The echoplanar technique in magnetic resonance (MR) imaging allows the acquisition of a series of images from a selected slice with a temporal resolution of 10/s. Simultaneous recording of physiological information on pulse and... more
The echoplanar technique in magnetic resonance (MR) imaging allows the acquisition of a series of images from a selected slice with a temporal resolution of 10/s. Simultaneous recording of physiological information on pulse and respiration allows correlation of the MR signal intensity with physiological signals, which can be obtained for each pixel examined. Such correlations can be found within the cerebrospinal fluid (CSF) spaces and within vessels if a flow-sensitive MR measurement technique is used. The use of an MR scanner with a field strength of 3 T improves the signal/noise ratio, but there is a stronger signal decay due to local magnetic inhomogeneities. This study shows that 3-T systems can be used for correlation of MR and physiological signals and that clear differentiation between signals from CSF and from vessels can be obtained due to their strongly different signal decays.
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PURPOSE The combination of ASL techniques with imaging sequences insensitive to susceptibility effects has been shown to provide useful applications on internal organs. Usually averaging of a large number of scans is necessary to achieve... more
PURPOSE The combination of ASL techniques with imaging sequences insensitive to susceptibility effects has been shown to provide useful applications on internal organs. Usually averaging of a large number of scans is necessary to achieve a sufficiently high SNR in perfusion images. Doing so, respiratory motion can influence the quality of FAIR images. At higher field strength the sensitivity of the ASL methods is expected to improve. The recently developed FAIR True-FISP technique is suitable for perfusion-weighted imaging of the kidneys at 3 T. The goal of this study was to present a possible strategy for quantitative perfusion measurements of the kidneys at 3 T in breath-hold technique. METHOD AND MATERIALS Examinations of the kidneys of healthy volunteers were performed on a 3 T whole body MR scanner (Siemens Medical Solutions, Erlangen, Germany). The FAIR True-FISP sequences with α=60�-80�, TR/TE=3.6/1.8 ms, TI=1.2 s, BW=890 Hz/pixel, matrix=128�128 and FoV=360�360 mm2 were impl...
Synopsis: In proton MR spectroscopy of the human brain, it is often difficult to select voxels that contain only one tissue type, such as gray matter (GM) or white matter (WM), due to relatively large voxel sizes. In this study,... more
Synopsis: In proton MR spectroscopy of the human brain, it is often difficult to select voxels that contain only one tissue type, such as gray matter (GM) or white matter (WM), due to relatively large voxel sizes. In this study, metabolite concentrations in pure GM and pure WM were calculated from the values obtained from short TE spectra of voxels with mixed tissue components. The tissue composition was determined by image segmentation. Significant differences between GM and WM were found for most of the major metabolites in the parietal region and the cerebellum. Methods: Examinations were performed on a 1.5 T whole-body imager (Magnetom Sonata, Siemens). Short-TE PRESS spectra (TE 30 ms, TR 3,000 ms, 64 acquisitions) were measured in the parietal region and in the cerebellum of nine healthy volunteers. In each of these brain regions, two volumes of interest (VOIs or voxels) of (2 cm) 3 were used, one of them containing mainly gray matter, the other mainly white matter (see Fig. 1...
ABSTRACT MR diffusion tensor imaging (DTI) allows the visualization of location and course of brain fiber bundles. To obtain these results, however, special evaluation techniques are necessary in addition to image acquisition and... more
ABSTRACT MR diffusion tensor imaging (DTI) allows the visualization of location and course of brain fiber bundles. To obtain these results, however, special evaluation techniques are necessary in addition to image acquisition and reconstruction. These include first the calculation of a preferential diffusional direction of water molecules in each voxel, and then the tracking of brain fibers or segmentation of regions with similar fiber directions. In both cases, the procedures available thus far require the interactive definition of seed points. In this paper, we propose a method to segment voxel groups of connected data points without the need of setting seed points. This method is based first on the identification of all voxels of a brain volume with a sufficiently unique preferential diffusional direction and with interconnection. For each selected voxel, neighboring voxels are then identified that have a small deviation from the chosen preferential direction and can therefore be grouped with this point. Finally, the largest partial volumes determined in this way are marked and color-coded to present them as three-dimensional structures. The present method was applied to a DTI data set of a healthy female volunteer, resulting in a largely automatic subdivision of the white matter in the brain in a number of bilateral partial volumes.
