Veterinary Ultrasound Suite
A structured, point-of-care-first tour of small-animal sonography — from probe choice and patient prep through the AFAST and TFAST/Vet BLUE emergency protocols, the abdominal organ survey, basic echocardiography and reproductive scanning. Dog and cat differences are called out throughout, because they are not the same patient.
Veterinary use only. This page describes canine and feline protocols and normal values. These are not human ultrasound protocols and do not transfer to human patients. Sonographic anatomy, reference intervals and scoring systems vary with species, breed, body condition and machine settings. Scanning and image interpretation should be performed by, or under the supervision of, a trained veterinary sonographer. Reference values are representative and must be confirmed against your own equipment, patient and current literature.
Getting started in veterinary ultrasound
Good images begin before the probe touches the patient. In small animals the two biggest variables are coupling (fur is the enemy of ultrasound) and patient cooperation. Get prep and restraint right and most scans become straightforward.
Patient preparation & coupling Fundamentals
Clip fur over the region of interest for diagnostic abdominal/echo studies. Air trapped in the coat completely blocks the beam. Emergency POCUS (AFAST/TFAST) is often done with alcohol and gel only, parting rather than clipping the fur, to save time.
Wet the skin with isopropyl alcohol to displace air, then apply generous coupling gel. Alcohol alone is inadequate for a full diagnostic study but is fine for a rapid focused look. Warm gel improves patient tolerance.
Fast 8–12 h before an elective abdominal study to reduce gastric/intestinal gas and to allow gallbladder filling. Withhold food but not water. Emergency and FAST scans are performed unfasted — do not delay a trauma workup to fast.
A moderately full urinary bladder aids the cysto-colic view and pelvic imaging; avoid letting the patient urinate immediately beforehand where practical.
Positioning — recumbency Fundamentals
Standard for a thorough diagnostic abdomen (often in a padded V-trough). Gives a consistent, reproducible window and gravity settles gas dorsally away from ventral organs. Least tolerated by dyspnoeic patients.
Preferred for AFAST/TFAST, echocardiography (right lateral for standard cardiac windows) and for dyspnoeic or fractious patients. Less stressful; the down-side lung/heart is imaged through a cut-out table or from underneath.
Useful for very dyspnoeic patients and for Vet BLUE lung scanning — minimises respiratory compromise. Image quality is variable but acceptable for focused questions.
Sometimes used for kidney/retroperitoneal or dorsal windows and for cats that resist being turned over.
Transducer (probe) choice Fundamentals
| Probe | Frequency | Best for | Notes |
|---|---|---|---|
| Microconvex (curved, small footprint) | ~5–10 MHz | Abdomen in cats & small/medium dogs; POCUS FAST | The workhorse small-animal probe; footprint fits between ribs and under the costal arch. |
| Curvilinear (convex) | ~2–5 MHz | Abdomen in large/giant dogs; deep structures | Deeper penetration, wider field; too large a footprint for very small patients. |
| Linear | ~7.5–15 MHz | Superficial & small parts: thyroid, eye, testes, superficial vessels, lung surface, cervical/inguinal | High resolution, shallow penetration; excellent for GI wall layering in small patients. |
| Phased array (sector) | ~4–8 MHz | Echocardiography | Small footprint slots into the intercostal cardiac window; narrow near-field, wide far-field. |
Restraint, sedation & safety Fundamentals
Most focused scans are achievable with calm, competent manual restraint and gentle handling. Minimise stress — a frightened cat that struggles gives worse images and higher stress markers.
Consider light sedation for prolonged diagnostic studies, painful abdomens, fractious patients, or guided procedures (cystocentesis, FNA). Choose agents that maintain cardiovascular stability if echo is planned — sedation alters chamber size and heart rate.
Low-stress handling is critical. Towel wraps, quiet environment and pheromone support help. Cats decompensate quietly — watch respiratory effort constantly.
Use clean gel and probe covers for guided procedures. Clip and asepsis for any needle guidance to reduce iatrogenic infection.
