What organ receives the highest dose from Tc exametazime (HMPAO)?

• A. Heart
• B. Kidneys and bladder
• C. Liver
• D. Brain

Answer: (B)

The highest dose from Tc exametazime (HMPAO) is received by the kidneys and bladder due to the pharmacokinetics of this radiopharmaceutical. Tc exametazime is a lipophilic compound that crosses the blood-brain barrier effectively, which makes it useful for brain imaging. However, it is also metabolized and excreted via the renal system.

This means that following administration, a significant amount of the radiopharmaceutical is processed by the kidneys, resulting in increased radiation exposure to these organs. After filtration by the kidneys, the tracer is excreted into the bladder, where it can accumulate. Therefore, both the kidneys and bladder experience increased doses of radiation due to the tracer's elimination path in the body.

In contrast, while the brain does receive radiation during imaging, it does not experience the same degree of exposure as the kidneys and bladder from the elimination of Tc exametazime. Other organs listed, such as the heart and liver, receive doses, but the renal system is primarily involved in the handling of the radiopharmaceutical, leading to the highest doses being directed there.