PubMed Health⌕ Search

Biomedical subjects

Stefan Hähnel

Publications and source records attributed to Stefan Hähnel.

17 recordsLinked to original sources
PubMed2006

Age- and tooth-related pulp cavity signal intensity changes in healthy teeth: a comparative magnetic resonance imaging analysis.

OBJECTIVE: To determine if it is possible to measure age-related pulp cavity signal intensity changes by using magnetic resonance imaging (MRI). STUDY DESIGN: Dental pulp cavity signal intensities were assessed in 92 test subjects on the basis of MRI signal intensity measurements at freely defined regions of interest by using T1 gradient echo sequences before and after contrast-agent administration. Relative signal intensity differences were calculated and provided the basis for age- and tooth-related comparisons. RESULTS: Significant signal intensity differences were noted between the oldest (born between 1930 and 1959) and the youngest (born after 1980) test subjects and the other groups (P < .05). In addition, the first molars showed significantly lower signal intensity differences than the second molars (P < .05). CONCLUSION: Magnetic resonance imaging can be used to determine pulp cavity signal-intensity changes with age.

Age Factors↗
PubMed2006

Visualization of intrarenal vessels by 3.0-T MR angiography in comparison with digital subtraction angiography using renal specimens.

BACKGROUND: MRI at 3.0 T enables high-spatial resolution for renal MR angiography. OBJECTIVE: Evaluation of an arterial tree model in animal kidney specimens with comparison of digital subtraction angiography (DSA) and high-field MRI to find out the maximum spatial resolution of intrarenal vessels. It was considered that objective quantitation of angiogram quality could be achieved. MATERIALS AND METHODS: A total of 27 pig kidney specimens were examined by MR angiography (flash 3D) using a 3.0-T scanner (TRIO; Siemens, Erlangen, Germany) with an eight-channel head coil and a voxel size of 0.9x0.9x1.1 mm in the early arterial phase after implantation of a 4F catheter in the renal artery. DSA (Integris, Philips, Best, The Netherlands) was performed immediately after the MRI. With the help of semiautomated segmentation, all vessels were marked for comparison of the vessel trees. The Wilcoxon rank test was used for statistical evaluation of vessel numbers and branching depths. RESULTS: Objective comparison between DSA and MR angiography was achieved. High-field MR angiography had the ability to depict vessels up to the seventh branching on average. Significant differences in vessel delineation and counts were found from the fifth level of intrarenal branching onwards with DSA showing an advantage. CONCLUSION: High-field MRI has great potential in the detection of intrarenal arteries and is comparable to DSA in visualization of the central intrarenal vessel tree.

Angiography, Digital Subtraction↗
PubMed2006

Treatment of intracranial stenoses using the Neuroform stent system: initial experience in five cases.

INTRODUCTION: We assessed the technical feasibility of balloon-assisted angioplasty with consecutive stenting using a flexible, self-expanding neurovascular stent for the treatment of intracranial arteriosclerotic vascular stenoses. METHODS: Five consecutive patients with symptomatic drug-resistant stenoses of the intracranial internal carotid artery (ICA) or the main stem of the middle cerebral artery (MCA) were treated by balloon-assisted angioplasty with consecutive stenting using the Neuroform stent system. RESULTS: Balloon dilatation of the stenoses and consecutive stent placement with complete coverage of the stenoses was feasible in all patients. One patient suffered acute thrombosis distally to the stented vessel segment which was successfully treated by fibrinolysis, and one patient suffered acute subarachnoid and parenchymal hemorrhage probably due to vessel perforation. In the other three patients, no complications occurred during or immediately after angioplasty. All patients were free of further ischemic events up to the 6-month follow-up. CONCLUSION: Our findings demonstrate that the Neuroform stent system can used successfully for the treatment of intracranial stenoses of the ICA and the main stem of the MCA. Although immediate angiographic results are promising, long-term angiographic and clinical follow-up is essential to demonstrate long-term outcome.

Aged↗
PubMed2005

Reconstruction of blood propagation in three-dimensional rotational X-ray angiography (3D-RA).