AFAST — Abdominal FAST
AFAST® (Abdominal Focused Assessment with Sonography for Trauma, Triage and Tracking; Lisciandro) is a rapid, four-site scan for free abdominal and retroperitoneal fluid. It is performed in lateral (or dorsal) recumbency and is designed to be repeated — serial scanning tracks a bleed. Views are always done in the same order to avoid missing a site.
The four standard sites POCUS
| Order | Site (abbrev.) | Landmark | Detects |
|---|---|---|---|
| 1 | DH — Diaphragmatico-hepatic | Subxiphoid, aimed cranially at the liver–diaphragm interface | Free peritoneal fluid cranially; also pericardial/pleural effusion & caudal vena cava — the “gateway” view. |
| 2 | SR — Spleno-renal | Left flank over spleen & left kidney | Fluid in the left gutter. |
| 3 | CC — Cysto-colic | Midline caudal abdomen over the urinary bladder | Fluid around the bladder; bladder integrity. |
| 4 | HR — Hepato-renal (umbilical / most gravity-dependent) | Right/gravity-dependent flank near the umbilicus, over liver & right kidney | The most gravity-dependent pooling site — where abdominocentesis is most likely to yield. |
Abdominal Fluid Score (AFS) Scoring
Each of the four sites scores as positive (fluid present) or negative. The Abdominal Fluid Score is the number of positive sites, 0 to 4.
| AFS | Positive sites | Interpretation |
|---|---|---|
| 0 | None | No detectable free fluid. |
| 1 | Any single site | Small-volume effusion. |
| 2 | Any two sites | Small-volume effusion. |
| 3 | Any three sites | Large-volume effusion. |
| 4 | All four sites | Large-volume effusion (maximum). |
Serial exams & tracking POCUS
A single normal AFAST does not exclude a slow bleed — fluid takes time to accumulate. Repeat at ~4 h (or sooner if the patient deteriorates) in trauma and suspected haemoabdomen.
An increasing AFS on serial scans indicates ongoing bleeding — escalate monitoring, resuscitation and consider intervention.
AFAST also screens non-trauma effusions: neoplasia, ruptured splenic mass, uroabdomen (bladder rupture at CC), septic peritonitis, right-heart failure.
The gravity-dependent HR/umbilical pocket is the target for ultrasound-guided abdominocentesis — analyse the fluid (PCV, cytology, biochem: creatinine/potassium for uroabdomen, lactate/glucose for sepsis).
TFAST & Vet BLUE — thoracic FAST & lung
TFAST® assesses the pleural space, pericardium and lung sliding for trauma and the dyspnoeic patient; Vet BLUE® is the regional lung ultrasound exam (Lisciandro) that grades “wet lung”. Together they answer, at the cage-side, “is there air, fluid, or wet lung?” — often faster and more sensitive than a radiograph, without moving a fragile patient.
TFAST acoustic windows POCUS
| Window | Location | Question answered |
|---|---|---|
| Chest tube site (CTS) — both sides | Dorsolateral thorax, upper third, ~7th–9th intercostal space (near where a chest drain would sit) | Pneumothorax (glide sign / lung point) and pleural effusion. |
| Pericardial site (PCS) — both sides | Lower thorax over the heart (right & left) | Pericardial & pleural effusion; a focused cardiac look (chamber size, contractility). |
| Diaphragmatico-hepatic (DH) | Shared with AFAST, subxiphoid | Pleural & pericardial effusion, caudal vena cava, and links the thoracic and abdominal exams. |
Pneumothorax — glide sign & lung point POCUS
Normal lung slides against the parietal pleura with respiration — a shimmering to-and-fro at the pleural line. Its presence effectively rules out pneumothorax at that spot.
No sliding suggests pneumothorax (air between pleural layers) — but also occurs with pleural adhesions, apnoea or main-stem intubation, so interpret in context.
The junction where sliding lung meets the non-sliding pneumothorax — the most specific sign of pneumothorax. Scan dorsal (air rises) to ventral to find it.
Identify the “Gator sign” (two rib heads with the pleural “lung line” between them) before calling glide present or absent.
Vet BLUE & wet lung POCUS
Vet BLUE examines four regions each side — caudodorsal, perihilar, middle and cranial — plus the DH view. Each region is scored for B-lines and consolidation signs.
