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In order to measure blood flow velocity noninvasively within a small sample area in cardiac chambers as well as in the great vessels, we have proposed a new modulation ultrasonic Doppler system with high range resolution using a pair of sequences whose cross-correlation values are zero except for the peak value. In the present study the effectiveness of the new modulation method in eliminating spurious waves was experimentally verified and also the method was compared with the M-sequence modulation method. Oscillator frequency and clock pulse repetition frequency were 2. 2 MHz and 275 kHz, respectively. One of the pairs of sequences, F1 (t) with a clock pulse of tc in width, was an M-sequence with a period of 31. The other, F2 (t), was a function, of which the value of F1 (t), when a clock pulse of tc/2 in width is 0, equals 1 when the clock pulse is 1. When the output of a modulator was directly put into a demodulator without transmission, the ratio in our method was 11.3 dB higher than that in an M-sequence modulation method. When ultrasound transmitted through the water and reflected from an aluminum plate was put into a demodulator, the ratio in our method was 6. 4 dB higher than that in an M-sequence modulation method. These results indicate that the proposed ultrasonic Doppler system with a new modulation method has a high range resolution and thus it is useful in practical use.
一般社団法人日本生体医工学会の論文