99mTcHMPAO

99mTcHMPAO, or technetium-99m hexamethylpropyleneamine oxime (exametazime), is a radiopharmaceutical used in single-photon emission computed tomography (SPECT) imaging to assess cerebral perfusion. It is a lipophilic complex formed by radiolabeled HMPAO that rapidly crosses the blood-brain barrier after intravenous injection.

Once inside brain tissue, HMPAO is sequestered as a hydrophilic complex, effectively trapping technetium-99m in neurons and glia. The resulting distribution reflects regional cerebral blood flow at the time of injection and remains relatively stable for several hours, permitting flexible imaging.

Clinical applications include evaluation of suspected stroke and transient ischemic attack, localization of epileptic foci in presurgical planning, and assessment of neurodegenerative disorders such as dementias by visualizing perfusion patterns. It can also be used in brain death assessments when perfusion is absent.

Imaging workflow: after injection, SPECT imaging is performed typically 30-60 minutes post-injection. The resulting images are often interpreted with co-registered CT or MRI and compared to normative databases. The modality provides functional information complementary to structural imaging.

Dose and safety: an adult typically receives about 20-25 millicuries (740-925 MBq) of 99mTc-HMPAO. The agent has a short physical half-life (about 6 hours) and has a favorable safety profile; adverse effects are rare. Use is guided by standard radiopharmaceutical safety practices, including pregnancy considerations.

Production and handling: prepared from a kit that reduces sodium pertechnetate using stannous ions; labeling yields the lipophilic complex. The name exametazime is often used to identify it.