Technetium-99m (Tc-99m) is the most widely used radionuclide in nuclear medicine. It is a metastable nuclear isomer of Tc-99 with a physical half-life of:

• A 6 hours ✓
• B 13 hours
• C 24 hours
• D 2.7 days

Explanation

Tc-99m has a physical half-life of exactly 6 hours, making it ideal for clinical nuclear medicine: long enough to allow labelling, quality control, and imaging (several hours of imaging window), yet short enough to minimise patient radiation dose. It decays by isomeric transition emitting a 140 keV gamma ray — optimal for gamma camera detection (close to ideal 100–200 keV window). It is eluted from a Mo-99/Tc-99m generator system (cow), where Mo-99 has a 66-hour half-life and continuously produces Tc-99m. Gallium-67 has a 78-hour half-life; I-131 has an 8-day half-life; F-18 (PET) has a 110-minute half-life.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.