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.
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Ultrasound imaging in the transverse approach shows the spinous process as a hyperechoic (bright) line immediately underneath the skin, continued with its acoustic shadow as a vertical triangular hypoechoic line (Figure 3).
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.
large calcifications with posterior acoustic shadow. b.
Access through the entrance of the thorax enabled the visualization of the masses in the topographical area of the sternal lymph node with the following features: heterogeneous echogenicity and echotexture, irregular margins, calcifications forming an acoustic shadow. The masses were able to be evaluated by Power Doppler, revealing mottled central vascularization (Figure 3), consistent with a malignant lesion, as previously discussed.
On ultrasound of total abdomen, there was evidence of echogenic curvilinear structure with posterior acoustic shadow in the ascending colon.
Occasionally, the foreign body may be identified on ultrasound as an echogenic intraluminal mass and may cast an acoustic shadow if surrounded by fluid.4 When plain radiographic findings are inconclusive, abdominal CT is able to correctly reveal the cause of obstruction in 73-95% of cases.1,3,6 Early diagnosis and therapeutic management has considerable importance.
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.
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. (13) Other favorable imaging modalities include MRI and MRCP.

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