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Ewald Moser

Publications and source records attributed to Ewald Moser.

31 records · Page 2Linked to original sources
PubMed2003

Relaxation times of 31P-metabolites in human calf muscle at 3 T.

Localized (31)P-STEAM experiments were performed at 3 T to estimate relaxation times of phosphorus-containing metabolites in the human calf muscle in vivo. T(1) and T(2) times of PCr, P(i), and NTPs were measured in the resting calf muscle of healthy subjects by varying TR and TE. The localization performance of the (31)P-STEAM sequence was evaluated on a test object, resulting in a relative selection efficiency of 78 +/- 1% and contamination from outside the voxel of 0 +/- 2% under fully relaxed conditions. T(1) relaxation times (+/-SD, n = 5) of P(i), PCr, gamma-NTP, alpha-NTP, and beta-NTP obtained at 3 T are 5.2 +/- 1.0 s, 6.4 +/- 0.2 s, 4.5 +/- 0.3 s, 2.6 +/- 0.9 s, and 3.5 +/- 1.1 s, respectively. T(2) relaxation times (+/-SD, n = 6) of these metabolites are 148 +/- 17 ms, 334 +/- 30 ms, 78 +/- 13 ms, 55 +/- 7 ms, and 55 +/- 10 ms, respectively. Spin-lattice relaxation times established at 3 T are consistent with literature data at lower field strengths, whereas spin-spin relaxation times are lower. Several methodological considerations are discussed which may help improve quantification of metabolite concentrations in the human (calf) muscle in vivo by using localized noninvasive (31)P-MRS at 3 T, which is currently being tested for routine clinical applications.

Adult↗
PubMed2003

Fuzzy cluster analysis of high-field functional MRI data.

Functional magnetic resonance imaging (fMRI) based on blood-oxygen level dependent (BOLD) contrast today is an established brain research method and quickly gains acceptance for complementary clinical diagnosis. However, neither the basic mechanisms like coupling between neuronal activation and haemodynamic response are known exactly, nor can the various artifacts be predicted or controlled. Thus, modeling functional signal changes is non-trivial and exploratory data analysis (EDA) may be rather useful. In particular, identification and separation of artifacts as well as quantification of expected, i.e. stimulus correlated, and novel information on brain activity is important for both, new insights in neuroscience and future developments in functional MRI of the human brain. After an introduction on fuzzy clustering and very high-field fMRI we present several examples where fuzzy cluster analysis (FCA) of fMRI time series helps to identify and locally separate various artifacts. We also present and discuss applications and limitations of fuzzy cluster analysis in very high-field functional MRI: differentiate temporal patterns in MRI using (a) a test object with static and dynamic parts, (b) artifacts due to gross head motion artifacts. Using a synthetic fMRI data set we quantitatively examine the influences of relevant FCA parameters on clustering results in terms of receiver-operator characteristics (ROC) and compare them with a commonly used model-based correlation analysis (CA) approach. The application of FCA in analyzing in vivo fMRI data is shown for (a) a motor paradigm, (b) data from multi-echo imaging, and (c) a fMRI study using mental rotation of three-dimensional cubes. We found that differentiation of true "neural" from false "vascular" activation is possible based on echo time dependence and specific activation levels, as well as based on their signal time-course. Exploratory data analysis methods in general and fuzzy cluster analysis in particular may help to identify artifacts and add novel and unexpected information valuable for interpretation, classification and characterization of functional MRI data which can be used to design new data acquisition schemes, stimulus presentations, neuro(physio)logical paradigms, as well as to improve quantitative biophysical models.

Artifacts↗
PubMed2003

Human motor cortex activity during mental rotation.

The functional role of human premotor and primary motor cortex during mental rotation has been studied using functional MRI at 3 T. Fourteen young, male subjects performed a mental rotation task in which they had to decide whether two visually presented cubes could be identical. Exploratory Fuzzy Cluster Analysis was applied to identify brain regions with stimulus-related time courses. This revealed one dominant cluster which included the parietal cortex, premotor cortex, and dorsolateral prefrontal cortex that showed signal enhancement during the whole stimulus presentation period, reflecting cognitive processing. A second cluster, encompassing the contralateral primary motor cortex, showed activation exclusively after the button press response. This clear separation was possible in 3 subjects only, however. Based on these exploratory results, the hypothesis that primary motor cortex activity was related to button pressing only was tested using a parametric approach via a random-effects group analysis over all 14 subjects in SPM99. The results confirmed that the stimulus response via button pressing causes activation in the primary motor cortex and supplementary motor area while parietal cortex and mesial regions rostral to the supplementary motor area are recruited for the actual mental rotation process.

