  We integrate a small and portable medical x-ray device with mechanical
testing equipment to enable in-situ, non-invasive measurements of a granular
material's response to mechanical loading. We employ an orthopedic C-arm as the
x-ray source and detector to image samples mounted in the materials tester. We
discuss the design of a custom rotation stage, which allows for sample rotation
and tomographic reconstruction under applied compressive stress. We then
discuss the calibration of the system for 3d computed tomography, as well as
the subsequent image reconstruction process. Using this system to reconstruct
packings of 3d-printed particles, we resolve packing features with 0.52 mm
resolution in a (60 mm)$^3$ field of view. By analyzing the performance bounds
of the system, we demonstrate that the reconstructions exhibit only moderate
noise.
