Thoracic radiograph (ventrodorsal projection)

Indications

The ventrodorsal projection is used as an orthogonal view to the lateral projection for evaluating thoracic structures, particularly heart size, mediastinal width, and laterality of pulmonary lesions. It is useful in cases with pleural effusion as it pools fluid ventral to the heart.

Patient position

• dorsal recumbency, with animal in a radiolucent trough positioning device
• the head is extended in a neutral position and restrained if necessary
• the thoracic limbs are positioned cranial to the thorax and the pelvic limbs are extended caudal to the abdomen

Technical factors

• ventrodorsal projection
  • ​place laterality marker in field of view
• time for inspiratory phase
• centering point
  • caudal margin of the scapula
• collimation
  • thoracic inlet
  • last rib 
  • include both body walls
• orientation  
  • portrait
• detector size
  • 14 x 17 inches
• exposure
• SID
  • grid
    • yes

Image technical evaluation

• The spinous process is centered within each vertebral body
• No limbs are superimposed on the thorax
• Positioning devices are radiolucent or 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 spinous processes are centered on the vertebral bodies.

The axillary skin folds will cause areas of increased opacity in some animals.

Imaging techniques