title: Optimization of inhomogeneous magnetization transfer (ihMT) MRI contrast for preclinical studies using dipolar relaxation time (T1D) filtering.
abstract: A pulsed inhomogeneous magnetization transfer (ihMT)-prepared fast imaging sequence was implemented at 11.75 T for preclinical studies on mouse central nervous system. A strategy based on filtering the ihMT signal originating from short dipolar relaxation time (T1D) components is proposed. It involves increasing the repetition time of consecutive radiofrequency (RF) pulses of the dual saturation and allows improved signal specificity for long T1Dmyelinated structures. Furthermore, frequency offset, power and timing saturation parameters were adjusted to optimize the ihMT sensitivity. The optimization of the ihMT sensitivity, whilst preserving the strong specificity for the long T1Dcomponent of myelinated tissues, allowed measurements of ihMT ratios on the order of 4-5% in white matter (WM), 2.5% in gray matter (GM) and 1-1.3% in muscle. This led to high relative ihMT contrasts between myelinated tissues and others (~3-4 between WM and muscle, and ≥2 between GM and muscle). Conversely, higher ihMT ratios (~6-7% in WM) could be obtained using minimal T1Dfiltering achieved with short saturation pulse repetition time or cosine-modulated pulses for the dual-frequency saturation. This study represents a first stage in the process of validating ihMT as a myelin biomarker by providing optimized ihMT preclinical sequences, directly transposable and applicable to other preclinical magnetic fields and scanners. Finally, ihMT ratios measured in various central nervous system areas are provided for future reference.
authors.affiliation: Aix Marseille Université, CNRS, Marseille, France.
authors.forename: V H
authors.initials: VH
authors.lastname: Prevost
authors.affiliation: Aix Marseille Université, CNRS, Marseille, France.
authors.forename: O M
authors.identifier: http://orcid.org/0000-0002-5296-638X
authors.initials: OM
authors.lastname: Girard
authors.affiliation: Aix Marseille Université, CNRS, Marseille, France.
authors.forename: S
authors.initials: S
authors.lastname: Mchinda
authors.affiliation: Department of Radiology, Division of MR Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
authors.forename: G
authors.initials: G
authors.lastname: Varma
authors.affiliation: Department of Radiology, Division of MR Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Alsop
authors.affiliation: Aix Marseille Université, CNRS, Marseille, France.
authors.forename: G
authors.identifier: http://orcid.org/0000-0001-5704-8513
authors.initials: G
authors.lastname: Duhamel
mesh_terms: D000818:Animals; D002490:Central Nervous System / Q000033:anatomy & histology; D003287:Contrast Media / Q000737:chemistry*; D005260:Female; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008810:Mice, Inbred C57BL; D013997:Time Factors
chemical_list: D003287:Contrast Media
keywords: T1D; T1D filtering; dipolar order; dipolar relaxation time; ihMT; inhomogeneous magnetization transfer; myelin