T<sub>1D</sub>‐weighted ihMT imaging – Part I. Isolation of long‐ and short‐T<sub>1D</sub> components by T<sub>1D</sub>‐filtering
Andreea Hertanu, Lucas Soustelle, Arnaud Le Troter, Julie Buron, Julie Le Priellec, Victor Carvalho, Myriam Cayre, Pascale Durbec, Gopal Varma, David C. Alsop, Olivier M. Girard, Guillaume Duhamel
Abstract
Abstract Purpose To identify T 1D ‐filtering methods, which can specifically isolate various ranges of T 1D components as they may be sensitive to different microstructural properties. Methods Modified Bloch‐Provotorov equations describing a bi‐T 1D component biophysical model were used to simulate the inhomogeneous magnetization transfer (ihMT) signal from ihMTRAGE sequences at high RF power and low duty‐cycle with different switching time values for the dual saturation experiment: Δ t = 0.0, 0.8, 1.6, and 3.2 ms. Simulations were compared with experimental signals on the brain gray and white matter tissues of healthy mice at 7T. Results The lengthening of Δ t created ihMT high‐pass T 1D ‐filters, which efficiently eliminated the signal from T 1D components shorter than 1 ms, while partially attenuating that of longer components (≥ 1 ms). Subtraction of ihMTR images obtained with Δ t = 0.0 ms and Δ t = 0.8 ms generated a new ihMT band‐pass T 1D ‐filter isolating short‐T 1D components in the 100‐µs to 1‐ms range. Simulated ihMTR values in central nervous system tissues were confirmed experimentally. Conclusion Long‐ and short‐T 1D components were successfully isolated with high RF power and low duty‐cycle ihMT filters in the healthy mouse brain. Future studies should investigate the various T 1D ‐range microstructural correlations in in vivo tissues.