Small Animal Spinal Radiography Series: Thoracic Spine Radiography

FOLLOW THESE PRECAUTIONS

As a general rule, general anesthesia or heavy sedation is necessary to evaluate the spine because, in most cases, spinal images taken in nonsedated patients are nondiagnostic. In addition, the presence or absence of disk space narrowing cannot be determined from a nonsedated animal’s radiographs due to unavoidable positioning artifacts.

If a back injury (fracture) is suspected, DO NOT flex or extend the spine of the injured dog or cat, and DO NOT turn the patient for an orthogonal image. If possible, a horizontal beam image is done for the ventrodorsal projection.

Lateral Projection: Thoracic Spine

For the lateral projection, position the patient in lateral recumbency (Figure 1).

• Tape the thoracic limbs together evenly and pull cranially, keeping the sternum and vertebrae equidistant to the table.
• A foam wedge may be placed under the cubital joints and/or sternum in order to maintain laterality of the patient; wedges are typically needed for large-breed and/or barrel-chested dogs.
• Tape the pelvic limbs together evenly and pull caudally, keeping the patient in lateral position.
• The thoracic spine should be aligned with the horizontal line of the collimated field of view (FOV). To accomplish this alignment, the pelvis of the dog or cat may need to be shifted ventrally.

To determine whether or not the patient is aligned in a lateral position and parallel to the table, gauge the superimposition of the iliac wings by palpating the wings to ensure they are even.

Lateral Collimation

For the lateral projection, the FOV should:

• Include the dorsum just above the spinous processes
• Exclude the sternum and ventral third of the thoracic cavity.

For all patients:

• Palpate the vertebrae of the thoracic spine by following the ribs dorsally to where they meet the vertebral bodies; place the horizontal line of the FOV at this plane.
• Accommodate the contour of the thoracic spine from a ventral position cranially to a more dorsal position caudally.
• Place the radiographic marker to the caudal right or left of the patient to keep it from overlapping with important anatomic areas.

Ventrodorsal Projection: Thoracic Spine

For the ventrodorsal projection, position the patient in dorsal recumbency (Figure 2).

• If a trough is used, place the entire thoracic spine within the trough to eliminate edge artifacts.
• Extend the skull and neck and align with the manubrium; the skull and cervical spine should also be aligned in a straight line cranially.
• Align the sternum over the thoracic spine; it should be superimposed onto the thoracic spine on the final image.
• Tape the thoracic limbs either together or individually and pull cranially.
• Tape the pelvic limbs individually and pull caudally.

Ventrodorsal Collimation

For the ventrodorsal projection, the FOV should:

• Include the thoracic vertebral bodies, with only the rib head and proximal rib bodies visualized.
• Exclude the lateral body wall and mid zone to peripheral portion of the middle and caudal lung fields.

For all patients:

• Palpate the manubrium and the xiphoid of the sternum; collimate just cranial to the manubrium and 3 finger widths caudal to the xiphoid.
• Place the center of the FOV halfway in between these landmarks, with the horizontal line of the FOV placed midline.
• Place the radiographic marker on the soft tissues of the ventrum at the most lateral edge of the collimated FOV.

Lateral Projection: Thoracolumbar Junction

Due to x-ray beam divergence, it is necessary to include a projection of the thoracolumbar (T-L) junction for a spinal radiographic survey that includes the thoracic and lumbar spine.

For the thoracolumbar junction lateral projection, position the patient in lateral recumbency (Figure 3).

• • Tape the thoracic limbs together evenly and pull cranially in the same manner as a lateral thoracic radiograph, keeping the sternum and vertebrae equidistant to the table.
  • A foam wedge may be placed under the elbows in order to maintain laterality of the patient.
  • Tape the pelvic limbs together evenly and pull caudally, keeping the patient in lateral position.

To determine whether or not the patient is aligned in a lateral position and parallel to the table, gauge the superimposition of the iliac wings by palpating the wings to ensure eveness.

Lateral Collimation

For the lateral projection, the FOV should include T10 through L3, including spinous processes of the respective vertebrae.

• Palpate the junction between the last thoracic vertebral body (T13) and the first lumbar vertebra (L1) by following the caudal border of the last rib dorsally to the point where it joins the vertebral column.
• Place the center of the FOV 2 finger widths caudal to this space.
• Place the radiographic marker to the caudal right or left of the patient to keep it from overlapping with important anatomic areas.

Ventrodorsal Projection: Thoracolumbar Junction

For the thoracolumbar junction ventrodorsal projection, position the patient in dorsal recumbency (Figure 4).

• If a trough is used, place the entire thoracic spine within the trough to eliminate edge artifacts.
• Extend the skull and neck and align with the manubrium.
• Align the sternum over the thoracic spine; it should be superimposed with the thoracic spine on the final image.
• Tape the thoracic limbs either together or individually and pull cranially.
• Tape the pelvic limbs individually and pull caudally.

Ventrodorsal Collimation

For the ventrodorsal projection, the FOV should:

• Include the thoracic vertebral bodies, with only the immediate rib heads and soft tissues visualized.
• Exclude the lateral body wall and lungs of the thoracic cavity.

For all patients:

• Palpate the xiphoid of the sternum and the curve of the last rib in the lateral body wall.
• Place the center of the FOV halfway in between these landmarks, with the horizontal line of the FOV placed midline.
• Place the radiographic marker on the soft tissues of the ventrum at the most lateral edge of the collimated FOV.

For quality control of any diagnostic image, follow a simple 3-step approach:

1. Is the technique adequate (appropriate exposure and development factors)?
2. Is the correct anatomy present within the image?
3. Is the positioning anatomically correctand straight?