Pulse imaging sequences and methods for T1p-weighted MRI

• US 6,836,114 B2
• Filed: 03/14/2003
• Issued: 12/28/2004
• Est. Priority Date: 03/15/2002
• Status: Active Grant

• Current Assignee: Trustees Of The University Of Pennsylvania (University of Pennsylvania)
• Original Assignee: Trustees Of The University Of Pennsylvania (University of Pennsylvania)
• Inventors: Borthakur, Ari, Reddy, Ravinder, Charagundla, Sridhar R., Shapiro, Erik M.
• Primary Examiner(s): ARANA, LOUIS M
• Application Number:
  US10/389,502
• Publication Number:
  US 20030218459A1
• Time in Patent Office: 655 Days
• Field of Search: 324/307, 324/306, 324/309, 324/312, 324/314, 324/300
• US Class Current: 324/307
• CPC Class Codes: G01R 33/4835 of multiple slices
• CPC Class Codes: G01R 33/50 based on the determination of relaxation times , e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences

Abstract

Provided are pulse imaging sequences and methods for 2D multi-slice T_1ρ-weighted and 3D T_1ρ-weighted magnetic resonance imaging (MRI). Further provided is a self-compensating spin-locking sequence for correcting and reducing artifacts in T_1ρ-weighted imaging. Also provided is a sequence combining 3D T_1ρ-weighted MRI with a self-compensating spin-locking pulse for facilitating T_1ρ-weighted imaging with surface coils.

Claims

1. A 2D multi-slice T_1ρ

-weighted pulse sequence for magnetic resonance imaging, comprising in sequential order;

a first radio frequency pulse for selectively exciting a band of spins;

a second radio frequency pulse, wherein the second pulse is a spin-locking pulse divided into at least two segments, wherein the spin-locking segments have 90°

alternating phase shift for spin-locking in a transverse plane of the spins;

a third radio frequency slice-selective pulse, phase-shifted 180°

from the first radio frequency pulse, which restores spin-locked magnetization to a longitudinal axis for imaging with any pulse sequence; and

a strong crusher gradient applied to destroy residual transverse magnetization.

2. The pulse sequence of claim 1, wherein each of the first and third radio frequency pulses is a π

/2 pulse.

3. A method of magnetic resonance imaging using a 2D multi-slice T_1ρ

-weighted sequence, comprising;

applying a first radio frequency pulse for selectively exciting a band of spins;

applying a spin-locking pulse, wherein the spin-locking pulse further comprises at least two segments with 90°

alternating phase shift for spin-locking in a transverse plane of the spins;

applying a third radio frequency slice-selective pulse, phase-shifted 180°

from the first radio frequency pulse which restores spin-locked magnetization to a longitudinal axis for imaging with any pulse sequence; and

applying a strong crusher gradient applied to destroy residual transverse magnetization.

4. The method of claim 3, wherein applying each of the first and third radio frequency pulses further comprises applying a π

/2 pulse.

5. A self-compensating spin-locking pulse sequence for correcting artifacts in T_1ρ

-weighted magnetic resonance imaging, comprising in sequential order;

a first radio frequency pulse for a selected θ

that nutates magnetization into a transverse plane;

a spin-locking pulse, wherein the spin-locking pulse further comprises at least two segments that are 90°

phase-shifted and have an amplitude B_s1, applied for time period TSL;

a second radio frequency pulse for a selected θ

applied, phase-shifted by 180°

to return a T_1ρ

-relaxed magnetization to a longitudinal axis for imaging; and

a crusher gradient to dephase residual transverse magnetization.

6. The sequence of claim 5, wherein each of the first and second radio frequency pulses for a selected θ

is a π

/2 pulse.

7. A method of correcting artifacts in T_1ρ

-weighted imaging with the self compensating spin-locking pulse, comprising applying a three-pulse preparatory cluster to an imaging sequence, including the following steps;

applying a first radio frequency pulse for a selected θ

that nutates magnetization into a transverse plane;

applying a spin-locking pulse, wherein the spin-locking pulse further comprises at least two segments that are 90°

phase-shifted and have an amplitude B_s1, applied for time period TSL;

applying a second radio frequency pulse for a selected θ

phase-shifted by 180°

to return a T_1ρ

-relaxed magnetization to a longitudinal axis for imaging; and

applying a crusher gradient to dephase residual longitudinal magnetization.

8. The method of claim 7, further comprising applying the three-pulse preparatory cluster pre-appended to a spin-echo-based imaging sequence.

9. The method of claim 7, further comprising applying the three-pulse preparatory cluster pre-appended to a gradient echo-based imaging sequence.

10. The method of claim 7, wherein B_s1 is a fraction of a maximum available radio frequency field B₁.

11. The method of claim 7, wherein each of the first and second radio frequency pulses is a π

/2 hard pulse.

12. A 3D T_1ρ

-weighted pulse sequence for magnetic resonance imaging, comprising a pulse cluster pre-encoded with a gradient echo sequence, wherein the pulse cluster further comprises in sequential order;

a first π

/2 hard pulse;

a spin-locking pulse having amplitude B₁;

a second π

/2 hard pulse phase shifted 180°

from the first hard pulse; and

a strong crusher gradient applied to destroy residual magnetization in a transverse plane and inhibit formation of unwanted coherences.

13. The pulse sequence of claim 12, wherein the spin-locking pulse further comprises two or more segments with alternating phases.

14. The pulse sequence of claim 13, wherein spin-locking pulse segments are +90°

and −

90°

phase-shifted from the phase of the first π

/2 pulse.

15. A method for magnetic resonance imaging using a 3D T_1ρ

-weighted pulse sequence, comprising applying a pulse cluster pre-encoded with a gradient echo sequence, wherein applying a pulse cluster further comprises;

applying a first π

/2 hard pulse;

applying a spin-locking pulse having amplitude B₁;

applying a second π

/2 hard pulse phase shifted 180°

from the first hard pulse; and

applying a strong crusher gradient to destroy residual magnetization in a transverse plane and inhibit the formation of unwanted coherences.

16. The method of claim 15, wherein the step of applying a spin-locking pulse further comprises applying a spin-locking pulse having at least two segments, wherein the at least two spin-locking segments have alternating phases for spin-locking in a transverse plane.

17. A method of obtaining 3D T_1ρ

-weighted images with a coil, comprising applying a pulse cluster pre-encoded with a gradient echo sequence, wherein applying a pulse cluster further comprises;

applying a first π

/2 hard pulse;

applying a spin-locking pulse having amplitude B₁ and having at least two segments, wherein the spin-locking segments have alternating phases for spin-locking in a transverse plane of the spins;

applying a second π

/2 hard pulse, phase shifted 180°

from the first hard pulse; and

applying a strong crusher gradient to destroy residual magnetization in the transverse plane and inhibit formation of unwanted coherences.

18. The method of claim 17, wherein the coil is a surface coil.

19. The method of claim 17, wherein the coil is a volume radio frequency coil.

20. The method of claim 17, wherein applying spin-locking segments further comprises applying spin-locking segments +90°

and −

90°

phase shifted from the first hard pulse.