  Progress in high-resolution x-ray microtomography has provided us with a
practical approach to determining three-dimensional (3D) structures of opaque
samples at micrometer to submicrometer resolution. In this review, we give an
introduction to hard x-ray microtomography and its application to the
visualization of 3D structures of biological soft tissues. Practical aspects of
sample preparation, handling, data collection, 3D reconstruction, and structure
analysis are described. Furthermore, different sample contrasting methods are
approached in detail. Examples of microtomographic studies are overviewed to
present an outline of biological applications of x-ray microtomography. We also
provide perspectives of biological microtomography as the convergence of
sciences in x-ray optics, biology, and structural analysis.
