On-Line Scan Conversion and Multi-Dimensional Image Processing
There exists a problem with all real-time ultrasound imaging devices; that being how to store the images in a dynamic mode for later study. The most popular and cost efficient method is storage on video tape. The problem becomes one of converting the primary display from its particular random vector format to standard TV raster format — in effect, perform an actual-time scan conversion process. In the past, this has been done in one of two ways. The first is to present the original scan in a rectilinear mode equivalent to TV raster. This has several disadvantages in that it restricts the scan geometry and is useful only with a large linear array. Also, it requires that each line be written perpendicular to the array (no steering). While this scan geometry may be acceptable for imaging the peripheral vasculature and unobstructed organs such as those in the abdomen, it is not the most desirable for imaging more obscured organs such as those in the thorax where the viewing window is very small. Since the viewing window is so small, beam steering to increase the area of view is almost imperative. The second method used in converting the primary scan format to TV raster is optical coupling. In this technique, a TV camera is focussed on the primary display unit and the camera output recorded on video tape.