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S Heiland

Publications and source records attributed to S Heiland.

At least 55 records · Page 3Linked to original sources
PubMed1999

[Magnetic resonance tomography in stroke--its methodological bases and clinical use].

Stroke is the third leading cause of death. Until recently, no diagnostic technique was available that could reliably depict ischemic tissue within a therapeutically promising time window. Since the beginning of this decade, a fundamental change has taken place: Perfusion- and diffusion-MRI have shown to be capable of depicting the ischemic injury immediately after vessel occlusion. While perfusion MRI is sensitive to abnormalities in cerebral capillary blood flow (micro-circulation), diffusion MRI indicates tissue damage on a cellular level. Combining perfusion- and diffusion-MRI with standard MR technique (T2-weighted sequences, MR angiography) results in an MR protocol that is complementary and gives insight into both structural and functional parameters.

Artifacts↗
PubMed1999

[The effect of the stimulus frequency, stimulus amplitude and blood pressure on the signal response in functional MRT: studies on an animal model].

PURPOSE: To examine the influence of frequency and amplitude of a stimulus and the effect of blood pressure on signal intensity changes in functional MRI. METHODS: Somatosensory stimulation of five (normotonic/hypotonic) anesthetized rats was performed with different stimulus frequencies and amplitudes. Measurements were performed with a 2.4 Tesla experimental scanner using a gradient-echo (GE) echo-planar imaging (EPI) sequence. RESULTS: The highest signal change was found at a frequency of 3 Hz and a stimulation amplitude of ten times the threshold value. A decrease of blood pressure to half the normotonic value gave rise to a decrease of the neuronal response of about 17%. CONCLUSION: Optimization of the stimulation frequency and stimulation amplitude maximizes signal changes in functional MRI of the somatosensory cortex. Even with a standardized paradigm, variations in measured neuronal activity may occur when blood pressure changes cannot be compensated by autoregulation.

Animals↗
PubMed1998

[Neuroradiologic diagnosis in acute arterial cerebral infarct. Current status of new methods].

At least three questions has to be answered by imaging methods, when new therapies in acute ischemic stroke should be used: 1. Is there a cerebral ischemia? 2. What is the size of the irreversible damaged tissue and what is the size of the safeable tissue? Is there still a vessel occlusion? New MRI-techniques including MR-angiography, diffusion-weighted imaging and perfusion-MRI, have the potential to describe the status of the brain in detail and to answer these questions. However, the value of these techniques for therapeutical decisions (thrombolysis) is unclear and has to be evaluated in clinical studies. Therefore in clinical routine these decisions should still be based on informations from CT and perhaps CT-angiography.

Brain↗
PubMed1998

[Can superparamagnetic contrast media improve MRI-tomographic images of experimental gliomas?].

PURPOSE: To investigate whether the margins of microscopic tumors can be delineated better with monocrystalline iron oxide nanoparticles (MION), a superparamagnetic contrast medium, than with Gd-DTPA by magnetic resonance imaging (MRI). METHODS: MRI and histological examinations were conducted in 28 Wistar rats with sterotactically implanted gliomas (C6 gliomas). Of the 28 animals, 14 were examined after intravenous administration of MION [nine animals received 179 mmol Fe/kg body weight (dose 1), and five, 893 mmol Fe/kg (dose 2)]. The other 14 animals were examined first after i.v. administration of Gd-DTPA (0.2 mmol/kg) and then after i.v. administration of MION. The extent of the tumors as seen on MRI and at histological study were compared. RESULTS: Iron particles were identified microscopically in tumor cells and in the tumoral interstitium. After administration of MION at dose 1, the contrast-enhanced area of tumor was 1.55-fold greater than the extent of tumor identified by histological study, at dose 2,2.15-fold. Compared with Gd-DTPA the area of contrast enhancement was greater by a factor of 1.38 with MION administration at dose 1 and by a factor of 1.91 at dose 2. CONCLUSION: MION provides intra- and extracellular contrast enhancement. The area of the contrast-enhanced tumor is dose-dependently greater with MION than with Gd-DTPA and also greater than the extent of tumor seen at histological study.

