An image may be defined as a two-dimensional function f(x, y) where x and y represent the spatial coordinates and the function (f) represents the amplitude at any given pair of coordinates (x, y). The amplitude (f) is also often referred to as the gray level or the intensity of that point in the image. A digital image is thus composed of a finite number of these x, y elements where all of them have an exact location and value. These picture elements are often referred to as pixels. 3D images may subsequently be defined by a three-dimensional function (x, y, z) and the individual elements are often referred to as voxels. The image quality is an important parameter in the field of radiology and the term spatial resolution refers to the capability of differentiating two neighboring objects in the image. Another important resolution property is the temporal resolution, which refers to the quality of the imaging with respect to time.