SPECT with dynamic 99mTc-ECD (ethyl cysteinate dimer) injection (stack 1). During the dynamic phase, there is perfusion in the carotids bilaterally but none in the anterior and middle cerebral arteries.
A static scan 20 minutes after 99mTc-ECD injection (stack 2) shows no radiotracer uptake (i.e. no brain perfusion) in the brain parenchyma, including the cerebral cortex, basal ganglia, cerebellum, and medulla.
The appearance of an "empty" cranium is referred to as the empty light bulb sign.