Whether recurrent epileptic seizures induce brain damage is debated. Disease progression in epilepsy has been evaluated only in a few community-based studies involving patients with seizures well ...controlled by medication. These studies concluded that epilepsy does not inevitably lead to global cerebral damage.
To track the progression of neocortical atrophy in pharmacoresistant temporal lobe epilepsy (TLE) using longitudinal and cross-sectional designs.
Using a fully automated measure of cortical thickness on MRI, we studied a homogeneous sample of patients with pharmacoresistant TLE. In the longitudinal analysis (n = 18), fixed-effect models were used to quantify cortical atrophy over a mean interscan interval of 2.5 years (range = 7 to 90 months). In the cross-sectional analysis (n = 121), we correlated epilepsy duration and thickness. To dissociate normal aging from pathologic progression, we compared aging effects in TLE to healthy controls.
The longitudinal analysis mapped progression in ipsilateral temporopolar and central and contralateral orbitofrontal, insular, and angular regions. In patients with more than 14 years of disease, atrophy progressed more rapidly in frontocentral and parietal regions that in those with shorter duration. The cross-sectional study showed progressive atrophy in the mesial and superolateral frontal, and parietal cortices.
Our combined cross-sectional and longitudinal analysis in patients with pharmacoresistant temporal lobe epilepsy demonstrated progressive neocortical atrophy over a mean interval of 2.5 years that is distinct from normal aging, likely representing seizure-induced damage. The cumulative character of atrophy underlies the importance of early surgical treatment in this group of patients.
The development of predictive models for fatigue behavior of materials is closely related to a quantitative assessment of damage nucleation and propagation phenomena. Conventional methods used for ...this purpose, such as microscope observations, conventional radiographs, ultrasonography techniques, either are destructive or do not reach an adequate resolution. Imaging techniques using synchrotron radiation, and in particular X-ray micro-computed tomography (micro-CT), however, combine the advantages of a non-destructive technique with a high spatial resolution.
In this paper, damage evolution in samples extracted from PA6.6GF35 specimens subjected to fatigue tests interrupted at different stages of fatigue life is investigated by means of synchrotron radiation micro-CT.
Although preliminary, our results suggest that the application of this technique for micro-voids detection within the glass short fibre polyamide reinforced samples offers unique possibilities of investigating the micro-scale internal structure of the samples but, at the same time, presents several criticalities at different stages of the analyses, ranging from specimen size to set-up configuration and threshold selection. A frank discussion of the critical issues encountered during the analyses supplements the presentation in an effort to help defining general guidelines for future developments in this field.
The hippocampus is a highly plastic brain structure supporting functions central to human cognition. Morphological changes in the hippocampus have been implicated in development, aging, as well as in ...a broad range of neurological and psychiatric disorders. A growing body of research suggests that hippocampal plasticity is closely linked to the actions of brain-derived neurotrophic factor (BDNF). However, evidence on the relationship between hippocampal volume (HCV) and peripheral BDNF levels is scarce and limited to elderly and patient populations. Further, despite evidence that BDNF expression differs throughout the hippocampus and is implicated in adult neurogenesis specifically in the dentate gyrus, no study has so far related peripheral BDNF levels to the volumes of individual hippocampal subfields. Besides its clinical implications, BDNF-facilitated hippocampal plasticity plays an important role in regulating cognitive and affective processes. In the current registered report, we investigated how serum BDNF (sBDNF) levels relate to volumes of the hippocampal formation and its subfields in a large sample of healthy adults (N = 279, 160 f) with a broad age range (20–55 years, mean 40.5) recruited in the context of the ReSource Project. We related HCV to basal sBDNF and, in a subsample (n = 103, 57 f), to acute stress-reactive change in sBDNF. We further tested the role of age as a moderator of both associations. Contrary to our hypotheses, neither basal sBDNF levels nor stress-reactive sBDNF change were associated with total HCV or volume of the dentate gyrus/cornu ammonis 4 (DG/CA4) subfield. We also found no evidence for a moderating effect of age on any of these associations. Our null results provide a first point of reference on the relationship between sBDNF and HCV in healthy mid-age, in contrast to patient or aging populations. We suggest that sBDNF levels have limited predictive value for morphological differences of the hippocampal structure when notable challenge to its neuronal integrity or to neurotrophic capacity is absent.
Measurement of fibre orientation in short fibre reinforced polymer is crucial for the description of their microstructure and subsequent multiscale modelling. Micro Computed Tomography is becoming ...the standard method for the reconstruction of the inner microstructure of short fibre reinforced polymers and different methods exist for the analysis of orientations. Applications of Digital Image Correlation to X-rays Micro Computed Tomography data sets to measure fibre orientation in continuous fibre reinforced polymers exist. In this work, the possibility of extending the application of the Digital Image Correlation technique to measure fibre orientation in short fibre reinforced polymers is investigated and a new procedure is proposed. The method is applied to two different data sets obtained by scanning the same sample using both a synchrotron micro CT equipment and an industrial scanner. Results are compared with other existing methods and discussed to identify possible future improvements.
Adhesively bonded joints are being increasingly applied in modern structures. However, manufacturing defects and particularly harsh operative conditions may cause local debonding and catastrophic ...failures. Structural health monitoring (SHM) and non-destructive testing (NDT) procedures
are then needed to evaluate the in-service structural integrity of adhesively bonded joints. In this research, an adhesively bonded single-lap joint, both adherends of which are manufactured using a carbon fibre-reinforced polymer (CFRP) composite, is subjected to constant amplitude fatigue
loading. During such a test, the integrity and damage condition of the joint is continuously monitored using acoustic emission (AE), while the test itself is periodically interrupted in order to apply micro-computed tomography (μCT) to the specimen, with the aim of investigating the real
features of the developing fatigue damage. The results show that, after suitable elaboration and filtering by means of pattern recognition algorithms, acoustic emission-based monitoring allows for effective identification and characterisation of the development of fatigue damage in adhesively
bonded joints.
