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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.)

T 1D , the relaxation time of dipolar order, is sensitive to slow motional processes. Thus T 1D is a probe for membrane dynamics and organization that could be used to characterize myelin, the lipid-rich membrane of axonal fibers. A mono-component T 1D model associated with a modified ihMT sequence was previously proposed for in vivo evaluation of T 1D with MRI. However, experiments have suggested that myelinated tissues exhibit multiple T 1D components probably due to a heterogeneous molecular mobility. A bi-component T 1D model is proposed and implemented. ihMT images of ex-vivo, fixed rat spinal cord were acquired with multiple frequency alternation rate. Fits to data yielded two T 1D s of about 500 μs and 10 ms. The proposed model seems to further explore the complexity of myelin organization compared to the previously reported mono-component T 1D model., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier Inc. All rights reserved.)