  Involuntary motion during weight-bearing cone-beam computed tomography (CT)
scans of the knee causes artifacts in the reconstructed volumes making them
unusable for clinical diagnosis. Currently, image-based or marker-based methods
are applied to correct for this motion, but often require long execution or
preparation times. We propose to attach an inertial measurement unit (IMU)
containing an accelerometer and a gyroscope to the leg of the subject in order
to measure the motion during the scan and correct for it. To validate this
approach, we present a simulation study using real motion measured with an
optical 3D tracking system. With this motion, an XCAT numerical knee phantom is
non-rigidly deformed during a simulated CT scan creating motion corrupted
projections. A biomechanical model is animated with the same tracked motion in
order to generate measurements of an IMU placed below the knee. In our proposed
multi-stage algorithm, these signals are transformed to the global coordinate
system of the CT scan and applied for motion compensation during
reconstruction. Our proposed approach can effectively reduce motion artifacts
in the reconstructed volumes. Compared to the motion corrupted case, the
average structural similarity index and root mean squared error with respect to
the no-motion case improved by 13-21% and 68-70%, respectively. These results
are qualitatively and quantitatively on par with a state-of-the-art
marker-based method we compared our approach to. The presented study shows the
feasibility of this novel approach, and yields promising results towards a
purely IMU-based motion compensation in C-arm CT.
