Feasibility of cardiac-synchronized quantitative T(1) and T(2) 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(1) and T(2) 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(1) and T(2) mapping on a 1.5 T MR-linac and test the reproducibility of these sequences on phantoms and in vivo 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(1) and T(2) 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(1) and T(2) 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 in vivo intra/inter scanner evaluation. RESULTS: Cardiac-synchronized T(1) and T(2) qMRI was enabled after successful hardware installation on the MR-linac. From the phantom experiments, the measured T(1)/T(2) 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(1)/T(2) of the myocardium were 1012 [Formula: see text] 34/51 [Formula: see text] 2 ms on the MR-simulator and 1034 [Formula: see text] 42/51 [Formula: see text] 1 ms on the MR-linac. CONCLUSIONS: Accurate cardiac-synchronized T(1) and T(2) mapping is feasible on a 1.5 T MR-linac and might enable novel plan adaptation workflows and cardiotoxicity assessments.