====== Three phase bone scan ======

[[Technetium-99m]] (99mTc) pertechnetate is a [[radioisotope]] that may be attached to various substrates
for use in bone scanning. It may be used to label polyphosphate (rarely used today), diphosphonate
((Handa J, Yamamoto I, Morita R, et al. 99mTc-
Polyphosphate and 99mTc-Diphosphonate Bone
Scintigraphy in Neurosurgical Practice. Surg Neurol.
1974; 2:307–310))

(MDP), or phosphorous (HDP) (the most widely used agent currently). Accumulates in areas of
osteoblastic activity.

Three-phase bone scan: uses technetium 99m-HDP. Images are obtained immediately after injection
(flow phase), at 15 min (blood pooling) and in 4 hours (bone imaging). Cellulitis shows up as
increased activity in the first 2 phases, and there is little or diffuse increased activity in the 3rd.
[[Osteomyelitis]] causes increased uptake in all 3 phases.

Used in evaluation of acute osteomyelitis with sensitivity and specificity of ≈ 95% each, and is usually
positive within 2–3 days. False positives can occur in conditions involving increased bone turnover,
e.g. fracture, septic arthritis, tumors. False negative can occur in cases with associated bone
infarction.

Applications for bone scans include:

1. infection

a) [[osteomyelitis]] of the spine—vertebral [[osteomyelitis]] —or [[skull osteomyelitis]].

b) discitis 

2. tumor

a) spine metastases 

b) primary bone tumors of the spine 

c) skull tumors 

3. diseases involving abnormal bone metabolism

a) Paget’s disease: of the skull or spine 

b) hyperostosis frontalis interna 

4. craniosynostosis 

5. fractures: spine or skull

6. “low back problems”: to help identify some of the above conditions