· uses technietium-99m attached to methylene diphosphonate (Tc-99m MDP)
· relies on blood flow to and within bone
· then relies on surface apposition of Tc-99 MDP on to hydroxyapatite crystal matrix
· increased bone tracer activity due to increased hydroxyapatite crystal turnover
· can be due to
· increased blood flow
· growth
· remodelling
· repair in response to inflammation / trauma / neoplasia
· three phases to uptake
· isotope diffuses passively through bone capillaries
· dependent on concentration gradient between intra and extravascular compartments
· increased local blood flow results in increased local flux of radionculide at affected site
· radionuclide concentrated in bone
· mechanism not fully inderstood
· some uptake in normal bone
· radionuclide avidly concentrated in new woven bone
· associated with increased osteoblastic activity
· taken up against a concentration gradient
· Tc-99 MDP is water soluble complex
· one half is excreted in urine
· remainder predominantly concentrated in skeleton
· syn. dynamic or arterial images
· series of rapid sequential regional images in 1st few seconds after injection of dye
· reflect initial blood flow
· useful when infection suspected
· syn. blood pool or venous images
· early equilibrium image at 5 min
· reflects blood and extracellular concentrations
· indicates vascularity of region
· syn. bone images
· at 2.5-3 hrs
· increased by using
· multiple projections
· collimator
· affected part as close as possible to collimator
· tomography
· pin-hole collimator views provide greater definition of small areas
· used for
· hands or wrists
· areas near growth plates in children
· localised area (eg. osteoid osteoma)
· single photon emmission computed tomography
· gamma camera rotated around patient
· provides localisation of abnormalities in axial, coronal or sagittal planes
· better contrast resolution
Uses
· vertebral column
· pars defects
· apophyseal disease
· solitary metastasis
· hip joints
· AVN
· knees
· ruptured ACL
· OCD
· exposure is 6 mSv
· kidney and bladder receive higher dose of radiation
· dose to critical organs (marrow, gonads) similar to lumbar spine x-rays or CT of lumbar spine or pelvis
· gallium-67 citrate is isotope that binds to white cells
· injected into circulation
· 6% bound
· remainder excreted into bowel
· leads to increased concentration in infection
· abscess
· osteomyelitis
· also accumulates in
· inflammation
· tumours
· fractures
· normal bone marrow
· interpretation requires comparison with technetium scan
· any inflammatory condition will concentrate gallium
· there is a low level of normal activity of bone
· thus infection likely when gallium intensity greater than that on technetium scan
· 2-3 day delay between injection and imaging required
· patient's white cells separated and labelled with radioactive agent
· with Tc-99m in Australia
· Indium-111 gives better scans but not available in Australia for this
· accumulates in
· abscess
· osteomyeleitis
· inflammation
· tumours
· fractures
· normal bone marrow
· more specific than gallium for infection
Child and adolescent
· growth plates
· more globular in younger children
Adult
· thoracic and lumbar spine (greater than in cervical spine or sacrum)
· anterior superior iliac spines
· anterior wing of ilium
· sacroiliac joints
· shoulder joints (esp. dominant shoulder)
· inferior wings of scapulae
· sternoclavicular area
· calcified tracheal, laryngeal and costal cartilages
Bladder
· radionuclide excreted in urine
· the fuller the bladder the larger the bladder image and the poorer the visualisation of the pelvis
· patient may need to be catheterised if pelvic pathology suspected
Renal uptake
· absent or very faint renal images may indicate superscan
· abnormally high but symmetrical uptake in skeleton
· may occur in metabolic bone disease or multiple diffuse skeletal metastases
· may make incidental diagnosis
· pelvic or ureteric obstruction
· unilateral functional impairment of kidney
Artefacts
Injection site
· commonest artefact
Urine
· at external meatus, on thigh or on other site
· may be problems with contaminated clothes in incontinent patient
Bladder diverticulum
· may simulate metastatic involvement of anterior pelvis
Incomplete labelling
· labelling may be incomplete so unbound pertechnate is available
· free pertechnate accumulates in stomach, bowel, salivary glands and thyroid gland
Superimposition of uptake
· inferior angle of scapula may overlie rib on one side and not the other and simulate pathological region
Soft tissues
· metastatic calcification
· lungs
· liver
