Bone scans

Definition

 

Technetium 99m labelled MDP (Mono - diphosphonate)

 

Advantages

 

1.  Pure gamma emitter

 

2.  Half life only 6 hours

- limits radiation exposure

 

3.  Localises in bone

- chemical interaction on the surface of the hydroxyapatite crystal of bone

- phosphorous component interacts with the endogenous calcium

- produces insoluble technetium calcium phosphate complexes.

 

Pharmocokinetics

 

50% goes to bone

50% in equilibrium throughout soft tissues

Excreted in urine

 

Uptake occurs in areas of

 

1.  Increased blood flow

- e.g. hypervascular tumours, fractures, inflammatory process

 

2.  Increased cellular activity and mineral turnover

- osteoblastic activity produces immature osteoid

- this has numerous binding sites for developing apatite crystals

- i.e. healing fractures, inflammatory foci, growth plates

- remodelling of trabeculae in response to stress

 

3.  Metabolic bone disease

- where there may be abundant immature unmineralised collagen

 

Imaging protocol

 

IV injection of 550 to 740 MBq of Tc 99 MDP

 

Patient encouraged to drink several glasses of water and micturate frequently

- dilute radiation dose to bladder wall

- accumulates in bladder

- a full bladder may obscure posterior abdominal wall

 

Gamma camera picks up emitted gamma rays

 

Anterior and posterior

- if just take anterior picture, posterior gamma rays will be absorbed by anterior body wall

 

3 phase scan

 

1. Flow phase

- patient positioned under camera

- images taken at 5 second intervals after injection into antecubital vein

 

2. Blood pool phase

- within next 5 - 10 minutes

- shows extent of soft tissue and bone hyperaemia

- shows soft tissue component of lesions

- i.e. cellulitis around osteomyelitis, soft tissue extent of bony tumours

- synovial hyperaemia in inflammatory arthritis

 

Bone Scan Blood Pool PhaseBone Scan Blood Pool Phase 2

 

3. Delayed scan

- 2-4 hours later

- soft tissue activity has cleared

- skeletal structures demonstrated

- separate anterior + posterior scans obtained

- takes 15-30 minutes

 

Bone Scan Static Bone Images

 

SPECT (Single photon emission CT)

 

Tomographic examination

- rotate gamma camera around the patient

- creates CT like slice

- useful in spine i.e. spondylysis

 

Normal scan

 

Children

- overall very active

- hot symmetrical epiphyseal growth zones

 

Adults

- slightly hot at ends of long bones, SI joints, tips of scapulae, nasal cavity

- age related changes (ACJ, DDD)

 

Bone Scan Normal Adult

 

Hot Lesions on Bone Scan

 

Metastasis

Primary Malignant Bone Tumour

Osteomyelitis

Trauma / Stress Fracture

Osteoid Osteoma

Paget's

Fibrous dysplasia

Arthritis

Locally increased blood flow

Primary hyperparathyroidism

Renal osteodystrophy

 

Specific Conditions

 

1.  Investigation for bony metastases

 

Bone Scan MetastasisBone scan Metastasis0001Bone scan Metastasis0002

 

95% sensitivity

- multiple scattered focal hot spots in axial skeleton

 

'Superscan'

- can occur if metastases coalesce

 

False Negative Bone Scan

- osteolytic and osteoblastic components are balanced

- multiple myeloma, melanoma, renal cell carcinoma

 

2. Primary malignant bone tumours

 

Indication

- detects metastasis

- detects extent of lesion for resection / skip lesions

 

3. Benign bone tumours

 

Most show low grade uptake

 

Giant cell tumours / osteoid osteomas

- have intense uptake

 

4. Fractures

 

Uses

- detection of stress fractures

- scaphoid fractures

- myositis ossificans

 

Findings

- initially blood flow & blood pool phases hot

- then only delayed scan positive which remains hot for several months

- when a fracture fails to unite, blood pool phase negative with delayed scan mildly positive

 

Sacral insufficiency fracture

- H / Honda sign

- bilateral linear uptake in sacral alar

- transverse uptake in mid sacrum

 

5. Infection

 

Cellulitis

- Hot flow and pool phases, negative delayed scan

 

Osteomyelitis

- All 3 phases positive

 

6. Investigation of pain around prostheses

 

Bone scan becomes normal at 12 months

- persistently positive scan means loosening or infection

 

Bone Scan TKRBone Scan Loose Revision TKR

 

7. Arthritis

 

Can differentiate between degenerative + inflammatory arthritis

 

Degenerative

- negative blood pool phase, positive delayed scan

 

Inflammatory

- all three phases positive

 

8. Avascular necrosis

 

Ischaemic bone cold, surrounding bone hot

- doughnut appearance in hip

 

9. Paget's disease

 

Intensely hot on all three

Pagets Bone Scan

 

10. Fibrous dysplasia

 

11. Superscan

 

Metabolic bone disease

- osteomalacia

- hyperparathyroidism

- enal osteodystrophy

 

Myelofibrosis

Disseminating coalescing metastasis

 

12. Undiagnosed bone pain

 

May reveal an osteoid osteoma / unsuspected AVN / microfractures / low grade osteomyelitis

 

Gallium Scan

 

Gallium Scan

 

Gallium

 

Gallium 67 citrate

- localises in areas of inflammation and neoplasia

- due to exudation of labelled serum proteins

 

Technique

 

Delayed imaging at 24-48 hrs

 

Frequently used in combination with a technetium bone scan

- a double tracer technique

 

Less dependent on vascular flow than technetium

 

Difficulty in distinguishing between cellulitis and osteomyelitis

 

Technetium or Indium  111-Labelled White cell scan

 

Technique

 

Label patients own WBC's with radioactive tracer

 

Labelled white cells accumulate in areas of inflammation but not in areas of neoplasia

 

Useful in diagnosing osteomyelitis or infection around joint replacement

 

Unlike gallium also useful in the presence of pseudarthrosis

 

Leukocyte ScanBone scan and Leucocyte Scan Infected TKR