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ABSTRACT Hintergrund: Bei der lokalisierten In-vivo-Protonenspektroskopie des Gehirns ist es oft nicht möglich, die relativ großen Messvolumina (Voxel) so zu platzieren, dass sie nur Anteile der interessierenden Gewebeart enthalten. Bei... more
ABSTRACT Hintergrund: Bei der lokalisierten In-vivo-Protonenspektroskopie des Gehirns ist es oft nicht möglich, die relativ großen Messvolumina (Voxel) so zu platzieren, dass sie nur Anteile der interessierenden Gewebeart enthalten. Bei kleineren, unregelmäßig geformten Läsionen, z. B. Metastasen, Entmarkungsherden oder Ischämien, liegt oft ein erheblicher Anteil des umgebenden Ödems oder Normalgewebes in demselben Voxel (Partialvolumen). Das akquirierte Spektrum stellt somit ein Mischspektrum verschiedener Gewebetypen im Voxel dar, das deutlich vom Spektrum der interessierenden reinen Gewebeart abweichen kann. Material und Methodik: Es wird eine Methode vorgestellt, mit der Spektren interessierender Gewebearten aus gemessenen Mischspektren berechnet werden können. Zur Aufnahme der Spektren wurde eine PRESS-Sequenz verwandt. Um eine Berechnung der Reingewebespektren zu ermöglichen, wurden bei Probanden- und Patientenuntersuchungen Spektren aus verschiedenen Voxeln aufgenommen, die jeweils unterschiedliche Anteile der verschiedenen reinen Gewebearten enthielten, wobei genauso viele Voxel gemessen werden müssen wie insgesamt verschiedene Gewebearten darin enthalten sind. Die Berechnung des Spektrums für die gesuchte reine Gewebeart erfolgte über die Lösung eines linearen Gleichungssystems. Dazu müssen die prozentualen Anteile der verschiedenen Gewebearten in den Voxeln bekannt sein. Um diese zu bestimmen, wurden bei den Probandenuntersuchungen hochaufgelöste native MP-RAGE-Datensätze und bei Patienten in Abhängigkeit von der Signalcharakteristik auch FLAIR- oder kontrastangehobene MP-RAGE-Datensätze aufgenommen, aus denen anschließend durch Bildsegmentierung die Anteile der reinen Gewebearten in den Voxeln bestimmt wurden. Für die Segmentierung wurden sowohl ein automatisches, standardisiertes als auch ein semiautomatisches, histogrammbasiertes Verfahren eingesetzt. Ergebnisse: Es wurden bei Probanden reine Spektren grauer (GS) und weißer Substanz (WS) berechnet. Hierbei zeigten sich bei den Reingewebespektren im Vergleich zu den gemessenen (Misch-)Spektren sehr viel deutlichere Unterschiede in der metabolischen Zusammensetzung von GS und WS sowohl im Kleinhirn als auch supratentoriell. Des Weiteren fanden sich in den Reingewebespektren deutliche Unterschiede der Metaboliten zwischen GS des Klein- und Großhirns, während die Zusammensetzung der WS supra- und infratentoriell identisch war. Auch konnte gezeigt werden, dass bei verschiedenen zerebralen Läsionen erhebliche Unterschiede zwischen den die Läsionen enthaltenden, gemessenen Spektren und den berechneten, reinen Spektren der Läsionen bestanden. Schlussfolgerung: Die Methode zeigt, dass es möglich ist, mit der Einzelvolumenspektroskopie Strukturen aufzulösen, die sehr viel kleiner als die minimal messbaren Voxelgrößen sind. Es gelingt somit, läsionsspezifischere spektrale Muster als mit den herkömmlichen Messungen, die bei kleineren oder unregelmäßig konfigurierten Läsionen immer partialvolumenbehaftet sind, darzustellen.
