Enhanced light extraction in flex-mold nanopatterned scintillators for TOF-PET

Area of Science:

• Materials Science and Engineering
• Medical Imaging Physics
• Nanotechnology

Background:

• Optical photon losses at the scintillator-photosensor interface degrade detector performance in time-of-flight positron emission tomography (TOF-PET).
• Limited energy and coincidence time resolution (CTR) in TOF-PET systems are directly impacted by inefficient light extraction from scintillators.

Purpose of the Study:

• To enhance light extraction from scintillation crystals for improved TOF-PET detector performance.
• To investigate the efficacy of diffractive nanopatterns applied to scintillator surfaces.

Main Methods:

• Flex mold-based soft lithography was employed to create 300 nm diffractive nanopatterns (holes and lines) on cm-scale scintillator surfaces (LYSO, BGO, GAGG).
• Scintillators were tested in four optical coupling configurations: bare with air, bare with grease, nanopatterned with air, and nanopatterned with grease.
• Measurements included light extraction gain, energy resolution, and coincidence time resolution (CTR).

Main Results:

• A BGO crystal with a hole-plaid nanopattern and optical grease achieved a 2.22-fold increase in light extraction, improving energy resolution from 18% to 11%.
• Nanopatterned LYSO and GAGG crystals showed light extraction gains of 1.58- and 1.72-fold, respectively.
• Coincidence time resolution (CTR) in nanopatterned LYSO improved from 250.6 ps to 132.0 ps with optimized optical coupling and thresholding. Nanopatterns maintained performance after mechanical stress and cleaning.

Conclusions:

• Flex-mold based soft nanoimprint lithography is a viable and high-fidelity method for surface engineering of TOF-PET scintillators.
• Diffractive nanopatterning effectively enhances light extraction, leading to significant improvements in energy and timing resolution for TOF-PET detectors.