of illustrative plates of conventional relaxed Method Of Time Measurement in the phantom measurement;
Fig. 8 is the knee relaxation time collection of illustrative plates of transverse relaxation time measuring method in the anthropological measuring;
Fig. 9 is the knee relaxation time collection of illustrative plates of conventional relaxed Method Of Time Measurement in the anthropological measuring.
[embodiment]
Fig. 1 shows the method flow that a T2 among the embodiment is measured, and may further comprise the steps:
In step S10, obtain echoed signal.In the present embodiment, obtain the step of echoed signal for to obtain echoed signal by magnetic resonance pulse sequence.Obtain the echoed signal of whole imaging region, but for reducing the calculated amount in the follow-up fit procedure, only calculate for the echoed signal in the area-of-interest.
For example, can adopt many echoes SE sequence (self-rotary echo-pulse series) to carry out cross-section bit scan, obtain echoed signal, so that this echoed signal is carried out match.
In step S30, echoed signal is carried out the priori valuation that the Fitting Calculation obtains the relaxation time.In the present embodiment, the echoed signal after the intercepting is carried out guestimate, obtain the priori valuation in relaxation time by match.Particularly, can obtain by the mode of least-squares algorithm linear fitting the priori valuation in relaxation time.Because the echoed signal signal to noise ratio (S/N ratio) of leading portion is higher in the echo train, so that match is comparatively accurate, can utilize the echoed signal of leading portion in the echo train to carry out match.The step of echoed signal being carried out linear fit by least square method refers to carries out least-squares algorithm linear fitting to front at least 3 echoed signals in the echoed signal.But, in fit procedure, the echo that participates in least-squares algorithm linear fitting is more, the needed time is also just longer, therefore in a preferred embodiment, only front 3 echoed signals in the echoed signal are carried out least-squares algorithm linear fitting, thereby in the situation that minimizing time and improved match speed also guaranteed the accuracy of match.
In step S50, valuation calculates the echo time interval and feeds back to the measured value that obtains the relaxation time in the Fitting Calculation according to priori.In the present embodiment, the echo time interval refers to the time interval between adjacent two echoed signals in the imaging sequence echo train.According to the priori valuation in conjunction with relaxation time signal to noise ratio (S/N ratio) (T
2-to-noise-ratio, T
2NR) calculate optimum echo time interval, and echo time interval that should optimum feeds back in the Fitting Calculation and go, utilize the echo time interval of the optimum that calculates to carry out least-squares algorithm linear fitting.To feed back to through the echo time interval that relaxation time signal to noise ratio (S/N ratio) optimization obtains in the linear fit of least square method, to obtain the relaxation time measured value through optimizing, effectively improve the accuracy of relaxation time measurement.
The priori valuation T that match is obtained
2And standard deviation
Bring in the following formula, to obtain echo time interval delta T E.
Wherein, S is echoed signal intensity, and σ is the standard variance of Gaussian noise,
Be the standard deviation of echoed signal, Δ TE is the echo time interval.S
1/ σ at imaging parameters one regularly can be used as scale parameter and process.
Particularly, in the measurement in relaxation time, corresponding standard deviation of relaxation time is the parameter of important sign noise transmission, satisfy TR＞＞TE, TR＞＞T
1Condition under, the expression formula of signal intensity can be approximately in the echoed signal:
S＝S
0exp(-TE/T
2)（2）
Wherein, TR is the repetition time, and TE is echo time (from the time interval between excitation pulse and the generation echo), T
1Be reversing time, S
0Signal intensity during for TE=0.
By the visible relaxation time T of (2) formula
2Can estimate with the echoed signal intensity ratio of two different echo time TE, suppose that two echo times are respectively TE
1And TE
2, and TE
2＞TE
1, then:
S
1＝S
0exp(-TE
1/T
2)（3）
S
2＝S
0exp(-TE
2/T
2)（4）
Wherein, S
1To be TE the echo time
1The time echoed signal intensity, S
2To be TE the echo time
2The time echoed signal intensity.
