Feasibility of cardiac-synchronized quantitative T₁ and T₂ mapping on a hybrid 1.5 Tesla magnetic resonance imaging...

The heart is important in radiotherapy either as target or organ at risk. Quantitative T₁ and T₂ 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 T₁ and T₂ 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.

Cardiac-synchronized MRI was performed on the MR-linac using a wireless peripheral pulse-oximeter unit. Diagnostically used T₁ and T₂ 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 T₁ and T₂ 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.

Cardiac-synchronized T₁ and T₂ qMRI was enabled after successful hardware installation on the MR-linac. From the phantom experiments, the measured T₁/T₂ 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 T₁/T₂ of the myocardium were 1012 $$ 34/51 $$ 2 ms on the MR-simulator and 1034 $$ 42/51 $$ 1 ms on the MR-linac.

Accurate cardiac-synchronized T₁ and T₂ mapping is feasible on a 1.5 T MR-linac and might enable novel plan adaptation workflows and cardiotoxicity assessments.