Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов
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on dolphins, the concept proved most helpful. Without goggles showing the ultrasound screen, two people were needed for imaging – one on the dock monitoring the ultrasound screen and directing the sonographer who was in the water with the dolphin, unable to see the ultrasound screen. Paying attention to external landmarks helped guide the sonographer to the AFAST target organs (and all of Global FAST) efficiently and confidently.
The same holds true with our small animal and exotic patients. Pay attention to where the probe is externally on your patient, double‐checking between the ultrasound screen and the probe's external location. Look at your patient! For example, if you can't find the urinary bladder then slide toward the patient’s pubis slightly off midline in lateral recumbency or along midline when standing or sternal. Some other examples – the gallbladder is right of midline in both dogs and cats so the probe has to be directed to that side of your patient; the TFAST chest tube site (CTS) view generally takes you to the caudodorsal transition zone, thus helping to prevent mistaking abdominal structures for lung pathology; and the kidneys are close to the caudal vena cava and aorta attached by their short renal artery and veins.
Not Visualizing the Path of the Beam from the Probe Head
Mental visualization of success prior to a motor skill performance such as an athletic event is important and so is mentally visualizing the path of the ultrasound beam from the probe head (Figure 5.10). To get the “cardiac bump” at the diaphragmatico‐hepatic (DH) view, the probe's beam must be directed toward the muscular apex of the heart which requires the probe being rocked far cranially and the beam approximating being parallel to the sternum. The AFAST CC pouch is in the most gravity‐dependent region of that view so the probe should be directed toward the tabletop (when in lateral recumbency), not at the spine! Visualizing the direction in which the ultrasound beam is projecting from the probe head will contribute to your imaging success, save time, and build confidence in locating structures of interest.
Figure 5.10. Paying attention to the direction of the beam. If the sonographer is to image the heart and its cardiac bump at the DH view, then the beam must be directed where the heart would be. In (A) the beam is directed in the correct direction whereas in (B) the heart will never be imaged. The "H" and red oval represent the heart; the black arrow the ultrasound beam; and the white curved line the diaphragm.
Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Losing Track of the Probe Orientation Marker
Make it a habit to have a finger or thumb on the probe marker or be able to clearly see the probe marker (Figure 5.11). It is easy to lose track of the probe marker without making this habitual while imaging. It not only helps with orientation but also prevents creating confusing planes through structures by the sonographer's awareness of being in longitudinal, sagittal, transverse, and short‐ and long‐axis planes. Moreover, keep the screen orientation marker to the left so you maintain the “head to the left, tail to the right” orientation, which is the same as radiography (see Figure 1.6).
Using More than One Probe Maneuver at a Time
One of the main rules of imaging is only performing one probe maneuver at a time. The five major maneuvers are rocking, fanning, rotating, sliding, sweeping and pressure/compression (see Figures 4.5–4.11). Performing only a single maneuver at a time while optimizing your image should become habitual. When you perform multiple maneuvers at the same time, you are really doodling and nothing productive typically results. This is very common with “flashing” the abdomen, thorax, and lung (see Preface). We strongly discourage flashing but rather stick with the exact clarity of the 15 acoustic windows of Global FAST.
Figure 5.11. Be aware of the probe marker. Every probe has a marker or notch that serves as its orientation marker. Always keep track of the marker and when in longitudinal or sagittal orientation, keep it directed toward the patient’s head. Getting into the habit of holding the probe with your index finger or thumb on the marker or be able to clearly see the probe marker keeps you from making mistakes and getting confused during image acquisition and interpretation. Screen orientation is also important (see Figure 1.6).
Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Ultrasound Machine Optimization
A trouble‐shooting algorithm is provided that incorporates the following major image optimization features of your machine (see Figure 5.15).
Failing to be Aware of the Focus Cursor
The position of the focus cursor can have profound effects on image quality (Figure 5.12). Most sonographers are familiar with gain, and its effect on making the image brighter or darker; and frequency, lower for better imaging of the larger patient and higher for more detail and imaging the smaller patient. However, the focus cursor is often forgotten. It is usually an arrow or an icon that moves along the centimeter scale. It can be increased from one to two or three or more on some machines, but generally it’s best to have only one, a single focus cursor, on your screen. Think of it as when having more focus cursors than just one, you are dividing up the energy in your ultrasound beam and the image will not be as high quality as a result.
The focus cursor should be directly across from the area or region of interest. A common mistake is moving the focus cursor to the “lung line” during Vet BLUE and then leaving the cursor in the very near‐field when you then image deeper thoracic, like heart, and abdominal structures. The deeper structures will often not look good no matter what you do to the gain and frequency until you move the focus cursor back to the center of the screen. Conversely, you may have the focus cursor in the center of the screen while imaging abdominal and thoracic structures that may be less than optimum for lung, in which the focus cursor placed in the near‐field across from the “lung line” could make a big difference in image quality (see Chapters 22 and 23). In some machines, the focus cursor actually moves on its own as depth settings are changed, and it may move to a less than optimal level within your image, so learn what your machine does to the focus cursor when you change the depth.
Figure 5.12. Focus cursor and depth. In (A) there are four focus cursors (upper right circle) and in (B) a single focus cursor (upper right circle). The best image is usually obtained by having a single focus cursor directly