Optical bone densitometry insensitive to skin thickness

Abstract

Skin thickness, including the adipose layer, which varies from individual to individual, affects the bone density measurement using light. In this study, we proposed a method to measure skin thickness using light and to correct the bias caused by differences in skin thickness and verified the proposed method by experiments using a phantom. We measured simulated skin of different thicknesses and bovine trabecular bone of different bone mineral densities (BMDs) using an optical system consisting of lasers of 850 and 515 nm wavelengths, lenses, and slits. Although the slope of the light intensity distribution formed on the surface of the material when irradiated by the 850 nm laser is affected by the thickness of the skin phantom. The difference of the intensity distribution peaks (δy) between the 850 and 515 nm lasers was strongly correlated with the thickness of the skin phantom. The coefficient of determination between the measurements and the BMD was improved by correcting the 850 nm laser measurements with δy. This result suggests that the method is applicable to optical bone densitometry, which is insensitive to differences in skin thickness.

Osteoporosis Prediction Using Machine-Learned Optical Bone Densitometry Data

“…In this study, the slope of the light intensity distribution (SLID) was measured in the Z range of 35–42 mm. This range of SLID has been shown in previous research to be correlated with BMD [ 24 , 25 ]. To detect unintended excessive target movement during measurements and eliminate improper measurement results, the light intensity distribution was measured twice in one measurement.…”

“…The optical system consists of two convex lenses, two annular slits, a photodetector, and a laser diode, as shown in Fig. 2 [ 24 , 25 ]. An avalanche photodiode (APD) module (C12703-01, Hamamatsu Photonics K.K., Japan) was used as the photodetector, and the analog light intensity data was converted to 10-bit digital data.…”

“…To achieve compact, safe, and reliable screening of osteoporosis, bone densitometry using near-infrared light has been studied as a new noninvasive method of BMD assessment [ 5 , 24 , 25 ]. Near-infrared light has excellent biological transparency [ 1 ], and there is a strong relationship between BMD and light scattering phenomena [ 43 , 45 ].…”

“…In addition, a linear correlation exists between light scattering coefficient and BMD [ 45 ]. We previously developed an optical bone densitometry (OBD) method using a simple optical consisting of a laser diode module, a photodiode, two plano-convex lenses, and two annular slits [ 24 , 25 ]. The OBD measures the change in light scattering caused by differences in BMD as the slope of the light intensity distribution formed when a near-infrared laser beam is irradiated on the skin surface [ 24 ].…”

“…We previously developed an optical bone densitometry (OBD) method using a simple optical consisting of a laser diode module, a photodiode, two plano-convex lenses, and two annular slits [ 24 , 25 ]. The OBD measures the change in light scattering caused by differences in BMD as the slope of the light intensity distribution formed when a near-infrared laser beam is irradiated on the skin surface [ 24 ]. Phantom experiments and numerical simulations for OBD showed that the slope of the light intensity distribution, which is formed on the skin's surface when irradiated with near-infrared light, correlated with BMD.…”