WO2017008262A1

WO2017008262A1 - Diffusion magnetic resonance imaging method with abnormal degree of diffusion weighting

Info

Publication number: WO2017008262A1
Application number: PCT/CN2015/084032
Authority: WO
Inventors: 龚启勇; 幸浩洋; 陈可鸣; 孙怀强; 周晓洪; 隋轶
Original assignee: 四川大学华西医院
Priority date: 2015-07-15
Filing date: 2015-07-15
Publication date: 2017-01-19

Abstract

A diffusion magnetic resonance imaging method with an abnormal degree of diffusion weighting comprising the following steps: step 1, using a pulse gradient spin echo (PGSE) signal to scan water molecules in tissue and recording a scanning result A; step 2, using an oscillation gradient spin echo (OGSE) signal to scan the water molecules in the tissue at a diffusion gradient value b that is the same as that in step 1, and recording a scanning result B; and step 3, obtaining a difference C between the scanning result A and the scanning result B. The method can reflect a change in a peak value K of diffusion of water molecules in tissue very well so as to provide a reference for disease diagnosis.

Description

A diffusion-weighted diffusion magnetic resonance imaging method

Technical field

The present invention relates to a magnetic resonance imaging method, and more particularly to a diffusion magnetic resonance imaging method with an abnormal diffusion degree weighting.

Background technique

DWI (Diffusion Weighted Imaging) is the only imaging method that can measure the movement of water molecules in tissues. It has been widely used in clinical practice. The theoretical hypothesis is based on the diffusion of water molecules in the tissue is Gaussian diffusion, the resulting signal satisfies S = S ₀ exp (-b × ADC), and the ADC is the apparent diffusion coefficient.

However, since water molecules in human tissues are interfered by various obstacles (such as cell membranes, biomacromolecules, etc.), the diffusion of water molecules often does not satisfy the Gaussian type of diffusion and exhibits a non-Gaussian characteristic. In order to describe this non-Gaussian phenomenon, a double exponential model, an extended exponential model, a DKI (diffusion peak imaging) model, and an IVIM (involvement in voxel) model have been proposed.

Among them, DKI is widely used in the current clinical practice. The model also uses the concept of peak to describe the non-Gaussian distribution of water molecules. The theoretical formula is:

The D _app and K _app distributions represent apparent diffusion coefficients and apparent peaks. It is obtained from the Taylor expansion of the DWI formula, and its physical image is not clear, and the problem that this technology faces at the same time is that multiple sets of b values are required in multiple directions (at least 3 b values and 15 directions), and data needs to be performed. The complex fitting process, the K _app obtained by fitting is not a real K. Although it is helpful in clinical diagnosis, it is doubtful whether it can truly reflect the degree of non-Gaussian. Unfavorable factors such as simultaneous fitting and multiple sampling directly lead to longer time-consuming DKI and unreliable data, which has many negative effects on clinical applications.

Summary of the invention

The invention aims to provide a diffusion magnetic resonance imaging method with a degree of abnormal diffusion degree, which can well reflect the change of the peak K of the water molecule dispersion in the tissue, and provides a reference for the diagnosis of the disease.

In order to achieve the above object, the present invention is achieved by the following technical solutions:

The abnormal diffusion degree weighted diffusion magnetic resonance imaging method disclosed in the present invention comprises the following steps:

Step 1, using a pulse gradient spin echo PGSE signal to scan the water molecules in the tissue, and recording the scan result A;

Step 2, using the same gradient dispersion b value in step 1 using an oscillating gradient spin echo OGSE signal to scan the water molecules in the tissue, and recording the scan result B;

Step 3. The scan result A is subtracted from the scan result B to obtain the difference C.

Further, after step 3, the difference C is taken to be an absolute value. The difference C can be uniformly characterized as a positive value.

Further, after step 3, the difference C is taken as an absolute value and multiplied by a normal number to obtain a value D. When the difference C value is small, the sensitivity of the later analysis can be improved.

Further, in steps 1, 2, the pulse gradient spin echo PGSE signal and the oscillation gradient spin echo OGSE signal are replaced by a bipolar dispersion gradient GRE signal and an oscillating dispersion gradient GRE signal, respectively.

Further, after step 3, the dispersion gradient b value is replaced, and steps 1, 2, and 3 are repeated.

