V/Q, bone and thyroid scans: when they are used
- Finding
Three common nuclear medicine scans: one compares air and blood flow in the lungs, one shows active bone, one shows how the thyroid takes up iodine.
What it is
These are the three scintigraphy studies a general doctor meets most. The ventilation-perfusion (V/Q) scan compares where air reaches the lungs with where blood reaches them: a pulmonary embolism blocks blood flow but not air, so it leaves a perfusion defect with normal ventilation (a mismatch). The bone scan uses a technetium-labelled phosphonate that sticks to bone where osteoblasts are active and blood flow is high, so it is very sensitive for metastases, occult fractures and osteomyelitis but not specific. The thyroid scan uses technetium pertechnetate or radioactive iodine, which the gland traps like iodide; it shows whether a hyperthyroid gland is diffusely or focally overactive, or not taking up tracer at all, and whether a nodule in a patient with low TSH is functioning («hot») or not («cold»).
What it looks like
- V/Q, pulmonary embolism: one or more wedge-shaped, segmental perfusion defects reaching the pleura, with normal ventilation in the same areas (mismatch).
- V/Q, matched defects (ventilation and perfusion both absent) point to airway or parenchymal disease such as COPD or pneumonia, not embolism.
- A normal perfusion scan practically excludes clinically important pulmonary embolism.
- Bone scan, metastases: multiple scattered hot spots, mostly in the axial skeleton (spine, ribs, pelvis), at random rather than in a line.
- Bone scan, «superscan»: intense, uniform uptake throughout the skeleton with faint or absent kidneys and little soft-tissue activity, from widespread metastases (classically prostate or breast) or metabolic bone disease.
- Triple-phase bone scan: osteomyelitis is hot in all three phases (flow, blood pool, delayed); cellulitis is hot in the early phases but without focal bone uptake on delayed images.
- Thyroid scan: Graves disease shows diffuse, uniformly increased uptake; toxic multinodular goitre shows several hot nodules with suppressed background; toxic adenoma shows one hot nodule with the rest suppressed.
- Thyroid scan: very low uptake in a thyrotoxic patient suggests thyroiditis (subacute, painless or postpartum), iodine load or exogenous thyroid hormone.
Why it looks that way
- Perfusion is shown with labelled albumin particles that lodge briefly in a small fraction of the lung capillaries; ventilation with an inhaled radioactive aerosol or gas.
- Bone tracer uptake follows blood flow and new bone formation; it shows the bone's reaction, not the tumour or infection itself.
- Purely lytic lesions with little osteoblastic response (multiple myeloma, some renal and thyroid metastases) may be normal or «cold» on a bone scan.
- The thyroid traps pertechnetate and iodide through the sodium-iodide symporter, which TSH drives; a recent iodine load (iodinated contrast, amiodarone) blocks uptake.
| Scan | Main uses | Classic finding |
|---|---|---|
| V/Q lung scan | Pulmonary embolism when CT angiography is unsuitable; chronic thromboembolic disease | Segmental perfusion defects with normal ventilation (mismatch) |
| Bone scan | Metastases (prostate, breast), occult or stress fracture, Paget disease | Multiple random hot spots in the axial skeleton; «superscan» with absent kidneys |
| Triple-phase bone scan | Osteomyelitis versus cellulitis, when MRI is not possible | Osteomyelitis hot in all three phases; cellulitis only early, without focal bone uptake |
| Thyroid scan | Cause of hyperthyroidism; nodule with low TSH | Graves diffuse high uptake; toxic adenoma single hot nodule; thyroiditis low uptake |
Differential and pitfalls
- V/Q is most useful when the chest X-ray is normal; an abnormal X-ray makes indeterminate results common, and CT angiography is then preferred.
- V/Q is chosen when iodinated contrast is a problem (severe kidney disease, previous serious reaction), in pregnancy with a normal chest X-ray, and to screen for chronic thromboembolic pulmonary hypertension.
- Bone scan pitfalls: degenerative joints, healing fractures and Paget disease are also hot; a «flare» (more uptake soon after effective treatment) can mimic progression.
- Myeloma is staged with low-dose whole-body CT, MRI or PET/CT, not with a bone scan.
- Thyroid nodules are assessed first with TSH and ultrasound; scintigraphy is added only when TSH is low. A hot nodule is rarely malignant; a cold nodule is managed by its ultrasound features and fine-needle aspiration.
- Thyroid scans are not done in pregnancy, and breastfeeding needs advice from nuclear medicine before the study.
Next step
- Suspected pulmonary embolism: clinical probability and D-dimer first; CT angiography for most, V/Q if contrast is contraindicated or the patient is pregnant with a normal chest X-ray.
- Bone scan request: state the primary cancer, the symptomatic site and any recent fracture or surgery; add MRI or CT for a single doubtful lesion.
- Suspected osteomyelitis: plain X-ray first; MRI is usually the best next test, triple-phase bone scan when MRI is not possible.
- Hyperthyroidism of unclear cause or a nodule with low TSH: request thyroid scintigraphy (with uptake if available); stop iodine sources as advised by nuclear medicine.
- Indeterminate or unexpected result: discuss with the nuclear medicine physician before further tests.
Test yourself
Think of the answer, then tap the question to see it.
What V/Q pattern suggests pulmonary embolism?
One or more segmental, wedge-shaped perfusion defects in areas where ventilation is normal: a ventilation-perfusion mismatch.
When is a V/Q scan preferred over CT pulmonary angiography?
When iodinated contrast is contraindicated (severe kidney disease, serious previous reaction), in pregnancy with a normal chest X-ray, and to screen for chronic thromboembolic pulmonary hypertension.
What is a «superscan» on bone scintigraphy?
Intense, uniform tracer uptake throughout the skeleton with faint or absent kidneys and soft tissue, caused by widespread bone metastases or metabolic bone disease.
A thyrotoxic patient has very low thyroid uptake on scintigraphy. What causes should you think of?
Thyroiditis (subacute, painless or postpartum), a recent iodine load, or exogenous thyroid hormone; Graves disease would show diffusely increased uptake.
Connections
Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.
Sources: Bone Scan (StatPearls (NCBI Bookshelf), 2026); Triple Phase Bone Scan (StatPearls (NCBI Bookshelf), 2026); Acute Pulmonary Embolism (StatPearls (NCBI Bookshelf), 2024); Thyroid Nodule (StatPearls (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.