Abel et al 2012 Micro-CT virtual preparation
palaeobiologist's guide and workflow to micro-CT virtual preparation of fossils
Download (.pdf) Optimal Use of Automatic Exposure Control in CT
by Borgny Ween
Published in Radiologic Technology March/April 2010; 81: 309-317
Key words: Image quality, Optimization, Pediatric radiography, Radiographic technology, Radiographer, Radiation doses
Background
Computed tomography (CT) examinations account for a significant portion of individuals’ increasing... more
Background
Computed tomography (CT) examinations account for a significant portion of individuals’ increasing exposure to medical radiation. Automatic exposure control (AEC) was introduced in CT scanners to decrease patient doses while maintaining appropriate image quality.
Objective
To identify areas for AEC optimization and suggest practical optimization methods.
Methods
A literature review was conducted to assess current knowledge regarding tube current modulation and AEC in CT from peer-reviewed journals and publications from national and international organizations involved in medical imaging and radiation protection.
Results
Four important aspects of AEC use were identified: interaction of user-selectable parameters with AEC, patient positioning and AEC, specific challenges with patient size groups and how to select appropriate input value.
Conclusion
AEC is a useful tool for dose optimization but dose savings are not guaranteed unless the equipment is used properly. Further research is required into optimal use of AEC, particularly for pediatric examinations.
Heterogeneity correction in the construction of optimized planning in radiotherapy using linear programming
Authors: VIANA, R. S. S. ; FLORENTINO, H. O. ; LIMA, E.A.B.F. ; FONSECA, P. R. ; HOMEM, T. P. D.
Published in: Pesquisa Operacional, v. 31, p. 527-540, 2011.
A radiotherapy planning is considered optimal when all the parameters involved, physical or biological, have been... more A radiotherapy planning is considered optimal when all the parameters involved, physical or biological, have been investigated and appropriate for each patient. In this type of planning, the major concern is with the tumor irradiation with the minimum possible damage to healthy tissues of the irradiated region, especially the organs at risk. The optimal planning for radiotherapy can be aided by Linear Programming and there is a wide literature addressing this subject. However, most published mathematical formulations do not contemplate a scenario in terms of practical applications, because they do not incorporate the heterogeneous composition of the irradiated tissue. This paper presents a methodology for heterogeneity correction in the composition of different types of irradiated tissues based on proportions among their different linear attenuation coefficient.
Microstructural modelling of nuclear graphite using multi-phase models
by James Marrow
C. Berre, S.L. Fok, B.J. Marsden, P.M. Mummery, T.J. Marrow and G.B. Neighbour
Journal of Nuclear Materials, 380, (1-3), pp 46-58 (2008)
This paper presents a new modelling technique using three-dimensional multi-phase finite element models in which... more This paper presents a new modelling technique using three-dimensional multi-phase finite element models in which meshes representing the microstructure of thermally oxidised nuclear graphite were generated from X-ray micro-tomography images. The density of the material was related to the image greyscale using Beer–Lambert’s law, and multiple phases could thus be defined. The local elastic and non-linear properties of each phase were defined as a function of density and changes in Young’s mod- ulus, tensile and compressive strength with thermal oxidation were calculated. Numerical predictions compared well with experimental data and with other numerical results obtained using two-phase mod- els. These models were found to be more representative of the actual microstructure of the scanned material than two-phase models and, possibly because of pore closure occurring during compression, compressive tests were also predicted to be less sensitive to the microstructure geometry than tensile tests.
