Time-efficient measurement of multi-phase arterial spin labeling MR signal in white matter.

White matter (WM) perfusion has great potential as a physiological biomarker in many neurological diseases. Although it has been demonstrated previously that arterial spin labeling magnetic resonance imaging (ASL-MRI) enables the detection of the perfusion-weighted signal in most voxels in WM, studies of cerebral blood flow (CBF) in WM by ASL-MRI are relatively scarce because of its particular challenges, such as significantly lower perfusion and longer arterial transit times relative to gray matter (GM). Recently, ASL with a spectroscopic readout has been proposed to enhance the sensitivity for the measurement of WM perfusion. However, this approach suffers from long acquisition times, especially when acquiring multi-phase ASL datasets to improve CBF quantification. Furthermore, the potential increase in the signal-to-noise ratio (SNR) by spectroscopic readout compared with echo planar imaging (EPI) readout has not been proven experimentally. In this study, we propose the use of time-encoded pseudo-continuous ASL (te-pCASL) with single-voxel point-resolved spectroscopy (PRESS) readout to quantify WM cerebral perfusion in a more time-efficient manner. Results are compared with te-pCASL with a conventional EPI readout for both WM and GM perfusion measurements. Perfusion measurements by te-pCASL PRESS and conventional EPI showed no significant difference for quantitative WM CBF values (Student's t-test, p = 0.19) or temporal SNR (p = 0.33 and p = 0.81 for GM and WM, respectively), whereas GM CBF values (p = 0.016) were higher using PRESS than EPI readout. WM CBF values were found to be 18.2 ± 7.6 mL/100 g/min (PRESS) and 12.5 ± 5.5 mL/100 g/min (EPI), whereas GM CBF values were found to be 77.1 ± 11.2 mL/100 g/min (PRESS) and 53.6 ± 9.6 mL/100 g/min (EPI). This study demonstrates the feasibility of te-pCASL PRESS for the quantification of WM perfusion changes in a highly time-efficient manner, but it does not result in improved temporal SNR, as does traditional te-pCASL EPI, which remains the preferred option because of its flexibility in use.