Technetium exits the generator in the form of the pertechnetate ion, TcO. The oxidation state of Tc in this compound is +7. This is directly suitable for medical applications only in bone scans (it is taken up by osteoblasts) and some thyroid scans (it is taken up in place of iodine by normal thyroid tissues). In other types of scans relying on Tc, a reducing agent is added to the pertechnetate solution to bring the oxidation state of the technecium down to +3 or +4. Secondly, a ligand is added to form a coordination complex. The ligand is chosen to have an affinity for the specific organ to be targeted. For example, the exametazime complex of Tc in oxidation state +3 is able to cross the blood–brain barrier and flow through the vessels in the brain for cerebral blood flow imaging. Other ligands include sestamibi for myocardial perfusion imaging and mercapto acetyl triglycine for MAG3 scan to measure renal function.