A description and explanation of an unexpected echographic appearance in a patient who had sustained an abdominal shotgun wound is presented. In the B-scans, a trail of dense continuous echoes, simulating a comet tail, is seen distal to each lead pellet. This comet tail appearance is shown to be a type of reverberation artifact. The effect of object size, shape, composition, and orientation on the appearance of this artifact is demonstrated.

The comet tail artifact appears as a dense tapering trail of echoes just distal to a strongly reflecting structure. This reverberation type of artifact occurs when there is a marked difference in acoustic impedances between an object and its surround. This paper presents a spectrum of comet tail artifacts seen in clinical practice and discusses their usefulness in decision making.

A case report of an ovarian dermoid tumor perforation the sigmoid colon in a pregnant woman is presentd. Various complications of dermoid perforation are discussed.

The authors show that the intrinsic ultrasonic attenuation of a gallstone is an important factor in determining the degree of shadowing. B scans in vivo and in vitro demonstrated that stones with higher attenuation also show the most shadowing. In addition, attenuation can be correlated with physical structure: more highly attenuating stones tend to have the largest percentage of crystalline material, a larger average crystal size, and a more rigid structure. The authors recommend that higher-frequency transducers be used where possible if nonshadowing structures are seen in the gallbladder.

The effects of black-echo (black dots on white background) and white-echo (white dots on black background) display formats on detectability of a wire embedded in an echogenic test object were compared. Trained observers were asked to note the presence or absence of the wire on a randomized series of 528 B scans (264 black-echo and 264 white-echo images), half of which contained a wire. The scans not containing a wire were used as controls. The specificity of the white-echo display (75 per cent) exceeded that of the black-echo display (54 per cent), with statistical significance at the 99 per cent confidence level. There was no measurable difference in sensitivity. These results are explained in terms of principles of visual physiology.

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