Статті в журналах: "Microstructural imaging"

1

Alotaibi, Abdulmajeed, Christopher Tench, Rebecca Stevenson, Ghadah Felmban, Amjad Altokhis, Ali Aldhebaib, Rob A. Dineen, and Cris S. Constantinescu. "Investigating Brain Microstructural Alterations in Type 1 and Type 2 Diabetes Using Diffusion Tensor Imaging: A Systematic Review." Brain Sciences 11, no. 2 (January 22, 2021): 140. http://dx.doi.org/10.3390/brainsci11020140.

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Type 1 and type 2 diabetes mellitus have an impact on the microstructural environment and cognitive functions of the brain due to its microvascular/macrovascular complications. Conventional Magnetic Resonance Imaging (MRI) techniques can allow detection of brain volume reduction in people with diabetes. However, conventional MRI is insufficiently sensitive to quantify microstructural changes. Diffusion Tensor Imaging (DTI) has been used as a sensitive MRI-based technique for quantifying and assessing brain microstructural abnormalities in patients with diabetes. This systematic review aims to summarise the original research literature using DTI to quantify microstructural alterations in diabetes and the relation of such changes to cognitive status and metabolic profile. A total of thirty-eight published studies that demonstrate the impact of diabetes mellitus on brain microstructure using DTI are included, and these demonstrate that both type 1 diabetes mellitus and type 2 diabetes mellitus may affect cognitive abilities due to the alterations in brain microstructures.

2

Talmon, Yeshayahu. "Cryo-TEM of amphiphilic polymer and amphiphile/polymer solutions." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 876–77. http://dx.doi.org/10.1017/s0424820100150216.

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To achieve complete microstructural characterization of self-aggregating systems, one needs direct images in addition to quantitative information from non-imaging, e.g., scattering or Theological measurements, techniques. Cryo-TEM enables us to image fluid microstructures at better than one nanometer resolution, with minimal specimen preparation artifacts. Direct images are used to determine the “building blocks” of the fluid microstructure; these are used to build reliable physical models with which quantitative information from techniques such as small-angle x-ray or neutron scattering can be analyzed.To prepare vitrified specimens of microstructured fluids, we have developed the Controlled Environment Vitrification System (CEVS), that enables us to prepare samples under controlled temperature and humidity conditions, thus minimizing microstructural rearrangement due to volatile evaporation or temperature changes. The CEVS may be used to trigger on-the-grid processes to induce formation of new phases, or to study intermediate, transient structures during change of phase (“time-resolved cryo-TEM”). Recently we have developed a new CEVS, where temperature and humidity are controlled by continuous flow of a mixture of humidified and dry air streams.

3

Kane, Genevieve A., M. David Frey, and Robert Hull. "Influence of Controlled Cooling Rates During Thermal Processing of Ti 6% Al 4% V Alloys Using In-Situ Scanning Electron Microscopy." MRS Advances 5, no. 29-30 (2020): 1603–11. http://dx.doi.org/10.1557/adv.2020.190.

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ABSTRACTWe describe experimental approaches to real time examination of the microstructural evolution of Ti 6%Al 4%V upon cooling from above the beta transus (~995 °C) while imaging in the scanning electron microscope. Ti 6%Al 4%V is a two phase, α+β titanium alloy with high strength and corrosion resistance. The β →α transformation on cooling can give rise to different microstructures and properties through various thermal treatments. Fully lamellar microstructures, bi-modal microstructures, and equiaxed microstructures can each be obtained by accessing different cooling rates upon the final treatment above the beta temperature, each resulting in uniquely enhanced material properties.Utilizing the capabilities of a heating/ tensile stage developed by Kammrath & Weiss Inc., are able to apply real-time imaging techniques in the scanning electron microscope to monitor the development of the microstructure. Annealing temperatures up to 1100 °C are attainable, with cooling rates ranging from 0.1 ° C per second to 3.3 °C per second. This has allowed us to directly observe the formation of lamellae at different annealing temperature/ cooling rate combinations to determine the lamellar microstructure width, separation, and colony size.

4

Jaganathan, Sudhakar, Hooman V. Tafreshi, and Behnam Pourdeyhimi. "Two-Scale Modeling Approach to Predict Permeability of Fibrous Media." Journal of Engineered Fibers and Fabrics 3, no. 2 (June 2008): 155892500800300. http://dx.doi.org/10.1177/155892500800300208.

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We previously demonstrated how one can develop a 3–D geometry to model the fibrous microstructure of a nonwoven fiberweb and use it to simulate its permeability at fiber level [1–6]. Developing 3–D models of most nonwoven fabrics (bonded fiberwebs), however, is cumbersome, as in the case of hydroentangled fabrics, for instance. In such cases, microscopic techniques are often used to generate 3–D images of the media's microstructures. Nevertheless, whether the microstructure is modeled or obtained from 3–D imaging, extensive computational resources are required to use them in fluid flow simulations [7]. To circumvent this problem, a two-scale modeling approach is proposed here that allows us to simulate the entire thickness of a commercial fabric/filter on a personal computer. In particular, the microscale permeability of a hydroentangled nonwoven is computed using 3–D reconstructed microstructures obtained from Digital Volumetric Imaging (DVI). The resulting microstructural permeability tensors are then used in a macroscale porous model to simulate the flow through the material's thickness and the calculation of its overall permeability.

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Vander Voort, George Frederic, Beatriz Suárez-Peña, and Juan Asensio-Lozano. "Metallographic Assessment of Al-12Si High-Pressure Die Casting Escalator Steps." Microscopy and Microanalysis 20, no. 5 (July 7, 2014): 1486–93. http://dx.doi.org/10.1017/s143192761400172x.

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AbstractA microstructural characterization study was performed on high-pressure die cast specimens extracted from escalator steps manufactured from an Al-12 wt.% Si alloy designed for structural applications. Black and white, color light optical imaging and scanning electron microscopy techniques were used to conduct the microstructural analysis. Most regions in the samples studied contained globular-rosette primary α-Al grains surrounded by an Al-Si eutectic aggregate, while primary dendritic α-Al grains were present in the surface layer. This dendritic microstructure was observed in the regions where the melt did not impinge directly on the die surface during cavity filling. Consequently, microstructures in the surface layer were nonuniform. Utilizing physical metallurgy principles, these results were analyzed in terms of the applied pressure and filling velocity during high-pressure die casting. The effects of these parameters on solidification at different locations of the casting are discussed.

6

Li, Kexue, Junliang Liu, Chris R. M. Grovenor, and Katie L. Moore. "NanoSIMS Imaging and Analysis in Materials Science." Annual Review of Analytical Chemistry 13, no. 1 (June 12, 2020): 273–92. http://dx.doi.org/10.1146/annurev-anchem-092019-032524.

