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ABSTRACT: This study was conducted to determine the risk factors and the clinical impact of intraprocedural aneurysm rupture (IAR) and periprocedural ischemia in the treatment of symptomatic and asymptomatic unruptured intracranial aneurysms (UIAs). A single-center retrospective data analysis of 563 UIAs treated between 2000 and 2010 was conducted. Treatment assignment was made on the basis of individual aneurysmal criteria in an interdisciplinary neurovascular conference with attending neurosurgeons, neuroradiologists and neurologists. In 363 microsurgical and 200 endovascular procedures, the permanent morbidity rate was 4.9 and 6 %. The overall mortality rate was 0.7 %-no procedure-related death occurred in microsurgery, and four patients had fatal outcomes after endovascular treatment. IAR occurred in 34 (9.4 %) microsurgical and 8 (4 %) endovascular procedures (p = 0.03). Risk factors for IAR were age, aneurysm diameter, symptomatic aneurysms, hypertension and smoking in microsurgery. IAR was associated with significantly worse outcome at discharge after microsurgical and at discharge and follow-up after endovascular procedures and was followed by fatal outcome in four endovascular cases. Periprocedural ischemia (12.1 vs. 9 %) resulted in significantly worse outcome in both groups. Risk factors for periprocedural ischemia were IAR during microsurgery, aneurysm diameter, symptomatic aneurysms and smoking in either group. Treatment of UIAs can be conducted with an equivalent low rate of permanent morbidity for clipping and coiling-treatment of symptomatic aneurysms elevates the procedural risk. IAR was less frequent during coiling, but was associated with relevant mortality. IAR and periprocedural ischemia represent significant treatment-associated risks, which should be taken into account in interdisciplinary treatment planning and patient counseling.
Journal of Neurology 12/2012; · 3.47 Impact Factor
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ABSTRACT: The number of elderly patients with aneurysmal subarachnoid hemorrhage (SAH) is increasing with the aging of the population. However, management recommendations based on long-term outcome data and analyses of prognostic factors are scarce. Our study focused exclusively on elderly patients aged ≥60 years at the onset of SAH. Patients were selected from an in-house database and compared in cohorts of age 60-69, 70-79, and ≥80, regarding pre-existing medical conditions, treatment, clinical course including complications, and outcome. A multivariate analysis was conducted to identify prognostic factors for death and disability. A total of 256 patients (138 aged 60-69, 93 aged 70-79, 25 aged ≥80) with putative aneurysmal SAH who had been admitted to our hospital between January 1, 1996 and June 30, 2007 were extracted. The median follow-up of our total cohort was 35.5 months (range <1-154 months). Endovascular or conservative aneurysm treatment was applied more often with increasing age (p < 0.006). The 1-year survival rate was 78, 65, and 38 % in the three age groups, respectively (p = 0.0002); most of the patients died from the initial hemorrhage or from medical complications. Patients aged <70 with an initial World Federation of Neurosurgical Societies (WFNS) score of I-III showed the best clinical recovery. WFNS score, age, and clipping/coiling were extracted as prognostic factors from the Cox model. Elderly patients who get admitted with a good WFNS score (I-III) seem to benefit from aggressive treatment whereas caution seems to be warranted particularly in patients ≥70 years of age who get admitted in a WFNS score of IV and V because of their limited short- and long-term prognosis.
Journal of Neurology 12/2012; · 3.47 Impact Factor
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ABSTRACT: Multimodal recanalization therapy in patients with acute basilar artery occlusion provides high recanalization rates. A substantial subset of treated patients survives with only minor or moderate functional handicap. However, long-term functional outcome and quality of life in these patients have rarely been systematically analyzed.
In this monocentric retrospective study, we analyzed mortality, long-term functional outcome (modified Rankin Scale), and quality of life (36-Item Short-Form Health Survey questionnaire) in all consecutive patients who had been treated for acute basilar artery occlusion in our institution between December 2002 and December 2009.
Ninety-one patients (57 male; median age, 65 years; range, 20-89 years) were treated by multimodal recanalization therapy. This included intravenous thrombolysis (n=32) with consecutive on-demand intra-arterial therapy (n=23) or intra-arterial therapy alone (n=59). The overall recanalization rate was 89%. After a median observation time of 4.2 years (range, 0.5-7.4 years), the mortality rate was 59%. Among the 35 survivors, 26 patients (74%) had a good or moderate long-term functional outcome (modified Rankin Scale ≤3). Health-related quality of life was better than that of unselected patients with stroke. Backward stepwise logistic regression identified intravenous thrombolysis (P=0.002) and female sex (P=0.001) as predictors of favorable functional long-term outcome (modified Rankin Scale ≤3). Coma at admission (Glasgow Coma Scale ≤8) was associated with poor outcome (modified Rankin Scale ≥4; P=0.036).
