Diffuse reflectance spectroscopy of epithelial tissue with a smart fiber-optic probe

Abstract

Diffuse reflectance spectroscopy (DRS) with a fiber-optic probe can noninvasively quantify the optical properties of epithelial tissues and has shown the potential as a cost-effective, fast and sensitive tool for diagnosis of early precancerous changes in the cervix and oral cavity. However, current DRS systems are susceptible to several sources of systematic and random errors, such as uncontrolled probe-to-tissue pressure and lack of a real-time calibration that can significantly impair the measurement accuracy, reliability and validity of this technology as well as its clinical utility. In addition, such systems use bulky, high power and expensive optical components which impede their widespread use in low- and middle-income countries (LMICs) where epithelial cancer related death is disproportionately high. In this paper we report a portable, easy-to-use and low cost, yet accurate and reliable DRS device that can aid in the screening and diagnosis of oral and cervical cancer. The device uses an innovative smart fiber-optic probe to eliminate operator bias, state-of-the-art photonics components to reduce size and power consumption, and automated software to reduce the need of operator training. The device showed a mean error of 1.4 ± 0.5% and 6.8 ± 1.7% for extraction of phantom absorption and reduced scattering coefficients, respectively. A clinical study on healthy volunteers indicated that a pressure below 1.0 psi is desired for oral mucosal tissues to minimize the probe effects on tissue physiology and morphology.

Keywords: (060.2370) Fiber optics sensors; (120.5475) Pressure measurement; (170.6510) Spectroscopy, tissue diagnostics.

Fig. 1

A smart optic sensor system: (a) schematic of the probe and instrument; (b) schematic of the DFPI pressure sensor head; and (c) photograph of the portable instrument and smart probe. LED – light emitting diode; Spec – spectrometer; R₁ and R₂ – reflection; P – external pressure; and D – diameter of the glass diaphragm.

Fig. 2

Flowchart of the LabVIEW software for instrument control and data collection and analysis.

Fig. 3

Schematic of experimental setup for pressure sensor test.

Fig. 4

Photograph of DRS measurement from the left cheek of a volunteer.

Fig. 5

Extracted v.s. expected phantom mean (a) μ_a; (b) μ_s’ and (c) THb. The errorbars were resulted from different phantom for reference.

Fig. 6

Pressure sensor characterization: (a) an interferogram measured under room pressure and (b) measured cavity length as a function of the nitrogen pressure. The errorbar in (b) was obtained from the 10 repeated measurements under each pressure level.

Fig. 7

Tissue HbO₂, Hb, THb, SO₂ and <μ_s’(λ)> measured from the left cheek of Vol 2 under increased probe pressure (8 pressure levels from 0.5 ± 0.5 psi to 7.5 ± 0.5 psi with 10 measurements under each pressure level).

Fig. 8

Tissue parameters measured from the right cheek of Vol 8 under a constant probe pressure of 1-2 psi. The open circles represent experimental data and solid lines represent a 9th degree fit.