  The use of computed tomography (CT) imaging has become of increasing interest
to academic areas outside of the field of medical imaging and industrial
inspection, e.g., to biology and cultural heritage research. The pecularities
of these fields, however, sometimes require that objects need to be imaged
on-site, e.g., in field-work conditions or in museum collections. Under these
circumstances, it is often not possible to use a commercial device and a custom
solution is the only viable option. In order to achieve high image quality
under adverse conditions, reliable calibration and trajectory reproduction are
usually key requirements for any custom CT scanning system. Here, we introduce
the construction of a low-cost disassemblable CT scanner that allows
calibration even when trajectory reproduction is not possible due to the
limitations imposed by the project conditions. Using 3D-printed in-image
calibration phantoms, we compute a projection matrix directly from each
captured X-ray projection. We describe our method in detail and show successful
tomographic reconstructions of several specimen as proof of concept.
