A method for analyzing scan data. In some embodiments, the method includes forming, from a first scan data array, a first mask, each element of the first mask being one or zero according to whether the corresponding element of the first scan data array exceeds a first threshold; forming, from the first scan data array, a second mask, each element of the second mask having a value of one or zero according to whether the corresponding element of the first scan data array exceeds a second threshold, the second threshold being less than the first threshold; and forming a fourth mask, the fourth mask being the element-wise product of the second mask and a third mask, the third mask being based on the first mask.