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. Our preliminary results indicate that the measurement system may achieve accuracy within 0.5 mm, especially for small motions, with improved accuracy possible Positron Emission Tomography (PET) relies on the injection of a radioactive tracer, which is then preferentially absorbed by specific tissues (based on the choice of tracer). The absorbed tracer emits positrons that react with nearby electrons, creating a pair of annihilation (gamma) photons that travel in opposite directions and are detected by the PET imaging ring. Higher sensitivity can be achieved by placing the PET detectors as close as possible to the subject.

Given the high safety requirement when moving a 15-20 kg weight over a human head with a robot, we plan to Positron Emission Tomography (PET) relies on the injection utilize both mechanical and optical measurement systems, of a radioactive tracer, which is then preferentially and possibly also inertial sensing, to attain redundant sensing absorbed by specific tissues (based on the choice of tracer). of the relative motion between the subject's head and The absorbed tracer emits positrons that react with nearby the PET imaging ring. This paper addresses the design, electrons, creating a pair of annihilation (gamma) photons calibration, and evaluation of a mechanical sensing system, that travel in opposite directions and are detected by the consisting of six string encoders connecting the PET detector PET imaging ring. Higher sensitivity can be achieved by to a safety helmet attached to the subject's head.

Studies of the human brain during natural activities, such as locomotion, would benefit from the ability to image deep brain structures during these activities. While Positron Emission Tomography (PET) can image these structures, the bulk and weight of current scanners are not compatible with the desire for a wearable device. This has motivated the design of a robotic system to support a PET imaging system around the subject's head and to move the system to accommodate natural motion. We report here the design and experimental evaluation of a prototype robotic system that senses motion of a subject's head, using parallel string encoders connected between the robot-supported imaging ring and a helmet worn by the subject. This measurement is used to robotically move the imaging ring (coarse motion correction) and to compensate for residual motion during image reconstruction (fine motion correction). Minimization of latency and measurement error are the key design goals, respectively, for coarse and fine motion correction. The system is evaluated using recorded human head motions during locomotion, with a mock imaging system consisting of lasers and cameras, and is shown to provide an overall system latency of about 80 ms, which is sufficient for coarse motion correction and collision avoidance, as well as a measurement accuracy of about 0.5 mm for fine motion correction.