This study is aimed at providing a better understanding of how artifacts arise in clinical sonograms. These, artifacts are undesirable distortions of the sonographic image and interfere with physicians' ability to accurately diagnose. The work proposed is a extension of a project already begun in describing from first principles, the geometric and intensity distortions that arise in clinical sonography. The mathematical physical model characterizes the effect of a cylindrical object possessing a low acoustic speed surrounded by tissue consisting of a uniform distribution of scattering points. The resulting refraction of the interrogating ultrasound beam results in an altered distribution of ultrasound intensity arriving at points distal to the refracting structure. The mathematical model accounts for the intensity alterations of the sound arriving at the scattering points and also for the amount of sound returning to the transducer. The resulting sonographic image is characterized both by analytical expressions and by computer simulations and image reconstruction. In so doing, the model provides predictions which can be tested both in the laboratory and in clinical observations. Initial efforts were based on a number of simplifying assumptions which now have to be modified in order to better approximate reality. These additional refinements to the model will include changes in the shape of the refracting body, changes in the relative refractive index, addition of reflections at the lens surface, and the effect of time variable gain. Computer generated images based on the model will be compared with experimental results using tissue equivalent phantoms in order to evaluate the validity of the model and to correct it where necessary. Verification of the model will also be accomplished by demonstrating the appearance of predicted artifacts in clinical sonograms.
|Ziskin, M C; LaFollette Jr, P S; Blathras, K et al. (1990) Effect of scan format on refraction artifacts. Ultrasound Med Biol 16:183-91|