Adaptation of an arterial spin labeling sequence for the assessment of brain perfusion on a 0.35 T MR-Linac.

OBJECTIVE

Hybrid MR-Linac devices allow the acquisition of functional MR images during a regular radiotherapy treatment workflow, which could improve target delineation and response assessment. In this work, we investigate the feasibility of acquiring arterial spin labeling (ASL) perfusion images on a 0.35 T MR-Linac.

MATERIALS AND

METHODS

A signal model for the flow-sensitive alternating inversion recovery (FAIR) balanced steady-state free precession (bSSFP) ASL sequence was introduced and an optimized set of sequence parameters for 0.35 T was determined. The signal dependence on the sequence parameters using the MR-Linac was examined in the brain of two healthy volunteers. Repeatability of cerebral blood flow (CBF) measurements with an adjusted MR-Linac protocol were compared to ASL images from a clinical 3 T scanner in six healthy volunteers that were scanned twice on each device.

RESULTS

The signal model described the observed measurements well, except for the dependence on inversion time. CBF values in gray and white matter in the six volunteers were systematically higher than at the 3 T scanner, but they had a similar percentage repeatability coefficient of 16-17%.

CONCLUSION

An adjusted 10-min FAIR bSSFP ASL protocol on a 0.35 T MR-Linac yielded repeatable CBF measurements. (glinicaltrials.gov NCT05565326, submitted 2022-09-29).