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S Posse

Publications and source records attributed to S Posse.

At least 19 recordsLinked to original sources
PubMed1998

Differential magnetic resonance signal change in human sensorimotor cortex to finger movements of different rate of the dominant and subdominant hand.

Functional magnetic resonance tomography (fMRI) analysis of unimanual and bimanual sequential movements in righthanders showed the following effects. First, a rate-dependent activation of the somato-motor cortex was confirmed, with faster movement rates producing higher activation both in terms of signal intensity and number of activated voxels. Second, the right hemisphere showed more activation than the left hemisphere during unimanual tasks. Third, during bimanual movements, the left hemisphere showed greater activation than the right hemisphere. Finally, while the left hemisphere showed a marked change in activation patterns from unimanual to bimanual task, the right hemisphere activation patterns were not sensitive to task changes. The hemispheric asymmetries suggest substantial left hemisphere involvement in the coordination of bimanual tasks.

Adult↗
PubMed1998

Human anterior intraparietal area subserves prehension: a combined lesion and functional MRI activation study.

It has been shown in nonhuman primates that the posterior parietal cortex is involved in coordination of arm and eye movements in space, whereas the anterior intraparietal area in the anterior lateral bank of the intraparietal sulcus plays a crucial role in fine finger movements, such as grasping. In this study we show by optoelectronic movement recordings that patients with cortical lesions involving the anterior lateral bank of the intraparietal sulcus have selective deficits in the coordination of finger movements required for object grasping, whereas reaching is much less disturbed. Patients with parietal lesions sparing the cortex lining the anterior intraparietal sulcus showed intact grasping behavior. Complementary evidence was obtained from functional MRI in normal control subjects showing a specific activation of the anterior lateral bank of the intraparietal sulcus during grasping. In conclusion, this combined lesion and activation study suggests that the anterior lateral bank of the intraparietal sulcus, possibly including the human homologue of the anterior intraparietal area, mediates the processing of sensorimotor integration of precisely tuned finger movements in humans.

Adult↗
PubMed1997

In vivo measurement of regional brain metabolic response to hyperventilation using magnetic resonance: proton echo planar spectroscopic imaging (PEPSI).

A new rapid spectroscopic imaging technique with improved sensitivity and lipid suppression, referred to as Proton Echo Planar Spectroscopic Imaging (PEPSI), has been developed to measure the 2-dimensional distribution of brain lactate increases during hyperventilation on a conventional clinical scanner equipped with a head surface coil phased array. PEPSI images (nominal voxel size: 1.125 cm3) in five healthy subjects from an axial section approximately 20 mm inferior to the intercommissural line were obtained during an 8.5-min baseline period of normocapnia and during the final 8.5 min of a 10-min period of capnometry-controlled hyperventilation (end-tidal PCO2 of 20 mmHg). The lactate/N-acetyl aspartate signal increased significantly from baseline during hyperventilation for the insular cortex, temporal cortex, and occipital regions of both the right and left hemisphere, but not in the basal ganglia. Regional or hemispheric right-to-left differences were not found. The study extends previous work using single-voxel MR spectroscopy to dynamically study hyperventilation effects on brain metabolism.

Adult↗
PubMed1997

Regional dynamic signal changes during controlled hyperventilation assessed with blood oxygen level-dependent functional MR imaging.

PURPOSE: To quantitate the amplitude changes and temporal dynamics of regional functional MR imaging signals during voluntary hyperventilation using blood oxygen level-dependent contrast echo-planar imaging. METHODS: Seven male subjects were studied during voluntary hyperventilation (PetCO2 = 20 mm Hg) regulated by capnometry. Measurements were made on multisection echo-planar MR images obtained with parameters of 1000/66 (repetition time/echo time), flip angle of 30 degrees, and voxel size of 3 x 3 x 5 mm3. Sensitivity of the functional MR imaging signal to changes in PetCO2, time delays in relation to PetCO2 changes, and time constants of functional MR imaging signal changes were assessed on a region-by-region basis. RESULTS: Within 20 seconds of starting hyperventilation, rapid and substantial decreases in the functional MR imaging signal (by as much as 10%) were measured in areas of gray matter, which were significantly greater than the modest changes observed in white matter. Regional-specific effects in areas of the frontal, occipital, and parietooccipital cortex were stronger than in subcortical regions or in the cerebellum. Signal decreases measured with functional MR imaging were significantly delayed with respect to the reduction in PetCO2. Apparent differences between regional time constants did not reach statistical significance. CONCLUSION: Regional and gray-white matter differences in functional MR imaging signal changes during controlled hyperventilation may reflect differences in metabolic activity, vascular regulation, and/or capillary density. When measuring brain activation with functional MR imaging, arterial PCO2 differences due to unregulated respiration may confound interpretation of activation-related functional MR imaging signal changes.

