Mickevicius NJ, Kim JP, Zhao J, Morris ZS, Hurst NJ, Jr., and Glide-Hurst CK. Toward magnetic resonance fingerprinting for low-field MR-guided radiation therapy. Med Phys 2021.
PURPOSE: The acquisition of multiparametric quantitative magnetic resonance imaging (qMRI) is becoming increasingly important for functional characterization of cancer prior to- and throughout the course of radiation therapy. The feasibility of a qMRI method known as magnetic resonance fingerprinting (MRF) for rapid T(1) and T(2) mapping was assessed on a low-field MR-linac system.
METHODS: A three-dimensional MRF sequence was implemented on a 0.35T MR-guided radiotherapy system. MRF-derived measurements of T(1) and T(2) were compared to those obtained with gold standard single spin echo methods, and the impacts of the radiofrequency field homogeneity and scan times ranging between 6 and 48 min were analyzed by acquiring between 1 and 8 spokes per time point in a standard quantitative system phantom. The short-term repeatability of MRF was assessed over three measurements taken over a 10-h period. To evaluate transferability, MRF measurements were acquired on two additional MR-guided radiotherapy systems. Preliminary human volunteer studies were performed.
RESULTS: The phantom benchmarking studies showed that MRF is capable of mapping T(1) and T(2) values within 8% and 10% of gold standard measures, respectively, at 0.35T. The coefficient of variation of T(1) and T(2) estimates over three repeated scans was < 5% over a broad range of relaxation times. The T(1) and T(2) times derived using a single-spoke MRF acquisition across three scanners were near unity and mean percent errors in T(1) and T(2) estimates using the same phantom were < 3%. The mean percent differences in T(1) and T(2) as a result of truncating the scan time to 6 min over the large range of relaxation times in the system phantom were 0.65% and 4.05%, respectively.
CONCLUSIONS: The technical feasibility and accuracy of MRF on a low-field MR-guided radiation therapy device has been demonstrated. MRF can be used to measure accurate T(1) and T(2) maps in three dimensions from a brief 6-min scan, offering strong potential for efficient and reproducible qMRI for future clinical trials in functional plan adaptation and tumor/normal tissue response assessment.
ePub ahead of print