SCANNING ACOUSTIC MICROSCOPE FOR CHARACTERIZATION OF ARTERIAL PLAQUE

Unstable arterial plaque is likely the key component of atherosclerosis, a disease which is responsible for two-thirds of heart attacks and strokes, leading to approximately 1 million deaths in the United States. Ultrasound imaging is able to detect plaque but as of yet is not able to distinguish unstable plaque from stable plaque. In this work a scanning acoustic microscope (SAM) was implemented and validated as tool to measure the acoustic properties of a sample. The goal for the SAM is to be able to provide quantitative measurements of the acoustic properties of different plaque types, to understand the physical basis by which plaque may be identified acoustically. The SAM consists of a spherically focused transducer which operates in pulse-echo mode and is scanned in a 2D raster pattern over a sample. A plane wave analysis is presented which allows the impedance, attenuation and phase velocity of a sample to be de- termined from measurements of the echoes from the front and back of the sample. After the measurements, the attenuation and phase velocity were analysed to ensure that they were consistent with causality. The backscatter coefficient of the samples was obtained using the technique outlined by Chen et al [8]. The transducer used here was able to determine acoustic properties from 10-40 MHz. The results for the impedance, attenuation and phase velocity were validated for high and low-density polyethylene against published results. The plane wave approximation was validated by measuring the properties throughout the focal region and throughout a range of incidence angles from the transducer. The SAM was used to characterize a set of recipes for tissue-mimicking phantoms which demonstrate indepen- dent control over the impedance, attenuation, phase velocity and backscatter coefficient. An initial feasibility study on a human artery was performed.This work was supported in part by CenSSIS the Center for Subsurface Sensing and Imaging Systems under the Engineering Research Centers Program of the National Science Foundation (Award EEC- 9986821

Monitoring HIFU lesion formation in vitro via the driving voltage

During insonation of tissue and tissue-mimicking materials with high-intensity focused ultrasound (HIFU), bubbles formed at or near the focus of the HIFU source have been shown to cause fluctuations in the HIFU driving voltage and current amplitudes. In this paper, we report the results of an investigation of these oscillations in an in vitro system - polyacrylamide phantoms with bovine serum albumin (BSA). The fluctuations in the HIFU driving voltage were interpreted to be the result of constructive and destructive interference at the transducer face caused by the incident HIFU and backscattered ultrasound from the bubbles in the lesion. Interpreting the fluctuations in this manner can lead to a determination of the location of the advancing interface of the bubbly lesion as it moves towards the HIFU transducer during CW insonation. © 2006 American Institute of Physics