A veterinary practice that replaced its film processor with a digital radiography system years ago and has not looked at its retake rate since is almost certainly accepting image quality that would not pass an objective review. Digital radiography's wide exposure latitude — the ability to produce a "usable" image across a broad range of kVp and mAs settings — is both its greatest advantage and its greatest trap. The team stops seeing underexposure, overexposure, and marginal positioning because the image processing software makes everything look acceptable on first glance. The retake rate drops, but so does diagnostic quality.

The American Society of Radiologic Technologists (ASRT) Best Practices in Digital Radiography white paper documents this shift: in the analog era, the standard repeat rate was approximately 8%. With digital systems, positioning errors now account for 51–85% of all repeated images, and the cause of most repeats has shifted from exposure errors (which digital latitude hides) to positioning errors (which it does not). A systematic review cited by ASRT found that "positioning errors emerged as the primary cause of repeated examinations" across multiple studies.

This article provides a practical QA workflow for a veterinary practice using digital radiography. It covers retake-rate measurement, exposure-index monitoring, positioning coaching, the sedation decision that prevents most positioning failures, image labeling standards, and the documentation that supports both radiation safety and medical-legal defensibility.

Why digital radiography QA drifts

Three dynamics erode image quality in veterinary digital radiography:

1. Exposure latitude creates complacency. A digital detector can produce a diagnostic-appearing image from significantly underexposed or overexposed technique settings. The ASRT white paper warns that "the increase in exposure latitude in digital radiography has led to an overall reduction in repeats due to the use of incorrect exposure techniques" — but this does not mean the images are optimal. Underexposed images have increased quantum noise that obscures subtle pulmonary patterns. Overexposed images clip soft-tissue detail. Both can look "fine" on a monitor to an untrained eye.

2. No film cost means no economic penalty for extra exposures. With film, every extra exposure was visible as a used sheet and a darkroom expense. With digital, there is no consumable cost — only the radiation dose to the patient and the staff member who restrains the animal. The invisible cost is real: the American College of Veterinary Radiology (ACVR) states that "exposure to radiation should always be As Low As Reasonably Achievable (ALARA)."

3. No structured QA program. Most veterinary practices have a technique chart taped to the wall and no systematic review of image quality. There is no retake log, no exposure-index tracking, and no periodic positioning audit. The New Zealand Ministry of Health's Compliance Guide for Veterinary Radiation recommends that "managing entities carry out regular image quality checks; this is commonly done by six-monthly or annual in-house image repeat analysis." Most U.S. practices do none of this.

Step 1: Track the retake rate

What counts as a retake

A retake is any radiographic exposure that is repeated because the initial image was diagnostically unacceptable. The New Zealand veterinary radiation compliance guide defines three image-quality tiers:

1. Excellent — no errors in positioning, exposure, or processing.
2. Diagnostically acceptable — some errors present but not sufficient to compromise diagnostic value.
3. Unacceptable — errors that render the image diagnostically inadequate; this is the retake.

The target

The AAPM's 1–3% target is the radiology-community standard for a mature digital system. The New Zealand <10% target is a regulatory ceiling. A veterinary practice should aim for ≤5% as a practical target — higher than the human-hospital standard because veterinary patients are less cooperative, but well below the regulatory ceiling.

How to measure

Most digital radiography systems and PACS platforms can track retakes. IDEXX Web PACS, for example, allows operators to enter repeat reasons against predefined categories. If the system does not automate this, maintain a simple log at the radiography station:

Review the retake log monthly. The practice's radiation safety officer or medical director should calculate the retake rate (total retakes ÷ total exposures × 100) and compare it to the ≤5% target. If the rate climbs, the next step is a reason analysis.

Retake-reason categories

The ASRT white paper and AAPM quality-control guidance identify these categories for digital radiography:

In veterinary digital radiography, positioning and motion dominate. The PASE (Philadelphia Animal Specialty & Emergency) radiography troubleshooting guide lists patient motion, incorrect exposure settings, inappropriate collimation, and positioning errors as the four most common causes of non-diagnostic veterinary radiographs — in that order.

Step 2: Monitor the exposure index

The exposure index (EI) is the digital equivalent of optical density on film. It quantifies the radiation dose delivered to the detector for a given exposure. Different manufacturers use different scales:

• IDEXX: Proprietary exposure index scale, displayed on the Image Capture window. The IDEXX PACS Operator's Guide notes: "If the radiograph is of diagnostic quality, don't worry about an exposure index that is a little high or low. Use the exposure index to troubleshoot nondiagnostic radiographs."
• Fuji/Konica: S-value — higher S means less exposure (underexposure).
• Agfa: lgM number.
• Standardized (IEC 62494-1): Deviation Index (DI) — the difference between the actual EI and the target EI for that exam type. DI of 0 is perfect; ±1 is acceptable; ±3 is a significant deviation.

