When MRI is not enough: the case for PET in neuroimaging

When MRI is not enough, PET to the rescue. I say this often, and I want to explain exactly what I mean — because it is not a dismissal of MRI, which is a magnificent and indispensable technology. It is a recognition that different imaging modalities answer fundamentally different questions, and that in the context of neurodegenerative disease, particularly Alzheimer's disease, there are questions that only Positron Emission Tomography (PET) can answer.

Magnetic Resonance Imaging (MRI) excels at revealing the structure of the brain: the size of different regions, the presence of lesions, the integrity of white matter tracts, the degree of atrophy in areas like the hippocampus. For many neurological conditions, this structural information is sufficient. But Alzheimer's disease begins not with visible structural damage, but with subtle changes in brain chemistry and protein accumulation — specifically the deposition of amyloid-beta plaques and tau tangles — that precede overt neuronal loss by years or even decades. By the time MRI can detect hippocampal atrophy, significant and often irreversible neurodegeneration has already occurred. This is the fundamental limitation that PET overcomes.

Amyloid PET and tau PET imaging use radiotracers that bind specifically to these pathological proteins, allowing us to visualize their distribution and burden across the brain with remarkable specificity. This is molecular imaging at its finest: not just a picture of what the brain looks like, but a map of what is happening inside it at the cellular and molecular level. For a patient in the early stages of cognitive decline — or even before any symptoms appear — PET can confirm whether the pathological cascade of Alzheimer's is already underway. That information is what unlocks access to the new disease-modifying therapies that require confirmed amyloid pathology before treatment can begin. At PraanaTech, we build the PET systems that make this kind of imaging accessible beyond the walls of elite research centers — because the power of PET should reach every patient who needs it, not just those lucky enough to live near a major academic hospital.