Conventional X-ray Absorption Imaging Research Articles

Enhancing Contrast of Spatial Details in X-ray Phase-Contrast Imaging through Modified Fourier Filtering

In-line X-ray phase contrast imaging, which is simple to experiment with, provides significantly higher sensitivity, compared to conventional X-ray absorption imaging. The inversion of the relationship between recorded Fresnel diffraction intensity and the phase shift induced by the object is called phase retrieval. The transport of intensity equation (TIE), a simple method of phase retrieval, which is solved by the fast Fourier transform algorithm proposed by Paganin et al., has been widely adopted. However, the existing method suffers from excessive suppression of high-frequency information, resulting in loss of image details after phase retrieval, or insufficient detail contrast, leading to blurry images. Here, we present a straightforward extension of the two-distance FFT-TIE method by modifying the Fourier filter through the use of a five-point approximation to calculate the inverse Laplacian in a discrete manner. Additionally, we utilize a combination of continuous Fourier transform and a four-point approximation to compute the gradient operator. The method is evaluated by simulating samples with a shape similar to the resolution test map and by using a photograph of a dog for further evaluation. The algorithm that incorporates the modified gradient operator and the algorithm that solely utilizes the continuous Fourier transform for gradient computation were compared with the results obtained using the two-distance FFT-TIE method. The comparisons were conducted using the results obtained from two distances from the sample to the detector. The results show that this method improves the contrast of spatial details and reduces the suppression of high spatial frequencies compared to the two-distance FFT-TIE method. Furthermore, in the low-frequency domain, our algorithm does not lose much information compared to the original method, yielding consistent results. Furthermore, we conducted our experiments using carbon rods. The results show that both our method and the FFT-TIE method exhibit low-frequency distortion due to the requirement of close proximity between the absorption maps and the detector. However, upon closer inspection, our proposed method demonstrates superior accuracy in reproducing the finer details of the carbon rod fibers.

X-ray Phase-Contrast Computed Tomography for Soft Tissue Imaging at the Imaging and Medical Beamline (IMBL) of the Australian Synchrotron

The Imaging and Medical Beamline (IMBL) is a superconducting multipole wiggler-based beamline at the 3 GeV Australian Synchrotron operated by the Australian Nuclear Science and Technology Organisation (ANSTO). The beamline delivers hard X-rays in the 25–120 keV energy range and offers the potential for a range of biomedical X-ray applications, including radiotherapy and medical imaging experiments. One of the imaging modalities available at IMBL is propagation-based X-ray phase-contrast computed tomography (PCT). PCT produces superior results when imaging low-density materials such as soft tissue (e.g., breast mastectomies) and has the potential to be developed into a valuable medical imaging tool. We anticipate that PCT will be utilized for medical breast imaging in the near future with the advantage that it could provide better contrast than conventional X-ray absorption imaging. The unique properties of synchrotron X-ray sources such as high coherence, energy tunability, and high brightness are particularly well-suited for generating PCT data using very short exposure times on the order of less than 1 min. The coherence of synchrotron radiation allows for phase-contrast imaging with superior sensitivity to small differences in soft-tissue density. Here we also compare the results of PCT using two different detectors, as these unique source characteristics need to be complemented with a highly efficient detector. Moreover, the application of phase retrieval for PCT image reconstruction enables the use of noisier images, potentially significantly reducing the total dose received by patients during acquisition. This work is part of ongoing research into innovative tomographic methods aimed at the introduction of 3D X-ray medical imaging at the IMBL to improve the detection and diagnosis of breast cancer. Major progress in this area at the IMBL includes the characterization of a large number of mastectomy samples, both normal and cancerous, which have been scanned at clinically acceptable radiation dose levels and evaluated by expert radiologists with respect to both image quality and cancer diagnosis.

A low cost method for hard x-ray grating interferometry

Grating interferometry is advantageous over conventional x-ray absorption imaging because it enables the detection of samples constituted by low atomic number elements (low-Z materials). Therefore, it has a potential application in biological science and medical diagnostics. The grating interferometry has some critical optics components such as absorption gratings which are conventionally manufactured by the lithography, electroplating, and molding (LIGA) technique and employing gold as the absorbent material in it. However, great challenge lies in its implementations for practical applications because of the cost and difficulty to achieve high aspect ratio absorbing grating devices. In this paper, we present a low-cost approach that involves using the micro-casting technique with bismuth (Bi) as the absorber in source grating and as well as filling cesium iodide thallium(CsI:Tl) in a periodically structured scintillator. No costly facilities as synchrotron radiation are required and cheap material is used in our approach. Our experiment using these components shows high quality complementary images can be obtained with contrast of absorption, phase and visibility. This alternative method conquers the limitation of costly grating devices for a long time and stands an important step towards the further practical application of grating interferometry.

Novelty detection of foreign objects in food using multi-modal X-ray imaging

In this paper we demonstrate a method for novelty detection of foreign objects in food products using grating-based multimodal X-ray imaging. With this imaging technique three modalities are available with pixel correspondence, enhancing organic materials such as wood chips, insects and soft plastics not detectable by conventional X-ray absorption radiography. We conduct experiments, where several food products are imaged with common foreign objects typically found in the food processing industry. To evaluate the benefit from using this multi-contrast X-ray technique over conventional X-ray absorption imaging, a novelty detection scheme based on well known image- and statistical analysis techniques is proposed. The results show that the presented method gives superior recognition results and highlights the advantage of grating-based imaging.

