Hybrid Semiconductor Detectors for High Spatial Resolution Phase-contrast X-ray Imaging

Abstract

When conventional x-ray radiography presents inadequate absorption-contrast, higher sensitivity can be achieved using phase-contrast methods. The implementation of phase-contrast x-ray imaging using propagation-based techniques requires stringent spatial resolution requirements that necessitate lengthy propagation distances and thin (and hence low detection efficiency) scintillator-based detectors. Thus, imaging throughput is limited, and the absorbed dose in the sample can be unacceptable for radiation sensitive life science and biomedical applications.

This work develops hybrid amorphous selenium and complementary metal-oxide-semiconductor detectors with a unique combination of high spatial resolution and detection efficiency for hard x-rays. A semiconductor fabrication process was developed for large-area compatible vertical detector integration by back-end processing. Characterization of signal and noise performance using Fourier-based methods was performed by modulation transfer function, noise power spectrum, and detective quantum efficiency experiments using radiography and microfocus x-ray sources.

The measured spatial resolution at each stage of detector development was one of the highest, if not the highest reported for hard x-rays. In fact, charge carrier spreading from x-ray interactions with amorphous selenium was shown physically larger than the pixel pitch for the first time. A simultaneous factor of four improvement in detection efficiency compared to thin gadolinium oxysulfide-based scintillator detectors was also achieved, despite the detector being a relatively unoptimized prototype.

Fast propagation-based phase-contrast x-ray imaging in compact geometries is demonstrated using a conventional microfocus source. This simple implementation of the phase-contrast technique was applied to imaging the mouse stifle joint. Using propagation-based edge-enhancement the articular cartilage was delineated, opening the possibility of studying diseases such as osteoarthritis using a compact, relatively simple laboratory setup.

This research suggests that hybrid semiconductor technology offers the potential to fill the large performance deficit in high spatial resolution scintillator-based detectors for propagation-based phase-contrast x-ray imaging.