Thoracic radiograph (lateral projection)

The lateral radiograph provides the optimal view of the thorax of most companion animals as this is the dimension of least thickness and superimposition of the skeleton. For consistency and restraint purposes, lateral radiographs are obtained in a recumbent position. Both the left and right lateral recumbent projections are used in a standard 3-view radiographic study.

While using 2 views provides orthogonal projections, the compression of the lung nearest the table from the animal's body weight reduces conspicuity of lesions in that less inflated lung. Obtaining both lateral views is optimal.

Indications

The thoracic radiograph is a common method of screening for thoracic diseases that include all types of disorders.

Patient position

• Left and/or right lateral recumbency
• The head is extended in a neutral position and restrained if necessary.
• The thoracic limbs are positioned cranial to the manubrium and the pelvic limbs are extended caudal to the pelvis.

Technical factors

• lateral-lateral projection
  • ​place laterality marker in field of view
• time for inspiration
• centering point
  • caudal margin of the scapula
• collimation
  • thoracic inlet
  • last rib 
  • sternum and soft tissues
  • spine and dorsal soft tissues if space allows, may be collimated out.
  •  
• orientation  
  • landscape
• detector size
  • 14 x 17 inches
• exposure
• SID
  • grid
    • yes

Image technical evaluation

• The rib heads are superimposed on each other
• No limbs are superimposed on the thorax
• Positioning devices are out of the field of view
• The entire lungs are included
• The radiograph is inspiratory
• The vascular structures are visible
• The laterality marker is visible

Practical points

Chemical restraint is often necessary in addition to positioning restraints such as sand bags and tape. Radiographers should not hand hold animals during exposure unless absolutely necessary. Local radiation safety guidelines must be followed.

Chemical restraint can increase heart size.

Obtain two overlapping radiographs in large dogs.

Note or mark skin lesions with barium if questionable lung lesions.

A certain amount of abdomen will be included in the radiograph, but the whole abdomen should not be included.

Inspiratory radiographs are critical to inflate the lungs and provide good contrast.

Rotation can be evaluated by seeing if the rib heads are superimposed. See second case for example of rotation.

Imaging Techniques