ESTRO 2025 - Abstract Book

S3027

Physics - Image acquisition and processing

ESTRO 2025

2706

Digital Poster Impact of the repetition scheme on the accuracy of T1 and T2 mapping with MR fingerprinting on a 1.5 T MR Linac Magali Nuixe 1 , Bastien Lecoeur 1,2 , Rosie Goodburn 1 , Prashant Nair 1 , Andreas Wetscherek 1 1 Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 2 Department of Computing, Imperial College London, London, United Kingdom Purpose/Objective: Hybrid MR-Linac systems enable the integration of quantitative magnetic resonance imaging (MRI) into the radiotherapy treatment workflow allowing for treatment response assessment for biologically adaptive radiotherapy [1]. MR fingerprinting (MRF) enables rapid and simultaneous acquisition of quantitative MRI parameters [2]. This work aims to evaluate the impact of the repetition scheme on T 1 and T 2 mapping with MRF on an MR-Linac. Material/Methods: A NIST/ISMRM phantom Model 130 (CaliberMRI, Inc, Boulder, CO, USA) and a head and neck volunteer were scanned on a 1.5 T MR-Linac Unity (Elekta AB, Stockholm, Sweden). A 2D gradient-spoiled MRF sequence with an adiabatic inversion pulse, a sinusoidal flip angle scheme with a maximum of 66.9°, and a golden angle radial trajectory was used [3]. Multiple repetitions were acquired either consecutively or with a 5-second pause between them, and the k-space sampling pattern was rotated by the golden angle between repetitions. Slice profile and trajectory errors were corrected [4,5]. To evaluate the accuracy of the technique, inversion recovery and multi-echo spin-echo sequences were acquired for gold standard (GS) T 1 and T 2 measurements, respectively. Table 1 summarises the acquisition parameters. Regions of interest within the phantom vials with physiologically relevant values ( T 1 [150;1500] ms and T 2 [15;260] ms) and within the volunteer’s parotid glands were delineated using ImageJ (1.54d, NIH, Bethesda, MD, USA). Linear regressions were performed between mean MRF T 1 and T 2 values within each vial and GS measurements.