Bone Scintigraphy
Snapshot
⁹⁹ᵐTc-diphosphonate bone scintigraphy images osteoblastic activity across the whole skeleton with high sensitivity. The three-phase technique (flow, blood-pool, delayed) helps separate infection and inflammation from simple bone turnover. Its non-specificity is its main limitation — addressed by SPECT/CT.
Diphosphonates adsorb onto hydroxyapatite wherever bone turnover is increased, so metastases, fractures, infection, arthritis and Paget’s all appear as increased uptake. Interpretation relies on pattern, distribution and correlation.
3-phaseFlow/pool/delayed
Whole-bodySensitive survey
Non-specificCorrelate/SPECT-CT
When to image
- Whole-body survey for skeletal metastases.
- Occult/stress fractures and bone trauma.
- Suspected osteomyelitis (three-phase screen).
- Metabolic and arthritic bone disease.
How to read it
- Delayed images show the distribution of bone turnover; multiple random lesions suggest metastases.
- Three-phase positivity (all phases) supports osteomyelitis in otherwise normal bone; specificity falls after fracture, surgery or with neuropathic joints (add infection imaging). Delayed-only uptake suggests remodelling.
- Correlate with radiographs and clinical context; escalate to SPECT/CT for equivocal foci.
Protocol
- ⁹⁹ᵐTc-MDP/HDP; delayed whole-body at ~2–5 h (usually 2–4 h); late 6–24 h images if soft-tissue clearance is poor.
- Add three-phase (flow/blood-pool) when infection or inflammation is the question.
- SPECT/CT of problem regions.
Pitfalls
- Purely lytic lesions are under-detected — bone scan is not indicated for myeloma/plasmacytoma (use MRI or PET/CT).
- Degenerative and traumatic uptake mimics disease — correlate.
- A “superscan” (diffuse high uptake) can be missed as normal.
Evidence & guidelines
- EANM bone scintigraphy guideline (Van den Wyngaert et al., Eur J Nucl Med Mol Imaging 2016;43:1723–1738) and SNMMI bone scintigraphy procedure standard 4.0 (Bartel et al., J Nucl Med Technol 2018;46:398–404).
- SPECT/CT markedly improves specificity of equivocal findings.
In depth
- Non-osseous soft-tissue MDP uptake groups into four mechanisms — metastatic calcification, dystrophic calcification, metabolic uptake, compartmental sequestration — plus a spurious/artefactual category.
- Metastatic calcification occurs with hypercalcaemia or a raised calcium–phosphate product (hyperparathyroidism, chronic renal failure, bone destruction, vitamin D excess, sarcoidosis, milk-alkali syndrome) and favours relatively alkaline tissues such as lung, stomach and kidney; diffuse lung and gastric uptake is typical of renal failure with secondary hyperparathyroidism.
- Dystrophic calcification (normal Ca/PO4): infarction of brain/heart/muscle, uterine myomata, myositis ossificans, DVT/phlebitis, scars, injection sites, dermatomyositis.
- Metabolic uptake occurs in tumours that form osteoid or calcify, such as osteosarcoma and its metastases, mucin-producing adenocarcinomas (lung, breast, gastrointestinal, ovary) and neuroblastoma, and in amyloid deposits.
- Compartmental sequestration: oedematous obstructed limbs, malignant pleural effusions, peritoneal ascites (slow washout, high permeability).
- Splenic uptake with sickle-cell autoinfarction (also lymphoma); marrow-expansion uptake in sickle-cell disease.
- Extravasated tracer at the injection site can drain via lymphatics to regional lymph nodes, which then take up activity; imaging the injection site confirms the cause.
- Radiolabelled urine reaching bowel (fistula, urinary diversion, ingestion) produces intestinal uptake.
- A poor bone-to-soft-tissue ratio, with persistent soft-tissue activity on 2–4 h delayed images, suggests renal impairment, poor hydration, imaging too early or poor radiopharmaceutical quality.
Sources: PMID 20513447 (Zuckier & Freeman 2010) · PMID 20513447 · PMID 8356264 · PMID 12968045 · PMID 12968045 (Loutfi 2003) · EANM bone scintigraphy guideline 2016