Multi-contrast dual-resolution UTE for myelin fraction mapping and structural imaging

To introduce and evaluate a novel multi-contrast dual-resolution 3D-UTE sequence (multi-UTE) for cerebral myelin fraction (MF) estimation in vivo and benchmark it against electron microscopy-based myelin volume fraction.

Direct detection of myelin in tissue is challenging due to the ultrashort $T_2^{\ast }$ of the myelin bilayer. In this work, a high-resolution UTE pulse sequence with 1-1 binomial water excitation pulses was combined with interleaved multi-echo UTE acquisitions at lower resolution, enabling simultaneous acquisition of quantitative, water-excited, high-resolution T1-weighted structural images. The study included two ex vivo sheep brains, five healthy volunteers, and three patients with multiple sclerosis (MS) were measured. MF maps were calculated using multi-UTE and compared to histology. Magnetization transfer ratio using routine sequences was also calculated as a reference.

Multi-UTE facilitates the simultaneous acquisition of quantitative and structural images in 20 min. Myelin fraction values tested in five healthy volunteers agreed well with the literature. The MF estimated using multi-UTE showed a high correlation with histology (R² = 0.86) across 120 samples from different brain regions.

Multi-UTE showed the strongest correlations with electron microscopy (EM) histology, and the MF maps overlapped with the lesions in MS patients. Multi-UTE may provide complementary insights for myelin quantification in various inflammatory and neurodegenerative diseases.