Characterizing the Mesencephalon Using Susceptibility-Weighted Imaging

TLDR

The mesencephalon, implicated in several neurodegenerative disorders, is usually imaged with T1-, T2-, and T2*-weighted MRI techniques. This study aimed to acquire high‑contrast susceptibility‑weighted imaging (SWI) data to distinguish the red nucleus, substantia nigra, and crus cerebri within the mesencephalon. High‑resolution SWI, 3D T1‑weighted, and T2‑weighted scans were obtained at 1.5 T and 4 T, and contrast between structures was quantified using SWI high‑pass‑filtered phase, T1 gradient‑echo, and spin‑echo T2 data. SWI high‑pass‑filtered phase produced comparable contrast for the red nucleus and substantia nigra as T2 imaging, revealed additional substructures invisible on T2, showed no measurable contrast on T1, matched india‑ink cadaver studies at 4 T, and overall provided superior anatomical detail of the mesencephalon compared with conventional sequences.

Abstract

<b>BACKGROUND AND PURPOSE:</b> The mesencephalon is involved in a number of human neurodegenerative disorders and has been typically imaged with T1-, T2- and T2*-weighted methods. Our aim was to collect high-contrast susceptibility-weighted imaging (SWI) data to differentiate among and within the basic mesencephalic structures: namely, the red nucleus, substantia nigra, and crus cerebri. <b>MATERIALS AND METHODS:</b> High-resolution SWI, 3D T1-weighted, and T2-weighted data were collected to study contrast in the mesencephalon at 1.5T and 4T. Contrast between structures was calculated for SWI high-pass (HP)-filtered-phase, T1 gradient-echo, and spin-echo T2-weighted data. <b>RESULTS:</b> SWI HP-filtered-phase data revealed similar contrast for the red nucleus and substantia nigra when compared with T2-weighted imaging. However, SWI was able to show structures within the red nucleus, substantia nigra, and medial geniculate body that were invisible on T2-weighted imaging. T1-weighted imaging, on the other hand, did not reveal measurable contrast for any of the structures of interest. SWI HP-filtered-phase data at 4T agreed well with india ink−stained cadaver brain studies, which appear to correlate with capillary density. <b>CONCLUSIONS:</b> With SWI, it is possible to create better anatomic images of the mesencephalon, with improved contrast compared with conventional T1- or T2-weighted sequences.