ABSTRACT

The performance of a particular B-mode system can be characterized in terms of image properties which fall into three groups, i.e. spatial, amplitude and temporal. At the simplest level, spatial properties determine the smallest separation of targets which can be resolved. The amplitude properties determine the smallest and largest changes in scattered or reflected echo amplitude which can be detected. When a point target is imaged by a real imaging system, the spread of the image in the axial direction is determined by the length of the ultrasound pulse. The ultrasound beam has significant width also at right angles to the scan plane, giving rise to the term ‘slice thickness’. Spatial resolution is an important aspect of imaging system performance and is normally assessed in terms of the system response to a small, high-contrast target such as a nylon filament, i.e. a target which generates an echo which is much brighter than those from the surrounding medium.