title: Technetium-99m-pertechnetate as a whole blood marker for brain perfusion studies.
abstract: In the brain, diffusible 99mTc-pertechnetate behaves as an intravascular indicator because it is confined within the circulation by the blood-brain barrier, allowing its use for noninvasive dynamic evaluation of cerebral circulation. For this application 99mTc has often been claimed to be a plasma marker. This study examines the validity of such a claim which has not yet been proven in vivo.
  
  
  METHODS
  The relative amount of 99mTc in the red cells circulating in large vessels was compared to the corresponding hematocrit (LV Hct) during the rapid (t/2 = 1.98 min) and slow (t/2 = 84 min) phases of 99mTc disappearance from the circulation after bolus intravenous injection. These comparisons were performed on rats at 2 (n = 3), 5 (n = 6), 10 (n = 6) and 20 (n = 9) sec after intravenous injection for the rapid phase and 5 (n = 5), 30 (n = 4), 60 (n = 6) and 120 (n = 6) min after intravenous injection for the slow phase.
  
  
  RESULTS
  The results show that the relative amount of intravascular 99mTc fixed to red cells did not differ statistically from LV Hct until at least 1 hr after intravenous administration. This homogeneous distribution of 99mTc in blood was indisputable during the first 20 sec but became progressively less evident and disappeared after 2 hr. Such behavior was attributed to a progressive increase of free 99mTc, which, in whole blood, amounted to 4% at 20 sec and 25% at 2 hr after injection.
  
  
  CONCLUSIONS
  Because it is a 96% whole blood marker early after intravenous administration, 99mTc is a reliable agent for first-pass studies of whole blood circulation in the brain.
authors.affiliation: Unit of Cardiovascular Physiology, Université Catholique de Louvain, School of Medicine, Brussels, Belgium.
authors.forename: A J
authors.initials: AJ
authors.lastname: Keyeux
authors.forename: D A
authors.initials: DA
authors.lastname: Ochrymowicz-Bemelmans
authors.forename: A A
authors.initials: AA
authors.lastname: Charlier
mesh_terms: D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004912:Erythrocytes; D005260:Female; D006400:Hematocrit; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley; D013670:Sodium Pertechnetate Tc 99m
chemical_list: D013670:Sodium Pertechnetate Tc 99m