Abstract: A foreground image is overlaid over a background image on a visual display. Specifically, an ultrasound signal is transmitted toward a target to be displayed in two dimensions. Echoes of the ultrasound signal are received from the target. Two-dimesional target data acquired from the received echoes are stored. The two-dimensional target data are presented on the visual display as a background image. Part of the target data are overlaid over the background image as a foreground image on the visual display. The size of the foreground image vis-a-vis the background image is changed by the user to permit better observation of an area of interest. Preferably, the size of the foreground image is changed without changing the area occupied by the foreground image on the visual display, which permits the invention to simulate the action of a magnifying glass. The user moves a cursor on the visual display to the center of an area of interest.

Abstract: An improved scan converter for converting received echo signals representative of the amplitude of ultrasound energy returning from sampled points along a plurality of spaced apart paths distributed in an image space into signals to be displayed as display pixels in a raster scan display system. The scan converter includes a scan data memory for storing the received echo signals in quadrants of the scan data memory. Each quadrant is associated with even and odd numbered paths and sample row combinations. Sample rows are related to sample points along the spaced apart paths. The scan converter further includes a circuit for determining a gray scale value to be assigned to each selected display pixel based on a predetermined combination of four received echo signals adjacent the selected display pixel and chosen from the quadrants of the scan data memory. The improved scan converter is capable of operation in both linear and sector scan modes, and, when in the sector mode, over 90.degree. and 180.degree.