Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions

Patent metadata

Field	Value
Publication number	US-RE47178-E
Application number	US-200114708875-A
Country	US
Kind code	E1
Filing date	Dec 21, 2001
Priority date	Dec 21, 2000
Publication date	Dec 25, 2018
Grant date	Dec 25, 2018

Abstract

A magnetic resonance imaging “MRI” method and apparatus for lengthening the usable echo-train duration and reducing the power deposition for imaging is provided. The method explicitly considers the t1 and t2 relaxation times for the tissues of interest, and permits the desired image contrast to be incorporated into the tissue signal evolutions corresponding to the long echo train. The method provides a means to shorten image acquisition times and/or increase spatial resolution for widely-used spin-echo train magnetic resonance techniques, and enables high-field imaging within the safety guidelines established by the Food and Drug Administration for power deposition in human MRI.

First claim

We claim:

1. A method for generating a spin echo pulse sequence for operating a magnetic resonance imaging apparatus for imaging an object that permits at least one of lengthening usable echo-train duration, reducing power deposition and incorporating desired image contrast into the tissue signal evolutions, said method comprising:
a) providing contrast-preparation, said contrast-preparation comprising generating at least one of at least one radio-frequency pulse, at least one magnetic-field gradient pulse, and at least one time delay, whereby said contrast preparation encodes the magnetization with at least one desired image contrast; b) calculating flip angles and phases of refocusing radio-frequency pulses that are applied in a data-acquisition step, wherein said calculation provides desired prescribed signal evolution and desired overall signal level, said calculation comprises:
i) selecting values of T1 and T2 relaxation times and selecting proton density;
ii) selecting a prescribed time course of the amplitudes and phases of the radio-frequency magnetic resonance signals that are generated by said refocusing radio-frequency pulses; and
iii) selecting characteristics of said contrast-preparation step, said data-acquisition step and a magnetization-recovery step, with the exception of the flip angles and phases of the refocusing radio-frequency pulses that are to be calculated; and
c) providing said-data acquisition step based on a spin echo train acquisition, said data-acquisition step comprises:
i) an excitation radio-frequency pulse having a flip angle and phase;
ii) at least two refocusing radio-frequency pulses, each having a flip angle and phase as determined by said calculation step; and
iii) magnetic-field gradient pulses that encode spatial information into at least one of said radio-frequency magnetic resonance signals that follow at least one of said refocusing radio-frequency pulses;
d) providing magnetization-recovery, said magnetization-recovery comprises a time delay to allow magnetization to relax; and e) repeating steps (a) through (d) until a predetermined extent of spatial frequency space has been sampled.

2. The method of claim 1 , wherein said calculation of the flip angles and phases is generated using an appropriate analytical or computer-based algorithm.

3. The method of claim 1 , wherein said calculation of the flip angles and phases is generated to account for, the effects of multiple applications of: said contrast-preparation, said data-acquisition and said magnetization-recovery steps, which are required to sample the desired extent of spatial-frequency space.

4. The method of claim 1 , wherein a two-dimensional plane of spatial-frequency space is sampled.

5. The method of claim 1 , wherein a three-dimensional volume of spatial-frequency space is sampled.

6. The method of claim 1 , wherein at least one of said contrast-preparation and magnetization-recovery steps is omitted.

7. The method of claim 1 , wherein said calculation step is performed once before one of said first contrast-preparation step and said first data-acquisition step.

8. The method of claim 1 , wherein at least one of at least one said contrast-preparation step, at least one said data-acquisition step and at least one said magnetization-recovery step is initiated by a trigger signal to synchronizes the pulse sequence with at least one of at least one external temporal event and at least one internal temporal event.

9. The method of claim 8 , wherein said external and internal events comprise at least one of at least one voluntary action, at least one involuntary action, at least one respiratory cycle and at least one cardiac cycle.

10. The method of claim 1 , wherein at least one of at least one radio-frequency pulse and at least one magnetic-field gradient pulse is applied as part of at least one of at least one said magnetization-preparation step and at least one said data-acquisition step is for the purpose of stabilizing the response of at least one of magnetization related system and said apparatus related hardware system.

11. The method of claim 1 , wherein time duration varies between repetitions for at least one of at least one said contrast-preparation step, at least one said data-acquisition step and at least one said magnetization-recovery step.

12. The method of claim 1 , wherein the time periods between consecutive refocusing radio-frequency pulses applied during said data-acquisition steps are all of equal duration.

13. The method of claim 1 , wherein time periods between consecutive refocusing radio-frequency pulses applied during said data-acquisition steps vary in duration amongst pairs of refocusing radio-frequency pulses during at least one said data-acquisition step.

14. The method of claim 1 wherein all the radio-frequency pulses are at least one of non-spatially selective and non-chemically selective.

15. The method of claim 1 , wherein at least one of the radio-frequency pulses is at least one of spatially selective in one of one, two and three dimensions, chemically selective, and adiabatic.

16. The method of claim 1 , wherein during each said data-acquisition step, the phase difference between the phase for the excitation radio-frequency pulse and the phases for all refocusing radio-frequency pulses is about 90 degrees.

17. The method of claim 1 , wherein during each data-acquisition step, the phase difference between the phase for any refocusing radio-frequency pulse and the phase for the immediately subsequent refocusing radio-frequency pulses is about 180 degrees, and the phase difference between the phase for the excitation radio-frequency pulse and the phase for the first refocusing pulse is one of about 0 degrees and about 180 degrees.

18. The method of claim 17 , wherein the flip angle for the excitation radio-frequency pulse is about one-half of the flip angle for the first refocusing radio-frequency pulse.

19. The method of claim 1 , wherein the spatial-encoding magnetic-field gradient pulses applied during each said data-acquisition step are configured so as to collect data, following each of at least one of the refocusing radio-frequency pulses, for one line in spatial-frequency space which is parallel to all other lines of data so collected, so as to collect the data using a magnetic resonance imaging technique selected from the group consisting of rapid acquisition with relaxation enhancement (RARE), fast spin echo (FSE), and turbo spin echo (TSE or TurboSE).

20. The method of claim 1 , wherein the spatial-encoding magnetic-field gradient pulses applied during each said data-acquisition step are configured so as to collect data, following each of at least one of the refocusing radio-frequency pulses, for two or more lines in spatial-frequency space which are parallel to all other lines of data so collected, so as to collect the data using a magnetic resonance imaging technique selected from the group consisting of gradient and spin echo (GRASE) and turbo gradient spin echo (TGSE or TurboGSE).

21. The method of claim 1 , wherein the spatial-encoding magnetic-field gradient pulses applied during each said data-acquisition step are configured so as to collect data, following each of at least one of the refocusing radio-frequency pulses, for one or more lines in spatial-frequency space, each of which pass through one of a single point in spatial-frequency space and a single line in spatial-frequency space, so as to collect the data using a magnetic resonance imagin

Assignees

• Univ Virginia Patent Foundation

Inventors

• Mugler Iii John P
• Brookeman James R

Classifications

• G01R33/586

  for optimal flip angle of RF pulses · CPC title

• G01R33/50

  based on the determination of relaxation times {, e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences} · CPC title

• G01R33/5617

  using RF refocusing, e.g. RARE · CPC title

• G01R33/5615 Primary

  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 title