Hybrid-State Free Precession in Nuclear Magnetic Resonance

Abstract

The dynamics of large spin-1/2 ensembles in the presence of a varying magnetic field are commonly described by the Bloch equation. Most magnetic field variations result in unintuitive spin dynamics, which are sensitive to small deviations in the driving field. Although simplistic field variations can produce robust dynamics, the captured information content is impoverished. Here, we identify adiabaticity conditions that span a rich experiment design space with tractable dynamics. These adiabaticity conditions trap the spin dynamics in a one-dimensional subspace. Namely, the dynamics is captured by the absolute value of the magnetization, which is in a transient state, while its direction adiabatically follows the steady state. We define the hybrid state as the co-existence of these two states and identify the polar angle as the effective driving force of the spin dynamics. As an example, we optimize this drive for robust and efficient quantification of spin relaxation times and utilize it for magnetic resonance imaging of the human brain.

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• Quantitative Magnetic Resonance Imaging by Nonlinear Inversion of the Bloch Equations
• Efficiency analysis for quantitative MRI of T1 and T2 relaxometry methods
• Rapid quantitative magnetization transfer imaging: utilizing the hybrid state and the generalized Bloch model
• Joint T1 and T2 Mapping with Tiny Dictionaries and Subspace-Constrained Reconstruction
• A three-dimensional MR-STAT protocol for high-resolution multi-parametric quantitative MRI
• Bias-Reduced Neural Networks for Parameter Estimation in Quantitative MRI
• Cramér-Rao Bound Optimized Subspace Reconstruction in Quantitative MRI