CN105572613A - Magnetic resonance chemical exchange saturation transfer imaging method and magnetic resonance chemical exchange saturation transfer imaging system - Google Patents

Abstract

The invention provides a magnetic resonance chemical exchange saturation transfer imaging method and a magnetic resonance chemical exchange saturation transfer imaging system. The magnetic resonance chemical exchange saturation transfer imaging method comprises a main RF pulse generating step, applying a short-time main RF saturation pulse which lasts for a first preset time for aiming at a specific RF point, thereby generating the contrast of a magnetic resonance imaging signal; an image acquisition step, segmentally acquiring image data in a reading-out direction or/and a phase encoding direction based on the applied main RF saturation pulse by means of a segmental planar echo acquisition method; and a sub-RF pulse generating step, after one-time image data acquisition by means of the segmental planar echo acquisition method, applying a sub-RF saturation pulse which lasts for a second preset time, thereby keeping the contrast of the magnetic resonance imaging signal. The magnetic resonance chemical exchange saturation transfer imaging method and the magnetic resonance chemical exchange saturation transfer imaging system settle problems of low signal sensitivity and low imaging efficiency in existing magnetic resonance chemical exchange saturation transfer imaging technology.

Description

Magnetic resonance chemical exchange saturation transfer imaging method and system

technical field

The invention relates to magnetic resonance CEST imaging technology, in particular to a magnetic resonance chemical exchange saturation transfer imaging method and system.

Background technique

Magnetic resonance CEST imaging method (Chemical exchange saturation transfer, CEST) research began in 2000, because of its new magnetic resonance contrast mechanism, it has quickly attracted widespread attention, and has become a new sensitive way to study chemical exchange and chemical dynamics of macromolecules. The principle is to selectively apply a radiofrequency (radiofrequency, RF) pulse signal of a special resonance frequency to saturate the corresponding protons (as shown in Figure 1(a), poolB), and these protons will interact with the surrounding water molecules ( As shown in Figure 1(a), poolA) undergoes chemical exchange, and then part of the saturation is transferred to water molecules, and the strength of the CEST effect is reflected by detecting the decrease in the signal of water molecules (as shown in Figure 1(b)). The loss of proton signal is significantly amplified by the chemical exchange process that occurs during saturation pulse application, thus making CEST contrast more sensitive than direct observation of these protons using magnetic resonance spectroscopy. Compared with other magnetic resonance contrast mechanisms, such as T1, T2 and diffusion weighted imaging, CEST can explore molecular targets containing exchangeable protons at a certain frequency, and is very sensitive to the internal metabolic substances and microenvironment of organisms. It is a unique molecular imaging method. Since chemical exchange is closely related to the physiological environment of biological tissues, CEST can be used to image many important physiological parameters such as intracellular and intracellular acid-base balance, metabolic characteristics, etc., in the detection and evaluation of metabolic disorders, tissue ischemia and other key role in disease.

Based on the existing magnetic resonance imaging technology, the change of CEST signal contrast of abnormal tissue is usually only about 3%-4%, so most of the current CEST research is carried out on ultra-high field (≥4.7T) magnetic resonance. Because the ultra-high field has a more excellent signal-to-noise ratio, it can effectively improve the detection sensitivity of the CEST signal, which is conducive to obtaining better image quality with fewer repeated acquisition times, and the problem of low imaging efficiency can be alleviated to a certain extent. However, the field strength of the mainstream magnetic resonance system currently used clinically is 3T, and the signal-to-noise ratio drops significantly. Therefore, the main disadvantages of the existing CEST imaging technology on the 3T MRI system include:

First, scanning efficiency is limited. In order to improve the signal-to-noise ratio, it is necessary to greatly increase the number of repeated acquisitions, which brings about the problem of too long scanning time, which greatly restricts the temporal and spatial resolution of the image, affects the image quality, and drags down the imaging efficiency. At the same time, it is not conducive to patient cooperation and Clinically widely used.

