Osteomyelitis is usually evident on the bone scan early, 1 week to 10 days before
x-ray changes become evident on film. Modification to the routine bone scan to a three
phase bone scan in addition to the routine delayed (2-3 hour) static images also includes
a radionuclide angiogram and blood pool images. Multiple delayed images (up to 24 hours
post injection) aid in the ability to distinguish between cellulitis and osteomyelitis.
Early images identify uptake of tracer independent of hyperemia.
Osteomyelitis demonstrates increasing lesion to background activity with time, whereas
cellulitis shows the opposite.