Coregistered photoacoustic and ultrasonic signatures of early bone density variations

Abstract

This study examines the application of backscattered ultrasound (US) and photoacoustic (PA) signals for assessment of bone structure and density variations. Both methods were applied in the frequency-domain, employing linear frequency modulation chirps. A near-IR laser (800 nm) was used for inducing the PA signal. The backscattered pressure waves were detected with a 2.2-MHz US transducer. Experiments were focused on detection and evaluation of PA and US signals from in-vitro animal and human bones with cortical and trabecular sublayers. It was shown that PA signals can be detected as deep as a few millimeters below trabecular and cortical layers. The occurrence of multiple scattering was demonstrated in PA detected signals from cancellous bone. Osteoporotic changes in the bone were simulated by using a very mild demineralization ethylenediaminetetraacetic acid solution. Changes in the time-domain signals as well as integrated backscattering spectra were compared for the samples before and after demineralization. The results demonstrated the sensitivity of PA to variations in bone minerals. In comparison to PA, US was capable of generating detectable signals from deeper bone sublayers (few centimeters). However, while US signal variations with changes in the cortical layer were insignificant, PA proved to be sensitive even to minor variations of the cortical bone density.

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.…”

Bone assessment via thermal photo-acoustic measurements

“…Recently, photoacoustic (PA) imaging, an emerging hybrid technology involving both ultrasound and light, has been explored for potential application in the diagnosis of osteoporosis [3, 4]. Unlike QUS which is more sensitive to trabecular bone, PA signal is sensitive to the variations in bone density in both cortical and trabecular parts of the bone [3].…”

“…Unlike QUS which is more sensitive to trabecular bone, PA signal is sensitive to the variations in bone density in both cortical and trabecular parts of the bone [3]. Multi-spectral PA signals from a biological sample can reflect the contents of the optically absorbing chemical components in the sample [4].…”

“…Due to the difference in acoustic impedance between hard tissue and coupling medium, the initial PA pressure from the bone matrix illumined by light can be expressed as [3]…”

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.…”