What tracer is preferred for first-pass cardiac function exams during stress and rest testing?

The preferred tracer for first-pass cardiac function exams during stress and rest testing is Technetium-99m Penetate (DTPA). This preference stems from its favorable characteristics, which include rapid clearance from the blood pool, the ability to provide clear images of the heart's overall function, and a favorable energy profile.

In first-pass studies, the tracer must circulate quickly through the heart so that accurate measurements of ejection fraction and regional wall motion can be made. Technetium-99m under these specific conditions allows for reliable assessment due to its technetium isotopes being widely used in nuclear medicine for their optimal properties, such as lower radiation dose, favorable half-life, and effective imaging capabilities.

While other tracers like Thallium-201 and Iodine-123 may have applications in cardiac imaging, they do not possess the same level of utility for first-pass studies due to factors such as slower kinetics or higher radiation exposure, making DTPA the more suitable choice in this context.