MYOCARDIAL PERFUSION TRACERS

Thallium has the advantage of not being taken up by adjacent tissues as much as MIBI. However, it has several disadvantages:

1. When it degrades the photons it gives off have an energy of 73keV and so the pictures are not as clear as the 140keV of Tc.
2. It has a half-life of 73 hours, so the patient receives a large dose of radiation.

The test protocol for Thallium is to stress the patient, take the image and then wait for 4 hours before taking the redistribution image. If all is not normal on this rest/redistribution image then a second dose is injected and reinjection images acquired to see if the defect goes away or if it is a true infarct.

With Tc-MIBI there is a lot of extra-cardiac uptake and so the times that one has to wait after the injection are:- 1/4 hour after a stress & 3/4 hour after a rest, because there is no sympathetic stimulus shutting down the GI system.