Pleural effusion POCUS
Anechoic fluid surrounding retracted (collapsed) lung lobes — the “jellyfish”/waving lung sign as atelectatic lobes float in effusion. Best seen in the dependent (ventral) thorax.
Distinguish at the PCS/DH: pericardial fluid is confined to the sac around the heart and moves with it; pleural fluid surrounds lung and is bounded by the pericardium. Tamponade physiology → see the Echo section.
Abdominal organ survey
A systematic sweep — liver, biliary, spleen, kidneys, bladder, GI tract, adrenals, pancreas — performed in a consistent order so nothing is skipped. Below are the high-yield normals and the classic abnormal patterns, with dog/cat differences where they matter.
Liver & gallbladder Organ
Homogeneous, mid-grey; less echogenic than spleen, similar to or slightly more echogenic than renal cortex. Portal vessels have echogenic walls; hepatic veins do not. Assess size, margins, echotexture and focal lesions.
Thin-walled anechoic sac with distal acoustic enhancement. A little gravity-dependent, mobile sludge is common and usually clinically silent.
Sludge is echogenic, mobile and gravity-dependent — it shifts when the patient is repositioned. A mucocele is immobile and shows the classic striated “kiwi-fruit” pattern (fine peripheral striations around central echogenic bile) or a stellate / star pattern (central echogenic bile with radiating stripes into peripheral hypoechoic bile). Mucocele does not move with repositioning.
Spleen Organ
Fine, homogeneous, the most echogenic of liver/spleen/renal cortex. Smooth capsule, uniform texture. The canine spleen is large and easily imaged along the left cranial abdomen.
Nodules/masses, “Swiss-cheese”/honeycomb (common with congestion, torsion, or neoplasia such as haemangiosarcoma), diffuse mottling. A ruptured splenic mass with free fluid links straight back to AFAST.
Kidneys Organ
Distinct cortex (echogenic) – medulla (hypoechoic) demarcation, smooth capsule, central hyperechoic renal pelvis/sinus fat. Cortex is less echogenic than spleen.
Increased cortical echogenicity, loss of corticomedullary distinction, pyelectasia/hydronephrosis, calculi (echogenic + shadowing), infarcts, cysts, mineralisation.
Urinary bladder Organ
Anechoic, thin smooth wall (wall thickness depends on distension — assess when moderately full). Look at the trigone and urethra where masses arise.
Calculi are hyperechoic with clean acoustic shadowing and gravitate to the dependent wall (move with repositioning). Suspended echogenic debris/crystals may swirl. Wall masses (e.g. transitional cell carcinoma at the trigone) are fixed and vascular.
Gastrointestinal tract — wall layers Organ
From lumen outward, alternating echogenicity: (1) mucosal surface / lumen interface hyperechoic; (2) mucosa hypoechoic (thickest layer); (3) submucosa hyperechoic; (4) muscularis hypoechoic; (5) serosa/subserosa hyperechoic. Preservation of this layering is reassuring; loss of layering suggests infiltrative/neoplastic disease.
Adrenal glands & pancreas Organ
Located craniomedial to each kidney beside the aorta (left) and caudal vena cava (right). Dogs classically peanut/bilobed and hypoechoic; measure the caudal pole thickness. Look for rounding/enlargement (hyperadrenocorticism), asymmetric mass, or invasion of the CVC by an adrenal tumour.
Often subtle; slightly hyperechoic to surrounding fat when normal. In pancreatitis: an enlarged hypoechoic pancreas surrounded by hyperechoic (inflamed) mesenteric fat, sometimes with local free fluid and a corrugated adjacent duodenum. The right limb (near duodenum) is easiest in dogs; the left limb is often more accessible in cats.
Go deeper with High Yield Ultrasound Pro Pro
The free suite gives you the framework. Pro adds the reference library that turns a survey into a diagnosis:
- Full breed- and species-specific reference-interval tables (organ dimensions, renal length:aortic ratio, wall thickness).
- Annotated normal-vs-abnormal image galleries for every organ, including the mucocele patterns and GI wall pathologies.
- Doppler protocols (portal, renal resistive index, splenic torsion) and contrast-enhanced ultrasound primers.