Adult↗
PubMed1996

Double-sampled echo-planar imaging at 3 tesla.

A persistent artifact in the images acquired by the echo-planar imaging (EPI) method is the Nyquist or N/2 ghost which interferes with the image and reduces the signal-to-noise ratio (SNR). The Nyquist ghost is the result of the time-reversal asymmetry between the even and odd echoes. To eliminate this artifact, the authors present a double-sampled EPI (DSEPI) method in which echoes from each even and odd echo pair are equally phase encoded. The even and odd echoes are separately reconstructed into two distinct images which are then added together. The DSEPI method has been applied to human brain at 3.0 T and shown to be a simple and effective way to eliminate the Nyquist ghost and restore image SNR loss.

Brain↗
PubMed1995

High speed 1H spectroscopic imaging in human brain by echo planar spatial-spectral encoding.

We introduce a fast and robust spatial-spectral encoding method, which enables acquisition of high resolution short echo time (13 ms) proton spectroscopic images from human brain with acquisition times as short as 64 s when using surface coils. The encoding scheme, which was implemented on a clinical 1.5 Tesla whole body scanner, is a modification of an echo-planar spectroscopic imaging method originally proposed by Mansfield Magn. Reson. Med. 1, 370-386 (1984), and utilizes a series of read-out gradients to simultaneously encode spatial and spectral information. Superficial lipid signals are suppressed by a novel double outer volume suppression along the contours of the brain. The spectral resolution and the signal-to-noise per unit time and unit volume from resonances such as N-acetyl aspartate, choline, creatine, and inositol are comparable with those obtained with conventional methods. The short encoding time of this technique enhances the flexibility of in vivo spectroscopic imaging by reducing motion artifacts and allowing acquisition of multiple data sets with different parameter settings.

Artifacts↗
PubMed1995

Anomalous transverse relaxation in 1H spectroscopy in human brain at 4 Tesla.

Longitudinal (T1) and apparent transverse relaxation times (T2) of choline-containing compounds (Cho), creatine/phosphocreatine (Cr/PCr), and N-acetyl aspartate (NAA) were measured in vivo in human brain at 4 Tesla. Measurements were performed using a water suppressed stimulated echo pulse sequence with complete outside volume presaturation to improve volume localization at short echo times. T1-values of Cho (1.2 +/- 0.1 s), Cr (1.6 +/- 0.3 s), and NAA (1.6 +/- 0.2 s) at 4 Tesla in occipital brain were only slightly larger than those reported in the literature at 1.5 Tesla. Thus, TR will not adversely affect the expected enhancement of signal-to-noise at 4 Tesla. Surprisingly, apparent T2-values of Cho (142 +/- 34 ms), Cr (140 +/- 13 ms), and NAA (185 +/- 24 ms) at 4 Tesla were significantly smaller than those at 1.5 Tesla and further decreased when increasing the mixing interval TM. Potential contributing factors, such as diffusion in local susceptibility related gradients, dipolar relaxation due to intracellular paramagnetic substances and motion effects are discussed. The results suggest that short echo time spectroscopy is advantageous to maintain signal to noise at 4 Tesla.

Artifacts↗
PubMed1994

Three-dimensional echo-planar MR spectroscopic imaging at short echo times in the human brain.

PURPOSE: To demonstrate the feasibility of three-dimensional echo-planar spectroscopic imaging (EPSI) at short echo time (13 msec) with a conventional clinical imager in the human brain. MATERIALS AND METHODS: Periodic inversions of a readout gradient were used during data acquisition to simultaneously encode chemical shift and one spatial dimension in one excitation. Aliasing artifacts were avoided with a modified acquisition-and-processing method based on oversampling. A double outer-volume suppression technique that adapts to the ovoid brain shape was used to strongly reduce extracranial lipid resonances. RESULTS: Three-dimensional spatial encoding in vivo of eight sections with 32 x 32 voxels each (0.75 cm3) was performed in 34 minutes with four signal averages. The spectral resolution and signal-to-noise ratio (S/N) of resonances of inositol, choline, creatine, glutamate and glutamine, and N-acetyl aspartate were consistent with those previously recorded with conventional phase encoding. CONCLUSION: EPSI substantially reduces acquisition time for three-dimensional spatial encoding and yields a spectral quality similar to that obtained with conventional techniques without affecting the S/N per unit time and unit volume.

Aspartic Acid↗
PubMed1993

Human brain: proton diffusion MR spectroscopy.

