阅读说明：本技术 化学交换饱和转移-磁共振成像cest-mri序列生成方法、装置及可读存储介质 (Generation method, device and readable storage medium of chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence ) 是由 张祎 吴丹 孙毅 于 2019-03-19 设计创作，主要内容包括：本发明提供化学交换饱和转移-磁共振成像CEST-MRI序列生成方法、装置及可读存储介质。方法包括：CEST-MRI扫描过程开始,MRI设备生成CEST预饱和脉冲并发射出去；CEST预饱和脉冲发射完毕,MRI设备生成脂肪压制脉冲并发射出去；脂肪压制脉冲发射完毕,MRI设备生成一个激励脉冲并发射出去；激励脉冲发射完毕,MRI设备生成多个非层面选择性重聚焦方波脉冲并发射出去。本发明提高了CEST-MRI成像的空间覆盖率和MR信号采集速度。(The invention provides a method and a device for generating a chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence and a readable storage medium. The method comprises the following steps: starting a CEST-MRI scanning process, generating a CEST pre-saturation pulse by an MRI device and transmitting the CEST pre-saturation pulse; after CEST pre-saturation pulse transmission is finished, the MRI equipment generates fat suppression pulse and transmits the fat suppression pulse; after the fat suppression pulse is transmitted, the MRI equipment generates an excitation pulse and transmits the excitation pulse; after the excitation pulse is transmitted, the MRI equipment generates a plurality of non-layer selective refocusing square wave pulses and transmits the pulse. The invention improves the space coverage rate of CEST-MRI imaging and the MR signal acquisition speed.)

1. The method for generating the CEST-MRI sequence through chemical exchange saturation transfer-magnetic resonance imaging is characterized by comprising the following steps:

starting a CEST-MRI scanning process, generating a CEST pre-saturation pulse by an MRI device and transmitting the CEST pre-saturation pulse;

after CEST pre-saturation pulse transmission is finished, the MRI equipment generates fat suppression pulse and transmits the fat suppression pulse;

after the fat suppression pulse is transmitted, the MRI equipment generates an excitation pulse and transmits the excitation pulse;

after the excitation pulse is transmitted, the MRI equipment generates a plurality of non-layer selective refocusing square wave pulses and transmits the pulse.

2. The method of claim 1, wherein the CEST pre-saturation pulse and the fat suppression pulse are both non-slice selective pulses.

3. The method of claim 1, wherein the excitation pulse is a square wave pulse or a non-square wave pulse.

4. The method of claim 1 or 3, wherein the number of refocusing square wave pulses is 50 ≦ 250;

the width of the refocusing square wave pulse is not less than 0.8ms and not more than 1.5 ms;

the interval between adjacent refocusing square wave pulses is less than or equal to 2ms and less than or equal to 5 ms.

5. The method of claim 1, wherein the flip angles of all refocusing square pulses are the same;

alternatively, the flip angles of the individual refocused square pulses are solved using the bloch equation for the T1 and T2 values of the imaged tissue and the k-space signal intensity profile to be achieved.

6. The method of claim 1, wherein the MRI apparatus generates and transmits an excitation pulse;

after the excitation pulse is transmitted, the MRI device generates a plurality of non-layer selective refocusing square wave pulses and transmits the refocusing square wave pulses to comprise:

the MRI device generates and transmits a perfectly sampled SPACE sequence with variable flip angles that optimizes contrast.

7. A chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence generation apparatus (80) located on an MRI device, characterized in that the apparatus comprises:

a pre-saturation pulse generation and emission module (81) for generating and emitting a pre-saturation pulse when a CEST-MRI scanning process starts;

the fat pressing pulse generating and transmitting module (82) is used for generating and transmitting the fat pressing pulse after the pre-saturation pulse is transmitted;

and the excitation and refocusing pulse generation and emission module (83) is used for generating and emitting an excitation pulse after the fat suppression pulse is emitted, and generating and emitting a plurality of non-layer selective refocusing square wave pulses after the excitation pulse is emitted.

