author Amanda Lowe of Digital Pathology Consultants, LLC
Hematology and Pathology devices advisory panel, who discussed whole slide
imaging (WSI) and its use for primary diagnosis in surgical pathology last week,
will use knowledge learned from FDA regulation of digital radiology to lay the
foundation for regulation of WSI systems.
microscopy in use for over 400 years, the practice today of diagnosis with an
optical microscope is not regulated by the FDA (class I exempt) and has no benchmark
or clinical trial data to compare to digital pathology. As clinical trial guidelines are designed for
510k approval and/or premarket analysis (PMA) of WSI manufacturers, a benchmark
may need to be established by the FDA to compare the clinical trial results to
optical microscopy. Also, there is no data
to account for reader variability and washout effects which could greatly
impact clinical trial results. A full
field mammography study, that evaluated side-by-side comparisons of film-based
and digital images of the same patients, failed to demonstrate substantial
equivalence because of reader variability.
The FDA is
also discussing the use of phantoms, which are common in full field mammography
for both PMA and post-market quality assurance of the hardware. A phantom in digital pathology would likely be
a glass slide that could mimic relevant clinical structures using artificial
materials like wire and aluminum that would create a standard for validation of WSI manufacturers.
In addition, display performance will likely play a role in the
regulation of digital pathology. In
digital radiology poor display quality has caused incorrect or inconsistent
diagnostic decisions, increased variability, and longer read times. The FDA will likely use the special controls
designed for displays in radiology as a starting point for regulating displays
in digital pathology, with one major difference- grey vs. color.
The FDA and their
advisory panel are learning from digital radiology. They posed challenging
questions last week and are reviewing the tough answers. The information will be compiled and utilized
to create an approval process for manufacturing and use of WSI systems in