Methods are provided for determining flow resistance within at least a portion of a vessel, whereby at least a partial biological tree image is obtained and resistance is calculated therefrom based upon at least the length of a defined vessel portion and a diameter of a stem vessel at a location proximal to a vessel crown. Methods are also provided for determining vessel volume, whereby at least a partial biological tree image is obtained and cumulative crown volume is calculated based on at least the diameter and length of the stem segment.