acoustic shadow

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a·cous·tic shad·ow

sonographic appearance of reduced echo amplitude from regions lying beyond an attenuating object. Compare: acoustic enhancement.

acoustic shadow

in an ultrasound image, the absence of echoes produced by the presence of dense material, such as calculi, which impede the transmission of sound waves. It is often used to detect biliary calculi.
References in periodicals archive ?
At this depth, the gate is partly below the popped-up die coating, with the result that some of the more or less linear structures in the image of the coating now are black acoustic shadows created by ultrasound reflected from below.
The cricoid cartilage is a hypoechoic, inverted U structure inferior to the thyroid cartilage; the posterior acoustic shadow corresponds to the airway Fig.
The decrease of the acoustic effectiveness could be explained by the fact that while moving away from the noise barrier, the effect of the diffraction of low frequency sound waves over the edges of the screen becomes more prominent, thus decreasing the acoustic shadow zone of noise damping.
Ultrasonography revealed presence of hyperechoic mass along with acoustic shadow underneath.
12) The characteristic sonographic feature of worms in the common bile duct is a long linear parallel echogenic strip, usually without acoustic shadow.
Sonographic evidence of an intraluminal mass with a hyperechoic arc-like surface and a marked acoustic shadow, suggestive of a bezoar, has been reported.
It can be hypothesized that the explosive wave of compression and rarefaction resulted in the rupture of the small blood vessels on the side facing the blast, but those on the other side were protected by the acoustic shadow of the skull.
On longitudinal scan, the upper boundary of the obturator hernia cannot be seen because it is obscured by the acoustic shadow of pubic ramus [Figure 1]b.
On the basis of X-rays and ultrasonographic findings, we gave possibilities of colonic bezoar/faecolith; however, bezoar was the first possibility given, as the density of the lesion was less than calcification on plain radiograph, and the posterior acoustic shadow on ultrasonography was somewhat dirty (like that of air).
In ultrasonography, it appears curvilinear bright echogenic band with marked posterior acoustic shadow over the left upper quadrant.
Micro calcifications are seen sonographically as multiple punctate bright echoes of size less than 2 mm, with or without acoustic shadow.
In red-eared sliders (Trachemys scripta elegans), the kidneys have a lobed appearance and are isoechogenic with surrounding tissues and, in sea turtles (Caretta caretta), present as oval or comma-shaped structures and are hyperechoic with the surrounding soft tissues in appearance, in addition to containing a small hyperechoic focus that does not project acoustic shadows (MARTORELL et al.

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