The importance of expression of uncertainty of acoustical parameters of ultrasonic phantoms

Abstract

The measurement of uncertainties in scientific experiments improves greatly quality and reliability of the results. However, in many cases, experimental results are only expressed by its average value and standard deviation. The longitudinal velocity and attenuation coefficient are acoustic parameters commonly used to characterize biological tissues and materials. In this work it is studied the uncertainty in experiments designed to evaluate these parameters on two different materials (silicone rubber and PVCP). The uncertainties were studied following the Guide to the Expression of Uncertainty in Measurement and calculated by a program in Labview8.6. One setup was developed to measure the acoustic parameters by a transmission/reception technique. Five signals of each medium (water and materials) were collected. The attenuation coefficient was calculated using the relation between the amplitude spectrum peak of the water signal and its respective point on the spectrum of the material signal. The longitudinal velocity was calculated using the time delay between signal peaks (from water and from the material). The individual uncertainties of each part of setup were estimated and these values permitted to identify which were the sources of uncertainty that most contributed to increase the value of associated uncertainty. It permitted to improve experiment's quality and reliability.