Bonescan lesions

3 +/- 1 phase Bone scan
1st phase: Arterial blood flow; immediately after injection
2nd phase: Blood pool (tissue phase) 10min after injection
3rd phase: Delayed phase (Skeletal phase) 2-5hr after injection
4th phase: 24hr delayed phase if renal insufficiency and as a result suboptimal image on 3rd phase

Standard whole body bone scan: Acquire at delayed phase (skeletal phase)
Mechanism: Radiotracer adsorbed on hydroxyapatite matrix of the bone, where the mineral phase is active.

Superscan:
Increased radiotracer uptake of bone in relative to the soft tissue background and (almost) absent renal activity.
Causes:

1. Widespread metastasis in: Breast / Lung / Prostate CA, +/- Lymphoma +/- Bladder CA
2. Metabolic bone disease: Renal osteodystrophy, Osteomalacia, Hyperparathyroidism
3. Myelofibrosis, Systemic mastocytosis

Hot lesions:

1. Fibrous dysplasia
2. Paget's disease
3. Brown tumors
4. ABC (because it is very vascular)
5. Osteoid osteoma
6. Chondroblastoma
7. Metastasis (Osteoblastic activities ie Sclerotic eg Prostate CA mets)
8. Joint diseases
9. Dental infection
10. Acute fracture (after 24 - 48hr)

3 phase positive lesions: (lesions that causes bone remodelling)

1. Osteomyelitis
2. Healing fracture
3. Orthopaedic implant
4. Neuropathic osteoarthropathy

Normal scan: (no increased or decreased uptake)

1. Acute fracture (acute phase)
2. Bone cyst, bone island, exostoses
3. Multiple myeloma ** there for this condition is monitored by skeletal survey radiograph**
4. Osteoporosis

Cold lesions:

1. Radiotherapy
2. Avascular lesion
3. Multiple myeloma 
4. Haemangioma
5. Advanced carcinoma

Varying lesions

Mixed lytic/sclerotic metastasis (Breast, Lung etc) may show hot or cold (with hot margins).