  The functional analysis of the left atrium (LA) is important for evaluating
cardiac health and understanding diseases like atrial fibrillation. Cine MRI is
ideally placed for the detailed 3D characterisation of LA motion and
deformation, but it is lacking appropriate acquisition and analysis tools. In
this paper, we present Analysis for Left Atrial Displacements and Deformations
using unsupervIsed neural Networks, \textit{Aladdin}, to automatically and
reliably characterise regional LA deformations from high-resolution 3D Cine
MRI. The tool includes: an online few-shot segmentation network (Aladdin-S), an
online unsupervised image registration network (Aladdin-R), and a strain
calculations pipeline tailored to the LA. We create maps of LA Displacement
Vector Field (DVF) magnitude and LA principal strain values from images of 10
healthy volunteers and 8 patients with cardiovascular disease (CVD). We
additionally create an atlas of these biomarkers using the data from the
healthy volunteers. Aladdin is able to accurately track the LA wall across the
cardiac cycle and characterize its motion and deformation. The overall DVF
magnitude and principal strain values are significantly higher in the healthy
group vs CVD patients: $2.85 \pm 1.59~mm$ and $0.09 \pm 0.05$ vs $1.96 \pm
0.74~mm$ and $0.03 \pm 0.04$, respectively. The time course of these metrics is
also different in the two groups, with a more marked active contraction phase
observed in the healthy cohort. Finally, utilizing the LA atlas allows us to
identify regional deviations from the population distribution that may indicate
focal tissue abnormalities. The proposed tool for the quantification of novel
regional LA deformation biomarkers should have important clinical applications.
The source code, anonymized images, generated maps and atlas are publicly
available: https://github.com/cgalaz01/aladdin_cmr_la.