8. The apparatus (80) of claim 7, wherein the pre-saturation pulse generated and transmitted by the pre-saturation pulse generation and transmission module (81) is a non-slice selective pulse;

the fat suppression pulses generated and emitted by the fat suppression pulse generation and emission module (82) are non-slice selective pulses.

9. The apparatus (80) according to claim 7, wherein the excitation pulse generated by said excitation and refocusing pulse generation and emission module (83) is a square wave pulse or a non-square wave pulse.

10. The apparatus (80) according to claim 7 or 9, wherein said excitation and refocusing pulse generation and emission module (83) generates refocusing square wave pulses satisfying: the number of the refocusing square wave pulses is more than or equal to 50 and less than or equal to 250, the width of the refocusing square wave pulses is more than or equal to 0.8ms and less than or equal to 1.5ms, and the interval of the refocusing square wave pulses is more than or equal to 2ms and less than or equal to 5 ms.

11. The apparatus (80) according to claim 7, wherein the excitation and refocusing pulse generation and emission module (83) generates all refocusing square wave pulses with the same flip angle;

alternatively, the flip angles of the individual refocused square pulses are solved using the bloch equation for the T1 and T2 values of the imaged tissue and the k-space signal intensity profile to be achieved.

12. The apparatus (80) according to claim 7, wherein said excitation and refocusing pulse generating and transmitting module (83) is configured to:

and generating a perfect sampling SPACE sequence with variable turning angles and optimized contrast and transmitting the perfect sampling SPACE sequence.

13. Readable storage medium having stored thereon a computer program, which when being executed by a processor carries out the steps of the method for generating a chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence as claimed in any one of the claims 1 to 6.

14. A chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence generation apparatus (90), characterized in that the apparatus comprises: a processor (91) and a memory (92);

the memory (92) has stored therein an application program executable by the processor (91) for causing the processor (91) to perform the steps of the chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence generation method as claimed in any one of claims 1 to 6.

Technical Field

The present invention relates to the field of MRI (Magnetic Resonance Imaging) technology, and in particular, to a CEST (Chemical Exchange Transfer) MRI sequence generation method, apparatus, and readable storage medium.

Background

MRI is a process in which a Radio Frequency (RF) pulse of a certain specific Frequency is applied to a human body in a static Magnetic field to excite hydrogen protons in the human body to generate a Magnetic Resonance phenomenon, and after the pulse is stopped, the protons generate MR (Magnetic Resonance) signals in a relaxation process, and an MR image is generated through processes such as reception, spatial encoding, and image reconstruction of the MR signals.

With the development of MRI technology, CEST (Chemical Exchange contamination Transfer) has become a hot spot in the MRI field. CEST is used to image solute molecules free in water at concentrations many orders of magnitude less than water molecules. Since the hydrogen nuclei in these solute molecules are in different chemical environments, the resonance frequency shifts slightly compared to the hydrogen nuclei of water molecules even under the same external magnetic field, and such shifts are called chemical shifts. In CEST studies, solute molecules constitute a collection, called a pool of solutes; while the free water molecules are called pools. When a pre-saturation RF pulse is applied to the resonance frequency of the solute pool, the hydrogen protons in the solute pool are saturated, chemical exchange then occurs in both pools, resulting in the transfer of the hydrogen protons in the saturated solute pool to the pool, replacing the hydrogen protons in the unsaturated pool, and over a period of time, the signal collected in the pool during imaging will produce additional attenuation from which many important physiological parameters can be estimated.

In an actual CEST imaging experiment, pre-saturation radio frequency pulses are not only applied to the resonance frequency of a solute pool, but a large number of frequency points are selected on a frequency axis in a certain range to apply the pulses, MRI signals of the water pool are respectively acquired at each frequency point after saturation, due to the existence of a chemical exchange saturation transfer mechanism, the MRI signals have obvious attenuation compared with the signals without the pre-saturation pulses, and information of CEST contrast agents is analyzed according to the attenuation quantitiveness, so that some important physiochemical parameters or structural information of an imaging area is obtained.

