1. A system, comprising: a memory; and one or more processing devices configured to: determine intersection points of a representation of a surface in an image space with cubes defining the image space, the surface defining a surface of an object, the determining the intersection points including: defining an initial representation of the surface in the image space; refining the initial representation of the surface in the image space by segmenting the object and refining the initial representation to correspond to a segmented portion of the object; and determining the intersection points of the refined representation of the surface with the cubes defining the image space; and determine an estimated mass of at least a portion of the object by: determining an estimated mass contribution of a first set of cubes contained entirely within the representation of the surface; determining an estimated mass contribution of a second set of cubes having intersection points with the representation of the surface; and estimating a mass of the at least a portion of the object based on the estimated mass contribution of the first set of cubes and the estimated mass contribution of the second set of cubes, wherein refining the initial representation comprises deforming the initial representation by iteratively applying local movement vectors to vertexes of a plurality of triangles defining the surface and a local movement vector u of a vertex of a triangle is defined by: 
 u=u 1 +u 2 +u 3 , where u 1 is a vector component representing local movement within the surface, u 2 is a vector component representing local movement along surface normal, and u 3 is a vector component representing local movement deforming the surface toward a surface of the segmented object.