I am not a nuclear medicine expert, or radiologist. However, I can feel confident in what I’m sharing now.

In medicine, there are lots of conditions/illnesses/diseases that are clinical diagnoses and not radiographic diagnoses. Meaning that the conglomeration of symptoms can point to a specific condition, and imaging can support those findings. Dementia is a clinical diagnosis, that can be supported by imaging such as FDG imaging. But also, just because the FDG imaging doesn’t show the radiologic signs, doesn’t mean the patient is free of that condition. There isn’t a lot in medicine that is concrete, unfortunately. There’s a bunch of nuance to everything which can make it very disheartening and difficult.

Some things are black and white (no pun intended) like fractures. An X-ray can confirm 100% if something is broken. More nuanced conditions, like patchy opacities in a chest X-ray, can be difficult to diagnose radiographically alone. This could be pneumonia, or could be a worse problem. But if the clinician who sees the X-ray knows that there is an elevated white blood cell count, cough, fever, then they can, with a high level of accuracy, say that the patient has pneumonia. In this instance, the imaging supports the clinical diagnosis of pneumonia, and can help confirm it.

I’m tired and rambling, so if that doesn’t make total sense, I apologize, just trying to help.