Second, the signal sensitivity is low. At present, techniques such as single-excitation gradient echo are usually used for data acquisition. Although the imaging speed can be improved to a certain extent, the longer echo chain, the signal attenuation is faster, and the signal-to-noise ratio is affected.

Based on the determinations in the prior art, the corresponding technology needs to be further improved.

Contents of the invention

Based on this, it is necessary to provide a magnetic resonance chemical exchange saturation transfer imaging method and system for the problems of limited signal sensitivity and low imaging efficiency in the existing magnetic resonance chemical exchange saturation transfer imaging technology.

A magnetic resonance chemical exchange saturation transfer imaging method, comprising:

Main radio frequency pulse generating step: apply a short-time main radio frequency saturation pulse lasting for a first preset time to a specific radio frequency point, so as to generate the contrast of the magnetic resonance imaging signal;

Image collection step: based on the applied main radio frequency saturation pulse, using a segmented echo-planar acquisition method, segmented acquisition of image data along the readout direction or/and phase encoding direction;

The step of generating the secondary radio frequency pulse: after acquiring the image data once by using the segmental echo planar acquisition method, applying a secondary radio frequency saturation pulse lasting for a second preset time, so as to maintain the contrast of the magnetic resonance imaging signal.

In one embodiment, the first preset time is 4-6 seconds.

In one embodiment, the second preset time is 1-2 seconds.

In one of the embodiments, the method further includes: multiple acquisition steps for repeatedly executing the image acquisition step and the secondary radio frequency pulse generation step until the entire image acquisition is completed.

In one of the embodiments, the method further includes: repeatedly executing the image acquisition step, the secondary radio frequency pulse generation step and the multiple acquisition steps in sequence until the multi-layer imaging of the specific radio frequency point is completed The layer scan steps of the scan.

In one of the embodiments, the method further includes: repeatedly executing the image acquisition step, the secondary radio frequency pulse generation step, the multiple acquisition step and the layer scanning step in sequence to perform multiple scans to obtain images Data rescan step.

In one of the embodiments, the method further includes: after each multi-slice imaging scan is performed, adjusting the frequency of the main radio frequency saturation pulse, and then repeatedly performing the steps of generating the main radio frequency pulse, the image acquisition step, the sub-radio frequency pulse generation step, the multiple acquisition step, the layer scanning step and the re-scanning step until the number of scans set by the multi-slice imaging scan is completed.

In one of the embodiments, in the method, a preset recovery time is given before each multi-slice imaging scan.

Based on the above method, the present invention also provides a magnetic resonance chemical exchange saturation transfer imaging system, which includes:

The main radio frequency pulse generation module is used to apply a short-time main radio frequency saturation pulse lasting for a first preset time to a specific radio frequency point, so as to generate the contrast of the magnetic resonance imaging signal;

An image acquisition module, configured to acquire image data in segments along the readout direction or/and phase encoding direction by using a segmented echo-planar acquisition method based on the applied main radio frequency saturation pulse;

The sub-radio frequency pulse generating module is used to apply a sub-radio frequency saturation pulse lasting for a second preset time after the image data is acquired by the segmental echo planar acquisition method, so as to maintain the contrast of the magnetic resonance imaging signal .

In one embodiment, the first preset time is 4-6 seconds.

In one embodiment, the second preset time is 1-2 seconds.

The imaging method and system of the present invention is a CEST imaging technology combined with a segmented (Segmented) echo planar imaging (Echoplanar imaging, EPI) acquisition method. First apply a primary RF saturation pulse to generate CEST contrast, then use a segmented EPI method in the readout direction or/and phase-encode direction to acquire partial k-space data, and then apply a secondary RF saturation pulse of shorter duration Keep the CEST contrast, repeat the EPI data acquisition and the sub-RF saturation pulse to maintain the CEST steady state, until the acquisition of the entire image is completed. The invention can effectively improve the intensity of the CEST signal, reduce the number of scanning repetitions, and further improve the scanning efficiency; can effectively improve the signal-to-noise ratio of the CEST signal, is beneficial to the improvement of the sensitivity of the CEST signal, and can effectively reduce distortion and improve image quality at the same time.

