Author: Les Butler, Joyoni Dey, Conner B Dooley, Victoria L Fontenot, Kyungmin Ham, Hunter Cole Meyer 👨🔬
Affiliation: Louisiana State University, Center for Advanced Microstructures and Devices, Linfield University 🌍
Purpose: X-ray interferometry is an emerging imaging modality with a wide variety of potential clinical applications, including lung and breast imaging. Small inaccuracies in grating position lead to a grating remnant artifact and we have developed an image recovery algorithm that uses additional harmonics to prevent grating remnants.
Methods: A grating interferometer uses a diffraction grating to produce a periodic interference pattern and measures how a patient perturbs the pattern, producing three unique images that highlight X-ray absorption, refraction, and small angle scattering, known as the attenuation, differential-phase, and dark-field images, respectively. Grating interferometers commonly use a technique known as phase stepping to acquire images. The grating is translated laterally and imaged multiple times to produce a phase stepping curve at each pixel. The phase stepping curves are typically assumed to be sinusoidal, and the fringe visibility is extracted to produce the dark-field image. Since the fringes are not perfectly sinusoidal, the fitted visibility is oscillatory, and small inaccuracies in grating position lead to remnant oscillations in the reconstructed dark-field images. We introduce an additional harmonic to the fit of the interference pattern to reduce the remnant oscillations present in the visibility, ultimately reducing the remnant fringes in the dark-field images.
Results: With the addition of the second harmonic, the oscillations in the visibility are greatly reduced, leading to a reduction or complete removal of the grating remnant artifact in the dark-field images.
Conclusion: X-ray interferometry has the potential for clinical applications in lung and breast imaging, but unique image artifacts are introduced when assuming the fringe pattern produced by the diffraction gratings is perfectly sinusoidal. By introducing an additional harmonic, the fit of the fringe pattern is much better, decreasing oscillations in the fringe visibility and removing the grating remnant artifact in the dark-field images.