The Role of Microtomy in Digital Pathology

General automated microtomy, digital pathology, microtomy

The Role of Microtomy in Digital Pathology

In 2017, the FDA granted permission to Phillips to sell its whole slide imaging system for primary diagnosis. This opened up a number of applications and advances utilizing digital pathology, including sharing slides for remote and rapid diagnosis and applying artificial intelligence (AI) and deep learning onto the digital images. As histology laboratories prepare for the onset of digital pathology, one may think that the most important step is to purchase a good slide scanner, but it is not. In fact, the most important step for histology laboratories to prepare for digital pathology can be taken even before researching a slide scanner – the most important step is to make sure the laboratory is producing consistent, high quality-slides, starting with microtomy.

Despite rapidly advancing quantitative diagnosis technologies associated with digital pathology, the bedrock of pathology remains the hematoxylin and eosin (H&E) slide. For successful sharing of images between institutions, sections will have to meet expectations regarding consistent thickness, orientation, and quality, even in a basic H&E slide. Many of these section characteristics are established during microtomy and cannot be changed further in the slide preparation process or fixed digitally. As such, slide quality and consistency appropriate for digital pathology and slide sharing must be met during microtomy.

Another reason that establishing best practices for digital pathology during microtomy today is that many laboratories are starting their journey into digital pathology by scanning archived slides. This means that successful digital pathology can begin years before purchasing the appropriate imaging instrumentation.

Below are some characteristics that should be considered in microtomy today to prepare histology laboratories for digital pathology:

  • Section thickness: Consistency of section thickness is important for scanned slides, especially if they are to be shared. Sections of different thicknesses stain differently (Download poster pdf from Chlipala et al.), so for pathologists to examine sections from other institutions, the thickness needs to be standardized and consistent. As well, thick sections can be difficult to scan, and scans of sections with variable thickness will have areas out of focus.
  • Section quality: Sections should be free of folds and wrinkles, which can obscure important characteristics of tissues necessary for diagnosis. This is best addressed during section floating, mounting, and drying.
  • Contamination: Contamination of slides should be minimized. Floaters on the tissue can hide important tissue characteristics, and can also add thickness to the specimen, leading to problems in focus. Furthermore, debris outside of the tissue area can add to the scanning area, increasing image size and scanning time.
  • Section placement and orientation: Sections must be placed so they are within the scanning boundaries of imagers, in order to not exclude any portion of mounted sections from the images.  As well, orientation and placement should be consistent to analyze images with different software.

Pathology is at the beginning of its digital age, but even laboratories that are not fully adopting digital pathology can prepare for its future by preparing standardized and consistent H&E slides.