Fat as a factor affecting resolution in diagnostic ultrasound: possibilities for improving picture quality.

Fat and air are the main factors affecting quality by causing interference in ultrasound. Deterioration in resolution with increasing thickness of overlapping fat has been verified experimentally. The following factors have provided better resolution in experimental studies: large aperture transducers; compound technique (good axial resolution compensates for poor lateral resolution); compression of fat and location of the fat in the focus of the transducer; large beam width of the ultrasound signal. In a clinical study with 663 patients the influence of compression and compound technique on visualisation of abdominal structures was tested with a Combison 100 real-time scanner, Combison 202 compound scanner and the Octoson system. The retroperitoneal space was not demonstrated in 66 patients. Compression with the real-time transducer improved demonstration in 50% of studies (33/66), as compared to 20% (19/66) with the compound technique. Resolution was affected by velocity errors and reflection in 30% of cases (19/66) examined with the compound technique.