  Ultrasound is a non-invasive imaging modality that can be conveniently used
to classify suspicious breast nodules and potentially detect the onset of
breast cancer. Recently, Convolutional Neural Networks (CNN) techniques have
shown promising results in classifying ultrasound images of the breast into
benign or malignant. However, CNN inference acts as a black-box model, and as
such, its decision-making is not interpretable. Therefore, increasing effort
has been dedicated to explaining this process, most notably through GRAD-CAM
and other techniques that provide visual explanations into inner workings of
CNNs. In addition to interpretation, these methods provide clinically important
information, such as identifying the location for biopsy or treatment. In this
work, we analyze how adversarial assaults that are practically undetectable may
be devised to alter these importance maps dramatically. Furthermore, we will
show that this change in the importance maps can come with or without altering
the classification result, rendering them even harder to detect. As such, care
must be taken when using these importance maps to shed light on the inner
workings of deep learning. Finally, we utilize Multi-Task Learning (MTL) and
propose a new network based on ResNet-50 to improve the classification
accuracies. Our sensitivity and specificity is comparable to the state of the
art results.