Description of drawings

Figure 1(a) is a schematic diagram of CEST chemical exchange, and Figure 1(b) is the curve of the signal intensity of water molecules changing with the saturation shift;

2 is a schematic flow chart of the magnetic resonance chemical exchange saturation transfer imaging method of the present invention;

3 is a sequence diagram of an optimal embodiment of the imaging method of the present invention, wherein gc represents a damage gradient, gs represents a layer selection gradient, gp represents a phase encoding gradient, gr represents a readout gradient, and Rf represents a radio frequency pulse;

FIG. 4 is a schematic flow diagram of an optimal embodiment of the imaging method of the present invention;

Fig. 5 is a structural schematic diagram of the magnetic resonance chemical exchange saturation transfer imaging system of the present invention;

FIG. 6 is a schematic structural diagram of an optimized embodiment of the imaging system of the present invention;

FIG. 7 is a schematic structural diagram of another optimized embodiment of the imaging system of the present invention.

detailed description

Based on the magnetic resonance chemical exchange saturation transfer imaging technology, the present invention proposes a CEST imaging technology combined with a segmented (Segmented) echo planar imaging (Echoplanar imaging, EPI) acquisition method on the basis of the traditional technology. The present invention utilizes the segmented EPI sequence data acquisition method to effectively increase the strength of the CEST signal, thereby reducing the number of scanning repetitions, thereby improving scanning efficiency; meanwhile, it can effectively improve the signal-to-noise ratio of the CEST signal, which is beneficial to the improvement of the sensitivity of the CEST signal, and at the same time Can effectively reduce distortion and improve image quality. Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 2 and Figure 3, the present invention provides a magnetic resonance chemical exchange saturation transfer imaging method, which comprises the following steps:

Main radio frequency pulse generation step 100: applying a short-time main radio frequency saturation pulse RF lasting for a first preset time Ts1 to a specific radio frequency point, so as to generate the contrast of the magnetic resonance imaging signal;

Image acquisition step 200: Based on the above-mentioned applied main radio frequency saturation pulse, using the segmented planar echo acquisition method, segmented acquisition of image data along the readout direction or/and phase encoding direction, each data acquisition time is Ti;

Step 300 of generating a secondary radio frequency pulse: after acquiring image data Ti for one time using the segmental echo planar acquisition method, applying a secondary radio frequency saturation pulse lasting for a second preset time Ts2 to maintain the contrast of the magnetic resonance imaging signal .

In the above embodiment, the first preset time is preferably 4-6 seconds, and the optimal setting is 5 seconds. The above-mentioned second preset time is preferably 1-2 seconds, and the optimal setting is 1 second.

Based on the above-mentioned various embodiments, as shown in FIG. 2 and FIG. 3 , the magnetic resonance chemical exchange saturation transfer imaging method of this embodiment further includes: a multiple acquisition step 400, which is used to repeatedly perform the above-mentioned image acquisition steps 200 and The above-mentioned secondary radio frequency pulse generation step 300 until the entire image acquisition is completed. As shown in Figure 2, the multiple collection step 400 herein preferably performs the following steps:

Execution step 401: judging whether the acquisition of the entire image is completed; if not, repeat the above image acquisition step 200 and the above secondary radio frequency pulse generation step 300 until the entire image acquisition is completed;

If yes, execute step 402: output and save the entire image obtained by the current scan.

In this embodiment, judging whether to complete the acquisition of the entire image can be judged by setting the number of scans of a single image, such as judging whether the number of scans of the entire image has been completed, and if so, it can be determined that the acquisition of the entire image has been completed . Of course, the present invention is not limited to only adopting this method for judging, and other methods may also be used.

