Calibration and evaluation of a motion measurement system for PET imaging studies (2311.18009v1)

Abstract: Positron Emission Tomography (PET) enables functional imaging of deep brain structures, but the bulk and weight of current systems preclude their use during many natural human activities, such as locomotion. The proposed long-term solution is to construct a robotic system that can support an imaging system surrounding the subject's head, and then move the system to accommodate natural motion. This requires a system to measure the motion of the head with respect to the imaging ring, for use by both the robotic system and the image reconstruction software. We report here the design, calibration, and experimental evaluation of a parallel string encoder mechanism for sensing this motion. Our results indicate that with kinematic calibration, the measurement system can achieve accuracy within 0.5mm, especially for small motions.

• The paper demonstrates a novel calibration technique achieving sub-0.5mm head motion tracking for PET imaging.
• The study introduces a Stewart platform-like robotic system with six string encoders to compensate for both coarse and fine movements.
• Experimental tests with dual robots confirmed the system's precision, marking a significant advancement in dynamic brain imaging.

Introduction

Positron Emission Tomography (PET) is a powerful tool used to capture images of bodily functions. PET scans require precision, as even small movements can disrupt the clarity and usability of the images. One area of significant interest is imaging the brain during natural human activities, like walking. However, the PET imaging devices are often too heavy and bulky to be worn, which makes scans during movement challenging.

Design of the Motion Measurement System

To address this challenge, researchers have developed a novel motion measurement system that can accurately track head movement to within 0.5mm – a prerequisite for PET imaging during natural activities. The system is essentially a robotic structure that holds the imaging equipment around a person's head and moves in response to head movements. The design resembles a parallel robot, known as a Stewart platform, with six string encoders (like sophisticated measuring tapes) connecting the PET detector to a helmet worn by the subject. This system's readings will guide the robot to reposition the imaging ring to compensate for larger, coarse movements and also to offer data for finer motion compensations during image reconstruction.

Calibration and Assessment of the System

Through rigorous calibration and experimental validation, researchers managed to fine-tune the system. The calibration corrected for small deviations in the string lengths and attachment points, a necessary adjustment due to manufacturing imperfections. Subsequent testing was carried out with a setup involving two robots: one to simulate the head's motion and another to hold the imaging ring. This setup verified the string system's measurement accuracy against the robot's precision movements.

Results and Future Work

The system was able to perform within the desired specifications, achieving less than 0.5mm error in head motion tracking, which is within the thresholds needed for accurate imaging. Although the motion tested was static, the results are promising for more dynamic testing scenarios. Future development includes replicating realistic human head movements and pairing these with robotic PET ring adjustments.

In conclusion, the paper presents a significant step toward mobile PET imaging that could shift the paradigm of neuroscientific studies and enable new insights by capturing brain functions during everyday tasks. The technology brings us closer to understanding the dynamics of the brain when the body is in motion.