Evaluation of a motion measurement system for PET imaging studies (2311.17863v2)

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 and experimental evaluation of a parallel string encoder mechanism for sensing this motion. Our preliminary results indicate that the measurement system may achieve accuracy within 0.5 mm, especially for small motions, with improved accuracy possible through kinematic calibration.

• The paper presents a novel mechanical sensing system using a Stewart platform with six string encoders, achieving translation errors under 0.3mm.
• It demonstrates the system’s ability to compensate for coarse and fine head motions, ensuring accurate PET imaging corrections.
• The study highlights the potential for dynamic, real-world PET imaging applications in neuroscience research by tracking natural movement.

Introduction

The relevance and intricate detail of Positron Emission Tomography (PET) imaging in capturing functional images of the brain's structures are vital in medical science. PET imaging is a critical tool in neuroscience, allowing researchers to measure brain activity by detecting gamma photons emitted from injected radioactive tracers. The technology, however, faces challenges when aimed to be used during natural human motions such as walking due to the substantial weight and size of current PET systems.

System Design and Kinematic Analysis

In response to the challenges posed by the significant weight of PET imaging systems, research has proposed a novel solution using a robotic system to support and move the PET imaging ring in sync with natural head movement. This robotic system aims to maintain the placement of the imaging ring around the subject's head through what is termed as 'coarse motion compensation.' To achieve fine motion compensation—motion corrected by image reconstruction algorithms—a measurement system is essential. The focus of this paper revolves around the design and experimental evaluation of a mechanical sensing system with a configuration known as a Stewart platform, which uses six string encoders determining the position of a helmet relative to the imaging ring.

Mechanical Measurement System Evaluation

The mechanical measurement system proposed in the paper operates with six parallel string encoders arranged similarly to a suspended parallel robot. This system approximates the PET imaging ring's structural dynamics and actively adjusts to measure the helmet's (and thus the head's) motion with a high degree of accuracy, possibly within 0.5mm for minimal motion. Initial results suggest that the errors in position measurements are less than 0.3mm for translations along all three axes and for certain axis rotations, aligning with the desired accuracy for PET imaging corrections.

Future Development and Applications

The implications of this mechanical system are significant as it could allow for PET imaging during natural motion, vastly expanding the contexts in which brain imaging could be applied. Future iterations of this research would involve using robots to simulate head movements based on previously collected human motion data, thus refining the accuracy of the system further. A potential development could be the robot's application for real 'head motion' providing ground truth displacements within experimental settings. This robust mechanical system adds value to the existing techniques of PET imaging, inviting new prospects for neuroscience research where PET imaging can be used in dynamic, real-world conditions.