9.2 Patient Positioning for Radiography

Patient Positioning for Radiography

Proper patient positioning is essential for obtaining diagnostic radiographs. An improperly positioned patient can lead to anatomical rotation, geometric distortion, and magnification, which may obscure pathology or lead to a misdiagnosis. As a veterinary assistant, you will be responsible for preparing positioning aids, measuring the patient, and safely securing the animal in the requested position.

Directional Terminology in Veterinary Radiography

To ensure clear communication within the veterinary team, standardized directional terminology is used to describe the patient's anatomy and the path of the X-ray beam:

• Cranial vs. Caudal: Cranial indicates toward the head, while caudal indicates toward the tail. For limbs, "cranial" and "caudal" are used to describe areas proximal to (above) the carpus (wrist) and tarsus (ankle).
• Rostral: Toward the nose, used specifically when describing positions on the head.
• Dorsal vs. Ventral: Dorsal refers to the animal's back (or the top surface of the paws/limbs), while ventral refers to the belly side.
• Palmar vs. Plantar: Palmar refers to the bottom/underside of the front paws (distal to the carpus), whereas plantar refers to the bottom/underside of the hind paws (distal to the tarsus).
• Medial vs. Lateral: Medial is toward the midline of the body, and lateral is away from the midline (toward the side).
• Proximal vs. Distal: Proximal means closer to the point of attachment or the torso, while distal means farther away (toward the toes).

Naming Conventions for Radiographic Views

Radiographic views are named according to the direction the X-ray beam enters the body, followed by where it exits. For example, in a Ventrodorsal (VD) view, the beam enters the ventral chest or abdomen and exits the dorsal spine.

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Standard Radiographic Positions

The three most common radiographic positions in small animal medicine are lateral recumbency, ventrodorsal, and dorsoventral.

1. Lateral Recumbency (Right or Left Lateral)

In lateral recumbency, the patient lies on their side. The view is named after the side of the patient's body that is in contact with the table or cassette.

• Right Lateral: The patient lies on their right side. The X-ray beam enters the left side of the body and exits the right side. This is the standard view for abdominal surveys.
• Left Lateral: The patient lies on their left side. The beam enters the right side and exits the left side.

2. Ventrodorsal (VD)

The patient is placed in dorsal recumbency (on their back). The X-ray beam enters the ventral surface (belly/chest) and exits through the dorsal surface (spine/back). This view is commonly used for abdominal surveys, pelvis evaluations, and general thoracic views.

3. Dorsoventral (DV)

The patient is placed in sternal recumbency (on their belly/sternum). The beam enters the dorsal surface and exits the ventral surface.

• Cardiac Evaluation: The DV view is preferred for cardiac evaluations because the heart lies in a more natural anatomical position without shifting or rotating, allowing for a more accurate measurement of heart size.
• Dyspneic Patients: Sternal recumbency is less stressful and makes breathing easier for patients in respiratory distress (dyspnea) compared to dorsal recumbency.

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Restraint and Positioning Aids

To minimize exposure to personnel and reduce patient stress, positioning aids should be used to stabilize the patient, eliminating the need for manual restraint.

• V-Troughs: V-shaped foam or plastic troughs are used to keep patients stable in dorsal recumbency for ventrodorsal (VD) projections. The patient's spine is nestled in the groove, preventing rolling.
• Sandbags and Foam Wedges: Sandbags of various weights and sizes are used to secure limbs or support the body. Foam wedges are placed under the chest, abdomen, or limbs to prevent rotation (e.g., maintaining a true lateral posture without tilting).
• Adhesive Tape: Medical paper or cloth tape can be wrapped around the patient's limbs or tail and secured to the table edges. This is an excellent tool for securing limbs in traction without manual restraint.
• Ropes and Gauze Ties: Soft cotton ropes or gauze strips can be tied around limbs to pull them cranially or caudally, allowing the assistant to pull from a distance outside the primary collimated area.

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Caliper Measurements and Technique Charts

A caliper is a metal or plastic slide-rule instrument used to measure the thickness of the animal's body part in centimeters. This measurement is critical because it dictates the machine settings needed to penetrate the tissue.

Proper Measurement Technique

1. Measure the Thickest Part: Always measure the thickest part of the anatomical region being radiographed. For an abdominal view, this is typically at the caudal border of the last rib (behind the liver). For a thoracic view, it is at the widest part of the chest (caudal border of the scapula).
2. Match the Positioning: The measurement must be taken with the patient in the exact position they will be radiographed. For instance, measuring a dog in lateral recumbency for a lateral projection is correct, but using that same measurement for a VD projection is incorrect because abdominal organs spread out differently when the animal is on its back, altering the thickness.
3. Read the Caliper Correctly: Read the caliper at the bottom of the slide bar, ensuring it is snug but not compressing soft tissue.
4. Reference the Technique Chart: Once measured, reference the clinic's technique chart. Look up the anatomical region (e.g., Canine Abdomen - Lateral) and find the row matching the measured thickness in centimeters. The chart will list the corresponding kVp and mAs settings to use on the X-ray console.