Adult↗
PubMed2003

The preparation and readiness for voluntary movement: a high-field event-related fMRI study of the Bereitschafts-BOLD response.

Activity within motor areas of the cortex begins to increase 1 to 2 s prior to voluntary self-initiated movement (termed the Bereitschaftspotential or readiness potential). There has been much speculation and debate over the precise source of this early premovement activity as it is important for understanding the roles of higher order motor areas in the preparation and readiness for voluntary movement. In this study, we use high-field (3-T) event-related fMRI with high temporal sampling (partial brain volumes every 250 ms) to specifically examine hemodynamic response time courses during the preparation, readiness, and execution of purely self-initiated voluntary movement. Five right-handed healthy volunteers performed a rapid sequential finger-to-thumb movement performed at self-determined times (12-15 trials). Functional images for each trial were temporally aligned and the averaged time series for each subject was iteratively correlated with a canonical hemodynamic response function progressively shifted in time. This analysis method identified areas of activation without constraining hemodynamic response timing. All subjects showed activation within frontal mesial areas, including supplementary motor area (SMA) and cingulate motor areas, as well as activation in left primary sensorimotor areas. The time courses of hemodynamic responses showed a great deal of variability in shape and timing between subjects; however, four subjects clearly showed earlier relative hemodynamic responses within SMA/cingulate motor areas compared with left primary motor areas. These results provide further evidence that the SMA and cingulate motor areas are major contributors to early stage premovement activity and play an important role in the preparation and readiness for voluntary movement.

Adult↗
PubMed2003

Bone homogeneity factor: an advanced tool for the assessment of osteoporotic bone structure in high-resolution magnetic resonance images.

RATIONALE AND OBJECTIVES: Osteoporosis is characterized by low bone mass and inferior structural competence. In this study we introduce the bone homogeneity factor (BHF) as a quantitative measurement of bone structure, which could be equally important as bone mineral density. METHODS: BHF represents an advanced texture analysis tool based on the spatial autocorrelation function calculated in 9 different directions. These calculations were performed on high-resolution magnetic resonance images of the calcaneus at 3.0 T and compared with dual-energy x-ray absorptiometry measurements of the femoral neck. RESULTS: The quality and resolution of the high-resolution magnetic resonance images is sufficient for reliably calculating BHF. The mean BHF of the control group (n = 5, mean BHF = 525,0) with normal bone is significantly (P = 0.009, Mann-Whitney U test) higher than in the osteoporotic group (n = 7, mean BHF = 137,8). The BHF correlates with the DXA measurements of the femoral neck (correlation coefficient = 0.75). CONCLUSIONS: By calculating the BHF, it was possible to distinguish between osteoporotic and nonosteoporotic bone structure. Hence, BHF could be a possible candidate for noninvasive assessment of osteoporotic bone structure giving additional information to routinely used bone mineral densitometry.

Absorptiometry, Photon↗
PubMed2003

Diffusivity- and T2 imaging at 3 Tesla for the detection of degenerative changes in human-excised tissue with high resolution: atherosclerotic arteries.

RATIONALE AND OBJECTIVES: We investigated whether it is possible to investigate degenerative changes in human tissue on a sub-100-microm resolution scale not only on special high-field small-bore MR-microscopy systems but also on a 3T whole-body MR-scanner. METHODS: Spin-spin relaxation, proton density, and diffusion microimaging were investigated in studying human atherosclerotic arteries. Strong diffusion weighting and high spatial resolution was achieved by means of a strong dedicated gradient system and a small birdcage radiofrequency resonator. RESULTS: Quantitative parameter maps were obtained at voxel sizes down to 73 x 73 x 600 microm3. The morphologic structure and pathology connected to lipid deposits, plaques, small thrombi, and bifurcations were well visualized. CONCLUSION: High-resolution parameter-weighted and parameter-imaging at sub-100-microm pixel resolution can be achieved for excised tissue on a 3.0 T whole body MR system. Perspectives for the characterization of atherosclerotic plaques imply not only cost advantages but also equivalence of contrast, especially as to T(2), for in vivo and high-resolution ex vivo investigations on the same MR scanner.

Aged↗
PubMed2003

Quantification of metabolic differences in the frontal brain of depressive patients and controls obtained by 1H-MRS at 3 Tesla.

