Beyond the Leak: Advanced MRI Assessment of the Blood-Brain Barrier in Neurodegeneration

The blood-brain barrier (BBB) is a specialized multicellular interface that maintains the CNS's tightly regulated microenvironment. BBB disruption is increasingly recognized as a key feature of neurodegeneration, documented across disorders including Alzheimer's disease (AD), Parkinson's disease (PD), and cerebral small vessel disease (cSVD). While the extent to which BBB breakdown is a cause or consequence of neuronal pathology remains unclear, its pronounced presence in disease states suggests a significant contributory role in progression. Advances in MRI have revolutionized our ability to visualize and quantify these alterations in vivo. This review provides a neuroradiological overview of advanced MRI approaches and their specific biomarkers, specifically Dynamic Contrast-Enhanced MRI (DCE) with Ktrans and Arterial Spin Labeling (ASL) with kw, detailing disease-specific BBB signatures in major neurodegenerative disorders. Current technological strides, including ultra-high-field MRI and AI-assisted post-processing, are pushing the sensitivity needed to detect subtle BBB changes. Ultimately, with technical refinement and standardization, MRI methods are transitioning from research tools into candidate neurovascular biomarkers with growing potential for early diagnosis, treatment monitoring, and longitudinal follow-up, pending multicenter standardization and normative validation.