Diffusion of brain metabolites was measured in 10 healthy volunteers by using localized proton diffusion magnetic resonance (MR) spectroscopy. Measurements were conducted with a clinical MR imager by using a stimulated-echo pulse sequence (3,000/60 [repetition time msec/echo time msec], 200-msec mixing time) with additional outside-volume suppression. Motion artifacts due to macroscopic brain movements were compensated by means of peripheral cardiac gating and separate collection of individual spectroscopic acquisitions into a two-dimensional data matrix. Phase errors due to macroscopic motion were subsequently corrected in individual data traces prior to spectral averaging. Mean (+/- 1 standard deviation) apparent diffusion coefficients of choline-containing compounds ([0.13 +/- 0.03] x 10(-3) mm2/sec), creatine and phosphocreatine ([0.15 +/- 0.03] x 10(-3) mm2/sec), and N-acetyl aspartate ([0.18 +/- 0.02] x 10(-3) mm2/sec) were substantially smaller than that of water and were consistent with recently published data obtained in anesthetized and paralyzed animals. Adequate diffusion sensitivity for metabolites in the human brain can be obtained with clinical whole-body imagers despite macroscopic head and brain movements.

Adult↗
PubMed1992

Direct imaging of magnetic field gradients by group spin-echo selection.

A new image processing method for single-echo gradient echo imaging is presented which extracts local phase gradient information by k-space filtering instead of by phased reconstruction and spatial differentiation. It is shown that local phase gradient directions and semiquantitative local phase gradient magnitudes can be directly measured, even in regions where phased image reconstruction suffers from multiple phase foldovers due to strong phase modulations. The directional information thus obtained can be used as a reference to identify and correct phase modulation foldovers in phase maps which may be computed from the same raw data. The method is applied here to measure static magnetic field gradients and illustrates fundamental k-space signal properties of gradient echo imaging. Based on this concept, image artifacts caused by conventional strong k-space filtering in gradient echo imaging are discussed.

Artifacts↗
PubMed1991

Neuro-Behçet: acute and sequential aspects by MRI and MRS.

Three patients with neuro-Behçet underwent MRI and MRS during acute illness. After therapy, MRI and MRS were performed in 3 and 1 patients, respectively. MRI revealed a marked improvement of the initial lesion in 2, a complete remission in 1 patient. MRS showed a reduction of the N-acetyl-aspartate (NAA)/phosphocreatine (CR) ratio within the acute lesion in all patients and a normalization in the follow-up spectrum of the examined patient.

Adrenal Cortex Hormones↗
PubMed1991

Magnetic resonance in preterm and term newborns: 1H-spectroscopy in developing human brain.

Localized proton magnetic resonance spectra were recorded from human cerebellum in vivo with a 1.5-T magnet. The spectra from healthy adults and preterm and term babies showed resonances from N-acetylaspartate, creatine and phosphocreatine, choline-containing compounds such as phosphocholine and glycerophosphocholine, taurine, and inositol. The age-dependent changes of in vivo molar concentrations of N-acetylaspartate, choline, taurine, and inositol were estimated in preterm babies, babies at term, and adults. The range of postconceptional age in the studied babies was 31 to 45 wk. Taking the biochemically measured creatine concentrations in age-corresponding autopsy material as an internal standard, the in vivo concentrations of the other metabolites were calculated from the proton spectra. N-acetylaspartate showed an increase from 1.9 mM in preterm babies to 3.1 mM in term babies and to 6.5 mM in adult brain. Taurine was noted to increase from 1.1 mM in preterm infants to 2.3 mM in term infants and did not decrease significantly in adult brain. Choline and inositol concentrations did not change significantly throughout the studied age groups. These new data on in vivo, localized 1H-spectroscopy show that it is a sensitive method for studying early metabolic brain development in humans.

Adult↗
PubMed1990

Brain development: 1H magnetic resonance spectroscopy of rat brain extracts compared with chromatographic methods.

We compared in vitro 1H magnetic resonance spectroscopy (MRS) measurements of rat brain extracts (rats: 2-56 days old) with chromatographic measurements and in a further step also with results of in vitro MRS. The following substances can be reliably measured in brain extracts by in vitro MRS: N-acetylaspartate (NAA), total creatine (Cr), phosphorylethanoloamine (PE), taurine (Tau), glutamate (Glu), glutamine (Gln), gamma-aminobutyrate (GABA) and alanine (Ala). Two different methods of MRS data evaluation compared with chromatographic data on Cr and NAA are shown. During development of the rat from day 2-56 brain concentrations of PE, Tau and Ala decrease, those of NAA, Cr, Glu and Gln increase, while GABA does not change. The developmental patterns of these substances are the same, whether measured by in vitro MRS or by chromatographic methods. Quantification of NAA, Cr, Tau, GABA and PE leads to the same results with both methods, while Glu, Gln and Ala concentrations determined by in vitro MRS are apparently lower than those measured chemically. The NAA/Cr ratios of 7 to 35-day-old rats were determined by in vivo 1H MRS. These results correlate with chromatographic and in vitro data. Using appropriate methods in the in vivo and in vitro MR-technique, the obtained data compare well with the chromatographic results.

