Is the quality of transvaginal images superior to transabdominal ones under matched conditions?
Transvaginal images, under matched conditions, are in general superior in quality to transabdominal sonograms. The difference is, however, not dramatic and instances frequently occur when the same quality and even inferior images are obtained on transvaginal examinations. The dominant factor is the amount of overlying tissues. For the same thickness, subcutaneous tissues have greater degrading characteristics. Subcutaneous tissues also mar the quality of images by giving rise to strong multiple reflection artifacts. The major factors for image degradation are associated with a moderate increase in the width of the ultrasonic beam and a large increase in the side lobes. The dramatic superiority of transvaginal imaging described in previous comparison studies is due principally to the use of higher frequencies, more strongly focused beams and closer positioning of tissues to the transducer.
Kossoff
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Ultrasonics Laboratory, Division of Radiophysics, CSIRO, Sydney, Australia.
Griffiths
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Dixon
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