Feasibility of Cardiac-synchronized Quantitative T and T Mapping on a Hybrid 1.5 Tesla Magnetic Resonance Imaging and Linear Accelerator System

Background And Purpose: The heart is important in radiotherapy either as target or organ at risk. Quantitative T and T cardiac magnetic resonance imaging (qMRI) may aid in target definition for cardiac radioablation, and imaging biomarker for cardiotoxicity assessment. Hybrid MR-linac devices could facilitate daily cardiac qMRI of the heart in radiotherapy. The aim of this work was therefore to enable cardiac-synchronized T and T mapping on a 1.5 T MR-linac and test the reproducibility of these sequences on phantoms and between the MR-linac and a diagnostic 1.5 T MRI scanner.

Materials And Methods: Cardiac-synchronized MRI was performed on the MR-linac using a wireless peripheral pulse-oximeter unit. Diagnostically used T and T mapping sequences were acquired twice on the MR-linac and on a 1.5 T MR-simulator for a gel phantom and 5 healthy volunteers in breath-hold. Phantom T and T values were compared to gold-standard measurements and percentage errors (PE) were computed, where negative/positive PE indicate underestimations/overestimations. Manually selected regions-of-interest were used for intra/inter scanner evaluation.

Results: Cardiac-synchronized T and T qMRI was enabled after successful hardware installation on the MR-linac. From the phantom experiments, the measured T/T relaxation times had a maximum percentage error (PE) of -4.4%/-8.8% on the MR-simulator and a maximum PE of -3.2%/+8.6% on the MR-linac. Mean T/T of the myocardium were 1012 34/51 2 ms on the MR-simulator and 1034 42/51 1 ms on the MR-linac.

Conclusions: Accurate cardiac-synchronized T and T mapping is feasible on a 1.5 T MR-linac and might enable novel plan adaptation workflows and cardiotoxicity assessments.