- Printable AFAST/TFAST/Vet BLUE scoring worksheets and a structured reporting template.
Echocardiography — the basics
A focused introduction to standard small-animal echo. Full diagnostic echo (Doppler, staging of myxomatous mitral valve disease and cardiomyopathies) is a specialist skill — but the basic 2D windows and the LA:Ao ratio answer the two commonest cage-side questions: “is the left atrium big?” and “is there a pericardial effusion?” Standard windows are usually obtained with the patient in right lateral recumbency through a cut-out table, using a phased-array probe.
Standard 2D windows Echo
Four-chamber and left-ventricular-outflow views — overall chamber sizes, valve motion, myocardial function, pericardial space.
Serial “sweep” from apex to base: LV mushroom (fractional shortening), papillary muscles, mitral “fish-mouth”, and the LA:Ao / “whale-sign” heart-base view.
Four- and five-chamber views for Doppler alignment of inflow/outflow (specialist).
The AFAST/TFAST DH view already screens the pericardium and caudal vena cava — a quick pericardial-effusion check without a formal cardiac window.
LA:Ao ratio Echo
The left-atrium-to-aorta ratio is measured on the right parasternal short-axis heart-base view. It is the single most useful cage-side index of left atrial enlargement — the hallmark of decompensating left heart disease.
| 2D short-axis LA:Ao | Interpretation |
|---|---|
| < ~1.5 | Normal / no left atrial enlargement. |
| ~1.5 – 1.6 | Borderline — ~1.6 is a reasonable upper limit, but ~10% of healthy dogs exceed it; interpret with the clinical picture. |
| > ~1.6 | Left atrial enlargement present. |
Pericardial effusion & tamponade POCUS
Anechoic space between the heart and the pericardial sac, following the heart’s motion. Look in the dependent pericardium; a swinging heart suggests a large volume.
Diastolic collapse of the right atrium/ventricle (the thin-walled chambers buckle inward in diastole) indicates the effusion is haemodynamically significant — an emergency requiring pericardiocentesis. A distended, non-collapsing caudal vena cava (from the DH view) supports raised right-heart pressure.
Species differences Dog vs cat
Reproductive scanning & guided procedures
Ultrasound is the tool of choice for early pregnancy diagnosis and, crucially, for confirming foetal viability — something radiographs cannot do. It also drives common guided procedures such as cystocentesis.
Pregnancy diagnosis & foetal viability Repro
Ultrasound detects pregnancy earliest (gestational sacs from ~day 20–25 post-LH/mating in the bitch; foetal heartbeat from ~day 23–25). It confirms pregnancy and viability but is unreliable for counting foetuses — radiographs late in gestation (after ~day 45, once skeletons mineralise) give a better count.
Foetal heart rate is the key viability sign. Normal foetal HR is high — roughly twice the dam’s rate, typically >200 bpm. A falling rate signals distress: <200 bpm = stress, and <~150–180 bpm = severe distress, prompting consideration of intervention (e.g. caesarean). Absent heartbeat = foetal death.
Pyometra Repro
Distended, tortuous, fluid-filled uterine horns — convoluted tubular structures between bladder and colon, containing anechoic-to-echogenic (turbid) fluid. Wall may be thin (open) or thickened with cystic endometrial hyperplasia.
No gestational sacs, no foetal parts, no heartbeats — and the clinical picture (recent oestrus, systemic illness, purulent discharge if open). Fluid-filled small-bowel loops can mimic uterine horns — trace continuity and check for peristalsis (bowel moves; uterus does not).
Prostate (dog) Repro
Symmetric, homogeneous, bilobed gland caudal to the bladder neck; small in neutered dogs. Image midline just cranial to the pelvic brim.
Benign hyperplasia (symmetric enlargement, cysts) in the intact dog; prostatitis/abscess (heterogeneous, fluid pockets); asymmetric mineralised mass in a neutered dog raises concern for neoplasia. Guided aspiration/biopsy can be performed under ultrasound.
Cystocentesis guidance Guided
With a moderately full bladder, aseptically guide the needle real-time into the bladder lumen (aim toward the apex/ventral wall, away from the trigone). Ultrasound confirms needle tip position and avoids adjacent bowel and vessels.
