In vivo measurement of mean sound speed using focus adjustment method (FAM) in ultrasonotomography

This paper describes a new method of IN-VIVO sound-speed measurement in the reflection mode. The mean sound speed between the reflector and the linear array transducer is measured using the following two parameters: time of flight and the distance between two receiver elements. To detect the time of flight, we adjust the delay line time compensator in the system to get the sharpest image of the reflector. The value of this compensated time corresponds to the sound speed in the medium. A new ultrasonic scanner employing a large modified-synthetic receiver aperture provides a high resolution image and high sound-speed measurement accuracy. This system also uses dynamic focusing in the time compensator, focusing in real time the ultrasonic beam at each reflector at each depth. Using this approach, the time required for this measurement is about 1 sec. System measurement error was less than 0.5% in water in the temperature range 5 to 40°C. For an IN VIVO measurement, we applied this method to a human liver, obtaining the mean sound speed between the diaphragm and the transducer. This method has potential application for detecting tissue abnormality in clinical use.