The variability of MR axon radii estimates in the human white matter

The noninvasive quantification of axonal morphology is an exciting avenue for gaining understanding of the function and structure of the central nervous system. Accurate non‐invasive mapping of micron‐sized axon radii using commonly applied neuroimaging techniques, that is, diffusion‐weighted MRI, has been bolstered by recent hardware developments, specifically MR gradient design. Here the whole brain characterization of the effective MR axon radius is presented and the inter‐ and intra‐scanner test–retest repeatability and reproducibility are evaluated to promote the further development of the effective MR axon radius as a neuroimaging biomarker. A coefficient‐of‐variability of approximately 10% in the voxelwise estimation of the effective MR radius is observed in the test–retest analysis, but it is shown that the performance can be improved fourfold using a customized along‐tract analysis.     

A set of specific miRNAs is connected with murine and human gastric cancer

MircoRNAs as a new class of regulatory molecules have been investigated in many specific cells and organs in healthy and diseased conditions. Although miRNA signatures can be directly assessed in patients' affected tissues such as tumor sections, recent studies revealed that miRNA profiles can also be obtained indirectly, that is, from the patients' peripheral blood. For better understanding of miRNA's contribution to gastric carcinoma (one of the leading causes of cancer‐related mortality worldwide), we screened for deregulated miRNAs in blood collected from human cancer patients and compared the expression patterns with a gastric carcinoma mouse model (Tff1 knock‐out). The profiles were assessed using species‐specific miRNA microarrays. Among many dozens of deregulated miRNAs (219 in H. sapiens; 75 in M. musculus), a subset of eight miRNAs comparable in sequence from both species was noted. By in silico analysis, their involvement in targeting neoplastic and MAPkinase pathways was demonstrated. We found a high probability of linkage of all noted miRNAs to pathways in cancer with P‐values of 0.013 and 0.018 in mice and humans, respectively. Linkage to the MAPK‐signaling pathway in mice was observed with a P‐value of 0.01. Moreover, when comparing the 219 deregulated miRNAs obtained from blood with deregulated miRNAs derived from gastric cancer (GC) tissues, as published previously, 24 miRNAs were identical. If confirmed in a larger patient pool, these miRNAs could constitute appropriate blood‐born biomarkers for GC. © 2012 Wiley Periodicals, Inc.     

Combined Computational and Experimental Approach to Improve the Assessment of Mitral Regurgitation by Echocardiography

Mitral regurgitation (MR) is one of the most frequent valvular heart diseases. To assess MR severity, color Doppler imaging (CDI) is the clinical standard. However, inadequate reliability, poor reproducibility and heavy user-dependence are known limitations. A novel approach combining computational and experimental methods is currently under development aiming to improve the quantification. A flow chamber for a circulatory flow loop was developed. Three different orifices were used to mimic variations of MR. The flow field was recorded simultaneously by a 2D Doppler ultrasound transducer and Particle Image Velocimetry (PIV). Computational Fluid Dynamics (CFD) simulations were conducted using the same geometry and boundary conditions. The resulting computed velocity field was used to simulate synthetic Doppler signals. Comparison between PIV and CFD shows a high level of agreement. The simulated CDI exhibits the same characteristics as the recorded color Doppler images. The feasibility of the proposed combination of experimental and computational methods for the investigation of MR is shown and the numerical methods are successfully validated against the experiments. Furthermore, it is discussed how the approach can be used in the long run as a platform to improve the assessment of MR quantification.     

Unique semantic space in the brain of each beholder predicts perceived similarity

