Diagnostic Procedures and Clinical Applications
Core concepts
Diagnostic nuclear medicine questions usually test a chain: indication → radiopharmaceutical → mechanism of localization → timing → expected normal distribution → common pitfalls. For bone scintigraphy with Tc-99m MDP, images are typically delayed 2–4 hours, with hydration and voiding before acquisition; a three-phase study adds flow and blood-pool phases. Myocardial perfusion uses rest/stress perfusion patterns; renal studies use tracers such as MAG3 or DTPA and require attention to hydration and bladder activity; hepatobiliary imaging uses IDA agents and timing after injection; thyroid imaging may use pertechnetate or radioiodine; V/Q and labeled-RBC studies have specific acquisition and contraindication issues. FDG PET requires fasting and glucose control per protocol.
Traps
A common trap is answering from the image pattern alone without matching the tracer’s biodistribution and the study timing. Urinary contamination, injection-site infiltration, and attenuation can mimic disease. Do not confuse blood-pool activity with delayed bone uptake. Know which studies are functional versus anatomic and when SPECT/CT adds localization.
Worked rule
If a delayed bone scan shows focal rib uptake, first confirm history of trauma, injection quality, and contamination; then correlate with prior imaging. A solitary focus is not automatically metastatic. Rule of thumb: interpret every finding against tracer, timing, and expected normal biodistribution.