Microscope slide scanning to produce digital histology images is a recent technology which is of interest to both histologists and pathologists. Microscope slide scanning to produce digital images is routinely used in various teaching organisations, however its implementation and utilization in everyday histology/pathology laboratories is still in its infancy. There are numerous opinions and preconceptions on the matter and in this article we will briefly address the pros and cons of microscope slide scanning versus more traditional slide storage systems.
Microscope slide scanning involves converting histology microscope slides into digital images using a digital scanner which can be adjusted to scan at various magnifications, typically from x5 to x40. One of the major negative perceptions regarding the use of digital microscope slide scanning is that there is will be a loss of detail compared to the original slides. However, the use of advanced scanning technology where each image is digitised into millions to billions of pixels means each scanned slide contains a high degree of detail ensuring excellent morphological and staining detail compared to original slides. Digital microscope slide scanning systems are now available that can accommodate greater than 200 slides at a time, allowing scanning of slides in batches which can reduce any inter-batch scanning variability.
Traditional methods of slide storage simply involve archiving glass slides in storage boxes in secure rooms. The benefits of this system are that, on an individual basis, slides take up limited space and can be stored in fairly compact boxes with relatively low storage costs. Slides can be retrieved from an archive and be viewed using any standard microscope which can be found in most labs around the world. This system is simple in nature and has formed the backbone of histology and pathology approaches.
This traditional system is, however not without its disadvantages. Storage can become a majorproblem in large hospital settings where vast numbers of slides are required to be archived for long periods of time, resulting in a logistical and financial burden for these institutions. In addition, retrieval of slides can result in a delay while the samples are recovered from the archive. Long term storage of stained sections can also be a problem in itself, due to the potential loss staining intensity, nuclear detail and leakage of stains from cells with time.
The Pros and Cons of Microscope Slide Scanning
One of the clear advantages of using digital microscope slide scanning is that this approach captures an image that can be stored for as long as is required without any degradation in the image quality. The digital nature of the image also means that it is possible to electronically archive images in a concise and searchable manner allowing simple and rapid access. In addition, the ability to view digital images on a computer monitor facilitates the sharing of images with colleagues in different countries over computer networks.
From a pharmaceutical research point of view, having easy access to digital slide images via microscope slide scanning can simplify R&D project audits and requests from the regulatory bodies. In addition, digital images from key drug efficacy / toxicity studies can be easily inserted into data reports and licensing / regulatory package. The easily retrieval and review of slide images years after a completed study can facilitate long term patient follow-up and allow further quantitative analysis.
Microscope slide scanning also has clear advantages when carrying out digital image analysis, as the high resolution images can allow image analysis packages to analyse across a whole slide section, rather than individual regions of interest which can increase reproducibility, reduce bias and simplify study designs.
One of the major strengths of using a microscope to view slides is that is it is possible to move through a tissue using the fine or course focus adjuster, allowing the investigator to view different focal planes, which is especially important for tissue with variable thickness.
In order to accommodate the ability to view different focal planes using a digital images generated via microscope slide scanning, some digital scanners can take numerous scans at different focal distances allowing the investigator to move between the different planes using an image viewer on their computer, in a similar fashion to adjusting the focus adjuster on a microscope. This is achieved by selecting the number of planes and spacing between each plane prior to scanning the slide. The ability to interrogate a slide in the z-axis is particularly important for tissues with a wide variation in thickness and for brain mapping, fluorescence work, cytology or morphometry studies.
One potential disadvantage of capturing digital images using microscope slide scanning is the size of the resultant data file. As a consequence of the need to capture all the details of the slide, the size of the files can range from 50MB up to 2GB per slide, depending on tissue size. Large file sizes can cause issues when storing large number of images or remotely sharing images over the Web. However, as technology advances and server costs become more affordable, such issues associated with digital storage / sharing will inevitably decline.
Overall, it is clear that digital microscope slide scanning has certain advantages over traditional microscope-based methods and as technology continues to advance it is inevitable that digital image capture will increasingly become commonplace within most histology and pathology labs.