Myelin bilayer mapping in the human brain in vivo

Abstract

PurposeTo quantitatively map the myelin lipid‐protein bilayer in the live human brain.MethodsThis goal was pursued by integrating a multi‐TE acquisition approach targeting ultrashort T2 signals with voxel‐wise fitting to a three‐component signal model. Imaging was performed at 3 T in two healthy volunteers using high‐performance RF and gradient hardware and the HYFI sequence. The design of a suitable imaging protocol faced substantial constraints concerning SNR, imaging volume, scan time, and RF power deposition. Model fitting to data acquired using the proposed protocol was made feasible through simulation‐based optimization, and filtering was used to condition noise presentation and overall depiction fidelity.ResultsA multi‐TE protocol (11 TEs of 20–780 μs) for in vivo brain imaging was developed in adherence with applicable safety regulations and practical scan time limits. Data acquired using this protocol produced accurate model fitting results, validating the suitability of the protocol for this purpose. Structured, grainy texture of myelin bilayer maps was observed and determined to be a manifestation of correlated image noise resulting from the employed acquisition strategy. Map quality was significantly improved by filtering to uniformize the k‐space noise distribution and simultaneously extending the k‐space support. The final myelin bilayer maps provided selective depiction of myelin, reconciling competitive resolution (1.4 mm) with adequate SNR and benign noise texture.ConclusionUsing the proposed technique, quantitative maps of the myelin bilayer can be obtained in vivo. These maps offer unique information content with potential applications in basic research, diagnosis, disease monitoring, and drug development.

3D balanced SSFP UTE MRI for multiple contrasts whole brain imaging

“…These have reported T 2min values of 0.01-0.1 ms in WM tissue samples 20,42,43 and also used these values to fit in vivo relaxometry data. 44 These studies concluded that a component with T 2min of 5.5 𝜇s and chemical shift of 1.1 ppm corresponds to the myelin bilayer, while a component with T 2min of 100 𝜇s and chemical shift of 2.1 ppm corresponds to other non-aqueous protons such as cell membranes and proteins. Imaging results were enabled by ZTE sequences and dedicated hardware including high-performance gradients and fast transmit/receive switches, while our data was acquired on conventional hardware which limits comparisons that can be made.…”