1 Test - Retest Reproducibility of perfusion measurements using PASL at 3 T

Introduction: Pulsed arterial spin labeling (PASL) perfusion imaging of cerebral blood flow (CBF) has already proven to be an useful instrument in studying brain pathologies [1,2]. However, validated quantitative imaging methods are not yet provided by the manufacturers. Therefore, the aim of the current study was to investigate the reproducibility of a PASL imaging sequence based on the previously presented PULSAR technique [3] combined with thin slice periodic saturation pulses (Q2TIPS) [4] to control for the length of the tagged bolus and facilitate CBF quantification with a single inversion time. Subjects and Methods: MRI was performed on a 3 T whole body scanner (body coil for transmit;8channel head coil for receive). The PULSAR sequence [3], as provided by the manufacturer, uses a conventional multislice signal targeting by alternating radiofrequency pulses (STAR) tagging scheme [5] for labeling and a WET presaturation of the imaging volume [6]. Thin slice periodic saturation pulses (Q2TIPS) [7] were added to control for the length of the tagged blood bolus and facilitate calculation of quantitative perfusion maps. PASL imaging parameters: single-shot EPI readout; TR/TE/α = 2500ms/17ms/90°; TI1/TI1S/TI2 = 700ms/ 1200ms/1500ms; 11 slices (aligned to Hippocampus, comprising parietal lobe); matrix 64x63; voxel size 3.75x3.75x6mm; gap 0.6mm; 80 pairs of labeled-control; scan time 7min 18sec). For spatial coregistration and normalization a single shot EPI (voxel size 3.75x3.75x3 mm; 40 slices) and a T1-weighted TFE volume (voxel size 1x1x1 mm; 170 slices) were acquired in the same session. Calculation of CBF-maps was performed as described previously [8] and included correction for partial volume effects [9]. Resting CBF maps were obtained from 16 subjects (8 male, 8 female, 30±10a) on two different days. Spatial preprocessing, calculation of CBF-maps and statistical analysis were performed with custom programs written in MATLAB and SPM5 (http://www.fil.ion.ucl.ac.uk/spm). The within-subject standard deviation (SDw= n CBF CBF i i 2 / ) ( 2 1 − ∑ )) and repeatability (95% confidence limit CL = ⋅ ⋅ 96 . 1 2 SDw)