Age-specific resources mitigate biases in human MRI processing arising from structural changes across the lifespan. There are fewer age-specific resources for preclinical imaging, and they only represent developmental periods rather than adulthood. Since rats recapitulate many facets of human aging, it was hypothesized that brain volume and each tissue’s relative contribution to total brain volume would change with age in the adult rat. However, the currently available tissue probability maps, which provide a priori information for tissue volume estimation, provide inaccurate grey matter probabilities in subcortical structures, particularly the thalamus. Consequently, age-specific templates and tissue probability maps were generated from a longitudinal study that scanned a cohort of rats at 3, 5, 11, and 17 months old. Mixed-effects models assessed the effect of age on brain, grey matter, white matter, and CSF volumes, and the relative tissue proportions. Grey and white matter volume increased with age, and the tissue proportions relative to total brain volume varied throughout adulthood. Furthermore, we present evidence of a systematic underestimation of thalamic grey matter volume with existing resources, which is mitigated with the use of age-specific tissue probability maps since the derived estimates better matched histological evidence. To reduce age-related biases in image pre-processing, a set of rat brain resources from across the adult lifespan is consequently released to expand the preclinical MRI community’s fundamental resources.
Morphological changes after cranial fractionated photon radiotherapy: localized loss of white matter and grey matter volume with increasing dose
