Arterial Transit Time Mapping Obtained by Pulsed Continuous 3D ASL Imaging with Multiple Post-Label Delay Acquisitions: Comparative Study with PET-CBF in Patients with Chronic Occlusive Cerebrovascular Disease

Abstract

Arterial transit time (ATT) is most crucial for measuring absolute cerebral blood flow (CBF) by arterial spin labeling (ASL), a noninvasive magnetic resonance (MR) perfusion assessment technique, in patients with chronic occlusive cerebrovascular disease. We validated ASL-CBF and ASL-ATT maps calculated by pulsed continuous ASL (pCASL) with multiple post-label delay acquisitions in patients with occlusive cerebrovascular disease. Fifteen patients underwent MR scans, including pCASL, and positron emission tomography (PET) scans with 15O-water to obtain PET-CBF. MR acquisitions with different post-label delays (1.0, 1.5, 2.0, 2.5 and 3.0 sec) were also obtained for ATT correction. The theoretical framework of 2-compartmental model (2CM) was also used for the delay compensation. ASL-CBF and ASL-ATT were calculated based on the proposed 2CM, and the effect on the CBF values and the ATT correction characteristics were discussed. Linear regression analyses were performed both on pixel-by-pixel and region-of-interest bases in the middle cerebral artery (MCA) territory. There were significant correlations between ASL-CBF and PET-CBF both for voxel values (r = 0.74 ± 0.08, slope: 0.87 ± 0.22, intercept: 6.1 ± 4.9) and for the MCA territorial comparison in both affected (R2 = 0.67, y = 0.83x + 6.3) and contralateral sides (R2 = 0.66, y = 0.74x + 6.3). ASL-ATTs in the affected side were significantly longer than those in the contralateral side (1.51 ± 0.41 sec and 1.12 ± 0.30 sec, respectively, p <0.0005). CBF measurement using pCASL with delay compensation was feasible and fairly accurate even in altered hemodynamic states.

Multimodal analysis using [11C]PiB-PET/MRI for functional evaluation of patients with Alzheimer’s disease

“…A pseudo-continuous ASL (pCASL, GE's product version) prepped 3D spiral fast spin-echo (FSE) acquisition combined with background suppression was used for calculation of MRI perfusion images [18]. Details of the method are described elsewhere [19]. In brief, the labeling duration for ASL preparation was 1.5 s, and the 3D-FSE readout signal was obtained with an interleaved stack of 7-arm acquisitions for each excitation at each of 36-42 centrically ordered slice encodes.…”

“…In brief, the labeling duration for ASL preparation was 1.5 s, and the 3D-FSE readout signal was obtained with an interleaved stack of 7-arm acquisitions for each excitation at each of 36-42 centrically ordered slice encodes. The labeling slab is automatically set at a level 2 cm inferior to the scan range, and images were acquired with the following parameters: 240 mm FOV; 128 × 128 matrix; in-plane resolution 1.8 mm; slice thickness 4.5 mm; fixed postlabeling delay (PLD) 2.0 s [19]. The number of excitations for the acquisition was three, and the total scan duration was 4 min 10 s. For blood flow quantification, an approximate proton density weighted image was also obtained with the same acquisition parameters.…”

Enhancement of automated blood flow estimates (ENABLE) from arterial spin‐labeled MRI

“…For instance, moderate to high similarity between 3.0T ASL and 15 O positron emission tomography CBF images was reported in vascular and dementia cohorts. 27,33 Wang et al 26 and Qiu et al 34 reported moderate similarity between multi-PLD ASL and CT in patients with delayed blood delivery, ie, long ATT. Liu et al compared 3.0T ASL and SPECT in young healthy adults and reported a high similarity between CBF images.…”

“…We examined ENABLE performance against a conventional (CONV) multi‐PLD ASL analysis, ie, no image quality evaluation . We modeled multi‐PLD images with an established ASL kinetic model tool (BASIL) to generate CBF images.…”

“…We examined ENABLE performance against a conventional (CONV) multi-PLD ASL analysis, ie, no image quality evaluation. 4,[25][26][27] We modeled multi-PLD images with an established ASL kinetic model tool (BASIL) 28 to generate CBF images. A free energy term provided a goodness-of-fit estimate such that lower free energy corresponds to a better fit.…”