In brain death, on Tc-99m HMPAO imaging there is absent or reduced flow in the internal carotid arteries and increased flow within the external carotid arteries. This leads to absent uptake in the brain with subsequent increased perfusion in the nasal region. This appearance has been called the empty light bulb sign.
It has also been described as the hot nose sign.
Although the sign is cute, it is not of any real diagnostic value. The medicolegal importance of brain death is such that direct assessment of cerebral perfusion is required for diagnosis irrespective of if the sign is present.