RATIONALE AND OBJECTIVES: This study compared metabolic differences in the frontal brain of depressed patients versus age- and sex-matched controls using proton magnetic resonance spectroscopy and absolute quantification of metabolites (NAA, Cr, Cho, mI) at 3 Tesla. METHODS: Short-echo-time stimulated echo acquisition mode (TE/TM/TR=20/30/6000 milliseconds) was applied in the prefrontal region of 17 depressed patients and 17 age- and sex-matched controls. Metabolic ratios, ie, N-acetyl-aspartate/creatine (Cr), choline/Cr, and myo-inositol/Cr, and absolute concentrations (using internal water as a reference together with LCModel-based spectra fitting) were calculated and compared between groups and published reference data. RESULTS: Metabolic ratios showed significantly lower N-acetyl-aspartate/Cr (P = 0.016/0.006, left/right), choline/Cr (P = n.s./0.016), and myo-inositol/Cr (P = 0.022/0.026) for depressive patients versus controls. However, depressive patients showed significantly higher absolute concentrations of Cr (P = 0.017/0.0004) compared with controls with no differences in all other metabolites estimated. CONCLUSIONS: The authors demonstrate that absolute quantification of metabolite concentration is essential in properly identifying pathologic differences of brain metabolites in depression.

Adult↗
PubMed2003

High-resolution diffusivity imaging at 3.0 T for the detection of degenerative changes: a trypsin-based arthritis model.

RATIONALE AND OBJECTIVES: To establish whether it is possible to quantitatively characterize the degenerative changes in cartilage that typify arthritis on a sub-150-microm resolution scale using a 3.0 T whole body MR-scanner with a reasonable measurement time. MATERIALS AND METHODS: This problem is addressed through diffusion-microimaging investigations on an arthritis model based on the enzymatic destruction of the proteoglycans in cartilage specimen. A 35-mm birdcage resonator made high spatial resolution possible, and diffusion-micro-imaging was achieved with the use of a strong gradient system. RESULTS: Diffusion-weighted and quantitative parameter maps were acquired with 117 x 234 microm2 pixel resolution in less than 9 minutes. Diffusivity profiles and parameter images exhibit an increase in diffusivity in degenerated tissue. CONCLUSION: In a trypsin-based arthritis model, the spatial localization and quantification of damaged areas have been shown to be possible on a whole body 3.0 T MR system. Measurement times achieved for these high spatial resolution studies make in vivo investigations feasible.

Animals↗
PubMed2002

Comparison of multi-echo spiral and echo planar imaging in functional MRI.

Multi-echo spiral and echo-planar (EPI) imaging sequences were compared in functional imaging experiments at 3 Tesla. Both sequence types allow calculation of the effective transversal relaxation time T(2)* and the initial signal intensity I(0). These parameters can be used in evaluation of the functional signal with respect to inflow effects and other vascular sources. Prior to functional magnetic resonance imaging (fMRI) experiments T(2)* measurements in the human brain were performed with single- and multi-echo FLASH (fast low angle shot) and compared with EPI und spiral imaging sequences. These experiments resulted in T(2)* values ranging from 42.9 to 53.8 ms in a ROI including white and gray matter and CSF in a prefrontal brain region, and allowed validation of the quantitative results of the fast single-shot techniques. In functional experiments with motor stimulation mean absolute T(2)* increases during stimulation of 1.1 +/- 0.6 ms and 1.4 +/- 0.9 ms were found with multi-echo EPI and spiral imaging, respectively, averaged over the activated pixels. In addition, absolute T(2)* values and the size of activated areas obtained with both sequences are comparable. In these investigations spiral imaging allowed higher spatial resolution due to more efficient use of available gradient performance.

Adult↗
PubMed2002

On the origin of respiratory artifacts in BOLD-EPI of the human brain.