The AAPM Task Group 116 report on exposure indicators recommends that every facility establish target EI values for each exam type and monitor DI trends over time. In veterinary practice, this means:

1. Establish baseline EI targets. For each common study (thorax lateral, thorax DV/VD, abdomen lateral, pelvis VD, extremity), record the EI for 10–20 well-positioned, diagnostically excellent images at the practice's standard technique settings. The average EI for each study becomes the target.
2. Monitor for drift. If the average EI for thoracic laterals has shifted upward by 20% over three months, the technique chart may need adjustment, or the generator may need calibration.
3. Use EI to coach. When a technician consistently produces images with EI values outside the target range, the technique chart or their technique selection needs review. The AAPM report notes that DI tracking "can be a valuable tool for standardization and stabilization of manual techniques."

The technique chart

Every veterinary radiography station should have a posted technique chart. The ACVR Radiation Safety Statement states that "facilities employing ionizing radiation as a diagnostic or therapeutic tool must establish policies, put standard operating procedures in place, and be familiar with current standards and techniques." A technique chart is the foundational SOP.

The chart should specify, for each study and patient-thickness range:

• kVp
• mAs
• Grid use (yes/no)
• Source-to-image distance (SID)
• Whether sedation is recommended

IMV Imaging publishes a widely used small-animal exposure chart for DR systems that provides kVp and mAs by body-region and patient-thickness. This is a starting template; the practice's installer (IDEXX, Sound, Asteris, etc.) should calibrate it to the specific generator and panel.

Step 3: The sedation decision

The Merck Veterinary Manual is direct: "Sedation or short-acting anesthesia is often necessary and usually desirable if medical circumstances permit. Chemical restraint lessens the need for and intensity of manual restraint, which leads to fewer poor or unacceptable radiographs and usually shortens the time required to complete the examination."

The ACVR Radiation Safety Statement adds: "Unless absolutely necessary for patient well-being, individuals should leave the room while a radiographic exposure is made. This may be facilitated through the use of sedation and/or manual positioning devices such as troughs, sandbags, and tape."

Sedation is a radiation-safety decision, not just a patient-comfort decision. Every exposure where a staff member holds the patient is an exposure where that person receives scatter radiation. Sedation allows the staff to step away from the primary beam and behind shielding.

Decision framework

IDEXX's Radiation Safety Center reports that "nearly 3 in 4 (74%) of veterinary professionals considering a job change put radiation safety high on their priority list." Practices that default to manual restraint for every study are exposing their technicians unnecessarily and making recruitment harder.

Step 4: Positioning coaching

Positioning is the skill gap that matters most in veterinary radiography. The ASRT white paper notes that "technology does not affect the radiographer's skills in accurately positioning the patient" — meaning that upgrading from CR to DR does not improve positioning, and practices should not expect it to.

The coaching cycle

1. Baseline audit. Have a veterinarian or, ideally, a radiologist review the last 50 radiographic studies. Score each image as excellent / diagnostically acceptable / unacceptable using the three-tier scale. Calculate the per-technician retake rate and the per-study retake rate.

2. Targeted training. If the audit shows that thoracic laterals are the most commonly repeated view, focus training on thoracic positioning. Key checkpoints for a lateral thorax:

   • Sternum and spine superimposed in the same vertical plane
   • Thoracic limbs pulled cranially to avoid overlap with the cranial thorax
   • Collimation to include the thoracic inlet through the caudal lung fields
   • Exposure at peak inspiration

   The PASE troubleshooting guide recommends "having access to positioning aids such as foam pads, sandbags, tape, and sedation when indicated" as the core toolkit.

3. Real-time feedback. The fastest way to improve positioning is immediate feedback after each study. A veterinarian reviews the images while the patient is still on the table and provides specific guidance: "This lateral thorax is rotated — the sternebrae are dorsal to the spine. Retake with more foam under the sternum." IDEXX's Image Coach software provides a real-time positioning aid photo and reference radiograph alongside the exposure — a useful tool, but not a substitute for a veterinarian who reviews images and coaches.

4. Re-audit quarterly. After the initial training intervention, repeat the 50-study audit every quarter. Track the retake rate trend. The goal is a sustained ≤5% rate.

Positioning aids

Every radiography station should have:

• Foam positioning wedges (multiple sizes)
• Sandbags (for limb positioning — not for weighting the patient onto the table)
• Medical tape
• A V-trough or similar body-conforming support for lateral recumbency
• A radiolucent positioning device for DV/VD thorax and abdomen views

The Merck Veterinary Manual notes: "In many cases, improper positioning for radiographic examination can result in a misdiagnosis or inability to appreciate major lesions."

Step 5: Image labeling and documentation

Every radiographic image must carry specific metadata. The CRCPD (Conference of Radiation Control Program Directors) CR/DR inspection protocol requires that facilities verify correct patient and examination information on all images.

Required labels/metadata:

• Patient name and ID (auto-populated from PIMS when integrated)
• Date and time of exposure (auto-populated from the system clock)
• Clinic/hospital name
• Left/right marker — placed on the patient or the detector at the time of exposure, not added digitally afterward (digital markers can be moved or misrepresented; physical markers are the standard of care in radiology)
• Technician initials (for internal tracking and QA)

The IDEXX PACS Operator's Guide warns that "for best image quality, the body part that you are imaging must match the selected shot. The shot type determines image processing values and image orientation." Selecting the wrong shot type in the software applies the wrong processing algorithm and orientation — an error that may not be visually obvious but degrades diagnostic quality.

