Interthalamic Adhesion Thickness and Its Ratio to Cerebral Height in Canine Brain MRI: Influence of Body Weight, MRI Sequence (T1W/T2W), and Imaging Plane

Canine brain MRI facilitates the quantitative assessment of changes, such as edema or atrophy. The measurement of interthalamic adhesion thickness (ITAt) potentially enables the evaluation of brain atrophy. In this study, we aimed to measure the ITA thickness and the ITA-to-cerebral height ratio (ITAr) in various small dog breeds to analyze differences and correlations with age, body weight, sex, and breed. Among 260 dogs without lesions, such as Chiari malformation, hydrocephalus, or brain atrophy, the ITAt was measured in the sagittal and transverse planes using T1-weighted (T1W) and T2-weighted (T2W) MRI sequences. Correlations with breed, age, weight, and sex variables were then analyzed. The results showed significant variations in ITAt between breeds, with a negative correlation with age and a positive correlation with body weight. ITAt showed significant differences across different body-weight ranges, and ITAr demonstrated consistency regardless of breed, body weight, and sex, suggesting its potential as an objective metric. The ITAr was lowest in the axial plane, T2W (0.15 ± 0.02), and highest in the sagittal plane, T1W (0.18 ± 0.02). Furthermore, ITAt values were higher in T1W than in T2W, which demonstrated a noticeable difference. This finding confirms the necessity of establishing sequence- and plane-specific reference ranges. This study provides reference ranges for ITAt and ITAr across various dog breeds, confirming that ITAt may be influenced by age and body weight, whereas the ITAr remains consistent across a wide range of body types and weights, which indicates its promise as a more objective assessment metric.