3 Lisciandro GR. 2016. The use of the diaphragmatico‐hepatic (DH) views of the abdominal and thoracic focused assessment with sonography for triage (AFAST/TFAST) examinations for the detection of pericardial effusion in 24 dogs (2011–2012). J Vet Emerg Crit Care 26(1):125–131.
4 Lisciandro GR, Lagutchik MS, Mann KA, et al. 2008. Evaluation of a thoracic focused assessment with sonography for trauma (TFAST) protocol to detect pneumothorax and concurrent thoracic injury in 145 traumatized dogs. J Vet Emerg Crit Care 18(3):258–269.
5 Lisciandro GR, Lagutchik MS, Mann KA, et al. 2009. Evaluation of an abdominal fluid scoring system determined using abdominal focused assessment with sonography for trauma in 101 dogs with motor vehicle trauma. J Vet Emerg Crit Care 19(5):426–437.
6 Lisciandro GR, Fosgate GT, Fulton RM. 2014. Frequency of ultrasound lung rockets using a regionally‐based lung ultrasound examination named veterinary bedside lung ultrasound exam (Vet BLUE) in 98 dogs with normal thoracic radiographic lung findings. Vet Rad Ultrasound 55(3):315–322.
7 Lisciandro GR, Fulton RM, Fosgate GT, Mann KA. 2017. Frequency of B‐lines using a regionally‐based lung ultrasound examination (the Vet BLUE protocol) in 49 cats with normal thoracic radiographical lung findings. J Vet Emerg Crit Care 27(3):267–277.
8 McMurray J, Boysen S, Chalhoub S. 2016. Focused assessment with sonography in nontruamtized dogs and cats in the emegrency and critivcal care setting. J Vet Emerg Crit Care 26(1):64–73.
9 Rozycki GS. 1998. Surgeon performed US: its use in clinical practice. Ann Surg 228:16–28.
10 Rozycki GS, Ballard RB, Feliciano DV, et al. 1998. Surgeon‐performed ultrasound for the assessment of truncal injuries: lessons learned from 1540 patients. Ann Surg 228(4):557–567.
11 Rozycki GS, Pennington SD, Feliciano DV. 2001. Surgeon‐performed ultrasound in the critical care setting: its use as an extension of the physical examination to detect pleural effusion. J Trauma 50(4):636–642.
12 Rozycki GS, Knudson MM, Shackford SR, et al. 2005. Surgeon‐performed bedside organ assessment with sonography after trauma (BOAST): a pilot study from the WTA Multicenter Group. J Trauma 59(6):1356–1364.
Further Reading
1 Mattoon JS, Nyland TG. 2015. Fundamentals of diagnostic ultrasound. In: Small Animal Diagnostic Ultrasound, 3rd edition, edited by Mattoon JS, Nyland TG. St Louis: Elsevier, pp 1–49.
Chapter Two POCUS: Basic Ultrasound Physics
Robert M. Fulton
Introduction
Turn on the machine. Apply acoustic coupling gel. Start scanning. In the realm of the busy veterinary general practice, emergency clinic, or intensive care unit, that statement really sums up the basic use of ultrasound. Just as it is natural for us to take the stethoscope from around our neck and place it on a patient's thorax, so should be picking up the ultrasound probe and placing it on the patient. No wonder that ultrasonography has been appropriately dubbed both “an extension of the physical exam” and the “modern stethoscope” (Rozycki et al. 2001; Filly 1988). Really, one doesn't need a whole lot of instruction to start scanning; however, as for a lot of things in life, the devil is in the details. Understanding how the ultrasound image is formed (Physics), understanding inherent physical limitations (Artifacts), and knowing how to acquire the image (Technique) are the keys to acquiring and interpreting the diagnostic ultrasound image.
The focus of this and the following several chapters is a brief review of the basic physics and principles of ultrasound, including the more common problematic artifacts. For interested readers, there are more comprehensive textbooks dedicated to the physics and interpretation of ultrasound imaging (Nyland et al. 2002; Penninck 2002; Bushberg et al. 2002).
What POCUS Basic Ultrasound Physics Can Do
Provide a basic review of ultrasound physics.
What POCUS Basic Ultrasound Physics Cannot Do
Cannot provide an in‐depth discussion of ultrasound physics and principles
Cannot replace experience and knowledge of your own ultrasound machine.
Indications
All sonographers performing POCUS and FAST for a basic understanding of the physics and principles of ultrasound imaging.
Objectives
Provide a basic understanding of ultrasound principles to maximize accurate image interpretation.
Provide an understanding of the fundamentals of ultrasound physics and how they relate to image formation.
Basic Ultrasound Principles
The ultrasound machine consists of two main parts, the probe and the processor. The probe is the “brawn” and the processor the “brains” of the operation. The probe has two main functions: first, to generate a sound wave (acts as a transmitter), and second, to receive a reflected sound wave (acts as a receiver). The processor, located within the ultrasound unit, takes these incoming signals and turns them into a useful image.
The transmitter and receiver functions of the transducer do not occur simultaneously but rather sequentially. When placed under mechanical stress, the ceramic crystals in the transducer generate a voltage. This process, known as the piezoelectric effect, occurs during the receiving phase, which is when returning sound waves strike the transducer. When an external voltage is applied to the crystals, they exhibit the reverse phenomenon and undergo a small mechanical deformation. The subsequent release of this energy generates the ultrasound wave. This is known as the reverse piezoelectric effect. World War I saw the first practical use of the piezoelectric effect in the development of sonar using a separate sound generator and detectors (Coltrera 2010).
The sound waves generated by diagnostic ultrasound machines are typically in the 3–14 megahertz (MHz) range and are thus too high pitched to be perceived by the human ear. We can hear sounds in the range of 20 Hz (cycles/second) to 20 000 Hz. In contrast, our average canine patient hears sounds in the range of 40 Hz to 60 000 Hz. The high frequencies are in the realm of what is termed the “ultrasonic” range, basically any sound above our ability to hear and hence the name for this clinical imaging tool (Nyland et al. 2002).
The sound waves produced by the transducer penetrate the body tissues and are subject to all the rules surrounding any sound wave, including reflection, refraction, reverberation, attenuation, and impedance. The processor analyzes the transmitted signals and the returning waves, including their quantity, strength, and the time they took to return. By applying preprogrammed algorithms, the processor translates this information into a pixel, gives it an appropriate intensity (its echogenicity), and places it on the monitor screen to give us the image (sometimes being “fooled” into creating artifacts).
Between the transducer and the processor, it is easy to see why the equipment for this modality can be rather pricey. However, by using the variety of POCUS and FAST ultrasound exams outlined in this textbook, we hope that your ultrasound machine will become an asset not only with improved patient care but also with a return on investment.
Velocity
Sound travels at specific known velocities through various materials. Remember from physics that sound travels faster though solids than