BOLD-based functional MRI (fMRI) can be used to explicitly measure hemodynamic aspects and functions of human neuro-physiology. As fMRI measures changes in regional cerebral blood flow and volume as well as blood oxygenation, rather than neuronal brain activity directly, other processes that may change the above parameters have to be examined closely to assess sensitivity and specificity of fMRI results. Physiological processes that can cause artifacts include cardiac action, breathing and vasomotion. Although there has been substantial research on physiological artifacts and appropriate compensation methods, controversy still remains on the mechanisms that cause the fMRI signal fluctuations. Respiratory-correlated fluctuations may either be induced by changes of the magnetic field homogeneity due to moving organs, intra-thoracic pressure differences, respiration-dependent vasodilation or oxygenation differences. The aim of this study was to characterize the impact of different breathing patterns by varying respiration frequency and/or tidal volume on EPI time courses of the resting human brain. The amount of respiration-related oscillations during three respiration patterns was quantified, and statistically significant differences were obtained in white matter only: p < 0.03 between 6 vs. 12 ml/kg body weight end tidal volume at a respiration frequency of 15/min, p < 0.03 between 12 vs. 6 ml/kg body weight and 15 vs. 10 respiration cycles/min. There was no significant difference between 15 vs. 10 respiration cycles/min at an end tidal volume of 6 ml/kg body weight (p = 0.917). In addition, the respiration-affected brain regions were very similar with EPI readout in the a-p and l-r direction. Based on our results and published literature we hypothesize that venous oxygenation oscillations due to changing intra-thoracic pressure represent a major factor for respiration-related signal fluctuations and increase significantly with increasing end tidal volume in white matter only.

Adult↗
PubMed2002

Consistency of inter-trial activation using single-trial fMRI: assessment of regional differences.

Recently, the technique of single-trial fMRI was introduced, which allows the assessment of hemodynamic responses to single task executions (e.g. sensory, motor, or cognitive). In this study, single-trial fMRI was used to examine regional differences in the inter-trial consistency (ITC) of brain activity related to the processing of a dynamic visuo-spatial imagery task. For every single trial, a t-statistic assessing task-related activation was calculated and thresholded at a p-value of P < or =l0.05 (uncorrected). The percentage of trials with t-values above the threshold was used to assess differences in the consistency of brain activity in occipital, parietal, premotor and prefrontal regions of interest. While most of these regions showed activation which was highly consistent across trials, the consistency of activation was significantly reduced in the dorsolateral prefrontal cortex. We hypothesize that the consistency of activation across trials may be interpreted as an indicator of the functional relevance of a brain region for processing and solving a cognitive task. Thus, the analysis concept presented here has the potential to provide new insights into the neuro-cognitive mechanisms of human information processing. In addition, the results of this study confirm that averaging across trials might result in a significant loss of information about functional neuroanatomy. Regions which are active in some trials only, which show only weak activity increases, or whose activity is not constant and time-locked, might not show up in averaged activation maps and could thus erroneously be interpreted as irrelevant for task processing.

Adult↗
PubMed2002

Oral beta-hydroxybutyrate supplementation in two patients with hyperinsulinemic hypoglycemia: monitoring of beta-hydroxybutyrate levels in blood and cerebrospinal fluid, and in the brain by in vivo magnetic resonance spectroscopy.

In persistent hyperinsulinemic hypoglycemia of infancy, ketone body concentrations are abnormally low at times of hypoglycemia, depriving the brain of its most important alternative fuel. The neuroprotective effect of endogenous ketone bodies is evidenced by animal and human studies, but knowledge about exogenous supply is limited. Assuming that exogenous ketone body compounds as a dietetic food might replace this alternative energy source for the brain, we have monitored the fate of orally supplemented DL sodium beta-hydroxybutyrate (beta-OHB) in two 6-mo-old infants with persistent hyperinsulinemic hypoglycemia for 5 and 7 mo, while on frequent tube-feedings and treatment with octreotide. Near total (95%) pancreatectomy had been ineffective in one patient and was refused in the other. In blood, concentrations of beta-OHB increased to levels comparable to a 16- to 24-h fast while on DL sodium beta-OHB 880 to 1000 mg/kg per day. In cerebrospinal fluid, concentrations of beta-OHB increased to levels comparable to a 24- to 40-h fast, after single dosages of 4 and 8 g, respectively. High ratios of beta-OHB to acetoacetate indicated exogenous origin of beta-OHB. An increase of intracerebral concentrations of beta-OHB could be demonstrated by repetitive single-voxel proton magnetic resonance spectroscopy by a clear doublet at 1.25 ppm. Oral DL sodium beta-OHB was tolerated without side effects. This first report on oral supplementation of DL sodium beta-OHB in two patients with persistent hyperinsulinemic hypoglycemia demonstrates effective uptake across the blood-brain barrier and could provide the basis for further evaluation of the neuroprotective effect of beta-OHB in conditions with hypoketotic hypoglycemia.

3-Hydroxybutyric Acid↗