Relaxation time T then
2Computing formula be:
Consider the impact of noise, Gaussian noise be superimposed on above-mentioned two echoed signals, by the fundamental error analysis principle, can with
Regard S as
1And S
2Function:
Can try to achieve the standard deviation in relaxation time through deriving is:
Finally, the relaxation time signal to noise ratio (S/N ratio) can ask into:
Wherein, S
1/ σ is TE
1The signal to noise ratio (S/N ratio) that constantly measures at imaging parameters one regularly, can be used as scale parameter and process, and Δ TE is two echo time intervals between the echo.
This shows T
2The optimization of NR is in fact about Δ TE and T
2Binary function maximal value Solve problems.As shown in Figure 2, as relaxation time T
2One regularly, optimum T
2The NR value is determined by the Δ TE of correspondence; As Δ TE one timing, corresponding relaxation time T
2Optimum T will be determined
2NR.Therefore, for relaxation time T
2Measurement, can be equivalent to and work as T
2Value one is regularly found the solution and is made T
2Δ TE when NR gets maximal value, i.e. optimum Δ TE, thus obtain be used to the optimum echo time interval that carries out curve fitting.
In addition, also be necessary to provide a kind of T2 measuring system.As shown in Figure 3, this system comprises acquisition module 10, fitting module 30 and computing module 50.
Acquisition module 10 is used for obtaining echoed signal.In the present embodiment, acquisition module 10 is by magnetic resonance imaging retrieval echoed signal.
For example, acquisition module 10 can adopt many echoes SE sequence (self-rotary echo-pulse series) to carry out cross-section bit scan, obtains echoed signal, so that this echoed signal is carried out match.
Fitting module 30 is used for echoed signal is carried out the priori valuation that the Fitting Calculation obtains the relaxation time, and obtains the measured value in relaxation time by the Fitting Calculation according to the echo time interval of feedback.In the present embodiment, the echoed signal after 30 pairs of interceptings of fitting module is carried out guestimate, obtains the priori valuation in relaxation time by match.
Fitting module 30 is carried out the priori valuation that linear fit obtains the relaxation time by least square method to the echoed signal after intercepting.Particularly, by least-squares algorithm linear fitting the relaxation time is estimated roughly, obtained the priori valuation in relaxation time.Among another embodiment, because the echoed signal signal to noise ratio (S/N ratio) of leading portion is higher in the echo train, so that match is comparatively accurate, fitting module 30 can utilize the echoed signal of leading portion in the echo train to carry out match.In a preferred embodiment, for further improving the accuracy of match, improve match speed, front at least 3 echoed signals in 30 pairs of echoed signals of fitting module are carried out least-squares algorithm linear fitting.
Fitting module 30 is further used for the echo time interval of feedback is obtained by the linear fit of least square method the measured value in relaxation time.In the present embodiment, fitting module 30 will feed back to through the echo time that relaxation time signal to noise ratio (S/N ratio) optimization obtains in the linear fit of least square method, to obtain the relaxation time measured value through optimizing, effectively improve the accuracy of relaxation time measurement.
Computing module 50 is for valuation calculates the echo time interval and feeds back to the Fitting Calculation according to priori.In the present embodiment, the echo time interval refers to the time interval between adjacent two echoed signals in the imaging sequence echo train.Computing module 50 obtains optimum echo time interval according to the priori valuation in conjunction with the relaxation time snr computation, and should the echo time interval feed back in the Fitting Calculation and go, utilize the echo time interval of the optimum that calculates to carry out least-squares algorithm linear fitting.
Particularly, computing module 50 priori valuation T that match is obtained
2Bring in the following formula, to obtain echo time interval delta T E.
Wherein, S
1Be echoed signal intensity, σ is the standard variance of Gaussian noise,
Be the standard deviation of echoed signal, Δ TE is the echo time interval, S
1/ σ at imaging parameters one regularly can be used as scale parameter and process.
