Accuracy and limitations of medical ultrasound are described in terms of several kinds of resolution, such as temporal, spatial, contrast and velocity resolution.
Ultrasound speed of about 1500 m/s in human soft tissue, limits the number of frames per second, the viewing area and the scanning line density. There are trade-offs among these parameters. In color Doppler flow imaging, frame rate limitation is much more severe.
Three kinds of spatial resolutions are defined as the range resolution, the lateral resolution and the slice width. A simple and practical drawing method for ultrasound beam width representing the lateral resolution is shown for non-focusing and focusing transducers. Upper and lower limitations of Doppler blood velocity measurements are described.
