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IMAGE INTERPRETATION · BONE IMAGING

Tc-99m Physical Half-Life

Whole-body Tc-99m MDP bone scan
Whole-body Tc-99m MDP bone scan

CC BY 3.0 · Myohan / Wikimedia Commons · source file

Question

Tc-99m is the most widely used radionuclide in nuclear medicine. What is its physical half-life?

  1. A2.1 hours
  2. B6.02 hours
  3. C13.2 hours
  4. D24 hours
Show the answer and explanation

B. 6.02 hours

Tc-99m has a physical half-life of 6.02 hours, making it ideal for nuclear medicine imaging. It decays by isomeric transition (IT) to Tc-99, emitting a 140 keV gamma ray — the optimal energy for SPECT gamma cameras (high enough for adequate tissue penetration, low enough for efficient collimation). It is produced from Mo-99/Tc-99m generators ('moly cows'), which are replenished weekly. Its 6-hour half-life allows completion of studies with reasonable radiation dose and rapid patient clearance. Compare: I-123 = 13.2 hrs; F-18 = 110 min; Ga-68 = 68 min; I-131 = 8 days.

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Tc-99m MDP bone scan — hip region with prosthesisPeriprosthetic Uptake After Hip Replacement Whole-body bone scan — delayed phase imagesBone Scan Timing: When to Acquire Delayed Images Whole-body Tc-99m MDP bone scan, anterior and posterior projectionsNormal Whole-Body Bone Scan (Tc-99m MDP) Whole-body bone scintigraphy (Tc-99m)Diffuse Skeletal Metastases on Bone Scan Tc-99m MDP bone scan, focal uptake in the hip regionFemoral Neck Stress Fracture on Bone Scan Tc-99m MDP bone scan showing focal uptake at the femoral neckFemoral Neck Insufficiency Fracture on Bone Scan
← Fibrous Dysplasia on Bone Scan (Shepherd’s Crook)Periprosthetic Uptake After Hip Replacement →

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