Martin Stauber

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Stauber

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Martin

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0000-0003-4285-4146

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Publications 1 - 10 of 10

Specimen-specific beam models for fast and accurate prediction of human trabecular bone mechanical properties
van Lenthe, G. Harry; Stauber, Martin; Müller, Ralph (2006)
Bone
Direct assessment of bone competence in vivo is not possible, hence, it is inevitable to predict it using appropriate simulation techniques. Although accurate estimates of bone competence can be obtained from micro-finite element models (μFE), it is at the expense of large computer efforts. In this study, we investigated the application of structural idealizations to represent individual trabeculae by single elements. The objective was to implement and validate this technique. We scanned 42 human vertebral bone samples (10 mm height, 8 mm diameter) with micro-computed tomography using a 20 μm resolution. After scanning, direct mechanical testing was performed. Topological classification and dilation-based algorithms were used to identify individual rods and plates. Two FE models were created for each specimen. In the first one, each rod-like trabecula was modeled with one thickness-matched beam; each plate-like trabecula was modeled with several beams. From a simulated compression test, assuming one isotropic tissue modulus for all elements, the apparent stiffness was calculated. After reducing the voxel size to 40 μm, a second FE model was created using a standard voxel conversion technique. Again, one tissue modulus was assumed for all elements in all models, and a compression test was simulated. Bone volume fraction ranged from 3.7% to 19.5%; Young's moduli from 43 MPa to 649 MPa. Both models predicted measured apparent moduli equally well (R2 = 0.85), and were in excellent agreement with each other (R2 = 0.97). Tissue modulus was estimated at 9.0 GPa and 10.7 GPa for the beam FE and voxel FE models, respectively. On average, the beam models were solved in 219 s, reducing CPU usage up to 1150-fold as compared to 40 μm voxel FE models. Relative to 20 μm voxel models 10,000-fold reductions can be expected. The presented beam FE model is an abstraction of the intricate real trabecular structure using simple cylindrical beam elements. Nevertheless, it enabled an accurate prediction of global mechanical properties of microstructural bone. The strong reduction in CPU time provides the means to increase throughput, to analyze multiple loading configuration and to increase sample size, without increasing computational costs. With upcoming in vivo high-resolution imaging systems, this model has the potential to become a standard for mechanical characterization of bone.
Increased dose efficiency of breast CT with grating interferometry
Rawlik, Michal Mateusz; Pereira, Alexandre; Spindler, Simon; et al. (2023)
Optica
Refraction-based x-ray imaging can overcome the fundamental contrast limit of computed tomography (CT), particularly in soft tissue, but so far has been constrained to high-dose ex vivo applications or required highly coherent x-ray sources, such as synchrotrons.Here we demonstrate that grating interferometry (GI) is more dose efficient than conventional CT in imaging of human breast under close-to-clinical conditions. Our system, based on a conventional source and commercial gratings, outperformed conventional CT for spatial resolutions better than 263 μm and absorbed dose of 16 mGy. The sensitivity of GI is constrained by grating fabrication, and further progress will lead to significant improvements of clinicalCT.
Gender Differences in Trabecular and Cortical Microstructure of the Distal Radius Shown in an Elderly Population as Assessed by High-Resolution 3D-pQCT
Müller, Ralph; Mueller, T.L.; Stauber, Martin; et al. (2005)
Bone
Vertebral body bone strength: the contribution of individual trabecular element morphology
Parkinson, Ian H.; Badiei, Arash; Stauber, Martin; et al. (2012)
Osteoporosis International
Summary Although the amount of bone explains the largest amount of variability in bone strength, there is still a significant proportion unaccounted for. The morphology of individual bone trabeculae explains a further proportion of the variability in bone strength and bone elements that contribute to bone strength depending on the direction of loading. Introduction Micro-CT imaging enables measurement of bone microarchitecture and subsequently mechanical strength of the same sample. It is possible using micro-CT data to perform morphometric analysis on individual rod and plate bone trabeculae using a volumetric spatial decomposition algorithm and hence determine their contribution to bone strength. Methods Twelve pairs of vertebral bodies (T12/L1 or L4/L5) were harvested from human cadavers, and bone cubes (10 × 10 × 10 mm) were obtained. After micro-CT imaging, a volumetric spatial decomposition algorithm was applied, and measures of individual trabecular elements were obtained. Bone strength was measured in compression, where one bone specimen from each vertebral segment was tested supero-inferiorly (SI) and the paired specimen was tested antero-posteriorly (AP). Results Bone volume fraction was the strongest individual determinant of SI strength (r 2 = 0.77, p < 0.0001) and AP (r 2 = 0.54, p < 0.0001). The determination of SI strength was improved to r 2 = 0.87 with the addition of mean rod length and relative plate bone volume fraction. The determination of AP strength was improved to r 2 = 0.85 with the addition of mean rod volume and relative rod bone volume fraction. Conclusions Microarchitectural measures of individual trabeculae that contribute to bone strength have been identified. In addition to the contribution of BV/TV, trabecular rod morphology increased the determination of AP strength by 57%, whereas measures of trabecular plate and rod morphology increased determination of SI strength by 13%. Decomposing vertebral body bone architecture into its constituent morphological elements shows that trabecular element morphology has specific functional roles to assist in maintaining skeletal integrity.
Volumetric spatial decomposition of trabecular bone: A new method for local bone morphometry
Stauber, Martin; Müller, Ralph (2005)
Bone
Bottom-up Gold Filling of Trenches in Curved Wafers
Josell, Daniel; Raciti, David; Gnaupel-Herold, Thomas; et al. (2024)
Journal of the Electrochemical Society
