Feasibility of Motion Compensation using Inertial Measurement in C-arm CT

C-arm cone-beam CT (CBCT) systems are highly flexible regarding patient position and scan trajectory, which enables scanning a subject's knee joint under weight-bearing conditions. This is of interest, since the knee joint has shown to have different properties under load. However, involuntary subject motion during these acquisitions results in motion artifacts in the reconstruction and thereby degrades image quality noticeably. A current state-of-the-art approach to correct for this motion tracks fiducial markers attached to the knee. However, the marker placement is tedious and time-consuming. To overcome this issue, in this work the feasibility of a novel approach for motion correction based on an Inertial Measurement Unit (IMU) attached to the subject is investigated. In a study, a moved pumpkin phantom with attached fiducial markers is scanned four times by a C-arm CBCT system moving on a horizontal trajectory. Simultaneously, the phantom's motion is recorded by an attached IMU measuring acceleration and angular velocity. The IMU measurements are validated against the motion estimates of the fiducial marker-based approach, which are transformed to the IMU's coordinate system beforehand. While the rotational signals show average correlations of up to 0.85, the translational signals do not show similarity, except for one axis with an average correlation of 0.75. A spectral analysis reveals that the frequencies of the C-arm movement during scanning overlap with those of the phantom motion. While the C-arm movement is estimated by the marker-based approach, it is not measured by the IMU, preventing a valid comparison of the signals with each other. Although these initial results indicate some challenges for further work, they also already show the potential of the IMU-based motion tracking.