Animals↗
PubMed1998

Comparison of echo-planar sequences for perfusion-weighted MRI: which is best?

We compared gradient-echo (GRE), spin-echo (SE) and stimulated-echo (STE) echo-planar imaging sequences for perfusion-weighted imaging at different field strengths. Focal cerebral ischaemia was induced by endovascular occlusion of the middle cerebral artery in eight rats. MR was performed at 4.7 T or 2.35 T. With each sequence, we acquired data sets before, during and after bolus injection of Gd-DTPA with a time resolution of 1.2 s per image. The perfusion-weighted images were assessed with regard to image quality, artefacts, signal-to-noise ratio (SNR), and signal-at-tenuation-to-noise ratio (delta SNR) of the non-ischaemic tissue. Visual assessment showed GRE-EPI images acquired at 4.7 T to suffer from distortion due to susceptibility artefacts. Artefacts were less marked with the SE and STE series. The GRE-EPI sequence gave the highest SNR and delta SNR. At 2.35 T, the SNR of the STE sequences was less than 3 and therefore did not allow construction of reliable signal-time curves. SE-EPI was best suited for perfusion-weighted imaging at high field strength thanks to its minimal distortion artefacts and high SNR. Using lower field strengths (2.35 T and less), susceptibility artefacts are reduced; GRE-EPI sequences are then best suited, because they have the highest SNR and T2* sensitivity.

Animals↗
PubMed1998

[Magnetization transfer contrast: experimental sequence optimization for study of the cerebral substantia alba].

PURPOSE: A new application for magnetization transfer (MT) MR imaging is the investigation of cerebral white matter. For that a pure MT effect is desirable. Our purpose was the optimization and testing of an MT sequence for investigations of cerebral white matter. MATERIAL AND METHODS: Experimental investigations were performed in phantom material and in 5 wistar rats using various frequency offsets (FO) (200 Hz-30,000 Hz). Relative signal suppression (rSS) for the phantom material and for callosal white matter of the rat was calculated. The optimized sequence was tested in 25 healthy volunteers. RESULTS: A relatively pure MT effect was achieved with FO > 4000 Hz. rSS for cerebral white matter structures was generally higher than rSS für cerebral gray matter structures. rSS for cerebral white matter structures ranged from 45-50%. CONCLUSION: We present a fast MT sequence with high rSS for cerebral white matter and a relatively pure MT effect. Owing to the high rSS-values we expect that this sequence improves differentiation of cerebral white matter lesions. Because of the confusing variety of MT sequence currently described in the literature we believe that standard parameters should be defined to make published results comparable.

Animals↗
PubMed1998

Are iodinated contrast agents detrimental in acute cerebral ischemia? An experimental study in rats.

PURPOSE: To study the effects of iothalamate sodium and two dosages of iopromide in acute cerebral ischemia on infarction volume, neurologic performance, and mortality in a rat model of middle cerebral artery occlusion. MATERIALS AND METHODS: Sixty-four rats underwent endovascular occlusion of the middle cerebral artery. Four hours later, 16 animals received iothalamate sodium (588 mg iodine per kilogram); 16, iopromide as a single bolus (518 mg iodine per kilogram); and 16, iopromide as a double bolus (1,036 mg iodine per kilogram). Sixteen animals received equivolumetric saline (control group). Neurologic score and body weight were recorded every 8 hours. Twenty-four hours after occlusion, all animals were killed; brains were stained to assess the infarction size. RESULTS: Single and double doses of iopromide did not affect infarction volume or neurologic performance. Iothalamate caused an increase in infarction volume and worsening of the neurologic score (p < .05). Mortality rate was 25% in the iothalamate group, 12% in the control group, and 6% in the iopromide groups. CONCLUSION: Bolus injection of the nonionic iopromide does not statistically significantly affect infarction volume or cerebral ischemia symptoms. Nonionic rather than ionic contrast agents should be preferred during acute cerebral ischemia.

