Fig 2. Top: Schematic comparison of relative VOI size and coverage between single-voxel, 2D or 3D multivoxel, and WBNAA in the human brain. Note that the single- and multivoxel VOIs cover only small fractions of the brain volume and must be kept away from the skull, missing most of the cortex, whereas WBNAA accounts for the entire brain. Bottom: The consequence of a 1-mm (1 guiding-image pixel) placemat error in each direction, x, y, and z, on a 1-cm voxel in a serial study. This 10% error leads to only 70% of the VOI common to both measurements. Note that though this error is technically unavoidable in localized spectroscopy, it is not an issue for WBNAA, as shown in the top portion of the lower panel.