To apply CEST imaging to routine clinics, the spatial coverage and MR signal acquisition speed must meet certain conditions, and in addition, the final CEST image needs to be substantially artifact-free.

Disclosure of Invention

In order to solve the problems, the invention provides a CEST-MRI sequence generation method to improve the space coverage rate of CEST-MRI imaging and the MR signal acquisition speed;

the invention also provides a CEST-MRI sequence generating device to improve the space coverage rate of CEST-MRI imaging and the MR signal acquisition speed;

the invention also provides a readable storage medium to improve the spatial coverage of CEST-MRI imaging and the MR signal acquisition speed.

In order to achieve the purpose, the invention provides the following technical scheme:

a method for generating a chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) sequence comprises the following steps:

starting a CEST-MRI scanning process, generating a CEST pre-saturation pulse by an MRI device and transmitting the CEST pre-saturation pulse;

after CEST pre-saturation pulse transmission is finished, the MRI equipment generates fat suppression pulse and transmits the fat suppression pulse;

after the fat suppression pulse is transmitted, the MRI equipment generates an excitation pulse and transmits the excitation pulse;

after the excitation pulse is transmitted, the MRI equipment generates a plurality of non-layer selective refocusing square wave pulses and transmits the pulse.

By adopting the embodiment, the space coverage rate of CEST-MRI imaging and the MR signal acquisition speed are improved by adopting the non-layer selective refocusing square wave pulse.

The CEST pre-saturation pulse and the fat suppression pulse are both non-slice selective pulses.

The excitation pulse is a square wave pulse or a non-square wave pulse.

The number of refocusing square wave pulses is more than or equal to 50 and less than or equal to 250;

the width of the refocusing square wave pulse is not less than 0.8ms and not more than 1.5 ms;

the interval between adjacent refocusing square wave pulses is less than or equal to 2ms and less than or equal to 5 ms.

Through the embodiment, the refocusing square-wave pulse with shorter width and gap is adopted, and the MR signal acquisition speed is improved.

The turning angles of all the refocusing square wave pulses are the same;

alternatively, the flip angles of the individual refocused square pulses are solved using the bloch equation for the T1 and T2 values of the imaged tissue and the k-space signal intensity profile to be achieved.

Through the embodiment, when the refocusing square wave pulses with different turning angles are adopted, the time existing on the transverse shaft during the acquisition of the MR signals is prolonged, the number of refocusing is increased, and the acquisition speed of the MR signals is accelerated.

The MRI device generates and transmits an excitation pulse;

after the excitation pulse is transmitted, the MRI device generates a plurality of non-layer selective refocusing square wave pulses and transmits the refocusing square wave pulses to comprise:

the MRI device generates and transmits a variable flip angle perfectly Sampled (SPACE) sequence that optimizes contrast.

Through the embodiment, the SPACE sequence is adopted, so that the SPACE coverage rate of CEST-MRI imaging and the MR signal acquisition speed can be improved, and susceptibility artifacts can be obviously reduced.

A chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence generating apparatus located on an MRI device, the apparatus comprising:

the pre-saturation pulse generation and emission module starts a CEST-MRI scanning process, generates a pre-saturation pulse and emits the pre-saturation pulse;

the fat pressing pulse generating and transmitting module is used for generating and transmitting the fat pressing pulse after the pre-saturation pulse is transmitted;

and the excitation and refocusing pulse generation and emission module generates and emits an excitation pulse after the fat suppression pulse is emitted, and generates and emits a plurality of non-layer selective refocusing square wave pulses after the excitation pulse is emitted.

The pre-saturation pulse generated and transmitted by the pre-saturation pulse generating and transmitting module is a non-layer selective pulse;

the fat suppression pulse generated and transmitted by the fat suppression pulse generation and transmission module is a non-layer selective pulse.

