01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Bone scintigraphy is functional imaging of tracer distribution related to active bone formation. After intravenous 99mTc-labelled phosphate or diphosphonate, delivery depends on blood flow and retention depends largely on osteoblastic activity and mineralisation. The same biological response occurs in malignant, traumatic, infectious, degenerative, metabolic and postoperative conditions, making the study sensitive in active bone turnover but often nonspecific.
Planar whole-body imaging surveys the skeleton, while spot views and SPECT add detail. SPECT/CT pairs functional activity with anatomic localisation and can show whether an uptake focus is in a facet joint, fracture line, prosthesis interface or cortical lesion. Multiphase imaging separates hyperaemia, soft-tissue blood pool and delayed skeletal activity when infection, fracture or complex regional pain is the question.
The result is an integrated report, not a list of hot spots. The interpreter should know the indication, symptoms, trauma or surgery, cancer type, relevant treatments, renal function, previous imaging and tracer details. Increased uptake is not synonymous with metastasis, and a normal study cannot exclude all lytic, marrow-based or low-turnover disease; CT, MRI, PET or biopsy may be the appropriate next test.
Key points
- 99mTc-labelled diphosphonates localise according to regional blood flow and osteoblastic activity; uptake therefore reflects bone response, not a tumour-specific marker.
- Common indications include suspected skeletal metastases, occult or stress fracture, osteomyelitis, painful prosthesis, Paget disease, avascular necrosis and unexplained focal bone pain.
- A standard study often includes delayed whole-body planar images; multiphase studies add flow and blood-pool images, while SPECT or SPECT/CT improves localisation and structural correlation.
- Focal increased uptake has a broad differential including metastasis, fracture, infection, arthritis, surgery, degenerative change and benign bone disease; distribution, shape, history and CT correlation matter.
- A negative scan is less reassuring for predominantly osteolytic disease such as myeloma and can miss early or low-activity lesions; it cannot exclude all skeletal malignancy.
- Hydration and frequent voiding improve soft-tissue clearance and reduce bladder dose; pelvic activity can obscure lesions, so repeat views, delayed imaging or SPECT/CT may be needed.
- Pregnancy is a major precaution for diagnostic radionuclide imaging; breastfeeding advice depends on the tracer and local radiopharmacy policy rather than one universal interruption period.
- A flare response can increase uptake during healing or treatment response, so comparison with prior imaging and the clinical timeline prevents premature declaration of progression.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
A patient with a cancer whose skeletal disease is likely to produce osteoblastic activity may benefit from whole-body imaging, interpreted with the primary tumour biology and anatomic imaging.
Focal activity in a painful region may precede radiographic change after stress or insufficiency injury, but the pattern must be correlated with load, trauma, MRI or CT when structural detail is required.
Hyperaemia, increased blood-pool activity and delayed uptake can support an active inflammatory or infective process, but prostheses, surgery and arthritis can produce overlapping patterns.
A cold focus may reflect absent bone, attenuation, artefact, avascular tissue or some metastases; isolated photopenia should trigger correlation rather than reassurance.
Diffuse intense skeletal uptake with relatively reduced renal and soft-tissue activity can indicate widespread osteoblastic disease or metabolic bone disease and requires biochemical and anatomic correlation.
Increasing uptake after therapy may represent healing osteoblastic repair rather than progression, so timing, symptoms and structural or metabolic comparison are essential.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Clinical indication and prior-imaging reviewFirst step - Why
- Decide whether functional bone imaging is the right question and provide cancer type, symptoms, trauma, surgery, prosthesis, medicines and previous radiology for interpretation.
- Interpretation and limitations
- A scan cannot compensate for an unclear question. Recent surgery, fractures, chemotherapy, radiotherapy, bisphosphonates and renal dysfunction can alter uptake or image quality and must be stated.
- 02
99mTc-diphosphonate planar bone scintigraphy - Why
- Survey the axial and appendicular skeleton for regional osteoblastic activity in selected metastatic, traumatic, infectious, metabolic and painful conditions.
- Interpretation and limitations
- Describe focal, multifocal or diffuse uptake and its anatomical distribution. Uptake is sensitive for active bone response but nonspecific; a normal result is weak for predominantly lytic or low-turnover lesions.
- 03
Multiphase bone scintigraphy - Why
- Separate arterial flow, immediate blood-pool and delayed skeletal phases when vascularity and soft-tissue hyperaemia help assess infection, fracture or complex regional pain.
- Interpretation and limitations
- Concordant increased flow, blood pool and delayed uptake supports active hyperaemic bone or soft-tissue pathology, but the pattern remains non-specific and needs clinical and anatomic correlation.
- 04
SPECT or SPECT/CT - Why
- Localise uptake in three dimensions and add CT morphology when planar images are equivocal, overlapping structures obscure a focus or a prosthesis or spine needs precise assessment.
- Interpretation and limitations
- SPECT/CT can improve localisation and characterisation, but CT dose, artefact and limited field of view remain relevant. It does not turn a non-specific tracer response into a tumour-specific diagnosis.
- 05
Targeted radiograph, CT or MRI - Why
- Define cortical destruction, fracture, hardware, marrow replacement, soft-tissue extension or cord compromise when bone-scan findings need structural clarification.
- Interpretation and limitations
- Choose modality by the suspected lesion and urgency. MRI is particularly valuable for marrow, infection and neural compression; CT is strong for cortex and hardware; plain radiographs remain useful for fracture and osteolysis.
- 06
Alternative radionuclide imaging such as 18F-NaF PET/CT or FDG PET/CT - Why
- Use a different tracer and hybrid modality when tumour biology, lytic disease, staging question or service availability makes conventional bone scintigraphy suboptimal.
