1. One or more computer-readable media comprising computer-readable instructions for performing: receiving a digital representation of at least a portion of an anatomical structure, wherein the digital representation comprises a representation of at least one feature; classifying digital representation components of the digital representation as being of respective tissue types based at least on proximity of the components to an iso-boundary of the digital representation and a curvature type of the iso-boundary, wherein the iso-boundary is positioned between representations of lumen and wall in the digital representation; and based on the respective tissue types of the digital representation components, determining an enclosing three-dimensional boundary of the at least one feature within the digital representation.