The excitation pulse generated by the excitation and refocusing pulse generation and emission module is a square wave pulse or a non-square wave pulse.

The refocusing square wave pulse generated by the excitation and refocusing pulse generation and emission module meets the following requirements: the number of the refocusing square wave pulses is more than or equal to 50 and less than or equal to 250, the width of the refocusing square wave pulses is more than or equal to 0.8ms and less than or equal to 1.5ms, and the interval of the refocusing square wave pulses is more than or equal to 2ms and less than or equal to 5 ms.

The overturning angles of all refocusing square wave pulses generated by the excitation and refocusing pulse generation and emission module are the same;

alternatively, the flip angles of the individual refocused square pulses are solved using the bloch equation for the T1 and T2 values of the imaged tissue and the k-space signal intensity profile to be achieved.

The excitation and refocusing pulse generation and transmission module is used for:

a SPACE sequence is generated and transmitted.

Readable storage medium, having stored thereon a computer program which, when being executed by a processor, carries out the steps of the method for generating a chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence as set forth in any of the previous claims.

A chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence generation apparatus, the apparatus comprising: a processor and a memory;

the memory has stored therein an application program executable by the processor for causing the processor to perform the steps of the chemical exchange saturation transfer-magnetic resonance imaging CEST-MRI sequence generation method as defined in any one of the above.

According to the invention, the CEST-MRI is constructed into a CEST pre-saturation pulse, a fat suppression pulse, an excitation pulse and a plurality of non-layer selective refocusing square-wave pulses, so that the space coverage rate of the CEST-MRI imaging and the MR signal acquisition speed are improved.

Drawings

Fig. 1 is a flowchart of a CEST-MRI sequence generation method according to an embodiment of the present invention;

fig. 2 is a flowchart of a CEST-MRI sequence generation method according to another embodiment of the present invention;

fig. 3 is an exemplary illustration of a scan of brain tissue using a CEST-MRI sequence as set forth in an embodiment of the present invention;

FIG. 4 shows a sagittal source S of the brain obtained by scanning brain tissue with a CEST-MRI sequence according to an embodiment of the present invention₀An image;

FIG. 5 shows a source S according to FIG. 4₀Image-computed APTw maps of skull exfoliation;

FIG. 6 is a transverse APTw plot obtained from a scan of brain tissue using a CEST-MRI sequence according to an embodiment of the present invention;

FIG. 7 is a coronal APTw plot of brain tissue scanned using a CEST-MRI sequence in accordance with an embodiment of the present invention;

fig. 8 is a CEST-MRI sequence generation apparatus according to an embodiment of the present invention;

fig. 9 shows a CEST-MRI sequence generating apparatus according to another embodiment of the present invention.

Wherein the reference numbers are as follows:

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are described in detail below with reference to the accompanying drawings according to embodiments.

As used in the specification of the invention and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the content clearly indicates otherwise.

The present invention is described in detail below:

fig. 1 is a flowchart of a CEST-MRI sequence generation method according to an embodiment of the present invention, which includes the following specific steps:

step 101: the CEST-MRI scan process begins and the MRI device generates and emits a CEST pre-saturation pulse.

Step 102: and after the CEST pre-saturation pulse is transmitted, the MRI equipment generates and transmits a fat suppression pulse.

In practical applications, both the CEST pre-saturation pulse and the fat-suppression pulse may be non-slice-selective pulses.

Step 103: after the fat suppression pulse is transmitted, the MRI device generates an excitation pulse and transmits the excitation pulse.

Step 104: after the excitation pulse is transmitted, the MRI equipment generates a plurality of non-layer selective refocusing square wave pulses and transmits the pulse.

In practical applications, the excitation pulse may be a square wave pulse or a non-square wave pulse. When the pulse is a square wave pulse, the width of the square wave pulse may have a range of values: the width of the square wave pulse is less than or equal to 1ms and less than or equal to 0.4 ms.

