Urinary excretion of 99mTc administered as microspheres

Area of Science:

• Nuclear Medicine
• Radiopharmacology
• Medical Imaging

Background:

• Technetium-99m (99mTc) labeled agents are widely used in nuclear medicine.
• Understanding the biodistribution and excretion of radiopharmaceuticals is crucial for dose assessment.
• Albumin microspheres are utilized in various diagnostic and therapeutic applications.

Purpose of the Study:

• To quantify the urinary excretion of 99mTc-albumin microspheres.
• To determine the radiation dose to the bladder wall following intravenous administration.
• To characterize the chemical form of excreted 99mTc.

Main Methods:

• Intravenous administration of 99mTc-albumin microspheres.
• Measurement of urinary radioactivity over 25 hours.
• Calculation of bladder wall radiation dose based on administered activity.
• Analysis of the chemical state of excreted 99mTc.

Main Results:

• Average accumulated urinary excretion reached 0.68% at 1 hour and 18.6% at 24 hours.
• The averaged bladder wall dose was 101.98 mrad (1,019.79 muGy) for a 3 mCi (111 MBq) dose.
• Excreted 99mTc was primarily free pertechnetate, with some reduced species also detected.
• Renal uptake within 15 minutes is not necessarily indicative of shunting.

Conclusions:

• Significant urinary excretion of 99mTc-albumin microspheres occurs within 24 hours.
• The bladder wall receives a measurable radiation dose, necessitating consideration in dosimetry.
• The chemical form of excreted 99mTc is predominantly pertechnetate.
• Early renal uptake should be interpreted cautiously in the context of potential shunting.