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- New MRI Metric Offers Reliable Measure of Brain Atrophy in Dogs Across Breeds
New MRI Metric Offers Reliable Measure of Brain Atrophy in Dogs Across Breeds
VRU 2025
Obi Veterinary Education
November 19, 2025
Minha Ji, Danbee Kwon, Sungsoo Kim, Hyungjin Park, Kichang Lee, Hakyoung Yoon
Background
Magnetic resonance imaging (MRI) allows precise, quantitative assessment of canine brain structures and abnormalities, including atrophy. The interthalamic adhesion (ITA), a central brain structure formed by the fusion of both thalami, decreases in size with age or neurodegenerative conditions such as dementia. Measuring interthalamic adhesion thickness (ITAt) is thus a proposed biomarker of brain atrophy. However, skull size and breed variability can confound ITAt readings. To normalize these differences, the ITA-to-cerebral height ratio (ITAr) has been suggested, but its reference ranges and breed effects had not been systematically studied.
Methods
This multicenter retrospective cross-sectional study analyzed 260 neurologically normal dogs (out of 511 initial cases) across 23 breeds. Dogs with Chiari-like malformation, hydrocephalus, or atrophy were excluded. MRI scans were obtained using 1.5T systems (GE Healthcare) in both T1-weighted (T1W) and T2-weighted (T2W) sequences, in sagittal and transverse planes. ITAt was measured vertically at its thickest point, and ITAr was computed by dividing ITAt by cerebral height. Measurements were repeated twice by the same observer to assess intraobserver reliability. Statistical analyses (ANOVA, regression, t-tests) examined correlations with age, body weight (BW), sex, and breed, with significance set at p < 0.05.
Results
Significant interbreed differences were observed in ITAt but not in ITAr. Retrievers had the largest ITAt (8.28 mm sagittal T1W), while Chihuahuas had the smallest (7.26 mm). ITAt increased with body weight and decreased slightly with age, while ITAr remained stable across breeds, weights, and sexes. Multiple regression confirmed a weak negative correlation between ITAt and age (β = −0.20, p < .05) and a weak positive correlation with BW (β = 0.15, p < .05). ITAr was unaffected by BW but decreased slightly with age (β = −0.12, p < .05). ITAt values were significantly higher in T1W than T2W sequences and in sagittal than transverse planes (p < .01). Intraobserver reliability was excellent (ICC > 0.99).
Limitations
Some breeds had small sample sizes, limiting generalizability. Weight variability within breeds could introduce bias. Absence of histopathologic confirmation of brain normalcy may have allowed unrecognized pathology. Slice thickness (2–3 mm) might have caused partial volume effects, affecting ITA measurement accuracy.
Conclusions
Breed and body weight influence ITAt, but ITAr remains consistent and independent of body size, supporting its use as an objective metric for evaluating canine brain atrophy. Sequence- and plane-specific reference values are recommended due to measurement variability across MRI conditions. Incorporating both ITAr and body-weight–adjusted ITAt enhances diagnostic precision, particularly in breeds with wide body size variation. Future studies with larger, breed-balanced samples and finer MRI resolution are warranted to refine clinical reference standards.
Magnetic resonance imaging (MRI) T2-weighted sequence images of a dog in the sagittal (A) and transverse (B) planes. (A) ITAt was measured vertically from the dorsal-to-ventral aspect of the interthalamic adhesion at the thickest level. The solid white lines and solid double-headed arrows indicate the ITAt and the measurement of ITAt, respectively. (B) The ITAt was measured vertically from the dorsal-to-ventral aspect of the interthalamic adhesion at the level where it was apparently the thickest. The cerebral height was measured perpendicularly from the dorsal aspect of the cerebrum to the base of the skull at the same level. The solid white and dashed lines indicate the ITAt and the height of the cerebral parenchyma, respectively. Solid and dashed double-headed arrows indicate the measurement of ITAt and the height of the cerebral parenchyma, respectively. ITAt: interthalamic adhesion thickness, ITAr: ITA-to-cerebral height ratio.
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