In the absence of light. Brain death or death by neurological criteria BD/DNC is the irreversible cessation of all brain and brainstem activity. Brain death testing requires a highly meticulous set of clinical neurological exams and apnea testing that assesses cerebral and brainstem function. These tests must be performed under the appropriate clinical settings and set of hemodynamic/pharmacological parameters to avoid any confounding variables.

In situations where the clinical examination alone is inadequate in assessing for BD/DNC, specific ancillary testing can be used to confirm the diagnosis. One such test is Nuclear perfusion imaging that follows radiotracer uptake. In a patient with brain death, there is reduced uptake in the cerebrum due to absent blood flow in the internal carotid arteries but relative increase uptake in the nasal/jaw-temporal regions due to flow in the external carotids arteries. This radiological sign is referred to as the empty light bulb sign or hot nose sign and confirms brain death.