Prediction of vertebral failure load by using x-ray vector radiographic imaging.

PURPOSE: To examine whether x-ray vector radiographic (XVR) parameters could predict the biomechanically determined vertebral failure load. MATERIALS AND METHODS: Local institutional review boards approved the study and donors provided written informed consent before death. Twelve thoracic vertebral bodies were removed from three human cadavers and embedded in resin. XVR measurements were performed by using a Talbot-Lau grating interferometer with the beam direction in anterior-posterior and lateral direction. The mean anisotropy and the mean local average scattering power were calculated for a region of interest within each vertebra. Trabecular bone mineral density (BMD) was determined in each vertebra by using a clinical multidetector computed tomographic scanner. Failure load of the vertebral bodies was determined from destructive biomechanical tests. Statistical analyses were performed with statistical software with a two-sided Pvalue of .05 to calculate Pearson correlation coefficients and multiple regression model. RESULTS: Statistically significant correlations (P < .05) for failure load with XVR parameters in the lateral direction (r = -0.84 and 0.68 for anisotropy and local average scattering power, respectively) and for failure load and anisotropy in anteroposterior direction (r = -0.65) were found. A multiple regression model showed that the combination of the local average scattering power in lateral direction and BMD predicted failure load significantly better than BMD alone (adjusted R = 0.88 compared with 0.78, respectively; P < .001). CONCLUSION: The study results imply that XVR can improve the prediction of osteoporosis.

X-ray dark-field vector radiography-a novel technique for osteoporosis imaging.

X-ray dark-field vector radiography (XVR) has emerged as an imaging technique which can efficiently yield dark-field scatter images of high quality, even with conventional X-ray tube sources. The XVR yields direction-dependent information about the X-ray scattering of the trabecular bone microstructure without the requirement of resolving the micrometer size structures directly causing the scattering. In this pilot study, we demonstrated that XVR-based degree of anisotropy correlated with femoral bone strength in the context of osteoporosis.

Emphysema diagnosis using X-ray dark-field imaging at a laser-driven compact synchrotron light source.

In early stages of various pulmonary diseases, such as emphysema and fibrosis, the change in X-ray attenuation is not detectable with absorption-based radiography. To monitor the morphological changes that the alveoli network undergoes in the progression of these diseases, we propose using the dark-field signal, which is related to small-angle scattering in the sample. Combined with the absorption-based image, the dark-field signal enables better discrimination between healthy and emphysematous lung tissue in a mouse model. All measurements have been performed at 36 keV using a monochromatic laser-driven miniature synchrotron X-ray source (Compact Light Source). In this paper we present grating-based dark-field images of emphysematous vs. healthy lung tissue, where the strong dependence of the dark-field signal on mean alveolar size leads to improved diagnosis of emphysema in lung radiographs.

Non-binary phase gratings for x-ray imaging with a compact Talbot interferometer.

X-ray imaging using a Talbot-Lau interferometer, consisting of three binary gratings, is a well-established approach to acquire x-ray phase-contrast and dark-field images with a polychromatic source. However, challenges in the production of high aspect ratio gratings limit the construction of a compact setup for high x-ray energies. In this study we consider the use of phase gratings with triangular-shaped structures in an x-ray interferometer and show that such gratings can yield high visibilities for significantly shorter propagation distances than conventional gratings with binary structures. The findings are supported by simulation and experimental results for both cases of a monochromatic and a polychromatic source.

Correlation of X-ray dark-field radiography to mechanical sample properties.

The directional dark-field signal obtained with X-ray grating interferometry yields direction-dependent information about the X-ray scattering taking place inside the examined sample. It allows examination of its morphology without the requirement of resolving the micrometer size structures directly causing the scattering. The local morphology in turn gives rise to macroscopic mechanical properties of the investigated specimen. In this study, we investigate the relation between the biomechanical elasticity (Young's modulus) and the measured directional dark-field parameters of a well-defined sample made of wood. In our proof-of-principle experiment, we found a correlation between Young's modulus, the average dark-field signal, and the average dark-field anisotropy. Hence, we are able to show that directional dark-field imaging is a new method to predict mechanical sample properties. As grating interferometry provides absorption, phase-contrast, and dark-field data at the same time, this technique appears promising to combine imaging and mechanical testing in a single testing stage. Therefore, we believe that directional dark-field imaging will have a large impact in the materials science world.

