Tc99mHDP

Tc-99m hydroxymethylene diphosphonate (Tc-99m HDP) is a radiopharmaceutical used in bone scintigraphy. It consists of technetium-99m bound to a diphosphonate compound, enabling preferential uptake in bone tissue. The agent is widely used for evaluating skeletal diseases due to its ability to reflect osteoblastic activity and regional blood flow.

Mechanism and imaging characteristics

Tc-99m HDP localizes to bone by chemisorption onto hydroxyapatite crystals at sites of active bone formation and remodeling. Uptake is influenced by blood flow and osteoblastic activity, resulting in increased signal in regions such as fractures, metastases, infections, or inflammatory processes. After intravenous administration, soft tissue clearance is relatively rapid, and imaging is typically performed 2 to 4 hours post-injection. Planar gamma camera imaging is common, with single-photon emission computed tomography (SPECT) often used to improve lesion localization.

Clinical uses

Tc-99m HDP is employed in bone scintigraphy to detect skeletal metastases, evaluate unexplained bone pain, assess fractures or vertebral compression injuries, and investigate suspected osteomyelitis or other inflammatory bone conditions. It can provide whole-body screening as well as targeted imaging with SPECT/CT for better anatomical correlation.

Administration and safety

The radiopharmaceutical is given by intravenous injection. Imaging protocols, including dose and timing, vary by facility. Tc-99m emits gamma rays suitable for medium-energy collimation, with a physical half-life of about six hours, providing adequate imaging windows while minimizing radiation exposure. Tc-99m HDP is generally well tolerated; as with all radiopharmaceuticals, use is limited in pregnancy and lactation, and rare hypersensitivity reactions may occur.

See also

Technetium-99m radiopharmaceuticals; bone scintigraphy; diphosphonate imaging agents.