1. Introduction

Medical imaging has been forever revolutionized by the technological and digital boom that has occurred over the last few decades. The idea of quantitative analysis of medical images by a computer was first reported in the 1960s (Lodwick et al, Radiology, 80(2):273–275, 1963, [1], Meyers et al, Radiology 83(6):1029–1034, 1964, [2], Winsberg et al, Radiology 89(2):211–215, 1967, [3], Kruger et al, IEEE Trans Biomed Eng, 3:174–186, 1972, [4], Kruger et al, IEEE Trans Syst Man Cybern, 1:40–49, 1974, [5], Toriwaki et al, Comput Graph Image Process, 2(3):252–271, 1973, [6]), and at that time it was generally assumed that computers could replace medical practitioners in detecting abnormalities, because computers and machines are better at performing certain tasks than human beings are. However, growth of this sector remained initially quite limited due to the fact that computers were not sufficiently powerful, advanced image-processing techniques were not available, and digital images were not easily accessible (Doi, Comput Med Imaging Graph, 31(4–5):198–211, 2007, [7]). Since those days, along with the evolution of technology and digital imaging in general, the idea of actually replacing medical practitioners has also evolved, bringing forth the idea of Computer Aided Diagnosis (CAD), in which the computer output can by utilized by medical practitioners, but not replace them. This field, which is based on the idea that digital medical images are analyzed quantitatively by computers, has spread widely and quickly, becoming one of the major research subjects in medical imaging. Therefore, the development of advanced image processing techniques is required in order to obtain quantitative information (Doi, Comput Med Imaging Graph, 31(4–5):198–211, 2007, [7]).