  Accurate diagnosis of Alzheimer's disease (AD) is both challenging and time
consuming. With a systematic approach for early detection and diagnosis of AD,
steps can be taken towards the treatment and prevention of the disease. This
study explores the practical application of deep learning models for diagnosis
of AD. Due to computational complexity, large training times and limited
availability of labelled dataset, a 3D full brain CNN (convolutional neural
network) is not commonly used, and researchers often prefer 2D CNN variants. In
this study, full brain 3D version of well-known 2D CNNs were designed, trained
and tested for diagnosis of various stages of AD. Deep learning approach shows
good performance in differentiating various stages of AD for more than 1500
full brain volumes. Along with classification, the deep learning model is
capable of extracting features which are key in differentiating the various
categories. The extracted features align with meaningful anatomical landmarks,
that are currently considered important in identification of AD by experts. An
ensemble of all the algorithm was also tested and the performance of the
ensemble algorithm was superior to any individual algorithm, further improving
diagnosis ability. The 3D versions of the trained CNNs and their ensemble have
the potential to be incorporated in software packages that can be used by
physicians/radiologists to assist them in better diagnosis of AD.
