Diagnostic Imaging: Radiograph Positioning, Exposure, and Digital Image Evaluation

Diagnostic Imaging in Veterinary Technology

Diagnostic radiography is one of the most frequently used imaging tools in veterinary practice. As a credentialed veterinary technician, you are responsible for producing diagnostic-quality images efficiently and safely, every time. This lesson covers the foundational knowledge you need before entering the radiology suite: radiation safety, patient positioning for five standard views, digital exposure principles, and systematic image evaluation.

Radiation Safety and the ALARA Principle

All personnel working with ionizing radiation must follow the ALARA principle — keep radiation exposure As Low As Reasonably Achievable. Practical steps include:

• Distance: Step away from the primary beam whenever possible. Doubling your distance from the source reduces exposure by approximately four times (inverse square law).
• Shielding: Always wear a lead apron (at least 0.5 mm lead equivalent), a thyroid shield, and lead gloves when your hands must be near the field. Never hold a patient with unprotected hands.
• Collimation: Restrict the primary beam to the area of interest using the collimator. This reduces scatter radiation and improves image contrast.
• Dosimetry: Wear a personal dosimeter (badge) every time you enter the radiology suite. Badges are monitored on a scheduled basis so that cumulative dose is tracked.
• Restraint priority: Chemical restraint (sedation or anesthesia) is preferred over manual restraint whenever clinically appropriate and approved by the veterinarian.

Before beginning any imaging session, complete a radiation safety checklist to confirm PPE is in good condition, the collimator light functions, and no unauthorized personnel are present.

Patient Positioning: Five Standard Views

Correct positioning is the technician's primary contribution to image quality. Use foam wedges, sandbags, and ties to maintain the patient in position without manual restraint.

1. Lateral Thorax (Right Lateral Recumbency — RL)

Place the patient in right lateral recumbency. Extend the forelimbs cranially so the triceps muscles do not superimpose over the cranial lung field. Use a foam wedge under the sternum so the spine and sternum are at the same height, keeping the thorax truly lateral. Center the beam at the caudal border of the scapula. Include the thoracic inlet cranially and the diaphragm caudally.

2. Ventrodorsal (VD) Thorax

Place the patient in dorsal recumbency in a V-trough. Extend the forelimbs cranially. The sternum should be directly superimposed on the spine on the resulting image; a rotated patient will show asymmetric rib spacing. Center the beam on the midsternum. Include the entire thoracic cavity.

3. Lateral Abdomen (Right Lateral Recumbency)

Position as for lateral thorax but center the beam at the umbilicus. The caudal lung field and the bladder should both be included. Avoid hyperextending the hindlimbs, which can displace abdominal organs.

4. Lateral Skull

Place the patient in lateral recumbency with the head supported on a foam pad so the sagittal plane is parallel to the table. Superimposition of the mandibles and tympanic bullae confirms true lateral positioning. Center the beam at the midpoint of the skull.

5. Craniocaudal (CrCd) Stifle

Place the patient in dorsal or sternal recumbency with the affected limb extended caudally. The femur and tibia should be collinear. Center the beam on the stifle joint. The patella should be centered in the trochlear groove on the resulting image.

Labeling Conventions

Every image must include: patient name and ID, date, clinic name, view marker (R, L, VD, DV, etc.), and a size marker if required. Markers are placed in the field before exposure — they cannot be added digitally after the fact in a legally defensible record.

Digital Exposure and Image Quality

Digital radiography systems (CR and DR) use an exposure index (EI) rather than film density to indicate whether exposure was appropriate. Each manufacturer defines acceptable EI ranges; in general, underexposure produces a grainy, noisy image and overexposure causes loss of contrast in dense structures. Unlike film, digital systems have a wide latitude, but gross errors still degrade diagnostic quality and increase patient dose.

Key factors: kVp (kilovoltage peak) controls penetrating power and contrast; mAs (milliampere-seconds) controls the quantity of photons and primarily affects exposure level. For thoracic views, use a high kVp / low mAs technique to capture the full dynamic range of soft tissue and air. For skeletal views, a lower kVp is appropriate to optimize bone-soft tissue contrast.

Five-Point Diagnostic Quality Rubric

After acquiring each image, evaluate it systematically:

1. Positioning — Is the anatomy displayed in the correct plane? Identify rotation, obliquity, or incorrect centering.

2. Exposure — Is the EI within the acceptable range? Is there excessive noise or overexposure?

3. Collimation — Is the beam restricted to the region of interest with clear borders visible?

4. Labeling — Are all required identifiers and view markers present and legible?

5. Artifact — Is the image free of positioning aid shadows, grid lines (if inappropriate), or processing artifacts?

Score each category 1–5. A score of 4 or 5 indicates diagnostic quality. If any category scores below 4, document the specific error and describe the corrective action before repeating the view.

Scope of Practice Reminder

Veterinary technicians position patients, acquire images, and perform initial quality evaluation. Interpretation of radiographic findings — diagnosis — is the exclusive responsibility of the licensed veterinarian. You may describe what you observe on the image critique form, but you do not diagnose pathology.