Step 6: Equipment QC

Daily

• Inspect the detector panel (DR) or cassette (CR) for damage, dirt, or moisture. Clean per manufacturer instructions.
• Confirm the x-ray tube and collimator are functioning. Check that the collimator light field matches the radiation field (a misaligned collimator means the beam is exposing tissue outside the intended field).

Quarterly

• Review exposure-index trends across all study types. Investigate any systematic shift.
• Review the retake log. Identify the top retake reasons and the top retake views.
• Verify the technique chart against current EI data. Adjust kVp/mAs if EI has drifted from targets.

Annually

• Schedule a qualified medical physicist or manufacturer service to perform:
  • Output calibration (kVp accuracy, mAs linearity, half-value layer)
  • Collimation and light-field alignment
  • Exposure-index calibration
  • Spatial resolution test (if applicable)
• The ACVR states: "Equipment quality control must be included in these protocols, including monitoring all personal protective equipment (PPE) at least once yearly for evidence of cracking or leaks."

PPE inspection

Lead aprons, gloves, and thyroid shields must be inspected annually for cracks, tears, and delamination. The ACVR recommends fluoroscopy or radiographic inspection of all PPE at least yearly. Damaged PPE must be replaced immediately — it provides a false sense of protection while allowing radiation through the defect.

Building the QA program

A functional digital radiography QA program in a veterinary practice has four components:

1. Written protocol. A document that specifies: retake-rate target (≤5%), retake-logging procedure, exposure-index targets by study type, technique chart, sedation policy, positioning-coaching schedule, equipment QC schedule, and PPE inspection schedule.
2. Retake log. Paper or digital, reviewed monthly by the radiation safety officer or medical director.
3. Quarterly audit. A 50-image review scored by a veterinarian, with per-technician feedback.
4. Annual equipment inspection. Performed by a qualified service provider, documented in the equipment maintenance log.

The New Zealand veterinary radiation compliance guide requires that "managing entities need to establish a quality assurance programme as part of their protection and safety management system" and that "quality programmes must be documented in writing, noting protocols and frequencies for each check and test." This is a regulatory requirement in many jurisdictions and an AAHA-accreditation expectation in the United States.

Sources

• ASRT. Best Practices in Digital Radiography (white paper). American Society of Radiologic Technologists. https://www.asrt.org/docs/default-source/research/whitepapers/best-practices-in-digital-radiography.pdf
• AAPM Task Group 116. An Exposure Indicator for Digital Radiography (Report No. 116). American Association of Physicists in Medicine. https://www.aapm.org/pubs/reports/rpt_116.pdf
• ACVR. Radiation Safety Statement. American College of Veterinary Radiology. https://acvr.org/how-we-do-it/types-of-imaging-therapy/radiology/acvrs-radiation-safety-statement
• Merck Veterinary Manual. Radiography of Animals. https://www.merckvetmanual.com/clinical-pathology-and-procedures/diagnostic-imaging/radiography-of-animals
• IDEXX. IDEXX-PACS Imaging Software Operator's Guide. https://www.idexx.com/files/idexx-pacs-operators-guide-4-9.pdf
• IDEXX. Radiation Safety Center — Safe Imaging Is Optimal Imaging. https://www.idexx.com/en/veterinary/diagnostic-imaging-telemedicine-consultants/radiation-safety-center
• IDEXX. How Diagnostic Imaging Systems Keep Veterinary Teams Safer. https://www.idexx.com/en/veterinary/diagnostic-imaging-telemedicine-consultants/how-idexx-diagnostic-imaging-systems-keep-veterinary-teams-safer
• Philadelphia Animal Specialty & Emergency (PASE). Taking the Perfect Radiograph: Troubleshooting Common Errors and Artifacts. https://www.pase.vet/pase-articles/taking-the-perfect-radiograph-troubleshooting-common-errors-and-artifacts.html
• New Zealand Ministry of Health. Compliance Guide for Veterinary Radiation. https://www.health.govt.nz/system/files/2023-12/compliance_guide_for_veterinary_radiation_ors_g9_12-12-2023.pdf
• IAEA. Handbook of Basic Quality Control Tests for Diagnostic Radiology. https://www-pub.iaea.org/MTCD/Publications/PDF/PUB2021_web.pdf
• CRCPD. CR and DR State X-Ray Inspection Protocol. Conference of Radiation Control Program Directors. https://crcpd.org/wp-content/uploads/2023/11/CRDR_Protocol.pdf
• Vets Choice Radiology. Avoid Blurry X-Rays: 3 Ways to Minimize Patient Movement. https://www.vetschoiceradiology.com/avoid-blurry-x-rays-3-ways-to-minimize-patient-movement
• IMV Imaging. Small Animal Exposure Chart — Direct Digital Radiography (DR). https://www.imv-imaging.com/wp-content/uploads/2023/01/small-animal-exposure-charts-digital-radiography-dr-80cm-distance-uk.pdf