Cryogenic cesium iodide as a potential PET material

TL;DR

This study explores cryogenic cesium iodide (CsI) as a promising, cost-effective material for Total Body PET scanners, demonstrating significant improvements in light yield and resolution at low temperatures.

Contribution

The paper presents experimental results showing cryogenic CsI's high light yield and resolution, suggesting its potential as a cheaper alternative for PET scanner materials.

Findings

Achieved 6.3% energy resolution at 511 keV

Attained 1.84 ns coincidence time resolution

Demonstrated high light yield (~100 photons/keV) at 104 K

Abstract

Total Body PET (TBPET) scanners have recently demonstrated the ability to significantly reduce both acquisition time and the administered radioactive dose, thanks to their increased sensitivity. However, their widespread adoption is limited by the high costs associated with the current available systems. Cesium iodide (CsI), though historically less favored for PET due to its lower stopping power and light yield compared to crystals like LYSO, shows remarkable improvement when operated at cryogenic temperatures ($\sim$100 K). Under these conditions, CsI light yield rises dramatically to about 100 photons/keV, providing excellent energy resolution and good coincidence time resolution at a lower cost - typically 3 to 5 times cheaper than other crystals at parity of radiation length. In our study, we measured the light yield, the energy resolution and the coincidence time resolution as a function of temperature for two pure CsI crystals read out by a pair of silicon photomultipliers (SiPMs). An energy resolution of 6.3% FWHM and a coincidence time resolution of 1.84 ns at 511 keV were achieved at a temperature of 104 K. These results point towards the potential of cryogenic CsI as a cost-effective, high-performance material for TBPET scanners.