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Hereditary spastic paraplegias (HSP) are a group of clinically and genetically heterogeneous disorders with the hallmark of progressive spastic gait disturbance. We used advanced neuroimaging to identify brain regions involved in SPG4,... more
Hereditary spastic paraplegias (HSP) are a group of clinically and genetically heterogeneous disorders with the hallmark of progressive spastic gait disturbance. We used advanced neuroimaging to identify brain regions involved in SPG4, the most common HSP genotype. Additionally, we analyzed correlations between imaging and clinical findings. We performed 3T MRI scans including isotropic high-resolution 3D T1, T2-FLAIR, and DTI sequences in 15 adult patients with genetically confirmed SPG4 and 15 age- and sex-matched healthy controls. Brain volume loss of gray and white matter was evaluated through voxel-based morphometry (VBM) for supra- and infratentorial regions separately. DTI maps of axial diffusivity (AD), radial diffusivity (RD), mean diffusivity (MD), fractional anisotropy (FA), and measured anisotropy (MA1) were analyzed through tract-based special statistics (TBSS). VBM and TBSS revealed a widespread affection of gray and white matter in SPG4 including the corpus callosum, ...
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Background: The brain stem is an anatomic structure of outstanding importance affecting all vital functions. This is the reason that even smallest lesions may lead to immense clinical symptoms for the patient. In conventional magnetic... more
Background: The brain stem is an anatomic structure of outstanding importance affecting all vital functions. This is the reason that even smallest lesions may lead to immense clinical symptoms for the patient. In conventional magnetic resonance imaging, the anatomic structures of the brain stem and the localization of the cerebellar peduncles are difficult to visualize. A differentiation of structures within the brain stem is possible by the use of diffusion tensor imaging (DTI). Material and Methods: The analysis of DTI datasets with high spatial resolution allows the calculation of single fiber bundles by fiber-tracking algorithms or the segmentation of regions with similar fiber directions. The segmentation technique can be used to completely separate an acquired complete volume dataset into several subvolumes. In this technique, those voxels are combined to clusters, in which the difference between the preference directions within neighbored voxels does exceed a chosen threshold. Results: In the region of the brain stem, this procedure allows the visualization of the major fiber bundles like the cerebrospinal tract and the cerebellar peduncles, if a multistep procedure with successively increasing threshold angles for the preference direction is used. The technique was successfully performed in datasets of three healthy volunteers.
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The purpose of the study was to develop a measuring technique, which allows the investigation of brainstem and auditory cortex activation after application of auditory stimuli by functional magnetic resonance imaging (fMRI). In addition... more
The purpose of the study was to develop a measuring technique, which allows the investigation of brainstem and auditory cortex activation after application of auditory stimuli by functional magnetic resonance imaging (fMRI). In addition to the conventional t-test analysis, a correlation analysis using, the signal in the acoustical cortex was applied. Eight healthy volunteers were examined on 3T scanner (Trio Tim, Siemens, Erlangen, Germany) with pure tones and music stimulation. Cortical and subcortical auditory structures were successfully visualized. Such investigation showed similar behavior comparing the both kind of created maps T and correlation. Maps of correlation demonstrated additional localization of brainstem structures which were not able to obtain after statistical analysis. These results demonstrate a tight functional relation between subcortical and cortical areas in the human brain.
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To prospectively compare the image quality and diagnostic performance of orbital MR images obtained by using a dual-source parallel transmission (pTX) 3D sequence (Sampling Perfection with Application optimized Contrasts using different... more
To prospectively compare the image quality and diagnostic performance of orbital MR images obtained by using a dual-source parallel transmission (pTX) 3D sequence (Sampling Perfection with Application optimized Contrasts using different flip angle Evolution, SPACE) with the image quality of conventional high-resolution standard protocol for clinical use in patients at 3T. After obtaining institutional review board approval and patient consent, 32 patients with clinical indication for orbital MRI were examined using a high-resolution conventional sequences and 3D pTX SPACE sequences. Quantitative measurements, image quality of the healthy orbit, incidence of artifacts, and the subjective diagnostic performance to establish diagnosis was rated. Statistical significance was calculated by using a Student's t-test and nonparametric Wilcoxon signed rank test. Length measurements were comparable in the two techniques, 3D pTX SPACE resulted in significant faster image acquisition with h...