Based on the above-mentioned various embodiments, as shown in FIG. 2 and FIG. 3 , the magnetic resonance chemical exchange saturation transfer imaging method of this embodiment further includes: a layer scanning step 500, which is used to repeatedly execute the above-mentioned image acquisition step 200, the above-mentioned times The radio frequency pulse generating step 300 and the above multiple acquisition steps 400 until the multi-layer imaging scanning of the above specific radio frequency point is completed. As shown in FIG. 2, the layer scanning step 500 here preferably performs the following steps:

Execution step 501: judging whether the preset number of layers of the multi-layer imaging scan has been completed, if not, repeating the above-mentioned image acquisition step, the above-mentioned secondary radio frequency pulse generation step and the above-mentioned multiple acquisition steps until the above-mentioned specific radio frequency point is completed. multi-layer imaging scan;

If yes, execute step 502: output and save the image data obtained by the multi-slice imaging scan for image reconstruction.

The preset number of layers in this example can be determined according to the nature of the object to be scanned and the scanned part, or the configuration of the scanning instrument. This embodiment is based on multi-layer imaging and scanning based on single-layer scanning and imaging. By increasing the number of detector layers to obtain higher spatial resolution and scanning speed, the imaging efficiency and image resolution can be effectively improved.

Based on the above-mentioned various embodiments, as shown in FIG. 2 , the magnetic resonance chemical exchange saturation transfer imaging method of this embodiment further includes: a re-scanning step 600, which is used to repeatedly execute the above-mentioned image acquisition step 200, the above-mentioned secondary radio frequency pulse The generation step 300, the above-mentioned multi-acquisition step 400 and the above-mentioned layer scanning step 500 perform multiple scans to acquire image data. As shown in Figure 2, the re-scanning step 600 here preferably performs the following steps:

Execute step 601: determine whether the number of scans set by the multi-layer imaging scan is completed, if not, repeat the above-mentioned image acquisition step 200, the above-mentioned secondary radio frequency pulse generation step 300, the above-mentioned multiple acquisition step 400 and the above-mentioned layer scanning step 500 for multiple times scan to obtain image data;

If yes, then output and save the image data obtained by multiple scans.

In this embodiment, the image signal-to-noise ratio can be improved by implementing multiple multi-layer imaging scans.

Based on the above-mentioned various embodiments, as shown in FIG. 4 and FIG. 3 , the magnetic resonance chemical exchange saturation transfer imaging method of this embodiment further includes performing the following step 700: after each multi-slice imaging scan is performed, adjust the above-mentioned main radio frequency saturation pulse frequency, and then repeatedly execute the above-mentioned main radio frequency pulse generation step 100, the above-mentioned image acquisition step 200, the above-mentioned secondary radio frequency pulse generation step 300, the above-mentioned multiple acquisition step 400, the above-mentioned layer scanning step 500 and the above-mentioned re-scanning step 600 until Complete the number of scans set for the multislice imaging scan. In this embodiment, the frequency of the main radio frequency saturation pulse can be adjusted (the frequency of the main radio frequency saturation pulse can be decreased or increased by the gradient) in combination with the segmented planar echo acquisition method to realize the acquisition of image data.

Based on the above-mentioned various embodiments, as shown in Fig. 2, Fig. 4 and Fig. 3, the magnetic resonance chemical exchange saturation transfer imaging method of this embodiment further includes: step 101, giving a certain preset before performing each multi-layer imaging scan The recovery time Tr makes the longitudinal magnetization vector fully recover, and ensures that the longitudinal magnetization vector collected at each radio frequency point is at the same level.

The method of the present invention uses the segmented EPI sequence data acquisition method to perform multi-layer imaging scanning of image data, and also uses the gradient to adjust the frequency of the main radio frequency saturation pulse to adjust the attributes of each scan, thereby obtaining more comprehensive image data for use in Subsequent image reconstruction calculations. In the method of the present invention, as shown in Figure 2, the number of times the main radio frequency saturation pulse needs to be repeated=the number of radio frequency offset points, and the number of times the secondary radio frequency saturation pulse needs to be repeated=the preset number of layers of the multi-layer imaging scan×multi-layer imaging For the set number of scans, since Ts2<<Ts1<Ts, the overall scan time is greatly shortened and the imaging efficiency is significantly improved.

