Veterinary Radiography — Dogs & Cats
A practical, radiographer-friendly tour of small-animal imaging: how the vet world differs from human radiography, how patients are restrained safely and humanely, the higher-risk radiation-safety reality of the vet room, the standard views for dogs and cats, exposure logic without AEC, and a brief educational primer on common findings.
How veterinary radiography differs from human
If you trained in human radiography, most of your physics and image-evaluation skills transfer directly. What changes is the patient: it cannot follow instructions, it has different anatomy and naming conventions, and the room is often built and staffed differently. Here are the differences that matter day to day.
No breath-hold on command
You cannot ask a dog or cat to “take a breath and hold.” Chest and cranial-abdomen images must be timed to the animal’s own respiratory cycle — you watch the chest and expose at peak inspiration (for lung detail) or expiration, depending on the goal. Under general anaesthesia the anaesthetist can deliver a controlled inflation, giving you a reproducible peak-inspiratory image.
Restraint is a clinical decision
Every study starts with the question: how will this animal be kept still and correctly positioned? Options run from positioning aids (troughs, sandbags, ties, foam wedges) through to sedation and general anaesthesia. Manual holding by a person is treated as a last resort (see Tabs 2 and 3).
Staff-in-room rules differ
In human imaging nobody stands in the room during the exposure. In veterinary practice this has historically happened — but modern guidance strongly discourages it. The legal and best-practice position varies by country (details below), so you must know your local rules.
Different anatomy & naming
Quadrupeds use directional terms built around a horizontal spine, not a standing human. Learning the vocabulary is the single fastest way to read vet request forms and communicate positioning.
Often no AEC
Many vet rooms have no automatic exposure control. Correct exposure comes from measuring the body part with calipers and reading a technique chart keyed to thickness. This makes disciplined measuring and chart-keeping essential (Tab 6).
Huge size range
One room images a 1.5 kg kitten and a 70 kg mastiff. Technique factors, grid decisions, and collimation vary enormously across a single day’s list — far more variation than a typical human department.
Directional terminology cheat-sheet
Veterinary anatomy replaces the human “anterior/posterior” with terms referenced to the body axis. Get comfortable with these; they define both the view name and the beam direction.
| Vet term | Meaning | Human analogue |
|---|---|---|
| Cranial | Toward the head | Superior (limbs) / anterior-ish |
| Caudal | Toward the tail | Inferior / posterior-ish |
| Dorsal | Toward the spine/back | Posterior (trunk) |
| Ventral | Toward the belly | Anterior (trunk) |
| Rostral | Toward the nose (head only) | Anterior (head) |
| Proximal / Distal | Nearer / farther from the body (limbs) | Same |
| Palmar | Back of the front paw, below the carpus | Palmar (hand) |
| Plantar | Back of the hind paw, below the tarsus | Plantar (foot) |
| Medial / Lateral | Toward / away from midline | Same |
Manual restraint — the legal picture varies
Whether a person may hold an animal during an exposure, and under what conditions, depends on where you practise. Never assume; confirm against your jurisdiction’s regulations and your practice’s local rules.
Restraint, sedation & welfare
Good positioning without hands in the room is the goal. The toolkit is a combination of physical aids, chemical restraint, and calm handling — chosen to get a diagnostic image with the least distress and the least radiation to people.
Positioning aids (the mechanical toolkit)
Radiolucent trough (V-trough)
A foam or acrylic V-shaped cradle that holds an animal in dorsal recumbency (on its back) for VD/DV views. Keeps the spine straight and stops the patient rolling — indispensable for symmetric pelvis and thorax VDs.
Sandbags
Weighted bags drape over limbs and neck to hold position. Keep them out of the primary beam where possible (they attenuate and can obscure anatomy). Cloth-covered, wipeable versions help infection control.
Ties / tapes
Soft ties around limbs, anchored to cleats at the table edge, extend and stabilise legs (essential for hip-extended and long-bone views) without a person holding. Padding under ties protects skin.
Foam wedges & troughs
Radiolucent foam pads rotate a body part into a true lateral or oblique, take up the “wedge” gap under a limb, and reduce rotation artefact. A stack of assorted wedges is one of the most-used items in the room.
