Deep Learning Models to Characterize Smooth Muscle Fibers in Hematoxylin and Eosin Stained Histopathological Images of the Urinary Bladder

Muscularis propria (MP) and muscularis mucosa (MM), two types of smooth muscle fibers in the urinary bladder, are major benchmarks in staging bladder cancer to distinguish between muscle-invasive (MP invasion) and non-muscle-invasive (MM invasion) diseases. While patients with non-muscle-invasive tumor can be treated conservatively involving transurethral resection (TUR) only, more aggressive treatment options, such as removal of the entire bladder, known as radical cystectomy (RC) which may severely degrade the quality of patient’s life, are often required in those with muscle-invasive tumor. Hence, given two types of image datasets, hematoxylin & eosin-stained histopathological images from RC and TUR specimens, we propose the first deep learning-based method for efficient characterization of MP. The proposed method is intended to aid the pathologists as a decision support system by facilitating accurate staging of bladder cancer. In this work, we aim to semantically segment the TUR images into MP and non-MP regions using two different approaches, patch-to-label and pixel-to-label. We evaluate four different state-of-the-art CNN-based models (VGG16, ResNet18, SqueezeNet, and MobileNetV2) and semantic segmentation-based models (U-Net, MA-Net, DeepLabv3+, and FPN) and compare their performance metrics at the pixel-level. The SqueezeNet model (mean Jaccard Index: 95.44%, mean dice coefficient: 97.66%) in patch-to-label approach and the MA-Net model (mean Jaccard Index: 96.64%, mean dice coefficient: 98.29%) in pixel-to-label approach are the best among tested models. Although pixel-to-label approach is marginally better than the patch-to-label approach based on evaluation metrics, the latter is computationally efficient using least trainable parameters