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 ± 34/51 ± 2 ms on the MR-simulator and 1034 ± 42/51 ± 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.
Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Eveline Alberts is an employee of Philips Healthcare.
(© 2022 The Authors.)