10. Anisotropic Hybrid Network for Cross-Dimension Transferable Feature Learning in 3D Medical Images

While deep convolutional neural networks (CNN) have been successfully applied for 2D image analysis, it is still challenging to apply them to 3D anisotropic volumes, especially when the within-slice resolution is much higher than the between-slice resolution and when the amount of 3D volumes is relatively small. On one hand, direct learning of CNN with 3D convolution kernels suffers from the lack of data and likely ends up with poor generalization; insufficient GPU memory limits the model size or representational power. On the other hand, applying 2D CNN with generalizable features to 2D slices ignores between-slice information. Coupling 2D network with LSTM to further handle the between-slice information is not optimal due to the difficulty in LSTM learning. To overcome the above challenges, 3D anisotropic hybrid network (AH-Net) transfers convolutional features learned from 2D images to 3D anisotropic volumes. Such a transfer inherits the desired strong generalization capability for within-slice information while naturally exploiting between-slice information for more effective modeling. We show the effectiveness of the 3D AH-Net on two example medical image analysis applications, namely, lesion detection from a digital breast tomosynthesis volume, and liver, and liver tumor segmentation from a computed tomography volume.