Multimodal hard X-ray imaging of a mammography phantom at a compact synchrotron light source.

The Compact Light Source is a miniature synchrotron producing X-rays at the interaction point of a counter-propagating laser pulse and electron bunch through the process of inverse Compton scattering. The small transverse size of the luminous region yields a highly coherent beam with an angular divergence of a few milliradians. The intrinsic monochromaticity and coherence of the produced X-rays can be exploited in high-sensitivity differential phase-contrast imaging with a grating-based interferometer. Here, the first multimodal X-ray imaging experiments at the Compact Light Source at a clinically compatible X-ray energy of 21 keV are reported. Dose-compatible measurements of a mammography phantom clearly demonstrate an increase in contrast attainable through differential phase and dark-field imaging over conventional attenuation-based projections.

Phase unwrapping in spectral X-ray differential phase-contrast imaging with an energy-resolving photon-counting pixel detector.

Grating-based differential phase-contrast imaging has proven to be feasible with conventional X-ray sources. The polychromatic spectrum generally limits the performance of the interferometer but benefit can be gained with an energy-sensitive detector. In the presented work, we employ the energy-discrimination capability to correct for phase-wrapping artefacts. We propose to use the phase shifts, which are measured in distinct energy bins, to estimate the optimal phase shift in the sense of maximum likelihood. We demonstrate that our method is able to correct for phase-wrapping artefacts, to improve the contrast-to-noise ratio and to reduce beam hardening due to the modelled energy dependency. The method is evaluated on experimental data which are measured with a laboratory Talbot-Lau interferometer equipped with a conventional polychromatic X-ray source and an energy-sensitive photon-counting pixel detector. Our work shows, that spectral imaging is an important step to move differential phase-contrast imaging closer to pre-clinical and clinical applications, where phase wrapping is particularly problematic.

Rapid dynamic radial MRI via reference image enforced histogram constrained reconstruction.

Exploiting spatio-temporal redundancies in sub-Nyquist sampled dynamic MRI for the suppression of undersampling artifacts was shown to be of great success. However, temporally averaged and blurred structures in image space composite data poses the risk of false information in the reconstruction. Within this work we assess the possibility of employing the composite image histogram as a measure of undersampling artifacts and as basis of their suppression. The proposed algorithm utilizes a histogram, computed from a composite image within a dynamically acquired interleaved radial MRI measurement as reference to compensate for the impact of undersampling in temporally resolved data without the incorporation of temporal averaging. In addition an image space regularization utilizing a single frame low-resolution reconstruction is implemented to enforce overall contrast fidelity. The performance of the approach was evaluated on a simulated radial dynamic MRI acquisition and on two functional in vivo radial cardiac acquisitions. Results demonstrate that the algorithm maintained contrast properties, details and temporal resolution in the images, while effectively suppressing undersampling artifacts.

Correlation of X-ray vector radiography to bone micro-architecture.

Besides the overall mass density, strength of trabecular bone depends significantly on its microstructure. However, due to dose constraints in medical CT imaging, it is impossible to gain sufficient information about very fine bone structures in vivo on the micrometer scale. Here we show that a recently developed method of X-ray vector radiography (XVR), an imaging method which uses X-ray scattering information to form an image, allows predictions on the bone microstructure without the explicit need to spatially resolve even individual trabeculae in the bone. We investigated thick human femoral bone samples and compared state-of-the-art µCT data with XVR imaging. A model is presented which proves that XVR imaging yields information directly correlated with the trabecular microstructure. This opens up possibilities of using XVR as a tool to help early diagnosis of bone diseases, such as osteoporosis.

