Combined PBR28 PET and Quantitative T1 Mapping Reveal Choroid Plexus Alterations in Multiple Sclerosis

BackgroundThe choroid plexus (CP), central to cerebrospinal fluid (CSF) regulation and immune cell trafficking, has been implicated in multiple sclerosis (MS). ObjectivesWe investigated TSPO-PET standardized uptake value ratio (SUVR) in the CP, with relation to T{square} relaxation times and CP volume using 7T MRI. MethodsQuantitative T1 (qT1) maps were obtained from 38 MS participants and 21 healthy controls (HCs) using 7T MRI. Within 4 weeks, PET imaging was conducted with [{superscript 1}{superscript 1}C]PBR28 to measure SUVR in the CP. Group differences and associations in CP SUVR, qT1, and CP volume were assessed. ResultsCP SUVR, CP qT1, and head{square}size-corrected CP volumes were higher in MS than HCs (p<0.05). CP volume associated strongly with CP qT1 (r=0.52, p<0.05). In MS, CP SUVR inversely correlated with qT1 ({rho}= -0.45, p<0.05). No significant associations were observed with disability scores, white{square}matter lesion burden and cortical lesion counts. ConclusionsOur findings support elevated microglial/macrophage activation in CP alongside structural alterations. CP volume emerges as a complementary MRI marker of inflammation rather than a direct surrogate for TSPO-PET tracer uptake. The inverse CP SUVR-qT{square} relationship in MS suggests that chronic extracellular expansion can accelerate tracer washout.