In practical applications, the number and width of the refocusing square wave pulses and the spacing between adjacent pulses may be in the following ranges: the number of the refocusing square wave pulses is more than or equal to 50 and less than or equal to 250, the width of the refocusing square wave pulses is more than or equal to 0.8ms and less than or equal to 1.5ms, and the gap between adjacent refocusing square wave pulses is more than or equal to 2ms and less than or equal to 5 ms.

In practical application, the turning angle of the refocusing square wave pulse sequence is variable, that is, the turning angles of all refocusing square wave pulses can be the same and are generally set to be a certain angle between 60 ° and 180 °;

alternatively, the flip angles of all refocusing square pulses may be partially or completely different, and specifically, the flip angles of the respective refocusing square pulses are obtained by solving with Bloch (Bloch) equations for the T1 and T2 values of the imaged tissue and the k-space signal intensity distribution curve to be realized. Wherein the distribution of k-space signal intensities determines the contrast of the finally generated image.

In practical applications, the MRI apparatus may generate and transmit a SPACE (Sampling perfect with Application-optimized Contrasts by using a differential flash angle evolution, Application with variable flip angle) sequence in steps 103 and 104.

Fig. 2 is a flowchart of a CEST-MRI sequence generation method according to another embodiment of the present invention, which includes the following specific steps:

step 201: the CEST-MRI scan process begins and the MRI device generates and transmits a preset number of non-slice selective CEST pre-saturation pulses.

The type and number of CEST pre-saturation pulses, as well as the width of each pulse, and the gap between adjacent pulses, may be set according to the tissue being scanned.

The types of pulses are: gaussian pulse, square wave pulse, etc.

Fig. 3 is an exemplary illustration of a scan of brain tissue using a CEST-MRI sequence as set forth in an embodiment of the present invention. As shown in fig. 3, wherein RF represents a CEST-MRI sequence, Gx, Gy, Gz represent gradient fields of the CEST-MRI sequence in three directions of x, y, z, ADC represents a data reading sequence of the CEST-MRI sequence, and sequence 1 represents a CEST pre-saturation pulse, where the CEST pre-saturation pulse may employ 10 frequency-selective gaussian pulses with a width of 100ms (milliseconds) and a gap of 10ms, and wherein a gradient pulse with a width of 5ms and an intensity of 15mT/m (millitesla/m) may be applied in the z direction of the bedding direction within the gap of 10 ms.

Step 202: and after the CEST pre-saturation pulse is transmitted, the MRI equipment generates a preset type of non-layer selective fat suppression pulse and transmits the pulse.

The type of fat pulse may be set according to the difference in the scanned fat tissue.

For example: in scanning brain tissue, as shown in fig. 3, an SPIR (spectral prediction with Inversion Recovery) pulse may be used. Wherein, upon completion of the SPIR pulse emission, a gradient pulse may be applied in the x-direction.

Step 203: after the fat suppression pulse is transmitted, the MRI device generates and transmits a SPACE sequence.

The SPACE sequence consists of one excitation pulse and several non-slice selective refocusing pulses. Wherein, the refocusing pulse is a square wave pulse, and the turning angle is variable.

For example: in scanning brain tissue, sequence 3 in the RF sequence shown in fig. 3 is a SPACE sequence, wherein the refocusing pulse may first use four preparation pulses with flip angles of 149 °, 122 °, 119 °, and 120 °, respectively, and then use an echo pulse with a constant flip angle of 1200, wherein gradient pulses are applied in the z, x, and y directions, respectively, in the gaps between adjacent refocusing pulses.

Examples of applications of the invention are given below:

CEST-MRI scans of the brains of 5 healthy volunteers were performed with a magnetic resonance system with a magnetic field strength of 3T and a 64-channel head and neck coil.