Tape & ties for heads
A tie behind the canine teeth and another behind the ears gently extends the head/neck for skull and cervical work under sedation/GA.
Compression band
A radiolucent band across the abdomen can steady a lightly sedated patient and reduce tissue thickness/motion — used judiciously and never as a substitute for adequate restraint.
When is sedation or general anaesthesia needed?
| Situation | Typical approach |
|---|---|
| Calm, cooperative patient, quick view | Aids + gentle handling may suffice |
| Painful region (fracture, abdomen), anxious or fractious animal | Sedation (often with analgesia) improves welfare and image quality |
| Views requiring full muscle relaxation — hip-extended (OFA/PennHIP), stress/dysplasia views | Heavy sedation or general anaesthesia is generally required for relaxation, positioning, and to eliminate manual restraint |
| Thoracic study needing controlled inflation | GA lets the anaesthetist deliver a reproducible peak-inspiratory hold |
| Multiple projections / long study in a fractious cat | Sedation reduces total handling, exposures, and repeat films |
Monitoring basics during sedation/GA
- Airway & breathing: observe rate and pattern; a pulse oximeter (SpO₂) on tongue/paw is standard under GA.
- Circulation: pulse rate/quality, mucous-membrane colour, capillary refill time; ECG and blood pressure under GA.
- Temperature: anaesthetised animals lose heat fast — use warming; monitor especially in small cats and thin dogs.
- Depth: jaw tone, eye position, reflexes; keep the plane only as deep as the procedure needs.
- Recovery: quiet, warm, observed area; do not leave a recovering patient unattended.
Minimising distress
- Low-stress handling: quiet room, non-slip surfaces, minimal people, calm voices; consider species-appropriate pheromone products.
- Prepare everything (settings, plates, aids) before the animal is positioned so the study is quick.
- Cats: reduce visual/auditory stress; a towel “burrito” wrap can settle a cat for a brief conscious view where appropriate.
- Analgesia for painful conditions is a welfare requirement, not an optional extra.
Radiation safety in the veterinary practice
The core physics is identical to human radiography, but the risk profile is higher for one reason: people have historically been in the room, sometimes holding patients. Add smaller rooms, mobile/older equipment, and mixed-experience teams, and disciplined radiation protection becomes essential.
The hierarchy of control (do these in order)
- Justify: is the radiograph clinically needed? Each exposure must be justified by the veterinary surgeon.
- Eliminate the holder: use sedation/GA and positioning aids so nobody is in the room during the exposure.
- Collimate tightly to the region of interest — less scatter, less patient dose, better image.
- Optimise technique (correct kVp/mAs, grid only when needed) — ALARA.
- If holding is unavoidable: trained adult, full PPE, dosimetry, and never in the primary beam.
Who may hold — and who may not
Never in the room / never holding
- Pregnant staff (or anyone who may be pregnant)
- Anyone under 18
- Untrained persons and, generally, members of the public/owners
If a trained adult must hold
- Wear lead apron, thyroid shield, and lead gloves
- Keep all body parts out of the primary beam
- Stand as far from the beam as the task allows; maximise distance
- Wear and correctly position a dosimeter
- Rotate the role so no one person is repeatedly exposed
PPE & equipment
| Item | Purpose / note |
|---|---|
| Lead apron (≥0.25–0.5 mm Pb equiv.) | Body protection; inspect/log for cracks; store on hangers, never folded. |
| Thyroid shield | Protects a radiosensitive organ; often overlooked. |
| Lead gloves | For hands only if holding is unavoidable — they do not protect against the primary beam. |
| Lead glasses | Consider for fluoroscopy/frequent operators. |
| Personal dosimeter (film/TLD/OSL) | Worn by classified/monitored staff; results reviewed by the practice and RPA. |
Room, controlled areas & local rules
- Controlled area: the region where exposures occur is designated and access is restricted during exposure; a designated Radiation Protection Supervisor (RPS) oversees local rules, advised by a Radiation Protection Adviser (RPA).
- Warning systems: signage and warning lights indicate when the set is live.
- Distance & shielding: operate from behind a barrier or at maximum practical distance; the exposure switch cabling should allow this.
- Local rules: a written scheme of work covering who does what, PPE, monitoring, and contingency — everyone must know it.