Acute Disease↗
PubMed1998

[Follow-up monitoring with magnetic resonance tomography after decompressive trephining in experimental "malignant" hemispheric infarct].

Acute ischemia in the complete territory of the carotid or the middle cerebral artery may lead to cerebral edema with raised intracranial pressure and progression to coma and death. Although clinical data suggest benefit for patients undergoing decompressive surgery for massive space occupying hemispheric stroke, little data about the effects of this procedure on morbidity and outcome is available. The experimental data support an early surgical approach. For early and probably most effective treatment of severe, space-occupying cerebral ischemia, the "malignant" character of the brain edema has to be recognized early after onset of vessel occlusion. Hereby magnetic resonance imaging (MRI) may allow to determine the clinical significance of brain edema early after onset, simultaneously allowing to monitor the evolution of ischemia. We performed serial SE-MRI in rats with acute hemispheric infarctions treated by decompressive craniectomy. Focal cerebral ischemia was induced in 36 rats using an endovascular occlusion technique. Decompressive craniectomy was performed 4 and 24 hours after vessel occlusion in groups of 12 animals each. Twelve animals were not treated by decompressive craniectomy (control group). Four, 24, 48, 72 and 168 hours after MCAO all animals were examined with conventional T1- and T2-weighted SE-MRI. Shift of the midline structures and compression of the ventricles were scored. Changes in weight and neurological performance were measured daily. The infarction volume was calculated by triphenyltetrazolium chloride staining 168 hours after MCAO. While mortality in the untreated group was 33.3%, none of the animals treated by a decompressive craniectomy died (mortality 0%). Neurological behaviour, weight loss and infarction volume were significantly better in the animals treated by early decompressive craniectomy (p < 0.05). Four hours after MCAO all untreated animals showed a massive shift of the midline structures and a massive compression of the ventricles; only 7 of 12 animals treated early by craniectomy showed mild mass effects. Correlation of the histological brain damage with T2-weighted MRI 4 hours after MCAO was poor (r = 0.41); later than 24 hours there was a good correlation (r > 0.7). Our results suggest that decompressive craniectomy in malignant cerebral ischemia reduces mortality and significantly improves outcome. If performed early after vessel occlusion, it also significantly reduces infarction size. In the acute phase of hemispheric infarction conventional SE-MRI is not sensitive in estimation of infarction size. Later than 24 hours, conventinal SE-MRI proved to be useful in monitoring brain edema and infarction size in this rat model of malignant hemispheric stroke.

Animals↗
PubMed1997

Properties and heterologous expression of the glucose transporter GHT1 from Schizosaccharomyces pombe.

Genomic DNA of the Schizosaccharomyces pombe glucose transporter, GHT1, was obtained by complementation of the glucose transport deficient Sz. pombe strain YGS-5. Here we describe the GHT1 gene that encodes a protein of 565 amino acids with a corresponding molecular mass of 62.5 kDa. This eukaryotic glucose transporter contains 12 putative transmembrane segments and is homologous to the HXT multigene family of S. cerevisiae with several amino acid motifs of this sugar transporter family. It is also homologous to other sugar carriers from human, mouse and Escherichia coli. The function of the Ght1 protein as a glucose transporter was proved both by homologous and heterologous expression in the Sz. pombe mutant YGS-5 and in the S. cerevisiae hxt mutant RE700A, respectively. Both transformed yeast strains transported D-glucose with substrate specificity similar to that in Sz. pombe wild-type cells. Moreover, the cells of the two transformed yeast strains accumulated 2-deoxy-D-glucose, a non-metabolizable D-glucose analogue, with an efficiency similar to Sz. pombe wild-type cells. The ability of the S. cerevisiae mutant RE700A to accumulate 2DG in an delta mu H+ dependent manner after transformation with GHT1 provides evidence that the Sz. pombe transporter catalyses an energy-dependent uptake of glucose.