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High-resolution SIMS analysis can be used to explore a wide range of problems in material science and engineering materials, especially when chemical imaging with good spatial resolution (50–100 nm) can be combined with efficient detection of light elements and precise separation of isotopes and isobaric species. Here, applications of the NanoSIMS instrument in the analysis of inorganic materials are reviewed, focusing on areas of current interest in the development of new materials and degradation mechanisms under service conditions. We have chosen examples illustrating NanoSIMS analysis of grain boundary segregation, chemical processes in cracking, and corrosion of nuclear components. An area where NanoSIMS analysis shows potential is in the localization of light elements, in particular, hydrogen and deuterium. Hydrogen embrittlement is a serious problem for industries where safety is critical, including aerospace, nuclear, and oil/gas, so it is imperative to know where in the microstructure hydrogen is located. By charging the metal with deuterium, to avoid uncertainty in the origin of the hydrogen, the microstructural features that can trap hydrogenic species, such as precipitates and grain and phase boundaries, can be determined by NanoSIMS analysis on a microstructurally relevant scale.

7

Leyssens, Lisa, Camille Pestiaux, and Greet Kerckhofs. "A Review of Ex Vivo X-ray Microfocus Computed Tomography-Based Characterization of the Cardiovascular System." International Journal of Molecular Sciences 22, no. 6 (March 23, 2021): 3263. http://dx.doi.org/10.3390/ijms22063263.

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Cardiovascular malformations and diseases are common but complex and often not yet fully understood. To better understand the effects of structural and microstructural changes of the heart and the vasculature on their proper functioning, a detailed characterization of the microstructure is crucial. In vivo imaging approaches are noninvasive and allow visualizing the heart and the vasculature in 3D. However, their spatial image resolution is often too limited for microstructural analyses, and hence, ex vivo imaging is preferred for this purpose. Ex vivo X-ray microfocus computed tomography (microCT) is a rapidly emerging high-resolution 3D structural imaging technique often used for the assessment of calcified tissues. Contrast-enhanced microCT (CE-CT) or phase-contrast microCT (PC-CT) improve this technique by additionally allowing the distinction of different low X-ray-absorbing soft tissues. In this review, we present the strengths of ex vivo microCT, CE-CT and PC-CT for quantitative 3D imaging of the structure and/or microstructure of the heart, the vasculature and their substructures in healthy and diseased state. We also discuss their current limitations, mainly with regard to the contrasting methods and the tissue preparation.

8

Sheng, Wei, Weipeng Li, Ji Qi, Teng Liu, Honghui He, Yang Dong, Shaoxiong Liu, Jian Wu, Daniel Elson, and Hui Ma. "Quantitative Analysis of 4 × 4 Mueller Matrix Transformation Parameters for Biomedical Imaging." Photonics 6, no. 1 (March 26, 2019): 34. http://dx.doi.org/10.3390/photonics6010034.

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Mueller matrix polarimetry is a potentially powerful technique for obtaining microstructural information of biomedical specimens. Thus, it has found increasing application in both backscattering imaging of bulk tissue samples and transmission microscopic imaging of thin tissue slices. Recently, we proposed a technique to transform the 4 × 4 Mueller matrix elements into a group of parameters, which have explicit associations with specific microstructural features of samples. In this paper, we thoroughly analyze the relationships between the Mueller matrix transformation parameters and the characteristic microstructures of tissues by using experimental phantoms and Monte Carlo simulations based on different tissue mimicking models. We also adopt quantitative evaluation indicators to compare the Mueller matrix transformation parameters with the Mueller matrix polar decomposition parameters. The preliminary imaging results of bulk porcine colon tissues and thin human pathological tissue slices demonstrate the potential of Mueller matrix transformation parameters as biomedical diagnostic indicators. Also, this study provides quantitative criteria for parameter selection in biomedical Mueller matrix imaging.

9

Alvis, Roger, David Dingley, and David Field. "Observation of grain superstructure in thin aluminum films by orientation imaging microscopy." Proceedings, annual meeting, Electron Microscopy Society of America 53 (August 13, 1995): 436–37. http://dx.doi.org/10.1017/s0424820100138555.

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The correlation of aluminum alloy reliability data to microstructure has long been the goal of those scientists seeking to model electromigration behavior of interconnects. Traditionally, microstructural information has been acquired through x-ray diffraction , and transmission electron microscopy (TEM). However, each of these techniques is capable of delivering only part of the characterization whole. We describe the application of orientation imaging microscopy (OIM) to thin aluminum alloy films and demonstrate its versatility in providing the key microstructural reliability parameters: namely texture and grain size, as well as providing insight to the microstructure of grain boundaries.OIM was performed on an electromigration test structure (figure 1). The Al-alloy was deposited on titanium and capped with an anti-reflective titanium nitride. Subsequently, the test structure was patterned and capped with a multilayer blanket consisting of silicon nitride (SiN), and SiO2. The structure was annealed after the SOG deposition at 450° C for 90 minutes, seeing no electrical stressing. The die was removed from the package and deprocessed before the OIM was acquired.

10

Morris, Jonathan C. "Imaging microstructural contact damage in silicon." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 1144–45. http://dx.doi.org/10.1017/s0424820100151556.

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The indentation of single crystal silicon has been shown to produce a metal to semiconducting structural phase transformation. This phase transformation dominates the effect of contact damage from both indentation and scratching at low loads and hence affects the results of related mechanical tests. We are examining the microstructure of contact damage in silicon in order to understand better the mechanisms which control its low-load mechanical and tribological behavior. Extensive transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) have been used to characterize both morphological and structural changes brought about by contact damage.The plan-view bright field image in Figure 1 exhibits strong crystallographic contrast outside of the indented area. The indented area as well as the extrusions emanating from it are amorphous as evidenced by their lack of crystallographic contrast regardless of tilt as well as their diffuse illumination in dark field. Small bits of fragmented polycrystalline silicon are visible at the indentation borders as well as at the tip of one extrusion.

11

Kiessling, Fabian, Daniel Razansky, and Frauke Alves. "Anatomical and microstructural imaging of angiogenesis." European Journal of Nuclear Medicine and Molecular Imaging 37, S1 (May 12, 2010): 4–19. http://dx.doi.org/10.1007/s00259-010-1450-0.

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12

Inoke, Koji, Kenji Kaneko, and Z. Horita. "Three-Dimensional Imaging of Shear Band Produced by ECAP Process in Al-Ag Alloy." Materials Science Forum 503-504 (January 2006): 603–8. http://dx.doi.org/10.4028/www.scientific.net/msf.503-504.603.

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A significant change in microstructure occurs during the application of severe plastic deformation (SPD) such as by equal-channel angular pressing (ECAP). In this study, intense plastic strain was imposed on an Al-10.8wt%Ag alloy by the ECAP process. The amount of strain was controlled by the numbers of passes. After 1 pass of ECAP, shear bands became visible within the matrix. With increasing numbers of ECAP passes, the fraction of shear bands was increased. In this study, the change in microstructures was examined by three-dimensional electron tomography (3D-ET) in transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM). With this 3D-ET method, it was possible to conduct a precise analysis of the sizes, widths and distributions of the shear bands produced by the ECAP process. It is demonstrated that the 3D-ET method is promising to understand mechanisms of microstructural refinement using the ECAP process.

