  Multimodal medical image fusion helps in combining contrasting features from
two or more input imaging modalities to represent fused information in a single
image. One of the pivotal clinical applications of medical image fusion is the
merging of anatomical and functional modalities for fast diagnosis of malignant
tissues. In this paper, we present a novel end-to-end unsupervised
learning-based Convolutional Neural Network (CNN) for fusing the high and low
frequency components of MRI-PET grayscale image pairs, publicly available at
ADNI, by exploiting Structural Similarity Index (SSIM) as the loss function
during training. We then apply color coding for the visualization of the fused
image by quantifying the contribution of each input image in terms of the
partial derivatives of the fused image. We find that our fusion and
visualization approach results in better visual perception of the fused image,
while also comparing favorably to previous methods when applying various
quantitative assessment metrics.