Amino Acid Sequence↗
PubMed1997

Functional neuroimaging in the assessment of cerebral ischaemia.

Cerebral infarct causes over 170, 000 deaths per year in the United States. Recent developments in neuroimaging are providing an insight into focal cerebral ischaemia, including its pathophysiology and the area of brain at risk. Perfusion-weighted magnetic resonance (MR) allows evaluation of the blood supply to the ischaemic area, and diffusion-weighted MR permits assessment of tissue damage. Although both functional imaging techniques require some refinement, it is likely that they will soon become part of the normal clinical routine and allow accurate characterisation of pathology. It is expected that this may eventually lead to the development of new treatments.

Animals↗
PubMed1997

Dynamic contrast-enhanced T2*-weighted MRI in patients with cerebrovascular disease.

Our purpose was to investigate the potential of dynamic susceptibility contrast-enhanced MRI in assessing regional haemodynamics in patients with cerebrovascular disease. T2*-weighted FLASH sequences were performed on a control group of 10 healthy subjects, 13 patients with unilateral stenosis or occlusion of the internal carotid artery and 6 patients with acute onset of neurological symptoms, the observed signal intensities being converted into concentration-time curves. A gamma-variate function was fitted to the measured concentration-time curves to eliminate effects of tracer recirculation. In each patient the two cerebral hemispheres were compared and the difference between the mean transit times and the percental change of the regional cerebral blood volume, calculated for each side. Patients with haemodynamically significant unilateral carotid obstruction can be divided into two subgroups: those with good and those with poor collateral supply. Patients with good collateral supply had a slight but not statistically significant increase in mean transit time and cerebral blood volume on the diseased side, whereas those with poor collaterals had a significant increase compared with the control group. In patients with acute onset of neurological symptoms perfusion maps clearly demonstrated the disturbed perfusion at a time when T2-weighted images were still normal. Perfusion imaging is a reliable and noninvasive method of assessing changes in cerebral perfusion in patients with unilateral carotid stenosis. This MR technique permits monitoring of haemodynamic changes during therapy and thus may become an alternative to SPECT and PET scanning. In patients with acute occlusion of a cerebral artery, perfusion imaging reveals the entire, perfusion deficit before conventional MRI and thus allows early intervention.

Acute Disease↗
PubMed1997

Accuracy of gamma-variate fits to concentration-time curves from dynamic susceptibility-contrast enhanced MRI: influence of time resolution, maximal signal drop and signal-to-noise.

Concentration-time curves derived from dynamic susceptibility-contrast enhanced magnetic resonance imaging are widely used to calculate cerebrovascular parameters. To exclude effects of recirculation, a non-linear regression method is used to fit a gamma-variate function to the concentration-time course. In previous studies the errors arising from the fitting procedure have not been quantified. In a computer simulation we investigate the uncertainties of parameters calculated from the fitted gamma-variate function, exploring the dependencies on signal-to-noise (SNR), time resolution (delta t), and maximal signal drop (MSD). Our study was performed to give a framework on how to design MR-sequences and choose contrast media and their application in order to yield concentration-time curves which allow a reliable performance of the gamma-variate fitting procedure. We recorded 396 concentration-time curves from regions of interest of 40 patients. The gamma-variate fitting procedure was applied to these curves resulting in 396 parameter sets. Ideal concentration-time curves as gamma-variate functions were generated from these sets with a given delta t, MSD, and SNR. Recirculation effect was simulated. Then the gamma-variate fitting was performed again. From ideal and simulated gamma-variate function the area and the normalized first moment were calculated. The uncertainties of the values calculated from the simulated curve relating to the values of the original one were determined. Increase of SNR decreases the involved errors. With SNR values of 100 and more there is only minor influence of delta t and MSD and the fitted curve approximates the original data very well. Smaller values of SNR lead to a stronger influence of delta t and MSD and a higher number of fitting failures. With increasing delta t the uncertainties also increase. Intermediate values of MSD (30% to 70%) yield the smallest errors while increasing or decreasing MSD yields an increase of uncertainty. To achieve low uncertainties in the calculation of cerebrovascular parameters from gamma-variate fits, delta t of the imaging sequence and MSD must be considered. This is more important the lower SNR is. The shown dependencies should be taken into account when choosing MR sequence parameters and application of contrast media.

