Effects of Operational Mode and Attenuation on the Characterization of Biological Tissues with Ultrasonic Backscattering Signals and Statistical Analysis

Abstract

The Nakagami statistical distribution of ultrasonic backscattering signals has shown it is capable of characterizing the variations of density and arrangement of scatterers in biological tissues This analysis of ultrasound signals has also found with less dependency on the effect of attenuation and the estimated statistical parameter can be affected by the board-band attenuation in the tissues and distortion of acquired echo signals Accordingly as the employed ultrasound frequency and pulse duration namely operational mode were increased several additional factors could come into play and further affect the precise estimation of the statistical parameters To further investigate the addressed issues experiments were arranged and performed using 3 5 7 5 and 10MHz focused transducer in vitro porcine liver tissues and using 30 50MHz focused transducer in vivo rat liver tissues The porcine liver tissues were obtained with either healthy (N=10) or pathological fibrosis (N=10) were obtained from a local slaughter house and rat liver tissues from 10-week-old male Sprague Dawley (SD) rat liver tissues (N=5) Various excitation cycles including 1 3 5 and 10 of tone bursts at pulse repetition frequency corresponding to ultrasound frequencies of 3 5 7 5 10 30 and 50 MHz were adjusted for driving the transducers Various thickness of attenuated phantoms with the attenuation coefficient of 1 62 dB/mm．MHz were placed on the surface of tissue to be measured The Nakagami statistical model which includes the shape parameter (Nakagami-m) was implemented to assess variations of the probability density function (PDF) estimated from the acquired ultrasonic backscattering signals Eventually the histological analysis using the H&E staining not only detect the pathological fibrosis liver status but also measure the number of scatterers in the resolution cell it’s corresponds to a volume of ultrasound signals within transducer pulse length and the lateral profile beamwidths Results of in vitro porcine liver tissues indicated that the attenuation could significantly vary the shape of PDF of backscattered envelopes Results of in vivo rat liver tissues indicated that the Nakagami-m increased with the increasing ultrasound frequencies and bandwidth and that those associated PDFs were nearly pre-Rayleigh distributed Results of histological analysis are shown the stronger scatterers distributed in the tissues the characterization of tissues both describe to pre-Rayleigh distribution All the results consistently demonstrated that the use of 3 cycles tone bursts may achieve the most appropriate performance to accommodate a trade-off between attenuation effect and image resolution Current study also verified that the operational modes of incident ultrasound need to be properly assured before that the statistical model may be further applied to parametric imaging and clinical applications

Date of Award	2015 Aug 20
Original language	English
Supervisor	Shyh-Hau Wang (Supervisor)