Digital Whole Slide Imaging in Cytology
Ioan C. Cucoranu, Anil Vasdev Parwani, Liron Pantanowitz · Archives of Pathology & Laboratory Medicine · 2014
We read with interest the recently published pilot study on digital whole slide imaging (WSI) for cervicovaginal cytology by Wright and colleagues.1 Their study employed 7 cytologists to review 11 Papanicolaou test slides using digital and conventional light microscope modalities. We acknowledge that their data indicate greater diagnostic accuracy and shorter mean times to reach diagnoses with Papanicolaou test glass slides. However, we would like to express our concern regarding the design of that study and the subsequent conclusion drawn, based on those data, that WSI is not yet ready for routine cytology use.Although we recognize that this was a pilot study, in our opinion, 11 cases is insufficient to reliably measure discordance between digital and conventional microscopy nor is it enough to ensure that users are familiar with a new technology. Prior validation studies comparing WSI and glass slides have demonstrated that, when too few cases are used, the diagnostic accuracy deteriorates. A meta-analysis of the literature indicates that, when an average of 20 cases was employed, the concordance between WSI and glass slides was 75% versus 95% when 60 cases were used.2 Furthermore, although the authors do not specify whether any WSI training was provided in their study, it is unlikely that those cytologists received equivalent exposure to digitized slides as they have had in handling glass slides during their careers. Indeed, previous published data show that accuracy with WSI was 79% without training pathologists to use that technology, compared with 95% when they did receive training.2 The authors do comment that their disagreement rates may, in part, be explained by their lack of familiarity with this new technology.The authors further remark about the current lack of available commercial technology to scan the edges of a glass slide, to help methodically screen WSI slides, and the inability of systems to handle large digital files. We would like to state that there are WSI scanners that are capable of scanning the entire glass slide (Figure), even including the label if required. Their study does highlight an important point, however, ensuring that all material present on a glass slide to be scanned is included in the digital image. Although we admit that it can be challenging to screen a digitized cytology slide, we also feel that it is important to point out that the task can be made much easier using currently available WSI viewer tools for easy and systematic navigation of virtual slides (such as thumbnails, autopanning, keyboard navigation, and tracker capabilities).3 It is important to train users to make use of these tools when viewing virtual slides. It is true that scanning a glass slide generates large WSI digital files. That is why vendors of those WSI devices specify that users employ adequate computers and monitors to handle and view the digital images. The computer workstation (1 gigabyte, random access memory, 64 video random access memory [1 GB RAM, 64 VRAM]) and display monitor (1600 by 1024 pixel resolution) the authors selected for their study seems to have less than the minimum required specifications for the iScan Coreo (Ventana Medical Systems, Tucson, Arizona) instrument they used (2 GB RAM and 1920 by 1200 pixel resolution). That may explain why their system frequently “froze,” causing delay and frustration for their participants. For digital imaging, the workstation's specifications should to be at least, if not higher, than those recommended by the vendor to achieve proper performance and user satisfaction.In conclusion, although we agree with Wright et al that there are still several obstacles to overcome, we believe that, if used effectively, WSI will soon be adopted for daily cytology diagnostic use. To accomplish that, laboratories will need to first invest in the necessary technology, appropriately validate those systems, and adequately train their cytologists to use them.