Figure 6.

Slices of representative off-diagonal elements in the axial plane at a fixed radius of 80 mm (the radius at which the highest nonstationarity in the NPS was observed). The images to the left are the axial NPS for each of the three objects (air, bowtie, and cylinder). For each object, we show slices of the first, second, and tenth off-diagonal elements in the x-direction. For example, the images of the first off-diagonal elements show the correlation between that frequency and a frequency one bin higher in the x-direction. Note that the images are zero-padded to be the same size. (i.e., the images for the tenth off-diagonal elements do not contain data for the last 10 frequencies in the x-direction.) The grayscale is the magnitude of an element of the NPS or off-diagonal elements of the Σ_DFT. The scales for the NPS are the same for each phantom configuration, and the scales for the ODEs are all 1 order of magnitude smaller to enhance visibility but allow comparison with the NPS.