Related Experiment Videos
Technetium-99m-pertechnetate as a whole blood marker for brain perfusion studies
A J Keyeux1, D A Ochrymowicz-Bemelmans, A A Charlier
1Unit of Cardiovascular Physiology, Université Catholique de Louvain, School of Medicine, Brussels, Belgium.
Unlabelled:
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.
Conclusion:
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.