Combined photoacoustic and ultrasonic diagnosis of early bone loss and density variations

Abstract

Over the past two decades, osteoporosis has been recognized among the most serious public health problems. Fortunately with the growing awareness of osteoporosis, new treatments have been developed for the prevention of fracture. At the same time, there is a rapid improvement in diagnostic methods. In this study biomedical photoacoustics (PA) is applied to the analysis of bone mineral concentration. The PA signal depends on optical as well as mechanical properties of the object and therefore has the potential to provide higher sensitivity to density variations compared with standard diagnostic methods, like ultrasound. A laser source with 800 nm wavelength and different ultrasonic transducers with resonance frequencies in the range 1 to 5 MHz were employed. The CW or frequency-domain (FD) PA radar method was utilized with linear frequency modulation chirps to provide temporal gating control over the transmitted signal and higher sensitivity in the detected signal. The laser intensity was set below the safety standards for skin exposure. The preliminary studies showed adequate optical absorption by cortical bone to generate measurable PA signals and the transmission of laser light through this layer. Experiments are focused on detection and evaluation of PA signals from in-vitro animal cortical bones with and without a trabecular sublayer. The trabecular layer is then diluted by chemical etching and differences in the PA signals are discussed.

Photoacoustic and ultrasound imaging of cancellous bone tissue

“…28 Recently, measurements of photoacoustic (PA) backpropagation from bones were reported for the first time. 30,31 Since PA is sensitive to the optical properties of tissue, it can detect composition variation and as such it can provide complementary information to US backscattering measurements. In our previous studies, we showed the sensitivity of PA with changes in minerals and organic phases of bone.…”

Photoacoustic imaging: a potential new platform for assessment of bone health

“…A recent study has examined the possibility of PA to the evaluation of bone mineral concentration and microstructure [12][13][14]. Although the findings from this study are mostly qualitative, it demonstrates potential advantages of PA based bone evaluation over conventional US based technologies.…”

“…Although the findings from this study are mostly qualitative, it demonstrates potential advantages of PA based bone evaluation over conventional US based technologies. Since the light-induced pressure waves are generated instantaneously from different layers, PA measurement from a bone can focus on the trabecular part as the region of interest (ROI) without being affected by the cortical part [12]. In this work, with an ultimate goal of establishing a quantitative photoacoustic (QPA) platform for assessment of bone health, we investigated the performance of several techniques, including photoacoustic imaging (PAI), thermal photoacoustic measurement (TPAM), photoacoustic spectral analysis (PASA), on ex vivo bone specimens.…”

Coregistered photoacoustic and ultrasonic signatures of early bone density variations

“…Our group introduced PA diagnostics for studies of bone density changes. In our previous work, 37 we showed that the PA signal is sensitive to large changes in the trabecular bone structure. We also showed that "coherent structure backscattering" similar to US 38 can be detected with PA at frequencies higher than 1 MHz.…”