T 1D -weighted ihMT imaging - Part I. Isolation of long- and short-T 1D components by T 1D -filtering.

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: Δt = 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 Δt 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 Δt = 0.0 ms and Δt = 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.
(© 2022 International Society for Magnetic Resonance in Medicine.)