Basic imaging - nuclear scans

Role

Nuclear medicine imaging (radiolabelled tracer studies, including PET) provides functional rather than purely structural information - particularly useful in infectious diseases for localising occult infection (fever of unknown origin, prosthetic device/graft infection) where structural imaging (CT/MRI) has been unrevealing or is confounded by post-surgical change
A second- or third-line investigation reserved for specific scenarios where structural imaging has failed to localise a source, given cost and limited availability relative to CT/MRI/ultrasound

18F-FDG PET exploits increased glucose metabolism in areas of active infection/inflammation (as well as malignancy) to localise abnormal metabolic activity; labelled white cell scans (using the patient's own radiolabelled leucocytes) are more specific for infection over sterile inflammation/malignancy in some scenarios (e.g. prosthetic joint infection)

Particularly valuable for fever of unknown origin after standard investigation has failed to localise a cause, and for prosthetic vascular graft or cardiac device infection where structural imaging is limited by metal artefact and post-surgical change
Findings direct targeted further investigation (biopsy, culture) of the abnormal site rather than blind, unfocused testing
Fever of unknown origin, prosthetic vascular graft infection, cardiac implantable device infection, vasculitis (large vessel) - another PET-detectable inflammatory process relevant to the differential

A positive focal finding directs targeted sampling/biopsy of that site for microbiological/histological confirmation, rather than treating the scan result as diagnostic in isolation
A negative scan in a still-unwell patient should prompt reconsideration of the differential rather than being treated as fully excluding infection, given imperfect sensitivity for some infection types

Nuclear imaging findings are localising, not diagnostic in isolation - a positive area of uptake still requires targeted sampling/biopsy for microbiological or histological confirmation before committing to a specific infective diagnosis and treatment course

4 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.