Effect of scan format on refraction artifacts.

Refraction artifacts occur when the ultrasound beam is bent from its original direction as it passes through a boundary between tissues having different sound speeds. Refraction artifacts result in both the improper positioning and the improper brightness of echoes displayed in clinical sonograms. The effect of scan format on the sonographic appearance of several refraction artifacts due to a circular object possessing a sonic speed differing from its surrounding tissue was studied using a mathematical model and computer generated images. A quantitative index of artifact prominence was developed to compare the differences between the rectilinear and the sector scan formats. Theoretically predicted results were compared with actual sonograms of a specially designed phantom. Results included the finding that the retrolenticular afterglow was more prominent in the sector scan format, and that differences were most prominent when the refracting object was close to the transducer.