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We sought to investigate the dependence of intravoxel incoherent motion (IVIM)-related perfusion fraction (f) estimates on the transverse relaxation of brain tissue, blood, and cerebrospinal fluid (CSF), attempting to overcome the... more
We sought to investigate the dependence of intravoxel incoherent motion (IVIM)-related perfusion fraction (f) estimates on the transverse relaxation of brain tissue, blood, and cerebrospinal fluid (CSF), attempting to overcome the influence of CSF on conventional f maps. Eighteen patients with gliomas underwent DWI with 14 b-values (0-1,300 s/mm(2)) and two distinct echo times (TEs). Regions of interest representing tumour and normal brain tissue were analysed by calculating the f values for both TEs. A mask for pixels with relevant CSF partial volume was subsequently created. The f values were tested for significant differences. We found statistically significant differences between the two TEs in the f values for cortical and juxtacortical structures and non-enhancing areas of the tumour /oedema. Normal white matter and gadolinium-enhancing tumour tissue appeared insensitive to TE variation. In all tissue types examined, the masking of voxels with considerable CSF content was able...
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Brain perfusion can be assessed non-invasively by modern arterial spin labeling MRI. The FAIR (flow-sensitive alternating inversion recovery)-TrueFISP (true fast imaging in steady precession) technique was applied for regional assessment... more
Brain perfusion can be assessed non-invasively by modern arterial spin labeling MRI. The FAIR (flow-sensitive alternating inversion recovery)-TrueFISP (true fast imaging in steady precession) technique was applied for regional assessment of cerebral blood flow in brain areas close to the skull base, since this approach provides low sensitivity to magnetic susceptibility effects. The investigation of the rhinal cortex and the amygdala is a potentially important feature for the diagnosis and research on dementia in its early stages. Twenty-three subjects with no structural or psychological impairment were investigated. FAIR-True-FISP quantitative perfusion data were evaluated in the amygdala on both sides and in the pons. A preparation of the radiofrequency FOCI (frequency offset corrected inversion) pulse was used for slice selective inversion. After a time delay of 1.2 sec, data acquisition began. Imaging slice thickness was 5 mm and inversion slab thickness for slice selective inve...
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MR diffusion tensor imaging (DTI) allows the visualization of location and course of brain fiber bundles. To obtain these results, however, special evaluation techniques are necessary in addition to image acquisition and reconstruction.... more
MR diffusion tensor imaging (DTI) allows the visualization of location and course of brain fiber bundles. To obtain these results, however, special evaluation techniques are necessary in addition to image acquisition and reconstruction. These include first the calculation of a preferential diffusional direction of water molecules in each voxel and then the tracking of brain fibers or segmentation of regions with similar fiber directions. In both cases, the procedures available thus far require the interactive definition of seed points. In this paper, we propose a method to segment voxel groups of connected data points without the need of setting seed points. This method is based first on the identification of all voxels of a brain volume with a sufficiently unique preferential diffusional direction and with interconnection. For each selected voxel, neighboring voxels are then identified that have a small deviation from the chosen preferential direction and can therefore be grouped w...
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In chronic liver dysfunction with portal hypertension the risk of variceal bleeding can be lowered by intrahepatic portosystemic shunting (TIPS). Although less pronounced than in surgical shunting, hepatic encephalopathy (HE) is a... more
In chronic liver dysfunction with portal hypertension the risk of variceal bleeding can be lowered by intrahepatic portosystemic shunting (TIPS). Although less pronounced than in surgical shunting, hepatic encephalopathy (HE) is a well-known undesired side effect. In cerebral proton MR spectroscopy (MRS), HE can be detected by a specific pattern of brain metabolite changes (increase of glutamine/glutamate (Glx) and decrease of myo-inositol (ml) and choline (Cho)). The aim of this study was to examine whether, after TIPS implantation, there is a correlation of the reduction of the portosystemic pressure gradient (PSPG) and the cerebral metabolite changes and their correspondence to the clinical status. We examined 10 cirrhotic patients (Child B, C) before and 3-20 days after TIPS implantation. Clinical examination was performed by a senior hepatologist. Localized MR spectra were acquired in parieto-occipital gray/white matter using a short echo time (TE = 5 ms) STEAM sequence. After ...