Pregnant staff
Standard views — dog canine
Below are the workhorse projections. For each: positioning, centring, collimation, and the faults that most often force a repeat. Two orthogonal views are the rule for almost every region.
Thorax
Right & left lateral thorax
- Positioning
- Lateral recumbency; forelimbs drawn cranially and tied clear of the chest; a small foam wedge under the sternum makes it level with the spine (prevents rotation).
- Centring
- Caudal border of the scapula, roughly the 5th–6th intercostal space, mid-thorax.
- Collimation
- Thoracic inlet to just past the diaphragm/last rib; include the whole lung field.
- Timing
- Expose at peak inspiration for maximum lung aeration/detail.
Common faults: rotation (rib heads/costochondral junctions not superimposed), expiratory film (looks like increased opacity/”false” disease), clipping the caudodorsal lung or diaphragm.
Why both laterals? The dependent (down) lung is partly collapsed by the patient’s weight, so a lesion there can be masked. Right and left laterals let each lung be the non-dependent, well-aerated side in turn.
DV & VD thorax
- Positioning
- DV: sternal recumbency (on the chest), often better tolerated and better for the cardiac silhouette/pulmonary vessels. VD: dorsal recumbency in a trough, forelimbs cranial — better for the accessory lung lobe and caudodorsal fields.
- Centring
- Midline at the caudal scapular border.
- Collimation
- Thoracic inlet to past the diaphragm; skin margins laterally.
- Timing
- Peak inspiration. Under GA the anaesthetist can give a controlled inflation for a reproducible image.
Common faults: asymmetry (spine not superimposed on the sternum), a dyspnoeic patient forced into VD (welfare/safety risk — prefer DV or sit up), motion blur from a fast respiratory rate.
Abdomen
Right lateral & VD abdomen
- Positioning
- Right lateral: right side down, hindlimbs pulled caudally, foam to prevent rotation. VD: dorsal recumbency in a trough, hindlimbs extended.
- Centring
- Roughly the last rib / mid-lumbar for a full abdomen; adjust caudally for a bladder/pelvic-inlet emphasis.
- Collimation
- Diaphragm (include the cupula) to the coxofemoral joints / greater trochanters.
- Timing
- Expose at expiration — the diaphragm moves cranially, giving the abdominal organs maximum room and contrast.
Common faults: clipping the diaphragm cranially or the bladder/pelvic inlet caudally, inspiratory film (crowded organs), overexposure that burns out gas-filled bowel detail.
Pelvis & hips
VD pelvis — hip-extended (OFA-style)
- Positioning
- Dorsal recumbency in a trough; hindlimbs extended caudally and parallel, stifles rotated inward so the patellae sit centred over the trochlear grooves; pelvis symmetric (obturator foramina equal, wings of ilium equal).
- Centring
- Midline at the hip joints (level of the greater trochanters).
- Collimation
- Wings of ilium to the stifles; include both femurs and both knees.
- Note
- Full muscle relaxation is needed for a valid extended-hip film, so heavy sedation/GA is standard. This is the projection used for OFA hip grading and is also one of the three views in a PennHIP study.
Common faults: pelvic tilt/rotation (unequal obturator foramina), femurs not parallel or not fully extended, patellae off-centre (inadequate inward rotation) — all can distort apparent hip congruity.
Stifle (knee)
Mediolateral & caudocranial stifle
- Positioning
- Lateral: affected limb down, stifle flexed ~90°, foam to prevent rotation, opposite limb pulled clear. Caudocranial: sternal/oblique with the stifle extended and centred, beam entering caudally.
- Centring
- The stifle joint (femorotibial articulation).
- Collimation
- Distal femur to proximal tibia/fibula, including the patella.
Common faults: rotation obscuring the femoral condyles, over-collimation cutting the patella/tibial tuberosity, joint not centred to the beam causing distortion. Look for joint effusion (loss of the infrapatellar fat pad) and cranial tibial displacement (cruciate disease).
Elbow (incl. dysplasia views)
Mediolateral (flexed & extended) + craniocaudal elbow
- Positioning
- Flexed lateral: elbow flexed >45° to project the anconeal process free of the humeral condyle (screens for ununited anconeal process). Extended lateral and craniocaudal complete the series for medial coronoid disease and OCD.
- Centring
- The elbow joint (humeroradioulnar articulation).
