Brain-Death Confirmation (Cerebral Perfusion)
Radionuclide cerebral perfusion imaging is a highly specific ancillary test to confirm brain death when clinical examination is limited or confounded. Absent intracranial perfusion — the “hollow/empty skull” (or “light-bulb”) sign with no intracranial tracer, including the posterior fossa — supports the diagnosis. It is an adjunct: clinical and, where required, apnoea testing remain primary.
Brain death produces cessation of intracranial blood flow. Lipophilic perfusion agents (⁹⁹ᵐTc-HMPAO/ECD) that normally show brain uptake instead show none, while scalp/face perfusion may persist — the basis of the classic sign.
When to use
- Confirmatory testing when clinical criteria cannot be fully applied or are confounded (e.g. sedation, facial trauma).
- When apnoea testing is unsafe or inconclusive.
- Institutional/legal requirement for an ancillary test.
How to read it
- Absent intracranial activity (cerebrum, cerebellum and brainstem) on a technically adequate study confirms absent brain perfusion; any intracranial activity indicates perfusion.
- Persistent scalp/facial (external carotid) activity is expected and does not indicate brain perfusion.
- A perfusion agent with brain uptake (HMPAO/ECD) makes parenchymal assessment more robust.
Protocol
- Ensure adequate tracer preparation and a good bolus injection.
- Acquire a dynamic flow phase, then parenchymal images at ~20 min (anterior and lateral, plus posterior/second lateral for the posterior fossa); SPECT(/CT) is optional but improves posterior-fossa assessment.
- Confirm technical adequacy before interpreting an absent-flow study.
Pitfalls
- Poor bolus or tracer preparation can falsely suggest absent flow — verify technique.
- It is an ancillary test; it does not replace clinical determination.
- Scalp activity should not be mistaken for cerebral perfusion; the “hot nose” sign is neither sensitive nor specific.
Evidence & guidelines
- Cerebral perfusion scintigraphy is an accepted ancillary confirmatory test in brain-death protocols.
- SNMMI/EANM guideline 3.0 (2025): lipophilic agents (HMPAO/ECD) are strongly preferred; hydrophilic agents (e.g. DTPA) remain acceptable when these are unavailable.
- Used within institutional and national brain-death determination guidance.
In depth
- The AAN lists ⁹⁹ᵐTc-HMPAO scintigraphy as an ancillary test; brain-specific lipophilic agents (HMPAO or ECD) are preferred, with an optional flow study followed by planar anterior and both lateral views (about 20 min or later after injection) and SPECT when feasible.
- Non-specific agents such as ⁹⁹ᵐTc-DTPA show only large-vessel flow and cannot reliably exclude isolated posterior-fossa perfusion, so current consensus favours brain-specific lipophilic agents to confirm whole-brain death.
- Absent parenchymal uptake gives the ‘hollow skull’ sign; increased activity in the nasal region on anterior views (‘hot nose’ sign), from external carotid flow, is supportive but not diagnostic on its own.
- With non-brain-specific agents, faint superior sagittal sinus activity on delayed images is seen in up to half of patients despite brain death (via external carotid and meningeal branches), so it should not by itself be read as cerebral perfusion.
- Meta-analysis (Joffe): planar sensitivity 77.8% / specificity 100%; SPECT 88.4% / 100% for absent brain perfusion in clinically confirmed brain death.
- SPECT is mainly supplemental (separates scalp/parotid/muscle from brain) and is often impractical in unstable ventilated patients.
- Demonstrable brainstem tracer means flow is present and does not meet whole-brain-death criteria; brain-specific agents give near-100% specificity.
Sources: AAN practice parameter 1995 (PMID 7746374) · SNM brain death scintigraphy guideline 2.0, J Nucl Med Technol 2012 · 40:198 · Günther et al. Diagnostics 2025 (PMID 41226026) · Joffe et al. J Intensive Care Med 2010 (PMID 20095080)