Three dimensional observations and modelling of intergranular stress corrosion cracking in austenitic stainless steel
by James Marrow
T.J. Marrow, L. Babout, A.P. Jivkov, P. Wood, D. Engelberg, N. Stevens, P.J. Withers, R.C. Newman
J Nuclear Materials, 352, pp. 62-74 (2006)
Presented E-MRS 2005 Spring Meeting Symposium N on Nuclear Materials, Strasbourg, France, 31 May-02 June 2005
Stress corrosion cracking is a life-limiting factor in many components of nuclear power plant in which failure of... more Stress corrosion cracking is a life-limiting factor in many components of nuclear power plant in which failure of struc- tural components presents a substantial hazard to both safety and economic performance. Uncertainties in the kinetics of short crack behaviour can have a strong influence on lifetime prediction, and arise due both to the complexity of the under- lying mechanisms and to the difficulties of making experimental observations. This paper reports on an on-going research programme into the dynamics and morphology of intergranular stress corrosion cracking in austenitic stainless steels in simulated light water environments, which makes use of recent advances in high resolution X-ray microtomography. In particular in situ, three dimensional X-ray tomographic images of intergranular stress corrosion crack nucleation and growth in sensitised austenitic stainless steel provide evidence for the development of crack bridging ligaments, caused by the resistance of non-sensitised special grain boundaries. In parallel a simple grain bridging model, introduced to quan- tify the effect of crack bridging on crack development, has been assessed for thermo-mechanically processed microstruc- tures via statically loaded room temperature simulant solution tests and as well as high temperature/pressure autoclave studies. Thermo-mechanical treatments have been used to modify the grain size, grain boundary character and triple junc- tion distributions, with a consequent effect on crack behaviour. Preliminary three-dimensional finite element models of intergranular crack propagation have been developed, with the aim of investigating the development of crack bridging and its effects on crack propagation and crack coalescence.
A New Generation of High- Resolution Benchtop Micro- CT Scanners for Application in Soil Science
"Co-authored with Markus Tuller, C.M.P Vaz", "published in 'Tuller, M., C.M.P. Vaz, and R. Kulkarni, 2010. "A New Generation of High- Resolution Benchtop Micro- CT Scanners for Application in Soil Science".
Proceedings of the 1st International Conference and Exploratory Workshop on Soil Architecture and Physico- Chemical Functions(CESAR), Research
Centre Foulum, Denmark, Nov 30 - Dec 2'"
Computed tomography and magnetic resonance imaging studies of Latimeria chalumnae
Authors: Schultze, H.-P. & R. Cloutier
Year: 1991
Reference: Environmental Biology of Fishes, 32: 159-181.
Recent radiologic imaging techniques (CT[Computed Tomography] and MRI[Magnetic Resonance Imaging]) were used to... more Recent radiologic imaging techniques (CT[Computed Tomography] and MRI[Magnetic Resonance Imaging]) were used to investigate the cranial anatomy of the coelacanth Latimeria chalumnae. The non-invasive CT and MRI techniques were performed successfully on a 1.45 m female specimen. This specimen had been frozen a year earlier for future research; the CT was conducted on the frozen animal, whereas the MRI method was performed immediately after thawing. The CT technique provides information about differential density of the organism (especially informative with respect to hard tissues, bone and cartilage), whereas three different types of MRI (proton resonance T,, T, and ‘flash’) distinguish cartilage, muscles, and different connective tissues. A total of 381 CT cross sections (2 mm thick with 1 mm of overlap) through the head region were used in a computerized three-dimensional reconstruction program to address questions concerning cranial morphology. The results obtained from these radiologic imaging techniques confirmed most of the basic anatomy known from traditional dissections. However, the morphology of complex structures, such as the cartilaginous processes of the neurocranium, and the integration of the branchial arches and palate can only now be described more accurately
Observations of intergranular stress corrosion cracking in a grain-mapped polycrystal
by James Marrow
A. King, G. Johnson, D. Engelberg, W. Ludwig and J. Marrow
Science, 321 (5887), pp. 382-385 (2008)
Nondestructive three-dimensional mapping of grain shape, crystallographic orientation, and grain boundary geometry by... more Nondestructive three-dimensional mapping of grain shape, crystallographic orientation, and grain boundary geometry by diffraction contrast tomography (DCT) provides opportunities for the study of the interaction between intergranular stress corrosion cracking and microstructure. A stress corrosion crack was grown through a volume of sensitized austenitic stainless steel mapped with DCT and observed in situ by synchrotron tomography. Several sensitization-resistant crack- bridging boundaries were identified, and although they have special geometric properties, they are not the twin variant boundaries usually maximized during grain boundary engineering
Diffraction Contrast Tomography of Polycrystalline Alumina
by James Marrow
T.J. Marrow, A. King, P. Reischig, S. Rolland du Roscoat, W. Ludwig
Presented at ACerS Sosman Award Symposium, Materials Science & Technology 2009, October 25-29, 2009: Pittsburgh, PA
Diffraction Contrast Tomography has been used to map the three-dimensional microstructure of a ceramic (coarse grain... more Diffraction Contrast Tomography has been used to map the three-dimensional microstructure of a ceramic (coarse grain size polycrystalline alumina) for the first time. This new synchrotron technique determines, non-destructively, the crystallographic orientation of each grain from its diffraction geometry. The 3D grain shapes are also obtained from projected images of the grains in the diffraction condition. Grain boundary structure can therefore be characterised in terms of the physical grain boundary plane orientation and the crystal misorientation of the adjacent grains.
