Design and Development of NeuroSphere PET: A Next-Generation 7-T MR-Compatible Dedicated Brain PET Scanner

PET is the most powerful imaging modality for studying neurotransmitters, receptors, and neuromodulation in humans, complementing the anatomic and hemodynamic information provided by MRI. However, PET temporal resolution remains constrained by sensitivity, limiting studies of fast, dynamic neurochemical processes. To address this gap, we are developing the Human Dynamic NeuroChemical Connectome, an imaging system integrating NeuroSphere PET, a novel ultra-high-sensitivity dedicated brain PET camera, with the Siemens Healthineers Magnetom Terra.X, a clinical 7-T MRI scanner. This article describes the design, engineering, and simulation-based performance estimation of NeuroSphere PET. Sensitivity maximization drove 2 core design choices: a partial spheric detector arrangement with a 32-cm inner diameter and 70% solid-angle coverage and the use of 26-mm lutetium oxyorthosilicate crystals for high stopping power (∼90% at 511 keV), coupled to silicon photomultipliers in a light-sharing, depth-of-interaction-capable configuration. The system comprises 872 detector blocks organized across 19 rings and 218 modules. At the detector level, measured performance includes energy resolution of approximately 11% full width at half maximum (FWHM), depth-of-interaction resolution of approximately 8 mm FWHM, and coincidence timing resolution of approximately 500 ps FWHM. System-level performance was evaluated using the ultrafast Monte Carlo PET simulator, accounting for realistic detector response, positron range, photon noncollinearity, and interdetector scatter. Sensitivity was estimated from a 30-cm uniform sphere, predicting a peak sensitivity of about 38% and a whole-brain average exceeding 25%. Spatial resolution and image quality were assessed through Derenzo phantom simulations evaluated at both the center of the field of view and 8 cm off-center, indicating that 1.6-mm structures can be resolved near the center of the field of view and that resolution of less than 2 mm can be maintained at the cortex. The system incorporates a 3-dimensional-printed MRI-compatible gantry, a dedicated 16-channel parallel transmit-receive radiofrequency head coil, and a custom radiofrequency shielding enclosure for simultaneous PET/MRI at 7 T. By targeting sensitivity an order of magnitude higher than that of commercial PET systems, NeuroSphere PET is expected to enable simultaneous neurochemical and hemodynamic studies with substantially improved spatiotemporal resolution, providing new insights into brain function and connectivity.