•Optical fibres are used to monitor the back face strain in adhesively bonded joints.•The Optical Backscatter Reflectometry (OBR) technique is applied.•Fatigue crack growth can be monitored by ...tracking the peak of the OBR strain profile.•The response of the OBR technique is compared with micro-CT and visual observations.•Two methods based on static and dynamic acquisitions, respectively, are compared.
Fatigue crack growth in composite, single lap bonded joints is analysed by back face distributed strain sensing, using optical backscatter reflectometry. Crack growth is inferred from the back-face strain profile measured with high spatial resolution along optical fibres bonded on the joints. The indications about the position of the crack front are compared with micro computed tomography scans conducted on specimens at suitable interruptions of the fatigue tests. By the proposed technique, crack initiation can be clearly detected, and measurements of crack growth are in good agreement with observations, with decreasing error with increasing crack length.
This study aimed at estimating crack tip position in adhesive bonded joints under mode II quasi‐static loading using experimental and numerical approaches. Experimental techniques were utilized and ...compared, including optical backscatter reflectometry, visual testing, and a novel strategy based on digital image correlation. Additionally, a finite element analysis was employed to identify the numerical crack tip position and the extent of damage within the bondline. This analysis revealed that a significant portion of the crack propagation region in the adhesive is occupied by the fracture process zone. Moreover, optical backscatter reflectometry shows the potential to detect this process zone within the adhesive that the other methods may not detect. This capability is particularly beneficial for detecting damage at early stages.
Highlights
OBR and DIC were used for crack initiation and propagation in ENF joint under mode II.
OBR back‐face strain demonstrated its ability to detect potential early‐stage damage.
Trapezoidal TSL outperformed bi‐linear TSL in FE crack propagation modeling.
A significant portion of crack propagation region was occupied by FPZ in adhesive.
Volumetric MRI studies based on manual labeling of selected anatomical structures have provided in vivo evidence that brain abnormalities associated with temporal lobe epilepsy (TLE) extend beyond ...the hippocampus. Voxel-based morphometry (VBM) is a fully automated image analysis technique allowing identification of regional differences in gray matter (GM) and white matter (WM) between groups of subjects without a prior region of interest. The purpose of this study was to determine whole-brain GM and WM changes in TLE and to investigate the relationship between these abnormalities and clinical parameters. We studied 85 patients with pharmacologically intractable TLE and unilateral hippocampal atrophy and 47 age- and sex-matched healthy control subjects. The seizure focus was right sided in 40 patients and left sided in 45. Student's
t test statistical maps of differences between patients' and controls' GM and WM concentrations were obtained using a general linear model. A further regression against duration of epilepsy, age of onset, presence of febrile convulsions, and secondary generalized seizures was performed with the TLE population. Voxel-based morphometry revealed that GM pathology in TLE extends beyond the hippocampus involving other limbic areas such as the cingulum and the thalamus, as well as extralimbic areas, particularly the frontal lobe. White matter reduction was found only ipsilateral to the seizure focus, including the temporopolar, entorhinal, and perirhinal areas. This pattern of structural changes is suggestive of disconnection involving preferentially frontolimbic pathways in patients with pharmacologically intractable TLE.
The fibre orientation distribution in a material sample extracted from an injection moulded plate, displaying the commonly encountered layered shell–core–shell structure, was analyzed. Starting from ...a micro-tomography reconstruction of the sample, instead of trying to isolate each single fibre and measuring its geometrical properties, we derived the components of a fabric tensor from the evaluation of a global anisotropy parameter, the mean intercept length MIL. This parameter, commonly employed for the analysis of biological and geological structures, proved to be an efficient tool for the analysis of the structure of short fibre reinforced composites. The local variations of the degree of anisotropy (ratio of the maximum and minimum eigenvalues of the fabric tensor) from the shell to the core layers of the injection moulded plate could be captured and information about the local average fibre orientation angle was also obtained.
High-resolution MRI of the brain has made it possible to identify focal cortical dysplasia (FCD) in an increasing number of patients. There is evidence for structural abnormalities extending beyond ...the visually identified FCD lesion. Voxel-based morphometry (VBM) has the potential of detecting both lesions and extra-lesional abnormalities because it performs a whole brain voxel-wise comparison. However, on T1-weighted MRI, FCD lesions are characterized by a wide spectrum of signal hyperintensity that may compromise the results of the segmentation step in VBM. Our purpose was to investigate gray matter (GM) changes in individual FCD patients using voxel-based morphometry (VBM). In addition, we sought to assess the performance of this technique for FCD detection with respect to lesion intensity using an operator designed to emphasize areas of hyperintense T1 signal. We studied 27 patients with known FCD and focal epilepsy and 39 healthy controls. We compared the GM map of each subject (controls and patients) with the average GM map of all controls and obtained a GM
z-score map for each individual. The protocol being designed to achieve a maximal specificity, no differences in GM concentration were found in the control group. The
z-score maps showed an increase in GM that coincided with the lesion in 21/27 (78%) patients. Five of the six remaining patients whose lesions were not detected by VBM presented with a strong lesion hyperintensity, and a significant part of their lesion was misclassified as white matter. In 16/27 (59%) patients, there were additional areas of GM increase distant from the primary lesion. Areas of GM decrease were found in 8/27 (30%) patients. In conclusion, individual voxel-based analysis was able to detect FCD in a majority of patients. Moreover, FCD was often associated with widespread GM changes extending beyond the visible lesion. In its current form, however, individual VBM may be unable to detect lesions characterized by strong signal intensity abnormalities.
PDF
