Bone Scan Timing: When to Acquire Delayed Images

D. 2–4 hours after injection

Whole-body bone scan 'delayed phase' images are typically acquired 2–4 hours after IV injection of Tc-99m MDP. This delay allows: (1) adequate time for bone uptake via chemisorption onto hydroxyapatite; (2) sufficient clearance of background soft-tissue and blood-pool activity via renal excretion; (3) optimal bone-to-soft tissue contrast. Imaging too early results in high background soft-tissue activity and poor bone-to-background ratio. In patients with renal impairment, the delay may need to be extended to 4–6 hours to allow adequate clearance.