Human olfactory bulb morphometry and olfactory sulcus depth measurement in normosmia

This study aimed to provide a comprehensive multiobserver magnetic resonance imaging (MRI)-based assessment of olfactory bulb (OB) morphology, including volume, width, height, anterior-posterior diameter (APD), as well as olfactory sulcus (OS) depth, in normosmic adults. High-resolution MRI scans of 118 healthy participants (mean age 28.47 ± 8.20) were manually segmented by multiple observers. Interobserver reliability was generally acceptable, with OS depth and APD showing excellent agreement. Single-observer assessments were sufficient for group-level OB morphology, but caution was advised when interpreting individual cases. Besides, right OS depth and left height decreased with age in normosmic participants, and odor discrimination was positively associated with left OB width. People with deeper right OS depth had bigger right volume and longer APD. No correlations were found between olfactory function and OB morphological parameters. OS depth was consistently deeper on the right side, supporting hemispheric asymmetry. OB shape was most often oval (≈78%). Over 70% of the subjects showed left-right consistency in OB shape, but the Cohen's κ value indicated only slight (below moderate) agreement, suggesting that left-right agreement was limited. In conclusion, we presented a standardized multiobserver segmentation and measurement workflow that enabled reliable assessment of OB structure and OS depth, and offered a comprehensive characterization of OB and OS depth morphology in normosmia.