Long-term survival is achieved in approximately 40% of patients with basilar artery occlusion treated with multimodal recanalization therapy. Approximately 75% of the survivors have a favorable functional long-term outcome with an acceptable quality of life.
Stroke 05/2012; 43(8):2130-5. · 5.73 Impact Factor
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ABSTRACT: Acute occlusions of the large intracranial arteries are relatively resistant to intravenous thrombolysis. Therefore, multimodal approaches combining intravenous thrombolysis with endovascular mechanical recanalization are increasingly being applied. In this setting, intravenous thrombolysis may facilitate subsequent mechanical thrombectomy. To test this hypothesis, we analyzed the influence of intravenous thrombolysis on net intervention time in subsequent endovascular mechanical recanalization.
In this retrospective single-center analysis, we compared net intervention time with and without preceding intravenous thrombolysis in patients treated by endovascular mechanical recanalization between 01/2003 and 06/2010. The net intervention time was defined as the interval between the onset of endovascular thrombus manipulation and successful vessel recanalization.
We identified 65 eligible patients, 35 of whom were treated by intravenous thrombolysis before mechanical therapy. Recanalization was achieved in 26 patients with (74%) and 23 patients without preceding intravenous thrombolysis (77%). In the case of successful recanalization, the net intervention time was significantly shorter in patients with preceding intravenous thrombolysis (24·8 ± 22·8 vs. 44·2 ± 40·5 min; P<0·05). This difference remained significant after restricting the analysis to the patients treated by the Penumbra Stroke System(©) (n=32). After three-months, patients with preceding intravenous thrombolysis were more likely to be functionally independent (modified Rankin Scale≤2) than those without (P<0·05).
Our findings suggest that preceding intravenous thrombolysis may reduce the intervention time in patients treated by endovascular mechanical recanalization. However, due to the retrospective design of our study, these findings have to be interpreted with caution and need confirmation in a larger patient population.
International Journal of Stroke 01/2012; 7(1):14-8. · 2.38 Impact Factor
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ABSTRACT: PURPOSE: Treatment of acute stroke by endovascular mechanical recanalisation (EMR) has shown promising results and continues to be further refined. We evaluated the impact of a temporary stent compared with our results using other mechanical devices. MATERIALS AND METHODS: We analysed clinical and radiological data of all patients who were treated by EMR after intravenous thrombolysis for acute carotid T- and middle-cerebral artery (M1) occlusions at our centre between 2007 and 2011. A comparison was performed between those patients in whom solely the stent-retriever was applied (group S) and those treated with other devices (group C). RESULTS: We identified 14 patients for group S and 16 patients for group C. Mean age, National Institute of Health Stroke Scale score, and time to treatment were 67.1 years and 16.5 and 4.0 h for group S and 61.1 years and 17.6 and 4.5 h for group C, respectively. Successful recanalisation (thrombolysis in cerebral infarction scores ≥IIb) was achieved in 93% of patients in group S and 56% of patients in group C (P < 0.05). Mean recanalisation times for M1 occlusions were 23 min (group S) and 29 min (group C) and for carotid-T occlusions were 39 min (group S) and 50 min (group C), and 45% of the patients in group S and 33% in group C had a favourable outcome (Modified Rankin Scale score ≤2). CONCLUSION: The findings suggest an improvement in recanalisation success by the application of a temporary stent compared with previously used devices. These results are to be confirmed by larger studies.
