Conception of an ultrasonic system for assistance to the diagnosis of the osteoporosis

Existing ultrasound devices for assessing the human tibia are based on detecting the first arriving signal, corresponding to a wave propagating at, or close to, the bulk longitudinal velocity in bone. However, human long bones are effectively irregular hollow tubes and should theoretically support the propagation of more complex guided modes similar to Lamb waves in plates. The present work is dedicated to a preliminary survey in order to have an approach on the interaction of the ultrasonic waves generated by focusing sensors to bone environment. In this context an ultrasonic system based on a pair of transducers (transmitter and receiver) vibrating at 100 kHz was set up to measure the wave velocity with great precision in a sample materials for the purpose of calibration before the measurement in bones. The constructed system includes a digital calliper for distance measurement with great precision and an electronic system including an emitter and a receiver circuit controlled by a programmable FPGA circuit. This latter was incorporated in the system in order to measure a shorts time flight between the two transducers. The measurement of these two parameters with a good precision will give the ultrasonic velocity between the two transducers that establish a link to mechanical parameters of the sample materials such as its thickness, density and Young modulus.