Scan sequence the RF sequence, shown in fig. 3, consists of three parts: 1. a CEST pre-saturation sequence; 2. SPIR fat suppression pulses; 3. SPACE sequence. Wherein:

1) the CEST pre-saturation sequence consists of 10 frequency-selective Gaussian pulses with the length of 100 milliseconds, and the root-mean-square power of each pulse is 2.5 uT;

between adjacent gaussian pulses there is a gap of 10ms in which a gradient field of 5ms width and 15mT/m strength is applied.

2) The SPACE sequence has an excitation pulse and a plurality of refocusing square-wave pulses, four preparatory refocusing pulses before entering a constant 120 DEG refocusing pulse, with respective flip angles: 149 °, 122 °, 119 °, 120 °.

Parameters were acquired using MR signals with a field of view (FOV) of 212 × 212 × 201mm³The matrix size is 76 × 76 × 72, and the resolution is 2.79 × 2.79.79 2.79 × 2.79.79 mm³The repetition Time (TR) is 3S (sec), the echo Time (TE) is 17ms (millisecond), the turbo factor is 140, the GRAPPA (Generalized automatic parallel partial acquisition) factor is 2 × 2, the imaging direction is the sagittal direction, and the imaging direction is unsaturated (S) in parallel₀) And APTw (Amide Proton Transfer-weighted) imaging at saturation frequency, APT imaging being a branching technique of CEST imaging, using frequency offsets of + -3 ppm, + -3.5 ppm and + -4 ppm, and a scan duration of 5 minutes.

In addition, the brain is scanned with a gradient echo sequence to obtain a B0 field frequency shift map, where TR is 30ms and dual TE is 4.92ms and 9.84 ms. Finally, an APTw map is calculated by using the CEST image corrected by the B0 field frequency offset map.

FIG. 4 shows a source S obtained by scanning brain tissue using a CEST-MRI sequence according to an embodiment of the present invention₀Image, which is a sagittal image of the entire brain.

As can be seen from this image, no significant magnetic susceptibility artifacts are found over the entire image, even near the nasal cavity, reflecting the robustness of the CEST-MRI sequence proposed by embodiments of the present invention.

FIG. 5 shows a diagram according to the source S₀The APTw map of skull stripping calculated from the images can be seen, and after the CEST-MRI sequence provided by the embodiment of the invention is adopted, the finally obtained APTw map is a high-quality whole brain image with good uniformity, wherein a cerebellum region has a tiny artifact, which is probably caused by the less-ideal shimming of the region and is possibly improved by the region self-adaptive shimming.

Fig. 6 and 7 are graphs of APTw in the lateral and coronal directions, respectively. Also, these APTw maps are of high quality.

By means of the APTw diagrams in the sagittal direction, the transverse direction and the coronal direction, target pathology can be revealed from different directions, and the accuracy of clinical diagnosis is improved.

In addition, the duty cycle of the CEST pre-saturation sequence in the CEST-MRI sequence proposed by the embodiment of the present invention is very high, as shown in fig. 3, the duty cycle is 91%, and the high duty cycle is helpful for reaching the highest achievable CEST contrast when the scan hardware is limited.

In addition, the CEST-MRI sequence provided by the embodiment of the invention can realize 2.79mm isotropic CEST imaging of the whole brain within 5 minutes without obvious magnetic sensitivity artifacts, and the characteristic meets the condition of converting the CEST imaging into conventional clinical application.

Fig. 8 is a schematic structural diagram of a CEST-MRI sequence generation apparatus 80 according to an embodiment of the present invention, the apparatus is located on an MRI device, and the apparatus mainly includes: a pre-saturation pulse generation and transmission module 81, a fat suppression pulse generation and transmission module 82, and an excitation and refocusing pulse generation and transmission module 83, wherein:

the pre-saturation pulse generation and emission module 81 generates and emits a pre-saturation pulse at the beginning of the CEST-MRI scan process.

And the fat suppression pulse generation and transmission module 82 is used for generating and transmitting the fat suppression pulse when the pre-saturation pulse generation and transmission module 81 finishes transmitting the pre-saturation pulse.

