Patient Positioning for Standard Projections: Small Animal

Why Positioning Accuracy Matters

A radiograph is only as useful as the positioning that produced it. Poor positioning creates geometric distortion, superimposes structures that should be separate, and hides pathology — or manufactures the appearance of pathology where none exists. Every repeated exposure increases radiation dose to the patient, staff, and the student. Accurate positioning the first time is both a clinical skill and a safety obligation under the ALARA (As Low As Reasonably Achievable) principle.

ALARA and Radiation Safety Basics

Before touching the positioning aids, review your safety fundamentals. All personnel in the room during exposure must wear a lead apron and, when hands are near the primary beam, lead gloves. Dosimetry badges must be worn at collar level, outside the apron. Never hold a patient manually when mechanical restraint aids or chemical restraint (sedation) can achieve the same result. Keep the primary beam collimated as tightly as the area of interest allows — this reduces scatter radiation to everyone in the room and improves image contrast. Pregnant team members should not remain in the room during exposures. These are not optional guidelines; they reflect federal and state radiation protection regulations.

Positioning Terminology You Must Know

• Ventrodorsal (VD): The beam enters the ventral (belly) surface and exits the dorsal (back) surface. Patient lies on its back.
• Dorsoventral (DV): Beam enters dorsal surface, exits ventral. Patient lies on its sternum (sternal recumbency). Used for thorax in some patients.
• Lateral: Patient lies on its side. "Right lateral" means the patient's right side is against the table/cassette.
• Centering point: The anatomical landmark placed over the center of the receptor (cassette or digital plate).
• Collimation: Restricting the primary beam so it covers only the area of interest.

Positioning Aids

Foam wedges, sandbags, tape, and trough positioning aids are your primary tools. For a lateral view, place sandbags over the neck and limbs to prevent rotation. Foam wedges under the sternum or between the legs keep the spine parallel to the table surface — critical for an undistorted image. Tape applied loosely over limbs can help, but never compromise the airway. For VD projections, a V-shaped foam trough holds the patient in dorsal recumbency without manual assistance.

Right Lateral Thorax

Place the patient in right lateral recumbency (right side down). Extend the forelimbs cranially and secure with sandbags or tape. The sternum and spine should be at the same height — use a foam wedge under the sternum if the thorax rotates. Centering point: caudal border of the scapula, which overlies the cardiac region. Borders to include: thoracic inlet cranially to the caudal border of the last rib. Expose at peak inspiration (watch the chest rise) to maximize lung field visibility. On a digital system, the technician or technologist calls for exposure at the moment of full chest expansion.

Ventrodorsal (VD) Thorax

Place the patient in dorsal recumbency in the V-trough. Extend forelimbs cranially and secure. The spine should be straight — rotate the trough slightly if the patient lists to one side. Centering point: mid-sternum at the level of the caudal heart border. Borders: thoracic inlet to the caudal last rib. Again, expose at inspiration. On a VD thorax, the cardiac silhouette appears slightly more rounded and larger than on the lateral; this is normal.

Right Lateral Abdomen

Patient in right lateral recumbency. Hindlimbs extended caudally and secured with sandbags. A foam wedge under the caudal abdomen keeps the spine parallel to the table when the patient's abdomen is deep. Centering point: midway between the last rib and the iliac wing — approximately the level of the umbilicus. Borders: caudal border of the last rib to the greater trochanter of the femur. Expose at end-expiration for the abdomen; the diaphragm moves cranially, giving the abdominal organs more room and reducing superimposition with the lung fields.

Ventrodorsal (VD) Abdomen

Dorsal recumbency in the V-trough. Hindlimbs extended caudally and secured. Verify the spine is straight — rotate the pelvis equally on both sides. Centering point: umbilicus. Borders: caudal border of the last rib to the greater trochanter. Expose at end-expiration. The VD abdominal view separates left and right structures (e.g., left vs. right kidney) and complements the lateral view.

Limb Projections: General Principles

For a forelimb or hindlimb, two orthogonal views are standard: a lateral and a craniocaudal (CrCd) or caudocranial (CdCr), depending on the segment. The joint immediately proximal and distal to the bone of interest should be included on the image. Center over the mid-shaft of the bone or the joint itself, as directed. Collimate closely. Use sandbags to hold the opposite limb out of the field.

Evaluating the Radiograph

Immediately after exposure, review the image on the diagnostic monitor before releasing the patient. Ask:

1. Is the area of interest fully included within the borders?

2. Is there rotation (are paired structures symmetric)?

3. Is exposure adequate (appropriate brightness and contrast for the tissue)?

4. Is there motion blur?

If any criterion is unsatisfactory, reposition and repeat before the patient leaves the table — not after. Calling a repeat when the patient has been moved costs extra time and extra radiation.

Scope of Practice Reminder

As a veterinary assistant or student technician, you position and expose under the direction and supervision of a licensed veterinarian or credentialed veterinary technician. Interpreting radiographs — making a diagnosis — is the veterinarian's responsibility. Your role is to produce a technically excellent, diagnostically acceptable image safely and efficiently.