Tc-99m MDP Bone Scintigraphy

Bone scintigraphy uses Tc-99m-labelled diphosphonates (MDP or HDP) that adsorb onto hydroxyapatite in proportion to osteoblastic activity and regional blood flow. It is a highly sensitive whole-body survey for skeletal disease, detecting osteoblastic turnover before radiographic change. The optional three-phase technique (dynamic flow, blood-pool and delayed images) distinguishes soft-tissue from osseous pathology and is particularly useful for infection and complex regional pain syndrome.

Indications

Detection and monitoring of osteoblastic skeletal metastases (breast, prostate, lung)
Suspected osteomyelitis and diabetic foot infection using the three-phase technique
Occult, stress or insufficiency fractures not evident on radiographs
Evaluation of painful joint prostheses for loosening versus infection
Assessment of metabolic bone disease, Paget disease, and complex regional pain syndrome

Contraindications & Cautions

Pregnancy is a relative contraindication; defer unless the benefit outweighs fetal dose
Breastfeeding: interruption is generally not required with Tc-99m diphosphonates, but close/prolonged infant contact and feeding immediately post-injection are minimised per local rules
No absolute contraindications otherwise; ensure the patient can lie still for imaging
Recent nuclear medicine studies with residual tracer may degrade image quality — check prior administrations
Renal impairment prolongs soft-tissue background but is not a contraindication; optimise hydration

Patient Preparation

No fasting required; encourage oral hydration after injection to improve target-to-background ratio
Void immediately before delayed imaging to reduce bladder activity and pelvic obscuration
Remove metallic objects and coins from pockets that could cause attenuation artefacts
Delay of 2-4 hours between injection and delayed static/whole-body images for bone uptake and soft-tissue clearance
Confirm pregnancy status and recent radiopharmaceutical or radiographic contrast administration

Technique & Parameters

Inject Tc-99m MDP/HDP 740-1110 MBq (20-30 mCi) intravenously
Three-phase option: (1) dynamic flow (radionuclide angiogram) over ~60 s, (2) immediate blood-pool image, (3) delayed images at 2-4 h
Acquire whole-body anterior and posterior planar sweeps with a large field-of-view gamma camera and high-resolution collimator
Add SPECT or SPECT/CT for problem-solving (spine, pelvis, feet) to localise and characterise lesions
Optional fourth-phase (24 h) delayed images improve specificity in osteomyelitis with poor renal clearance

Systematic Review

Assess tracer distribution symmetry, kidney and bladder visualisation, and overall image quality
On three-phase studies, correlate flow and blood-pool with delayed uptake to localise pathology
Review the whole skeleton systematically: skull, axial spine, ribs, pelvis, and appendicular bones
Identify focal versus diffuse uptake and any photopenic (cold) defects
Correlate suspicious foci with SPECT/CT or radiographs to distinguish benign degenerative from metastatic disease

Key Findings & Significance

Multiple randomly distributed focal foci in the axial skeleton and ribs favour metastatic disease
Superscan: diffusely increased skeletal uptake with faint or absent renal and soft-tissue activity ("absent kidney sign") from widespread metastases or metabolic bone disease
Three-phase positivity in all phases at bone suggests osteomyelitis; blood-pool-only positivity suggests cellulitis/soft-tissue infection
Photopenic (cold) lesions occur with aggressive lytic metastases (e.g. renal, myeloma), infarction or avascular disease
Flare phenomenon: apparent increase in uptake at 3-6 months after successful therapy reflecting healing, not progression

Differential Considerations

Solitary focus: fracture, degenerative change, metastasis, osteoid osteoma, Paget disease
Multiple foci: metastases, healing/traumatic fractures (linear, aligned with ribs), polyostotic Paget or fibrous dysplasia
Superscan: diffuse osteoblastic metastases, renal osteodystrophy, hyperparathyroidism, osteomalacia
Photopenic lesion: aggressive lytic metastasis, myeloma, bone infarct, radiotherapy port, avascular necrosis (early)
Periarticular uptake: osteoarthritis, inflammatory arthropathy, complex regional pain syndrome (periarticular pattern)

Pearls & Pitfalls

Rib metastases are typically rounded and randomly placed, whereas traumatic fractures align linearly along a rib and at consecutive levels
The flare phenomenon can mimic progression — interpret early post-treatment scans with the clinical and biochemical picture
SPECT/CT dramatically improves specificity in the spine and feet by localising uptake to a benign or malignant substrate
A superscan can be missed because it looks "too good" — the absent-kidney sign is the clue
Purely lytic lesions (myeloma, renal cell) may be normal or cold on bone scan; correlate with skeletal survey or FDG PET

Structured Report

State tracer, injected activity, phases performed and any SPECT/CT
Describe the pattern and distribution of abnormal uptake and any photopenic defects
Correlate with prior imaging and note flare versus true progression on treatment follow-up
Give a probability of metastatic disease and recommend correlative imaging where indicated
Provide a concise impression addressing the referring clinical question

References

Van den Wyngaert T, et al. The EANM practice guidelines for bone scintigraphy. Eur J Nucl Med Mol Imaging 2016
SNMMI Procedure Standard for Bone Scintigraphy 3.0
Love C, et al. Radionuclide bone imaging: an illustrative review. RadioGraphics 2003
Palestro CJ, et al. Combined labeled leukocyte and technetium-99m sulfur colloid bone marrow imaging for diagnosing musculoskeletal infection. RadioGraphics 2006

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

Tc-99m MDP Bone Scintigraphy

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References