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Published on: February 12, 2014
Asymmetric spectral filtering for spectral-overlap suppression and differential phase-contrast reconstruction in
Hyunwoo Lim1, Jonghyeok Lee2, Seohee Han3
1Dept. of Radiation Convergence Engineering, Yonsei University - Mirae Campus, 1 Yonseidae-gil, Wonju, Gangwon-do, 26493, Korea (the Republic of).
Objective:
Spatial harmonic imaging (SHI) enables single-shot multi-contrast X-ray imaging, including dark-field imaging (DFI) and differential phase-contrast imaging (DPCI). However, spectral overlap between the first-harmonic band and adjacent spectra can produce wraparound artifacts and structural distortions. Asymmetric spectral filtering (ASF) has recently been proposed to suppress such artifacts in SHI-based DFI, but its effect on the first-harmonic signal and its applicability to DPCI remain unclear. This study aimed to analyze the effect of ASF on the first-harmonic signal and systematically investigate its applicability to DPCI, with particular emphasis on the delineation of small calcification-like inclusions in a breast-equivalent phantom and soft-tissue boundaries and internal structures in a biological specimen.
Approach:
The effect of ASF on the first-harmonic signal was analyzed using a first-order approximation. Monte Carlo simulations and X-ray imaging experiments were conducted using symmetric filtering, low-frequency-only filtering, and ASF for comparison.
Main Results:
In simulations of a breast-equivalent phantom containing small hydroxyapatite inclusions, ASF increased the edge-based signal-to-noise ratio (ESNR) by a factor of 1.96 compared with symmetric filtering. In fish specimen experiments, ASF achieved a 2.46-fold improvement in ESNR and enabled clearer delineation of boundaries and internal structures. In the experiment involving a banana specimen with an inserted pencil lead, ASF yielded the highest ESNR and clearest target delineation.
Significance:
These results suggest that ASF reduces spectral-overlap artifacts while allowing phase-related information relevant to DPCI to remain reflected in the reconstructed phase. The resulting improvements in the delineation of small calcification-like inclusions in a breast-equivalent phantom and soft-tissue boundaries and internal structures in a biological specimen support the biomedical relevance of ASF for single-shot SHI-based DPCI under the investigated low-energy and small-specimen conditions.
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