Biomedical x-ray imaging with a GaAs photon-counting detector: A comparative study

J Scholz,C Petrich,L Birnbacher,T Sellerer,L Heck,J Herzen,K Achterhold,S Gkoumas,M Riedel

doi:10.1063/5.0020262

Abstract

Photon-counting detectors provide several potential advantages in biomedical x-ray imaging including fast and readout noise free data acquisition, sharp pixel response, and high dynamic range. Grating-based phase-contrast imaging is a biomedical imaging method, which delivers high soft-tissue contrast and strongly benefits from photon-counting properties. However, silicon sensors commonly used in photon-counting detectors have low quantum efficiency for mid- to high-energies, which limits high throughput capabilities when combined with grating-based phase contrast imaging. In this work, we characterize a newly developed photon-counting prototype detector with a gallium arsenide sensor, which enables imaging with higher quantum efficiency, and compare it with a silicon-based photon-counting and a scintillation-based charge integrating detector. In detail, we calculated the detective quantum efficiency (DQE) of all three detectors based on the experimentally measured modulation transfer function, noise power spectrum, and photon fluence. In addition, the DQEs were determined for two different spectra, namely, for a 28 kVp and a 50 kVp molybdenum spectrum. Among all tested detectors, the gallium arsenide prototype showed the highest DQE values for both x-ray spectra. Moreover, other than the comparison based on the DQE, we measured an ex vivo murine sample to assess the benefit using this detector for grating-based phase contrast computed tomography. Compared to the scintillation-based detector, the prototype revealed higher resolving power with an equal signal-to-noise ratio in the grating-based phase contrast computed tomography experiment.

Highlights

In contrast to widely used scintillation-based detectors, photon-counting detectors use direct conversion semiconductor sensors, which convert incident x-rays directly into an electrical signal
Silicon sensors commonly used in photon-counting detectors have low quantum efficiency for mid- to high-energies, which limits high throughput capabilities when combined with grating-based phase contrast imaging
The normalized NPS (NNPS) recorded with the 50 kVp spectrum and a Talbot–Lau interferometer along with a water container are indicated with solid lines, whereas the dashed lines represent the NNPS recorded with the Mo/Al filtered Mo 28 kVp spectrum

Summary

Introduction

In contrast to widely used scintillation-based detectors, photon-counting detectors use direct conversion semiconductor sensors, which convert incident x-rays directly into an electrical signal. Photon-counting technology features several advantages for x-ray related imaging applications including a sharp pixel response, scitation.org/journal/app high dynamic range, electronic noise free readout, and spectral energy discrimination.. Silicon sensors achieve extremely high crystal quality, their stopping power is limited due to the low atomic number (Z = 14). The resulting comparably low quantum efficiency of silicon based photon-counting in contrast to scintillation-based detectors, limits a wider range of application in x-ray imaging. Recent advances have made sensor materials with higher atomic numbers such as gallium arsenide (GaAs) (Z = 31/33) and cadmium telluride (CdTe) (Z = 48/52) available for photon-counting technology to increase the conversion efficiency..

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