Graphic processing unit based phase retrieval and CT reconstruction for differential X-ray phase contrast imaging

Compared with the conventional X-ray absorption imaging, the X-ray phase-contrast imaging shows higher contrast on samples with low attenuation coefficient like blood vessels and soft tissues. Among the modalities of phase-contrast imaging, the grating-based phase contrast imaging has been widely accepted owing to the advantage of wide range of sample selections and exemption of coherent source. However, the downside is the substantially larger amount of data generated from the phase-stepping method which slows down the reconstruction process. Graphic processing unit (GPU) has the advantage of allowing parallel computing which is very useful for large quantity data processing. In this paper, a compute unified device architecture (CUDA) C program based on GPU is introduced to accelerate the phase retrieval and filtered back projection (FBP) algorithm for grating-based tomography. Depending on the size of the data, the CUDA C program shows different amount of speed-up over the standard C program on the same Visual Studio 2010 platform. Meanwhile, the speed-up ratio increases as the size of data increases.

Spatial frequency heterodyne imaging in the soft x-ray water window

An x-ray imaging modality called Spatial Frequency Heterodyne Imaging (SFHI) is applied in the soft x-ray water window. SFHI permits the computational decomposition of the images acquired with a single-shot exposure into an x-ray absorption image and into two image pairs formed exclusively by x-rays scattered and refracted normally to the orientation of the grid wires. In the experiments, a laser-driven plasma soft x-ray source is used in an imaging setup consisting of a linear arrangement of source, object, a metal grid, and an image detector. Theoretical simulations and experimental results are found to be in a good agreement. SFHI is demonstrated to deliver more detailed sample information than conventional x-ray absorption imaging.

Phase-contrast X-ray CT Imaging of Esophagus and Esophageal Carcinoma

The electron density resolution is 1000 times higher for synchrotron-radiation phase-contrast CT imaging than conventional X-ray absorption imaging in light elements, with which high-resolution X-ray imaging of biological soft tissue can be achieved. In the present study, we used phase-contrast X-ray CT to investigate human resected esophagus and esophageal carcinoma specimens. This technology revealed the three-layer structure of the esophageal wall-- mucous, submucosa and muscular layers. The mucous and muscular layers were clearly separated by a loose submucosa layer with a honeycomb appearance. The surface of the mucous layer was smooth. In esophageal carcinoma, because of tumor tissue infiltration, the submucosa layer was absent, which indicated destruction of the submucosa. The boundary between normal tissue and tumor was comparatively fuzzy, the three-layer structure of the esophageal wall was indistinct. The surface of the mucous layer was rugose. The technology might be helpful in tumor staging of esophageal carcinoma.

Grating based x-ray differential phase contrast imaging without mechanical phase stepping.

Grating-based x-ray differential phase contrast imaging (DPCI) often uses a phase stepping procedure to acquire data that enables the extraction of phase information. This method prolongs the time needed for data acquisition by several times compared with conventional x-ray absorption image acquisitions. A novel analyzer grating design was developed in this work to eliminate the additional data acquisition time needed to perform phase stepping in DPCI. The new analyzer grating was fabricated such that the linear grating structures are shifted from one detector row to the next; the amount of the lateral shift was equal to a fraction of the x-ray diffraction fringe pattern. The x-ray data from several neighboring detector rows were then combined to extract differential phase information. Initial experimental results have demonstrated that the new analyzer grating enables accurate DPCI signal acquisition from a single x-ray exposure like conventional x-ray absorption imaging.

Synchrotron-radiation phase-contrast imaging of human stomach and gastric cancer:in vitrostudies

The electron density resolution of synchrotron-radiation phase-contrast imaging (SR-PCI) is 1000 times higher than that of conventional X-ray absorption imaging in light elements, through which high-resolution X-ray imaging of biological soft tissue can be achieved. For biological soft tissue, SR-PCI can give better imaging contrast than conventional X-ray absorption imaging. In this study, human resected stomach and gastric cancer were investigated using in-line holography and diffraction enhanced imaging at beamline 4W1A of the Beijing Synchrotron Radiation Facility. It was possible to depict gastric pits, measuring 50-70 µm, gastric grooves and tiny blood vessels in the submucosa layer by SR-PCI. The fine structure of a cancerous ulcer was displayed clearly on imaging the mucosa. The delamination of the gastric wall and infiltration of cancer in the submucosa layer were also demonstrated on cross-sectional imaging. In conclusion, SR-PCI can demonstrate the subtle structures of stomach and gastric cancer that cannot be detected by conventional X-ray absorption imaging, which prompt the X-ray diagnosis of gastric disease to the level of the gastric pit, and has the potential to provide new methods for the imageology of gastric cancer.

Wavelength Dispersive X-ray Absorption Fine Structure Imaging by Parametric X-ray Radiation

The parametric X-ray radiation (PXR) generator system at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University is a monochromatic and coherent X-ray source with horizontal wavelength dispersion. The energy definition of the X-rays, which depends on the horizontal size of the incident electron beam on the generator target crystal, has been investigated experimentally by measuring the X-ray absorption near edge structure (XANES) spectra on Cu and CuO associated with conventional X-ray absorption imaging technique. The result demonstrated the controllability of the spectrum resolution of XANES by adjusting of the horizontal electron beam size on the target crystal. The XANES spectra were obtained with energy resolution of several eV at the narrowest case, which is in qualitative agreement with the energy definition of the PXR X-rays evaluated from geometrical consideration. The result also suggested that the wavelength dispersive X-ray absorption fine structure measurement associated with imaging technique is one of the promising applications of PXR.