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Syringomyelia can result in major functional disability. Conventional imaging techniques frequently fail to detect the underlying cause of syringomyelia. The prediction as to whether syringomyelia might lead to neurological deficits is... more
Syringomyelia can result in major functional disability. Conventional imaging techniques frequently fail to detect the underlying cause of syringomyelia. The prediction as to whether syringomyelia might lead to neurological deficits is still challenging. We hypothesized that fractional anisotropy (FA) derived from diffusion tensor imaging (DTI) is a parameter to detect dynamic forms of syringomyelia. Six patients with cervical syringomyelia, all comparable in size, shape, and location, were examined, along with 2 volunteers. Patients underwent electrophysiological recordings (somatosensory evoked potentials, motor evoked potentials, silent periods). Magnetic resonance imaging (1.5 T) was performed with a 6-element spine coil. Anatomic images were acquired with a 3-dimensional, constructive interference in steady-state sequence, and DTI with an echo-planar imaging sequence (5-mm thickness, b value 800 s/mm) using the generalized autocalibrating partially parallel acquisitions technique. The positions were centered on the syrinx in the volunteers between the C2 and Th1. DTI data were interpolated to a spatial resolution of 0.5 mm. After calculation of a diffusion tensor in each pixel, an FA map was calculated and profiles of the FA values across the spinal cord were calculated in all slices. FA values were lower at the level of all examined syrinxes and reached normal values beyond them. Electrophysiological results correlated with the decrease in FA value. There were no presyrinx changes in the white matter tracts in terms of signs of FA changes beneath the syrinx. DTI of syringomyelia can demonstrate white matter fiber tracts around and beyond the syrinx consistent with electrophysiological values. DTI of the cervical spine can provide quantitative information about the pathological characteristics beyond the abnormalities visible on magnetic resonance imaging.
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Research Interests: Cognitive Science, Algorithms, Artificial Intelligence, Brain Imaging, Neuroanatomy, and 15 moreMagnetic Resonance Imaging, Diffusion Tensor Imaging, Anisotropy, Brain Mapping, Humans, Color, Female, Male, Diagnostic Imaging, Image Enhancement, Adult, Neural pathways, Eigenvectors, Magnetic resonance image, and Diffusion magnetic resonance imaging
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Research Interests: Medicinal Chemistry, Magnetic Resonance Imaging, Flow Cytometry, Confocal Microscopy, Humans, and 12 moreGlioma, Cell Death, Peptides, Cell nucleus, Liquid Chromatography / Electrospray Ionization Mass Spectrometry, Confocal Laser Scanning Microscopy, Organometallic Compounds, Cell Survival, Cytoplasm, Heterocyclic compounds, Magnetic resonance image, and fluorescent dyes
The reproducibility of three evaluation techniques for high angular resolution diffusion imaging (HARDI) data, the diffusion tensor model, q-ball reconstruction and spherical deconvolution, are compared. Two healthy volunteers were... more
The reproducibility of three evaluation techniques for high angular resolution diffusion imaging (HARDI) data, the diffusion tensor model, q-ball reconstruction and spherical deconvolution, are compared. Two healthy volunteers were measured in a 3 T MR system six times with the same measurement parameters; one subject was measured with different b-values. The data was evaluated to compare the consistency and reproducibility of reconstructed diffusion directions and anisotropy values for the three investigated diffusion evaluation techniques. The angle difference between the reconstructed main directions of diffusion for the investigated techniques was evaluated. For q-ball and spherical deconvolution the consistency of the second dominant diffusion direction was additionally examined. The differences between the tensor model and q-ball or spherical deconvolution in the estimated diffusion direction decrease with an increase in fractional anisotropy. Increasing the smoothing kernel in q-ball reconstruction renders the results similar to the ones from the diffusion tensor evaluation. Consistency in the reconstructed directions did increase for larger b-values. The evaluation of HARDI data in clinical conditions with q-ball or spherical deconvolution shows consistency and reproducibility similar to the diffusion tensor model, but provides valuable additional information about a second dominant direction of diffusion.
