Impact of a single distance phase retrieval algorithm on spatial resolution in X-ray inline phase sensitive imaging

Abstract

A single-projection based phase retrieval method based on the phase attenuation duality principle (PAD) was used to compare the spatial resolution of the acquired phase sensitive and PAD processed phase retrieved images. An inline phase sensitive prototype was used to acquire the phase sensitive images. The prototype incorporates a micro-focus x-ray source and a flat panel detector with a 50 μm pixel pitch. A phantom composed of a 2 cm thick 50-50 adipose-glandular mimicking slab sandwiched with a 0.82 cm thick slanted PMMA sharp edge was used. Phase sensitive image of the phantom was acquired at 120 kV, 3.35 mAs with a 16 μm tube focal spot size under a geometric magnification (M) of 2.5. The PAD based method was applied to the acquired phase sensitive image for the retrieval of phase values. With necessary data processing, modulation transfer function (MTF) curves were determined for the estimation and comparison of the spatial resolution. The PAD processed phase retrieved values of the phantom were in good agreement with the theoretically calculated values. Phase sensitive images showed higher spatial resolution at all spatial frequencies compared to the phase retrieved images. It was noted that the highfrequency signal components in the retrieved image were suppressed that resulted in lower MTF values. When compared to the phase sensitive image, the cutoff resolution (10% MTF) for phase retrieved image dropped 32% from 15.6 lp/mm (32 μm) to 10.6 lp/mm (47 μm). The resolution offered by this phase sensitive prototype is radiographically enough to detect breast cancer.

Quantitative evaluation on 3D fetus morphology via X‐ray grating based imaging technique

“…Both gratings G1and G2, with grating pitch 10 μm and area size 25 × 25 mm, are made of tantalum with a pattern thickness of 2.1 μm and gold with a pattern thickness of 16.6 μm, respectively. The design X‐ray energy 18.8 keV of phase grating G1 can undergo a phase shift of π /2 when penetrating the grating pattern for providing the maximum fringe visibility . However, the incident X‐ray energy of 25 keV was employed in this actual measurement to secure the adequate X‐ray transmission through a water cell, in which the biological sample is immersed during the measurement.…”

“…The design X-ray energy 18.8 keV of phase grating G1 can undergo a phase shift of π/2 when penetrating the grating pattern for providing the maximum fringe visibility. 27,28 However, the incident X-ray energy of 25 keV was employed in this actual measurement to secure the adequate X-ray transmission through a water cell, in which the biological sample is immersed during the measurement. The phase shift of the phase grating G1 should be 0.376π only at 25 keV, and the fringe visibility for the third order Talbot distance will change following the equation below:…”