The relative effects of system parameters on texture in gray-scale ultrasonograms

Texture in B-mode ultrasonography of the abdomen can, in many cases, serve as an important diagnostic tool. Unfortunately, because texture as it is now presented depends on many parameters which are independent of pathology, it is not always a reliable sign. Parameters such as transducer size, center frequency, and bandwidth; B-mode display and storage methods; near and far field wave effects; and the type of intervening tissue all influence the display of texture. We have investigated these parameters of texture through the analysis of computer simulated B-mode ultrasonograms based on in vitro A-line data collected under a variety of circumstances and conditions. A freshly excised bovine pancreas served as the target tissue. Computer generated textured B-mode images, produced with different gray-scale and scan converter storage algorithms, were evaluated by a panel of six radiologists who individually divided sixty images into groups of images with similar texture. These evaluations were mapped into a six feature hyperspace with each axis representing a particular parameter. By applying a variation of the principal components transformation, each parameter could be ranked according to its effect on texture. We found that the type of gray-level preprocessing map had the most effect on texture; intervening tissue and transducer variations had intermediate effects. So long as the target distance did not exceed the focal length of the transducer, the distance between the transducer and the target tissues had the least effect on texture.