Bone Scan — Types, Indications and Limitations
DNB Orthopaedics • May 2024 • Paper I • 10 Marks
Introduction
Bone scintigraphy is a functional nuclear-medicine investigation that demonstrates regional skeletal blood flow and osteoblastic activity by detecting the distribution of a radiopharmaceutical within bone.
It is particularly useful because abnormalities of bone metabolism may become apparent on scintigraphy before structural changes are visible on plain radiographs.
Key concept: Bone scan shows bone turnover, not simply bone anatomy.
Principle of Bone Scintigraphy
The most commonly used tracers for conventional skeletal scintigraphy are technetium-99m-labelled diphosphonates, such as:
- 99mTc-MDP — methylene diphosphonate
- 99mTc-HDP/HMDP — hydroxymethylene diphosphonate
These compounds localize predominantly in bone by adsorption onto hydroxyapatite crystals, especially where blood flow and osteoblastic activity are increased.
IV radiotracer
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Circulates through blood
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Delivered to skeleton
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Adsorbs onto hydroxyapatite
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Uptake proportional mainly to:
• regional blood flow
• osteoblastic activity
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Gamma photons detected by gamma camera
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Scintigraphic image
Hot and Cold Lesions
| Pattern | Meaning | Examples |
|---|---|---|
| Hot spot | Increased tracer uptake due to increased perfusion/osteoblastic activity | Fracture, metastasis, infection, arthritis |
| Cold spot | Reduced tracer uptake | Some avascular lesions, very aggressive purely lytic tumour, infarction in selected settings |