1. An apparatus for selecting a candidate image frame, the apparatus comprising: a processor configured to generate at least one lesion value that represents a characteristic of a lesion included in each of a plurality of 2-dimensional image frames that form a 3-dimensional image; extract, from the image frames, at least one candidate image frame usable for correcting a boundary of the lesion based on the at least one lesion value; wherein the processor is configured to obtain a lesion value sum by adding the generated lesion values together to obtain the lesion value sum, or by applying a respective weight to each of the at least one lesion value and adding the weighted at least one lesion value together to obtain the lesion value sum; and extract the at least one candidate image frame from the image frames based on the lesion value sum.