  Identifying the type of kidney stones can allow urologists to determine their
cause of formation, improving the prescription of appropriate treatments to
diminish future relapses. Currently, the associated ex-vivo diagnosis (known as
Morpho-constitutional Analysis, MCA) is time-consuming, expensive and requires
a great deal of experience, as it requires a visual analysis component that is
highly operator dependant. Recently, machine learning methods have been
developed for in-vivo endoscopic stone recognition. Deep Learning (DL) based
methods outperform non-DL methods in terms of accuracy but lack explainability.
Despite this trade-off, when it comes to making high-stakes decisions, it's
important to prioritize understandable Computer-Aided Diagnosis (CADx) that
suggests a course of action based on reasonable evidence, rather than a model
prescribing a course of action. In this proposal, we learn Prototypical Parts
(PPs) per kidney stone subtype, which are used by the DL model to generate an
output classification. Using PPs in the classification task enables case-based
reasoning explanations for such output, thus making the model interpretable. In
addition, we modify global visual characteristics to describe their relevance
to the PPs and the sensitivity of our model's performance. With this, we
provide explanations with additional information at the sample, class and model
levels in contrast to previous works. Although our implementation's average
accuracy is lower than state-of-the-art (SOTA) non-interpretable DL models by
1.5 %, our models perform 2.8% better on perturbed images with a lower standard
deviation, without adversarial training. Thus, Learning PPs has the potential
to create more robust DL models.
