Ultra-high-field MRI reveals a venous-dominant microbleed phenotype in cerebral amyloid angiopathy: a comparative...

Cerebral microbleeds (CMB) are core MRI markers of cerebral amyloid angiopathy (CAA). Ultra-high-field 7T MRI may improve CMB detection and visualization of venous-associated CMB (vCMB), but the extent to which this reflects additional lesion detection versus field-dependent phenotypic reclassification remains uncertain. We compared CMB burden and venous phenotyping at 7T versus 3T in patients with probable CAA.

In this single-center retrospective study, 22 patients with probable CAA underwent paired 3T and 7T MRI within 6 months. Two blinded neuroradiologists assessed total CMB, vCMB, simple/non-venous CMB (sCMB), and the vCMB-to-total ratio on susceptibility-weighted imaging. Paired comparisons used Wilcoxon signed-rank tests; inter-scanner analyses used Spearman correlations and Bland-Altman analysis. Lesion-level distributions were descriptive only because of within-subject clustering.

7T detected more total CMB and vCMB than 3T (1551 versus 818 and 1173 versus 385), whereas sCMB counts did not differ significantly (p = 0.47). The median vCMB-to-total ratio was higher at 7T than at 3T (0.70 versus 0.33; p < 0.001). Inter-scanner correlations were strong for total CMB (r = 0.95) and vCMB count (r = 0.88), but weak and non-significant for the vCMB-to-total ratio (r = 0.32, p = 0.16; n = 21). Inter-rater reliability for the vCMB-to-total ratio was higher at 7T than at 3T (ICC = 0.76 versus 0.54). Cohort-level delta analyses showed that the increase in vCMB approximated the increase in total CMB, whereas the change in sCMB was close to zero.

7T MRI robustly improves CMB detection in CAA and provides higher inter-rater reliability for vCMB classification than 3T. However, weak cross-scanner correlation and agreement for the vCMB-to-total ratio preclude interchangeability across field strengths. The higher 7T vCMB burden is most consistent with additional small-lesion detection, with partial reclassification also possible. 3T remains suitable for global CMB burden assessment, whereas 7T adds value for mechanistic and longitudinal studies. Note: 3T and 7T are retained as standard MRI field-strength designations.