Dual‐Pathway sequences for MR thermometry: When and where to use them

Purpose Dual‐pathway sequences have been proposed to help improve the temperature‐to‐noise ratio (TNR) in MR thermometry. The present work establishes how much of an improvement these so‐called “PSIF‐FISP” sequences may bring in various organs and tissues. Methods Simulations and TNR calculations were validated against analytical equations, phantom, abdomen, and brain scans. Relative TNRs for PSIF‐FISP, as compared to a dual‐FISP reference standard, were calculated for flip angle (FA) = 1 to 85 º and repetition time (TR) = 6 to 60 ms, for gray matter, white matter, cervix, endometrium, myometrium, prostate, kidney medulla and cortex, bone marrow, pancreas, spleen, muscle, and liver tissues. Results PSIF‐FISP was TNR superior in the kidney, pelvis, spleen, or gray matter at most tested TR and FA settings, and benefits increased at shorter TRs. PSIF‐FISP was TNR superior in other tissues, e.g., liver, muscle, pancreas, for only short TR settings (20 ms or less). The TNR benefits of PSIF‐FISP increased slightly with FA, and strongly with decreasing TR. Up to two‐ to three‐fold reductions in TR with 20% TNR gains were achievable. In any given tissue, TNR performance is expected to further improve with heating, due to changes in relaxation rates. Conclusion Dual‐pathway PSIF‐FISP can improve TNR and acquisition speed over standard gradient‐recalled echo sequences, but optimal acquisition parameters are tissue dependent. Magn Reson Med 77:1193–1200, 2017. © 2016 International Society for Magnetic Resonance in Medicine