Abstract
PurposeDiffusion MRI is confounded by the need to acquire at least two images separated by a repetition time, thereby thwarting the detection of rapid dynamic microstructural changes. The issue is exacerbated when diffusivity variations are accompanied by rapid changes in T2. The purpose of the present study is to accelerate diffusion MRI acquisitions such that both reference and diffusion‐weighted images necessary for quantitative diffusivity mapping are acquired in a single‐shot experiment.MethodsA general methodology termed incomplete initial nutation diffusion imaging (INDI), capturing two diffusion contrasts in a single shot, is presented. This methodology creates a longitudinal magnetization reservoir that facilitates the successive acquisition of two images separated by only a few milliseconds. The theory behind INDI is presented, followed by proof‐of‐concept studies in water phantom, ex vivo, and in vivo experiments at 16.4 and 9.4 T.ResultsMean diffusivities extracted from INDI were comparable with diffusion tensor imaging and the two‐shot isotropic diffusion encoding in the water phantom. In ex vivo mouse brain tissues, as well as in the in vivo mouse brain, mean diffusivities extracted from conventional isotropic diffusion encoding and INDI were in excellent agreement. Simulations for signal‐to‐noise considerations identified the regimes in which INDI is most beneficial.ConclusionsThe INDI method accelerates diffusion MRI acquisition to single‐shot mode, which can be of great importance for mapping dynamic microstructural properties in vivo without T2 bias. Magn Reson Med 79:2198–2204, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Highlights
Methods enabling rapid acquisition of dynamic MRI data have greatly affected contemporary MRI
Diffusion functional MRI evidenced faster activation dynamics and more localized activation foci compared with BOLD, suggesting it may be more closely correlated with underlying neural activity [29,30,31]
Dynamic changes in tissue ADC are at the core of diffusion fMRI methods, aiming to map functional signals more intimately related with neural activity compared with their
Summary
Methods enabling rapid acquisition of dynamic MRI data have greatly affected contemporary MRI. Diffusion MRI (dMRI) methods [9], typically relying on single-diffusion-encoded schemes [10], are not usually acquired dynamically, but their ability to probe microarchitectural features such as anisotropy [11], complex fiber configurations [12,13], microscopic anisotropy [14,15,16,17], and cellular-scale dimensions [18,19,20] have made them widely applicable [21]. Rapid and dynamic determination of diffusion-derived metrics, is important for diffusion functional MRI (dfMRI) [29, 30], a method aiming to detect neural activity through non-blood-oxygenation-leveldependent (BOLD) mechanisms. DfMRI’s temporal resolution can be limited by the necessity to acquire at least two signals
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