13

Sklenička, Vàclav, Petr Král, Jiří Dvořák, Marie Kvapilová, and Milan Svoboda. "Microstructure Evolution and Creep Behavior in ECAP Processed Metallic Materials." Materials Science Forum 783-786 (May 2014): 2689–94. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.2689.

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The creep behavior of high purity aluminum and copper, Al-0.2wt.%Sc and Cu-0.2wt.%Zr alloys was examined after processing by equal-channel angular pressing (ECAP) with an emphasis on the link between microstructure and creep. The microstructure was revealed by electron backscatter diffraction (EBSD) and analyzed by stereological methods. Representative microstructural parameters were obtained using orientation imaging microscopy and EBSD on the relationship between creep behavior and microstructure.

14

Hubbard, Nicholas A., Monroe Turner, Joanna L. Hutchison, Austin Ouyang, Jeremy Strain, Larry Oasay, Saranya Sundaram, et al. "Multiple sclerosis-related white matter microstructural change alters the BOLD hemodynamic response." Journal of Cerebral Blood Flow & Metabolism 36, no. 11 (July 22, 2016): 1872–84. http://dx.doi.org/10.1177/0271678x15615133.

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Multiple sclerosis (MS) results in inflammatory damage to white matter microstructure. Prior research using blood-oxygen-level dependent (BOLD) imaging indicates MS-related alterations to brain function. What is currently unknown is the extent to which white matter microstructural damage influences BOLD signal in MS. Here we assessed changes in parameters of the BOLD hemodynamic response function (HRF) in patients with relapsing-remitting MS compared to healthy controls. We also used diffusion tensor imaging to assess whether MS-related changes to the BOLD-HRF were affected by changes in white matter microstructural integrity. Our results showed MS-related reductions in BOLD-HRF peak amplitude. These MS-related amplitude decreases were influenced by individual differences in white matter microstructural integrity. Other MS-related factors including altered reaction time, limited spatial extent of BOLD activity, elevated lesion burden, or lesion proximity to regions of interest were not mediators of group differences in BOLD-HRF amplitude. Results are discussed in terms of functional hyperemic mechanisms and implications for analysis of BOLD signal differences.

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Ouyang, Minhui, Tina Jeon, Aristeidis Sotiras, Qinmu Peng, Virendra Mishra, Cathy Halovanic, Min Chen, et al. "Differential cortical microstructural maturation in the preterm human brain with diffusion kurtosis and tensor imaging." Proceedings of the National Academy of Sciences 116, no. 10 (February 19, 2019): 4681–88. http://dx.doi.org/10.1073/pnas.1812156116.

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During the third trimester, the human brain undergoes rapid cellular and molecular processes that reshape the structural architecture of the cerebral cortex. Knowledge of cortical differentiation obtained predominantly from histological studies is limited in localized and small cortical regions. How cortical microstructure is differentiated across cortical regions in this critical period is unknown. In this study, the cortical microstructural architecture across the entire cortex was delineated with non-Gaussian diffusion kurtosis imaging as well as conventional diffusion tensor imaging of 89 preterm neonates aged 31–42 postmenstrual weeks. The temporal changes of cortical mean kurtosis (MK) or fractional anisotropy (FA) were heterogeneous across the cortical regions. Cortical MK decreases were observed throughout the studied age period, while cortical FA decrease reached its plateau around 37 weeks. More rapid decreases in MK were found in the primary visual region, while faster FA declines were observed in the prefrontal cortex. We found that distinctive cortical microstructural changes were coupled with microstructural maturation of associated white matter tracts. Both cortical MK and FA measurements predicted the postmenstrual age of preterm infants accurately. This study revealed a differential 4D spatiotemporal cytoarchitectural signature inferred by non-Gaussian diffusion barriers inside the cortical plate during the third trimester. The cytoarchitectural processes, including dendritic arborization and neuronal density decreases, were inferred by regional cortical FA and MK measurements. The presented findings suggest that cortical MK and FA measurements could be used as effective imaging markers for cortical microstructural changes in typical and potentially atypical brain development.

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Toda, Hiroyuki, Keisuke Minami, Masakazu Kobayashi, Kentaro Uesugi, Akihisa Takeuchi, and Toshiro Kobayashi. "Observation of Precipitates in Aluminium Alloys by Sub-Micrometer Resolution Tomography Using Fresnel Zone Plate." Materials Science Forum 519-521 (July 2006): 1361–66. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.1361.

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An X-ray microtomography combined with hard X-ray imaging microscopy, that potentially has a spatial resolution of the order of 10 to 100 nm, has been applied to the three-dimensional observation of internal microstructural features in overaged Al-Ag alloys. A Fresnel zone plate is used as an objective with a magnification of 49.3 times. Imaging of resolution test patterns has indicated spatial resolutions of around 180 and 200 nm in the vertical and horizontal directions, respectively. This paper reports the first impression of the microstructural imaging by means of such a high-resolution imaging microtomography. Precipitate microstructures are readily observed and quantified in terms of volume fraction and orientation. Conventional microtomography with a simple projection geometry is also applied for comparison purpose at the highest resolution level currently available at a third generation synchrotron facility. It would appear that the present technique provides a unique potential to observe the 3-D geometry and spatial distribution of nanoscopic features inside samples that are several orders of magnitude thicker than thin-foil specimens for TEM observation.

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Barrick, Thomas R., Catherine A. Spilling, Matt G. Hall, and Franklyn A. Howe. "The Mathematics of Quasi-Diffusion Magnetic Resonance Imaging." Mathematics 9, no. 15 (July 26, 2021): 1763. http://dx.doi.org/10.3390/math9151763.

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Quasi-diffusion imaging (QDI) is a novel quantitative diffusion magnetic resonance imaging (dMRI) technique that enables high quality tissue microstructural imaging in a clinically feasible acquisition time. QDI is derived from a special case of the continuous time random walk (CTRW) model of diffusion dynamics and assumes water diffusion is locally Gaussian within tissue microstructure. By assuming a Gaussian scaling relationship between temporal (α) and spatial (β) fractional exponents, the dMRI signal attenuation is expressed according to a diffusion coefficient, D (in mm2 s−1), and a fractional exponent, α. Here we investigate the mathematical properties of the QDI signal and its interpretation within the quasi-diffusion model. Firstly, the QDI equation is derived and its power law behaviour described. Secondly, we derive a probability distribution of underlying Fickian diffusion coefficients via the inverse Laplace transform. We then describe the functional form of the quasi-diffusion propagator, and apply this to dMRI of the human brain to perform mean apparent propagator imaging. QDI is currently unique in tissue microstructural imaging as it provides a simple form for the inverse Laplace transform and diffusion propagator directly from its representation of the dMRI signal. This study shows the potential of QDI as a promising new model-based dMRI technique with significant scope for further development.