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An inhomogeneous radiofrequency (RF) magnetic field is an essential source of error for the quantification of MRI and MRS parameters. To correct for effects of RF inhomogeneities in 3D data sets, it is necessary to have knowledge of the... more
An inhomogeneous radiofrequency (RF) magnetic field is an essential source of error for the quantification of MRI and MRS parameters. To correct for effects of RF inhomogeneities in 3D data sets, it is necessary to have knowledge of the 3D RF distribution in the sample. In this paper a method for fast 3D RF mapping is presented. The method is based on the simultaneous acquisition of a spin echo (SE) and a stimulated echo (STE) using echo-planar imaging (EPI). The acquisition of the 3D RF map using 64 partitions and TR = 500 ms requires 1.5 min. The use of the sequence in vivo is demonstrated by the calculation of the RF maps in the human brain at 3T. The comparison of calculated flip angles with the flip angles obtained by fitting signal behavior in the 3D stimulated-echo acquisition mode (STEAM)-EPI sequence and the analysis of errors due to spatially dependent T(1) values in the brain show that the accuracy of the calculated flip angles in the human brain is about 2 degrees.
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Research Interests: Neurology, MRI, Humans, Diffusion, Female, and 15 moreSpinal Cord, Difusion, Clinical Sciences, Aged, Middle Aged, High Resolution, Adult, Edema, Time Factors, Cerebral Ischemia, Disease Progression, Nuclear Magnetic Resonance Imaging, Neurosciences, Infarction, and Diffusion magnetic resonance imaging
To evaluate the suitability of a 12- or 32-channel head coil and of a prescan normalization filter for functional magnetic resonance imaging (fMRI) studies at different brain regions. fMRI was obtained from 36 volunteers executing a... more
To evaluate the suitability of a 12- or 32-channel head coil and of a prescan normalization filter for functional magnetic resonance imaging (fMRI) studies at different brain regions. fMRI was obtained from 36 volunteers executing a visually instructed motor paradigm using a 12-channel head matrix coil and a 32-channel phased-array head coil with and without prescan normalization filtering at 3 T. The time-course signal-to-noise ratio (tSNR) and the magnitude of functional activation (beta-value, t-value, percent signal change) were statistically compared between experimental conditions for the contralateral primary motor and visual cortex, contralateral thalamus, and ipsilateral anterior cerebellar hemispheres. tSNR was higher overall measuring with the 32-channel array and with prescan normalization. Without filtering, the 32-channel array delivered higher functional activation magnitudes for the visual cortex, whereas the 12-channel array seemed superior in this respect in thalamus and cerebellum. Filtering did not considerably affect the fMRI-activation magnitude detected from the 12-channel coil; its application favored the 32-channel coil at the subcortical and cerebellar locations but disfavored it at the cortical ones. The 32-channel coil detected more fMRI-activation cortically but less subcortically than the 12-channel coil; prescan normalization improved activation parameters only at central brain structures.
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To describe a technique for the detection of distinct brain fibers in sets of magnetic resonance (MR) diffusion tensor imaging (DTI) data. MR-DTI can be used for a tractography of brain fibers presuming a data set of high spatial... more
To describe a technique for the detection of distinct brain fibers in sets of magnetic resonance (MR) diffusion tensor imaging (DTI) data. MR-DTI can be used for a tractography of brain fibers presuming a data set of high spatial resolution and high signal to noise. A less demanding technique for the visualization of discrete brain fiber bundles involves segmentation. By using a region-growing algorithm, those voxels that have a direction similar to that of the major eigenvector in neighboring voxels of a data set can be marked. It has been shown recently by Mori et al (1) that this technique can be successfully applied to data from a single slice of a mouse brain. In this study, the segmentation technique was applied with modifications to multislice DTI data from the human brain. A distinct segmentation of various brain fiber bundles could be achieved by the use of a two-step algorithm. In the first step, voxels within large fiber tracts-such as corticofugal tracts (e.g., corticospinal tract) and the optic radiation-were segmented by starting the region-growing algorithm in the corpus callosum (CC) and erasing this major structure from the data set. In the second step, remaining voxels were segmented by the same algorithm; this revealed a good assignment of the similarly oriented fibers derived by segmentation to the anatomically given brain lobes. This two-step procedure was successfully applied to DTI data of six healthy volunteers. The segmentation technique for DTI data proposed by Mori et al (1) for data from mouse brains can be applied to multislice data from the human brain by using a two-step algorithm including a masking of the major fiber tracts.
