1. A method for nodule segmentation comprising: selecting an image series group of image slices for a nodule; initializing segmentation comprising: selecting one image slice from the image series group where a nodule periphery is the most distinguishable as a center slice; for the center slice, calculating major and minor axes of an ellipse model by searching for image intensity peaks from intensity gradients representing the nodule; calculating mean and standard deviation intensity estimates from the ellipse model for beginning mean and standard deviation intensity estimate values; selecting an adaptive intensity model based on the beginning mean and standard deviation intensity estimate values; performing an Iterated Condition Mode (ICM) comprising: pre-segmenting the nodule on the center slice using the adaptive intensity model in conjunction with Markov Random Field (MRF) based modeling to calculate conditional intensity probability mean and standard deviation values for the nodule and background intensities; updating the adaptive intensity model with the conditional intensity probability mean and standard deviation values for the nodule and background intensities obtained from pre-segmentation; segmenting the nodule using the updated adaptive intensity model in conjunction with MRF based modeling to calculate conditional intensity probability mean and standard deviation values for the nodule and background intensities; updating the adaptive intensity model with the conditional intensity probability mean and standard deviation values for the nodule and background intensities obtained from segmentation; and calculating a growth rate measurement for the nodule.