Bone scans



Technetium 99m labelled MDP (Mono - diphosphonate)




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.




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



- overall very active

- hot symmetrical epiphyseal growth zones



- 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



Primary Malignant Bone Tumour


Trauma / Stress Fracture

Osteoid Osteoma


Fibrous dysplasia


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



- 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



- 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



- detection of stress fractures

- scaphoid fractures

- myositis ossificans



- 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



- Hot flow and pool phases, negative delayed scan



- 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



- negative blood pool phase, positive delayed scan



- 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



Disseminating coalescing metastasis


12. Undiagnosed bone pain


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


Gallium Scan


Gallium Scan




Gallium 67 citrate

- localises in areas of inflammation and neoplasia

- due to exudation of labelled serum proteins




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




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




CT Scan



Irradiate a slice of tissue from multiple angles


Measure the output from different sides


Tissues have different densities

- with denser tissue fewer x-rays reach the detectors


Hounsfield scale


Bone    2000

ST        40

Water   0

Fat       -100

Air       -1000




Grey scale

- eye can only see 11 different shades


Adjust settings to bone or soft tissue


Osteoblastoma Soft Tissue CTOsteoblastoma Bone Window




Multiple detectors at any one time

- increase amount of data acquired in a single slice

- increased speed

- reduces artefact


Slice thickness


Decreased slice thickness

- increased info

- increased radiation








Axial Spine CTSagittal CTCoronal CT




3D CT Reconstruction3D CT Hip


Radiation dose


CXR                 1

Pelvis               35

CT Chest          400

CT Abdo/pelvis  500





Creation of images


Placing patient into a strong magnetic field

- 30 000 x stronger than the earth's magnetic field


Stronger magnets, better images, shorter times

- 1.5 Tesla 

- 3 Telsa


The nuclei of elements with odd numbers of protons line up

- i.e. hydrogen atoms

- hydrogen is plentiful in fat and water


A radiofrequency is then applied, exciting the protons

- as the excited protons relax back into equilibrium, a RF signal is emitted

- a receiver coil or antenna listens for an emitted radiofrequency signal

- the method and timing of the application of the radiofrequency signal can be varied 

- T1 / T2 weighted, fast spin echo, fat suppressed or a gradient echo sequences


TE / time echo

- time for 90o RF to echo from tissue

- vary the time to detect the signal


TR / time repetition

- time between 90o RF


The hydrogen atoms return to a relaxed state by two mechanisms

- T1 relaxation

- T2 relaxation

- these are dependent on molecule size and binding to larger macromolecules

- all tissues have different T1 and T2 relaxation times



- long T1 and T2 values



- short T1 and T2 values


By varying TE and TR can weight the sequences as T1 or T2

- if increase TE and TR

- produce T2 weighting

- sensitive for fluid i.e. oedema and inflammation






Intracerebral aneurysm clip

Cardiac pacemakers

Automatic defibrillators

Implanted infusion devices

Internal hearing aids

Metallic orbital foreign bodies

Dorsal column stimulators

Vascular clips anywhere less than 2 weeks after insertion unless proven to be MRI compatible



- 1st + 2nd trimester of pregnancy

- middle ear prosthesis

- penile prosthesis

- internal orthopaedic hardware is safe but can create local artefact

- Claustrophobia   





Can be claustrophobic

Very loud

- difficult for young children to cooperate, need sedation




No radiation used


When to use which sequences in the musculoskeletal system


Types of images / Sequences





- TE < 60 ms

- TR < 1000ms

- T1 relaxation - 1s


T1 weighted films

- fat has a bright signal e.g. bone marrow

- those tissues with little fat or water e.g. cortical bone, tendons, ligaments are dark in both T1 & T2


Standard workhorse for anatomy


MRI T1Ankle T1 MRI



- post gadolinium

- spin echo

- gradient echo

- fat saturation (important to improve contrast when using gadolinium)


Gadolinium usually performed in T1 with STIR to determine if patient has abscess




High TE/TR

- TE > 60 ms

- TR > 1000 ms

- T2 relaxation - 40 ms


T2 weighted films

- fluid has a bright signal

- Highlights pathology / fluid


MRI T2Spine T2 MRI



- spin echo (SE)

- gradient echo (GE)

- turbo / fast spin echo (TSE/FSE)




A method for fat suppression

- very important for TI and gadolinium

- changing the appearance of fat from white to black

- important for T2 to highlight fluid


Proton density


Intermediate between T1 and T2

- fat is high signal intensity

- oedema is high signal intensity


Usually done as part of a standard T2 spin echo image


Long TR / Short TE

- TR > 1000 ms

- TE < 60 ms


Can be useful on its own to look at the anatomy of tendons and ligaments

- good for menisci

- good for cartilage


MRI Proton DensityMRI Spine Proton DensityMRI PD Hip


Gradient echo


Accelerated T2 sequence

- very good for ligaments and articular cartilage


Images are fast but very susceptible to chemical shifts which can produce artefacts


