Deep Learning

Reducing the amount of radiation in X-ray computed tomography has been an
active area of research in the recent years. The reduction of radiation has the downside of
degrading the quality of the CT scans by increasing the ratio of the noise. Therefore, some
techniques must be utilized to enhance the quality of images. In this research, we approach
the denoising problem using two class of algorithms and we reduce the noise in CT scans
that have been acquired with 75% less dose to the patient compared to the normal dose
scans.
Initially, we implemented wavelet denoising to successfully reduce the noise in
low-dose X-ray computed tomography (CT) images. The denoising was improved by
finding the optimal threshold value instead of a non-optimal selected value. The mean
structural similarity (MSSIM) index was used as the objective function for the
optimization. The denoising performance of combinations of wavelet families, wavelet
orders, decomposition levels, and thresholding methods were investigated. Results of this study have revealed the best combinations of wavelet orders and decomposition levels for
low dose CT denoising. In addition, a new shrinkage function is proposed that provides
better denoising results compared to the traditional ones without requiring a selected
parameter.
Alternatively, convolutional neural networks were employed using different
architectures to resolve the same denoising problem. This new approach improved
denoising even more in comparison to the wavelet denoising.

In this research, image segmentation and visual odometry estimations in real time
are addressed, and two main contributions were made to this field. First, a new image
segmentation and classification algorithm named DilatedU-NET is introduced. This deep
learning based algorithm is able to process seven frames per-second and achieves over
84% accuracy using the Cityscapes dataset. Secondly, a new method to estimate visual
odometry is introduced. Using the KITTI benchmark dataset as a baseline, the visual
odometry error was more significant than could be accurately measured. However, the
robust framerate speed made up for this, able to process 15 frames per second.

Melanoma, a severe and life-threatening skin cancer, is commonly misdiagnosed
or left undiagnosed. Advances in artificial intelligence, particularly deep learning,
have enabled the design and implementation of intelligent solutions to skin lesion
detection and classification from visible light images, which are capable of performing
early and accurate diagnosis of melanoma and other types of skin diseases. This work
presents solutions to the problems of skin lesion segmentation and classification. The
proposed classification approach leverages convolutional neural networks and transfer
learning. Additionally, the impact of segmentation (i.e., isolating the lesion from the
rest of the image) on the performance of the classifier is investigated, leading to the
conclusion that there is an optimal region between “dermatologist segmented” and
“not segmented” that produces best results, suggesting that the context around a
lesion is helpful as the model is trained and built. Generative adversarial networks,
in the context of extending limited datasets by creating synthetic samples of skin
lesions, are also explored. The robustness and security of skin lesion classifiers using
convolutional neural networks are examined and stress-tested by implementing
adversarial examples.

Automatic target recognition capabilities in autonomous underwater vehicles has
been a daunting task, largely due to the noisy nature of sonar imagery and due to the lack
of publicly available sonar data. Machine learning techniques have made great strides in
tackling this feat, although not much research has been done regarding deep learning
techniques for side-scan sonar imagery. Here, a state-of-the-art deep learning object
detection method is adapted for side-scan sonar imagery, with results supporting a simple
yet robust method to detect objects/anomalies along the seabed. A systematic procedure
was employed in transfer learning a pre-trained convolutional neural network in order to
learn the pixel-intensity based features of seafloor anomalies in sonar images. Using this
process, newly trained convolutional neural network models were produced using
relatively small training datasets and tested to show reasonably accurate anomaly
detection and classification with little to no false alarms.