Radiographic positioning
Femur & Humerus
If leg is fractured, make sure affected leg is down
Medial-lateral is the usual projection
Always collimate to joint above and below
Center on pathology
Might add kVp to compensate for Fx hematoma
Medial Lateral of Scapulo Humeral Joint
This position and view is important in cases of osteochondrosis dissecans (OCD - mainly a large dog breed issue)
Shoulder
Diagnostic image of OCD
Medial Lateral of RIGHT humerus
Caudal Cranial of Humerus
May need anesthesia, as this position may be painful
Place animal in dorsal recumbency with front legs stretched out (especially the one to be radiographed)
Center beam about midshaft on humerus
May be difficult to position long axis of bone parallel to cassette
Cranial Caudal of Shoulder
Place dog in ventral recumbency
Stretch out front leg to be radiographed
May be difficult to position long axis of bone parallel to cassette
(Same goes for cranial caudal of humerus)
What is geometric distortion?
When the image is distorted from anatomic accuracy due to improper positioning.
e.g. elongation, foreshortening, magnification
How does magnification of scale occur?
The bone is positioned off the cassette
How does foreshortening occur?
The bone is not parallel to the plane of the film/sensor.
Stifle
Medial Lateral of Elbow
Affected area in center
1/3 of bone above and below as well
May need flexed, unflexed and oblique projections as well
Extreme flexion is needed to expose anconeal process (GSDs older than 7 mos commonly have ununited anconeal process)
Cranial Caudal of Elbow
Flexed Lateral of Elbow
Forearm (Antebrachium)
DorsoPalmar of Carpus
Control angulation of leg from elbow w/gloved hand
Can soft tissue injuries be seen on x-rays?
No, maybe on an MRI!
Lateral projection of Carpus
DorsoPalmar Metacarpus/Phalanges
VD Pelvis/Coxofemoral Joints
For a diagnostic image:
Need to be perfectly symmetrical
Obturator foramina have to be identical
Stifle on both legs need to be symmetrical
Directional terms
Projections are named by a two-part term relating to beam orientation as it enters and exits the targeted area
First part of term is incoming direction of beam
Second part of term is direction of beam exiting from target
Third part of projection term is naming the targeted body part
Examples:
- VD of abdomen
- DV of thorax
- Dorsopalmar of L Metacarpus
- Lateral-Medial of R Carpus (Flexed)
- DorsoPalmar L P3/Navicular 45 degree oblique
Exposure Rules: Centering
Restrict the area imaged to the area of clinical interest
Center anatomy to center of cassette
Center cassette to center of beam
Critically important for joints in spine and extremities
Whole body studies not done unless no other option (e.g. small pets, birds, reptiles, pocket pets)
Exposure Rules: Collimate
Tightly restrict beam geometry to only what’s needed
Improves film quality by reducing scatter & fog (less scattered radiation plus better film)
Collimation & Aids
Collimate and use proper aids to achieve proper positioning of targeted anatomy
e.g. heavy sedation, sandbags to keep desired position
Exposure Rules: Two Views
Two views of same area
Taken at right angles to each other (to get 3 dimensional pic)
Example: VD and Lateral
Exceptions:
- can’t position for exposure
- no practical info to be gained
- dental x-rays are usually just a lateral
Define orthogonal
2 views taken at right angles to each other to achieve a diagnostic all-around image
With one view, you may not know exact pathology
Anode Heel Effect
Place thickest part of anatomy towards cathode
(at CAVT Cathode is to the left)
Exposure Rules: Affected Side Down
Clinically affected side down = closest to cassette
Sharpens the image
Helps keep anatomy as parallel to cassette as possible to reduce geometric distortion
Reduces enlargement (a projection artifact)
- some radiologists like enlargement and will create a bigger buffer between cassette and PT on purpose
Exposure Rules: Work Clean
Always examine hair coat for being wet, dirty, or caked with manure
Spilled contrast agts on hair are the worst and need to be dealt with carefully or they may compromise exposure
Positioning accessories are friends
Positioning Checks: Lateral View
Rib heads are superimposed
Intervertebral foramina are the same size
Transverse processes are superimposed at the origin from the vertebral bodies
Coxofemoral joints are superimposed
Positioning Checks: Ventrodorsal View
Spinous processes are aligned in the center of the vertebral bodies
Rib and abdominal symmetry
Wings of the ilium are symmetrical
Obturator foramina are symmetrical
Hanging your Films - Lateral
Head is to the left
Spine is up (toward viewbox clips)
Hanging your Films - VD/DV
Head is toward viewbox clips (up)
Animal’s right side is mounted to viewer’s left side
