Microstructure Informed Susceptibility Source Separation (MI-SSS) Improves Correlation with Translocator Protein PET in Multiple Sclerosis

Motivation: Noninvasive detection of immune activity of chronic active MS lesions is of great interest. Specific biomarkers of immune activity such as quantitative susceptibility mapping (QSM) was proposed for this purpose. However, QSM suffers from the contamination of diamagnetic myelin. Goal(s): The aim of this study is to show that paramagnetic susceptibility component derived from susceptibility source separation is more specific to immune activity than QSM. Approach: The correlation of QSM and paramagnetic susceptibility against TSPO PET in 34 chronic lesions from 7 MS patients are obtained. Results: Higher correlation of paramagnetic susceptibility shows its higher specificity to immune activity than QSM. Impact: Chronic active MS lesions with immune activity are of great importance as they demonstrate ongoing demyelination. Susceptibility source separation provides an improved noninvasive biomarker for the in vivo quantification of immune activity.