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https://todaysveterinarypractice.com/table-of-contents-january-february-2022/
Imaging Essentials, Radiology/Imaging

Small Animal Spinal Radiography Series: Thoracic Spine Radiography

Danielle MauragisCVT

Danielle Mauragis, CVT, is a radiology technician at University of Florida College of Veterinary Medicine, where she teaches diagnostic imaging. She coauthored the Handbook of Radiographic Positioning for Veterinary Technicians and received the Florida Veterinary Medical Association’s 2011 Certified Veterinary Technician of the Year award.

Clifford R. BerryDVM, DACVR

Clifford R. Berry, DVM, DACVR, is a professor of diagnostic imaging at University of Florida College of Veterinary Medicine. His research interests include cross-sectional imaging of the thorax, nuclear medicine, and biomedical applications of imaging. He received his DVM from University of Florida and completed a radiology residency at University of California–Davis.

Small Animal Spinal Radiography Series: Thoracic Spine Radiography

Imaging Essentials provides comprehensive information on small animal radiography techniques. This article is the second in a 3-part series covering cervical, thoracic, and lumbar spine radiography.

The following anatomic areas have been addressed in previous columns; these articles are available at todaysveterinarypractice.com (search “Imaging Essentials”).

  • Thorax
  • Scapula, shoulder, and humerus
  • Abdomen
  • Elbow and antebrachium
  • Pelvis
  • Carpus and manus
  • Stifle joint and crus
  • Tarsus and pes

Spinal radiographs are indicated for:

  • Evaluation of traumatic injuries
  • Neck and back pain
  • Pain or neurologic issues associated with thoracic or pelvic limb lameness isolated to these regions.

Each radiographic projection is a separate study and should be radiographed as such. High quality, correctly positioned and collimated radiographs are required in order to provide an accurate assessment of the area of interest, especially for surgical planning.

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.

ROUTINE VIEWS

Lateral and ventrodorsal views are considered the minimum orthogonal radiographs for the spine. Due to the angled, divergent nature of the x-ray beam, the area of the spine in the center of the field of collimation will be the area that provides the correct anatomic detail and intervertebral disk space widths.

A routine thoracic spine study includes:

  1. Lateral image of the thoracic spine
  2. Ventrodorsal image of the thoracic spine
  3. Lateral image of the thoracolumbar spine
  4. Ventrodorsal image of the thoracolumbar spine.

Lateral Projection: Thoracic Spine

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

050613 ie fig 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.

Measuring the Thoracic Spine

Measure the thickest portion of the spine that is within the area of collimation.

Ventrodorsal Projection: Thoracic Spine

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

050613 ie fig 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).

050613 ie fig 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).

050613 ie fig 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.


ADDITIONAL VIEWS
 

Ventrodorsal Oblique Projection: Thoracic Spine

Subtle lesions, fractures, and intervertebral disk disease are a few of the conditions that may require a ventrodorsal oblique projection of the spine (Figure 5).

050613 ie fig 5

  • From the straight ventrodorsal position of the thoracic spine, obliquely rotate the patient to the left approximately 10° to 15°; then take the radiograph.
  • Rotate the patient to the right approximately 10° to 15° and take a second radiograph.

Collimate as described for the ventrodorsal projection of the thoracic spine. The ventrodorsal oblique thoracic spine projection requires a larger collimated FOV on the lateral aspect due to the curvature of the spine in that region.

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?

QUALITY CONTROL

To make certain the desired technique has been achieved, use the following guidelines to determine whether the appropriate anatomy is included in the images.

Thoracic Spine

For the lateral projection of the thoracic spine:

  • The cranial border should include the caudal aspect of the cervical spine (C7).
  • The caudal border should, at least, include lumbar vertebra 1 (L1).
  • For the lateral position, the rib heads should be superimposed at the vertebral body level.

For the ventrodorsal projection of the thoracic spine:

  • The cranial border should include the caudal aspect of the cervical spine at the level of C7.
  • The caudal border should, at least, include lumbar vertebra 1 (L1).
  • The spinous processes should be superimposed over the thoracic vertebral bodies.

Thoracolumbar Junction

For the lateral projection of the thoracolumbar junction:

  • The cranial border should include the caudal aspect of the thoracic spine near the level of thoracic vertebra 11 (T11).
  • The caudal border should, at least, include lumbar vertebra 3 (L3).
  • For a true lateral position, the rib heads should be superimposed at the vertebral body level.

For the ventrodorsal projection of the thoracolumbar junction:

  • The cranial border should include the caudal aspect of the thoracic spine at the level of T11.
  • The caudal border should, at least, include L3.
  • The spinous processes should be superimposed over the thoracic and lumbar vertebral bodies.
  • In a straight dorsoventral projection, the dorsal spinous processes should have a tear drop appearance.
References

Suggested Reading

Burk RL, Feeney DA. Small Animal Radiology and Ultrasonography: A Diagnostic Atlas and Text, 3rd ed. Philadelphia: Saunders Elsevier, 2003.

Keely JK, McAllister H, Graham JP. Diagnostic Radiology and Ultrasonography of the Dog and Cat, 5th ed. Philadelphia: Saunders Elsevier, 2011.

Sirois M, Anthony E, Mauragis D. Handbook of Radiographic Positioning for Veterinary Technicians. Clifton Park, NY: Delmar Cengage Learning, 2010.

Thrall DE (ed). Textbook of Veterinary Radiology, 5th ed. Philadelphia: Saunders Elsevier, 2008.

Thrall DE, Robertson ID. Atlas of Normal Radiographic Anatomy and Anatomic Variants in the Dog and Cat. Philadelphia: Elsevier Saunders, 2011.

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