System and method for flip angle determination in magnetic resonance imaging

• US 10,324,153 B2
• Filed: 03/02/2017
• Issued: 06/18/2019
• Est. Priority Date: 08/21/2015
• Status: Active Grant

• Current Assignee: Shanghai United Imaging Healthcare Co., Ltd.
• Original Assignee: Shanghai United Imaging Healthcare Co., Ltd.
• Inventors: Li, Guobin, Wang, Chaohong
• Primary Examiner(s): Patel, Rishi R
• Application Number:
  US15/447,390
• Publication Number:
  US 20170176562A1
• Time in Patent Office: 838 Days
• CPC Class Codes: A61B 2576/026 for the brain
• CPC Class Codes: A61B 5/0042 for the brain
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/4244 liver
• CPC Class Codes: A61B 5/425 pancreas
• CPC Class Codes: A61B 5/4519 Muscles A61B5/389, A61B5/224 take precedence
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take precedence
• CPC Class Codes: A61B 5/4566 Evaluating the spine A61B5/4561 takes precedence
• CPC Class Codes: A61B 5/4571 Evaluating the hip
• CPC Class Codes: A61B 5/4585 Evaluating the knee
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01R 33/288 Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room
• CPC Class Codes: G01R 33/4808 Multimodal MR, e.g. MR combined with positron emission tomography [PET], MR combined with ultrasound or MR combined with computed tomography [CT]
• CPC Class Codes: G01R 33/543 Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription G01R33/546 takes precedence
• CPC Class Codes: G01R 33/5615 Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
• CPC Class Codes: G01R 33/5617 using RF refocusing, e.g. RARE
• CPC Class Codes: G16H 30/40 for processing medical images, e.g. editing

Abstract

A system and method for calculating a flip angle schedule is provided. The technique includes selecting an initial condition, providing a function for calculating flip angles, calculating flip angles, assessing the flip angles, and repeating the calculation of the flip angles by adjusting the function until a desired flip angle schedule is obtained.

Claims

1. A magnetic resonance imaging (MRI) system comprising:

an MRI scanner, a control unit, and a processing unit, wherein

the processing unit is configured to determine a flip angle schedule corresponding to an echo train having a plurality of phases by performing operations comprising;

for each phase of the plurality of phases of the echo train,

a) determining an initial condition relating to the phase, the initial condition including initial values of a starting flip angle of the phase, an ending flip angle of the phase, a spin echo number of the phase, and a characteristic parameter of the phase;

b) determining a function corresponding to the phase, the function relating to the starting flip angle of the phase, the ending flip angle of the phase, the spin echo number of the phase, and the characteristic parameter of the phase;

c) calculating, based on the function, one or more flip angles corresponding to one or more spin echoes of the phase;

d) assessing the one or more flip angles of the phase according to a criterion; and

e) if the criterion is not satisfied, revising the function by adjusting at least one of the starting flip angle, the ending flip angle, the spin echo number, or the characteristic parameter, and repeating (c) and (d);

wherein the function provides a portion of the flip angle schedule corresponding to the phase of the echo train for MRI, and

the control unit is configured to control the MRI scanner according to the flip angle schedule,

wherein the function includes;

2. The MRI system of claim 1, wherein the assessing of the one or more flip angles of each phase comprises:

calculating, based on the one or more flip angles of each phase, a signal evolution; and

evaluating the signal evolution according to the criterion.

3. The MRI system of claim 2, wherein

the criterion comprises a threshold, and

the assessing of the one or more flip angles of each phase comprises determining whether a maximum signal in the signal evolution equals to or exceeds the threshold.

4. The MRI system of claim 1, wherein the processing unit further performs:

(f) providing a reference signal schedule corresponding to each phase, the reference signal schedule comprising one or more reference signals corresponding to the one or more spin echoes of each phase.

5. The MRI system of claim 4, wherein the assessing of the one or more flip angles of each phase comprises:

calculating, based on the one or more flip angles of each phase, a first signal evolution; and

comparing the first signal evolution with the reference signal schedule.

6. The MRI system of claim 4, wherein the reference signal schedule relating to T1 or T2 of a tissue to be imaged uses the flip angle schedule corresponding to each phase of the echo train for magnetic resonance imaging.

7. The MRI system of claim 1, wherein the starting flip angle of each phase is the same as the initial value of the ending flip angle or the adjusted ending flip angle of the previous phase.

8. A method for determining a flip angle schedule corresponding to an echo train having a plurality of phases, comprising:

for each phase of the plurality of phases of the echo train,

a) determining an initial condition relating to the phase, the initial condition including initial values of a starting flip angle of the phase, an ending flip angle of the phase, a spin echo number of the phase, and a characteristic parameter of the phase;

b) determining a function corresponding to the phase, the function relating to the starting flip angle of the phase, the ending flip angle of the phase, the spin echo number of the phase, and the characteristic parameter of the phase;

c) calculating, based on the function, one or more flip angles corresponding to one or more spin echoes of the phase;

d) assessing the one or more flip angles of the phase according to a criterion; and

e) if the criterion is not satisfied, revising the function by adjusting at least one of the starting flip angle, the ending flip angle, the spin echo number, or the characteristic parameter, and repeating (c) and (d);

wherein the function provides a portion of the flip angle schedule corresponding to the phase of the echo train for MRI,

wherein the function includes;

9. The method of claim 8, wherein the assessing of the one or more flip angles of each phase comprises:

calculating, based on the one or more flip angles of each phase, a signal evolution; and

evaluating the signal evolution according to the criterion.

10. The method of claim 9, wherein the calculating of the signal evolution comprises using the Bloch equation or the EPG algorithm.

11. The method of claim 9, wherein

the criterion comprises a threshold, and

the assessing of the one or more flip angles of each phase comprises determining whether a maximum signal in the signal evolution equals to or exceeds the threshold.

12. The method of claim 8 further comprising:

(f) providing a reference signal schedule corresponding to each phase, the reference signal schedule comprising one or more reference signals corresponding to the one or more spin echoes of each phase.

13. The method of claim 12, wherein the assessing of the one or more flip angles of each phase comprises:

calculating, based on the one or more flip angles of each phase, a first signal evolution; and

comparing the first signal evolution with the reference signal schedule.

14. The method of claim 8, wherein the magnetic resonance imaging comprises T1 weighted imaging, T2 weighted imaging, or proton density weighted imaging.

15. The method of claim 8, wherein the adjusting of the at least one of the starting flip angle, the ending flip angle, or the characteristic parameter comprises using recursion, a bisection method, an exhaustive search, a greedy algorithm, a divide and conquer algorithm, a dynamic programming method, an iterative method, a branch-and-bound algorithm, or a backtracking algorithm.

16. The method of claim 8, wherein the initial condition relating to each phase comprises at least one of an echo train duration time, an echo train length, or a phase number.