Date Published: February 9, 2018
Publisher: Public Library of Science
Author(s): Christopher T. Lam, Jenna Mueller, Betsy Asma, Mercy Asiedu, Marlee S. Krieger, Rhea Chitalia, Denali Dahl, Peyton Taylor, John W. Schmitt, Nimmi Ramanujam, Kurt I. Anderson.
We have previously developed a portable Pocket Colposcope for cervical cancer screening in resource-limited settings. In this manuscript we report two different strategies (cross-polarization and an integrated reflector) to improve image contrast levels achieved with the Pocket Colposcope and evaluate the merits of each strategy compared to a standard-of-care digital colposcope. The desired outcomes included reduced specular reflection (glare), increased illumination beam pattern uniformity, and reduced electrical power budget. In addition, anti-fogging and waterproofing features were incorporated to prevent the Pocket Colposcope from fogging in the vaginal canal and to enable rapid disinfection by submersion in chemical agents.
Cross-polarization (Generation 3 Pocket Colposcope) and a new reflector design (Generation 4 Pocket Colposcope) were used to reduce glare and improve contrast. The reflector design (including the angle and height of the reflector sidewalls) was optimized through ray-tracing simulations. Both systems were characterized with a series of bench tests to assess specular reflection, beam pattern uniformity, and image contrast. A pilot clinical study was conducted to compare the Generation 3 and 4 Pocket Colposcopes to a standard-of-care colposcope (Leisegang Optik 2). Specifically, paired images of cervices were collected from the standard-of-care colposcope and either the Generation 3 (n = 24 patients) or the Generation 4 (n = 32 patients) Pocket Colposcopes. The paired images were blinded by device, randomized, and sent to an expert physician who provided a diagnosis for each image. Corresponding pathology was obtained for all image pairs. The primary outcome measures were the level of agreement (%) and κ (kappa) statistic between the standard-of-care colposcope and each Pocket Colposcope (Generation 3 and Generation 4).
Both generations of Pocket Colposcope had significantly higher image contrast when compared to the standard-of-care colposcope. The addition of anti-fog and waterproofing features to the Generation 3 and 4 Pocket Colposcope did not impact image quality based on qualitative and quantitative metrics. The level of agreement between the Generation 3 Pocket Colposcope and the standard-of-care colposcope was 75.0% (kappa = 0.4000, p = 0.0028, n = 24). This closely matched the level of agreement between the Generation 4 Pocket Colposcope and the standard-of-care colposcope which was also 75.0% (kappa = 0.4941, p = 0.0024, n = 32).
Our results indicate that the Generation 3 and 4 Pocket Colposcopes perform comparably to the standard-of-care colposcope, with the added benefit of being low-cost and waterproof, which is ideal for use in resource-limited settings. Additionally, the reflector significantly reduces the electrical requirements of the Generation 4 Pocket Colposcope enhancing portability without altering performance compared to the Generation 3 system.
The World Health Organization’s recommends a “see and treat” paradigm for cervical cancer prevention in low and middle-income countries. Current recommendations include human papilloma virus (HPV) testing (screening) and visual inspection with acetic acid (VIA) of HPV-positive women (diagnosis), followed by cryotherapy for women diagnosed with pre-cancerous lesions (treatment) . If HPV testing is not available, visual inspection with acetic acid (VIA) is often used both as a screening and diagnosis tool . However, VIA has several limitations including poor specificity, high inter-observer variability, and lack of image capture . Several of these limitations could be addressed through the use of a low-cost portable colposcope as a screening or diagnostic tool at the primary care level.
The World Health Organization’s recommends a “see and treat” paradigm for cervical cancer prevention in low and middle-income countries using VIA (if HPV screening is not available) and cryotherapy. VIA has several limitations including poor specificity, high inter-observer variability, and lack of image capture . Thus, there is an unmet need for a low-cost portable colposcope that could address several of these limitations and improve women’s access to cervical cancer screening. This study describes our strategy to develop a solution with comparable image quality to standard-of-care digital colposcopes and compatible with liquid chemical cleaning procedures used in the field. The primary goals of this study were to improve image contrast levels, increase the illumination beam pattern uniformity, reduce the required electrical power budget of our system, improve anti-fogging and incorporating water resistant features into our device, and enhance system portability.