Explanations of MTF discrepancy in grating-based X-ray differential phase contrast CT imaging
arxiv(2024)
摘要
As a multi-contrast X-ray computed tomography (CT) imaging system, the
grating-based Talbot-Lau interferometer is able to generate the absorption
contrast and differential phase contrast (DPC) images concurrently. However,
experiments found that the absorption CT (ACT) images have better spatial
resolution, i.e., higher modulation transfer function (MTF), than the
differential phase contrast CT (DPCT) images. Until now, the root cause of such
observed discrepancy has not been rigorously investigated. Through physical
experiments, this study revealed that the phase grating in the Talbot-Lau
interferometer induces direct superposition of paired split absorption signals
and inverse superposition of paired split phase signals via diffraction.
Further simulation experiments demonstrated that this splitting leads to a
reduction in MTF in both ACT and DPCT images, with distinct superposition
mechanisms contributing to the lower MTF in DPCT. Besides, such MTF discrepancy
may also be affected in a minor extent by object composition, sample size, beam
spectra and detector pixel size. Based on this study, the spatial resolution
could be optimized when designing a grating-based DPC imaging system.
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