CardioVascular and Interventional Radiology 12/2011; · 2.09 Impact Factor
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ABSTRACT: In cerebral arterioveneous malformations (AVMs) detailed intraoperative identification of feeding arteries, nidal vessels and draining veins is crucial for surgery. Intraoperative imaging techniques like indocyanine green videoangiography (ICG-VAG) provide information about vessel architecture and patency, but do not allow time-dependent analysis of intravascular blood flow. Here we report on our first experiences with analytical indocyanine green videoangiography (aICG-VAG) using FLOW 800 software as a useful tool for assessing the time-dependent intraoperative blood flow during surgical removal of cerebral AVMs. Microsope-integrated colour-encoded aICG-VAG was used for the surgical treatment of a 38-year-old woman diagnosed with an incidental AVM, Spetzler Martin grade I, of the left frontal lobe and of a 26-year-old man suffering from seizures caused by a symptomatic AVM, Spetzler Martin grade III, of the right temporal lobe. Analytical ICG-VAG visualization was intraoperatively correlated with in situ micro-Doppler investigation, as well as preoperative and postoperative digital subtraction angiography (DSA). Analytical ICG-VAG is fast, easy to handle and integrates intuitively into surgical procedures. It allows colour-encoded visualization of blood flow distribution with high temporal and spatial resolution. Superficial major and minor feeding arteries can be clearly separated from the nidus and draining veins. Effects of stepwise vessel obliteration on velocity and direction of AVM blood flow can be objectified. High quality of visualization, however, is limited to the site of surgery. Colour-encoded aICG-VAG with FLOW 800 enables intraoperative real-time analysis of arterial and venous vessel architecture and might, therefore, increase efficacy and safety of neurovascular surgery in a selected subset of superficial AVMs.
Acta Neurochirurgica 09/2011; 153(11):2181-7. · 1.52 Impact Factor
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ABSTRACT: Postpartum cerebral angiopathy (PCA) is a cerebral vasoconstriction syndrome developing shortly after delivery, without signs of preceding eclampsia. The risk for recurrence of PCA is unknown. Here, we report on a closely monitored, uneventful pregnancy of a woman with a previous severe episode of PCA. In summary, this case report demonstrates that PCA does not necessarily recur in following pregnancies, even after previous severe episodes.
Case Reports in Neurology 01/2011; 3(3):252-7.
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ABSTRACT: Acute carotid-T occlusion generally responds poorly to thrombolysis. Endovascular mechanical thrombectomy (EMT) seems to be a promising alternative. However, there are few data on EMT in carotid-T occlusions.
We reviewed data of 14 consecutive patients with acute carotid-T occlusions treated with mechanical recanalisation devices. A clot separation/aspiration system was used in 11 patients; different other mechanical retriever devices were used in seven patients; and stents were used in four patients. Modified Rankin Scale scores at 90 days were recorded to assess functional outcome.
Six women and eight men were included in the study. Mean patient age was 59.2 years; median National Institute of Health Stroke Scale score on admission was 19; and mean time to treatment was 4.2 h. Successful recanalisation (Thrombolysis in Myocardial Infarction [TIMI] score II and III) was achieved in 11 patients (78.6%). Seven patients (50.0%) were treated with more than one device, leading to successful recanalisation in six of these patients (85.7%). Subarachnoid haemorrhage and large space-occupying bleedings occurred in one (7.1%) and three (21.4%) patients, respectively. At follow-up, three patients (21.4%) were functionally independent, and six (42.9%) had died.
When applying different mechanical devices, we found a high recanalisation rate. However, discrepancy between recanalisation and clinical outcome remained. More data are needed to assess the effect of the different methods on the prognoses of stroke patients.
CardioVascular and Interventional Radiology 10/2010; 34(2):280-6. · 2.09 Impact Factor
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ABSTRACT: Recent technical developments have led to an extension of perfusion computed tomography (PCT) scan range to cover nearly the entire brain and to reconstruct time resolved (4d) CT-angiography (CTA) datasets from the PCT data. The purpose of this study was to compare the results of simulated standard PCT and extended PCT with 4d-CTA.
Extended multimodal stroke CT (unenhanced cranial CT, CTA, and PCT) was acquired in 72 patients. PCT images with a scan coverage of 9.6 cm in the z-axis, simulated 2 cm PCT images at the level of the basal ganglia comparable to standard PCT, standard supra-aortic CTA, and 4d-CTA images were reconstructed. Two readers assessed the PCT image quality as well as pathologic findings in extended and simulated PCT, CTA, and 4d-CTA. The brain was divided into 4 axial segments. The independent samples t test was applied to test differences between data for significance.
In 75.0% of all patient exams, pathologic findings were observed in the PCT; these were located in 138 brain segments. In 24.1% of all 54 exams with pathologic PCT findings, the pathology would have been missed on standard PCT. The longer scan coverage resulted in a different final diagnosis in 34.7% of all exams. Quality of the PCT parameter maps was on average very good both for the supratentoric and the infratentoric brain areas (4.28 and 4.18, respectively, on a 5-point scale). In 90% of all exams with pathologic changes in the CTA, these abnormalities were also noted on 4d-CTA. In only 2.8% of all cases, the additional time resolution of the 4d-CTA provided additional information.