Preferably, the waveform of the oscillation gradient spin echo OGSE signal is a square wave, a cosine wave, a sine wave, a mixed waveform or a triangular wave.

Further, the dispersion gradient b value, the frequency of the oscillation gradient spin echo OGSE signal, and the pulse The diffusion time Δ and the dispersion δ of the gradient spin echo PGSE signal scan can be set.

Preferably, the waveform of the bipolar diffusion gradient GRE signal is a square wave, a cosine wave, a sine wave, a mixed waveform or a triangular wave.

Further, the frequency of the bipolar dispersion gradient GRE signal and the oscillation diffusion gradient GRE signal, the diffusion time Δ of the bipolar diffusion gradient GRE signal scan, and the value of the dispersion δ can be set.

The disclosed diffusion magnetic resonance imaging method based on pulsed gradient spin echo (PGSE) and oscillating gradient spin echo (OGSE) signal is named DOOP (the Difference Of OGSE and PGSE); DOOP signal can reflect water molecules well The change in the peak value of the dispersion K, which changes with the structure of the human body to help diagnose the disease. The DOOP signal is calculated as follows:

_{_Signal} DOOP = Signal _PGSE -Signal OGSE

Signal _PGSE represents the PGSE signal and Signal _OGSE represents the OGSE signal.

The DOOP signal is the difference C.

The definition of peak K is as follows:

Where s=r _t -r ₀ , r _t and r ₀ respectively represent the spatial position of the water molecule at time t and the spatial position at the initial moment. n indicates the selected measurement direction. On the premise of Gaussian distribution, the standard Gaussian distribution obtained when K is equal to 0, the distribution obtained when K>0 has a sharper peak, and the K<0 gives a more gradual peak. In the case where the mean and variance of the distribution function are the same, the K value can well reflect the concentration of water molecules.

In diffusion imaging, due to the existence of cell membranes, biomacromolecules and other structures, the dispersion of water molecules is disturbed by various obstacles, thus deviating from the standard Gaussian distribution. At this time, the K value can well describe the interference. Happening.

Due to the rapidly changing dispersion gradient of OGSE, the measure of short-term diffusion effect is provided, and the measure of such short-term effect will be similar to the diffusion of obstacles in the tissue as a non-obstacle diffusion in the measurement, mainly reflecting the reflection In the case of free diffusion of water molecules, the OGSE signal is subtracted from the PGSE signal, and the resulting portion can be regarded as the interference of water molecules due to various obstacles in the tissue, that is, the degree of deviation from the Gaussian distribution.

Since DOOP and K both react to the deviation of Gaussian water molecules, there is a certain relationship between them, and because K is difficult to measure directly in the organization, DOOP provides a good means to measure the change of K. This reflects the difference in cellular tissue structure.

Advantageous Effects of the Invention: Compared with the current mainstream imaging methods (DKI (diffusion abundance imaging), DTI (diffusion tensor imaging), etc., the invention has faster time, is easy to use, has good imaging effect, and does not depend on the simulation. The advantages of DOOP signal can reflect the change of peak K of water molecule dispersion, which changes with the change of human tissue structure to help diagnose the disease.

DRAWINGS

Figure 1 is a timing diagram of PGSE and OGSE pulses;

Fig. 2 is a schematic diagram showing changes in DOOP and K with R when b=1500.

detailed description

In order to make the objects, technical solutions and advantages of the present invention more comprehensible, the present invention will be further described in detail with reference to the accompanying drawings.

Example 1

This embodiment includes the following steps:

Step 2. Using the same gradient dispersion b value in step 1 using an oscillating gradient spin echo OGSE The signal scans the water molecules in the tissue and records the scan result B;

Step 3: Obtain a difference C between the scan result A and the scan result B; then take an absolute value of the difference C. According to the magnitude of the difference C, when the value of the difference C is small, the absolute value of the difference C may be obtained. Multiply by a normal number to get the value D

After step 3, the dispersion gradient b value is replaced, and steps 1, 2, and 3 are repeated; a plurality of difference values C are obtained to more objectively reflect the extent to which the water molecules diffuse away from the Gaussian distribution in the tissue.

The PGSE and OGSE pulse timings used in this embodiment are shown in FIG. 1. Of course, the parameters of the signal (b, the frequency of the OGSE) can be set to different values, and the OGSE waveform can adopt various variants, such as a cosine wave, a sine wave, Mixed waveforms, triangular waves, rectangular waves, etc., PGSE parameters such as b value, diffusion time Δ, dispersion δ, etc. are set to different values.

