| 摘要 |
<p>@ The frequency of a reflected ultrasonic wave decreases in frequency as the wave is attenuated in passing through tissue. A measure of attenuation is obtained by applying an electrical signal generated from the ultrasonic wave to a phase detector along with a signal from a voltage controlled oscillator and controlling the voltage controlled oscillator with the output of the phase detector. By measuring the voltage applied to control the oscillator, an estimation of the mean frequency (first moment) of the power spectrum is obtained. This frequency estimator can, in turn, be used to estimate the attenuation of the ultrasonic wave as it propagates through the media by noting the shift in frequency with propagation depth.</p> |