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McKenna, Faye, James Babb, Laura Miles, Donald Goff, and Mariana Lazar. "Reduced Microstructural Lateralization in Males with Chronic Schizophrenia: A Diffusional Kurtosis Imaging Study." Cerebral Cortex 30, no. 4 (December 10, 2019): 2281–94. http://dx.doi.org/10.1093/cercor/bhz239.

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Abstract Decreased brain lateralization is considered a trait marker of schizophrenia. Whereas reductions in both functional and macrostructural gray matter laterality in schizophrenia are well established, the investigation of gray matter microstructural lateralization has so far been limited to a small number of ex vivo studies, which limits the understanding of neurobiological substrates involved and development of adequate treatments. The aim of the current study was to assess in vivo gray matter microstructure lateralization patterns in schizophrenia by employing the diffusion kurtosis imaging (DKI)–derived mean kurtosis (MK) metric. MK was calculated for 18 right-handed males with chronic schizophrenia and 19 age-matched healthy control participants in 46 bilateral gray matter regions of interest (ROI). Microstructural laterality indexes (μLIs) were calculated for each subject and ROI, and group comparisons were conducted across regions. The relationship between μLI values and performance on the Wisconsin Card Sorting Test (WCST) was also evaluated. We found that compared with healthy controls, males with chronic schizophrenia had significantly decreased μLI across cortical and subcortical gray matter regions, which was correlated with poorer performance on the WCST. Our results suggest the ability of DKI-derived MK to capture gray matter microstructural lateralization pathology in vivo.

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Fei, Jingtong, Shanshan Nie, Bo Zhang, Xinli Teng, Ying Chen, Yikun Qu, Zhuoxin Cheng, and Linqi Guo. "Study on the Cytotoxic Microstructure of Titanium Dioxide Nanoparticles by X-Ray Phase-Contrast CT Imaging." Contrast Media & Molecular Imaging 2022 (July 30, 2022): 1–6. http://dx.doi.org/10.1155/2022/2413922.

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To address the problem of microstructural analysis of titania nanoparticles with high cytotoxicity, the authors propose X-ray phase-comparative CT imaging studies. In this method, the HE-stained section samples were compared with the X-ray phase-contrast CT imaging microscopic images, and 3D texture analysis was used to observe the changes in the preparation of hepatocyte microstructures in the two groups. The results show that X-ray phase-contrast CT imaging microscopic images and their larger image size are closely related to HE staining images, and X-ray phase-contrast CT microscopic images can observe important data of hepatocytes from multiple angles. The ship skeleton extraction method based on the endpoint limit also has advantages over traditional algorithms in extraction accuracy and can provide more 3D feature files, confirming the growth and transformation of normal hepatocytes into hepatocyte cytotoxic microstructures. The distribution effect of using the ensemble process is better than the simple 2D feature set and 3D feature set, and the overall accuracy is improved; the result distribution of the tree determination and random forest methods is also better than that of the support vector machine method. The experimental results show that the X-ray phase-contrast CT images can highlight the 2D and 3D imaging features of the hepatotoxic microstructure of TiO2 nanoparticles and provide data for quantitative analysis.

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Alawneh, Mai, and Haithem Soliman. "Using Imaging Techniques to Analyze the Microstructure of Asphalt Concrete Mixtures: Literature Review." Applied Sciences 13, no. 13 (July 3, 2023): 7813. http://dx.doi.org/10.3390/app13137813.

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The performance of asphalt concrete (AC) mixtures depends highly on their internal structure and the interaction of the mixture components under different loading conditions. Imaging techniques provide effective tools that can assess the microstructure and failure mechanisms of materials. Imaging techniques have been used in recent research studies to examine and analyze the evolution of the internal structure of AC mixtures resulting from traffic and environmental loading. Increasing knowledge of the microstructural properties and mechanical behaviour of AC mixtures could improve the design process and enable researchers to develop more accurate prediction models for the long-term performance of pavements. This paper reviews three imaging techniques which were used to characterize the microstructure of AC mixtures. These three imaging techniques are digital camera imaging, scanning electron microscope (SEM) imaging, and X-ray computed tomography (CT) scan. Extensive insight has been presented into these imaging techniques, including their principles, methods, sample preparation, and associated instruments. This review provides guidelines for future research on using these imaging techniques to analyze the microstructure of AC mixtures and assess their long-term performance.

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Kobayashi, Toshiro, and Hiroyuki Toda. "Strength and Fracture of Aluminium Alloys." Materials Science Forum 539-543 (March 2007): 127–34. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.127.

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Synchrotron X-ray microtomography has been utilized for the 3D characterisation of microstructure of aluminium foams. A combination of phase contrast imaging technique and several application techniques, such as local area tomography, microstructural gauging and in-situ observation, has enabled the assessment of microstructural effects on compressive deformation behaviours. It has been clarified that ductile buckling of a cell wall occurs regardless of any of the above microstructural factors in the case of a pure aluminium foam, while rather brittle fracture of a cell wall is induced by the existence of coarse micro-pores independently of the intermetallic particles and the grain boundary in the case of Al-Zn-Mg alloy foams. When cooling rate during foaming is high, however, lower energy absorption might be attributable to the significant amount of residual foaming agent particle and its inhomogeneous distribution. These tendencies are also confirmed by 3D strain mapping by tracking internal microstructural features.

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Burke, M. G., and M. K. Miller. "A Comparison of Tem and Apfim to the Interpretation of Modulated Microstructures." Proceedings, annual meeting, Electron Microscopy Society of America 43 (August 1985): 70–71. http://dx.doi.org/10.1017/s042482010011742x.

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Interpretation of fine-scale microstructures containing high volume fractions of second phase is complex. In particular, microstructures developed through decomposition within low temperature miscibility gaps may be extremely fine. This paper compares the morphological interpretations of such complex microstructures by the high-resolution techniques of TEM and atom probe field-ion microscopy (APFIM).The Fe-25 at% Be alloy selected for this study was aged within the low temperature miscibility gap to form a <100> aligned two-phase microstructure. This triaxially modulated microstructure is composed of an Fe-rich ferrite phase and a B2-ordered Be-enriched phase. The microstructural characterization through conventional bright-field TEM is inadequate because of the many contributions to image contrast. The ordering reaction which accompanies spinodal decomposition in this alloy permits simplification of the image by the use of the centered dark field technique to image just one phase. A CDF image formed with a B2 superlattice reflection is shown in fig. 1. In this CDF micrograph, the the B2-ordered Be-enriched phase appears as bright regions in the darkly-imaging ferrite. By examining the specimen in a [001] orientation, the <100> nature of the modulations is evident.

