Optimising digital pathology at St. Olavs Hospital

Film coverslipping of H&E stained slides enables standardised and high-quality digital pathology. According to one of Norway’s largest pathology departments (Department of Pathology at St. Olavs Hospital in Trondheim), the benefits of film coverslipping outweigh the hazard of using xylene required for film coverslipping. For this reason, the hospital decided to integrate the reagent and changed from glass to film coverslipping. 

St. Olavs Hospital has significant experience providing diagnostic pathology services. The hospital serves the Central Norway Regional Health Authority (Helse MidtNorge) and the other four regional Norwegian health enterprises. 

The Department of Pathology has four distinct departments: 

• Medical department, which is responsible for diagnostics and medical and forensic autopsies. 
• Biopsy and autopsy department covers numerous histopathology techniques and services including pre and post-analytical handling, frozen sections, sectioning and routine staining, autopsies and managing projects. 
• Special analysis department covers special staining, immunohistochemistry, molecular pathology, electron microscopy, scanning and special surveys. 
• Cytology department handles cytology and HPVanalysis.

 The laboratory also contributes to research and development and contributes to the growing BioBank1 (the regional research databank) by donating biological material. 

To maintain a high level of service, the department recognised the need to increase efficiency in the laboratory. Therefore, the laboratory started the Digital Pathology project. With their move towards digital pathology, the Department of Pathology noticed some difficulties that were caused by coverslipping their slides with glass coverslips. These difficulties included skewed glass coverslips and an abundance of artefacts such as air bubbles that affected the quality of their slide scans. 

The department believed that coverslipping with film would alleviate many of these issues and that changing to film coverslipping would improve efficiency and workflow and therefore provides a great advantage when switching to digital pathology. 

Challenge and examination

In 2017, the Department of Pathology at the St. Olavs Hospital purchased the Tissue-Tek Prisma^® stainer. When considering future developments, the institute also decided to test the Tissue-Tek Film^® coverslipper using the TissueTek^® Coverslipping Film, which required the use of xylene. Initially, there was some hesitation as the department was working xylene-free. They decided to evaluate the use of film coverslipping without xylene, which resulted in H&E stained slides that appeared pale and had air bubbles trapped underneath the coverslip due to no solvent being used in the dehydration step. Therefore the decision was made to continue with the Tissue-Tek Glas^TM g2 coverslipper as using film without xylene was not an option. 

However, in 2019 the pathology department scaled up the scanning process and moved to high-throughput scanners. For logistical reasons, the staining and coverslipping instruments were moved to the same room as the scanners. With an increase in slide throughput, it became rapidly apparent that glass coverslipping was causing a bottleneck due to air bubbles and mounting media spills that affected the scanning process and image quality, resulting in rescanning of many slides. Therefore, the search started for a more sustainable substitute. 

The use of film coverslipping in combination with xylene, was reconsidered. Examining the benefits and limitations, the laboratory decided that the benefits of using film coverslipping outweigh the challenges caused by the use of xylene for the following reasons: 

1. Film coverslipping is much faster compared to glass coverslipping. This increase in speed provides an improved synchronisation with the high-throughput scanners. 
2. Slides coverslipped with film have a shorter drying time. After coverslipping, slides can be scanned almost immediately. 
3. There are fewer risks in the scanning process when using film, such as broken glass or misaligned coverslips. 
4. With the use of film, there are no mounting medium excesses and fewer air bubbles that might disrupt the scanning process and ultimately affect the image quality. 
5. Slides coverslipped with film can be archived immediately after scanning reducing wait times.

Air quality was assessed during the switch to film coverslipping to ensure the highest health and safety levels for employees. Prior to routine use, the Prisma stainer and Film coverslipper were connected to an exhaust to minimise fumes. Film coverslipped slides were placed into a fume hood post coverslipping and air quality measurements monitored. Results showed that xylene levels were well within acceptable limits.

Maintaining image quality

With the switch from glass to film coverslipping, the Pathologists wanted to guarantee that the same quality was maintained compared to glass. They performed a comparative study between glass and film coverslips. Multiple Pathologists scored the scanned images of a selection of tissue types including bone marrow, from which optimal sections can be difficult to obtain. The pathologists were unanimous about the results, stating: “The image quality of sections covered with film are just as good as with sections covered with glass.”

Conclusion

Film coverslipping of H&E stained slides greatly enables standardised and high-quality digital pathology. It creates an environment where digital slide scanning is an efficient, cost-effective and trouble-free process at the St. Olavs Hospital. After comprehensive evaluation, St. Olavs Hospital’s pathology department decided to fully implement film coverslipping and as a result, the digital slide scanning process was greatly improved. Slides are more quickly and readily available for scanning, there is no mounting medium spillage, there are fewer disruptions, there is no need for extra drying time, and the slides can be archived immediately. The Department of Pathology at St. Olavs Hospital managed to implement the Digital Pathology project successfully facilitated by the use of film coverslipping.