Simulation of motion artifacts in offset flat-panel cone-beam CT

Cone-beam computed tomography (CBCT) with a tangentially offset flat-panel detector is used for target imaging in image-guided radiotherapy and for localization and attenuation correction in SPECT/CT imaging. The offset-detector geometry offers a large field-of-view for a given detector size. Data are acquired on a circular trajectory over 360 degrees, with gantry rotation times ranging from 12 s to 60 s and longer on commercially available systems. These acquisition times, much longer than in conventional CT, make flat-panel CBCT more susceptible to motion artifacts from voluntary or involuntary patient motion. Here, we present phantom studies on motion artifacts in flat-panel CBCT, with the goal to facilitate better artifact assessment on clinical cases and to provide a basis for future investigations into artifact mitigation methods. Software phantoms for five typically observed motion types were simulated; phantom reconstructions are presented and compared to clinical cases. In addition, three analytic and iterative reconstruction methods were evaluated with respect to their performance on motion-affected data.