The second most frequent type of SPECT study is brain perfusion imaging, for similar reasons as those described at the beginning of the previous section. Although brain SPECT is used to assess several types of abnormalities of cere­bral circulation, an especially difficult task is to investigate epilepsy. The prob­lem is that the patient usually cannot remain still during seizure, so it is hard to take images of any kind. However, the radiopharmaceutical HMPAO (99mTc-D, L-hexamethylene-propyleneamine oxime) reaches an equilibrium distribution in the brain in only 1—2 min after injection, and then the distribution does not change for several hours. So if we succeed in administering HMPAO during sei­zure, we may take images 1—2 h following the seizure, when the patient is able to lie still for 20—30 min. An epileptic focus is hyperperfused during seizure, while it is hypoperfused in an interictal state.