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Objective: Paramagnetic rim lesions (PRLs) are a biomarker of chronic active lesions (CALs), and an important driver of neurological disability in multiple sclerosis (MS). The reason subtending some acute lesions evolvement into CALs is not known. Here we ask whether a relatively lower oxygen content is linked to CALs. Methods: In this prospective cross‐sectional study, 64 people with multiple sclerosis (PwMS), clinically isolated syndrome and radiologically isolated syndrome underwent a 7.0 Tesla (7 T) brain magnetic resonance imaging (MRI). The scanning protocol included a T2‐w fluid‐attenuated inversion recovery (FLAIR), and a single echo gradient echo from which susceptibility‐weighted imaging (SWI) was derived. WM lesions were identified on the T2‐w‐FLAIR whilst PRLs were identified on the SWI sequence. T2‐lesions were classified as PRLs and rimless lesions (PRLs‐). We registered a universal vascular atlas to each subject's T2‐w‐FLAIR and classified each T2‐lesions according to its location into watershed‐ (ws), non‐watershed‐ (nws), and mixed‐lesion (m). Ws‐lesions were defined as lesions that were fully located in a region between the territories of two major arteries. Results: Out of 1,975 T2‐lesions, 88 (4.5%) were PRLs. Ws‐regions had a higher number (p = 0.005) and proportion (p < 0.001) of PRLs‐ compared to nws‐regions. Ws‐PRL‐ were larger compared to nws‐ones (p = 0.009). The number (p = 0.043) and proportion (p < 0.001) of PRLs was higher in ws‐regions compared to nws‐ones. Ws‐PRLs were not significantly larger than nws‐ones (p = 0.195). Interpretation: We propose the novel concept of a link between arterial vascularization and chronic activity in MS by demonstrating a preferential localization of CALs in ws‐territories. [ABSTRACT FROM AUTHOR]

Rationale and Objectives: Several quantitative magnetic resonance imaging (MRI) methods are available to measure tissue injury in multiple sclerosis (MS), but their pathological specificity remains limited. The multi-compartment diffusion imaging using the spherical mean technique (SMT) overcomes several technical limitations of the diffusion-weighted image signal, thus delivering metrics with increased pathological specificity. Given these premises, here we assess whether the SMT-derived apparent axonal volume (V ax ) provides a better tissue classifier than the diffusion tensor imaging (DTI)-derived axial diffusivity (AD) in the white matter (WM) of MS brains., Methods: Forty-three treatment-naïve people with newly diagnosed MS, clinically isolated syndrome, or radiologically isolated syndrome and 18 healthy controls (HCs) underwent a 3.0 Tesla MRI inclusive of T 1 -weighted (T 1 -w) and T 2 -w fluid-attenuated inversion recovery (FLAIR) sequences, and multi-b shell diffusion-weighted imaging. In patients only, pre- and post-gadolinium diethylenetriamine penta-acetic acid T 1 -w sequences were obtained for the evaluation of contrast-active lesions (CELs). V ax and AD were calculated in T 2 -lesions, chronic black holes (cBHs), and normal appearing (NAWM) in patients and normal WM (NWM) in HCs. V ax and AD values were compared across all the possible combinations of these regions. CELs were excluded from the analyses., Results: V ax differed in all comparisons (p ≤ 0.047 by paired t-test); AD differed in most comparisons (p < 0.001) except between NAWM and NWM, and between cBHs and T 2 -lesions. V ax had higher accuracy (p ≤ 0.029 by DeLong test) and larger effect size (p ≤ 0.038 by paired t-test) than AD in differentiating areas with even minimal tissue injury., Conclusions: V ax provides a better radiological quantitative discriminator of different degrees of axonal-mediated tissue injury even between areas with expected minimal pathology. Our data support further studies to assess the readiness of V ax as a measure of outcome for clinical trials on neuroprotection in MS., Competing Interests: Declaration of Competing Interest The authors declare no financial interests/personal relationships which may be considered as potential competing interests., (Copyright © 2024 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)