Quantitative physiology of the precancerous cervix in vivo through optical spectroscopy

Abstract

Cervical cancer is the second most common female cancer worldwide. The ability to quantify physiological and morphological changes in the cervix is not only useful in the diagnosis of cervical precancers but also important in aiding the design of cost-effective detection systems for use in developing countries that lack well-established screening and diagnostic programs. We assessed the capability of a diffuse reflectance spectroscopy technique to identify contrasts in optical biomarkers that vary with different grades of cervical intraepithelial neoplasia (CIN) from normal cervical tissues. The technology consists of an optical probe and an instrument (with broadband light source, dispersive element, and detector), and a Monte Carlo algorithm to extract optical biomarker contributions including total hemoglobin (Hb) concentration, Hb saturation, and reduced scattering coefficient from the measured spectra. Among 38 patients and 89 sites examined, 46 squamous normal sites, 18 CIN 1, and 15 CIN 2(+) sites were included in the analysis. Total Hb was statistically higher in CIN 2(+) (18.3 +/- 3.6 microM, mean +/- SE) compared with normal (9.58 +/- 1.91 microM) and CIN 1 (12.8 +/- 2.6 microM), whereas scattering was significantly reduced in CIN 1 (8.3 +/- 0.8 cm(-1)) and CIN 2(+) (8.6 +/- 1.0 cm(-1)) compared with normal (10.2 +/- 1.1 cm(-1)). Hemoglobin saturation was not significantly altered in CIN 2(+) compared with normal and CIN 1. The difference in total Hb is likely because of stromal angiogenesis, whereas decreased scattering can be attributed to breakdown of collagen network in the cervical stroma.

Figure 1

A schematic of the fiber-optic-based spectrometer. Currently, the system is housed on amobile cart in the colposcopy clinic.

Figure 2

(A) Typical fits of calibrated diffuse reflectance (450–600 nm) from a normal site (blue diamonds), a CIN 1 site (black squares), and a CIN 2⁺ site (red asterisks) of the same patient. Dashed lines are fits to the measured diffuse reflectance data (100 fits) using the Monte Carlo-based inverse model. Diffuse reflectance from a CIN 2⁺ site has lower reflectance due to higher absorption and lower scattering. The CIN 1 site has intermediate scattering and absorption. (B) Extracted absorption spectrum (µ_a(λ)) from a normal site (blue diamonds), a CIN 1 site (black squares), and a CIN 2⁺ site (red asterisks) from the same patient. Absorption is significantly increased in CIN 2⁺ compared with normal cervical tissue and CIN 1. (C) Extracted reduced scattering spectrum (µ_s′(λ)) from a normal site (blue shaded line), a CIN 1 site (black squares), and a CIN 2⁺ site (red broken line) from the same patient. Scattering decreases from normal cervical tissue to CIN 1 and decreases further from CIN 1 to CIN 2⁺. Scattering spectrum is fairly featureless and monotonically decreases from 450 to 600 nm.

Figure 3

(A) Total Hb concentrations ([total Hb]) for different tissue types extracted from diffuse reflectance between 450 and 600 nm. Compared with normal and CIN 1, [total Hb] increased significantly in CIN 2⁺ (P < .002). [Total Hb] can also be used to distinguish CIN (CIN 1 + CIN 2⁺) from normal tissue (P < .023). (B) Mean reduced scattering coefficient (<µ_s′(λ)>) from 450 to 600 nm was not significantly decreased in CIN 2⁺ compared with normal and CIN 1, although there was a significant decrease of (<µ_s′(λ)>) in CIN compared with normal tissue (P < .002). Asterisks refer to significance at the P < .025 level with the Bonferroni correction.