西山 久司¹, 片倉 景義²

Hisashi NISHIYAMA¹, Kageyoshi KATAKURA²

¹（株）日立製作所本社, ²（株）日立製作所情報通信事業部

¹Head Office Hitachi, Ltd., ²Telecommunications Division Hitachi, Ltd.

キーワード : MTI filter, Non-aliasing, Nyquist frequency, Pulsed Doppler, Non-equally spaced pulse transmission

Non-equally spaced pulse transmission in pulsed Doppler ultrasonography is a method for measuring velocity of blood flow that is not subject to the Nyquist limit; transmission of non-equally spaced ultrasonic pulses to a blood vessel in vivo makes it possible to measure blood velocity that exceeds the Nyquist limit unambiguously and without aliasing. For removal of clutter from the imaged blood vessel, a new design principle, that of a moving target indication (MTI) filter capable of processing non-equally spaced pulse transmission sequences, is discussed. Two approaches toward delay time in the MTI filter are proposed: Sum-PRT-MTI and Respective-PRT-MTI; addition times and respective times between two pulse repetition times (PRT) must be applied for this purpose. A phase comparator was used to test the proposed method analytically with model Doppler signals. The method was also verified experimentally using computer-simulated Doppler signals to which white noise had been added. We then compare the proposed MTIs for color flow mapping (CFM) and discuss the characteristics of these filters.