Brain perfusion single-photon emission computed tomography (SPECT) imaging is a functional nuclear imaging technique performed to evaluate regional cerebral perfusion.Because cerebral blood flow is closely linked to neuronal activity, the activity distribution is presumed to reflect neuronal activity levels in different areas of the brain. A lipophilic, PH-neutral radiopharmaceutical (most commonly99m Tc-hexamethylpropyleneamine oxime [HMPAO] and99m Tc-ethylene cysteine diethylester [ECD], with a half-life of 6.02 hours) is injected into the patient, which crosses the blood-brain barrier and continues to emit gamma rays. A 3-dimensional representation of cerebral blood flow can be iterated using gamma detectors, allowing for interpretation. Brain SPECT imaging has many different clinical applications.