Arterial spin-labeled (asl) multiplexed echo planar imaging (m-epi)

Abstract

An MRI system and method for imaging perfusion in an arterial spin labeled (ASL) process in which multiplexed echo-planar imaging (M-EPI) is used rather than conventional EPI, to thereby speed up imaging and generate sets of images that show different phases of perfusion and provide additional benefits. A single multiband RF excitation pulse can be used to excite multiple slices for imaging, or a time sequence of multiband pulses can be used to further increase the number of slices.

What is claimed is: 
     
         1 . A magnetic resonance imaging (MRI) method of imaging perfusion in a patient using arterial spin labeling (ASL) and multiplexed echo planar imaging (M-EPI) comprising:
 positioning a patient in an MRI scanner;   applying arterial spin labeling to a selected portion of the patient's anatomy;   applying a first multiband RF excitation pulse that essentially simultaneously excites multiple selected slices of the patient's anatomy;   applying magnetic gradients to the patient;   essentially simultaneously acquiring a first set of magnetic resonance (MR) signals generated for the multiple selected slices in response to the first multiband RF excitation pulse in an M-EPI process;   said acquiring being selectively timed relative to arterial, capillary and/or venous perfusion in the patient related to the applying of arterial labeling; and   computer-processing the first set of MR signals to generate a first set of ASL perfusion images of the slices and display the imaged on a computer display.   
     
     
         2 . The method of  claim 1  further including:
 applying a second multiband RF excitation pulse after applying the first one, to thereby again excite the multiple selected slices but in a subsequent phase of said perfusion, and 
 essentially simultaneously acquiring a second set of MR signals generated for the multiple selected slices in response to the second multiband RF excitation pulse; 
 wherein the computer system is further configured to computer-process the second set of MR signals to generate a second set of ASL perfusion images of the slices, and wherein the first and second set of images show respective different phases of the perfusion. 
 
     
     
         3 . The method of  claim 2  further including applying additional multiband RF excitation pulses in a time succession after the first and second RF excitation pulses to excite the slices at respective different times, acquiring additional sets of MR signals essentially simultaneously for said slices at times related to the respective additional RF excitation pulses, and including said additional sets of MR signals in said computer-processing to thereby generate additional sets of slice images showing respective additional phases of the perfusion. 
     
     
         4 . A magnetic resonance imaging (MRI) system for imaging perfusion in a patient using arterial spin labeling (ASL) and multiplexed echo planar imaging (M-EPI) comprising:
 an MRI scanner having an imaging volume for a patient;   an arterial spin labeling source configured to apply ASL pulses to the patient in the imaging volume;   RF coils configured to selectively apply a first multiband RF excitation pulse that essentially simultaneously excites multiple selected slices of the patient in the imaging volume;   magnetic gradient coils configured to apply magnetic gradients to the patient in the imaging volume;   MR signal acquisition coils configured to essentially simultaneously acquire magnetic resonance (MR) signals generated for the multiple selected slices in response to the first multiband RF excitation pulse in an M-EPI process;   said acquiring being selectively timed relative to arterial, capillary and/or venous perfusion in the patient related to the applying of arterial labeling; and   a computer system configured to computer-processing the MR signals to generate a first set of ASL perfusion images of the slices.   
     
     
         5 . The system of  claim 4  in which:
 the RF coils are further configured to apply a second multiband RF excitation pulse after applying the first one, to thereby again excite the multiple selected slices but in a subsequent phase of said perfusion, 
 the MR signal acquisition coils are further configured to essentially simultaneously acquire a second set of magnetic resonance (MR) signals generated for the multiple selected slices in response to the second multiband RF excitation pulse; and 
 the computer system is further configured to computer-process the second set of MR signals to thereby generate a second set of ASL perfusion images of the slices, wherein the first and second set of images show respective phases of the perfusion. 
 
     
     
         6 . The system of  claim 5  in which:
 the RF coils are further configured to apply a sequence of additional multiband RF excitation pulses after applying the first and second RF excitation pulses, to thereby excite the multiple selected slices in respective subsequent phase of said perfusion; 
 the MR signal acquisition coils are further configured to essentially simultaneously acquire additional sets of MR signals generated for the multiple selected slices in response to the respective additional multiband RF excitation pulses; and 
 the computer system is further configured to computer-process the additional sets of MR signals to thereby generate additional sets of ASL perfusion images of the slices that show additional respective phases of the perfusion.