Artifacts↗
PubMed1997

[Diffusion-weighted magnetic resonance tomography: a highly promising MR technic for the early recognition of cerebral ischemia].

PURPOSE: The aim of this study was to show the temporal and spatial evolution of ischaemia over time using diffusion-weighted magnetic resonance imaging, and to correlate the extent of ischaemia with the postmortem infarct size after 24 hours. MATERIAL AND METHODS: In 8 rats focal cerebral ischaemia was induced by intravascular occlusion of the middle cerebral artery. The evolution of the ischaemic lesion was examined over 180 min with an experimental MR scanner. RESULTS: Diffusion-weighted magnetic resonance imaging displayed a hyperintense area in the lateral part of the putamen as early as 5 min after the onset of ischaemia. The mean volume of ischaemia on diffusion mapping after 5 min was 62.5 +/- 12.9 microliters and increased to 224.4 +/- 48.5 microliters after 180 min. This correlated well with the corrected infarct volume at postmortem examination (194.0 +/- 23.1 microliters, r = 0.72, p < 0.05) using the TTC staining. CONCLUSION: Diffusion-weighted magnetic resonance imaging is a reliable tool in the early diagnosis of cerebral ischaemia. Due to the non-invasiveness this method can be used for therapy monitoring and might help to develop new therapeutic strategies.

Animals↗
PubMed1997

[Diffusion-weighted MR tomography in focal cerebral ischemia: possibilities offered by a 1.0 Tesla clinical device].

PURPOSE: To develop and to implement a fast, highly diffusion-weighted MR-sequence on a conventional 1 T MR scanner and to examine this sequence as to its capability of characterising tissue damage due to focal cerebral ischaemia. METHODS: Within a CE-FAST-sequence diffusion gradients were inserted in all gradient directions. By phantom measurements the maximal diffusion weighting was determined for different T1 and T2 values and flip angles. The optimised sequence was used for monitoring the diffusion of focal cerebral ischaemia in 14 rats following endovascular occlusion of the middle cerebral artery. RESULTS: The ischaemic lesion could be easily visualised as a bright area in the images with high diffusion weighting. The mean relative decrease of the diffusion coefficient in the ischaemic brain parenchyma was 29%. The diffusion coefficient, decreased significantly with increasing occlusion time. CONCLUSION: Our study suggests that the installed sequence is capable of producing highly diffusion weighted images without requiring a special gradient system. The sequence is potentially useful for monitoring cerebral ischaemia on the basis of calculating the change of the diffusion coefficient.

Animals↗
PubMed1997

[Studies on contrast medium dosage in perfusion-weighted MR imaging].

PURPOSE: In this study we investigated, whether increasing the dosage of a paramagnetic contrast agent results in a stronger signal decrease in T2*-weighted perfusion sequences and therefore more meaningful parameter maps. MATERIAL AND METHODS: In a prospective study bolus injection of gadolinium-DTPA was performed at dosages of 0.1, 0.2, and 0.3 mmol/kg body weight (BW) in 10 patients each. Before, during and after bolus injection 40 T2*-weighted images of a reference brain slice were acquired within 65.6 seconds on a 1.0 T clinical scanner and perfusion parameters were calculated. RESULTS: Due to the limited signal decrease during bolus passage and the resulting low signal-difference-to-noise ratio (delta S/N) no reliable differentiation of gray and white matter was possible at a contrast agent dosage of 0.1 mmol/kg BW. Only at higher dosages, both, signal decrease and delta S/N were strong enough to allow differentiation of gray and white matter and to yield reliable parameter maps. CONCLUSION: For meaningful MR perfusion imaging at 1.0 T and with the given sequence a contrast agent dosage of at least 0.2 mmol/kg BW is necessary, if a 0.5-molar contrast agent is used.

