Tc99mMDP

Tc-99m MDP, or technetium-99m methylene diphosphonate, is a radiopharmaceutical used for bone scintigraphy. It consists of technetium-99m bound to methylene diphosphonate, a bone-seeking ligand that localizes to hydroxyapatite at sites of active bone remodeling.

Preparation and mechanism: Tc-99m pertechnetate is obtained from a molybdenum-99/technetium-99m generator and is reduced in a methylene diphosphonate kit by stannous ions to form a Tc-99m MDP complex. After intravenous administration, the agent rapidly clears from soft tissues and concentrates in bone, with uptake proportional to blood flow and osteoblastic activity. The majority of the radiopharmaceutical is excreted by the kidneys.

Indications: Tc-99m MDP is used in bone scintigraphy to evaluate metastatic bone disease, osteomyelitis, fractures and occult injuries, prosthetic loosening, Paget disease, and other conditions with abnormal bone turnover.

Imaging and interpretation: Following injection, planar whole-body images are typically acquired 2–4 hours later, with additional SPECT or SPECT/CT as needed for localization and characterization. The technique is highly sensitive but not disease-specific.

Safety: The examination delivers a moderate radiation dose. Adverse reactions are rare. Pregnancy and lactation require special consideration; breastfeeding can usually continue with post-imaging breast milk handling. Preparation includes hydration and voiding to reduce radiation exposure. The procedure requires licensed facilities and trained personnel.

Limitations and interpretation: Tc-99m MDP uptake is influenced by perfusion, bone turnover, and renal function. Increased uptake occurs in malignancy, infection, fracture, and inflammation; decreased uptake may occur in certain metabolic bone conditions. Correlation with clinical findings and other imaging improves specificity.