The excitation and refocusing pulse generating and transmitting module 83 generates and transmits an excitation pulse when the fat suppression pulse generating and transmitting module 82 has transmitted the fat suppression pulse, and generates and transmits a plurality of non-layer selective refocusing square wave pulses after the excitation pulse has been transmitted.

In practical application, the pre-saturation pulse generated and transmitted by the pre-saturation pulse generating and transmitting module 81 is a non-layer selective pulse;

the fat suppression pulses generated and transmitted by the fat suppression pulse generation and transmission module 82 are non-slice selective pulses.

In practical applications, the excitation pulse generated by the excitation and refocusing pulse generation and transmission module 83 is a square wave pulse or a non-square wave pulse.

In practical applications, the refocusing square wave pulse generated by the excitation and refocusing pulse generation and transmission module 83 satisfies the following conditions: the number of the refocusing square wave pulses is more than or equal to 50 and less than or equal to 250, the width of the refocusing square wave pulses is more than or equal to 0.8ms and less than or equal to 1.5ms, and the interval of the refocusing square wave pulses is more than or equal to 2ms and less than or equal to 5 ms.

In practical application, the turning angles of all refocusing square wave pulses generated by the excitation and refocusing pulse generation and emission module 83 are the same;

alternatively, the flip angles of the individual refocused square pulses are solved using the bloch equation for the T1 and T2 values of the imaged tissue and the k-space signal intensity profile to be achieved.

In practical applications, the excitation and refocusing pulse generation and transmission module 83 is configured to: a SPACE sequence is generated and transmitted.

Fig. 9 is a schematic structural diagram of a CEST-MRI sequence generation apparatus provided in an embodiment of the present invention, where the CEST-MRI sequence generation apparatus is located on an MRI device, and the CEST-MRI sequence generation apparatus mainly includes: a processor 91 and a memory 92, wherein:

the memory 92 stores an application program executable by the processor 91 for causing the processor 91 to execute the steps of the CEST-MRI sequence generation method as described in step 101-.

An embodiment of the present invention further provides a readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the CEST-MRI sequence generation method as described in any one of steps 101-104 or steps 201-203.

The readable storage medium has stored thereon machine readable instructions which, when executed by a processor, cause the processor to perform any of the methods previously described. In particular, a system or apparatus may be provided which is provided with a readable storage medium on which software program code implementing the functionality of any of the embodiments described above is stored and which causes a computer or processor of the system or apparatus to read and execute machine-readable instructions stored in the readable storage medium.

In this case, the program code itself read from the readable storage medium can realize the functions of any of the above-described embodiments, and thus the machine-readable code and the readable storage medium storing the machine-readable code constitute a part of the present invention.

Examples of the readable storage medium include floppy disks, hard disks, magneto-optical disks, optical disks (e.g., CD-ROMs, CD-R, CD-RWs, DVD-ROMs, DVD-RAMs, DVD-RWs, DVD + RWs), magnetic tapes, nonvolatile memory cards, and ROMs. Alternatively, the program code may be downloaded from a server computer or from the cloud via a communications network.

It will be understood by those skilled in the art that various changes and modifications may be made in the above-disclosed embodiments without departing from the spirit of the invention. Accordingly, the scope of the invention should be determined from the following claims.

It should be noted that not all steps and modules in the above flows and system structure diagrams are necessary, and some steps or modules may be omitted according to actual needs. The execution order of the steps is not fixed and can be adjusted as required. The apparatus structures described in the above embodiments may be physical structures or logical structures, that is, some modules may be implemented by the same physical entity, or some modules may be implemented by a plurality of physical entities, or some components in a plurality of independent devices may be implemented together.

While the invention has been shown and described in detail in the drawings and in the preferred embodiments, it is not intended to limit the invention to the embodiments disclosed, and it will be apparent to those skilled in the art that various combinations of the code auditing means in the various embodiments described above may be used to obtain further embodiments of the invention, which are also within the scope of the invention.