- Collimation
- Distal humerus to proximal radius/ulna.
Common faults: insufficient flexion hiding the anconeal process, rotation superimposing the medial coronoid, exposure too high burning out subtle sclerosis. Elbow dysplasia screening often follows a specific protocol (e.g. IEWG) — confirm the required projections.
Spine
Lateral & VD spine (regional)
- Positioning
- Under sedation/GA for straightness. Support the spine with foam pads so it is parallel to the table — each intervertebral disc space must be square to the beam. Image one region (cervical, thoracic, thoracolumbar, lumbosacral) at a time.
- Centring
- The centre of the region of interest, with the beam over the target disc spaces.
- Collimation
- Tightly to the vertebral column for the region; include one segment above and below the area of interest.
Common faults: “sagging” spine giving false disc-space narrowing at the ends of the film, rotation (transverse processes/rib heads asymmetric), trying to cover the whole spine on one film (oblique disc spaces at the periphery). Use collimated, centred regional films for disc-space assessment.
Go deeper
Full vet positioning atlas with faults gallery — Pro. Step-by-step positioning photos, annotated correct-vs-faulted examples for every dog and cat view, printable technique-chart templates, and dysplasia-protocol checklists (OFA, PennHIP, IEWG elbow).
What Pro will includeStandard views — cat feline
Cats use the same projections as dogs, but their size, temperament, and physiology change how you approach the study. The principles below sit on top of the dog protocols in Tab 4.
Smaller = higher geometry stakes
A cat’s thorax is only a few centimetres thick, so small errors in centring, rotation, or exposure show up proportionally more. Tight collimation and accurate caliper measurement matter even more than in dogs.
Less tolerant of handling
Cats stress quickly and can decompensate — especially the dyspnoeic cat. Minimise handling, work fast, and lower your threshold for sedation. Never wrestle a struggling cat into a VD if it is in respiratory distress.
Resist the “whole-body” film
Because a cat fits on one plate, there is a temptation to shoot the entire animal in one exposure. Don’t — a single collimated view of one region gives correct geometry, less scatter, and a diagnostic image. Image the region the clinical question needs.
Lower exposure factors
Thin body parts mean low mAs and modest kVp; a grid is rarely needed (most cat body parts are under the grid threshold — see Tab 6). Beware overexposure burning out fine detail.
Thorax (cat)
Lateral & DV/VD thorax
- Positioning
- As for the dog but with a light touch. For the dyspnoeic cat, a DV (sternal) view or even a standing/”horizontal-beam” approach is far safer than forcing dorsal recumbency.
- Timing
- Peak inspiration; cats breathe fast, so watch closely and be ready. Motion blur is a frequent cause of repeats.
- Collimation
- Thoracic inlet to just past the diaphragm.
Common faults: motion blur (fast RR), stress-induced tachypnoea worsening the patient, over-restraint of a compromised cat. Prioritise the patient over the perfect film.
Abdomen (cat)
Right lateral & VD abdomen
- Positioning
- As for the dog; a trough helps hold the small body in dorsal recumbency for the VD.
- Collimation
- Diaphragm to coxofemoral joints. Cats have relatively more falciform fat, which gives useful serosal contrast when exposure is correct.
Common faults: overexposure (small patient) erasing serosal detail, clipping the bladder caudally, rotation.
Cat-specific notes
- Aortic thromboembolism (“saddle thrombus”): a classic feline emergency presenting as acute hindlimb pain/paralysis — often these cats also have cardiac disease and can be fragile; handle minimally.
- Feline asthma / bronchial disease: a common reason for a stressed, coughing cat needing chest films — sedate rather than fight.
- Small skeleton, delicate positioning: use smaller foam wedges and lighter ties; the same aids as dogs but scaled down.
- Thermoregulation: small anaesthetised cats cool very quickly — active warming is essential.
- Temperament first: low-stress handling (towel wraps, quiet room, pheromones) often makes the difference between a diagnostic study and a dangerous struggle.
