Intimate combination of low- and high-resolution image data: I. Real-spacePET and (H2O)-H-1 MRI, PETAMRI

Two different types of (co-registered) images of the same slice of tissue w ill generally have different spatial resolutions, The judicious pixel-by-pi xel combination of their data can be accomplished to yield a single image e xhibiting properties of both. Here, axial (18)FDG PET and (H2O)-H-1 MR imag es of the human brain are used as the low- and high-resolution members of t he pair. A color scale is necessary in order to provide for separate intens ity parameters from the two image types. However, not all color scales can accommodate this separability. The HSV color model allows one to choose a c olor scale in which the intensity of the low-resolution image type is coded as hue, while that of the high-resolution type is coded as value, a reason ably independent parameter. Furthermore, the high-resolution image must hav e high contrast and be quantitative in the same sense as the low-resolution image almost always is. Here, relaxographic MR images (naturally segmented quantitative (H2O)-H-1 spin-density components) are used. Their essentiall y complete contrast serves to effect an apparent editing function when enco ded as the value of the color scale. Thus, the combination of 1(8F)DG PET i mages with gray-matter (GM) relaxographic (H2O)-H-1 images produces visuall y "GM-edited" (18)FDG PETAMR (positron emission tomography and magnetic res onance) images, These exhibit the high sensitivity to tracer amounts charac teristic of PET along with the high spatial resolution of (H2O)-H-1 MRI, At the same time, however, they retain the complete quantitative measures of each of their basis images. Magn Reson Med 42:345-360, 1999. Published 1999 Wiley-Liss, Inc.dagger