Radiopharmaceutical: Tc-99m HMPAO (Ceretec) or Tc-99m ECD (Neurolite), 20–25 mCi IV. Both cross an intact blood-brain barrier and are retained in viable neurons proportional to cerebral perfusion.
Protocol: Flow study (2 sec/frame × 60 frames) immediately after injection → static images at 30–60 min. SPECT optional but improves detection of residual perfusion.
Findings and Interpretation
| Finding | Interpretation |
|---|---|
| "Hollow skull" sign — absent cerebral parenchymal activity on planar; no cortical, cerebellar, or brainstem uptake; facial/scalp activity preserved (external carotid territory) | Brain death confirmed — no cerebral perfusion |
| Hot nose sign — prominent nasal soft tissue activity | Supportive of brain death; ECA territory continues perfusing nasal mucosa when ICA flow ceases; high specificity when combined with absent cerebral uptake |
| No sagittal sinus activity on flow images | Absent venous drainage consistent with brain death; helps confirm absent parenchymal perfusion |
| Normal symmetric cortical + cerebellar + deep grey uptake ("bat wings" on anterior view) | Viable cerebral perfusion — brain death NOT confirmed |
Confounders that can suppress perfusion — must be excluded clinically before the study is interpreted as brain death: Barbiturate / sedative coma · Severe hypothermia (<32°C) · Toxic-metabolic encephalopathy · Profound hypotension
Spinal cord and peripheral reflexes may persist with true brain death and do not invalidate the study.
Spinal cord reflexes do not invalidate a brain death scan. Peripheral and spinal cord activity reflects intact spinal arc reflexes below the level of brain death — it is not evidence of intact cerebral perfusion.