  To estimate the spatial resolution of microtomographs, a test object on the
submicrometer scale was prepared by focused ion beam milling and subjected to
microtomographic analysis. Since human tissues are composed of cells and
extracellular matrices with micrometer and submicrometer structures, it is
important to investigate the three-dimensional spatial resolution of
microtomographs used to visualize microstructures of human tissues. The
resolutions along the direction within the tomographic slice plane (in-plane
resolution) and perpendicular to it (through-plane resolution) were determined
from the modulation transfer function of square-wave patterns. The in-plane
resolution was estimated to be 1.2 um from the modulation transfer function of
the non-zoom image. In contrast, the zoom image gave the in-plane resolution of
0.8 um. This in-plane resolution is comparable to the through-plane resolution,
which was estimated to be 0.8 um. Although the two-dimensional radiographs were
taken with the pixel width of half the x-ray optics resolution, these
three-dimensional resolution analyses indicated that the zoom reconstruction
should be performed to achieve the in-plane resolution comparable to the x-ray
optics resolution. The submicrometer three-dimensional analysis was applied in
the structural study of human cerebral tissue stained with high-Z elements and
the obtained tomograms revealed that the microtomographic analysis allows
visualization of the subcellular structures of the cerebral tissue.
