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  • Journal cover
    Springer
    Online: 1.1993 –
    Publisher: Springer
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-12-10
    Description: Objectives We present a method based on a proposed statistical definition of white matter hyperintensities (WMH), which can work with any combination of conventional magnetic resonance (MR) sequences without depending on manually delineated samples. Materials and methods T1-weighted, T2-weighted, FLAIR, and PD sequences acquired at 1.5 Tesla from 119 subjects from the Kings Health Partners-Dementia Case Register (healthy controls, mild cognitive impairment, Alzheimer’s disease) were used. The segmentation was performed using a proposed definition for WMH based on the one-tailed Kolmogorov–Smirnov test. Results The presented method was verified, given all possible combinations of input sequences, against manual segmentations and a high similarity (Dice 0.85–0.91) was observed. Comparing segmentations with different input sequences to one another also yielded a high similarity (Dice 0.83–0.94) that exceeded intra-rater similarity (Dice 0.75–0.91). We compared the results with those of other available methods and showed that the segmentation based on the proposed definition has better accuracy and reproducibility in the test dataset used. Conclusion Overall, the presented definition is shown to produce accurate results with higher reproducibility than manual delineation. This approach can be an alternative to other manual or automatic methods not only because of its accuracy, but also due to its good reproducibility.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-10-28
    Description: Objectives Acceleration selective arterial spin labeling (AccASL) is a spatially non-selective labeling technique, used in traditional ASL methods, which labels spins based on their flow acceleration rather than spatial localization. The exact origin of the AccASL signal within the vasculature is not completely understood. To obtain more insight into this, the acceleration selective module was performed followed by a velocity selective module, which is used in velocity selective arterial spin labeling (VS-ASL). Materials and methods Nine healthy volunteers were scanned with various combinations of the control and label conditions in both the acceleration and velocity selective module. The cut-off acceleration (0.59 m/s 2 ) or velocity (2 cm/s) was kept constant in one module, while it was varied over a large range in the other module. With the right subtractions this resulted in AccASL, VS-ASL, combined AccASL and VS-ASL signal, and signal from one module with crushing from the other. Results The label created with AccASL has an overlap of approximately 50% in the vascular region with VS-ASL, but also originates from smaller vessels closer to the capillaries. Conclusion AccASL is able to label spins both in the macro- and meso-vasculature, as well as in the microvasculature.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
    Published by Springer
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  • Publication Date: 2016-11-05
    Description: Objectives To determine whether cumulative brain damage produced adjacent to a minor stroke that is followed by a mild transient ischemia is detectable with MRI and histology, and whether acute or chronic recovery between insults influences this damage. Materials and methods A minor photothrombotic (PT) stroke was followed acutely (1–2 days) or chronically (7 days) by a mild transient middle cerebral artery occlusion (tMCAO). MRI was performed after each insult, followed by final histology. Results The initial PT produced small hyperintense T 2 and DW infarct lesions and peri-lesion regions of scattered necrosis and modestly increased T 2 . Following tMCAO, in a slice and a region adjacent to the PT, a region of T 2 augmentation was observed when recovery between insults was acute but not chronic. Within the PT slice, a modest region of exacerbated T 2 change proximate to the PT was also observed in the chronic group. Corresponding histological changes within regions of augmented T 2 included increased vacuolation and cell death. Conclusion Within regions adjacent to an experimental minor stroke, a recurrence of a mild transient cerebral ischemia augmented T 2 above increases produced by tMCAO alone, reflecting increased damage in this region. Exacerbation appeared broader with acute versus chronic recovery between insults.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-10-14
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-03-07
    Description: Objectives The aim of this study was to demonstrate that eloquent cortex and epileptic-related hemodynamic changes can be safely and reliably detected using simultaneous electroencephalography (EEG)–functional magnetic resonance imaging (fMRI) recordings at ultra-high field (UHF) for clinical evaluation of patients with epilepsy. Materials and methods Simultaneous EEG–fMRI was acquired at 7 T using an optimized setup in nine patients with lesional epilepsy. According to the localization of the lesion, mapping of eloquent cortex (language and motor) was also performed in two patients. Results Despite strong artifacts, efficient correction of intra-MRI EEG could be achieved with optimized artifact removal algorithms, allowing robust identification of interictal epileptiform discharges. Noise-sensitive topography-related analyses and electrical source localization were also performed successfully. Localization of epilepsy-related hemodynamic changes compatible with the lesion were detected in three patients and concordant with findings obtained at 3 T. Local loss of signal in specific regions, essentially due to B 1 inhomogeneities were found to depend on the geometric arrangement of EEG leads over the cap. Conclusion These results demonstrate that presurgical mapping of epileptic networks and eloquent cortex is both safe and feasible at UHF, with the benefits of greater spatial resolution and higher blood-oxygenation-level-dependent sensitivity compared with the more traditional field strength of 3 T.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-06-24
