6/17/2023 0 Comments Ring down artifactThis often obscures the far wall of the intestine and limits the ability to evaluate that section of intestine. Feces within the colon or barium contrast material anywhere in the intestinal tract can attenuate the sound beam (Figure 16-1). These artifacts can obscure normal or diseased tissue and also can mimic disease. It has the appearance of vertical hyperechoic lines extending from the first encounter with the surface of the air interface to deep within the image. A ring-down artifact is a streaklike reverberation phenomenon, typically occurring deep to a fluid-gas interface. A comet-tail artifact is a streaklike or cone-shaped reverberation phenomenon, typically occurring deep to metallic objects. Gas within the lumen often is manifested by reverberation, comet tails, and acoustic shadowing artifacts. An enema is not recommended or usually needed because this introduces gas into the colon, which may interfere with the examination. This is especially helpful when examining the patient for suspected foreign bodies within the intestinal lumen and when evaluating intestinal walls. Withholding food for 8 to 12 hours can reduce interference from gas and ingested contents. It is preferred, but not always necessary, that the patient be held off food before the ultrasonographic examination. It is especially important to correlate ultrasound findings with the history, clinical findings, laboratory results, and ultimately cytological and histopathological findings. One example is differentiating the various etiological causes for the appearance of the thickened muscular layer of the small intestine. However, these improvements also have raised questions about the significance of some findings, and a great deal remains to be learned regarding the feline intestinal tract. Ultrasound is faster, is more cost-effective, and often provides as much or more information than these other diagnostic modalities. Ultrasound imaging now has become so integral to the diagnostic evaluation of small animals with gastrointestinal signs that there has been a marked reduction in radiographic contrast procedures. Intestinal ultrasound provides additional and complementary information to other diagnostic modalities (e.g., survey radiographs, computed tomography, nuclear medicine, magnetic resonance imaging, and contrast radiography). Ultrasound can guide needle placement for either an aspirate or biopsy of a detected abnormality. It also can interrogate the surrounding organs such as the peritoneum, pancreas, liver, and lymph nodes. ![]() It is particularly useful in evaluating the intestinal wall, the luminal contents, and function evidenced by peristalsis. At diagnostic frequencies (1 to 25 MHz) it is noninvasive and does not pose any known significant biological risk. Ultrasound uses sound reflected from the tissue boundaries within the body to form an image that we can recognize and interpret. ![]() Higher resolution (12 to 18 MHz and higher) transducers and more affordable equipment-along with the availability of Doppler ultrasound-have made it possible to image the gastrointestinal tract more thoroughly, enhancing the ability to evaluate and understand changes produced by diseases affecting that organ. ![]() However, experience has shown that these artifacts, although present and at times obstructive, rarely interfere significantly with a thorough ultrasonographic examination. Initially it was thought that artifacts created by gas and ingested material would significantly limit or exclude the use of ultrasound for examining the gastrointestinal tract. Ultrasound imaging has become widely accepted as an important diagnostic tool for imaging the gastrointestinal tract in veterinary patients.
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