The unique way in which each of us perceives the world must arise from our brain representations. If brain imaging could reveal an individual’s unique mental representation, it could help us understand the biological substrate of our individual experiential worlds in mental health and disease. However, imaging studies of object vision have focused on commonalities between individuals rather than individual differences and on category averages rather than representations of particular objects. Here we investigate the individually unique component of brain representations of particular objects with functional MRI (fMRI). Subjects were presented with unfamiliar and personally meaningful object images while we measured their brain activity on two separate days. We characterized the representational geometry by the dissimilarity matrix of activity patterns elicited by particular object images. The representational geometry remained stable across scanning days and was unique in each individual in early visual cortex and human inferior temporal cortex (hIT). The hIT representation predicted perceived similarity as reflected in dissimilarity judgments. Importantly, hIT predicted the individually unique component of the judgments when the objects were personally meaningful. Our results suggest that hIT brain representational idiosyncrasies accessible to fMRI are expressed in an individual''s perceptual judgments. The unique way each of us perceives the world thus might reflect the individually unique representation in high-level visual areas.Everyone’s perception of the world is unique. Psychologists and psychotherapists, using methods including questionnaires and free association, have long attempted to peer into an individual’s subjective experiential world. The unique aspects of our experience coexist with a shared experiential component. We can all recognize the objects that surround us and name them in a common language. Consistent with this shared component of experience, there is evidence that visual stimuli are processed similarly in the brains of different individuals (1). However, the unique way in which each of us perceives an object also must arise from brain activity. Is there an individually unique component to our brain representations?Unidimensional aspects of subjective visual percepts, ranging from estimates of object size, color, vividness, and emotional valence, have separately been found to correlate with interindividual variation in both univariate regional-average activation and cortical anatomy (2, 3). However, it remains unclear how a person’s multidimensional subjective percept reflects the multivariate brain-activity pattern that represents a particular object.Functional magnetic resonance imaging (fMRI) studies of object vision have focused largely on commonalities among subjects and category averages across particular stimuli. These studies have revealed regions in human inferior temporal cortex (hIT) that preferentially respond to specific categories (4–9) as well as widely distributed category information (10). More recently, similarity analyses of response patterns to particular stimulus images have revealed exemplar-specific representations (11–14), clustering of response patterns by natural categories (15–17), and reinstatement of neural representations during memory recall (18, 19). These prior studies either tacitly assumed similar representations across individuals or explicitly demonstrated commonalities between individuals and even between species (14, 20–29).Previous studies have shown that the hIT representation has a semantic component (23) and is reflected in perception at the level of group averages (30). Here we tested the hypothesis that an individual’s hIT representation predicts idiosyncrasies in his or her perception of natural objects. Because of hIT’s reciprocal connections to the memory regions of the medial temporal lobe (31), we further predicted that personally meaningful objects elicit individually unique mnemonic associations and are more distinctly represented in each individual.We presented familiar and unfamiliar object images to subjects during fMRI and investigated whether early visual cortex (EVC) and hIT exhibit individually unique representations. We characterized the representational geometry of each region by the dissimilarity matrix of activity patterns elicited by particular object images. This matrix is called the “representational dissimilarity matrix” (RDM) (16). To address whether the detailed representational geometries are reflected in behavior, we tested whether individual idiosyncrasies in similarity judgments can be predicted on the basis of a subject’s brain RDM.     

Accuracy assessment of cone beam computed tomography-derived laboratory-based surgical templates on partially edentulous patients

Objectives: The aim of the present prospective clinical study was to evaluate the match between the positions and axes of the virtually planned and the placed implants using laboratory‐based surgical guides generated from cone beam computed tomography (CBCT). Materials and methods: A total of 132 implants were placed with the aid of 3D‐based transfer templates in 52 consecutive partially edentulous patients between April 2008 and March 2010. After individual adaptation of the scan templates and CBCT scanning, the acquired data for virtual implant planning and simulation were processed using the med3D software program. After finalizing the virtual placement of the implants the radiographic templates were converted into operative guides containing titanium sleeves for cavity preparation. Preoperative planning was merged with postoperative CBCT data to identify linear and angular deviations between virtually planned and placed implants. Results: Compared with the planned implants the installed implants showed linear deviations in the median at the neck and apex of 0.27 mm (range 0.01–0.97 mm), and of 0.46 mm (range 0.03–1.38 mm), respectively. The angle deviation was 1.84° in median, with a range of 0.07–6.26°. The extent of deviation depends on the size of the tooth gap and the distribution of the remaining teeth. Conclusion: The results of this study suggested that laboratory‐fabricated surgical guides using CBCT data may be reliable in implant placement under prosthodontic considerations in partial edentulism. To cite this article:
Behneke A, Burwinkel M, Knierim K, Behneke N. Accuracy assessment of cone beam computed tomography‐derived laboratory‐based surgical templates on partially edentulous patients.
Clin. Oral Impl. Res. 23 , 2012; 137–143.
doi: 10.1111/j.1600‐0501.2011.02176.x