X-ray energy spectrum plays an essential role in imaging and related tasks. Due to the high photon flux
of clinical CT scanners, most of the spectrum estimation methods are indirect and are usually suffered from
various limitations. The recently proposed indirect transmission measurement-based method requires at least
the segmentation of one material, which is insufficient for CT images of highly noisy and with artifacts. To
combat for the bottleneck of spectrum estimation using segmented CT images, in this study, we develop a
segmentation-free indirect transmission measurement based energy spectrum estimation method using dual-energy
material decomposition. The general principle of the method is to compare polychromatic forward
projection with raw projection to calibrate a set of unknown weights which are used to express the unknown
spectrum together with a set of model spectra. After applying dual-energy material decomposition using high-and
low-energy raw projection data, polychromatic forward projection is conducted on material-specific images.
The unknown weights are then iteratively updated to minimize the difference between the raw projection and
estimated projection. Both numerical simulations and experimental head phantom are used to evaluate the
proposed method. The results indicate that the method provides accurate estimate of the spectrum and it may
be attractive for dose calculations, artifacts correction and other clinical applications.
A grating-based x-ray multi-contrast imaging system integrates a source grating G0, a diffraction grating G1, and an analyzer grating G2 into a conventional x-ray imaging system to generate images with three contrast mechanisms: absorption contrast, differential phase contrast, and dark field contrast. To facilitate the potential translation of this multi-contrast imaging system into a clinical setting, our group has developed several single-shot data acquisition methods to eliminate the necessity of the time-consuming phase stepping procedure. These methods have enabled us to acquire multi-contrast images with the same data acquisition time currently used for absorption imaging. One of the proposed methods is the use a staggered G2 grating. In this work, we propose to incorporate this staggered G2 grating into a state-of-the-art breast tomosynthesis imaging system to generate tomosynthesis images with three contrast mechanisms. The introduction of this staggered G2 grating will reject scatter and thus improve image contrast at the detector plane, but it will also absorb some x-ray photons reaching detector, thus increasing noise and reducing the contrast to noise ratio (CNR). Therefore, a key technical question is whether the CNR and dose efficiency can be maintained for absorption imaging after the introduction of this staggered G2 grating. In this paper, both the CNR and scatter-to-primary ratio (SPR) of absorption imaging were investigated with Monte Carlo simulations for a variety of staggered G2 grating designs.
This paper provides a fast and patient-specific scatter artifact correction method for cone-beam computed tomography (CBCT) used in image-guided interventional procedures. Due to increased irradiated volume of interest in CBCT imaging, scatter radiation has increased dramatically compared to 2D imaging, leading to a degradation of image quality. In this study, we propose a scatter artifact correction strategy using an analytical convolution-based model whose free parameters are estimated using a rough estimation of scatter profiles from the acquired cone-beam projections. It was evaluated using Monte Carlo simulations with both monochromatic and polychromatic X-ray sources. The results demonstrated that the proposed method significantly reduced the scatter-induced shading artifacts and recovered CT numbers.