  The penetration power of x-rays allows one to image large objects. For
example, centimeter-sized specimens can be imaged with micron-level resolution
using synchrotron sources. In this case, however, the limited beam diameter and
detector size preclude the acquisition of the full sample in a single take,
necessitating strategies for combining data from multiple regions. Object
stitching involves the combination of local tomography data from overlapping
regions, while projection stitching involves the collection of projections at
multiple offset positions from the rotation axis followed by data merging and
reconstruction. We compare these two approaches in terms of radiation dose
applied to the specimen, and reconstructed image quality. Object stitching
involves an easier data alignment problem, and immediate viewing of subregions
before the entire dataset has been acquired. Projection stitching is more
dose-efficient, and avoids certain artifacts of local tomography; however, it
also involves a more difficult data assembly and alignment procedure, in that
it is more sensitive to accumulative registration error.