Shows cancellous bone as black which can be helpful


Spin echo (SE)


A spin echo is a 90o RF followed by 180o RF


Turbo spin echo or fast spin echo

- faster than standard spin echo

- an accelerated way of acquiring T2 and PD images


Fat remains bright

- cannot differentiate between water and fat

- therefore fat suppression is required & can be performed using STIR


Can reduce metal artefact


OOPS (Out of Phase Sequence)


A technique for separating water and fat

- useful if there is watery fat or fatty water in two adjacent structures


Magic angle effect


When collagen bundles are 55o to the magnetic field

- artifactual high signal on T2

- reduce with STIR

- i.e. PD show increased peroneal signal, but not seen on T2

- therefore is due to magic angle


























Radiation Exposure

Radiation Units



- is a measure of quantity of ionisation, produced in air, by x-ray, or gamma radiation per unit mass

- SI unit is the Coulomb per kg (C/kg)


Absorbed dose 

- is a measure of the amount of energy imparted to matter by ionising radiation per unit mass of irradiated material

- SI unit is the Gray(Gy)


Dose equivalent

- is a quantity introduced for radiation protection purposes

- correlates better with the harmful effects caused by exposure to the various types of ionising radiation

- SI unit is the Sievert (Sv)

- the subunit, millisievert (mSv), one thousandth of a Sv, is used more often because of the large size of a Sievert

- Dose equivalent = Absorbed dose X quantity factor X modifying factor

- for xrays, dose equivalent and absorbed dose are the same in magnitude


Background radiation


Depends on where you live

- 2 mSv / yr  = 5 micro SV/day

- flying = 3-4 micro Sv/hr


Xray Doses


AP CXR            20microSv (4 days)

Lat CXR           50microSv

AXR                100microSv (20 days)

Lumbar Spine

- AP&Lat          500microSv (100 days)

- 5 view series  1milliSv


Pelvic XR          100 microSv

Wrist XR           4 microSv


Bone Scan        


6mSV = 200 CXR = 2.5 years




CT Chest/Abdo/ Pelvis

- 8-12 mSV each (5 years)

- whole series is 30 mSV (15 years)


CT Spine          8-10 milliSv

CT Head           20 milliSv (10 years)

CT Hand           4 milliSv


Ratios of exposure


CXR = 20 microSV (4d)


Pelvis XR = 5 CXR


Spine XR (AP/L) = 25 CXR


NMBS = 200 CXR


CT chest / abdo / pelvis = 400 CXR


CT head = 800 CXR





- directly related to trauma load

- use of Image Intensifier


Average Orthopaedic Trainee

- exposed to 1.6 mSv per year on outside lead gown

- normal background radiation 2.5 milliSieverts / yr

- thyroid shield can reduce radiation by X13

- most commonly with NOF pin and plate / IM Nailing / MUA

- highest dose during IM Nail Femur

(Long procedure, increased scatter, close proximity during distal locking)


Exposure reduced by

- increased distance from source > 50 cm

- wearing lead apron

- minimise screening times

- with lead apron, maximum exposure to head & neck & hands




Lymphatic depression > 100mSv

Radiation sickness & increased solid neoplasia ~ 1000mSv


NHMRC Recommended Maximum Dose in addition to background radiation

- Occupational < 5mSv over 3/12

- General population < 0.25mSv over 3/12

- Average orthopedic trainee  0.4 mSv over 3/12


Primary concern is malignancy

- minimum safe dose unknown

- ? > 25 Gy


Areas in question are

- Eyes / Thyroid / RES / Gonads / Hands (Skin)


Absolute risk from low-dose radiation not determined




Wear protective lead apron at all times

- check regularly for cracks in lead

- thyroid protector & lead-lined glasses


Safety Procedures

- minimise exposure time

- use sparingly

- avoid live screening

- avoid cavalier operating

- do not handle tube

- do not place hand in tube

- don't operate II without radiographer




As low as reasonably achievable (ALARA)

- Operative planning

- Inform all staff

- Consider set-up and positioning of equipment

- Operating surgeon to set the example

- Lead gown - 0.5mm / thyroid protector / lead glasses

- Gloves in high exposure procedure

- Advise all staff to wear appropriate protection

- Wear a radiation monitor (beneath lead gown)

- Never stand behind someone for protection

- Sign on door - ionizing radiating in use

- Maintain distance from beam

- Lead shield if possible

- Don't use II as table

- Single exposure (not continuous)

- Minimise exposure time

- Clear warning when to be used

- Consider altering surgical technique to avoid excess exposure

- Minimise II distance from pt

- Minimise field size

- Exposure tube side > II side

- Don't use saline bags







Very high frequency sound waves

- 3 - 15 MHz




Piezoelectric effect

- run electric current through a crystal

- produces ultrasound waves




Density of substance determines velocity of the US

- reflected back to the probe at different velocities

- converted into 2D image on monitor