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Cao, Fei, Ruosi Wang, Peng Zhang, Tongmin Wang, and Kexing Song. "In Situ Investigation of Microstructural Evolution and Intermetallic Compounds Formation at Liquid Al/Solid Cu Interface by Synchrotron X-ray Radiography." Materials 15, no. 16 (August 17, 2022): 5647. http://dx.doi.org/10.3390/ma15165647.

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Synchrotron radiation dynamic imaging technology combined with the static characterization method was used to study the microstructural evolution and the growth kinetics of intermetallic compounds (IMCs) at the liquid Al/solid Cu interface. The results show that the interfacial microstructure can be divided into layered solid diffusion microstructures (AlCu3, Al4Cu9, Al2Cu3 and AlCu) and solidification microstructures (Al3Cu4, AlCu and Al2Cu) from the Cu side to the Al side. Meanwhile, the growth of bubbles formed during the melting, holding and solidification of an Al/Cu sample was also discussed, which can be divided into three modes: diffusion, coalescence and engulfment. Moreover, the growth of AlCu3 and (Al4Cu9 + Al2Cu3) near the Cu side is all controlled by both interfacial reaction and volume diffusion. The growth of Al3Cu4 adjacent to the melt is mainly controlled by the interfacial reaction, which plays a major role in the growth of the total IMCs.

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Momot, Konstantin I. "Microstructural magnetic resonance imaging of articular cartilage." Biomedical Spectroscopy and Imaging 1, no. 1 (2012): 27–37. http://dx.doi.org/10.3233/bsi-2012-0003.

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25

Lee, A. S., R. Weissleder, T. J. Brady, and J. Wittenberg. "Lymph nodes: microstructural anatomy at MR imaging." Radiology 178, no. 2 (February 1991): 519–22. http://dx.doi.org/10.1148/radiology.178.2.1987619.

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Edwards, Luke J., Evgeniya Kirilina, Siawoosh Mohammadi, and Nikolaus Weiskopf. "Microstructural imaging of human neocortex in vivo." NeuroImage 182 (November 2018): 184–206. http://dx.doi.org/10.1016/j.neuroimage.2018.02.055.

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Black, David R. "Microstructural characterization using x-ray diffraction imaging." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 504–5. http://dx.doi.org/10.1017/s0424820100148356.

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X-ray diffraction imaging, also known as x-ray topography, is a powerful tool to study the defect microstructure of single crystals. As the name implies, this technique is based on recording an image of the diffracted x-ray beam from a crystal. Contrast in the image results from point-to-point variation in the diffracted intensity through the crystal. An example of a diffraction image is shown in figure 1. That this image is in some way a topographic representation of the sample can be seen in the impression of differing elevations and textures in different parts of the image. However, since this image is a result of diffraction from the sample the interpretation of the image is much more complex.Diffraction contrast is usually separated into two types: mosaic contrast and extinction contrast. Mosaic contrast occurs for crystals considered to be formed from a collection of small perfect crystal blocks. These blocks have a well defined rocking curve width, the angular range over which they will diffract, and may be slightly misoriented with respect to each other and/or may have different lattice spacing.

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Filippi, Massimo, Paolo Preziosa, and Maria A. Rocca. "Microstructural MR Imaging Techniques in Multiple Sclerosis." Neuroimaging Clinics of North America 27, no. 2 (May 2017): 313–33. http://dx.doi.org/10.1016/j.nic.2016.12.004.

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29

Huang, Shuning, and David E. Sosnovik. "Molecular and Microstructural Imaging of the Myocardium." Current Cardiovascular Imaging Reports 3, no. 1 (January 21, 2010): 26–33. http://dx.doi.org/10.1007/s12410-010-9007-y.

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30

Stephens, Rebecca L., Benjamin W. Langworthy, Sarah J. Short, Jessica B. Girault, Martin A. Styner, and John H. Gilmore. "White Matter Development from Birth to 6 Years of Age: A Longitudinal Study." Cerebral Cortex 30, no. 12 (June 27, 2020): 6152–68. http://dx.doi.org/10.1093/cercor/bhaa170.

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Abstract Human white matter development in the first years of life is rapid, setting the foundation for later development. Microstructural properties of white matter are linked to many behavioral and psychiatric outcomes; however, little is known about when in development individual differences in white matter microstructure are established. The aim of the current study is to characterize longitudinal development of white matter microstructure from birth through 6 years to determine when in development individual differences are established. Two hundred and twenty-four children underwent diffusion-weighted imaging after birth and at 1, 2, 4, and 6 years. Diffusion tensor imaging data were computed for 20 white matter tracts (9 left–right corresponding tracts and 2 commissural tracts), with tract-based measures of fractional anisotropy and axial and radial diffusivity. Microstructural maturation between birth and 1 year are much greater than subsequent changes. Further, by 1 year, individual differences in tract average values are consistently predictive of the respective 6-year values, explaining, on average, 40% of the variance in 6-year microstructure. Results provide further evidence of the importance of the first year of life with regard to white matter development, with potential implications for informing early intervention efforts that target specific sensitive periods.

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Reislev, Nina Linde, Tim Bjørn Dyrby, Hartwig Roman Siebner, Ron Kupers, and Maurice Ptito. "Simultaneous Assessment of White Matter Changes in Microstructure and Connectedness in the Blind Brain." Neural Plasticity 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/6029241.

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Magnetic resonance imaging (MRI) of the human brain has provided converging evidence that visual deprivation induces regional changes in white matter (WM) microstructure. It remains unclear how these changes modify network connections between brain regions. Here we used diffusion-weighted MRI to relate differences in microstructure and structural connectedness of WM in individuals with congenital or late-onset blindness relative to normally sighted controls. Diffusion tensor imaging (DTI) provided voxel-specific microstructural features of the tissue, while anatomical connectivity mapping (ACM) assessed the connectedness of each voxel with the rest of the brain. ACM yielded reduced anatomical connectivity in the corpus callosum in individuals with congenital but not late-onset blindness. ACM did not identify any brain region where blindness resulted in increased anatomical connectivity. DTI revealed widespread microstructural differences as indexed by a reduced regional fractional anisotropy (FA). Blind individuals showed lower FA in the primary visual and the ventral visual processing stream relative to sighted controls regardless of the blindness onset. The results show that visual deprivation shapes WM microstructure and anatomical connectivity, but these changes appear to be spatially dissociated as changes emerge in different WM tracts. They also indicate that regional differences in anatomical connectivity depend on the onset of blindness.

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Robert Sinclair and Kai Tang. "Magnetic Imaging Of Recording Media." Microscopy and Microanalysis 5, S2 (August 1999): 28–29. http://dx.doi.org/10.1017/s1431927600013465.

