Battiston, M;
Grussu, F;
Ianus, A;
Schneider, T;
Prados, F;
Fairney, J;
Ourselin, S;
... Samson, R; + view all
(2018)
An optimized framework for quantitative Magnetization Transfer imaging of the cervical spinal cord in vivo.
Magnetic Resonance in Medicine
, 79
(5)
pp. 2576-2588.
10.1002/mrm.26909.
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Abstract
Purpose: To develop a framework to fully characterize quantitative magnetization transfer indices in the human cervical cord in vivo within a clinically feasible time. Methods: A dedicated spinal cord imaging protocol for quantitative magnetization transfer was developed using a reduced field-of-view approach with echo planar imaging (EPI) readout. Sequence parameters were optimized based in the Cramer-Rao-lower bound. Quantitative model parameters (i.e., bound pool fraction, free and bound pool transverse relaxation times [ math formula, math formula], and forward exchange rate [kFB]) were estimated implementing a numerical model capable of dealing with the novelties of the sequence adopted. The framework was tested on five healthy subjects. Results: Cramer-Rao-lower bound minimization produces optimal sampling schemes without requiring the establishment of a steady-state MT effect. The proposed framework allows quantitative voxel-wise estimation of model parameters at the resolution typically used for spinal cord imaging (i.e. 0.75 × 0.75 × 5 mm3), with a protocol duration of ∼35 min. Quantitative magnetization transfer parametric maps agree with literature values. Whole-cord mean values are: bound pool fraction = 0.11(±0.01), math formula = 46.5(±1.6) ms, math formula = 11.0(±0.2) µs, and kFB = 1.95(±0.06) Hz. Protocol optimization has a beneficial effect on reproducibility, especially for math formula and kFB. Conclusion: The framework developed enables robust characterization of spinal cord microstructure in vivo using qMT. Magn Reson Med, 2017.
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