Abstract
.Significance: Spatial frequency domain imaging (SFDI) is a quantitative imaging method to measure absorption and scattering of tissue, from which several chromophore concentrations (e.g., oxy-/deoxy-/meth-hemoglobin, melanin, and carotenoids) can be calculated. Employing a method to extract additional spectral bands from RGB components (that we named cross-channels), we designed a handheld SFDI device to account for these pigments, using low-cost, consumer-grade components for its implementation and characterization.Aim: With only three broad spectral bands (red, green, blue, or RGB), consumer-grade devices are often too limited. We present a methodology to increase the number of spectral bands in SFDI devices that use RGB components without hardware modification.Approach: We developed a compact low-cost RGB spectral imager using a color CMOS camera and LED-based mini projector. The components’ spectral properties were characterized and additional cross-channel bands were calculated. An alternative characterization procedure was also developed that makes use of low-cost equipment, and its results were compared. The device performance was evaluated by measurements on tissue-simulating optical phantoms and in-vivo tissue. The measurements were compared with another quantitative spectroscopy method: spatial frequency domain spectroscopy (SFDS).Results: Out of six possible cross-channel bands, two were evaluated to be suitable for our application and were fully characterized (; ). The other four cross-channels presented a too low signal-to-noise ratio for this implementation. In estimating the optical properties of optical phantoms, the SFDI data have a strong linear correlation with the SFDS data (, for , , for ).Conclusions: We extracted two additional spectral bands from a commercial RGB system at no cost. There was good agreement between our device and the research-grade SFDS system. The alternative characterization procedure we have presented allowed us to measure the spectral features of the system with an accuracy comparable to standard laboratory equipment.
Highlights
Biomedical imaging using light can be a powerful, noninvasive, and inexpensive tool to detect biological markers associated with metabolic functions or diseases.[1]
The main advantage of Spatial frequency domain imaging (SFDI) compared to other diffuse optical techniques is the ability to separate the effects of scattering and absorption based on their spatial frequencydependent effect on reflectance
We present an approach to improve the spectral resolution of a nonmodified commercial RGB projector and an RGB CMOS camera in the development of a low-cost compact SFDI system
Summary
Biomedical imaging using light can be a powerful, noninvasive, and inexpensive tool to detect biological markers associated with metabolic functions or diseases.[1]. It allows one to quantitatively measure chromophores concentrations in turbid media, such as tissues and tissue-simulating phantoms.[4] Another advantage of this technique is its depth sensitivity depending on the spatial frequencies employed, which allows one to reconstruct a three-dimensional map of optical properties.[5] SFDI has been employed in clinical studies for a number of different applications, such as vascular assessment in patients with diabetes,[6] evaluation of burn wounds severity,[7,8] enhancement of cancer detection in vitro,[9,10,11] and skin characterization for cosmetic surgery.[12,13,14]
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