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Phase Retrieval in Grating-Based X-Ray Differential Phase Contrast CT with Twin-Peaks in Phase-Stepping Curves

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Y Yang

Y YANG1*, H Xie1 , W Cai2 , X Tang1 , (1) Emory University School of Medicine, Atlanta, GA, (2) Brigham and Women's Hospital, Boston, MA


TH-AB-204-8 (Thursday, July 16, 2015) 7:30 AM - 9:30 AM Room: 204

Purpose: As a promising new technique with high potential for translation into clinical applications, x-ray differential phase contrast (DPC) CT implemented with Talbot interferometry has drawn increasing interest. Usually, the x-ray DPC-CT employs a phase-stepping procedure to extract the phase signal. Since the fabrication processes may cause defects in analyzer grating G₂, the actual period of G₂ may double the nominal period of G₂, and twin peaks with remarkably different heights can be within a period of the experimental determined phase-stepping curve (PSC). For such a DPC-CT system with twin-peak PSCs, we develop an approach to retrieve the phase contrast for imaging.

Methods: Based on the paraxial Fresnel-Kirchhoff theory, an analytical formula is derived to characterize the PSCs of an x-ray Talbot interferometry with flawed analyzer grating. In addition, an experimental investigation into the phase retrieval in x-ray DPC-CT with twin-peak PSCs is conducted by utilizing an x-ray Talbot interferometry with detector cell dimension and nominal period of G₂ being 96x96 micron² and 4.6 micron, respectively.

Results: Theoretical analysis demonstrates that the twin-peak feature of PSCs depends on not only the flaw in G₂, but also the mismatch between the phase grating and the spectrum of x-ray source. For a DPC-CT system with twin-peak PSCs (Figure 1), experimental results show that in comparison with scanning G₂ over its nominal period g₂, stepping the analyzer grating over its actual period 2g₂ can provide data to enable a significantly improved reconstruction of the phase-contrast CT images (Figures 2(b) and 2(d)).

Conclusion: Our theoretical analysis and experimental investigation show that for an x-ray DPC-CT imaging system with twin-peak PSCs, the PSCs should be determined by scanning G₂ over the double of its nominal period g₂; and then the PSCs can be utilized to retrieve the phase signal for x-ray phase contrast imaging.

Funding Support, Disclosures, and Conflict of Interest: Research Grant: W81XWH-12-1-0138 (DoD).

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