T1D-weighted ihMT imaging - Part I. Isolation of long- and short-T1D components by T1D-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: Delta 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 Delta 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 Delta t = 0.0 ms and Delta t = 0.8 ms generated a new ihMT band-pass T-1D-filter isolating short-T-1D components in the 100-mu s 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.

Automated summary

This study investigated T-1D-filtering methods for isolating different ranges of T-1D components based on their microstructural properties. The results showed that high RF power and low duty-cycle ihMT filters could successfully isolate long-T-1D and short-T-1D components in the brain.