X-ray microtomographic observation of intergranular stress corrosion cracking in sensitised austenitic stainless steel
by James Marrow
L Babout, T J Marrow, D Engleberg, and P J Withers
J. Mater Sci Tech, 22, pp. 1068-1075 (2006)
Intergranular stress corrosion cracking in a sensitised type 302 stainless steel wire has been observed in situ using... more Intergranular stress corrosion cracking in a sensitised type 302 stainless steel wire has been observed in situ using high resolution X-ray microtomography. Tomography enables the development and failure of crack bridging ligaments to be studied in detail in three dimensions. Direct comparison of these features has been made with scanning electron microscopy fractography. The crack bridges failed in a ductile manner, with a morphology that is consistent with non-sensitised low energy grain boundaries.
X-ray tomography observation of crack propagation in nuclear graphite
by James Marrow
A Hodgkins, T J Marrow, P Mummery, B Marsden and A Fok
J. Mater Sci. Tech, 22, pp. 1045-1051 (2006)
X-ray microtomography has been used to investigate the mechanisms responsible for rising crack growth resistance with... more X-ray microtomography has been used to investigate the mechanisms responsible for rising crack growth resistance with crack propagation (R curve behaviour) in polygranular nuclear graphite. Tomography can be used to observe changes in the crack shape with propagation, and a side grooved specimen has been developed to produce the planar straight fronted crack necessary for fracture toughness measurement. Crack bridging from frictional contact between the fracture surfaces is observed. A zone of reduced X-ray attenuation, attributed to microstructural damage, is also observed around the crack tip and in its wake. These are the first in situ observations of the mechanisms of the R curve behaviour in nuclear graphites.
X-ray microtomography studies of localised corrosion and transitions to stress corrosion cracking
by James Marrow
B. J. Connolly, D. A. Horner, S. J. Fox, A. J. Davenport, C. Padovani, S. Zhou,A. Turnbull,M. Preuss,N. P. Stevens, T.J. Marrow, J.-Y. Buffiere, E. Boller, A. Groso and M. Stampanoni
Mat Sci Tech, 22, pp. 1076-1085, (2006)
Two forms of high resolution X-ray tomographic experiments (i.e. synchrotron based X-ray microtomography and desktop... more Two forms of high resolution X-ray tomographic experiments (i.e. synchrotron based X-ray microtomography and desktop microfocus computed X-ray tomography) are demonstrated in the present paper to illustrate the wide application of these techniques for qualitative and quantitative studies of localised corrosion and environmentally assisted cracking. Specifically, synchrotron based X-ray tomography was used to investigate the localised corrosion morphology within aluminium specimens when exposed in situ to a chloride environment while microfocus computed X-ray tomography was used to investigate the morphology and quantify the transition from localised corrosion to stress corrosion cracking in steel specimens exposed ex situ to a simulated corrosive condensate environment.
In situ analysis of cracks in structural materials using synchrotron X-ray tomography and diffraction
by James Marrow
A. Steuwer, L. Edwards, S. Pratihar, S. Ganguly, M. Peel, M.E. Fitzpatrick, T.J. Marrow, P.J. Withers, I. Sinclair, K.D. Singh, N. Gao, T. Buslaps and J-Y Buffiere
Nuclear Instruments & Methods in Physics Research, B 246, pp. 217-225, (2006)
Recent advances in synchrotron based X-ray imaging and diffraction techniques offer interesting new possibilities for... more Recent advances in synchrotron based X-ray imaging and diffraction techniques offer interesting new possibilities for mapping 3D grain shapes and crystallographic orientations in different classes of poly- crystalline materials. X-ray diffraction contrast tomography (DCT) is a monochromatic beam imaging technique combining the principles of X-ray micro-tomography and three-dimensional X-ray diffraction microscopy (3DXRD). DCT provides simultaneous access to 3D grain shape, crystallographic orientation and attenuation coefficient distribution at the micrometer length scale. The microtexture of the material can be quantified in more detail by post-processing of the volume data provided by DCT. In particular one can determine the local crystallographic habit plane of the grain boundary by analysing the surface nor- mal of the grain boundary with respect to the crystal orientation. The resulting five parameter description of the character of individual grain boundaries could previously be produced only by destructive charac- terization techniques. Statistical analysis of this kind of data can be expected to provide new insight into various physico-chemical processes, driven by the grain boundary energy (corrosion, coarsening).
