An apparatus for sizing a stent for placement in a vessel, the apparatus comprising: a processor having imaging data for the vessel which will be stented, the processor being configured to execute a program having the steps: dividing the vessel into a plurality of segments, each segment being defined as the space between branches of the vessel; selecting a segment as a starting point that appears to be substantially disease free; defining a diameter at the starting point to be a maximum diameter; characterized in that the program further has the following steps: calculating a maximum diameter of an adjacent segment according to a power law; measuring an actual diameter of the adjacent segment; selecting the larger of the calculated maximum diameter or the actual diameter as the selected maximum diameter of the adjacent segment; using the selected maximum diameter to find a maximum diameter of the next segment; iteratively proceeding until each segment in the plurality of segments is examined; and displaying the results to allow a user to select a stent size based on the selected maximum diameter of an end proximal segment and the selected maximum diameter of an end distal segment of a landing zone for the stent within the plurality of segments. a processor having imaging data for the vessel which will be stented, the processor being configured to execute a program having the steps: dividing the vessel into a plurality of segments, each segment being defined as the space between branches of the vessel; selecting a segment as a starting point that appears to be substantially disease free; defining a diameter at the starting point to be a maximum diameter; dividing the vessel into a plurality of segments, each segment being defined as the space between branches of the vessel; selecting a segment as a starting point that appears to be substantially disease free; defining a diameter at the starting point to be a maximum diameter; calculating a maximum diameter of an adjacent segment according to a power law; measuring an actual diameter of the adjacent segment; selecting the larger of the calculated maximum diameter or the actual diameter as the selected maximum diameter of the adjacent segment; using the selected maximum diameter to find a maximum diameter of the next segment; iteratively proceeding until each segment in the plurality of segments is examined; and displaying the results to allow a user to select a stent size based on the selected maximum diameter of an end proximal segment and the selected maximum diameter of an end distal segment of a landing zone for the stent within the plurality of segments. measuring an actual diameter of the adjacent segment; selecting the larger of the calculated maximum diameter or the actual diameter as the selected maximum diameter of the adjacent segment; using the selected maximum diameter to find a maximum diameter of the next segment; iteratively proceeding until each segment in the plurality of segments is examined; and displaying the results to allow a user to select a stent size based on the selected maximum diameter of an end proximal segment and the selected maximum diameter of an end distal segment of a landing zone for the stent within the plurality of segments.