A New Concept of Liquid Xenon Time Projection Chamber for Medical Imaging

Abstract

Liquid xenon time projection chambers offer a homogeneous detection medium with excellent intrinsic energy resolution, fast scintillation, and true three-dimensional position sensitivity, making them an attractive alternative to crystal-based detectors for positron emission tomography (PET). In this work, we present a new single-phase liquid xenon time projection chamber (TPC) concept optimized for medical imaging, employing combined scintillation and electroluminescence-based ionization readout to enable low-noise signal amplification and intrinsic depth-of-interaction measurement. We evaluate the system-level performance of this detector concept using Monte Carlo simulations based on OpenGATE and Geant4, with direct comparison to conventional LYSO-based PET systems. The study focuses on detection sensitivity, energy-based event selection efficiency, and reconstructed spatial resolution. While LYSO detectors provide higher absolute stopping efficiency due to their higher density, liquid xenon detectors exhibit improved photopeak purity as a result of superior intrinsic energy resolution, leading to enhanced rejection of scattered events. Point-source reconstruction studies demonstrate that the intrinsic three-dimensional position sensitivity of the liquid xenon TPC translates into a reconstructed spatial resolution of approximately 1~mm full width at half maximum (FWHM) at the system level, compared to approximately 4~mm for LYSO-based systems under comparable conditions. These results indicate that liquid-xenon-based PET detectors can achieve competitive or superior imaging performance, particularly for applications requiring high spatial resolution, large axial acceptance, and scalable detector geometries.

Figures (3)

• Figure 1: (Left) Operating principle of an individual liquid xenon (LXe) detector module, illustrating the detection of prompt scintillation light and delayed ionization signals via field-enhanced electroluminescence near the anode. The monolithic LXe volume provides high light collection efficiency and intrinsic depth-of-interaction sensitivity. Single-ended photosensor readout reduces channel count and system cost while maintaining sub-millimeter three-dimensional spatial resolution. The LXe target thickness can be adjusted to optimize detection efficiency and cost. (Right) Conceptual layout of a liquid-xenon-based PET imaging system consisting of concentric rings of LXe detector modules detecting coincident, back-to-back 511 keV gamma rays from positron–electron annihilation. Figures are adapted from Backues:2025.
• Figure 2: (Left) Detection efficiency of true 511 keV gamma rays within the $2\sigma$ energy window centered at 511 keV, relative to the total simulated events, for different radial thickness of the PET detectors. (Right) Fraction of true 511 keV gamma rays, relative to the total number of events, containing also scattered gammas, within the $2\sigma$ energy window centered at 511 keV. Statistical uncertainties (binomial) are at the level of 0.005% (left) and 0.02% (right) and are smaller than the marker size; therefore, error bars are not shown.
• Figure 3: Reconstructed images from a simulated point-source in a single axial slice for a LYSO-based PET system (left) and an LXe-based PET system (right). The FWHM X&Y resolutions (numbers shown on figures) are extracted by applying a two-dimensional Gaussian fit to the smoothed reconstruction.