Grain Tracking at the High Energy Materials Science Beamline of the Petra III Synchrotron Radiation Source
by James Marrow
A, King, N. Schell, R.V. Martins, F. Beckmann, H-U Ruhnau, R, Kiehn, J. Marrow, W. Ludwig, A Schreyer
Materials Science Forum, 652, (2010), pp70-73
Grain tracking is a term used to describe experiments that investigate polycrystalline materials in terms of the... more Grain tracking is a term used to describe experiments that investigate polycrystalline materials in terms of the crystallites or grains from which they are composed, non-destructively and in three dimensions. The new German high brilliance synchrotron radiation source, Petra III, will become available to users in 2010. The GKSS research centre will operate two beamlines, including the high energy materials science beamline (HEMS). HEMS will feature an instrument dedicated to grain tracking, able to support a range of experiments of this kind. This paper describes the design and specification of this instrument, and gives examples of the types of experiments that will be possible.
Applications of Computed Tomography to Museum Conservation and Exhibit
by Girish Tembe
This is the abstract of a poster presented at a poster at the Society of Vertebrate Paleontology, November 2011.
A calibration methodology of QCT BMD for human vertebral body with registered micro-CT images
Dall'Ara E, Varga P, Pahr D, Zysset P
Medical Physics, May 2011, 38 (5), Pages 2602-2608
Purpose: The accuracy of QCT-based homogenized finite element (FE) models is strongly related to the accuracy of the... more Purpose: The accuracy of QCT-based homogenized finite element (FE) models is strongly related to the accuracy of the prediction of bone volume fraction (BV/TV) from bone mineral density (BMD). The goal of this study was to establish a calibration methodology to relate the BMD computed with QCT with the BV/TV computed with micro-CT (CT) over a wide range of bone mineral densities and to investigate the effect of region size in which BMD and BV/TV are computed. Methods: Six human vertebral bodies were dissected from the spine of six donors and scanned submerged in water with QCT (voxel size: 0.391 0.391 0.450 mm 3) and CT (isotropic voxel size: 0.0183 mm3). The CT images were segmented with a single level threshold. Afterward, QCT-grayscale, CT-grayscale, and CT-segmented images were registered. Two isotropic grids of 1.230 mm (small) and 4.920 mm (large) were superimposed on every image, and QCTBMD was compared both with CTBMD and CTBV/TV for each grid cell. Results: The ranges of QCTBMD for large and small regions were 9-559 mg/cm3 and -90 to 1006 mg/cm3, respectively. QCTBMD was found to overestimate CTBMD. No significant differences were found between the QCT BMD-CTBV/TV regression parameters of the two grid sizes. However, the R2 was higher, and the standard error of the estimate (SEE) was lower for large regions when compared to small regions. For the pooled data, an extrapolated QCTBMD value equal to 1062 mg/cm3 was found to correspond to 100 CTBV/TV. Conclusions: A calibration method was defined to evaluate BV/TV from QCTBMD values for cortical and trabecular bone in vitro. The QCTBMD-CTBV/TV calibration was found to be dependent on the scanned vertebral section but not on the size of the regions. However, the higher SEE computed for small regions suggests that the deleterious effect of QCT image noise on FE modelling increases with decreasing voxel size. © 2011 American Association of Physicists in Medicine.
HR-pQCT-based homogenised finite element models provide quantitative predictions of experimental vertebral body stiffness and strength with the same accuracy as μFE models.
Pahr DH, Dall'ara E, Varga P, Zysset PK.
Comput Methods Biomech Biomed Engin. 2011 Apr 1:1. [Epub ahead of print]
This study validated two different high-resolution peripheral quantitative computer tomography (HR-pQCT)-based finite... more This study validated two different high-resolution peripheral quantitative computer tomography (HR-pQCT)-based finite element (FE) approaches, enhanced homogenised continuum-level (hFE) and micro-finite element (μFE) models, by comparing them with compression test results of vertebral body sections. Thirty-five vertebral body sections were prepared by removing endplates and posterior elements, scanned with HR-pQCT and tested in compression up to failure. Linear hFE and μFE models were created from segmented and grey-level CT images, and apparent model stiffness values were compared with experimental stiffness as well as strength results. Experimental and numerical apparent elastic properties based on grey-level/segmented CT images (N = 35) correlated well for μFE ([image omitted] ) and hFE models ([image omitted] ). Vertebral section stiffness values from the linear μFE/hFE models estimated experimental ultimate apparent strength very well ([image omitted] ). Calibrated hFE models were able to predict quantitatively apparent stiffness with the same accuracy as μFE models. However, hFE models needed no back-calculation of a tissue modulus or any kind of fitting and were computationally much cheaper.
