JPS642631A - Ultrasonic doppler blood flowmeter - Google Patents

Abstract

PURPOSE: To reduce the clutter component contained in an echo signal and to expand the dynamic range at the time of A/D conversion, by extracting the clutter component contained in the orthogonal echo converted to digital data by an A/D converter by a clutter feedback loop and converting said component to analogue quantity by a D/A converter to negatively feed back the same to the echo signal.

CONSTITUTION: Clutter feedback loops 20 are independently provided to the signal systems of real and imaginary parts and digital low-pass filters (LPF) 10a, 10b consist of delay circuits 10a1, 10b1 performing the data delay corresponding to one cycle of an trigger signal and adder circuits 10a2, 10b2. Clutter components having the characteristic of a primary low-pass filter and present in low frequency are extracted between the input and output of the LPFs 10a, 10b. The clutter components are returned to analogue quantities by D/A converters 11a, 11b and said analogue quantities are added to echo signals in an inverse phase to make it possible to reduce only the clutter components of the orthogonal echo signals inputted to A/D converters 9a, 9b. Therefore, the dynamic range at the time of A/D conversion can be expanded and diagnostic data having high sensitivity and high image quality can be obtained.

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