Photoacoustic and ultrasonic signatures of early bone density variations

Abstract

This study examines the application of backscattered ultrasound (US) and photoacoustics (PA) for assessment of bone structure and density variations. Both methods are applied in the frequency-domain, employing linear frequency modulation chirps. An 800-nm CW laser and a 3.5-MHz ultrasonic transducer are used for transmitting the signal. The backscattered pressure waves are detected with a 2.2-MHz US transducer. Experiments are focused on detection and evaluation of PA and US signals from in-vitro animal and human bones with cortical and trabecular sublayers. Osteoporotic changes in the bone are simulated by using a very mild demineralization solution (EDTA). Changes in the time-domain signal as well as integrated backscattering spectra are compared for each sample before and after demineralization. Results show the ability of US to generate detectable signals from deeper bone sublayers, whereas the PA signals show higher sensitivity to the variation in bone density. While US signal variation with changes in the cortical layer is insignificant, PA has proven to be able to detect minor variation of the cortical bone density.