Veterinary Ultrasound Basics

• Ultrasound is a continuous stream of live, digitized data during a scan.

What is Ultrasound?

• The area of interest is examined in real time.
• The probe can be moved in any direction to obtain more information.
• Fluid can be viewed.
• Ultrasound is safer than radiology because it reduces radiation exposure.
• No PPE is required.
• The transducer produces sound waves.
• The transducer receives sound waves back and translates them to a computer.
• The translated information will be live feed video.
• The intensity and speed of reflections depend on the various tissue densities.

Indications for Ultrasound

• X-rays suggest fluid.
• Palpable mass is present.
• Radiographic mass of unknown origin is found.
• Organomegaly is suspected (organ enlargement).
• Blood loss has occurred.
• Pregnancy is possible.
• Soft tissue assessment is needed.
• Guided cysto is performed.
• Guided nerve block is performed.

Limitations of Ultrasound

• Ultrasound does not transfer through fat or air well.
• Patient movement can affect image quality.
• Sedation might be required.
• The cost of the machine, training, and expertise can be a barrier.

Getting Ready for Ultrasound

• Room preparation requires a trough.
• The ultrasound machine must be set up and the appropriate transducer picked, then the patient information must be inputted.
• Acceptable patient positions are dorsal, lateral, and standing.

Patient Preparation for Ultrasound

• A 12-hour fast is best to reduce gas in the GI tract.
• The area should be shaved for better viewing.
• If shaving is not possible, wet the area with alcohol.
• Alcohol spray can be used to remove fat and oils from the skin.
• Ultrasound gel can be used to reflect sound waves.

Terminology

Echogenicity

• Echogenicity is the brightness of tissues that are being projected.

Anechoic

• Anechoic refers to a structure lacking internal echoes or echo-free, and appears very dark or almost black.

Hypoechoic

• Hypoechoic: The tissue reflects fewer sound waves with less intensity, making it darker than surrounding tissues, such as fluid or blood.

Hyperechoic

• Hyperechoic: The tissue reflects back more intense sound waves and appears brighter than the surrounding tissues, such as bone or mineralization.

Isoechoic

• Isoechoic refers to two structures that have similar echogenicity toward each other.

Attenuation

• Attenuation is the loss of sound wave energy as it traverses tissue or the medium due to absorption, reflection, or scattering.

Reverberation

• Reverberation is the sound wave repeatedly reflected between two highly reflective surfaces.

Near Field

• Near field references the area of a structure that is closest to the probe.

Far Field

• Far field references the area of the structure that is furthest from the probe

Controls and Knobs

Basic Controls

• On/off switch
• Patient input
• Transducer selection
• Depth and focal zone adjustments
• Focus and gain adjustments

Knobology

• Gain affects the brightness of the image.
• Depth sets the maximum and minimum depth to send and receive sound waves for the area of interest, this provides better resolution.
• Time Gain Compensation (TGC) contains sliding tabs that affect the level of brightness at various depths.
• Focal zones converge the beam at a particular depth

Transducers

• Transducers contain piezoelectric crystals.
• Micro convex transducers are used for small parts and abdomens, intercostal studies, and exotics.
• Phased array transducers are used for cardiac studies.
• Convex transducers have a wider field, and are used for general scans or large abdomens.
• Linear transducers have high resolution and are used for fine detail imaging.
• Excess gel should be wiped off with a dry or slightly damp cloth.
• Transducers are easily damaged so prevent drops.

Modes

B Mode

• B mode stands for brightness mode.
• Returning echo is displayed as a digitalized pixel in a 2D image on the screen.

M Mode

• M mode stands for motion mode.
• Creates a continuous waveform; used for evaluating the heart.
• M mode creates a B-mode image while displaying the motion of that image, and can measure heart rate.

Doppler Mode

• Doppler mode is used to image the flow of blood and other liquids to measure their velocity.
• It identifies blood in a vessel versus fluid in a mass or cyst.

Colour Doppler Mode

• Colour doppler mode maps the flow of blood away or towards the transducer.
• Blue indicates flow away, and red indicates flow towards

Artifacts

Comet Tail

• Appears as closely interspaced and intense reverberations/reflections, looking like the tail of a comet.
• A comet tail occurs where there is reflection of a sound wave off small reflector targets.

Edge Shadowing

• Occurs due to refraction, or redirection of the sound wave, as it passes through a fluid-tissue interface.
• It's associated with curved, fluid-filled structures.

Acoustic Enhancement

• Occurs when the sound beam travels through a weakly attenuating structure.
• Useful in differentiating certain hypoechoic masses from cystic or fluid-filled structures.

Reverberation

• Is due to the repeated back-and-forth reflection of echoes trapped between two strong reflectors.
• It appears like a bright veil.
• Reverberation is seen in superficially positioned, gas-filled loops of the bowel.

Acoustic Shadowing

• Occurs when a sound beam contacts a highly attenuating surface, such as a urolith.
• Most of the sound beam is reflected away or absorbed.
• Creates a lack of echo information distal to the dense object.
• Acoustic shadowing appears as a dark streak or shadow below the object.