Equivariant Symmetry-Aware Head Pose Estimation for Fetal MRI

We present E(3)-Pose, a novel fast pose estimation methodthat jointly and explicitly models rotation equivariance and object sym-metry. Our work is motivated by the challenging problem of accountingfor fetal head motion during a diagnostic MRI scan. We aim to enableautomatic adaptive prescription of diagnostic 2D MRI slices with 6-DoFhead pose estimation, supported by rapid low-resolution 3D MRI vol-umes acquired before each 2D slice. Existing pose estimation methodsstruggle to generalize to clinical volumes due to pose ambiguities inducedby inherent anatomical symmetries, as well as low resolution, noise, andartifacts. In contrast, E(3)-Pose captures anatomical symmetries andrigid pose equivariance by construction, and yields robust estimates ofthe fetal head pose. Our experiments on publicly available and represen-tative clinical fetal MRI datasets demonstrate the superior robustnessand generalization of our method across domains. Crucially, E(3)-Poseachieves state-of-the-art accuracy on clinical MRI volumes, supportingfuture clinical translation. Our implementation is publicly available1 .