Based on the imaging methods of the foregoing embodiments, the present invention also provides a magnetic resonance chemical exchange saturation transfer imaging system 1, as shown in FIG. 5 , which includes:

The main radio frequency pulse generation module 11 is used to apply a short-time main radio frequency saturation pulse lasting for a first preset time to a specific radio frequency point, so as to generate the contrast of the magnetic resonance imaging signal;

The image acquisition module 12 is configured to acquire image data in segments along the readout direction or/and phase encoding direction by using the segmented planar echo acquisition method based on the applied main radio frequency saturation pulse;

The sub-radio frequency pulse generation module 13 is used to apply a sub-radio frequency saturation pulse lasting for a second preset time after the acquisition of image data by the segmental echo planar acquisition method, so as to maintain the contrast of the above-mentioned magnetic resonance imaging signal . In this embodiment, the above-mentioned first preset time is preferably 4-6 seconds, and the optimal setting is 5 seconds. The above-mentioned second preset time is preferably 1-2 seconds, and the optimal setting is 1 second.

Based on the imaging system of the above-mentioned embodiment, as shown in FIG. 6, the imaging system of this embodiment also includes:

Multiple acquisition module 14 is used to judge whether to complete the acquisition of the entire image; otherwise, repeatedly call the image acquisition module 12 and the secondary radio frequency pulse generation module 13 until completing the entire image acquisition; if so, then output and save the current time scan the entire image;

Based on the imaging system of the above-mentioned embodiment, as shown in FIG. 6, the imaging system of this embodiment also includes:

The layer scanning module 15 is used to judge whether the preset number of layers of multi-layer imaging scanning has been completed, if not, then repeatedly call the image acquisition module 12, the secondary radio frequency pulse generation module 13 and the above-mentioned multiple acquisition module 14 in sequence Until the multi-layer imaging scanning of the above-mentioned specific radio frequency point is completed; if yes, output and save the image data obtained by the multi-layer imaging scanning.

Based on the imaging system of the above-mentioned embodiment, as shown in FIG. 6, the imaging system of this embodiment also includes:

The re-scan module 16 is used to judge whether the number of scans set by the multi-layer imaging scan is completed, otherwise, the image acquisition module 12, the secondary radio frequency pulse generation module 13, the above-mentioned multiple acquisition module 14 and the above-mentioned The layer scanning module 15 performs multiple scans to obtain image data; if yes, output and save the image data obtained by multiple scans.

Based on the imaging system of the above-mentioned embodiment, as shown in FIG. 7, the imaging system of this embodiment also includes:

The adjustment module 17 is used to adjust the frequency of the above-mentioned main radio frequency saturation pulse after each multi-layer imaging scan is performed, and then repeatedly call the above-mentioned main radio frequency pulse generation module 11, the above-mentioned image acquisition module 12, and the above-mentioned secondary radio frequency pulse generation module. 13. The above multiple acquisition module 14, the above layer scanning module 15 and the above rescan module 16 until the number of scans set by the multi-layer imaging scan is completed. In this embodiment, the frequency of the main radio frequency saturation pulse can be adjusted in gradient to realize the acquisition of image data in combination with the segmented planar echo acquisition method.

Based on the above-mentioned various embodiments, as shown in Fig. 2, Fig. 4 and Fig. 3, the magnetic resonance chemical exchange saturation transfer imaging system of this embodiment further includes: a timing module, which is used to give a certain amount of time before performing each multi-layer imaging scan. The recovery time Tr is preset so that the longitudinal magnetization vector is fully recovered, ensuring that the longitudinal magnetization vector collected at each radio frequency point is at the same level.

For the specific implementation methods of each functional unit of the imaging system in each of the above embodiments, refer to the relevant description of the imaging method above.

