A tour of the abdomen: Scanning in lateral recumbency – The right side (Proceedings)


A tour of the abdomen: Scanning in lateral recumbency – The right side (Proceedings)

Aug 01, 2010

This brief overview of abdominal ultrasound is meant to be just that – an overview. If you are serious about ultrasound, you will take it upon yourself to review on the ultrasound references in physics such as that by Kremkau. Ultrasound images can be 100% artifactual, when inappropriate use of the technology is applied. Ultrasound examinations require time and effort on the part of the sonographer. These types of introductory classes are great for getting an overview, but they are not the ends of the line for learning how to perform an ultrasound examination. Most abdominal ultrasounds can be performed in 20 to 40 minutes; however, complex studies may require additional time. Ultrasound requires patience and technical expertise that is only learned after mastering your equipment, the physics of ultrasound and ramifications in identifying abnormal sonographic anatomy. As you are starting to do ultrasound examinations, read and thoroughly digest Nyland and Mattoon's book on small animal ultrasound. Find a colleague with the same interest and start a journal club weekly to review this book in depth and other articles/references that come up. Additionally, start collecting a normal database and scan everything. Look at specifics (left kidney for 2 to 3 weeks) vs. trying you do a complete study and over 6 months you will start to recognize normal from abnormal. Be sure to take at least 2 weekend short courses with different instructors each year for 3 years. This is a minimum investment of 3 years on your part and in order to get "good" at it, you need to practice, practice and practice.

A Tour of the Abdomen

One of the most difficult aspects of abdominal imaging is establishing a set pattern of "exploration", especially compared with echocardiography, where well established imaging planes are preset. The goal then is to evaluate the heart from these imaging planes and take specific measurements. In abdominal imaging, conventional windows are not pre-established. Each structure or organ has a characteristic echogenicity, shape, pattern, location, margin and number. Each organ should be evaluated using multiple imaging planes. When abnormalities are identified, they should be evaluated in multiple imaging planes. The two most common methods used for evaluating the abdomen include dorsal or lateral recumbency. I currently use lateral recumbency as a starting point. HOWEVER, you should learn to use both techniques, as there are advantages and disadvantages of each. You should be comfortable in doing both. I will roll the dog or cat into dorsal recumbency only when required to evaluate a particular structure or a possible abnormality more completely. Aspirates and biopsies are done with the animal in the appropriate recumbency that puts the area of interest the closest to the surface with the least amount of possible structures between the area of interest and the skin. Abdominal radiographs are still the best way to "survey" the abdomen and should be used as the first line for evaluating abdominal disorders. Ultrasound can then be used to evaluate specific structures for specific reasons. The two imaging modalities are in fact complimentary as they provide different information.

Transducer placement and eye-hand coordination takes some practice and getting used to making adjustments while monitoring the screen. There are three basic movements of the ultrasound transducer that one needs to master. The first is distance motion. This means that the transducer moves in a cranial or caudal direction and thereby the structures in the image move also in a cranial or caudal direction. The other distance motions include dorsal and ventral directions and oblique directions. The second type of transducer motion is non-distance, angular motions. In this case, the transducer stays in the same position on the animal, but is angled in a cranial, caudal, dorsal or ventral direction. The third type of transducer motion is a rotational motion whereby the orientation of the beam is redirected from a cranial-caudal orientation to a dorsal-ventral orientation or an oblique orientation. This type of motion would be one used when moving from a right, parasternal long axis image to a right, parasternal, short-axis image of the heart. When moving the ultrasound transducer, the motions should be smooth. Usually you do not have to press very hard wit the probe. Tweaking the transducer can be just as much of an art form with technical expertise as playing with the ultrasound instrumentation. One should remember that more often than not, one is using an oblique imaging plane versus a true dorsal, sagittal or transverse imaging plane. On every transducer is a small point or marker that gives the orientation of the primary ultrasound beam. On the ultrasound screen, there is also a marker that identifies the mark on the transducer. Place one finger on this marker on the transducer so that you always know the appropriate image orientation and you do not get lost during the scan.