X-ray phase-contrast tomosynthesis for improved breast tissue discrimination.

PURPOSE: Attenuation-based tomosynthesis has proven to successfully resolve the glandular tissue overlap present in mammography. However, the ability of tomosynthesis to differentiate tumorous and glandular tissue remains limited, due to the small differences in X-ray attenuation in breast tissue. One possibility to overcome this limitation and to further increase the diagnostic value of tomosynthesis exams, is the application of recently developed grating-based phase-contrast methods, which provide complementary information on the phase shift and the local scattering power of the sample. In this study, we report on first phase-contrast breast tomosynthesis results of a mastectomy sample slice with an invasive ductal carcinoma. MATERIAL AND METHODS: A slice of a mastectomy sample with histologically proven invasive ductal cancer was imaged at the synchrotron radiation source ESRF (Grenoble, France). We used a two-grating interferometer setup at the ninth fractional Talbot distance and with an X-ray energy of 23 keV. In grating interferometry absorption, differential phase, and scattering images are recorded simultaneously. The tomosynthesis scan comprises 61 projections. Multimodal tomosynthesis results were reconstructed using a standard filtered back-projection approach. Our findings are supported by a comparison of tomographic views to histopathology. RESULTS: Phase-contrast tomosynthesis combines the advantage of improved soft-tissue discrimination in phase-contrast imaging with the ability of tomosynthesis to provide a third dimension so that improved feature visibility is not hampered by superposition artifacts. Our results indicate superior diagnostic value due to the depth resolution supplied in tomosynthesis imaging; a region of necrotic tissue that is obscured in a projection image can clearly be depicted in one single tomosynthesis slice. Compared to absorption tomosynthesis alone, soft tissue contrast is significantly enhanced in phase-contrast tomosynthesis views, where fibrous structures are clearly visible. CONCLUSION: In this article we present the first proof-of-principle grating-based phase-contrast tomosynthesis of a mastectomy sample section. A comparison of conventional attenuation with phase-contrast and dark-field tomosynthesis indicates that complementary information from three signals yields an increase in diagnostic value, which is verified in a comparison of our results to histological sections of the sample. As grating-based phase-contrast mammography efficiently works with conventional lab sources, our benchmark results indicate the potential benefit of translating phase-contrast tomosynthesis into a clinical setting.

Coherent superposition in grating-based directional dark-field imaging.

X-ray dark-field scatter imaging allows to gain information on the average local direction and anisotropy of micro-structural features in a sample well below the actual detector resolution. For thin samples the morphological interpretation of the signal is straight forward, provided that only one average orientation of sub-pixel features is present in the specimen. For thick samples, however, where the x-ray beam may pass structures of many different orientations and dimensions, this simple assumption in general does not hold and a quantitative description of the resulting directional dark-field signal is required to draw deductions on the morphology. Here we present a description of the signal formation for thick samples with many overlying structures and show its validity in experiment. In contrast to existing experimental work this description follows from theoretical predictions of a numerical study using a Fourier optics approach. One can easily extend this description and perform a quantitative structural analysis of clinical or materials science samples with directional dark-field imaging or even direction-dependent dark-field CT.

X-ray vector radiography for bone micro-architecture diagnostics.

The understanding of large biophysical systems at the systems level often depends on a precise knowledge of their microstructure. This is difficult to obtain, especially in vivo, because most imaging methods are either limited in terms of achievable field of view, or make use of penetrating ionizing radiations such as x-rays, in which case the resolution is severely limited by the deposited dose. Here, we describe a new method, x-ray vector radiography (XVR), which yields various types of information about the local orientation, anisotropy and average size of the sample microstructures. We demonstrate the feasibility by showing first experimental XVRs of human vertebra bone samples, giving information on the trabecular structures even with a pixel resolution of half a millimetre, much larger than the structures themselves. This last point is critical for the development of low-dose measurement methods which will allow for in vivo studies and potentially in the future for new medical diagnostics methods of bone metabolic disorder diseases such as osteoporosis.