Effect of finite phosphor thickness on detective quantum efficiency

Area of Science:

• Medical Physics
• Radiological Imaging
• Materials Science

Background:

• The detective quantum efficiency (DQE) is a critical metric for imaging systems, quantifying signal-to-noise transfer.
• Phosphor screens are widely used in X-ray detectors, but their physical properties can influence image quality.
• Understanding the relationship between screen characteristics and DQE is essential for optimizing diagnostic performance.

Purpose of the Study:

• To theoretically investigate the impact of finite phosphor screen thickness on spatial-frequency-dependent DQE.
• To characterize how variations in light burst magnitude and spatial distribution affect DQE.
• To establish criteria for maximizing DQE based on phosphor screen properties.

Main Methods:

• Theoretical modeling of light quantum emission from phosphor screens following X-ray interactions.
• Analysis of the spatial Fourier spectrum of light bursts to determine their moments.
• Development of functions (As and Rc(f)) to characterize DQE variations due to screen thickness.

Main Results:

• Finite screen thickness leads to a spatial-frequency-independent DQE reduction (As) due to variations in light burst magnitude.
• Screen thickness also causes a spatial-frequency-dependent DQE roll-off (Rc(f)) due to changes in light burst spatial distribution (PSF).
• Both As and Rc(f) are related, with As acting as a scaling factor for Rc(f).

Conclusions:

• Maximizing DQE requires uniform light burst magnitude (to maximize As) and uniform burst shape (to maximize Rc(f)).
• The optimal phosphor screen for DQE may not be the one with the highest modulation transfer function (MTF).
• Finite screen thickness is a significant factor influencing the DQE(f) performance of X-ray imaging detectors.