Cytology Screening Using Z-Stack Digital Slides: A Validation Study

For applications of digital pathology in cytology, challenges such as focal precision and data volume remain. The goals of this validation study are to compare diagnostic accuracy, screening time, annotation counts, and inter- and intra-observer agreement between digital slides using Z-stack scanning (z-WSI) and conventional glass slides in liquid-based cervical cytology (LBC).

We collected 91 LBC samples, with an equal number of NILM, LSIL, HSIL, and SCC cases. Four cytotechnologists evaluated cases using glass slides and z-WSI separately. They classified cases under two separate schemas: (1) "Screening-2-Category": NILM (normal) vs. other lesions (ASC-US and above); and (2) "Morpho-3-Category": NILM vs. LSIL (mild dysplasia) vs. ASC-H and higher (moderate dysplasia to squamous cell carcinoma) to reflect lesion severity and treatment implications.

For Screening-2-Category classifications, inter-observer agreement was 0.685 for glass slides and 0.637 for z-WSI, with intra-observer agreement ranging from 82.4% to 95.6%. For Morpho-3-Category classifications, inter-observer agreement was 0.700 for glass slides and 0.598 for z-WSI, indicating reduced agreement with z-WSI. Accuracy was 91.2% (glass slides) and 87.1% (z-WSI) for Screening-2-Category, and 86.5% and 81.0% for Morpho-3-Category, with no significant differences. In both modalities, cytotechnologists tended to apply more annotations in true positive cases but fewer in false negative cases. Screening time for z-WSI was 2-5 min longer on average for all cytotechnologists.

z-WSI is not completely equivalent to glass slides, but it has the potential to be used as a tool for cytology screening. Training specifically designed for WSI is expected to enhance diagnostic accuracy and improve workflow efficiency.