Digital acquisition and interactive processing of ultrasonic echoes

The requirements for an interactive digital signal processing system for ultrasonic pulse-echo signals are discussed. A system based on an Interdata Model 80 mini-computer and micro-processor interface is described. The system is capable of acquiring ultrasonic data at a sampling rate of 6 MHz. Ultrasonic B-mode data may be acquired in Line Mode, when echo waveform data and transducer position and orientation are stored, or in Section Mode when the data is converted directly into picture form in memory in the same way that a standard echogram is formed on the screen of an oscilloscope. In each case the data for single complete high resolution echogram may be acquired in less than 15 sec. It is shown that the 6 MHz sampling rate is sufficient to faithfully preserve the echo waveshape of a 2 MHz system independently of the relation to the phase of the sampling. Also shown is a cross-sectional echogram of the pregnant uterus, and its digital representation with a raster density of 80 × 100 and 160 × 200 picture elements.The computer is programmed with an interactive program to allow ultrasonic signals to be acquired, stored, processed and examined with the convenience of a desk calculator. Sample operations are illustrated including data interpolation, spectrum analysis, filtering and complex signal deconvolution. The ability of deconvolution techniques to resolve targets separated by less than one wavelength in depth is demonstrated. Possibilities of further processing techniques are outlined.