西山 久司¹, 片倉 景義²

Hisashi NlSHIYAMA¹, Kageyoshi KATAKURA²

¹Head Office , ²Central Research Laboratory Hitachi, Ltd.

キーワード : Aliasing, Direct velocity difference method, Nyquist frequency, Pulsed Doppler, Ultrasound

Velocity in pulsed Doppler measurement cannot be determined unambiguously when it exceeds the Nyquist frequency. We propose the velocity direct difference method (VDD), which integrates acceleration values directly, to overcome this limit. The new limit associated with this method is given by condition where the difference between two phase differences (acceleration) approximates π. Experimental results obtained by measuring flow in phantoms show that this method can be used to measure velocity when flow is up to five times higher than the Nyquist frequency. Ability to measure blood flow at velocities above the Nyquist limit but with the same signal/noise ratio as that of the conventional method was confirmed by experiments to determine carotid artery echo signal.