A split‐label design for simultaneous measurements of perfusion in distant slices by pulsed arterial spin labeling

Abstract

Purpose Multislice arterial spin labeling (ASL) MRI acquisitions are currently challenging in skeletal muscle because of long transit times, translating into low‐perfusion SNR in distal slices when large spatial coverage is required. However, fiber type and oxidative capacity vary along the length of healthy muscles, calling for multislice acquisitions in clinical studies. We propose a new variant of flow alternating inversion recovery (FAIR) that generates sufficient ASL signal to monitor exercise‐induced perfusion changes in muscle in two distant slices. Methods Label around and between two 7‐cm distant slices was created by applying the presaturation/postsaturation and selective inversion modules selectively to each slice (split‐label multislice FAIR). Images were acquired using simultaneous multislice EPI. We validated our approach in the brain to take advantage of the high resting‐state perfusion, and applied it in the lower leg muscle during and after exercise, interleaved with a single‐slice FAIR as a reference. Results We show that standard multislice FAIR leads to an underestimation of perfusion, while the proposed split‐label multislice approach shows good agreement with separate single‐slice FAIR acquisitions in brain, as well as in muscle following exercise. Conclusion Split‐label FAIR allows measuring muscle perfusion in two distant slices simultaneously without losing sensitivity in the distal slice.

Feasibility of Arterial Spin Labeling Magnetic Resonance Imaging for Musculoskeletal Tumors with Optimized Post-Labeling Delay

“…These merits make ASL suitable not only for routine brain perfusion examination but also for perfusion studies in other body parts [ 12 , 13 , 14 , 16 , 17 , 18 , 21 , 22 , 23 , 33 ]. Although many studies have been published in the musculoskeletal field, those studies have focused mainly on exercise and peripheral arterial disease [ 26 , 34 , 35 , 36 ]. Recently, a study investigating musculoskeletal tumors found that ASL was able to diagnose malignant tumors efficiently and effectively [ 22 ].…”

“…The lower flow velocity may result in delayed enhancement in lesions at the extremities, and a PLD of 1500–2000 ms may not be optimal for perfusion study of the extremities. One previous study used a split-label design to improve measurements of muscle perfusion due to the long transit times in the extremities [ 26 ]. However, the influence of different PLDs in ASL perfusion imaging of musculoskeletal tumors has not been fully clarified Therefore, this study aimed to evaluate changes in the ASL-derived perfusion in different PLDs and to assess the performance of ASL in differentiating musculoskeletal tumors.…”

Microvascular response to exercise varies along the length of the tibialis anterior muscle

“…The split‐label pulsed FAIR ASL scan, based on Baligand et al, 13 was used to assess muscle perfusion. The labeling scheme consisted of presaturation of the imaging slice, followed by either a slice‐selective or nonselective frequency offset‐corrected inversion (FOCI) 16 pulse of 15‐ms duration, after which postsaturation of the imaging slice was applied.…”

“…However, this technique limits the gap between the slices, thereby limiting muscle coverage. In previous work, we have overcome this limitation by adapting the FAIR 12 sequence in such a way that the label is also created in between two slices separated by a relatively large distance 13 . This new split‐label FAIR method enables the assessment of perfusion in two widely separated slices without the need for additional corrections.…”

“…In the current study, we used the split‐label FAIR 13 method to quantitatively assess differences in muscle microvascular response to a standardized exercise between two separated slices covering the lower leg. We combined this with a Look‐Locker scheme to acquire images at multiple PLDs and with a multiecho readout to measure BOLD information.…”