Quantitative characterization of edge enhancement in phase contrast x‐ray imaging

Abstract

The aim of this study was to model the edge enhancement effect in in-line holography phase contrast imaging. A simple analytical approach was used to quantify refraction and interference contrasts in terms of beam energy and imaging geometry. The model was applied to predict the peak intensity and frequency of the edge enhancement for images of cylindrical fibers. The calculations were compared with measurements, and the relationship between the spatial resolution of the detector and the amplitude of the phase contrast signal was investigated. Calculations using the analytical model were in good agreement with experimental results for nylon, aluminum and copper wires of 50 to 240 microm diameter, and with numerical simulations based on Fresnel-Kirchhoff theory. A relationship between the defocusing distance and the pixel size of the image detector was established. This analytical model is a useful tool for optimizing imaging parameters in phase contrast in-line holography, including defocusing distance, detector resolution and beam energy.

The effects of x-ray beam hardening on detective quantum efficiency and radiation dose

“…A higher x-ray energy than current clinical values was utilized in this preliminary study in an effort to target future clinical applications in phase contrast imaging, as initial investigations have indicated the potential of increasing the x-ray energy to reduce the dose without impacting the image quality [6, 39, 44–46]. Subsequent studies will further evaluate the feasibility of beam hardening through comparisons with a range of diagnostic energies, including current clinical mammography values.…”

Phase imaging using polycapillary optics

“…Such types of images produce high contrast for objects where the electron density differences are substantial, e.g., bone and flesh, but result in poor contrast for soft tissue imaging where the tissues exhibit similar attenuation, e.g., glandular tissue and infiltrating ductal carcinoma in breast imaging. 1 However, X rays can accumulate significant differential phase delay even in weakly absorbing materials. If the change of phase of X rays can be imaged, tissues which would normally be indistinguishable under attenuation contrast can be distinguished.…”

“…Phase contrast imaging renders different phase delays as intensity variation in the detector plane. The amount of attenuation and phase delay of a given material can be described by its complex-valued index of refraction, (1) where β and δ are real-valued parameters describing the absorption and phase delay of X rays, respectively. For X-ray energies of 10 to 100 KeV, δ of tissues is about 10 -6 to 10 -8 and is about 10 -9 to 10 -11 , so the phase delay term is approximately 1000 times greater than the absorption term.…”

Image quality and dose efficiency of high energy phase sensitive x-ray imaging: Phantom studies

“…The similar composition between normal and malignant breast tissue [9–11] produces very low attenuation contrast, which presents a significant challenge for early cancer detection. Improving the image quality in conventional x-ray imaging can only be accomplished a few ways: lowering the x-ray energy to increase the amount of radiation absorbed by the tissue [9,11,12], and utilizing an anti-scatter grid between the object and detector to reduce the image degradation caused by scattered x-rays [9,13]. Both methods improve the signal-to-noise ratio, and thus the image quality, of the image; however, this is accomplished at the expense of an increased radiation dose to the patient.…”