Digital Recording, Display, and Storage of Echocardiograms

Summary Digital acquisition, display, and storage are new options available for handling echocardiographic images. These types of image management offer many practical advantages and are excellent supplements to standard videotape recordings. For routine M-mode and Doppler studies this digital approach, when combined with videotape, can virtually eliminate the necessity for strip chart recordings. Probably the principal advantage of digital storage techniques is for two-dimensional echocardiography. The continuous loop display is extremely convenient for rapid review, quantitation, and serial studies. When considering the implementation of these techniques, there are many limitations and practical considerations that must be kept in mind. Recording two-dimensional echocardiograms in a continuous loop mode requires that the same number of frames or cells must be used if one wants to display more than one image simultaneously. When creating a continuous loop of a single cardiac cycle, the number of cells and the interval between cells are greatly influenced by the heart rate. One must be able to display simultaneous images with varying heart rates. Last, the number of cells, the resolution, and the gray scale determine the amount of digital information that has to be stored, retrieved, or transmitted. The cost and size of the medium and the speed with which the images can be retrieved or transmitted become factors in how one elects to digitally acquire this information. One approach that has been used, which seems to work quite well in most cases, is to use an eightcell sequence for two-dimensional echocardiograms. When primarily interested in looking at ventricular function, especially regional wall motion, a 50 msec interval between frames is most appropriate. When one wants to evaluate diastolic events, 67 or 83 msec intervals would be better. The general rule is that the continuous loop display should closely resemble the actual echocardiogram, as noted during the real-time examination. Irrespective of the interval between frames, the playback interval should be 100 msec. In so doing, the images are displayed in slow motion, and the bulk of diastole is represented as a single 100 msec interval. Although one might initially believe that this type of display eliminates too much important information, clinical experience has shown that this approach is extremely practical and meets most of the needs inherent in digital recordings. Furthermore, the two-dimensional resolution probably does, not need to be greater than 256 × 256. Even the gray scale is subject to compromise, depending on the speed and the amount of information one wants to store or transmit. Obviously, as digital technology changes, this approach also will likely change. A convenient, practical method of digital recording of echocardiograms has been in place for over 4 years at Indiana University, Indianapolis. We have accumulated over 10,000 floppy disks, which are easily stored on bookshelves in the laboratory. Managing echocardiographic images in this way has had a major, favorable impact on our laboratory and represents another in a series of important technologic advances in echocardiography.