  Inspired by classic generative adversarial networks (GAN), we propose a novel
end-to-end adversarial neural network, called SegAN, for the task of medical
image segmentation. Since image segmentation requires dense, pixel-level
labeling, the single scalar real/fake output of a classic GAN's discriminator
may be ineffective in producing stable and sufficient gradient feedback to the
networks. Instead, we use a fully convolutional neural network as the segmentor
to generate segmentation label maps, and propose a novel adversarial critic
network with a multi-scale $L_1$ loss function to force the critic and
segmentor to learn both global and local features that capture long- and
short-range spatial relationships between pixels. In our SegAN framework, the
segmentor and critic networks are trained in an alternating fashion in a
min-max game: The critic takes as input a pair of images, (original_image $*$
predicted_label_map, original_image $*$ ground_truth_label_map), and then is
trained by maximizing a multi-scale loss function; The segmentor is trained
with only gradients passed along by the critic, with the aim to minimize the
multi-scale loss function. We show that such a SegAN framework is more
effective and stable for the segmentation task, and it leads to better
performance than the state-of-the-art U-net segmentation method. We tested our
SegAN method using datasets from the MICCAI BRATS brain tumor segmentation
challenge. Extensive experimental results demonstrate the effectiveness of the
proposed SegAN with multi-scale loss: on BRATS 2013 SegAN gives performance
comparable to the state-of-the-art for whole tumor and tumor core segmentation
while achieves better precision and sensitivity for Gd-enhance tumor core
segmentation; on BRATS 2015 SegAN achieves better performance than the
state-of-the-art in both dice score and precision.