Below in conjunction with computer simulation emulation, phantom measurement and anthropological measuring, the accuracy of above-mentioned transverse relaxation time measuring method and system is assessed and contrasted.Phantom and human experimentation are all carried out at the 0.35T magnetic resonance device, and used coil is knee coil.Computer simulation emulation and Data Post all on Windows XP platform, are used MATLAB R2008a, realize with the software of voluntarily establishment, and wherein view data is the DICOM form.
Computer simulation emulation produces the spin echo signal of simulation by (1) formula, TE=5～130ms wherein, echo sounding Δ TE=5ms, T
2=10～120MS.Be that Gaussian noise and the echoed signal of σ superposes with zero-mean, standard variance, obtain final signals and associated noises.Signal to noise ratio snr (SNR=S during TE=0
0/ σ) be respectively 10 and 50.To different SNR and T
210,000 tests are respectively done in combination, calculate at last T
2Average and the standard variance of value are assessed T
2The accuracy of measuring.
In the conventional relaxed Method Of Time Measurement, noise gate σ
NoiseEqual the standard variance σ of noise, signal intensity S in the echo train＜2 σ
NoiseFirst echoed signal and echo afterwards thereof will be clipped, remaining echoed signal will be for the Fitting Calculation.And T in the transverse relaxation time measuring method
2The priori valuation obtained by first three the echoed signal match in the echo train.
Compared under different SNR conditions the performance of conventional relaxed Method Of Time Measurement and above-mentioned transverse relaxation time measuring method among Fig. 4 to Fig. 5.Under the high s/n ratio condition, namely during SNR=50, two kinds of methods all obtain more accurately result, all show with the fine of actual value to coincide, but at T
2Be the part of 10～50ms, the conventional relaxed Method Of Time Measurement is to T
2The priori valuation have a little higher, and above-mentioned transverse relaxation time measuring method is at whole T
2All keep stable in the dynamic range of value and accurately valuation.Under Low SNR (Fig. 5), namely during SNR=10, two kinds of methods all show T
2Over-evaluate.Comparatively speaking, the conventional relaxed Method Of Time Measurement to over-evaluate degree larger, and at whole T
2Continue to over-evaluate in the dynamic range of value, and above-mentioned transverse relaxation time measuring method is at T
2Value is the part of 80～120ms, over-evaluates situation and restrains oneself, and tends to gradually accurate valuation.In general, above-mentioned transverse relaxation time measuring method has more accurately T than the conventional relaxed Method Of Time Measurement
2Valuation, and at whole T
2Show the robustness stronger to noise in the dynamic range of value.The size of SNR can affect two kinds of methods to T
2Valuation, SNR is lower, T
2Valuation higher, larger with the deviation of ideal value, error is larger.
The multi-functional phantom of phantom measurement experiment Application standard is measured, and the imaging aspect has 5 cylindrical regions, is filled with respectively 0.001%, 0.002%, 0.004%, 0.007% and 0.012% MnCl
24H
2O and distilled water.Peripheral filling material is 0.125%NiSO
46H
2O, 0.5%NaCl and distilled water.The concentration difference causes solution T
2The difference of value, and concentration is larger, T
2Be worth less.The room temperature of scanning room is controlled at 24 ℃.
Adopt the many echo sequences of individual layer to carry out cross-section bit scan, imaging parameters is: FOV=220mm * 220mm, TR=5000ms, TE=20～500ms, echo sounding Δ TE=20ms, echo train length ETL=25, times of collection Nacq=1, bandwidth BW=80Hz/pixel, bed thickness TH=7mm, image array 256 * 256.
