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Nuclear Medicine

Biological half-life

Is there a formal, precise industry-standard definition for the biological half-life of radiopharmaceutica ls? Consider an agent that is excreted exclusively by the kidneys, 50% of the circulating agent every 10 minutes. Does that make its biological half-life 10 minutes? Or is it longer because of the time the agent spends sitting in the bladder? That would require some MIRD-like assumptions about urine output, voiding frequency, and post-void residual. Or is the biological half-life 10 minutes on the ground that after 10 minutes, half as much agent remains available to do its intended job?  (Sep 15, 2012 | post #1)