| 摘要 |
PURPOSE:To enhance the image quality of the tomographic image of the shallow part in the vicinity of the surface of the body by relatively reducing the intensity of multiple reflection with respect to the echo of the shallow part by filtering, by constituting a filter circuit of a variable zone film having center frequency almost same to the resonance frequency of an ultrasonic vibrator. CONSTITUTION:Noticing that the shape of the frequency spectrum of multiple reflection is different from that of the spectrum of the original reflected wave from a shallow part, the characteristics 1, 2, 3 of a BPF are respectively provided to the shallow part, a deep part and an intermediate depth part. In circuit constitution an ultrasonic probe 11 equipped with a piezoelectric vibrator converting an electric signal to sound is connected to a rate pulse generator 13 through a pulser 12. The ultrasonic wave reflected from the boundary of the tissue in a living body is received by the probe and the signal thereof is amplified by a preamplifier 14 in a receiver and, after the pair echo signal ratio of multiple reflection is reduced by a variable band pass filter 15, said signal is converted to a digital signal by an A/D converter 18 through a logarithmic amplifier 16 and an envelope detection circuit 17 to be sent to an image memory 19 and said digital signal is converted to a TV format to be displayed on a TV monitor 20. |
