Imaging characteristics and artifacts

Abstract

In this chapter, we will address the components of the ultrasound image that convey the structural differences between various normal tissues encountered in a detailed evaluation of the abdomen. We will then characterize the pathologic processes that superimpose themselves upon normal structures and give hints as to how to better recognize them. During any ultrasound examination, various artifacts are encountered, some result from correctable technical errors, such as poor transducer contact or excessive power, while others are a result of limitations of the modality itself such as the presence of overlying bowel gas that prevents through transmission of sound waves in the usable clinical spectrum. Yet a third category is those artifacts that are created by the existence of a specific pathologic process that represents a "signature artifact," whereby that condition can be definitively diagnosed. Occasionally, an expected artifact, such as overlying gas in the left upper quadrant obscuring the pancreatic tail, is displaced by a large cyst or pseudocyst, thereby endorsing the fact that one should always inspect the abdomen in a systematic, four-quadrant manner as one would perform a manual physical examination. The ubiquity of CAT and MRI has not diminished the value of abdominal ultrasound but has allowed it to find its proper place as part of the surgeon's clinical toolbox - the so-called surgeon's stethoscope. At the conclusion of this chapter, the reader will appreciate the imaging characteristics of the solid abdominal organs and will understand the derivation of frequently encountered sonographic artifacts. One will be able to recognize the difference between those artifacts that are technical and therefore correctable from those that are consequent on the limitations of the modality itself and, by their existence, allow us to increase our ability to diagnose specific entities.