Avoid in bleeding disorders or a suspected bladder tumour at the puncture site (seeding risk). Watch for a small amount of post-procedure fluid; a rising AFAST-style fluid pocket suggests leakage.
References & further reading
- Lisciandro GR. Abdominal and thoracic focused assessment with sonography for trauma, triage, and monitoring in small animals. J Vet Emerg Crit Care. 2011;21(2):104–122.
- Lisciandro GR, et al. Evaluation of an abdominal fluid scoring system determined using AFAST in 101 dogs with blunt trauma. J Vet Emerg Crit Care. 2009;19(5):426–437.
- Lisciandro GR. AFAST Target-Organ Approach and Fluid Scoring System in Dogs and Cats. Vet Clin North Am Small Anim Pract. 2021;51(6):1119–1145. vetsmall.theclinics.com
- FASTVet. AFAST® and its Abdominal Fluid Scoring System — dogs and cats. fastvet.com
- Lisciandro GR. TFAST Accurate Diagnosis of Pleural and Pericardial Effusion, Caudal Vena Cava in Dogs and Cats. Vet Clin North Am Small Anim Pract. 2021;51(6):1169–1182. vetsmall.theclinics.com
- Lisciandro GR, et al. Vet BLUE regional lung ultrasound examination — introduction and image acquisition. In: Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Wiley; 2021. Wiley
- Cole L, et al. Diagnostic accuracy of the Vet BLUE lung ultrasound protocol for pleural fluid, pneumothorax and lung pathology in dogs and cats. J Small Anim Pract. 2021;62(4):271–280. Wiley
- Ward JL, et al. / Lisciandro GR. Vet BLUE for lung ultrasound in small animals and its six lung signs. vet-etc.com
- Mattoon JS, Nyland TG (eds). Small Animal Diagnostic Ultrasound. 4th ed. Elsevier; 2021.
- Penninck D, d’Anjou M-A (eds). Atlas of Small Animal Ultrasonography. 2nd ed. Wiley-Blackwell; 2015.
- Boysen SR, Lisciandro GR. The use of ultrasound for dogs and cats in the emergency room: AFAST and TFAST. Vet Clin North Am Small Anim Pract. 2013;43(4):773–797. vetsmall.theclinics.com
- Rademacher N. Two-dimensional echocardiographic left-atrial-to-aortic ratio in healthy adult dogs: reference intervals. J Vet Cardiol. 2019. ScienceDirect
- Hansson K, et al. Left atrial to aortic root indices using 2D and M-mode echocardiography in Cavalier King Charles Spaniels. Vet Radiol Ultrasound. 2002;43(6):568–575.
- Animal Ultrasound Association. Veterinary echocardiography — the left atrium (LA:Ao). animalultrasoundassociation.org
- Besso JG, et al. Ultrasonographic appearance and clinical findings in 14 dogs with gallbladder mucocele. Vet Radiol Ultrasound. 2000;41(3):261–271.
- Jaffey JA, et al. Ultrasonographic patterns, clinical findings and prognostic variables in dogs with gallbladder mucocele. J Vet Intern Med. 2022;36(3):875–885. Wiley
- Choi J, et al. / VetFolio. Canine gallbladder mucoceles — sonographic patterns (kiwi/stellate). vetfolio.com
- Penninck DG, et al. Gastrointestinal tract ultrasonography — the five wall layers and intussusception. Today’s Vet Pract. todaysveterinarypractice.com
- Griffin S. Feline abdominal ultrasonography: the normal and diseased gastrointestinal tract. J Feline Med Surg. 2019;21(11):1046–1063. PMC
- England GCW, Russo M, Freeman SL. Ultrasonographic assessment of foetal viability and heart rate in the bitch and queen. In: BSAVA Manual of Canine and Feline Reproduction and Neonatology. 2nd ed. BSAVA; 2010.
- Zambelli D, Prati F, et al. Ultrasound diagnosis of pregnancy and foetal heart rate as a viability marker in the queen. Theriogenology. 2002.
High Yield Ultrasound — Veterinary Ultrasound Suite. Educational content for veterinary professionals; representative values only, confirm against current literature and your own equipment.