Key Points:

• lipophilic perfusion agents like 99mTc-HMPAO and 99mTc-ECD cross the blood-brain barrier and should be taken up by perfusing brain parenchyma. They also allow for more delayed imaging, including SPECT imaging.
• hydrophilic perfusion agents like 99mTc-DTPA are flow agents that do not cross the blood-brain barrier, so tight bolus and imaging timing is required to demonstrate intracranial flow.
• brain death scans are an adjunctive confirmatory tool to appropriate clinical diagnosis of brain death. They do not diagnose brain death.