Aging↗
PubMed1990

Brain damage and recovery in hyperphenylalaninemic rats.

Rats were made hyperphenylalaninemic by injecting a mixture of alpha-methylphenylalanine and phenylalanine. Brain development was measured by biochemical, histological and 31-P nuclear magnetic resonance (NMR) methods. In 17-day-old hyperphenylalaninemic rats, brain myelinogenesis was disturbed. Compared to controls, test animals had lower body weights, brain weights, cerebrosides, sulfatides, myelin basic protein (MBP) and reduced cerebroside sulfotransferase (CST) and 2'3'-cyclic nucleotide-3'-phosphohydrolase (CNP) activities. No changes were found in total proteins, total lipids, total phospholipids, phosphatidylethanolamine and phosphorylethanolamine. In the brain of 17-day-old hyperphenylalaninemic rats no changes in phosphomonoesters, phosphodiester and phosphocreatine were found using in vivo 31-P NMR spectroscopy. Because body weights of hyperphenylalaninemic rats were significantly lower than those of controls, we compared them with undernourished rats. Undernourished rats had lower body weights, brain weights and CNP activity. No other changes were found. Therefore, we conclude that hyperphenylalaninemia per se and not undernutrition affected myelinogenesis in test animals. After treatment was discontinued, test rats recovered completely within 6 weeks with regard to biochemical and histological measurements; at 59 days they had normal body weights, cerebrosides, sulfatides, MBP, total proteins, total lipids, total phospholipids, phosphatidylethanolamine, phosphorylethanolamine and normal CST and CNP activities. Brain weights were significantly reduced.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1989

Study of acute renal ischemia in the rat using magnetic resonance imaging and spectroscopy.

Magnetic resonance (MR) imaging and spectroscopy, chemical lactate measurements, and microscopic examinations were performed to investigate acute renal ischemia in rats. MR images (1H) and spectra (31P and 1H) were acquired on a 2.0-T superconducting small-bore magnet by using implanted coils. Occlusion of the renal artery induced a significant decrease in signal intensity of the renal parenchyma on T2-weighted images, which was most obvious in the outer medulla (-50 +/- 15%, n = 8, P less than 0.001) and was the result of venous congestion, as verified histologically, 31P spectroscopy demonstrated a drop in pH from 7.3 +/- 0.2 to 6.6 +/- 0.2 (n = 18, P less than 0.001), characterized by a time constant (Tc) in the same range as that of the depletion of ATP (2.3 +/- 1.3 min versus 1.9 +/- 1.2 min, n = 10, P = ns). By means of 1H spectroscopy, a lactate peak was detected within 1.5 to 4 min of ischemia, still increasing in intensity after 1 h of ischemia. The Tc of the lactate buildup (15.9 +/- 7.5 min, n = 8) was significantly longer than that of the drop in pH (P less than 0.005). The chemically measured intrarenal concentration of lactate was 1.3 +/- 0.5 mumol/g in control kidneys and 8.7 +/- 3.2 mumol/g (P less than 0.005) in kidneys made ischemic for 1 h. The present study demonstrated important features of acute renal ischemia: (a) acute ischemia induces venous congestion in the medulla; (b) accumulation of lactate is not the main cause of the intracellular acidification observed during ischemia.

Animals↗
PubMed1989

1H spectroscopic imaging at high spatial resolution.

Spectroscopic imaging and single voxel localization are compared with respect to the signal to noise ratio per unit time and unit volume. It is shown experimentally that, when using the same experiment time and the same voxel size, both methods give similar results. In order to investigate the localization limits of spectroscopic imaging, lipid distribution in a single large cell was measured and correlated with gradient echo microscopy.

Animals↗
PubMedDate not supplied

Short echo time proton MR spectroscopic imaging.

Proton spectroscopic imaging at short TEs (20-30 ms) in human brain requires volume preselection inside the brain to suppress overwhelming lipid and water signals from surrounding tissue. In this article we discuss limitations of conventional volume preselection using stimulated echoes that lead to spectral contamination from surrounding tissue. Improved volume preselection was obtained by adding a complete outer volume suppression (presaturation). The performance of the method is illustrated on normal volunteers and on clinical cases with brain tumors and multiple sclerosis (MS) plaques. In normal human brain, we detected resonances with short T2 values and complex J-coupling, including rather broad methyl/methylene resonances in the chemical shift range between 0 and 2 ppm. Spectroscopic images obtained on patients with intracranial tumors and on one patient with several MS plaques demonstrate the possibility of detecting regional distributions of increased methyl/methylene resonances between 0 and 2 ppm in brain lesions.

Adult↗