Exposure & technique — working without AEC
Many vet rooms have no automatic exposure control, so you are the AEC. Consistent, diagnostic images come from measuring the part and reading a technique chart — plus understanding what kVp and mAs each do.
kVp and mAs logic
kVp — beam penetration & contrast
Kilovoltage sets how penetrating the beam is and therefore the contrast. Thicker or denser parts need higher kVp. Higher kVp = longer grey scale (lower contrast) and more scatter; lower kVp = higher contrast but needs the part to be penetrable. Bone/skeletal work often uses higher-contrast (lower-kVp) technique; soft-tissue abdomen uses a longer grey scale.
mAs — quantity / density
Milliampere-seconds sets the number of photons and therefore image density/exposure. Too little mAs = mottled, underexposed; too much = dark, burnt-out. Keep exposure time short to freeze respiratory/patient motion — favour higher mA with short time.
Building a technique chart
A technique chart converts a measured thickness (in cm) into kVp/mAs for your specific machine, detector, and film-focus distance. It is the single most valuable document in an AEC-free room.
- Measure with calipers. Measure the part at the point the central ray enters, in centimetres, on the positioned patient. Guessing is the #1 cause of repeats.
- Fix your variables: a set FFD/SID, a set grid (or no grid), a set detector. Change one thing at a time.
- Derive kVp from thickness: many charts start from a baseline and add a set number of kVp per additional cm (a common convention is roughly +2 kVp per cm above a reference, then adjust). Calibrate to your equipment with test exposures.
- Set mAs by region (thorax vs abdomen vs extremity) and by grid use.
- Record & refine: log the settings that produced diagnostic images and update the chart. Keep separate columns for grid/non-grid.
| Region | Measure at | Timing | Grid? |
|---|---|---|---|
| Thorax | Caudal scapular border (thickest point of the chest) | Peak inspiration | Only if > grid threshold |
| Abdomen | Thickest point (usually mid/caudal abdomen) | Expiration | Often, in larger dogs |
| Extremity | Over the joint/region of interest | n/a | Rarely (thin) |
| Pelvis / spine | Over the target | n/a | Usually, in medium/large dogs |
Grid threshold
When you switch a grid in, you must increase exposure (the grid absorbs scatter and some primary beam), so grid and non-grid columns on your chart will differ substantially. Watch for grid faults: off-centre/upside-down focused grids cause grid cut-off (density falls toward the edges).
Common exposure faults
| Appearance | Likely cause | Fix |
|---|---|---|
| Too dark / burnt-out | Excess mAs or kVp; small patient over-exposed | Reduce mAs/kVp; re-measure |
| Too light / mottled & noisy | Insufficient mAs; under-penetration | Increase mAs (then kVp if under-penetrated) |
| Flat, “foggy,” low contrast | Scatter — no grid on a thick part, or too-high kVp | Add/appropriate grid; tighten collimation; lower kVp |
| Motion blur | Exposure time too long vs patient/respiration | Higher mA, shorter time; time to breathing; sedate |
| Density falls off toward edges | Grid cut-off (off-centre, angled, or inverted focused grid) | Centre beam to grid; correct grid orientation/distance |
Digital systems in vet practice
- CR and DR are now common in vet practice; DR gives near-instant images and faster lists.
- Wide latitude is a double-edged sword: digital detectors tolerate exposure error and rescale to a “normal-looking” image, which quietly hides under- and over-exposure. Monitor the exposure indicator (EI/DI/S-number, vendor-specific) to keep dose in the correct window — do not let dose creep upward just because images “look fine.”
- Collimation still matters: tight collimation improves contrast and lets processing work correctly; some systems mis-process if the field is too large.
- Post-processing is not a substitute for correct positioning, centring, and exposure — rubbish in, rubbish out.
Common findings primer educational
GDV — gastric dilatation-volvulus (the “double bubble”)
Why it matters: a true emergency in (typically large, deep-chested) dogs — the stomach dilates and twists, compromising blood supply. Minutes count; imaging is quick and the patient is often unstable.
What you’d see: a massively gas-distended stomach. On the right lateral view the twisted stomach classically shows two gas-filled compartments separated by a soft-tissue fold — the “double bubble” / “reverse-C” / “Popeye arm” appearance — indicating volvulus rather than simple dilatation. The right lateral is the key view for this distinction.
Handling note: these dogs are shocky — coordinate with the vet, image fast, minimal restraint, and expect the patient to go straight to treatment.
