Effects of unequal interval quantization for ultrasonic echo on ultrasonic B-mode imaging

An amplitude quantizing method for analog-to-digital (A/D) conversion of an ultrasonic echo from biological tissue is discussed. The unequal interval quantization (UIQ) method, which precisely quantizes a small amplitude signal and roughly quantizes a large-amplitude signal, is proposed. The B-mode images of sponge and of liver are constructed using 10-b equal interval quantization (EIQ, the quantizing method used in general A/D converters), 6-b UIQ, and 6-b EIQ. There is practically no difference between the images made by 10-b EIQ and 6-b UIQ, whereas weak signals are not displayed in the image made by 6-b EIQ. Using UIQ A/D conversion, one can construct an image as good as that made by a high-resolution A/D converter using the EIQ with a smaller number of output bits.