Analysis of acetic acid-induced whitening of high-grade squamous intraepithelial lesions

Immature and dysplastic cervical squamous epithelium whitens after the application of acetic acid during a colposcopic examination. The whitening process occurs visually over several minutes and subjectively discriminates between dysplastic and normal tissue. In this work, examples of the acetowhitening process are detailed in three ways: the color-imaged colposcopic appearance of the acetowhitening of high-grade cervical intraepithelial neoplasia (CIN 2/3), the kinetics of these reflectance patterns transformed to reduce noise in the signal, and a self-normalized green to red ratio measurement of the kinetics of these reflectance patterns. A total of six patients with biopsy confirmed CIN 2/3 were examined to obtain a set of timed images tracking the acetowhitening and the whitening-decay process over the course of 5-10 min. Regions of normal mature squamous epithelium within the same patients were also followed as an internal control. We determined that the temporal change over a 10 min time period in the ratio of green to red light intensities, taken from the respective color channels of the CCD, provides a reliable measure to clearly distinguish CIN 2/3 from normal cervical epithelium. This imaging and data normalization procedure may be applied to cervical lesions of different grades, to determine if a quantitative estimate provides predictive value during the colposcopic diagnosis.