Extending the scan coverage of PCT from 2 cm to 9.6 cm led to an augmentation of clinically important information in the imaging of acute stroke.
Investigative radiology 07/2010; 45(7):363-9. · 4.85 Impact Factor
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Journal of Neurology 05/2010; 257(5):843-5. · 3.47 Impact Factor
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ABSTRACT: The cortical, cerebellar and brainstem BOLD-signal changes have been identified with fMRI in humans during mental imagery of walking. In this study the whole brain activation and deactivation pattern during real locomotion was investigated by [(18)F]-FDG-PET and compared to BOLD-signal changes during imagined locomotion in the same subjects using fMRI. Sixteen healthy subjects were scanned at locomotion and rest with [(18)F]-FDG-PET. In the locomotion paradigm subjects walked at constant velocity for 10 min. Then [(18)F]-FDG was injected intravenously while subjects continued walking for another 10 min. For comparison fMRI was performed in the same subjects during imagined walking. During real and imagined locomotion a basic locomotion network including activations in the frontal cortex, cerebellum, pontomesencephalic tegmentum, parahippocampal, fusiform and occipital gyri, and deactivations in the multisensory vestibular cortices (esp. superior temporal gyrus, inferior parietal lobule) was shown. As a difference, the primary motor and somatosensory cortices were activated during real locomotion as distinct to the supplementary motor cortex and basal ganglia during imagined locomotion. Activations of the brainstem locomotor centers were more prominent in imagined locomotion. In conclusion, basic activation and deactivation patterns of real locomotion correspond to that of imagined locomotion. The differences may be due to distinct patterns of locomotion tested. Contrary to constant velocity real locomotion (10 min) in [(18)F]-FDG-PET, mental imagery of locomotion over repeated 20-s periods includes gait initiation and velocity changes. Real steady-state locomotion seems to use a direct pathway via the primary motor cortex, whereas imagined modulatory locomotion an indirect pathway via a supplementary motor cortex and basal ganglia loop.
NeuroImage 05/2010; 50(4):1589-98. · 5.89 Impact Factor
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ABSTRACT: In acute basilar artery occlusion, intra-arterial thrombolysis or endovascular mechanical recanalization may result in higher recanalization rates than intravenous thrombolysis. However, many patients are admitted to community hospitals, where endovascular therapy is usually not readily available. We initiated a "drip, ship, and retrieve" cooperative treatment protocol in 2006, in which thrombolysis was initiated in the community hospital with simultaneous referral to our stroke center and the use of endovascular mechanical recanalization as required.
The outcome of all consecutive patients treated by this protocol between 2006 and June 2009 was compared with that of a similar population of referred patients who had received primary intra-arterial therapy with or without tirofiban bridging at our center between 2003 and 2005.
In both groups, 26 patients were identified. The rate of symptomatic intracranial hemorrhage was 12% in previous patients and 8% in those treated under the new protocol. Recanalization rates were similar: 92% in previous patients and 85% with the new protocol; 38% of these had recanalization after intravenous thrombolysis alone. Functional outcome was better among those treated with the new protocol, with more patients achieving a modified Rankin scale score < or = 2 (38% versus 12%; P=0.03) and < or = 3 (50% versus 23%; P=0.04).
"Drip, ship, and retrieve" seems to be feasible and safe in acute basilar artery occlusion. Patients appear to benefit from initiation of intravenous thrombolysis in the community hospital before transfer. Randomized controlled trials will have to confirm the expected benefit of subsequent on-demand mechanical recanalization on clinical outcome.
Stroke 02/2010; 41(4):722-6. · 5.73 Impact Factor
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ABSTRACT: In functional magnetic resonance imaging (fMRI) studies, brain areas that are commonly associated with the processing of olfactory stimuli, i.e., piriform cortex and orbitofrontal cortex, are often obscured by susceptibility-induced signal loss. The authors hypothesized that using a short echo time (TE) should not only reduce susceptibility artifacts but also increase the overall signal-to-noise ratio and allow to retrieve a blood oxygenation level-dependent (BOLD) signal in regions normally affected by these artifacts.