· infarction (cerebral, myocardial)
· fat necrosis
· myonecrosis, muscle haematoma or abscess
Artefacts
Metal objects
· pendants, buckles, coins
· external splints
· implants for replacements and internal fixation
Equipment failure
· abnormalities in crystal or photomultiplier tubes
Malignant disease
· skeletal metastases
· primary malignant bone tumours
· soft tissue metastases from osteosarcoma
Benign bone lesions
· benign tumours associated with new bone formation
· infection (acute or chronic)
· arthridities
· fractures and osteotomies
· bone grafts
· Paget's disease
· miscellaneous
· osteomalacia
· hypertrophic pulmonary osteoarthropathy
Irradiation
Avascular lesions
· Perthes disease
· avascular necrosis
Occasional tumours
· multiple myeloma
· occasional metastases
Anatomical defects
· amputations
· congenital anomalies
Absence of activity
· scleroderma
· Buerger's disease
· neuropathy
Skeletal metastases
· most common indication
· most active and sensitive method for detection
· uses
· diagnosis of symptomatic lesion
· assessment of extent of dissemination of neoplasm
· multiple myeloma often not detected
· lesion does not provoke osteoblastic reaction
Primary bone tumours
· use not as extensive
· uses
· extent of tumour
· identification of skip lesions and spread
· presence and location of some tumours like osteoid osteoma
· identification of malignant change (eg diaphyseal aclasis)
Polyarthritis
· most sensitive for early diagnosis and distribution of polyarthritis
· nonspecific and thus not diagnostic alone
Ankylosing spondylitis
· quantitative estimation of uptake in sacroiliac joints can assist with diagnosis
· indication of response to treatment
Osteoarthritis
· of little use
Acute osteomyelitis
· useful in early diagnosis and localisation
· may be negative in first 24 hours but usually positive at 3 days
· increase in both blood pool and skeletal phases
· in soft tissue infection, only blood pool phase increased
· pitfalls in interpretation can occur with
· fracture
· septic arthritis
· prior antibiotic treatment
· unreliable in neonates
· specificity can be increased by combination with Gallium or white cell labelled scan
· white cells localised in infection
· not reliant on reaction of bone to infection with increased osteoblastic activity
· particularly useful for lesions near the growth plate
Chronic osteomyelitis
· useful to assess whether new pain is due to acute flare-up or soft tissue infection
Septic arthritis
· slightly less sensitive
· useful to localise site of infection
· esp. in children with hip pain
· increased sensitivity when combined with Gallium or white cell labelled scan
· does not replace need for joint aspiration
· normal bone reaction around cemented components subsides after 9-12 months
· persists longer in 20% of patients
· bone reaction may be more prolonged in cementless prostheses
· diagnostic scanning of little use under 12 months post-surgery
· used to detect and differentiate infection and loosening
· infection characterised by increased uptake in vascular phase but this is not pathognomic
· Gallium and white cell labelled scan may be more specific for infection
· secondary to plain x-rays
· useful in diagnosis of
· recent vertebral crush fractures in osteoporotic patient with multiple compressed vertebrae
· demented patient in pain with possibility of fracture somewhere
· scaphoid tenderness with normal x-rays
· femoral neck fractures in the elderly
· stress fractures
· usually becomes positive within 24 hrs
· slower response in older and osteoporotic patients
· preferable to wait 3-7 days
· remains positive for variable period
· depends on degree of repair and remodelling
· may remain positive for several years
Femoral head
· in adult AVN and Perthes disease
· initial diminished uptake
· later patchy increased uptake
· changes precede x-ray changes
· bone scan 4 weeks after internal fixation of subcapital fracture is of prognostic significance
· enhanced uptake associated with uncomplicated healing
· nonunion and collapse associated with reduced uptake
· not reliable earlier
Knee
· useful in
· osteochondritis dessicans
· idiopathic osteonecrosis of femoral condyle
Other
· Kienboch's disease of carpal lunate
· Kohler's disease of tarsal navicular
· early findings are increase in both blood pool and delayed images
· chronic RSD shows decrease in both blood pool and delayed images
· useful to establish extent of skeletal involvement and response to therapy
· not useful in detecting fractures or sarcomatous change because of high uptake with or without these complication