As shown in Fig. 2, this embodiment performs a simulation of the Monte Carlo method. The simulated object is a water molecule diffusion inside a circular cell with a water molecule diffusion coefficient of 2.5×10 ^-3 mm ² /s. The time step Δt = 0.2 × 10 ^-5 s, and the total dispersion time is 0.1 s. Change R to measure the corresponding DOOP, K. The general value of R was determined to be 5 μm according to the experiment, the general value of VR was taken as 0.65, and the variation range of R was 3-10 μm. The simulation of each R variable will be repeated 30 times to obtain the mean and uncertainty of the relevant parameters.

From the simulation results, the DOOP signal has a good correlation with K for the change of R, and the correlation coefficient reaches 0.95. We can use DOOP to reflect the change in K. Because K embodies the extent to which water molecules deviate from quasi-Gaussian, the DOOP signal also reflects the extent to which water molecules deviate from Gaussian. This method can be used to reflect changes in K values caused by changes in tissue structure caused by disease. Because the standard deviation of the DOOP signal is small, it is not clearly shown in Figure 2.

Example 2

This embodiment includes the following steps:

Step 1. Scan the water molecules in the tissue with a bipolar diffusion gradient GRE signal, and record Recording scan result A;

Step 2: using the same diffusion gradient b value in step 1 to scan the water molecules in the tissue using the oscillating diffusion gradient GRE signal, and recording the scan result B;

Step 3: Obtain a difference C between the scan result A and the scan result B; then take an absolute value of the difference C. According to the magnitude of the difference C, when the value of the difference C is small, the absolute value of the difference C may be obtained. Multiply by a normal number to get the value D.

Of course, the parameters of the signal (b, the frequency of the oscillation gradient) can be set to different values, and the oscillation gradient waveform can adopt various varieties, such as a cosine wave, a sine wave, a mixed waveform, a triangular wave, a rectangular wave, etc., a bipolar diffusion gradient GRE Parameters such as b value, diffusion time Δ, dispersion δ, etc. are set to different values.

The invention may, of course, be embodied in a variety of other embodiments, and various changes and modifications can be made in accordance with the present invention without departing from the spirit and scope of the invention. And modifications are intended to fall within the scope of the appended claims.

Claims

An abrupt diffusion degree weighted diffusion magnetic resonance imaging method, comprising the steps of:

Step 1, using a pulse gradient spin echo PGSE signal to scan the water molecules in the tissue, and recording the scan result A;

Step 2, using the same gradient dispersion b value in step 1 using an oscillating gradient spin echo OGSE signal to scan the water molecules in the tissue, and recording the scan result B;

Step 3: Obtain a difference C between the scan result A and the scan result B.
The method of claim 1, wherein the step C is followed by the absolute value of the difference C.
The method of claim 2, wherein after step 3, the difference C is taken as an absolute value and multiplied by a normal number to obtain a value D.
The method for diffusing magnetic resonance imaging of an abnormal diffusion degree weighting according to claim 1, wherein in steps 1, 2, the pulse gradient spin echo PGSE is replaced by a bipolar diffusion gradient GRE signal and an oscillating diffusion gradient GRE signal, respectively. Signal and oscillation gradient spin echo OGSE signals.
The method according to claim 1, wherein the diffusion gradient b value is replaced after step 3, and steps 1, 2, and 3 are repeated.
The method according to claim 1, wherein the waveform of the oscillation gradient spin echo OGSE signal is a square wave, a cosine wave, a sine wave, a mixed waveform or a triangular wave.
The method according to claim 1, wherein the dispersion gradient b value, the oscillation gradient spin echo OGSE signal frequency, the pulse ladder The diffusion time Δ and the value of the dispersion δ of the degree spin echo PGSE signal scan can be set.
The method according to claim 4, wherein the waveform of the bipolar diffusion gradient GRE signal is a square wave, a cosine wave, a sine wave, a mixed waveform or a triangular wave.
The method according to claim 4, wherein the frequency of the bipolar diffusion gradient GRE signal and the oscillation dispersion gradient GRE signal, and the diffusion time of the bipolar diffusion gradient GRE signal scanning are Δ The value of the dispersion δ can be set.