What are the different types of radiotracers available for stress testing?
There are three basic categories: thallium-201 ( 201 Tl) and technetium-99m ( 99m Tc)-labeled compounds for SPECT, and positron emitting compounds for PET.
The below table compares 201 Tl and 99m Tc-labeled compounds. The most commonly used 99m Tc-labeled compounds are tetrofosmin and sestamibi, which have similar imaging and chemical characteristics. 99m Tc-labeled compounds generally provide more flexibility in terms of imaging times.
Because of the photon energy and the number of photons emitted, 99m Tc-labeled compounds are generally easier to use for image acquisition and analysis. PET radiotracers, such as rubidium-82 ( 82 Rb), nitrogen-13 ( 13 N) ammonia, and fluorine-18 ( 18 F) fluorodeoxyglucose (FDG), can be used to evaluate myocardial perfusion and glucose metabolism, respectively. 13 N ammonia has a short (20 minute) half-life, so there are some logistical limitations in using this for PET cardiac imaging.
Comparison of 99m Tc-Labeled Compounds and 201 Tl for Cardiac SPECT SMPI
| 99m TC-LABELED COMPOUNDS | 201 TL | |
|---|---|---|
| Energy | 140 keV (ideal for gamma camera) | 69-83 keV (suboptimal for gamma camera) |
| First-pass studies of ventricular function | Feasible | Not feasible |
| Gated imaging | Readily accomplished | Count rate marginal for gated imaging |
| Stress/rest imaging | Two injections required since there is no radiotracer redistribution over time | Can be accomplished with one injection since there is radiotracer redistribution over time |
