X-ray imaging performance of structured cesium iodide scintillators

Area of Science:

• Medical Physics
• Materials Science
• Imaging Technology

Background:

• Columnar cesium iodide (CsI) scintillators doped with Thallium (Tl) are crucial for indirect x-ray imaging detectors.
• Optimizing CsI layer design is essential for advancing x-ray imaging applications.

Purpose of the Study:

• To develop a methodology for systematically investigating the inherent imaging performance of CsI.
• To analyze CsI performance as a function of thickness and design type (High Light Output - HL, High Resolution - HR).
• To validate physical models of light channeling in columnar CsI.

Main Methods:

• Experimental measurement of Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), and Detective Quantum Efficiency (DQE) for CsI samples (150-600 microns thick).
• Utilized a high-resolution CMOS optical sensor (48-micron pixel pitch) in direct contact with CsI samples.
• Determined CsI aperture function, pulse height distribution, x-ray quantum efficiency, Swank factor, and x-ray conversion gain.

Main Results:

• High-Resolution (HR) CsI exhibited a 50% higher MTF at 5 cycles/mm compared to High-Light Output (HL) CsI, but with 36% less light output.
• Both HR and HL CsI types showed nearly identical DQE(0) due to similar Swank factors (0.91 for HR, 0.93 for HL).
• Presampling MTF decreased with increasing CsI thickness (L), while universal MTF (f*L) increased, indicating improved light channeling in thicker layers.

Conclusions:

• The light channeling process in columnar CsI significantly enhances the MTF of thicker layers.
• Understanding the trade-off between light output and resolution is key for optimizing CsI for specific x-ray imaging needs.
• This systematic investigation provides a framework for validating physical models and optimizing CsI scintillator design.