Principles of equine radiology Flashcards
How is X-ray produced?
there are two electrodes within a vacuum tube, a anode and a cathode
a high electric potential is applied and accelerated from the cathode to anode
when they impact the anode, X-rays is produced
Principles of X-ray
X-rays passes through the body
Captured behind a patient by a detector
variance in absopriton of X-rays by different tissues - produces contrast and gives 2D representation (depends on thickness and atomic weigth/density)
More radiation absorbed – whiter (radiopaque)
More radiation passed through – darker (radiolucent)
grade the radiation of
- soft tissue
- water
- gas
- bone
- metal
- fat
from more radiation passe dthorugh to more radiation absorbed metal bone soft tissue, fat, water gas
How does X-ray travel?
in a straight line and at the speed of light
what are the biological and chemical effects of x-ray
ionising and cellular changes
secondary and scattered radiaiton?
affects image and health hazard
when do you get the best quality x-rays, in regards to position
if the x-ray is perpendicular to the imaged are and the plate
The X-ray machine (generator)
• Portable • Ceiling-mounted • Settings o KV: energy of electrons – penetration o mAs: amount of radiation produced over a set time (number of electrons) – contrast
What are the different methods of X-ray detection?
conventional radiograpy
computed radiography
digital (direct) radiography
conventional radiography
x-ray sensitive film
light emission
chemical process
computed radiography
photostumulate phosphorous plates stores enery as latent image
stimulated by a laser beam in the reader, energy is released - image
digital (direct) radiography
x-ray photons are directly converted to a digital signal
scintillation and recording layers
image seen in a few seconds
faster examination
lower radiation dose
can produce better quality images
radiographer, radiography
obtains radiographs
radiologist, radiology
interprets radiographs
orthopaedic imaging - indication
lameness localised by diagnostic analgesia
obvious lesions (swelling, suspected fracture etc)
pre pruchased examination
non-orthopedic imaging - indications
head (teeth, sinuses)
thorax (heart, lungs)
abdomen
patient preparation
- restraining
• Ensure patient is adequately restrained – safety and image quality o Always use a bridle or chiffney o Majority of cases are sedated o Nose twitch o Stocks o Blinkers o Cotton wool ear plugs
patient preparation - feet and fur
• Brush the coat in areas to be radiographed
• Feet
o Remove shoes and bare the foot
o Brush foot with a wire brush
o Pack the sulci of the frog with play doh
patient preparation - head and general positioning
• Head
o Once sedated replace headcollar and bridle with web headcollar
• Spend enough time on correct positioning
personnel - your responsibility
ensure that all personnel are competent and adequately briefed
plan and discuss procedure before starting
work quickly but calmly and quietly
horses can be unpredictable even when sedated
radiation safety - general
keep radiation exposure to a minimum
as low as reasonably achevable (ALARA)
established max radiation dose for health workers
Public’s background radiation 2-3 mSv/year
Chest Xray 0.014 mSv, head CT 1.4 mSv, transatlantic flight 0.08 mSv
Time, distance, shielding
radiation safety - time
during one exposure (exposure time)
cumulative
radiation safety - Distance
during one exposure (exposure time)
radiation safety
- shielding
• Shielding
o Building, cages
o Protective clothing
radiation safety- factors to consider
• Practical factors to consider: o People in the room o Protective equipment o Methods of plate holding o Exposure
Cassette holding and positioning of the horse
o Ceiling mounted cassette holder
o Stand
o Cassette holder with an arm
o Hand-held
Radiation safety - exposure
o The horse is large..
o Digital radiography – good quality images with considerably lower exposures
o Keep repeat X-rays to a minimum, get it right for the first time
Adequate restraint, preparation, positioning
Perfect your technique
Use the lowest exposure possible
radiation safety - people
• Horse can never be left alone • Keep number of people to a minimum o But sufficient to ensure safety (ie. the handler shouldn’t hold the plate) o Ensure protective equipment is worn o Personnel monitored – dosimeters o < 16 years not allowed in the room o 16-18 years minimum exposure only o pregnant women not allowed
special considerations, horse - radiation safety
- The patient is usually sedated rather than anaesthetised and therefore must be held
- The cassette is usually held
- The patient is large therefore larger exposures are required
- Greater need for radiation safety and monitoring
last check before you get started - radiation safety
• Labelling of the cassette
o Identification, limb, orientation (label always on the lateral side), vet/institute
o Manual or set in the computer
• Does the horse need any markers to aid orientation?
