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Oblique incidence effects in direct x-ray detectors: a first-order approximation using a physics-based analytical
Aldo Badano1, Melanie Freed, Yuan Fang
1Division of Imaging and Applied Mathematics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, FDA, Silver Spring, Maryland 20993, USA. aldo.badano@fda.hhs.gov
Medical Physics
|June 2, 2011
Summary
This study modifies an analytical model to analyze oblique x-ray incidence effects in direct semiconductor detectors, revealing differences in resolution degradation compared to indirect detectors.
Area of Science:
- Medical Physics
- Radiological Imaging
- Detector Technology
Background:
- Indirect detectors (e.g., CsI:Tl) and direct semiconductor detectors are used in X-ray imaging.
- Oblique X-ray incidence can affect detector performance, particularly resolution.
- Previous models focused on indirect detector responses to oblique X-rays.
Purpose of the Study:
- To modify an existing analytical model for indirect detectors to study oblique X-ray incidence effects in direct semiconductor detectors.
- To analyze the degradation in resolution for direct detectors under oblique X-ray incidence.
- To compare the model's predictions with published data for indirect detectors.
Main Methods:
- Adapted a physics-based analytical model originally developed for indirect detectors (CsI:Tl).
- The modified model describes direct detector response, considering X-ray energy, transducer thickness, and depth-dependent blur/collection efficiency.
- Analyzed detector response functions for typical full-field digital mammography detector thicknesses (150 µm indirect, 200 µm direct).
Main Results:
- Direct detector models show a sharper overall point response function (PRF) than indirect detectors at normal incidence.
- Oblique incidence causes a larger relative increase in blur along the incidence direction in direct detectors compared to indirect detectors.
- The study quantifies these differences for typical mammography detector configurations.
Conclusions:
- Direct detectors exhibit a sharper response at normal incidence and greater relative blur increase along the incidence direction under oblique angles compared to indirect detectors.
- The oblique incidence effect in direct detectors is primarily attributed to the geometry of energy deposition within the semiconductor layer.
- The findings highlight distinct performance characteristics of direct detectors under oblique X-ray incidence.
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