Alleviating the trade-off between coincidence time resolution and sensitivity using scalable TOF-DOI detectors.

Area of Science:

• Medical Imaging
• Nuclear Physics
• Detector Technology

Background:

• Advancements in time-of-flight positron emission tomography (TOF-PET) have improved coincidence time resolution (CTR).
• Achieving sub-100 ps CTR is hindered by the need for thick scintillators (approx. 20 mm) to maintain sensitivity, as photon transit time spread within them degrades CTR.
• A trade-off exists between TOF capability and detector sensitivity in current PET designs.

Purpose of the Study:

• To propose and evaluate a novel readout scheme for PET detectors that addresses the trade-off between TOF capability and sensitivity.
• To enable the use of thinner scintillators for improved CTR while maintaining adequate sensitivity.
• To introduce a detector design that inherently provides depth-of-interaction (DOI) information.

Main Methods:

• A cross-stacked detector (xDetector) design was developed, utilizing two orthogonally stacked one-dimensional PET detectors.
• This configuration reduces scintillator thickness to approximately 13 mm by stacking detectors along the depth-of-interaction (DOI) axis.
• Experimental evaluations were performed using lutetium oxyorthosilicate crystals coupled with silicon photomultipliers.

Main Results:

• The xDetector achieved a coincidence time resolution (CTR) of 175 ps FWHM and an energy resolution of 11% FWHM at 511 keV.
• Single detector timing resolution was measured at 111.2 ± 0.8 ps FWHM.
• The xDetector design inherently provides DOI information and exhibits asymmetric xy-spatial resolution.

Conclusions:

• The xDetector design effectively resolves the trade-off between TOF capability and sensitivity in PET scanners.
• This scalable design offers integrated DOI capability, crucial for advanced PET imaging.
• The xDetector scheme, combined with advanced components, presents a practical pathway to achieving 100 ps CTR and high DOI resolution in future PET systems.