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Magnetic recording forms the basis of one of the largest international industries. Electron microscopy has of course played a significant role in relating magnetic performance to the underlying microstructure. However, relatively little attention has been paid to the ways in which imaging of the magnetic structure can be correlated with processing conditions and microstructural parameters. The present research has been aimed to address this deficiency.A method was devised to prepare samples with large electron transparent areas (e.g., 250 microns square) from real computer hard discs. Fresnel TEM images were taken in a Philips CM20 FEG equipped with a special Lorentz pole piece, and with the objective lens off. Upon defocusing, the ferromagnetic domain structure strikingly appears. The characteristics of the recorded tracks depend on the magnetic state of the disc prior to magnetic “writing”, and much information about the local direction of magnetization could be obtained from the nature of the magnetic “ripple” structure.

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Wiskel, J. Barry, Ry Karl, Maro Emakpor, Fateh Fazeli, Chad Cathcart, Tom Zhou, Saber Yu, Doug G. Ivey, and Hani Henein. "Development and Application of a Thermal Microstructure Model of Laminar Cooling of an API X70 Microalloyed Steel." Materials Science Forum 1105 (November 29, 2023): 7–12. http://dx.doi.org/10.4028/p-y88gpk.

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A thermal microstructure model of laminar cooling of X70 microalloyed steel skelp was developed to predict the effect of the laminar cooling temperature profile on the through thickness skelp microstructure. Plant trials using infrared video imaging were undertaken to establish the laminar cooling conditions prevalent in the industrial cooling system. The infrared video temperature measurements were used to develop a finite element thermal model of the skelp transiting the entire laminar cooling system. Dilatometer testing of the X70 steel with cooling rates ranging from 1 °C/s to 120 °C/s was undertaken to develop the CCT curve and to quantify austenite decomposition. The predicted thermal profile from the finite element model and the phase transformation behaviour were combined into a thermal microstructural model capable of predicting the phases that would develop through the skelp thickness as a function of the laminar cooling profile. The predicted through thickness microstructures were verified from electron backscattered diffraction (EBSD) phase analysis of industrially produced API X70 skelp.

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Sun, Qing, Wenliang Fan, Yuan Liu, Yan Zou, Natalie Wiseman, Zhifeng Kou, and Ping Han. "Characterization of brain microstructural abnormalities in cirrhotic patients without overt hepatic encephalopathy using diffusion kurtosis imaging." Brain Imaging and Behavior 14, no. 2 (September 11, 2019): 627–38. http://dx.doi.org/10.1007/s11682-019-00141-4.

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Abstract Cirrhosis is a major public health concern. However, little is known about the neurobiological mechanisms underlying brain microstructure alterations in cirrhotic patients. The purpose of this prospective study was to investigate brain microstructural alterations in cirrhosis with or without minimal hepatic encephalopathy (MHE) and their relationship with patients’ neurocognitive performance and disease duration using voxel-based analysis of diffusion kurtosis imaging (DKI). DKI data were acquired from 30 cirrhotic patients with MHE, 31 patients without MHE (NMHE) and 59 healthy controls. All DKI-derived parametric maps were compared across the three groups to investigate their group differences. Correlation analyses were further performed to assess relationships between altered imaging parameters and clinical data. Voxel-based analysis of DKI data results showed that MHE/NMHE patients had increased radial diffusivity, axial diffusivity (AD) and mean diffusivity in addition to decreased axial kurtosis (AK) and fractional anisotropy of kurtosis in several regions. Compared to controls, these regions were primarily the cingulum, temporal and frontal cortices. The DKI metrics (i.e., AK and AD) were correlated with clinical variables in the two patient groups. In conclusion, DKI is useful for detecting brain microstructural abnormalities in MHE and NMHE patients. Abnormal DKI parameters suggest alterations in brain microstructural complexity in cirrhotic patients, which may contribute to the neurobiological basis of neurocognitive impairment. These results may provide additional information on the pathophysiology of cirrhosis.

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Coad, Bethany M., Emma Craig, Rebecca Louch, John P. Aggleton, Seralynne D. Vann, and Claudia Metzler-Baddeley. "Precommissural and postcommissural fornix microstructure in healthy aging and cognition." Brain and Neuroscience Advances 4 (January 2020): 239821281989931. http://dx.doi.org/10.1177/2398212819899316.

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The fornix is a key tract of the hippocampal formation, whose status is presumed to contribute to age-related cognitive decline. The precommissural and postcommissural fornix subdivisions form respective basal forebrain/frontal and diencephalic networks that may differentially affect aging and cognition. We employed multi-parametric magnetic resonance imaging (MRI) including neurite orientation density and dispersion imaging, quantitative magnetization transfer (qMT), and T1-relaxometry MRI to investigate the microstructural properties of these fornix subdivisions and their relationship with aging and cognition in 149 asymptomatic participants (38–71 years). Aging was associated with increased free water signal and reductions in myelin-sensitive R1 and qMT indices but no apparent axon density differences in both precommissural and postcommissural fibers. Precommissural relative to postcommissural fibers showed a distinct microstructural pattern characterised by larger free water signal and axon orientation dispersion, with lower apparent myelin and axon density. Furthermore, differences in postcommissural microstructure were related to performance differences in object-location paired-associate learning. These results provide novel in vivo neuroimaging evidence for distinct microstructural properties of precommissural and postcommissural fibers that are consistent with their anatomy as found in axonal tracer studies, as well as for a contribution of postcommissural fibers to the learning of spatial configurations.

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Roth, Don J., Mark R. DeGuire, Leonard E. Dolhert, and Aloysius F. Hepp. "Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O7−x superconductor and their correlation with room-temperature ultrasonic measurements." Journal of Materials Research 6, no. 10 (October 1991): 2041–53. http://dx.doi.org/10.1557/jmr.1991.2041.

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The purpose of this study was to (1) examine the spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O7−x specimens over the pore fraction range 0.10–0.25 and (2) determine the viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability. Spatial variations in a.c. susceptibility were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in a.c. shielding and loss behavior. Optical quantitative image analysis on sample cross sections revealed pore fraction to be the varying microstructural feature.

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Prior, David J., Patrick W. Trimby, Ursula D. Weber, and David J. Dingley. "Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope." Mineralogical Magazine 60, no. 403 (December 1996): 859–69. http://dx.doi.org/10.1180/minmag.1996.060.403.01.

