Figure 1a. Geometry of isotropic and anisotropic acquisitions. Anisotropic data consist of voxels that have a section thickness greater than the x- and y-axis dimensions of the facing pixels. Section thickness along the z-axis is four times the size of each pixel in a but only twice the size of each pixel in b. Although both data sets are anisotropic, there is a significant difference in image quality for three-dimensional applications, with improved longitudinal spatial resolution in b compared with that in a. When the section thickness is equal to the pixel size, as in c, the data are isotropic.