Pulse imaging sequences and methods for T1p-weighted MRI

Abstract

Provided are pulse imaging sequences and methods for 2D mulfi-slice T 1p -weighted and 3D T 1p -weighted magnetic resonance imaging (MRI). Further provided is a self-compensating spin-locking sequence for correcting and reducing artifacts in T 1p -weighted imaging. Also provided is a sequence combining 3D T 1p -weighted MRI with a self-compensating spin-locking pulse for facilitating T 1p -weighted imaging with surface coils.

1 . A 2D multi-slice T 1p -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 2D multi-slice T 1p -weighted imaging using the sequence of  claim 1 , 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 1p -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 1p -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 1p -weighted imaging with the self compensating spin-locking pulse of  claim 5 , comprising applying a three-pulse preparatory cluster to an imaging sequence.  
   
   
       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 applying the three-pulse preparatory cluster further comprises: 
 applying a first radio frequency pulse for a selected 0 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 1p -relaxed magentization to a longitudinal axis for imaging; and    applying a crusher gradient to dephase residual longitudinal magnetization.    
   
   
       11 . The method of  claim 10 , wherein B s1  is a fraction of a maximum available radio frequency field B 1 .  
   
   
       12 . The method of  claim 10 , wherein each of the first and second radio frequency pulses is a π/2 hard pulse.  
   
   
       13 . A 3D T 1p -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 B 1 ;    a second π/2 hard pulse phase shifted 180° from the first hard pulse; and    a strong crusher gradient applied before a ax pulse to destroy residual magnetization in a transverse plane and inhibit the formation of unwanted coherences.    
   
   
       14 . The pulse sequence of  claim 13 , wherein the spin-locking pulse further comprises two or more segments with alternating phases.  
   
   
       15 . The pulse sequence of  claim 14 , wherein spin-locking pulse segments are +90° and −90° phase-shifted from the phase of the first π/2 pulse.  
   
   
       16 . A method of providing 3D T 1p -weighted magnetic resonance imaging using the sequence of  claim 13 , 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 B 1 ;    applying a second π/2 hard pulse phase shifted 180° from the first hard pulse; and    applying a strong crusher gradient before a a pulse to destroy residual magnetization in a transverse plane and inhibit the formation of unwanted coherences.    
   
   
       17 . The method of  claim 16 , 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.  
   
   
       18 . A method of obtaining 3D T 1p -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 B 1  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 before a a pulse to destroy residual magnetization in the transverse plane and inhibit the formation of unwanted coherences.    
   
   
       19 . The method of  claim 18 , wherein the coil is a surface coil.  
   
   
       20 . The method of  claim 18 , wherein the coil is a volume radio frequency coil.  
   
   
       21 . The method of  claim 18 , wherein applying spin-locking segments further comprises applying spin-locking segments +90° and −90° phase shifted from the first hard pulse.