  Involuntary subject motion is the main source of artifacts in weight-bearing
cone-beam CT of the knee. To achieve image quality for clinical diagnosis, the
motion needs to be compensated. We propose to use inertial measurement units
(IMUs) attached to the leg for motion estimation. We perform a simulation study
using real motion recorded with an optical tracking system. Three IMU-based
correction approaches are evaluated, namely rigid motion correction, non-rigid
2D projection deformation and non-rigid 3D dynamic reconstruction. We present
an initialization process based on the system geometry. With an IMU noise
simulation, we investigate the applicability of the proposed methods in real
applications. All proposed IMU-based approaches correct motion at least as good
as a state-of-the-art marker-based approach. The structural similarity index
and the root mean squared error between motion-free and motion corrected
volumes are improved by 24-35% and 78-85%, respectively, compared with the
uncorrected case. The noise analysis shows that the noise levels of
commercially available IMUs need to be improved by a factor of $10^5$ which is
currently only achieved by specialized hardware not robust enough for the
application. The presented study confirms the feasibility of this novel
approach and defines improvements necessary for a real application.