    Description: Objective The objective of this study was to examine age-dependent changes in both T 1 -weighted and T 2 -weighted image contrasts and spin-echo T 2 relaxation time in the human brain during healthy ageing. Methods A total of 37 participants between the ages of 49 and 87 years old were scanned with a 3 Tesla system, using T 1 -weighted, T 2 weighted and quantitative spin-echo T 2 imaging. Contrast between image intensities and T 2 values was calculated for various regions, including between individual hippocampal subfields. Results The T 1 contrast-to-noise (CNR) and gray:white signal intensity ratio (GWR) did not change in the hippocampus, but it declined in the cingulate cortex with age. In contrast, T 2 CNR and GWR declined in both brain regions. T 2 relaxation time was almost constant in gray matter and most (but not all) hippocampal subfields, but increased substantially in white matter, pointing to an age effect on water relaxation in white matter. Conclusions Changes in T 1 and T 2 MR characteristics influence the appearance of brain images in later life and should be considered in image analyses of aged subjects. It is speculated that alterations at the cell biology level, with concomitant alterations to the local magnetic environment, reduce dephasing and subsequently prolong spin-echo T 2 through reduced diffusion effects in later life.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-06-30
    Description: Objective To accelerate super-selective arterial spin labeling (ASL) angiography by using a single control condition denoted as cycled super-selective arterial spin labeling. Materials and methods A single non-selective control image is acquired that is shared by selective label images. Artery-selective imaging is possible by geometrically changing the position of the labeling focus to more than one artery of interest during measurement. The presented approach is compared to conventional super-selective imaging in terms of its labeling efficiency inside and outside the labeling focus using numerical simulations and in vivo measurements. Additionally, the signal-to-noise ratios of the images are compared to non-selective ASL angiography and analyzed using a two-way ANOVA test and calculating the Pearson’s correlation coefficients. Results The results indicate that the labeling efficiency is not reduced within the labeled artery, but can increase as a function of distance to the artery of interest when compared to conventional super-selective ASL. In the final images, no statistically significant difference of image quality can be observed while the acquisition duration could be reduced when the major brain feeding arteries are being tagged. Conclusion Using super-selective arterial spin labeling, a single non-selective control acquisition suffices for reconstructing selective angiograms of the cerebral vasculature, thereby accelerating image acquisition of the major intracranial arteries without notable loss of information.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-07-09
    Description: Objective Measuring the pure form of GABA has become increasingly important because of its association with behaviour and certain pathologies. The aim of this study was to assess the reproducibility of GABA measurements using a shim and motion navigated MEGA-SPECIAL sequence with LCModel, jMRUI and GANNET software. Materials and methods Motion and shim navigated MEGA-SPECIAL scans were acquired in 20 healthy subjects. Two acquisitions were performed for each of two regions: the anterior cingulate (ACC) and medial-parietal (PAR) cortices. Absolute GABA concentration ( \({\text{GABA}}_{{{\text{H}}_{2} {\text{O}}}}\) ) and GABA-to-Creatine ratio (GABA/Cr) were quantified using the three software packages. Results Using the within-subject coefficient of variation (CV ws ) as an index, reproducibility for both GABA H20 and GABA/Cr ranged from 13 to 22 % in the ACC and 13 to 18 % in PAR using the three software packages. Conclusion Based on CV ws , GABA concentrations in both the ACC and PAR are reproducible using a shim and motion navigated MEGA-SPECIAL sequence with any of the three software packages, thus demonstrating the ability to quantify the pure form of GABA using these software in studies relating GABA to pathology and healthy behaviour.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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  • Publication Date: 2016-03-18
    Description: Objectives Atlas-based segmentation is a powerful method for automatic structural segmentation of several sub-structures in many organs. However, such an approach has been very scarcely used in the context of muscle segmentation, and so far no study has assessed such a method for the automatic delineation of individual muscles of the quadriceps femoris (QF). In the present study, we have evaluated a fully automated multi-atlas method and a semi-automated single-atlas method for the segmentation and volume quantification of the four muscles of the QF and for the QF as a whole. Subjects and methods The study was conducted in 32 young healthy males, using high-resolution magnetic resonance images (MRI) of the thigh. The multi-atlas-based segmentation method was conducted in 25 subjects. Different non-linear registration approaches based on free-form deformable (FFD) and symmetric diffeomorphic normalization algorithms (SyN) were assessed. Optimal parameters of two fusion methods, i.e., STAPLE and STEPS, were determined on the basis of the highest Dice similarity index (DSI) considering manual segmentation (MSeg) as the ground truth. Validation and reproducibility of this pipeline were determined using another MRI dataset recorded in seven healthy male subjects on the basis of additional metrics such as the muscle volume similarity values, intraclass coefficient, and coefficient of variation. Both non-linear registration methods (FFD and SyN) were also evaluated as part of a single-atlas strategy in order to assess longitudinal muscle volume measurements. The multi- and the single-atlas approaches were compared for the segmentation and the volume quantification of the four muscles of the QF and for the QF as a whole. Results Considering each muscle of the QF, the DSI of the multi-atlas-based approach was high 0.87 ± 0.11 and the best results were obtained with the combination of two deformation fields resulting from the SyN registration method and the STEPS fusion algorithm. The optimal variables for FFD and SyN registration methods were four templates and a kernel standard deviation ranging between 5 and 8. The segmentation process using a single-atlas-based method was more robust with DSI values higher than 0.9. From the vantage of muscle volume measurements, the multi-atlas-based strategy provided acceptable results regarding the QF muscle as a whole but highly variable results regarding individual muscle. On the contrary, the performance of the single-atlas-based pipeline for individual muscles was highly comparable to the MSeg, thereby indicating that this method would be adequate for longitudinal tracking of muscle volume changes in healthy subjects. Conclusion In the present study, we demonstrated that both multi-atlas and single-atlas approaches were relevant for the segmentation of individual muscles of the QF in healthy subjects. Considering muscle volume measurements, the single-atlas method provided promising perspectives regarding longitudinal quantification of individual muscle volumes.
    Print ISSN: 0968-5243
    Electronic ISSN: 1352-8661
    Topics: Medicine , Physics
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