Adult↗
PubMed1997

Bolus injection of MR contrast agents: hemodynamic effects evaluated by intracerebral laser Doppler flowmetry in rats.

PURPOSE: To determine the effects on arterial blood pressure and cerebral blood flow of intravenous bolus injection of three MR contrast agents: gadopentetate dimeglumine, polylysine-Gd-DTPA, and superparamagnetic iron particles (SPIO). METHODS: A single-fiber laser Doppler flowmetry probe was placed intracerebrally in 56 anesthetized rats. Cerebral blood flow and mean arterial blood pressure were measured before (baseline), during, and up to 30 minutes after intravenous bolus administration of the three contrast agents: 0.1 mmol/kg and 0.3 mmol/kg gadopentetate dimeglumine (n = 18 per group), 0.3 mmol/kg polylysine-Gd-DTPA (n = 10), and 0.03 mmol/kg SPIO (n = 10). RESULTS: Neither the higher nor lower dose of gadopentetate dimeglumine had any statistically significant effect on cerebral blood flow, and there was no change in blood pressure during administration of either dose of gadopentetate dimeglumine. Administration of polylysine-Gd-DTPA caused a transient drop in blood pressure in two animals, marked in one (decrease to 21% of baseline values) and mild in the other (84% of baseline). After administration of SPIO, a significant decrease in blood pressure occurred in one animal (41% of baseline). Despite this decrease in mean arterial blood pressure, there were no statistically significant changes in cerebral blood flow after administration of polylysine-Gd-DTPA or SPIO. CONCLUSION: Our results suggest that bolus injection of these contrast agents at clinically relevant doses causes no significant alteration in cerebral blood flow. We conclude that gadopentetate dimeglumine is well suited for cerebral MR perfusion imaging without inherent influence on cerebral blood flow and that the same is probably true for polylysine-Gd-DTPA and SPIO.

Animals↗
PubMed1996

Decompressive craniectomy in a rat model of "malignant" cerebral hemispheric stroke: experimental support for an aggressive therapeutic approach.

Acute ischemia in the complete territory of the carotid artery may lead to massive cerebral edema with raised intracranial pressure and progression to coma and death due to uncal, cingulate, or tonsillar herniation. Although clinical data suggest that patients benefit from undergoing decompressive surgery for acute ischemia, little data about the effect of this procedure on experimental ischemia are available. In this article the authors present results of an experimental study on the effects of decompressive craniectomy performed at various time points after endovascular middle cerebral artery (MCA) occlusion in rats. Focal cerebral ischemia was induced in 68 rats using an endovascular occlusion technique focused on the MCA. Decompressive craniectomy was performed in 48 animals (in groups of 12 rats each) 4, 12, 24, or 36 hours after vessel occlusion. Twenty animals (control group) were not treated by decompressive craniectomy. The authors used the infarct volume and neurological performance at Day 7 as study endpoints. Although the mortality rate in the untreated group was 35%, none of the animals treated by decompressive craniectomy died (mortality 0%). Neurological behavior was significantly better in all animals treated by decompressive craniectomy, regardless of whether they were treated early or late. Neurological behavior and infarction size were significantly better in animals treated very early by decompressive craniectomy (4 hours) after endovascular MCA occlusion (p < 0.01); surgery performed at later time points did not significantly reduce infarction size. The results suggest that use of decompressive craniectomy in treating cerebral ischemia reduces mortality and significantly improves outcome. If performed early after vessel occlusion, it also significantly reduces infarction size. By performing decompressive craniectomy neurosurgeons will play a major role in the management of stroke patients.

Animals↗