When the supply of 99m Technetium became unavailable from vendors, old-standby Thallium protocols kept Nuclear Cardiology labs open for business without missing a beat.
Thallium imaging is historically significant as the epitome of myocardial perfusion imaging for decades, becoming a sort of ‘gold standard’ for its time.
The scintigraphic images obtained early after injection reflect the blood flow conditions at the time of tracer administration.
Perfusion defects observed on the Tl-201 images obtained 10 minutes after exercise indicate transient ischemia or a scar, or a combination of the two.
It remained popular even after 99m Technetium based tracers became available for single-day imaging protocols, viability studies, or in conjunction with 99m Tc tracers in ‘hybrid’ dual-isotope protocols.
It was common to do resting Thallium perfusion imaging, followed by 99m Tc-sestamibi gated SPECT stress imaging, combining the best characteristics of both radiopharmaceuticals.
The local concentration of Tl-201 changes until equilibrium is reached and the ratio between input and output becomes constant.
Several factors that contribute to the washout rate of Tl-201 include: ischemia; the target-to-background ratio; alterations in myocardial blood flow after tracer administration; and elevation in blood glucose levels resulting from eating soon after injection (Thallium shifts to the stomach).
Unless your patients are all males under 150 lbs., the 3 m Ci stress dose may not yield the counting statistics or image quality physicians have grown accustom to since the development of Technetium tracers.Tl-201 scintigraphy is most often performed in conjunction with exercise stress in patients suspected or known to have CAD.In addition to detection of stress-induced ischemia with exercise, the radionuclide test permits simultaneous assessment of regional myocardial viability.Thus, several hours after initial tracer administration the scintigraphic images depict an equilibrated pattern.This is the basis of the “stress-redistribution” imaging strategy that has been used in the detection of CAD.
We are planning to contact the BASILISK party attendees who won “door prizes” personally by email sometime next week.