The following provides an exemplary method. An image is generated. Scan data generated by the sensing of a subject brain is received and a sequence of volumetric-images are accessed. For at least some of the voxels in at least some of the volumetric images, a change value is determined for the voxel by comparing the current-intensity value of the voxel to the adjacent-intensity value of the comparison voxel. For at least some of the plurality volumetric images, a first-aggregate is determined using at least a mean value of change values of the volumetric image and a second-aggregate is determined using at least a median value of change values of the volumetric image. At least one, but not all, of the volumetric images is determined as invalid as a result of the aggregates.