Arterial spin labeling using spatio‐temporal encoding readout for robust perfusion imaging in inhomogenous magnetic fields

PURPOSE: To evaluate the feasibility of spatio‐temporal encoding (SPEN) readout for pseudo‐continuous ASL (pCASL) in brain, and its robustness to susceptibility artifacts as introduced by aneurysm clips. METHODS: A 2D self‐refocused T(2)*‐compensated hybrid SPEN scheme, with super‐resolution reconstruction was implemented on a 1.5T Philips system. Q (=BW(chirp)*T(chirp)) was varied and, the aneurysm clip‐induced artifact was evaluated in phantom (label‐images) as well as in vivo (perfusion‐weighted signal (PWS)‐maps and temporal SNR (tSNR)). In vivo results were compared to gradient‐echo EPI (GE‐EPI) and spin‐echo EPI (SE‐EPI). The dependence of tSNR on TR was evaluated separately for SPEN and SE‐EPI. SPEN with Q ˜ 75 encodes with the same off‐resonance robustness as EPI. RESULTS: The clip‐induced artifact with SPEN decreased with increase in Q, and was smaller compared to SE‐EPI and GE‐EPI in vivo. tSNR decreased with Q and the tSNR of GE‐EPI and SE‐EPI corresponded to SPEN with a Q‐value of approximately ˜85 and ˜108, respectively. In addition, SPEN perfusion images showed a higher tSNR (p < 0.05) for TR = 4000 ms compared to TR = 2100 ms, while SE‐EPI did not. tSNR remained relatively stable when the time between SPEN‐excitation and start of the next labeling‐module was more than ˜1000 ms. CONCLUSION: Feasibility of combining SPEN with pCASL imaging was demonstrated, enabling cerebral perfusion measurements with a higher robustness to field inhomogeneity (Q > 75) compared to SE‐EPI and GE‐EPI. However, the SPEN chirp‐pulse saturates incoming blood, thereby reducing pCASL labeling efficiency of the next acquisition for short TRs. Future developments are needed to enable 3D scanning.