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M Forsting

Publications and source records attributed to M Forsting.

At least 91 records · Page 5Linked to original sources
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

Early carotid endarterectomy after non-disabling ischaemic stroke: adequate therapeutical option in selected patients.

OBJECTIVE: To evaluate neurological outcome and long-term results of early carotid endarterectomy (CEA) after non-disabling stroke. MATERIALS: Retrospective study between 1980 and 1995 of 56 patients undergoing CEA within 4 weeks of a transient (n = 15) or a permanent non-disabling (n = 41) ischaemic stroke. METHODS: Analyses of preoperative cerebral CT imaging, neurological outcome (mod. Rankin-scale) and long-term results (life-table analyses according to Kaplan-Meier). RESULTS: Incidence of early CEA increased from 1.7% (27 out of 1636) in the period 1980-1993 to 7.8% (29 out of 374) between 1994 and 1995. CEA was indicated after a neurological plateau phase was established (median interval 14 days). Fifty-seven per cent of the CEA patients had a minor ischaemic infarction (area < 2 cm), 18% showed a large territorial ischaemic infarction (area 2-5 cm) in cerebral CT imaging. Two patients deteriorated postoperatively (minor stroke rate 4%) but no major stroke or death occurred. Life-table probability of stroke-free survival (mean follow-up 42.7 months) was 94%, 90% and 84%, respectively, after 1, 2 and 5 years. Kaplan-Meier survival rates were 96%, 91% and 86% after 1, 2 and 5 years. CONCLUSIONS: Early CEA after non-disabling stroke is a safe procedure in selected patients.

Adult↗
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

MR enhancement of the internal auditory canal induced by tissue implant after resection of acoustic neurinoma.

PURPOSE: We studied intrameatal changes in MR enhancement induced by free-tissue implant over time after surgery for acoustic neurinoma. METHODS: Twenty-one patients were examined by MR imaging after suboccipital resection of an acoustic neurinoma. Precontrast and postcontrast MR images were obtained within 3 days after surgery (early MR images), then 6 weeks (intermediate MR images) and 6 months (late MR images) after surgery. A muscle graft as a free-tissue implant was used within the internal auditory canal in 18 of the 21 patients to seal pneumatic cells of the petrosal bone inadvertently opened and to prevent leakage of cerebrospinal fluid. RESULTS: On the early MR images, only minimal leptomeningeal or perineural enhancement was seen in 16 patients. There was no sign of residual tumor; however, enhancement increased and changed from linear to nodular on the intermediate MR images in 16 of the 18 cases in which a muscle graft had been used during surgery, mimicking a small intrameatal tumor. This nodular enhancement was still visible on the late MR images in 13 of the 16 cases. CONCLUSION: Nodular MR enhancement within the internal auditory canal a few weeks to months after surgery for acoustic neurinoma may be induced by packing material and should be considered when interpreting postoperative MR images.

Adult↗
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

Cohort study of multiple brain lesions in sport divers: role of a patent foramen ovale.

OBJECTIVE: To investigate the role of a patient foramen ovale in the pathogenesis of multiple brain lesions acquired by sport divers in the absence of reported decompression symptoms. DESIGN: Prospective double blind cohort study. SETTING: Diving clubs around Heidelberg and departments of neuroradiology and neurology. SUBJECTS: 87 sport divers with a minimum of 160 scuba dives (dives with self contained underwater breathing apparatus). MAIN OUTCOME MEASURES: Presence of multiple brain lesions visualised by cranial magnetic resonance imaging and presence and size of patent foramen ovale as documented by echocontrast transcranial Doppler ultrasonography. RESULTS: 25 subjects were found to have a right-to-left shunt, 13 with a patent foramen ovale of high haemodynamic relevance. A total of 41 brain lesions were detected in 11 divers. There were seven brain lesions in seven divers without a right-to-left shunt and 34 lesions in four divers with a right-to-left shunt. Multiple brain lesions occurred exclusively in three divers with a large patent foramen ovale (P = 0.004). CONCLUSIONS: Multiple brain lesions in sport divers were associated with presence of a large patent foramen ovale. This association suggests paradoxical gas embolism as the pathological mechanism. A patent foramen ovale of high haemodynamic relevance seems to be an important risk factor for developing multiple brain lesions in sport divers.

Brain Injuries↗
PubMed1997

Image guided excision of a ruptured feeding artery "pedicle aneurysm" associated with an arteriovenous malformation in a child: case report.

Excision of a ruptured aneurysm located at a lenticulostriate feeding artery associated with an arteriovenous malformation was performed using image guided neuronavigation in an 8-year-old child. The management of this lesion, which is rare in childhood, demonstrates the potential of combining frameless stereotaxy for precise target approach with conventional open microneurosurgery to minimize morbidity. Because of the unavoidable shifting of the brain that occurs during surgery, a catheter pointing towards the dome of the aneurysm was placed using image guidance prior to insertion of spatulae.

Aneurysm, Ruptured↗
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

Progressive cerebellar ataxia, proximal neurogenic weakness and ocular motor disturbances: hexosaminidase A deficiency with late clinical onset in four siblings.

Tay-Sachs disease is a genetically determined neurodegenerative disorder, resulting from mutations of the hexosaminidase (Hex) A gene coding for the alpha-subunit of beta-D-N-acetyl-hexosaminidase. Clinically, there is severe encephalomyelopathy leading to death within the first few years of life. Hex A activity is usually absent in tissue and body fluids of these patients. Juvenile and adult Hex A deficiencies are less severe but rare variants with some residual Hex A activity. All these variants are most prevalent among Ashkenazi Jews. We describe a non-Jewish family in which four adult brothers and sisters had markedly reduced Hex A activities and onset of symptoms in the second decade of life. The phenotypical expression was remarkably homogeneous, consisting in a combination of slowly progressive motor neuron disease, ataxia and ocular motor disturbances. None of the patients were demented at this stage of their illness. Magnetic resonance studies showed severe cerebellar atrophy, but were otherwise normal. Hex A deficiency was established by biochemical measurements in the serum and skin fibroblasts using the fluorogenic substrates 4-MUG and 4-MUGS as well as by gel electrophoresis. Molecular genetic studies revealed that the patients are compound heterozygotes for the 'adult' mutation Gly269 --> Ser and the 'infantile' 4-base insertion in exon 11 of the Hex A gene.

Adult↗
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

Infection-associated cervical artery dissection. Three cases.

BACKGROUND: The pathogenesis of cervical artery dissection remains unknown. Infection-mediated damage of the arterial wall may be one contributing mechanism. We present three male patients with respiratory infection prior to cervical artery dissection. CASE DESCRIPTIONS: Case 1: During an upper respiratory tract infection, a 49-year-old patient developed bilateral carotid and vertebral artery dissection with complete vessel restitution. Case 2: Within 3 years, a 40-year-old patient experienced two episodes of bilateral internal carotid artery dissection, both preceded by febrile upper respiratory tract infection. Case 3: A 52-year-old patient developed right-sided and, 2 years later, left-sided internal carotid artery dissection, each following upper respiratory tract infection. CONCLUSIONS: Infection may be a trigger factor in the pathogenesis of cervical artery dissection.

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↗