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Today's VeTerinary PracTice | november/december 2015 | tvpjournal.com small animal abdominal UlTrasonograPhy Peer reviewed 24 3. Patient Preparation Clip the patient's hair. Alcohol can be applied to the skin prior to using the US gel. Apply liberal amounts of US gel to ensure adequate contact between the transducer and the skin. 4. Organs/Areas for Evaluation Specify a sequence of organs and areas for evaluation (to be discussed in the fourth article in this series), which allows the sonographer to start and end at the same points for each study. 5. Depth & Focal Zone Control The 2 most common controls adjusted during each study are depth and focal zone, which go hand in hand. The depth is adjusted to the organ of interest. For example, evaluation of the kidney might only require a depth of 3 cm, whereas evaluation of the entire liver might require a depth of 6 to 7 cm. Every US beam (primary) is narrowest at the focal zone and then broadens or diverges deep to the focal zone. The focal zone: • Provides the best detail in the x-direction because this is the thinnest section of the US beam • Should be set at or just below the area or organ of interest (Figure 2) • Is typically displayed as a triangle or arrowhead that can be moved between the near and far field. 6. Transducer Position & Frequency Position • Hold the transducer perpendicular to the skin, over the area of interest according to the anatomy of the dog or cat. For example, if evaluating the spleen in a cat, place the probe over the left cranial and lateral abdomen caudal to the costal arch, with a shallow field of view in order to visualize the spleen. • Position the transducer so that the area of interest is as close to the surface as possible. • If there is an abnormality, always examine it in 2 imaging planes (long and short axes). Frequency • Use the highest frequency on the multifrequency transducer first. Higher US frequencies provide better resolution but do not penetrate as deep as lower frequencies. • Know the limits of your transducer's highest frequency: The sonographer can only scan as deep as the probe is capable. A lower frequency probe may be needed to scan deeper structures or the entire abdomen in a deep chested or large breed dog. • A higher frequency probe, such as a linear transducer, provides better spatial resolution than a curved-array transducer for 2 reasons: Linear transducers (1) typically have higher frequencies, and (2) their US beams do not diverge at depth. • Note that each transducer has a marker that FIGURE 2. Three different images in which the focal zone has been set at 3 levels within an US phantom: Focal zone placed in the near feld—the anechoic circle in the near feld is sharper, but the echogenic circles in the far feld are not (A); focal zone placed at the level of the echogenic circles in the midzone for image optimization of these structures (B); focal zone placed in the far feld, resulting in a decrease in resolution of the near feld and midzone structures (C). In all 3 images, depth is adjusted appropriately. A B C a n imaging phantom is a specially designed object that is scanned or imaged to evaluate, analyze, and tune the performance of various imaging devices.