A nonlinear finite element model validation study based on a novel experimental technique for inducing anterior wedge-shape fractures in human vertebral bodies in vitro
Dall'Ara E, Schmidt R, Pahr D, Varga P, Chevalier Y, Patsch J, Kainberger F, Zysset P.
J Biomech. 2010 Aug 26;43(12):2374-80. Epub 2010 May 11.
Vertebral compression fracture is a common medical problem in osteoporotic individuals. The quantitative computed... more Vertebral compression fracture is a common medical problem in osteoporotic individuals. The quantitative computed tomography (QCT)-based finite element (FE) method may be used to predict vertebral strength in vivo, but needs to be validated with experimental tests. The aim of this study was to validate a nonlinear anatomy specific QCT-based FE model by using a novel testing setup. Thirty-seven human thoracolumbar vertebral bone slices were prepared by removing cortical endplates and posterior elements. The slices were scanned with QCT and the volumetric bone mineral density (vBMD) was computed with the standard clinical approach. A novel experimental setup was designed to induce a realistic failure in the vertebral slices in vitro. Rotation of the loading plate was allowed by means of a ball joint. To inimize device compliance, the specimen deformation was measured directly on the loading plate with three sensors. A nonlinear FE model was generated from the calibrated QCT images and computed vertebral stiffness and strength were compared to those measured during the experiments. In agreement with clinical observations, most of the vertebrae underwent an anterior wedge-shape fracture. As expected, the FE method predicted both stiffness and strength better than vBMD (R2 improved from 0.27 to 0.49 and from 0.34 to 0.79, respectively). Despite the lack of fitting parameters, the linear regression of the FE prediction for strength was close to the 1:1 relation (slope and intercept close to one (0.86kN) and to zero (0.72kN), respectively). In conclusion, a nonlinear FE model was successfully validated through a novel experimental technique for generating wedge-shape fractures in human thoracolumbar vertebrae.
An accurate estimation of bone density improves the accuracy of subject-specific finite element models
Schileo E, Dall'ara E, Taddei F, Malandrino A, Schotkamp T, Baleani M, Viceconti M.
J Biomech. 2008 Aug 7;41(11):2483-91. Epub 2008 Jul 7. Erratum in: J Biomech. 2008 Nov 14;41(15):3294.
An experimental–numerical study was performed to investigate the relationships between computed tomography... more
An experimental–numerical study was performed to investigate the relationships between computed tomography (CT)-density and ash density, and between ash density and apparent density for bone tissue, to evaluate their influence on the accuracy of subject-specific FE models of human bones.
Sixty cylindrical bone specimens were examined. CT-densities were computed from CT images while apparent and ash densities were measured experimentally. The CT/ash-density and ash/apparent-density relationships were calculated. Finite element models of eight human femurs were generated considering these relationships to assess their effect on strain prediction accuracy.
CT and ash density were linearly correlated (R2 = 0.997) over the whole density range but not equivalent (intercept > 0, slope < 1). A constant ash/apparent-density ratio (0.598 +- 0.004) was found for cortical bone. A lower ratio, with a larger dispersion, was found for trabecular bone (0.459 +- 0.100), but it became less dispersed, and equal to that of cortical tissue, when testing smaller trabecular specimens (0.598 +- 0.036). This suggests that an experimental error occurred in apparent-density measurements for large trabecular specimens and a constant ratio can be assumed valid for the whole density range. Introducing the obtained relationships in the FE modelling procedure improved strain prediction accuracy (R2 = 0.95, RMSE = 7%).
The results suggest that: (i) a correction of the densitometric calibration should be used when evaluating bone ash-density from clinical CT scans, to avoid ash-density underestimation and overestimation for low- and high-density bone tissue, respectively; (ii) the ash/apparent-density ratio can be assumed constant in human femurs and (iii) the correction improves significantly the model accuracy and should be considered in subject-specific bone modelling.