Rigid and non-rigid motion compensation in weight-bearing cone-beam CT of the knee using (noisy) inertial measurements

TL;DR

This study explores using inertial measurement units (IMUs) to correct involuntary knee motion artifacts in weight-bearing cone-beam CT, demonstrating comparable effectiveness to marker-based methods but highlighting hardware noise limitations.

Contribution

The paper introduces IMU-based motion correction methods for knee CBCT, including rigid and non-rigid approaches, and evaluates their performance through simulation with real motion data.

Findings

IMU-based correction methods improve image quality metrics by up to 35% and 85%.

All proposed IMU approaches perform comparably to marker-based methods.

Current IMU noise levels are insufficient for practical application without hardware improvements.

Abstract

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.