Two sequences with TEs of 60 and 32 ms were compared using a 1.5-T MRI scanner: in a standard motor paradigm, activations of the contralateral motor cortex were measured. In an olfactory stimulation paradigm, activations in piriform cortex were compared.
Reducing TE from 60 to 32 ms reduced the observed signal intensity changes in the motor paradigm by 51%. Concomitant to this, geometric distortions and signal dropout artifacts were decreased at orbitofrontal and temporomesial brain areas in both paradigms. Contrary to the authors' expectations, the signal intensity changes in the piriform cortex were also reduced by 48% in the olfactory paradigm. Moreover, piriform cortex activation was detected in less subjects at TE = 32 ms than at TE = 60 ms. Changes in cortical activation were significant in the right, but not in the left piriform cortex.
Although a shorter TE reduces signal dropouts due to susceptibility artifacts, this shorter TE is not sufficient to recover the BOLD signal from regions affected by susceptibility artifacts such as the piriform cortex. Thus, reducing the TE to the T2* of the investigated region is not an effective approach to improve the results of olfactory fMRI studies.
Clinical Neuroradiology 11/2009; 19(4):275-82.
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ABSTRACT: The aim of the study was to evaluate the sensitivity and reliability of assessing hemispheric language dominance with functional magnetic resonance imaging (fMRI) using a 'free reversed association task.'
Thirty-nine healthy subjects (13 dextrals, 13 sinistrals and 13 bimanuals) underwent two repeated fMRI sessions. In the active phases sets of words were presented via headphones, and an associated target item was named. During the baseline phases a standard answer was given after listening to unintelligible stimuli. Data were preprocessed with SPM, and then laterality indices (LI) and reliability coefficients (RC) were calculated.
Extensive frontal, temporal and parietal activations were found. Seventy-eight percent of the subjects showed left-hemispheric dominance, 5% showed right-hemispheric dominance, and 17% had bilateral language representations. The incidence of right-hemispheric language dominance was 4.3 times higher in a left-hander with a handedness quotient (HQ) of -90 than in a right-hander with a HQ of +90. The RC was 0.61 for combined ROIs (global network). Strong correlations were found between the two session LIs (r = 0.95 for the global network).
'Free reversed association' is a sensitive and reliable task for the determination of individual language lateralization. This suggests that the task may be used in a clinical setting.
European Radiology 09/2009; 20(3):683-95. · 3.22 Impact Factor
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ABSTRACT: Since the work of Penfield & Rasmussen it is well established that the human primary somatosensory cortex is organized somatotopically. However, the order of the representation of the face is still a matter of discussion, i.e., it is yet unclear whether the face is represented upside-down or vice versa in the somatosensory cortex.
In a functional magnetic resonance imaging study (n = 30), tactile stimuli to three different locations on each side of the face were applied using a pneumatic device. Locations of stimulation corresponded to the three branches of the trigeminal nerve (forehead, cheek, chin). To determine the representation of the face on primary and secondary somatosensory cortices, peak coordinates within these regions were analyzed subjectwise.
Contralateral activation of the primary somatosensory cortex following tactile stimulation of the face was found, whereas the secondary somatosensory cortices were activated bilaterally. However, differences between activation coordinates of different tactile stimuli applied to one side of the face were not statistically significant.
Tactile stimulation of the face leads to contralateral activation of primary and bilateral activation of secondary somatosensory cortices. Using the authors' methodological approach it was not possible to detect a somatotopic organization related to different facial areas.
Clinical Neuroradiology 06/2009; 19(2):135-44.
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ABSTRACT: Most functional imaging data are collected in single session experiments; little is known about the reproducibility or test-retest reliability of the activation patterns found in these experiments. In our study, 15 healthy volunteers performed four simple motor-paradigms ("Hand", "Foot", "Mouth" and "Tongue") for functional magnetic resonance imaging (fMRI) in 3 sessions on different days. Reproducibility of activations in four anatomical regions (pre- and postcentral gyri, paracentral lobule and the supplementary motor area) was measured in terms of voxels active in all sessions (common voxels) relative to voxels active in single sessions, giving reliability coefficients from 0 to 1. Two significance levels were used to identify active voxels. Reproducibility of activations was highest for foot and hand movements in the primary motorsensory areas; reliability coefficients were in the range of 0.62 to 0.78. Activations for mouth movements showed a very poor reproducibility. Application of the more stringent statistical threshold always led to a reduction of reproducible voxels. Reliability of fMRI data is not only a theoretical issue, but is of special practical importance in clinical settings such as integration of fMRI into neuronavigation for neurosurgical planning. Much care has to be taken if only single session data are available for interpretation.
