ESTIMATION OF LOCAL ATTENUATION FROM MULTIPLE VIEWS USING COMPENSATEDVIDEO SIGNALS

The effects of time gain control, nonlinear compression, beam diffract ion, and nonuniform bandpass characteristic in an ultrasonic imaging i nstrument are compensated by video signal processing to calculate regi onal ultrasonic attenuation under a narrow-band assumption. Compensati on for time gain control and amplitude compression is accomplished usi ng a measurement of the digitized output value as a function of the ti me gain control. Compensation for beam diffraction is performed using the scattering from a random medium reference. Compensation for nonuni form bandpass characteristics employs a measurement of the relative am plitude response over the attenuation-induced frequency downshift expe rienced by the signal. The decay of the compensated signal envelope wi th range yields an attenuation value which is assigned to the nominal centre frequency of the instrument. The method is applied to calculate the attenuation in a model random medium using multiple views to obta in an attenuation of 4.0 +/- 0.5 dB/cm at 3.5 MHz in the relatively sm all region of 1.6 x 1.5 cm2. The calculations of attenuation value are within 5% of the value obtained using a radiation force balance syste m. The results indicate that video signal processing and multiple view s can be used to quantify attenuation in regions of about 2 cm2 with a n accuracy of the order of 10%.