Whole Slide Images for primary diagnostics in pathology

Abstract

Whole slide imaging is the process of digitizing glass slides resulting in the creation of Whole Slide Images (WSI). WSI are usually explored with the aid of an image viewer in a manner that closely simulates examining glass slides with a conventional microscope, permitting the manipulation of an entire tissue section in any direction and at any magnification. There are several advantages of digital pathology over the conventional way of practicing pathology. The ease of accessing and sharing can only be seen as a flexible way of rendering diagnostics. With the aid of WSI, problematic or difficult cases can be efficiently shared with an expert within suitable time constrains. The digital nature of WSI allows their integration into a patient’s medical report permitting the pathologists to work within an integral environment including the clinical information, pathology data and pathology specimens. WSI can also be electronically archived and retrieved, sparing the time spent on searching glass slides for consultation, conferences, teaching and research purposes. Furthermore WSI can be subjected to automated image analysis which is believed to improve productivity and objectivity in daily diagnostics. As results of the above mentioned virtues, WSI have been incorporated into several applications within pathology. Nevertheless their use in primary diagnostics is still limited, possibly because it is not approved yet from the Food and Drug Administration (FDA) for such purposes. The main aim of this thesis was therefore to assess the validity of using WSI as a platform for primary diagnostics in pathology. The validity of WSI in primary diagnostic purposes have been studied thoroughly by reviewing 500 cases originated form different body systems. These cases were examined in five system specific validation studies covering a wide spectrum of surgical pathology, namely the gastrointestinal tract, skin, breast, pediatrics and the urinary system. Furthermore, the validity of WSI for examining fine cellular details was tested by performing two studies assessing the reliability of evaluating the Mitotic Activity Index (MAI) and the HER2 gene amplification in breast cancer cases using high resolution WSI. Additionally we have presented the experience of implementing WSI in routine pathology diagnostics in a medium-sized pathology laboratory where WSI have been integrated on gradual basis in daily routine diagnostics to reveal the difficulties and the pitfalls when using this novel technology in primary diagnostics. The main conclusion to be drawn from this thesis is that WSI contain sufficient information for rendering most of the diagnostics within pathology. This was confirmed by the comparable diagnostic performance of the WSI when compared to that of the microscope. Nevertheless, several issues need to be addressed before the transition to digital pathology can be completed including the availability of faster scanners which are able to scan the entire specimen in less than 30 second, proper navigation interface helping in simple exploration of WSI, convenient data management systems to store and retrieve images and eventually the availability of adequate quality control of the general image quality and controlling scanning errors.