With 25 width of cloth T that obtain
2Weighted image calculates the priori valuation in relaxation time through least-squares algorithm linear fitting.Wherein, in the conventional relaxed Method Of Time Measurement, noise gate σ
NoiseStandard variance by signal homogeneous area in first echo is determined signal amplitude S in the echo train＜2 σ
NoiseFirst echoed signal and echoed signal afterwards thereof will be clipped, remaining echoed signal will be for the Fitting Calculation.In the above-mentioned transverse relaxation time measuring method, T
2The priori valuation obtained by first three echo match.The T that after the Fitting Calculation, obtains
2Collection of illustrative plates as shown in Figure 6.
Among Fig. 7, see on the whole the T of above-mentioned transverse relaxation time measuring method gained
2The signal to noise ratio (S/N ratio) of collection of illustrative plates is better than the conventional relaxed Method Of Time Measurement, especially is 0.012% and 0.007% zone (short T in concentration
2).
Phantom is tested and is shown, the priori valuation of resulting relaxation time of self-adaptation type approximating method is on the low side than conventional relaxed Method Of Time Measurement acquired results, and at whole T
2In the dynamic range of value, can both obtain more accurately T
2Measured value.Especially for short T
2The measurement of value, the advantage of above-mentioned transverse relaxation time measuring method has clearly demonstrated fully the robustness of the method to noise, and T
2The optimization of NR is to T
2The improvement effect of measurement accuracy.
Anthropological measuring is carried out the knee imaging to 25 years old healthy volunteer, and room temperature is controlled at 24 ℃.Adopt the many echo sequences of multilayer to carry out cross-section bit scan, imaging parameters is: FOV=160mm * 160mm, TR=1250ms, TE=15～120ms, echo sounding Δ TE=15ms, echo train length ETL=8, image array 256 * 256, times of collection Nacq=2, bandwidth BW=130Hz/pixel, bed thickness TH=4mm gets 9 layers of cross-section positions, interlamellar spacing 4mm, total scanning time TA=6 ' 44 ".
In the conventional relaxed Method Of Time Measurement, noise gate σ
NoiseDetermine consistent with the process of above-mentioned phantom measurement.In the transverse relaxation time measuring method, T
2The priori valuation obtained by first three echo match.
By Fig. 8 and shown in Figure 9, such as articular cartilage, muscle etc., with the resulting T of transverse relaxation time measuring method
2Measured value is on the low side than the conventional relaxed Method Of Time Measurement, so the conventional relaxed Method Of Time Measurement is to T
2The phenomenon that value is over-evaluated is confirmed again.From T
2See on the collection of illustrative plates, the collection of illustrative plates that transverse relaxation time measuring method obtains is more level and smooth, and details is abundanter, has higher signal to noise ratio (S/N ratio).
Above-mentioned transverse relaxation time measuring method and system can be applicable in the diagnosis of osteoarthritis; knee joint is the most complicated prudent joint of human body maximum; articular cartilage is indispensable important feature in the knee joint normal activity, and age growth and various joint disease all can cause the regression of cartilage or damage and affect kneed normal activity.But because it can't directly jeopardize people's life, often unlike other diseases, come into one's own, fail in time to treat and easily be left in the basket, cause nonreversibility to change.Osteoarthritis (osteoarthritis, OA) is the key factor that affects knee Stability, also is simultaneously modal a kind of joint diseases in the global range.Along with the development of each related discipline such as molecular biology, materia medica, make the early treatment of cartilage lesion become possibility, this just need to carry out early diagnosis to cartilage lesion.Magnetic resonance has larger diagnostic value as a kind of method of Noninvasive is verified for cartilage lesion, can come the long term monitoring osteoarthritis by the variation of measuring magnetic resonance relaxation time quantitative test articular cartilage inner tissue composition, extensively be approved at present.
Above-mentioned transverse relaxation time measuring method and system carry out the guestimate in relaxation time by the Fitting Calculation, and then have realized the optimization to relaxation time signal to noise ratio (S/N ratio) in the echoed signal, have effectively improved the accuracy of relaxation time measurement.
The above embodiment has only expressed several embodiment of the present invention, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to claim of the present invention.Should be pointed out that for the person of ordinary skill of the art, without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection domain of patent of the present invention should be as the criterion with claims.
