SYSTEM AND METHOD FOR FLIP ANGLE DETERMINATION IN MAGNETIC RESONANCE IMAGING

• US 20170176562A1
• Filed: 03/02/2017
• Published: 06/22/2017
• 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
• Granted Patent: US 10,324,153 B2
• Time in Patent Office: 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,

the processing unit performing operations comprising;

a) selecting an initial condition relating to a first phase of an echo train, the initial condition including initial values of a first flip angle, a second flip angle, and a first characteristic parameter;

b) providing a first function corresponding to the first phase echo train, the first function relating to at least one of the first flip angle, the second flip angle, or the first characteristic parameter;

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

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

e) if the first criterion is not satisfied,

revising the first function by adjusting at least one of the first flip angle, the second flip angle, or the first characteristic parameter, and

repeating (c) and (d);

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

the control unit controlling the MRI scanner according to the flip angle schedule.

2. The MRI system of claim 1, the first function comprising a function of the spin echo number.

4. The MRI system of claim 1, the assessing of the one or more flip angles of the first phase comprising:

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

evaluating the first signal evolution according to the first criterion.

5. The MRI system of claim 4,

the first criterion comprising a first threshold, and

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

7. The MRI system of claim 1, the processing unit further performing:

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

8. The MRI system of claim 7, the assessing of the one or more flip angles of the first phase comprising:

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

comparing the first signal evolution with the reference signal schedule.

9. The MRI system of claim 7, the reference signal schedule relating to T1 or T2 of a tissue to be imaged using the flip angle schedule corresponding to the first phase of the echo train for magnetic resonance imaging.

12. The MRI system of claim 1, the processing unit further performing:

g) selecting an initial condition relating to a second phase of the echo train, the initial condition including initial values of a third flip angle, a fourth flip angle, and a second characteristic parameter;

h) providing a second function corresponding to the second phase, the second function relating to at least one of the third flip angle, the fourth flip angle, or the second characteristic parameter;

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

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

k) if the second criterion is not satisfied,

revising the second function by adjusting at least one of the third flip angle, the fourth flip angle, or the second characteristic parameter, and

repeating (i) and (j);

wherein the second function provides a flip angle schedule corresponding to the second phase of the echo train for magnetic resonance imaging.

13. The MRI system of claim 12, the third flip angle being the same as the initial value of the second flip angle or the adjusted second flip angle.

3. (canceled)

6. (canceled)

10. (canceled)

11. (canceled)

14. (canceled)

15. A method comprising:

a) selecting an initial condition relating to a first phase of an echo train, the initial condition including initial values of a first flip angle, a second flip angle, and a first characteristic parameter;

b) providing a first function corresponding to the first phase of the echo train, the first function relating to at least one of the first flip angle, the second flip angle, or the first characteristic parameter;

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

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

e) if the first criterion is not satisfied,

revising the first function by adjusting at least one of the first flip angle, the second flip angle, or the first characteristic parameter, and

repeating (c) and (d);

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

16. The method of claim 15, the first function comprising the Bloch equation, the EPG algorithm, a polynomial, a linear function, a trigonometric function, an anti-trigonometric function, an exponential function, a power function, a logarithmic function.

17. The method of claim 15, the assessing of the one or more flip angles of the first phase comprising:

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

evaluating the first signal evolution according to the first criterion.

18. The method of claim 17, the calculating of the first signal evolution comprising using the Bloch equation or the EPG algorithm.

19. The method of claim 17,

the first criterion comprising a first threshold, and

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

20. The method of claim 15 further comprising:

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

21. The method of claim 20, the assessing of the one or more flip angles of the first phase comprising:

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

comparing the first signal evolution with the reference signal schedule.

22. The method of claim 15, the magnetic resonance imaging comprising T1 weighted imaging, T2 weighted imaging, or proton density weighted imaging.

23. The method of claim 15, the adjusting of the at least one of the first flip angle, the second flip angle, or the first characteristic parameter comprising 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.

24. The method of claim 15 further comprising:

g) selecting the initial condition including initial values of a third flip angle, a fourth flip angle, and a second characteristic parameter;

h) providing a second function corresponding to a second phase, the second function relating to the third flip angle, the fourth flip angle, and the second characteristic parameter;

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

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

k) if the second criterion is not satisfied,

revising the second function by adjusting at least one of the third flip angle, the fourth flip angle, or the second characteristic parameter, and

repeating (i) and (j);

wherein the second function provides a flip angle schedule corresponding to the second phase of the echo train for magnetic resonance imaging.

25. The method of claim 15, the initial condition relating to the first phase comprising at least one of an echo train duration time, an echo train length, a phase number, or a number of echoes in the first phase.