Room: Track 2
Purpose: Quantitative Magnetic Resonance Imaging (qMRI) has gained increasing interest for tumor response assessment and functional changes. MR-linacs offer strong potential for routine qMRI acquisitions; however, their application in low field MR-linacs have not been widely established. This work sought to benchmark quantitative T1 mapping based on a novel acquisition method, Strategically Acquired Gradient Echo (STAGE) with conventional Variable Flip Angle (VFA) and Inversion recovery (IR) approaches, as well as R2* and Proton Density (PD) mapping acquired by STAGE in phantom on a 0.35T MR-linac.
Methods: For 3 quantitative maps (T1, R2* and PD) a benchmarking ISMRM/NIST phantom consisting of vials with variable NiCl2, MnCl2 and H2O concentrations was scanned using STAGE, VFA and IR methods at 0.35T. Low field strength T1 mapping was compared to reference 1.5T and 3.0T data. Measures of agreement with reference values and repeatability, relative error (RE) and coefficient of variation (CV) were calculated, respectively, for qMRI values within the phantom vials. STAGE (6 repeat measurements, TE/TR=[5/20/34]/40ms, 1×1×3mm3, FA=10°/50°) and VFA (5 repeat measurements TE/TR=5.35/15ms, 1×1×3mm3, FA=5°/15°/30°) images were acquired. For IR, scanning protocol was optimized for low field to increase fitting accuracy. IR was acquired by a spin echo sequence with FA=90°, TE/TR=10/5000ms, TI= [25,100,500,1000,2500]ms. Total acquisition times are 9, 14 and 105 mins respectively.
Results: For STAGE, measured T1 RE as compared to VFA and IR reference values were 4.8%±2.8% and 9.3%±2.6%, respectively. For VFA T1, results demonstrated mean RE (across all vials and the six VFA measurements) of 6.7%± 2.8% to IR T1. RE for the PD vials was 2.6%±2.0% and CV for phantom R2* measurements was 9.0%± 7.8%.
Conclusion: Overall, quantitative T1, PD and R2* mapping yielded acceptable agreement with the reference data. STAGE offers potential for qMRI comparable to conventional methods in a fraction of the acquisition time.
Funding Support, Disclosures, and Conflict of Interest: The submitting institution holds research agreements with Philips Healthcare, ViewRay, Inc., and Modus Medical. Research partially supported by the National Cancer Institute of the National Institutes of Health under Award Number R01CA204189. The PI is on the Philips Healthcare Advisory Board.
Not Applicable / None Entered.