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英文誌(2004-)

Journal of Medical Ultrasonics

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1996 - Vol.23

Vol.23 No.02

Original Article(原著)

(0101 - 0108)

高速血流超音波パルスドプラ計測における速度直接差分法の問題点とその対策

Improvement of Velocity Direct Difference Method (VDD) for Non-aliasing Ultrasonic Pulsed Doppler Measurement

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 once, Hitachi, Ltd., 2Telecommunication Divisions, Hitachi , Ltd.

キーワード : Acceleration aliasing, MTI, Nyquist limit, Pulsed Doppler, Velocity direct difference method

Velocity cannot be measured unambiguously when it exceeds the Nyquist limit in pulsed Doppler Ultrasonography. We propose the use of a velocity direct difference (VDD) method, which integrates acceleration directly, as a way to improve the depth and velocity product limit. The limit associated with the VDD method is approached when the difference between the two phase differences (acceleration) approximates the value of ±π. The VDD method has two problems, however. First, any error in the initial value remains until it has been corrected. Second, false acceleration aliasing may occur when the signal-to-noise ratio (SNR) is low. The SNR may deteriorate, for example, around the null frequency of the moving-target indication (MTI) filter. We developed three kinds of algorithms to correct errors introduced in this way. We were able to experimentally determine the velocity of the blood flow in the carotid artery when blood velocity exceeded the Nyquist limit.