New spectral imaging method for the in-vivo detection and grading of epithelial dysplasias and malignancies based on the quantitative assessment of acetic acid-tissue interaction

Abstract

Cervical cancer is the commonest form of cancer in females under 35 years of age and the second most common in females of all ages. Limitations of the existing diagnostic methods have led to the development of new diagnostic approaches. Acetic acid is a marker used for more than 70 years in gynecology for the detection of abnormal lesions. Local application of acetic acid causes a temporal whiting to abnormal areas (acetowhite) while normal areas are not affected. Extensive clinical trials have shown that the visual assessment of acetowhitening exhibits similar diagnostic performance to other methods such as Test Pap. The diagnostic method proposed in this project is based on the quantitative and objective assessment of the acetic acid-tissue interaction by means of an Imaging Spectroscopy System. For the purpose of this study a new Imaging Spectroscopy system has been designed and developed. The method was used for the in vivo detection of dysplasias in the cervix and the results, from measurements of 181 women, indicated that there is a strong correlation between the histological condition of the tissue and the kinetics of the acetowhitening development. The best fit of the time course measurements of acetowhitening was achieved by the triple exponential function. Statistical analysis of several parameters that characterize the acetowhitening kinetics, have indicated that the combined evaluation of the parameters that express the duration (t5) and the intensity of acetowhitening (EDRmax) differentiates sufficiently all the examined histological conditions. Estimation of the sensitivity and the specificity of this method indicates that its diagnostic performance is comparable or better than that of the existing methods. In order to explain the experimental results, a model for the acetic acid-tissue interaction is proposed. According to this model the tissue-pH alterations induced by the application of acetic acid can be simulated with a 3-compartment model (the intracellular, the extracellular and the blood sink compartments). The solution of the model has shown that, after the application of acetic acid, the intracellular pH exhibits the same kinetics with the acetowhitening. The alterations of the intracellular pH cause increment in the relative refractive index of the nuclear proteins, and consequently increase the light scattering by the nuclei. Furthermore, this model correlates qualitatively the kinetics of the acetowhitening with some structural, compositional and functional features of the epithelial tissue and successfully interprets the experimental results. In particular, epithelial tissue features such as the nuclear size and inhomogeneity, the epithelium thickness, the cellular energy reserves (e.g. glycogen), the density of cell-packing, the cellular metabolism, and the efficiency of the vascularity determine the acetowhitening kinetics.