  Advancement in digital pathology and artificial intelligence has enabled deep
learning-based computer vision techniques for automated disease diagnosis and
prognosis. However, WSIs present unique computational and algorithmic
challenges. WSIs are gigapixel-sized, making them infeasible to be used
directly for training deep neural networks. Hence, for modeling, a two-stage
approach is adopted: Patch representations are extracted first, followed by the
aggregation for WSI prediction. These approaches require detailed pixel-level
annotations for training the patch encoder. However, obtaining these
annotations is time-consuming and tedious for medical experts. Transfer
learning is used to address this gap and deep learning architectures
pre-trained on ImageNet are used for generating patch-level representation.
Even though ImageNet differs significantly from histopathology data,
pre-trained networks have been shown to perform impressively on histopathology
data. Also, progress in self-supervised and multi-task learning coupled with
the release of multiple histopathology data has led to the release of
histopathology-specific networks. In this work, we compare the performance of
features extracted from networks trained on ImageNet and histopathology data.
We use an attention pooling network over these extracted features for
slide-level aggregation. We investigate if features learned using more complex
networks lead to gain in performance. We use a simple top-k sampling approach
for fine-tuning framework and study the representation similarity between
frozen and fine-tuned networks using Centered Kernel Alignment. Further, to
examine if intermediate block representation is better suited for feature
extraction and ImageNet architectures are unnecessarily large for
histopathology, we truncate the blocks of ResNet18 and DenseNet121 and examine
the performance.