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AbstractWe have developed a system using ‘forescatter detectors’ for backscattered imaging of specimen surfaces inclined at 50–80° to the incident beam (inclined-scanning) in the SEM. These detectors comprise semiconductor chips placed below the tilted specimen. Forescatter detectors provide an orientation contrast (OC) image to complement quantitative crystallographic data from electron backscatter patterns (EBSP). Specimens were imaged using two detector geometries and these images were compared to those collected with the specimen surface normal to the incident beam (normal-scanning) using conventional backscattered electron detector geometries and also to an automated technique, orientation imaging microscopy (OIM). When normal-scanning, the component of the BSE signal relating to the mean atomic number (z) of the material is an order of magnitude greater than any OC component, making OC imaging in polyphase specimens almost impossible. Images formed in inclined-scanning, using forescatter detectors, have OC and z-contrast signals of similar magnitude, allowing OC imaging in polyphase specimens.OC imaging is purely qualitative, and by repeatedly imaging the same area using different specimen-beam geometries, we found that a single image picks out less than 60% of the total microstructural information and as many as 6 combined images are required to give the full data set. The OIM technique is limited by the EBSP resolution (1–2°) and subsequently misses a lot of microstructural information. The use of forescatter detectors is the most practical means of imaging OC in tilted specimens, but it is also a powerful tool in its own right for imaging microstructures in polyphase specimens, an essential asset for geological work.

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Telang, A. A., T. T. Bieler, S. Choi, and K. K. Subramanian. "Orientation imaging studies of Sn-based electronic solder joints." Journal of Materials Research 17, no. 9 (September 2002): 2294–306. http://dx.doi.org/10.1557/jmr.2002.0337.

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Single shear lap specimens were subjected to creep, isothermal aging, and thermomechanical fatigue (TMF). Scanning electron microscopy micrographs of previously polished specimens revealed changes in surface morphology. Orientation imaging microscopy was carried out on the same specimens to study the microstructural evolution and crystal orientation changes. As-fabricated joints consistently show a preferred crystal orientation with a few minority orientations with highly preferred misorientations. Alloy additions caused an increase in the number of statistically significant crystal orientations and misorientations. The solidification microstructure was unchanged due to room-temperature creep. Aging caused development and motion of well-defined subgrain boundaries and removal of most minority orientations. TMF causes heterogeneous refinement of the microstructure that accounts for the localized grain boundary sliding in regions of high strain concentration. This study implies that the lead-free solder joints are not polycrystals, but multicrystals, so that deformation is very heterogeneous and sensitive to strain and temperature history.

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Krejsa, M. R., and J. L. Koenig. "NMR Imaging Studies of Vulcanized Butyl Rubber." Rubber Chemistry and Technology 64, no. 4 (September 1, 1991): 635–40. http://dx.doi.org/10.5254/1.3538578.

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Abstract NMR imaging is a useful technique for studying the physical and spatial microstructure of cured elastomers. Different swelling agents can be used as chemical probes to detect varying amounts of microstructural differences. Imaging can be used to detect highly cured regions due to aging, poor mixing, and thermal gradients. NMRI is thus useful to study spatial distribution of crosslinks and is sensitive to changes in this distribution of crosslinks due to thermal gradients and the effects of aging and reversion processes. It can also be used to observed entrapped air in air-aged samples. Spin-lattice T1, relaxation times for solvent in cured elastomers have been shown to be shorter than the bulk solvent T1 values, providing a new method for determining the crosslink density. NMRI results have suggested that cure reversion and postcuring processes produce similar spatial results.

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Farrher, Ezequiel, Farida Grinberg, Tamara Khechiashvili, Irene Neuner, Kerstin Konrad, and N. Jon Shah. "Spatiotemporal Patterns of White Matter Maturation after Pre-Adolescence: A Diffusion Kurtosis Imaging Study." Brain Sciences 14, no. 5 (May 13, 2024): 495. http://dx.doi.org/10.3390/brainsci14050495.

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Diffusion tensor imaging (DTI) enables the assessment of changes in brain tissue microstructure during maturation and ageing. In general, patterns of cerebral maturation and decline render non-monotonic lifespan trajectories of DTI metrics with age, and, importantly, the rate of microstructural changes is heterochronous for various white matter fibres. Recent studies have demonstrated that diffusion kurtosis imaging (DKI) metrics are more sensitive to microstructural changes during ageing compared to those of DTI. In a previous work, we demonstrated that the Cohen’s d of mean diffusional kurtosis (dMK) represents a useful biomarker for quantifying maturation heterochronicity. However, some inferences on the maturation grades of different fibre types, such as association, projection, and commissural, were of a preliminary nature due to the insufficient number of fibres considered. Hence, the purpose of this follow-up work was to further explore the heterochronicity of microstructural maturation between pre-adolescence and middle adulthood based on DTI and DKI metrics. Using the effect size of the between-group parametric changes and Cohen’s d, we observed that all commissural fibres achieved the highest level of maturity, followed by the majority of projection fibres, while the majority of association fibres were the least matured. We also demonstrated that dMK strongly correlates with the maxima or minima of the lifespan curves of DTI metrics. Furthermore, our results provide substantial evidence for the existence of spatial gradients in the timing of white matter maturation. In conclusion, our data suggest that DKI provides useful biomarkers for the investigation of maturation spatial heterogeneity and heterochronicity.

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Ashton, M. J., and John F. Humphreys. "Inhomogeneous Deformation and Microstructural Evolution during the Hot Deformation of Al-4.98%Mg." Materials Science Forum 467-470 (October 2004): 117–22. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.117.

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Plane strain channel die compression (PSC) deformation has been carried out on Al-Mg alloys with Mg contents of 0.1 to 5 % at 350°C, and the deformed microstructures characterised by channelling contrast backscattered electron imaging (BSE), secondary electron imaging (SE) and high resolution electron backscatter diffraction (EBSD). Measurements of orientation spread and misorientation gradient obtained from EBSD maps have been used to quantify the microstructural inhomogeneity developing in the 4.98 % Mg alloy. The results are consistent with inhomogeneous plasticity with more deformation occurring in the grain boundary regions. In-situ FEGSEM hot deformation experiments on the Al-4.98 % Mg alloy have provided evidence of stress driven boundary migration at low strains.

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Hilger, A., N. Kardjilov, T. Kandemir, I. Manke, J. Banhart, D. Penumadu, A. Manescu, and M. Strobl. "Revealing microstructural inhomogeneities with dark-field neutron imaging." Journal of Applied Physics 107, no. 3 (February 2010): 036101. http://dx.doi.org/10.1063/1.3298440.

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43

Bumb, Jan M., Marc A. Brockmann, Christoph Groden, and Ingo Nolte. "Microstructural analysis of pineal volume using trueFISP imaging." World Journal of Radiology 5, no. 4 (2013): 166. http://dx.doi.org/10.4329/wjr.v5.i4.166.

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44

Cocco, Alex P., George J. Nelson, William M. Harris, Arata Nakajo, Timothy D. Myles, Andrew M. Kiss, Jeffrey J. Lombardo, and Wilson K. S. Chiu. "Three-dimensional microstructural imaging methods for energy materials." Physical Chemistry Chemical Physics 15, no. 39 (2013): 16377. http://dx.doi.org/10.1039/c3cp52356j.

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45

Nazarian, Ara, and Ralph Müller. "Time-lapsed microstructural imaging of bone failure behavior." Journal of Biomechanics 37, no. 1 (January 2004): 55–65. http://dx.doi.org/10.1016/s0021-9290(03)00254-9.

