Perfusion mapping with multiecho multishot parallel imaging EPI.
Echo-planar imaging (EPI) is the standard technique for dynamic susceptibility-contrast (DSC) perfusion MRI. However, EPI suffers from well-known geometric distortions, which can be reduced by increasing the k-space phase velocity. Moreover, the long echo times (TEs) used in DSC lead to signal saturation of the arterial input signal, and hence to severe quantitation errors in the hemodynamic information. Here, through the use of interleaved shot acquisition and parallel imaging (PI), rapid volumetric EPI is performed using pseudo-single-shot (ss)EPI with the effective T(*)(2) blur and susceptibility distortions of a multishot EPI sequence. The reduced readout lengths permit multiple echoes to be acquired with temporal resolution and spatial coverage similar to those obtained with a single-echo method. Multiecho readouts allow for unbiased R(*)(2) mapping to avoid incorrect estimation of tracer concentration due to signal saturation or T(1) shortening effects. Multiecho perfusion measurement also mitigates the signal-to-noise ratio (SNR) reduction that results from utilizing PI. Results from both volunteers and clinical stroke patients are presented. This acquisition scheme can aid most rapid time-series acquisitions. The use of this method for DSC addresses the problem of signal saturation and T(1) contamination while it improves image quality, and is a logical step toward better quantitative MR PWI.
Lucas MRS/I Center, Department of Radiology, Stanford University, Stanford, California, USA.
Rexford D
RD
Newbould
Lucas MRS/I Center, Department of Radiology, Stanford University, Stanford, California, USA.
Stefan T
ST
Skare
Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
Thies H
TH
Jochimsen
Lucas MRS/I Center, Department of Radiology, Stanford University, Stanford, California, USA.
Marcus T
MT
Alley
Lucas MRS/I Center, Department of Radiology, Stanford University, Stanford, California, USA.
Michael E
ME
Moseley
Stanford Stroke Center, Department of Neurology, Stanford University, Stanford, California, USA.
Gregory W
GW
Albers
Lucas MRS/I Center, Department of Radiology, Stanford University, Stanford, California, USA.
Roland
R
Bammer
D001921:Brain; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010477:Perfusion; D020521:Stroke / Q000175:diagnosis