Introduction
Thoracic radiography is one of the most common diagnostic imaging procedures performed in veterinary practice. Accurate positioning is essential for obtaining diagnostic quality images while minimizing the need for repeat exposures. Proper positioning not only ensures clear visualization of thoracic structures but also reduces radiation exposure to both patients and personnel.
The thoracic radiograph should include the entire thoracic cavity, extending from the thoracic inlet (first ribs) to the diaphragm. Ideally, the image should also include a small portion of the cranial abdomen and caudal cervical region for anatomical reference.
General Preparation
- Ensure the patient is properly restrained, typically in a stable position using sandbags, foam wedges, or tape
- Remove any collars, harnesses, or other objects that may create artifacts
- Check for proper sedation if needed based on the patient's temperament and stress level
- Place appropriate radiation safety measures for all personnel in the room
- Use appropriate radiographic settings based on patient size, body condition, and suspected pathology
Lateral Projection (Right and Left)
The lateral view is one of the two standard views for thoracic radiography and provides excellent visualization of the heart, pulmonary vessels, and diaphragm. Both right and left lateral views are recommended for complete thoracic evaluation.
Right Lateral Positioning
- Place the dog in right lateral recumbency with the right side against the cassette
- Extend the front legs cranially and secure them
- Extend the hind legs caudally, keeping them parallel to the spine
- Place foam wedges or sandbags to maintain position
- Ensure the spine is parallel to the table
- Center the x-ray beam at the level of the heart (approximately 5th-6th intercostal space)
Left Lateral Positioning
- Place the dog in left lateral recumbency with the left side against the cassette
- Follow the same positioning principles as for the right lateral view
- Ensure the arms are extended and not superimposing over the thorax
- Center the x-ray beam similarly to the right lateral view
Ventrodorsal (VD) Projection
The ventrodorsal view provides a different perspective of thoracic structures, particularly useful for evaluating lung fields and the relationship of the heart to the ribs.
- Place the dog in dorsal recumbency
- Extend the forelimbs cranially, ensuring equal extension
- Position the hind limbs caudally, keeping the pelvis level
- Use foam wedges to elevate the sternum and ensure the thorax is symmetrical
- Ensure the spine is superimposed over the midline
- Center the x-ray beam at the level of the heart
Dorsoventral (DV) Projection
The dorsoventral view is an alternative to the VD projection, often preferred in patients with respiratory compromise or those who cannot tolerate dorsal recumbency.
- Place the dog in sternal recumbency
- Extend the forelimbs cranially and position them so they don't superimpose over the thorax
- Extend the hind limbs caudally, keeping the pelvis level
- Ensure the sternum is centered over the midline
- Center the x-ray beam at the level of the heart
Oblique Projections
Oblique views may be indicated to better visualize specific structures or to overcome positioning challenges.
Dorsal Right and Left Oblique
- Begin with the dog in lateral recumbency
- Rotate the patient 15-30 degrees so that the sternum is turned toward (for right oblique) or away from (for left oblique) the x-ray tube
- Extend forelimbs cranially
- Center the x-ray beam at the level of the heart
Ventral Right and Left Oblique
- Begin with the dog in dorsal recumbency
- Rotate the patient 15-30 degrees toward one side
- Extend forelimbs cranially
- Center the x-ray beam at the level of the heart
Common Positioning Errors
- Rotation: Asymmetry of rib pairs or unequal lung field appearance indicates the patient was rotated
- Under or over inflation: Results in artificial increase or decrease in lung opacity
- Limbs superimposition: Forelimbs over the thorax can obscure important structures
- Off-center beam: Can result in uneven exposure across the image
- Inadequate lung inclusion: Missing cranial or caudal thoracic margins
Conclusion
Proper thoracic radiograph positioning in dogs requires attention to detail and understanding of the underlying anatomy. By following the principles outlined in this guide, veterinary professionals can obtain diagnostic quality images while minimizing radiation exposure and patient stress. As with all radiographic procedures, practice and experience lead to improved efficiency and image quality.
