Respiratory motion compensation studies using a 3D robotic motion simulator and optical/electromagnetic tracking technologies

Respiratory motion can degrade the quality of nuclear medicine images, especially when attempting to identify small abnormalities, make quantitative estimates of activity concentration, or track the time-varying location of a tumor. Thus, we are developing methods for respiratory motion compensation and testing these methods using robotic devices. The testing device is a computer controlled 3-axis motion simulator that can hold activity-filled phantoms or spheres and move them along pre-programmed paths to simulate respiratory motion. The motion of the platform is programmed in advance and can also be monitored using an optical tracking system, thus providing a solid ground truth for the time-dependent activity concentration. Registration between the coordinate space of the PET or SPET scanner and the optical tracker coordinate system is based on a set of common points (mapped out using the motion simulator) that are visible to both systems. We have also used electromagnetic tracking and optical tracking to obtain realistic respiratory motion data from patients and animal models. These data can be transformed into motion simulator paths, thus providing us with breathing patterns that accurately reflect the nonstationary and variable nature of human respiration. The simulator thus provides a highly useful tool for repeatably testing different approaches to motion-compensated image reconstruction or gated acquisition schemes.