Mastering Small-Animal Abdominal Ultrasound: A Comprehensive Guide

Choosing the Right Probe

For most abdominal examinations, a microconvex probe is the ideal choice. Its small footprint makes it easy to manoeuvre between ribs and around the costal arch. Additionally, its broad frequency range suits both dogs and cats.

A linear probe can be extremely useful for superficial structures such as abdominal wall masses, lymph nodes, or paediatric patients. However, its wider footprint can make deep abdominal imaging more awkward.

Probe Orientation: A Simple Rule That Prevents Confusion

Correct orientation ensures consistent interpretation and prevents left–right errors. Here’s a quick reference:

• Sagittal views: Marker towards the head

• Transverse views: Marker to the patient’s right

• Dorsal/medial views: Marker towards the midline

• Longitudinal limbs: Marker proximally

  
  

Most machines display a small marker at the top left of the image—this should always match the probe marker.

Image Optimisation: Adjust Settings in This Order

Optimising your image is not random. Following a consistent sequence ensures you get the best possible view every time.

1. Time Gain Compensation (TGC)

TGC controls brightness at different depths. For abdominal scanning, a gentle “slope” works best:

• Lower gain in the near field

• Higher gain in the far field

  
  

This compensates for natural attenuation and prevents the top of the image from appearing washed out.

2. Depth

Set the depth so the organ of interest fills around 75% of the screen. If it’s too shallow, you lose context; if it’s too deep, you waste resolution.

3. Focus

The focal zone marks the point of highest lateral resolution. Place it:

• At the level of small structures (e.g., adrenal glands)

• At the deepest part of large organs (e.g., liver, urinary bladder)

  
  

A misplaced focal zone is one of the most common causes of soft, blurry images.

4. Frequency

Higher frequency = better detail, less penetration. Lower frequency = deeper penetration, less detail. Use the highest frequency that still allows you to see the entire organ. This single adjustment can dramatically improve parenchymal detail.

5. Overall Gain

Gain brightens or darkens the entire image.

• Higher gain helps when imaging solid organs like the liver.

• Lower gain is essential for fluid‑filled structures like the bladder to avoid artefacts.

• Bright rooms (e.g., kennel side) often require higher gain.

  
  

Aim for fluid to appear black and soft tissue to sit in a mid‑grey range.

Harmonic Imaging

Most modern machines offer harmonic imaging, which can improve contrast and reduce artefacts. Try scanning with harmonics both on and off—some patients benefit from it, while others do not.

Recognising Common Ultrasound Artefacts

Examples of common ultrasound artifacts in veterinary abdominal imaging, including mirror image, reverberation, posterior acoustic enhancement, and acoustic shadowing.

Artefacts are not always a problem—many are diagnostically useful once you know how to interpret them.

Acoustic Shadowing

This occurs when the beam hits something highly reflective (e.g., mineralisation, bone, dense foreign bodies). It is useful for identifying calculi or confirming mineral content.

Acoustic Enhancement

Seen deep to fluid‑filled structures such as the gallbladder or cysts. This helps differentiate true cysts from solid nodules.

Reverberation (“dirty shadowing”)

Associated with gas. It is helpful for identifying gastrointestinal gas or free abdominal gas.

Side‑Lobe & Slice‑Thickness Artefacts

These appear as false echoes within fluid, often mistaken for bladder sludge. True sludge moves; artefact does not.

Practical Tips for Everyday Scanning

To enhance your scanning experience, consider these practical tips:

• Reset TGC when switching between organs.

• Use plenty of gel and clip fur generously.

• Keep the probe perpendicular to the skin to avoid beam‑angle distortion.

• Always scan abnormalities in at least two planes.

• If the image looks wrong, return to your preset and start again.

  
  

Final Thoughts

Setting up your ultrasound machine correctly is one of the fastest ways to improve diagnostic confidence. By following a consistent optimisation sequence—TGC → Depth → Focus → Frequency → Gain—you’ll produce clearer, more reliable images across all patients.

Want to Build Your Confidence in Abdominal Ultrasound?

At Echo Vet Solutions, we offer bespoke in-practice ultrasound and echocardiography training delivered at your own practice, on your own patients, using your own equipment. Our training is hands-on from the outset and is tailored to your current experience level and the case mix you see in practice.

Our instructors hold advanced qualifications in small animal imaging, bringing the kind of clinical depth that translates directly into better scanning in day-to-day practice.

• Find out more about our in-practice abdominal ultrasound training

• View all our ultrasound CPD for veterinary practices

• Contact us to discuss a training day at your practice

  
  

References and Further Reading

• Forrest LJ et al. (2003). Tissue harmonic ultrasound for imaging normal abdominal organs in dogs and cats. Veterinary Radiology & Ultrasound, 44(3), 330–334. PubMed

• Ziegler LE et al. (2002). Harmonic ultrasound: A review. Veterinary Radiology & Ultrasound, 43(6), 501–509. Wiley Online Library

• Berry CR, Mauragis D. (2015). Small Animal Abdominal Ultrasonography, Part 3: Basics of Imaging Optimization. Today's Veterinary Practice. Read article

• Mattoon J, Nyland T. (2014). Small Animal Abdominal Ultrasound, 3rd ed. Philadelphia: Saunders-Elsevier.

• Penninck D, d'Anjou M. (2015). Atlas of Small Animal Abdominal Ultrasound, 2nd ed. Ames, IA: Wiley Blackwell.