Alternative approaches to in-situ intensity estimation [medical diagnostic ultrasound]

Experimental results from a study of three alternative approaches to the estimation of in-situ or derated ultrasonic intensity parameters are presented. The existing regulatory approach uses the exponential derating factor e exp(-0.069F_cd), where F_c is the center frequency of the ultrasonic pulse and d is the focal depth in centimeters. This derating is applied to the values of ultrasonic intensity as measured in water, which are significantly influenced by nonlinear propagation effects. This first alternative approach applies the same general formula to all the frequency components of the ultrasonic pulse spectrum. The second alternative involves reconstructing a time waveform from only the dominant spectral peak of the pulse spectrum, adjusted to account for the energy lost in the higher harmonics. In the third approach, the centroid of the frequency spectrum is used rather than the center frequency. Results of axial beam scans at low and high energy levels (where nonlinear effects dominate) show that the alternative methods may be appropriate for regulatory purposes