Technetium-99m exametazime (brain perfusion)

Technetium-99m exametazime (Ceretec, GE Healthcare) is a cold kit reconstituted with the user's own technetium-99m generator eluate. Its FDA-labelled indications are cerebral scintigraphy as an adjunct in the detection of altered regional cerebral perfusion in stroke, and, as a separate use of the same kit, radiolabelling of autologous leukocytes for localising intra-abdominal infection and inflammatory bowel disease; it is approved in adults and in paediatric patients aged 2-17. It is a much older, non-specific perfusion agent rather than a targeted molecular tracer: unlike the amyloid, tau and dopamine transporter tracers in this group, HMPAO shows blood flow, not a disease-specific molecular target.

For cerebral scintigraphy the FDA label recommends 370-740 MBq (10-20 mCi) intravenously, with dynamic imaging in the first 10 minutes and static (planar or SPECT) imaging from 15 minutes up to 6 hours after injection; an SNMMI fact sheet on the brain-death application cites a higher adult range of 370-1110 MBq (10-30 mCi). For leukocyte labelling the recommended adult dose is 185-370 MBq (5-10 mCi) of labelled cells, re-injected within about an hour of labelling. Effective dose at the upper cerebral dose of 1110 MBq is roughly 10.3 mSv.

Beyond its labelled stroke indication, Tc-99m HMPAO brain SPECT is used clinically, per SNMMI practice guidance, as an ancillary test to help confirm the absence of cerebral blood flow in patients with an equivocal clinical diagnosis of brain death, a use it shares conceptually with EEG and cerebral angiography. It has also historically been used for perfusion patterns in dementia work-up, but F-18 FDG PET has largely superseded SPECT perfusion imaging for that purpose because of better spatial resolution and more extensive validation.