• Back – DSP’s
• Wound
basic principles of interpretation
• Helpful if radiographs are orientated in a standard fashion o Dorsal/cranial to the left on lateral o Medial to the left on DP o Left side to the right for head DP • Is the radiograph of adequate quality? o Artefacts o Exposure • Consistent approach • Record everything on each view • Artefact? Repeatable? • Consider other variables that might be important to interpretation o Age Physes, separate centres of ossification o Any overlying soft tissue swelling • Thorough anatomical knowledge • If an abnormality is suspected, is it real? • Can it be seen on another view? • Is it repeatable? • Would additional views be useful? • Is it the same on the other limb?
describing a lesion
Inactive: smooth, regular, well defined
o Generally indicate normal, benign, or long standing lesions
Active: roughened, irregular, sharp, poorly demarcated
significance of lesion
Should always be interpreted in conjunction with clinical (and other imaging) findings
Useful to have some bone specimens
Anatomy and radiology textbooks
for how long has it been present?
osteophyte formation: at least 3 weeks
incomplete fissure fracture may take weeks from injury to become visible
large productive changes: may take months
aging of lesion is not always possible
Bone
- wolff’s law
- responses
- what does x-ray detect?
Wolff’s law
o Bone models due to stress applied to it
Ability of bone to respond is affected by
o Training
o (diet and disease)
X-rays detects changes in mineralisation
o Early stages – not visible
increase bone production
• Increase in bone density and therefore the image appears more radiopaque
• Cortical thickening
o Due to increased stresses
o Eg. bucked shin in racehorses
Periosteal and endosteal new bone
- Periosteum – on the outside of bone
- Endosteum – on the inside of bone
- May result from inflammation, fracture, trauma, infection, inflammation, neoplasia
Sclerosis
- = densification, increased opacity
- localised increased opacity due to increased bone mass
- most readily seen within the trabecular pattern of bone
- can occur in response to stress, in an attempt to wall off infection (eg. osteomyelitis) or to protect a weakened area (eg. OCLL)
Focal new bone production
- osteophyte – at the margins of articular cartilage and periarticular new bone
- Entheseophyte – where tendons, ligaments or joint capsules attach on the bone
- Differentiating between osteophyte or entheseophyte might be difficult
Demineralization – general
- Thinning of the cortices
- More obvious trabecular pattern
- More apparent radiographic over exposure due to reduced bone density
- Most commonly due to osteopenia (fractured limb, long standing non-weightbearing lameness)
- May be due to pregnancy, dietary imbalance, metabolic imbalance
Demineralization – focal
• Infection, inflammation or neoplasia • Continued pressure on bone – chronic proliferative synovitis • Cyst o Subchondral bone cyst o Osseous cyst-like lesion
Radiographic signs of common diseases - fractures
o Lacation
o Complete/incomplete/comminuted
o Displace/non displaced
o Articular/non articular
Radiographic signs of • Physitis
o Widening and bony irregularity at the epiphyseal and metaphyseal margins of the growth plate in immature horses
o Soft tissue swelling is also often present
Radiographic signs of • Joint abnormalities
Soft tissue swelling especially in the big joints
Periarticular
Intra-articular
Radiographic signs of • Osteochondrosis dissecans (OCD)
o Developmental disease
o Most common in hock and stifle
o Discrete osteochondral fragments
o Alteration in the contour of the articular surface (flattening, depression)
o Irregular lucent zones in the subchondral bone, can be surrounded by increased opacity
o Secondary modelling of joint margins
Radiographic signs of • Osteoarthritis
o (synovitis – inflammation of joint without bone involvement) o osteoarthritis – bone is involved o periarticular osteophyte formation o subchondral bone lysis and/or sclerosis o lucent zones in the subchondral bone o narrowing of the joint space o osseous cyst like lesions o joint capsule distension o periarticular soft tissue swelling
Radiographic signs of • Neoplasia
o primary bone tumours are rare in the horse
o metastatic malignancy to bone is also rare
o usually proliferative changes
Contrast radiography
o Injection of radiodense contrast medium
o Indication
Wound, penetrating foot injury – is there synovial involvement?
Communication between synovial cavities