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The aim of the study is to elucidate the location and amount of spinal cerebrospinal fluid pulsations and to differentiate and quantify the cardiac and the respiratory influence. An echo planar imaging sequence was applied to 5 different... more
The aim of the study is to elucidate the location and amount of spinal cerebrospinal fluid pulsations and to differentiate and quantify the cardiac and the respiratory influence. An echo planar imaging sequence was applied to 5 different levels of the spinal canal of 7 healthy volunteers. The amount of maximal flow and respiratory signal variation were determined by a time and frequency domain analysis, respectively. CSF pulsation was high in the anterior cervical and in the thoracolumbar spine. Respiratory influence rose by 19% at C1 and by 28% at T12. The systolic flow was elevated during late expiration and the diastolic upward movement was pronounced by early expiration. The pulsation in the lower spine seems to be related to a second motor of CSF movement because there is a rising respiratory influence and a reappearance of pulsation waves. Physiological spinal CSF pulsation contains a relevant respiratory component.
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Research Interests: Magnetic Resonance Imaging, Imaging, Flow Cytometry, Confocal Microscopy, Transport, and 12 moreHumans, Peptides, European, Cell nucleus, Liquid Chromatography / Electrospray Ionization Mass Spectrometry, Confocal Laser Scanning Microscopy, Organometallic Compounds, Heterocyclic compounds, Contrast Media, NLS, Magnetic resonance image, and fluorescent dyes
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Commonly, in lesion-behaviour studies structural changes in brain matter are depicted and analysed. However, in addition to these structural changes, brain areas might be structurally intact but non-functional due to malperfusion. These... more
Commonly, in lesion-behaviour studies structural changes in brain matter are depicted and analysed. However, in addition to these structural changes, brain areas might be structurally intact but non-functional due to malperfusion. These changes may be detected using perfusion-weighted MRI (PWI). Perfusion parameters most commonly used [e.g. time-to-peak (TTP)] are semi-quantitative and perfusion is evaluated in relation to a non-affected reference area. Traditionally, the mean of a larger region in the non-affected hemisphere or the cerebellum has been used ["mean contra-region of interest (ROI) comparison"]. Our results suggest that this method is prone to biases (in particular in periventricular regions) because perfusion differs between different parts of the brain, for example, between grey and white matter. We reduced such potential biases with voxelwise inter-hemispheric comparisons. Each voxel is compared with its homologous voxel and thus white matter with white matter and grey matter with grey matter. This automated method seems to correspond with results deriving from manual delineation of perfusion deficits. The TTP delay maps with a threshold of 3 s seem to be best comparable to manual delineation. Our method avoids the observer-dependent choice of a reference region and involves the spatial normalisation of perfusion maps. It is well suited for whole-brain analysis of abnormal perfusion in neuroscience studies as well as in clinical contexts.
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Since the advent of high angular resolution diffusion imaging (HARDI) techniques in diffusion MRI great efforts have been taken in order to reconstruct complex whitematter structures, such as crossing, branching and kissing fibers.... more
Since the advent of high angular resolution diffusion imaging (HARDI) techniques in diffusion MRI great efforts have been taken in order to reconstruct complex whitematter structures, such as crossing, branching and kissing fibers. However, even highly sophisticated fiber tracking schemes, such as probabilistic tracking, suffer from the data’s poor signal-to-noise (SNR) ratio. In this paper we present a novel regularization approach for q-ball fields, exploiting structural information within the data. We also propose a straightforward deterministic tracking algorithm, allowing delineation of even non-dominant pathways through crossing regions. Results from a phantom study with a biological phantom as well as a patient study, in which we reconstruct a part of the pyramidal tract, emphasize the method’s efficiency. KeywordsHARDI-ODF-Regularization-Fiber Tracking
To detect oscillations of the cerebrospinal fluid (CSF) flow related to the heartbeat and frequencies lower than 0.6 Hz and to compare these oscillations of CSF and blood flow in cerebral vessels by using echo planar imaging in real time... more
To detect oscillations of the cerebrospinal fluid (CSF) flow related to the heartbeat and frequencies lower than 0.6 Hz and to compare these oscillations of CSF and blood flow in cerebral vessels by using echo planar imaging in real time mode. The existence of such waves has been well known but has not yet been shown by MRI. In a slice perpendicular to the aqueduct, CSF flow as well as CBF, could be determined in sagittal sinus, basilar artery, and capillary vessels. After Fourier analysis, four frequency bands were assigned. In the very high-frequency (heart rate) range, the integrals under the CSF curves were more closely related to arterial CBF than to changes in the sinus. Also, in the high-frequency (respiration rate), low-frequency (0.05-0.15 Hz), and very-low-frequency (0.008-0.05 Hz) ranges, the integrals under the CSF curves corresponded with arterial and capillary CBF. Slow and fast oscillations in CSF flow are detectable in healthy persons with a proportional allotment to...