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46

Xi, Hanmi, Aiden Zhu, Gerard R. Klinzing, Liping Zhou, Shawn Zhang, Andrew J. Gmitter, Kristin Ploeger, Pavithra Sundararajan, Majid Mahjour, and Wei Xu. "Characterization of Spray Dried Particles Through Microstructural Imaging." Journal of Pharmaceutical Sciences 109, no. 11 (November 2020): 3404–12. http://dx.doi.org/10.1016/j.xphs.2020.07.032.

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47

Chamberland, Maxime, Sila Genc, Chantal M. W. Tax, Dmitri Shastin, Kristin Koller, Erika P. Raven, Adam Cunningham, et al. "Detecting microstructural deviations in individuals with deep diffusion MRI tractometry." Nature Computational Science 1, no. 9 (September 2021): 598–606. http://dx.doi.org/10.1038/s43588-021-00126-8.

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AbstractMost diffusion magnetic resonance imaging studies of disease rely on statistical comparisons between large groups of patients and healthy participants to infer altered tissue states in the brain; however, clinical heterogeneity can greatly challenge their discriminative power. There is currently an unmet need to move away from the current approach of group-wise comparisons to methods with the sensitivity to detect altered tissue states at the individual level. This would ultimately enable the early detection and interpretation of microstructural abnormalities in individual patients, an important step towards personalized medicine in translational imaging. To this end, Detect was developed to advance diffusion magnetic resonance imaging tractometry towards single-patient analysis. By operating on the manifold of white-matter pathways and learning normative microstructural features, our framework captures idiosyncrasies in patterns along white-matter pathways. Our approach paves the way from traditional group-based comparisons to true personalized radiology, taking microstructural imaging from the bench to the bedside.

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Yu, Qinlin, Yun Peng, Huiying Kang, Qinmu Peng, Minhui Ouyang, Michelle Slinger, Di Hu, Haochang Shou, Fang Fang, and Hao Huang. "Differential White Matter Maturation from Birth to 8 Years of Age." Cerebral Cortex 30, no. 4 (December 9, 2019): 2674–90. http://dx.doi.org/10.1093/cercor/bhz268.

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Abstract Comprehensive delineation of white matter (WM) microstructural maturation from birth to childhood is critical for understanding spatiotemporally differential circuit formation. Without a relatively large sample of datasets and coverage of critical developmental periods of both infancy and early childhood, differential maturational charts across WM tracts cannot be delineated. With diffusion tensor imaging (DTI) of 118 typically developing (TD) children aged 0–8 years and 31 children with autistic spectrum disorder (ASD) aged 2–7 years, the microstructure of every major WM tract and tract group was measured with DTI metrics to delineate differential WM maturation. The exponential model of microstructural maturation of all WM was identified. The WM developmental curves were separated into fast, intermediate, and slow phases in 0–8 years with distinctive time period of each phase across the tracts. Shorter periods of the fast and intermediate phases in certain tracts, such as the commissural tracts, indicated faster earlier development. With TD WM maturational curves as the reference, higher residual variance of WM microstructure was found in children with ASD. The presented comprehensive and differential charts of TD WM microstructural maturation of all major tracts and tract groups in 0–8 years provide reference standards for biomarker detection of neuropsychiatric disorders.

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Vogt, Nicholas M., Jack F. Hunt, Nagesh Adluru, Douglas C. Dean, Sterling C. Johnson, Sanjay Asthana, John-Paul J. Yu, Andrew L. Alexander, and Barbara B. Bendlin. "Cortical Microstructural Alterations in Mild Cognitive Impairment and Alzheimer’s Disease Dementia." Cerebral Cortex 30, no. 5 (February 25, 2020): 2948–60. http://dx.doi.org/10.1093/cercor/bhz286.

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Abstract In Alzheimer’s disease (AD), neurodegenerative processes are ongoing for years prior to the time that cortical atrophy can be reliably detected using conventional neuroimaging techniques. Recent advances in diffusion-weighted imaging have provided new techniques to study neural microstructure, which may provide additional information regarding neurodegeneration. In this study, we used neurite orientation dispersion and density imaging (NODDI), a multi-compartment diffusion model, in order to investigate cortical microstructure along the clinical continuum of mild cognitive impairment (MCI) and AD dementia. Using gray matter-based spatial statistics (GBSS), we demonstrated that neurite density index (NDI) was significantly lower throughout temporal and parietal cortical regions in MCI, while both NDI and orientation dispersion index (ODI) were lower throughout parietal, temporal, and frontal regions in AD dementia. In follow-up ROI analyses comparing microstructure and cortical thickness (derived from T1-weighted MRI) within the same brain regions, differences in NODDI metrics remained, even after controlling for cortical thickness. Moreover, for participants with MCI, gray matter NDI—but not cortical thickness—was lower in temporal, parietal, and posterior cingulate regions. Taken together, our results highlight the utility of NODDI metrics in detecting cortical microstructural degeneration that occurs prior to measurable macrostructural changes and overt clinical dementia.

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Middleton, Dana M., Jonathan Y. Li, Hui J. Lee, Steven Chen, Patricia I. Dickson, N. Matthew Ellinwood, Leonard E. White, and James M. Provenzale. "Diffusion tensor imaging tensor shape analysis for assessment of regional white matter differences." Neuroradiology Journal 30, no. 4 (June 20, 2017): 324–29. http://dx.doi.org/10.1177/1971400917709628.

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Purpose The purpose of this study was to investigate a novel tensor shape plot analysis technique of diffusion tensor imaging data as a means to assess microstructural differences in brain tissue. We hypothesized that this technique could distinguish white matter regions with different microstructural compositions. Methods Three normal canines were euthanized at seven weeks old. Their brains were imaged using identical diffusion tensor imaging protocols on a 7T small-animal magnetic resonance imaging system. We examined two white matter regions, the internal capsule and the centrum semiovale, each subdivided into an anterior and posterior region. We placed 100 regions of interest in each of the four brain regions. Eigenvalues for each region of interest triangulated onto tensor shape plots as the weighted average of three shape metrics at the plot's vertices: CS, CL, and CP. Results The distribution of data on the plots for the internal capsule differed markedly from the centrum semiovale data, thus confirming our hypothesis. Furthermore, data for the internal capsule were distributed in a relatively tight cluster, possibly reflecting the compact and parallel nature of its fibers, while data for the centrum semiovale were more widely distributed, consistent with the less compact and often crossing pattern of its fibers. This indicates that the tensor shape plot technique can depict data in similar regions as being alike. Conclusion Tensor shape plots successfully depicted differences in tissue microstructure and reflected the microstructure of individual brain regions. This proof of principle study suggests that if our findings are reproduced in larger samples, including abnormal white matter states, the technique may be useful in assessment of white matter diseases.

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