Journal of Neurology 05/2006; 253(4):471-6. · 3.47 Impact Factor
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ABSTRACT: Lesion size is an important outcome parameter in experimental stroke research. However, most methods of measuring the infarct volume in rodents either require expensive equipment or render the brain tissue unusable for further analysis. We report on an inexpensive, tissue-saving method for quantifying the infarct volume in small rodents. After 3 h of middle cerebral artery occlusion (MCAO) and 24 h of reperfusion in male Wistar rats, the lesion was first identified using MRI with T2-weighted sequences. The infarct was then visualized in unfixed brain cryosections using microtubule associated protein 2 (MAP2)-immunohistochemistry and silver infarct staining. The lesion areas detected by all three different methods completely overlapped. The infarct volume was calculated for each method from the lesion area size on serial sections and the distance between them. Significant differences in lesion size were found between the individual animals (p = 0.000056), but not between different methods (p > 0.05). MAP2 immunohistochemistry is a convenient and valid method to measure stroke lesion volume; in addition 98% of the brain tissue is saved and available for use in further histological, immunohistochemical, and biochemical analysis.
Neurological Research 10/2002; 24(7):713-8. · 1.52 Impact Factor
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ABSTRACT: The thin hypoglossal nerve can be very difficult to distinguish on magnetic resonance (MR) images. The authors used a combination of sequences to increase the reliability of MR imaging in its demonstration of the 12th cranial nerve as well as to assess the course of the nerve, display its relationships to adjacent vessels, and provide landmarks for evaluating the nerve in daily practice.
The study group consisted of 34 volunteers (68 nerves) in whom a three-dimensional (3D) Fourier-transformation constructive interference in steady-state (CISS) sequence and a 3D T1-weighted contrast-enhanced magnetization-prepared rapid-acquisition gradient-echo (MPRAGE) sequence were applied. Two trained neuroradiologists collaboratively identified the hypoglossal trigone, preolivary sulcus, 12th cranial nerve, posterior inferior cerebellar artery, vertebral artery, 12th nerve root sleeve, and the hypoglossal canal on each side. The 3D CISS sequence successfully demonstrated the hypoglossal trigone (100% of images), 12th nerve root bundles (100% of images), and 12th nerve sleeves (88.2% of images). The canalicular segment was exhibited with the aid of plain 3D CISS sequences in 74% of images and by using contrast-enhanced 3D CISS sequences and contrast-enhanced MPRAGE sequences in 100% of images. The landmarks that proved useful to identify the cisternal segment of the 12th cranial nerve included the hypoglossal trigone, preolivary sulcus, and 12th nerve root sleeve. Neurovascular contact was identified in 61% of root bundles. The roots were distorted in 44% of these contacts.
The contrast-enhanced 3D CISS sequence consistently displayed the cisternal segment as well as the canalicular segments of the hypoglossal nerve and is, therefore, the best sequence to visualize the complete cranial course of this nerve. Landmarks such as the 12th nerve sleeves can assist in the identification of this nerve.
Journal of Neurosurgery 07/2002; 96(6):1113-22. · 2.96 Impact Factor
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Neurocase 09/2000; 6(5):415-421. · 1.11 Impact Factor
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ABSTRACT: Flow and diffusion of water in natural porous media, quartz sand, and calcareous gravel were measured using a 1.5-T clinical magnetic resonance tomograph. The spatial resolution of the dynamic measurements was 1.32 x 1.32 x 5 mm3, and the time between two cross-sectional measurements was approximately 10 s. The measured coefficients of molecular diffusion for water were in good agreement with theoretical data. Flow was measured without any tracer at velocities between 0.15 and 6.67 mm/s. The results, based on a calibration within one part of the column, were in good agreement with data obtained from a tracer experiment and from a numerical model. It was possible to measure the flow velocity in larger pores and preferential flow paths directly. The results of the flow measurements in smaller pores reflected the mean velocity within that volume element. In that case the obtained values were close to the average linear velocity. Since the time resolution is high a monitoring of flow processes is possible. The pore space was imaged with a spatial resolution of 0.5 x 0.5 x 0.5 mm3. Here, the porosity of pores that are larger than 0.2 mm can be measured directly; for smaller pores a calibration is necessary.
Journal of Environmental Quality 31(2):470-6. · 2.32 Impact Factor
