Technical and practical limitations of whole slide digital imaging in the analysis of intracranial thrombectomies

Abstract

Whole slide digital imaging (WSDI) is a technology in which stained slides are entirely digitized, usually at 200X to 400X magnification, in an automated fashion. The advantage of this technique is that image analysis software can then be applied globally to the entire tissue area or focally as needed. With an Aperio ScanScope XT system, we digitized 125 hematoxylin and eosin stained slides from 52 patients who had intracranial intravascular thrombi removed by mechanical clot retrieval devices. In analyzing the WSDIs, we identified a number of challenges: (1) Public freeware such as Image J and Cellprofiler could not analyze large high quality image files (1‐5 gigabytes) (2) Tissue section thickness can change staining intensity and cellular overlap (3) Tissue folds can increase color intensity (4) Faded staining of archival specimens can decrease color intensity (5) Identification of some cellular features may require manipulations like removing the condenser that are not easily done with a digitizer. These findings suggest that upfront preparation of high quality tissue sections of the correct thickness and staining intensity is particularly important for WSDI analysis. Cropping large image files and assigning pseudocolors with Adobe Photoshop can reduce file sizes. Development of image analysis freeware that can handle large image files will be crucial for greater adoption of WSDIs as a research tool.