MTF and DQE enhancement using an apodized-aperture x-ray detector design

Area of Science:

• Medical Imaging Physics
• Detector Technology
• Radiographic Imaging

Background:

• High-quality X-ray imaging necessitates detectors with high detective quantum efficiency (DQE) for low patient exposures.
• Current detector designs face limitations in achieving optimal modulation transfer function (MTF) and DQE at high spatial frequencies.

Purpose of the Study:

• To introduce and evaluate a novel apodized-aperture pixel (AAP) design for X-ray detectors.
• To demonstrate how the AAP design enhances MTF and DQE by synthesizing larger image pixels from smaller sensor elements.

Main Methods:

• A cascaded systems model was employed to analyze signal and noise propagation, evaluating MTF, Wiener noise power spectrum (NPS), and DQE.
• Experimental validation used CMOS/CsI and Se detectors with varying sensor element sizes to synthesize larger image pixels.
• Monte Carlo simulations and imaging of phantoms (star-pattern, rat leg) were performed for visual comparison.

Main Results:

• The AAP design, with sensor elements one quarter the size of image pixels, increased MTF by 53% and DQE by 2.3x at the image sampling cut-off frequency.
• Simulated and demonstration images exhibited improved high-frequency content detectability and reduced aliasing artifacts.
• Minor Gibbs ringing was observed near high-contrast edges in some images.

Conclusions:

• The AAP approach effectively preserves the MTF of small sensor elements while attenuating frequencies above the sampling cut-off.
• This design improves MTF and reduces signal/noise aliasing, leading to increased DQE at high spatial frequencies.
• Optimal performance requires a high-resolution converter layer and low detector readout noise.