Effect of recombination in a high quantum efficiency prototype ionization-chamber-based electronic portal imaging...

Area of Science:

• Medical Physics
• Detector Technology
• Radiological Imaging

Background:

• Increasing detector quantum efficiency (QE) is key for better imaging.
• However, image quality depends on detection quantum efficiency (DQE), which can be limited by secondary quantum sinks like ion recombination in ionization-type detectors.
• Understanding signal loss mechanisms is crucial for high QE detector benefits.

Purpose of the Study:

• To investigate ion recombination as a secondary quantum sink in a high QE prototype electronic portal imaging device (EPID), the kinestatic charge detector (KCD).
• To analyze signal loss due to recombination and its effect on DQE.
• To validate the KCD's performance against theoretical models and simulations.

Main Methods:

• Studied ion recombination in a kinestatic charge detector (KCD) using high pressure noble gases (krypton/xenon at 100 atm) and thick detector configurations.
• Conducted experiments to measure fractional recombination loss under standard operating conditions.
• Applied theoretical treatment of recombination's effect on signal-to-noise ratio to quantify DQE loss.
• Validated results using Monte Carlo simulations.

Main Results:

• The KCD demonstrated significantly higher DQE compared to commercial imagers, with DQE(0) = 0.20 for xenon and DQE(0) = 0.34 for thicker xenon chambers.
• Experimental measurements showed fractional recombination losses of approximately 14% for krypton and 18% for xenon.
• Theoretical calculations indicated a limited effect (<2%) of recombination on DQE under standard conditions.
• Experimental DQE measurements showed good agreement with Monte Carlo simulations that did not account for recombination.

Conclusions:

• Ion recombination in the KCD, while present, has a limited impact on DQE under standard operating conditions.
• The kinestatic charge detector (KCD) offers a promising high QE imaging solution with high DQE.
• Experimental and simulation results validate the KCD's performance and the theoretical models used.