- Interpretation and limitations
- Tracer uptake reflects different biology: NaF highlights bone turnover and FDG highlights glucose metabolism. Results must be interpreted with the primary cancer, treatment and the modality's known strengths and weaknesses.
04Clinical next stepsHow the result changes management or prompts escalation.
01Worked case: focal painLocalise an equivocal hot spotFirst stepA patient has focal mid-foot pain after increased training; radiographs are normal and the clinician asks whether a stress injury is present.+
- 1Check trauma, training load, infection symptoms, pregnancy or breastfeeding, renal function and the precise pain site; decide whether MRI would answer a high-risk structural question more directly.
- 2If bone scintigraphy is selected, obtain the protocol requested by nuclear medicine, ensure hydration and voiding advice, and acquire delayed images with spot views or SPECT/CT targeted to the symptomatic foot.
- 3Interpret uptake with the location and shape: a focal linear or cortical pattern may support stress injury, but degenerative joints, accessory bones, trauma and infection remain alternatives.
- 4Correlate with CT or MRI when the result will alter weight-bearing or when uptake is atypical, and verify response clinically rather than repeating a scan simply because it is positive.
02Worked case: cancer stagingInterpret a multifocal pattern cautiouslyA patient with newly diagnosed prostate cancer has multifocal increased uptake in the ribs, spine and pelvis and asks whether all foci are metastases.+
- 1Confirm the indication, tumour phenotype, PSA or relevant markers, prior trauma, degenerative symptoms, recent surgery and any previous bone scan for comparison.
- 2Assess distribution and morphology: multifocal axial uptake can be metastatic, but rib trauma, facet degeneration, healing fractures and urinary or injection artefact can mimic spread.
- 3Use targeted SPECT/CT, radiographs, CT, MRI or another tumour-appropriate modality for indeterminate sites, especially where treatment intent depends on metastatic classification.
- 4Report a ranked interpretation with limitations and compare future imaging using the same clinical context; verify any suspected progression against treatment timing because flare can increase osteoblastic uptake.
03Safety and special situationsAdapt the study to tracer and patientA patient is pregnant, breastfeeding, has renal insufficiency or cannot tolerate the standard delayed imaging schedule.+
- 1AlternativePause before injection and contact the responsible nuclear medicine physician or radiopharmacist to confirm tracer identity, pregnancy status, breastfeeding advice, renal function and whether an alternative modality is safer.
- 2If proceeding, tailor activity and acquisition to the validated local protocol, document administered tracer, activity, injection site and timing, and optimise hydration and voiding when clinically appropriate.
- 3Use delayed, additional or hybrid imaging only when it will resolve a defined limitation such as bladder overlap, poor clearance or uncertain localisation; avoid indiscriminate extra radiation.
- 4Communicate the specific result and residual uncertainty to the referrer, arrange structural imaging or follow-up when necessary, and document any tracer-specific breastfeeding instructions rather than a generic rule.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Check that the scan indication, cancer biology, symptoms, trauma, surgery, prosthesis, relevant medicines and prior imaging were available to the reporting physician.
- Document tracer name, activity, injection site, injection time, phases acquired, SPECT or SPECT/CT use and any technical difficulty or contamination.
- Compare uptake with prior studies and treatment timing; an apparent increase may be disease progression or a healing flare and needs clinical correlation.
- Escalate new neurological deficit, suspected pathological fracture, fever with focal bone pain or severe uncontrolled pain through the appropriate acute pathway.
- After equivocal findings, track whether targeted radiograph, CT, MRI, PET or biopsy resolved the question rather than treating the bone scan as a definitive diagnosis.
- For renal impairment, hydration and voiding advice should be adapted to fluid status and local nuclear medicine guidance; poor clearance can increase background and obscure interpretation.
- Record tracer-specific pregnancy and breastfeeding advice and ensure the patient knows whom to contact about delayed symptoms or further imaging.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Hot is a response
Diphosphonate accumulation signals delivery and osteoblastic mineralising activity, so metastasis, fracture, infection and degeneration can look similar without context.
Cold is not normal
Photopenia can result from artefact or absent bone but also from some lytic or avascular lesions; an isolated cold focus deserves anatomical correlation.
SPECT/CT adds anatomy
Hybrid imaging can relocate a planar focus to a facet, fracture, prosthesis interface or cortex, improving the differential while retaining tracer nonspecificity.
Lytic disease can be missed
Predominantly osteoclastic processes such as many myeloma lesions may show little tracer uptake, so a negative scan cannot exclude all malignant bone involvement.
Bladder can hide pelvis
Voiding, additional views, delayed images or SPECT can reduce pelvic obscuration when urinary activity overlaps the symptomatic or suspected site.
Breastfeeding advice is tracer-specific
Ask nuclear medicine or radiopharmacy for the exact radiopharmaceutical instruction; advice should not be copied from a different tracer or assumed from the scan name alone.
07Common pitfallsFrequent interpretation and management errors.
- 01
Calling every hot focus metastatic without considering fracture, infection, arthritis, surgery, prosthesis, Paget disease and benign lesions.
- 02
Using a negative bone scan to exclude myeloma, predominantly lytic metastases, early marrow disease or every cause of bone pain.
- 03
Ignoring the timing of recent trauma, operation, radiotherapy or systemic therapy when interpreting uptake.
- 04
Failing to use SPECT/CT or anatomic imaging when planar overlap leaves the lesion's location or cause uncertain.
- 05
Reporting progression from increased uptake during a possible treatment flare without clinical and structural comparison.
- 06
Giving generic pregnancy or breastfeeding instructions without checking the actual tracer and local radiopharmacy guidance.
- 07
Allowing a non-urgent radionuclide scan to delay emergency MRI, CT, radiograph or surgical assessment.