Claims (10)
1. transverse relaxation time measuring method may further comprise the steps:
Obtain echoed signal;
Described echoed signal is carried out the priori valuation that the Fitting Calculation obtains T2;
Calculate the echo time interval and feed back to the measured value that obtains T2 in the Fitting Calculation according to described priori valuation.
2. transverse relaxation time measuring method according to claim 1 is characterized in that, the described step of obtaining echoed signal is:
Obtain echoed signal by magnetic resonance pulse sequence.
3. transverse relaxation time measuring method according to claim 1 is characterized in that, describedly described echoed signal is carried out the step that the Fitting Calculation obtains the priori valuation of T2 is:
By least square method described echoed signal is carried out the priori valuation that linear fit obtains T2.
4. transverse relaxation time measuring method according to claim 3 is characterized in that, described step of echoed signal being carried out linear fit by least square method is that front at least 3 echoed signals in the echoed signal are carried out least-squares algorithm linear fitting.
5. according to claim 3 transverse relaxation time measuring method is characterized in that, the described step that calculates the echo time interval and feed back to the measured value that obtains T2 in the Fitting Calculation according to described priori valuation is:
Calculate the echo time interval according to described priori valuation;
Described echo time interval is fed back to the measured value that obtains T2 in the linear fit of least square method.
6. a T2 measuring system is characterized in that, comprises at least:
Acquisition module is used for obtaining echoed signal;
Fitting module is used for described echoed signal is carried out the priori valuation that the Fitting Calculation obtains T2, and obtains the measured value of T2 by the Fitting Calculation according to the echo time interval of computing module feedback;
Computing module is used for calculating described echo time interval and feeding back to fitting module according to described priori valuation.
7. T2 measuring system according to claim 6 is characterized in that, described acquisition module is used for obtaining echoed signal by magnetic resonance pulse sequence.
8. T2 measuring system according to claim 6 is characterized in that, described fitting module is used for by least square method described echoed signal being carried out the priori valuation that linear fit obtains T2.
9. transverse relaxation time measuring method according to claim 8 is characterized in that, described fitting module is used for front at least 3 echoed signals of echoed signal are carried out least-squares algorithm linear fitting.
10. transverse relaxation time measuring method according to claim 8 is characterized in that, described fitting module is further used for the echo time interval of feedback is obtained by the linear fit of least square method the measured value of T2.
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| CN103675722B (en) * | 2013-11-27 | 2016-05-25 | 中国石油大学(华东) | Rock T2-G experiment acquisition parameter automatic matching method |
| WO2017125790A1 (en) | 2016-01-22 | 2017-07-27 | Synaptive Medical (Barbados) Inc. | Systems and methods for magnetic field-dependent relaxometry using magnetic resonance imaging |
| CN106597338B (en) * | 2016-12-28 | 2019-03-29 | 北京航空航天大学 | A method of atom lateral relaxation time is measured based on electron resonance phase frequency analysis |
| CN107015181B (en) | 2017-04-07 | 2020-01-14 | 厦门大学 | Method for measuring proton longitudinal relaxation time under inhomogeneous magnetic field |
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| CN110174632B (en) * | 2019-06-10 | 2021-06-01 | 上海东软医疗科技有限公司 | Magnetic resonance imaging method and device, imaging equipment and magnetic resonance imaging system |
| CN110855356B (en) * | 2019-10-21 | 2021-06-04 | 同济大学 | Resonance wave beam communication device based on detection feedback control |
| CN111721795B (en) | 2020-06-29 | 2021-05-11 | 无锡鸣石峻致医疗科技有限公司 | Material measurement method and system based on nuclear magnetic resonance system |
| CN113093078B (en) * | 2021-03-31 | 2021-11-30 | 无锡鸣石峻致医疗科技有限公司 | Method and device for determining linear relation between radio frequency pulse intensity and flip angle, computer equipment and storage medium |
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