Principles of Radiography

Question 1

Give the three features of a good radiograph

Answer 1

Accurate portrayal
Easy perception
No misleading artefacts

Question 2

How many views do you need for a standard radiograph?

Answer 2

• As a general principle, you need at least two orthogonal views to fully evaluate any body area

Question 3

How many views do you need for equine joints?

Answer 3

4 standard views
Lateromedial
Dorsopalmar/plantar
2 x 45 degree oblique views

Question 4

Describe a DLPMO

Answer 4

DorsoLateral-PalmaroMedialOblique

Question 5

Describe a DMPLO

Answer 5

DorsoMedial-PalmaroLateralOblique

Question 6

Describe how you would prepare dogs and cats for an abdominal radiograph

Answer 6

– Try to starve dogs and cats for 24 hours for abdominal radiography and allow to urinate/defaecate beforehand

Question 7

Describe how you would prepare horses for a limb radiograph

Answer 7

– Make sure horses’ limbs are clean of mud/dirt and feet are cleaned/brushed/pared and packed to avoid air artefacts

Question 8

Describe the methods of restraint for radiographic imaging and their use for different animals and areas

Answer 8

Sedation
o Suitable for most thoracic and abdominal radiography
o May be used for some musculoskeletal studies where general anaesthesia is undesirable
General anaesthesia is generally required for:
o Some musculoskeletal radiography (e.g. spine, fractured long bones)
o Good quality, inspiratory thoracic radiographs
o Most contrast studies (NOT oral Barium)

Question 9

How can you reduce the risk of movement blur

Answer 9

• As movement blur is related to time (mAs), short exposures are needed:
o Increase the mA and decrease the time (secs)
o Do you need to use a grid (2x or 3x mAs)?

Question 10

Describe the process of positioning

Answer 10

Position the part of interest as close as possible to the cassette
Position accurately with the part of interest parallel to the cassette
Standard radiographic positions - Always use these first – as they allow comparison with other images

Question 11

What can be used to assess axial rotation

Answer 11

Level of superimposement of the caudodorsal rib heads

Question 12

Describe the importance of centering

Answer 12

Allows focus of radiograph to be on point of interest

Particularly important for large animal limbs and all joints

Question 13

Describe the importance and process of collimation (include landmarks for joints and long bone collimation)

Answer 13

Scatter contributes to general image opacity and increases radiation hazard
Collimate beam to minimum size necessary
e.g. for joints include associated 1/3rd of adjacent bone
for long bones, include whole bone including both adjacent joints
When making the radiograph, the primary beam should always be contained within the area of the cassette, i.e. four unexposed borders should be present if they can be seen. [OSCE FAIL IF NOT!!]

Question 14

Define collimation

Answer 14

1. Collimation is described by the number of unexposed borders that are seen within the plate (0, 25, 50, 75 and 100% for 1, 2, 3, and 4 sides). This is important for safety. (important to see the margin)

Question 15

Describe the structure and function of a radiographic grid

Answer 15

• Consist of alternating strips of plastic and lead which filter out x-ray photons that are not passing in a forward direction
• Reduce scattered radiation reaching the x-ray cassette and therefore improve radiographic contrast

Question 16

When are grids used?

Answer 16

• ONLY used in body regions greater than 10-15 cm thick

Question 17

What are the considerations when using a grid in radiography?

Answer 17

• Grid absorbs a proportion of primary beam, therefore a higher exposure (increased mAs) is required. This amount of increased exposure needed is described as the grid factor (typically 2-3 times).
• Focused grids must be aligned with the centre of the primary beam, the correct way up and the correct film-focal distance used