Optimization of pseudo-continuous arterial spin labeling for brain perfusion imaging in the intraoperative setting

Pseudo-continuous arterial spin labeling (PCASL) efficiency during intraoperative MRI is degraded due to large field inhomogeneities observed in some patients and lower arterial blood velocities induced by anesthesia. The purpose of this work was to maximize labeling efficiency during intraoperative MRI by optimizing PCASL parameters at 3 T.

Effects of PCASL labeling pulse interval and gradient parameters on labeling efficiency were first investigated by numerical simulations based on Bloch equations. PCASL parameters were modified accordingly, considering hardware constraints, and evaluated experimentally. An experiment in healthy volunteers compared three labeling pulse intervals. In intraoperative brain tumor patients, different configurations were tested in two experiments: different labeling pulse intervals in patient experiment 1, and different labeling pulse interval and gradient average ( $G_{\mathrm{ave}}$ ) in experiment 2.

Numerical simulations showed that shortening the labeling pulse interval improved robustness of PCASL to off-resonance effects and that raising the $G_{\mathrm{ave}}$ increased labeling efficiency for lower blood velocity profiles. In healthy volunteers for large off-resonance, perfusion signal obtained with the labeling pulse interval of 600 μs was significantly higher than the one obtained with 1000 μs and 1400 μs (p-value < 0.001). In patients, a short labeling pulse interval of 600 μs and $G_{\mathrm{ave}}$ of 0.9 mT/m improved the quality of perfusion maps and significantly increased quantified cerebral blood flow values (p-value = 0.0078).

Shortening the labeling pulse interval and increasing the gradient average improves PCASL efficiency in the intraoperative setting.