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VetBooks.ir 7 Applications of Serial Focal

Ultrasound Techniques in the

Hospitalized Small Animal Patient

Danielle M. HunDley*

VCA Midwest Referral and Emergency Center, Omaha, Nebraska, USA

The use of abdominal focal assessment sonographi- static propagation speed [rate that sound travels
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cally for trauma/triage/tracking (AFAST ) to docu- through a medium in number of cycles per second
ment the incidence of traumatic canine hemoabdomen (cycles/s or Hz)] remains the same). Frequencies
was first documented by Boysen et al. in 2004. Since commonly utilized in medical imaging vary between
this study, AFAST has become a valuable resource 3–12 MHz. In US imaging, the frequency of a
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in veterinary triage and serial monitoring in the probe determines the depth of penetration as well
critically ill patient. Ultrasound (US) in veterinary as the resolution/detail of the images acquired. An
medicine is now used in numerous applications US probe with a higher frequency will have shorter
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including but not limited to: AFAST , thoracic focal wavelength and will thus have greater resolution/
assessment sonographically for trauma /triage/ detail for tissues that are superficial and have less
tracking (TFAST ), veterinary beside lung ultrasound detail in deeper structures. An US probe with a
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examination (VetBLUE), cage-side organ assessments lower frequency will have lower resolution/detail
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for trauma triage and tracking (COAST ), US-guided overall but will have deeper penetration because of
vascular access, and US-based cardiac output moni- the associated longer wavelength.
toring. The purpose of this chapter is to give an The amplitude and intensity of US waves decrease
overview of basic concepts and clinical applications as they travel through tissue, a phenomenon known
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of AFAST , TFAST , VetBLUE, and US-guided vas- as attenuation. Given a fixed propagation distance,
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cular access in the veterinary emergency and critical attenuation affects high-frequency US waves to a
care patient for the non-radiologist veterinarian. greater degree than lower frequency waves. This
dictates the use of lower frequency transducers for
7.1 Ultrasound Fundamentals deeper areas of interest, albeit at the expense
of resolution.
Sound waves Ultrasound probes are constructed of piezoelec-
Sound waves have variable wavelengths and ampli- tric crystals. The exact alignment of these crystals
tude with a frequency defined as the number of varies based upon the function of the US probe.
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cycles repeated over a given time interval. The Commonly, during AFAST assessments the US
equation that describes the relationship between probe is a micro convex US probe, which is ideal
wavelengths and frequency is: for abdominal scanning due to its small footprint
and wide scanning field.
propagation speed Ultrasound images are constructed secondary to
(
wavelength mm =
)
(
frequencyMHz) reflections of sound waves as they travel through
tissues. Returning waves/echoes of the sound waves
Therefore, a higher frequency results in a shorter that return to the US probe cause vibration and
wavelength than a lower frequency (assuming the create an electric current. The electric current, in
* Corresponding author: dhundley1@gmail.com

© CAB International, 2020. Basic Monitoring in Canine and Feline Emergency Patients 129
(eds E.J. Thomovsky, P.A. Johnson and A.C. Brooks)