Pleural effusion vs pneumothorax in the dyspnoeic cat
Why it matters: both cause acute breathing distress but look and behave differently; the fragile dyspnoeic cat must be handled minimally.
- Fluid opacity in the ventral/dependent chest
- Lung lobes retracted from the chest wall, “scalloped” lobe margins
- Silhouetting of the cardiac/diaphragm borders
- Lucent (black) gas in the dorsal/free pleural space
- Lungs collapse away from the chest wall — heart may appear “lifted” off the sternum
- Absent lung markings peripherally
Handling note: prefer a DV or horizontal-beam view with oxygen; do not force a distressed cat into VD.
Hip dysplasia — the grading concept
Why it matters: a common inherited orthopaedic disease; screening drives breeding decisions and treatment.
What you’d see: on the hip-extended VD, features of a poorly-fitting joint — a shallow acetabulum, incomplete coverage of the femoral head, subluxation (the head sitting out of the socket), and, over time, secondary osteoarthritis (osteophytes, sclerosis, remodelling). Grading systems (OFA in North America; the BVA/KC scheme in the UK; PennHIP’s distraction index) quantify laxity and/or arthritic change. PennHIP’s distraction index measures how far the head can be levered from the socket — a laxity number rather than a subjective grade.
Positioning note: the validity of grading depends entirely on a correctly positioned, symmetric, fully-relaxed film (Tab 4). Rotation or inadequate extension can fake or mask disease.
Fracture basics
Why it matters: fractures need at least two orthogonal views and often the joint above and below.
What you’d see / describe: a lucent fracture line and cortical disruption; then the descriptors clinicians use — location (which bone/third), pattern (transverse, oblique, spiral, comminuted), displacement and angulation, whether it is open vs closed, and whether it involves a growth plate (Salter-Harris types) or a joint (articular). Always include both orthogonal views: a non-displaced or incomplete fracture can be invisible on one projection.
Positioning note: handle the injured limb gently and with analgesia on board; sedation both protects welfare and improves the image.
Foreign bodies
Why it matters: ingested objects (especially in young dogs and string in cats) can obstruct the gut — an emergency.
What you’d see: radiopaque objects (stones, metal, some bones) are directly visible. Radiolucent objects (fabric, plastic, rubber) are inferred indirectly — a mechanical obstruction pattern: segmental gas/fluid-distended bowel loops of two populations (dilated vs normal), sometimes a “gravel sign.” Linear foreign bodies (classically string in cats) cause plication — the bowel bunches/accordions around the anchored string, with abnormal “comma-shaped” gas bubbles. Contrast studies or ultrasound may be added by the vet.
Views: right lateral + VD abdomen, well collimated and correctly exposed so gas/serosal detail is preserved.
References & further reading
Regulatory and professional guidance changes — always confirm the current edition and your local rules before relying on specifics.
- British Veterinary Association (BVA) — Ionising Radiations guide. Manual restraint, PPE, local rules under IRR17.
- BVA — Ionising Radiation (IRR17) myth-busting guide.
- Ionising Radiations Regulations 2017 (IRR17), UK.
- RCVS — Practice Standards Scheme (practice requirements, incl. imaging).
- American College of Veterinary Radiology (ACVR) — Radiation Safety Statement.
- California Veterinary Medical Board — Radiation Safety guide (example US state guidance).
- Merck Veterinary Manual — Radiography of Animals.
- Antech / PennHIP — What is PennHIP (distraction, compression, hip-extended views).
- PennHIP Manual (PDF).
- Orthopedic Foundation for Animals (OFA) — Hip Dysplasia (hip-extended grading).
- BVA/Kennel Club Hip Dysplasia Scheme.
- University textbook radiology resources — e.g. Thrall, Textbook of Veterinary Diagnostic Radiology; Dennis et al., Handbook of Small Animal Radiology and Ultrasound.
- Lavin’s Radiography for Veterinary Technicians (positioning, technique charts, grid use).
- International Elbow Working Group (IEWG) — elbow dysplasia screening protocol.
Disclaimer. High Yield Imaging is an educational resource. Nothing here is clinical, diagnostic, legal, or regulatory advice. Follow your jurisdiction’s regulations, your practice’s local rules, and the direction of your Radiation Protection Adviser/Supervisor and veterinary surgeon. Verify all regulatory claims against current primary sources.