Radiography Flashcards
Outline the restraint of small animals for radiography
- Chemical and physical
- Sedation/GA
- Positioning aids
- Never manual restraint
- Positioning may depend on condition-
Outline the restraint of large animals for radiography
- Most radiographed sedated and standing
- Manual restraint usually required
- Occasionally GA for some body areas e.g. pelvis
What is the importance of movement blur in radiography?
- Leads to poor image quality
- Can be due to voluntary or involuntary movements
How can movement blur be minimised?
- Correct machine settings
- Use of good restraint
- Short exposure (increase mA, decrease exposure time)
Outline sedation for radiography
- Suitable for most thoracic and abdominal radiography
- May be used for some MSK studies
- A2A and butorphanol commonly used
- Close monitoring required, oxygen supplementation often also important
Outline general anaesthesia for radiography
- Some MSK radiography as require critical positioning
- Required for good quality, inspiratory thoracic radiographs
- Most contrast studies except oral barium
- May be safer for patient vs sedation
What are the Roentgen signs?
- Number
- Location
- Size
- Shape
- Margination
- Radiopacity
- Internal architecture and function in some cases
What are the characteristics of a good radiograph?
- Accurate portrayal
- Easy perception (sharp shadows, wide range of shades of grey)
- No misleading artefacts
- Consistent results
- No unnecessary risks taken
Outline positioning for radiogrpahy
- Part of interest as close as possible to cassette to minimise distortion
- Use standard radiographic positions first
How is axial rotation in the thorax assessed?
- Look at rib heads overlying as opposed to the ribs
- The caudodorsal rib heads should be superimposed
Outline centring for radiography
- Centre primary beam over area of interest
- Means that x-rays will go through area of interest vertically minimising distortion
Outline the importance of collimation for radiography
- Scatter contributes to general image opacity and increases radiation hazard
- Collimation means minimum size beam is used and so reduces scatter
What is the collimation required for joints and long bones?
- Joints: include associated 1/3rd of adjacent bones
- Long bones: include whole bone including both adjacent joints
Outline how to appraise collimation
- Primary beam must be contained within area of cassette, so 4 unexposed borders should be visible if are not shuttered by digital machine -
- Collimation described by number of unexposed borders seen on plate, given as percentage i.e. 0%, 25%, 50%, 75%, 100%
- Then describe how closely the image has been collimated to the area of interest
Outline the considerations regarding exposure factors in radiography
- Cannot tell correct exposure from visual appearance of a digital image
- Need to use minimum exposure possible
Why are grids used in radiography?
- X-ray scatter more significant with thicker animal
- Presents safety issue and poorer image quality
- Grids reduce scattered radiation reaching the cassette and improve radiographic contrast
How do grids reduce the scattered radiation reaching the cassette?
- Alternating strips of palstic and leda in a thin sheet
- Filter out x-ray photons not passing in a forward direction
- Absorbs proportion of primary beam
- Width and height of lead strips determine how much scattered radiation is filtered
Describe how to use a grid in radiography
- Only legally allowed for body regions greater than 10-15cm thick
- Placed between patient and cassette
- Focused grids must be aligned with centre of primary beam, correct way up and correct film focal distance used
- Increase exposure (called grid factor, usually increased by 2-3 times)
What are the different types of grids available?
- Parallel
- Focused
- Pseudofocused
Describe the labelling of a radiographic image
- Patient and date may be entered into computer and embedded in digital image file and linked to radiograph
- Side markers should always be exposed on the image
Why is radiography an important part of many imaging work-ups?
- Time and cost effective
- Easy
- Can be easily submitted for a second opinion (teleradiology)
- Useful where bone or air/gas is present
What are the disadvantages of radiography?
- Less useful where fluid and soft tissue structures are present and in contact
- Patients need to be well restrained
- Good radiographic technique needed for diagnostic images
- Hazards of ionising radiation to personnel
What conditions are likely to give the best imaging results?
- Chonic, and where clinical signs are severe or persistent/recurrent despite treatment
- Significant changes will have taken place in the patient
What is the general principle for radiographic views taken and why?
- 2 perpendicular orthogonal views
- To fully evaluate any body area
- Certain views may hide certain pathologies