Recognition and Storage of Metal Heart Marker Position from Biplane X-Ray Images at Video Rates

We have developed a semiautomatic microcomputer-based instrument for recording the three-dimensional positions of metal heart markers from biplane X-ray images at 60 frames/s. This instrument eliminates the need for film processing and tedious digitizing by human operators. Markers are recognized electronically on each video line using criteria of density changes (edge detection), size, and location. Only the X-Y or Z-Y location of each marker is stored. This transformation of the gray scale image into a list of coordinates achieves a data compression of 250 fold. A small fast memory and a second large one provide an effective slowing of the high peak rates of the marker location data. This buffering allows the marker coordinates to be permanently stored on a floppy disk for later analysis. Four s of data can be stored in one burst when 20 markers are used. The instrument was designed to measure the pumping action of the heart through the calculation of instantaneous local strain, wall thickness, and chamber volume. This paper compares alternate recognition strategies and storage methods.