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Magnetic resonance perfusion and diffusion studies were undertaken to clarify the significance of ischemia in the pathogenesis of peritumoral brain edema in patients with meningiomas. Included in this study were 26 patients with 27... more
Magnetic resonance perfusion and diffusion studies were undertaken to clarify the significance of ischemia in the pathogenesis of peritumoral brain edema in patients with meningiomas. Included in this study were 26 patients with 27 meningiomas and 5 gliomas. Perfusion-weighted imaging (PWI) was performed using a gradient-echo, echo-planar-imaging (EPI) sequence for calculation of the relative regional cerebral blood volume (rrCBV) and the relative regional cerebral blood flow index (rrCBFi). Furthermore, multi-slice spin-echo EPI sequences were applied in order to obtain anisotropic and isotropic diffusion-weighted imaging (DWI). Apparent diffusion coefficient (ADC) values were then calculated for peritumoral brain parenchyma from tumors, with and without edema, using various diffusion sensitivities. Meningiomas without edema demonstrated a minimal increase of perfusion parameters in the peritumoral brain tissue. In contrast, cases with brain edema had highly significant (p<0.000...
Fast and accurate segmentation of deep gray matter structures is important for clinical applications such as for example surgery planning for the placement of deep brain stimulation implants. We implemented a segmentation method that is... more
Fast and accurate segmentation of deep gray matter structures is important for clinical applications such as for example surgery planning for the placement of deep brain stimulation implants. We implemented a segmentation method that is solely based on local diffusion information and did evaluate it on a group of 53 healthy volunteers to investigate the reproducibility and thereby the usability of this method. We were able to show that the segmentation produces subdivisions which are reproducible for a large population. We could also show that not only the three previously reported large clusters were reproducible but also four smaller clusters could be found in the same position in more than 60% of the subjects.
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ABSTRACT Proton MR Spectroscopy without water suppression has the advantage of the availability of intact water signal which can be used as an internal reference in quantitative analysis and for baseline correction. Moreover spectra... more
ABSTRACT Proton MR Spectroscopy without water suppression has the advantage of the availability of intact water signal which can be used as an internal reference in quantitative analysis and for baseline correction. Moreover spectra obtained with this technique do not need phase correction. However, spectroscopy without water suppression is hampered by the sideband artifacts. These artifacts seriously complicates the quantitative analysis and therefore it is necessary to remove them. The aim of this study was to develop a method that will enable to reduce the influence of the sideband artifacts on the spectra and will gain all the advantages of spectroscopy without water suppression. Spectra from six healthy volunteers were acquired on 3T (TimTrio, Siemens, Erlangen, Germany) scanner with a PRESS sequence for volume selection. Postprocessing was performed in three steps: correcting the water peak position in all spectra (frequency correction), subtracting the Gaussian convolution of all FID’s (water signal reduction) and subtracting the FID of a water phantom from the volunteer’s FID signal (reduction of sidebands). For the postprocessing a customized software was developed with Matlab 2007b (MathWorks Inc. Natick, MA, USA). The described technique provides spectra with reduced water signal and sidebands. Moreover since all acquired spectra do not need phase correction, it is possible to calculate a mean spectrum from a few voxels which lies within the particular region of interest. With this averaging procedure an additional gain in Signal-to-Noise-Ratio (SNR) can be obtained. Keywordshi-res CSI-water suppression-average spectrum-phase correction-sidebands