Through the description of the above embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus a necessary general-purpose hardware platform, and of course also by hardware, but in many cases the former is better implementation. Based on this understanding, the essence of the technical solution of the present invention or the part that contributes to the prior art can be embodied in the form of software products, and the computer software products are stored in a non-volatile computer-readable storage medium (such as ROM, magnetic disk, optical disk), including several instructions to make a terminal device (which can be a mobile phone, computer, server, or network device, etc.) execute the system structure and method described in various embodiments of the present invention.

In the method and system of the present invention, after the main radio frequency saturation pulse is applied, the segmental EPI method in the readout direction or/and phase encoding direction is used to collect data; Sub-RF saturation pulses of shorter duration maintain CEST contrast, thereby improving scanning efficiency and signal sensitivity, increasing signal-to-noise ratio, and improving image quality.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. a magnetic resonance chemical exchange saturation transfer formation method, it comprises:

Main radio-frequency pulse generating step: apply the main in short-term radio frequency saturation pulse that continues the first Preset Time, to produce the contrast of magnetic resonance imaging signal for particular radio-frequency point;

Image acquisition step: based on the described main radio frequency saturation pulse applied, utilize sectional plan echo acquirement method, along readout direction or/and phase-encoding direction piecewise acquisition view data;

Secondary radio-frequency pulse generating step: utilizing after sectional plan echo acquirement method carries out the collection of a view data, apply the secondary radio frequency saturation pulse that continues the second Preset Time, in order to keep the contrast of described magnetic resonance imaging signal.

2. magnetic resonance chemical exchange saturation transfer formation method according to claim 1, is characterized in that, described first Preset Time is 4-6 second, and described second Preset Time is 1-2 second.

3. magnetic resonance chemical exchange saturation transfer formation method according to claim 1, it is characterized in that, described method also comprises: for repeatedly repeating described image acquisition step and described radio-frequency pulse generating step until complete the multi collect step that entire image gathers.

4. magnetic resonance chemical exchange saturation transfer formation method according to claim 3, it is characterized in that, described method also comprises: for repeating described image acquisition step, described radio-frequency pulse generating step and described multi collect step successively until complete the layer scanning step of described particular radio-frequency point being carried out to multilayer imaging scanning.

5. magnetic resonance chemical exchange saturation transfer formation method according to claim 4, is characterized in that,

Described method also comprises: for repeating described image acquisition step successively, described radio-frequency pulse generating step, described multi collect step and described layer scanning step carry out the weight time scanning step that Multiple-Scan obtains view data.

6. magnetic resonance chemical exchange saturation transfer formation method according to claim 5, it is characterized in that, described method also comprises: after executing multilayer imaging scanning each time, adjust the frequency of described main radio frequency saturation pulse, then repeat described main radio-frequency pulse generating step, described image acquisition step, described radio-frequency pulse generating step, described multi collect step, described layer scanning step and described heavy scanning step successively until complete the scanning times of multilayer imaging scanning setting.

7. magnetic resonance chemical exchange saturation transfer formation method according to claim 6, is characterized in that, in the process, before carrying out multilayer imaging scanning each time, gives default release time.

8. a magnetic resonance chemical exchange saturation transfer imaging system, it is characterized in that, described system comprises:

Main radio-frequency pulse generation module, for applying the main in short-term radio frequency saturation pulse that continues the first Preset Time for particular radio-frequency point, to produce the contrast of magnetic resonance imaging signal;

Image capture module, for based on the described main radio frequency saturation pulse applied, utilizes sectional plan echo acquirement method, along readout direction or/and phase-encoding direction piecewise acquisition view data;

Secondary radio-frequency pulse generation module, for utilizing after sectional plan echo acquirement method carries out the collection of a view data, applies the secondary radio frequency saturation pulse that continues the second Preset Time, in order to keep the contrast of described magnetic resonance imaging signal.

9. magnetic resonance chemical exchange saturation transfer imaging system according to claim 8, is characterized in that, described first Preset Time is 4-6 second.

10. magnetic resonance chemical exchange saturation transfer imaging system according to claim 8, is characterized in that, described second Preset Time is 1-2 second.