A Bi³⁺-stimulated Au electrodeposition process in slightly alkaline Na₃Au(SO₃)₂ + Na₂SO₃ electrolytes has been previously demonstrated for void-free extreme bottom-up filling of high aspect ratio trenches in gratings that are key to advanced X-ray imaging technologies. Effective use of the full area of the gratings with conventional X-ray sources requires they have a finite radius of curvature to align the high aspect ratio Au-filled trenches with divergent X-rays. With that in mind, this work demonstrates bottom-up Au filling in gratings that are attached to curved holders. Contactless mapping of the Au-filled gratings captures residual curvature that is retained after their release from the curved holders (i.e., intrinsic curvature). X-ray diffraction captures the elastic strains in the Si underlying the Au-filled trenches of the grating. Complementary measurements on the surfaces of unpatterned Si wafers mounted on curved holders capture the actual curvatures and strains imposed in the mounted gratings. The gratings, either intrinsically curved or re-bent, provide high visibility across the entire field of view of an X-ray phase contrast imaging system with elastic strains substantially below those in planar gratings bent to the same radius.
Towards clinical-dose grating interferometry breast CT with fused intensity-based iterative reconstruction
van Gogh, Stefano; Rawlik, Michał; Pereira, Alexandre; et al. (2023)
Optics Express
X-ray grating interferometry CT (GI-CT) is an emerging imaging modality which provides three complementary contrasts that could increase the diagnostic content of clinical breast CT: absorption, phase, and dark-field. Yet, reconstructing the three image channels under clinically compatible conditions is challenging because of severe ill-conditioning of the tomographic reconstruction problem. In this work we propose to solve this problem with a novel reconstruction algorithm that assumes a fixed relation between the absorption and the phase-contrast channel to reconstruct a single image by automatically fusing the absorption and phase channels. The results on both simulations and real data show that, enabled by the proposed algorithm, GI-CT outperforms conventional CT at a clinical dose.
The interaction of microstructure and volume fraction in predicting failure in cancellous bone
Nazarian, Ara; Stauber, Martin; Zurakowski, David; et al. (2006)
Bone
Inroads have been made in the diagnosis and treatment of osteoporosis, yet dual-energy X-ray absorptiometry is still the primary diagnostic modality. This method provides 2D projections of an irregular 3D construct. However, human cancellous bone is highly heterogeneous with varying material properties. Therefore, to properly assess fracture risk, it is imperative to take into consideration microstructural indices besides subregional bone volume fraction (BV/TV). A power law model with average BV/TV as the independent variable describes 38% of the variation in yield strength; however, this predictive power is increased to 56% when BV/TV of the weakest subregion is considered. Of twenty-five specimens studied, 76% had minimum BV/TV, maximum principal Eigen value of the fabric tensor (H1) and minimum connectivity density (Conn.D) values within the visually determined failure regions. These three independent morphometric indices yielded significant differences between the failure and non-failure regions of each specimen. From the results, we conclude that subregions with minimal BV/TV values are better predictors of mechanical failure in cancellous bone than average specimen BV/TV. Addition of microstructural indices augments this predictive power to generate a trabecular failure prediction model based on volume fraction and cancellous bone microstructure specifically in areas where trabecular failure is most likely to occur.
Data-driven gradient regularization for quasi-Newton optimization in iterative grating interferometry CT reconstruction
van Gogh, Stefano; Mukherjee, Subhadip; Rawlik, Michał; et al. (2024)
IEEE Transactions on Medical Imaging
Grating interferometry CT (GI-CT) is a promising technology that could play an important role in future breast cancer imaging. Thanks to its sensitivity to refraction and small-angle scattering, GI-CT could augment the diagnostic content of conventional absorption-based CT. However, reconstructing GI-CT tomographies is a complex task because of ill problem conditioning and high noise amplitudes. It has previously been shown that combining data-driven regularization with iterative reconstruction is promising for tackling challenging inverse problems in medical imaging. In this work, we present an algorithm that allows seamless combination of data-driven regularization with quasi-Newton solvers, which can better deal with ill-conditioned problems compared to gradient descent-based optimization algorithms. Contrary to most available algorithms, our method applies regularization in the gradient domain rather than in the image domain. This comes with a crucial advantage when applied in conjunction with quasi-Newton solvers: the Hessian is approximated solely based on denoised data. We apply the proposed method, which we call GradReg, to both conventional breast CT and GI-CT and show that both significantly benefit from our approach in terms of dose efficiency. Moreover, our results suggest that thanks to its sharper gradients that carry more high spatial-frequency content, GI-CT can benefit more from GradReg compared to conventional breast CT. Crucially, GradReg can be applied to any image reconstruction task which relies on gradient-based updates.
Quantifying grating defects in X-ray Talbot-Lau interferometry through a comparative study of two fabrication techniques
Pereira, Alexandre; Spindler, Simon; Shi, Zhitian; et al. (2025)
Scientific Reports
The performance of an X-ray grating interferometry system depends on the geometry and quality of the gratings. Fabrication of micrometer-pitch high-aspect-ratio gold gratings, which are essential for measuring small refraction angles at higher energies, is challenging. The two widely used technologies for manufacturing gratings are based on gold electroplating in polymeric or silicon templates. Here, gratings manufactured by both approaches were inspected using conventional microscopy, X-ray synchrotron radiography, and computed laminography to extract characteristic features of the gratings profile to be modeled accurately. These models were used in a wave-propagation simulation to predict the effects of the gratings’ geometry and defects on the quality of a Talbot-Lau interferometer in terms of visibility and absorption capabilities. The simulated outcomes of grating features produced with both techniques could eventually be observed and evaluated in a table-top Talbot-Lau-Interferometer.

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