  Structural magnetic resonance imaging (MRI) has been widely utilized for
analysis and diagnosis of brain diseases. Automatic segmentation of brain
tumors is a challenging task for computer-aided diagnosis due to low-tissue
contrast in the tumor subregions. To overcome this, we devise a novel
pixel-wise segmentation framework through a convolutional 3D to 2D MR patch
conversion model to predict class labels of the central pixel in the input
sliding patches. Precisely, we first extract 3D patches from each modality to
calibrate slices through the squeeze and excitation (SE) block. Then, the
output of the SE block is fed directly into subsequent bottleneck layers to
reduce the number of channels. Finally, the calibrated 2D slices are
concatenated to obtain multimodal features through a 2D convolutional neural
network (CNN) for prediction of the central pixel. In our architecture, both
local inter-slice and global intra-slice features are jointly exploited to
predict class label of the central voxel in a given patch through the 2D CNN
classifier. We implicitly apply all modalities through trainable parameters to
assign weights to the contributions of each sequence for segmentation.
Experimental results on the segmentation of brain tumors in multimodal MRI
scans (BraTS'19) demonstrate that our proposed method can efficiently segment
the tumor regions.
