Measuring the effects of remifentanil on cerebral blood flow and arterial arrival time using 3D GRASE MRI with pulsed arterial spin labelling

Arterial spin labelling ( ASL) has proved to be a promising magnetic resonance imaging ( MRI) technique to measure brain perfusion. In this study, volumetric three- dimensional ( 3D) gradient and spin echo ( GRASE) ASL was used to produce cerebral blood flow ( CBF) and arterial arrival time ( AAT) maps during rest and during an infusion of remifentanil. Gradient and spin echo ASL perfusion- weighted images were collected at multiple inflow times ( 500 to 2,500ms in increments of 250 ms) to accurately fit an ASL perfusion model. Fit estimates were assessed using z- statistics, allowing voxels with a poor fit to be excluded from subsequent analyses. Nonparametric permutation testing showed voxels with a significant difference in CBF and AAT between conditions across a group of healthy participants ( N= 10). Administration of remifentanil produced an increase in end- tidal CO2, an increase in CBF from 57 +/- 12.0 to 77 +/- 18.4 mL/ 100 g tissue per min and a reduction in AAT from 0.73 +/- 0.073 to 0.64 +/- 0.076 secs. Within grey matter, remifentanil produced a cerebrovascular response of 5.7 +/- 1.60 % CBF per mmHg. Significant differences between physiologic conditions were observed in both CBF and AAT maps, indicating that 3D GRASE- ASL has the sensitivity to study changes in physiology at a voxel level.