This paper presents a framework of non-interactive algorithms for the mapping of blood flow information to vessels in 3D-RA images. With the presented method, mapping of flow information to 3D-RA images is done automatically without user interaction. So far, radiologists had to perform this task by extensive image comparisons and did not obtain visualizations of the results. In our approach, flow information is reconstructed by forward projection of vessel pieces in a 3D-RA image to a two-dimensional projection series capturing the propagation of a short additional contrast agent bolus. For accurate 2D-3D image registration, an efficient patient motion compensation technique is introduced. As an exemplary flow-related quantity, bolus arrival times are reconstructed for the vessel pieces by matching of intensity-time curves. A plausibility check framework was developed which handles projection ambiguities and corrects for noisy flow reconstruction results. It is based on a linear programming approach to model the feeding structure of the vessel. The flow reconstruction method was applied to 12 cases of cerebral stenoses, AVMs and aneurysms, and it proved to be feasible in the clinical environment. The propagation of the injected contrast agent was reconstructed and visualized in three-dimensional images. The flow reconstruction method was able to visualize different types of useful information. In cases of stenosis of the middle cerebral artery (MCA), flow reconstruction can reveal impeded blood flow depending on the severeness of the stenosis. With cases of AVMs, flow reconstruction can clarify the feeding structure. The presented methods handle the problems imposed by clinical demands such as non-interactive algorithms, patient motion compensation, short reconstruction times, and technical requirements such as correction of noisy bolus arrival times and handling of overlapping vessel pieces. Problems occurred mainly in the reconstruction and segmentation of 3D-RA images in cases of complex AVMs. The concentration of injected contrast agent was often not sufficient to provide highly contrasted vessels in 3D-RA images. Another segmentation-related problem is known as 'kissing vessels' [19]. Kissing vessel artifacts introduce artificial vessel junctions and thereby distort the feeding structure of the vessel. This may finally cause implausible flow reconstruction results and inverse flow directions in vessel segments. We are currently planning to validate our reconstruction results using particle imaging velocimetry (PIV). PIV experiments with phantoms, for which the true flow parameters are known, will allow for the assessment of the accuracy of our contrast agent based method. In the context of computational fluid dynamics techniques, the potential of the presented flow reconstruction method is high. Flow reconstruction results based on the presented method could be used both as boundary conditions for simulations and as a reference for the validation of simulation results. Computational fluid dynamics provide useful information such as arterial wall shear stress and complex flow patterns in aneurysms.

Algorithms↗
PubMed2005

MRI volumetry for the preoperative diagnosis of trigeminal neuralgia.

To assess whether quantitative measuring methods can help improve the reliability of MRI-based evaluations of the pathological role of a neurovascular conflict between an artery and the trigeminal nerve. In a prospective study, magnetic resonance images were obtained from 62 patients with unilateral facial pain and 50 healthy test subjects. In coronal T1- and T2-weighted sequences volume measurements were performed by regions of interest and compared intraindividually (healthy versus affected side in the patient populations and right versus left side in the group of test subjects) and on the basis of the different clinical pictures (t test for dependent and independent samples, p<0.05). In patients with trigeminal neuralgia, the affected nerve showed a smaller volume than the trigeminal nerve on the healthy side (p<0.001). Such a volume difference was noted neither in the other patients nor in the healthy test subjects. Quantitative MRI measurements allow a pathological neurovascular conflict to be distinguished from a nonpathological condition where an artery is in close proximity to the trigeminal nerve. The measured volume difference between the healthy and the affected nerve in patients with neuralgia is indicative of trigeminal nerve atrophy resulting from damage to the nerve.

Adult↗
PubMed2005

MR imaging-based volumetry in patients with early-treated phenylketonuria.

BACKGROUND AND PURPOSE: Our purpose was to specify the most severely affected brain structures in early treated phenylketonuria regarding volume loss and establish possible correlations between volume loss and plasma levels of phenylalanine (Phe). METHODS: In 31 patients with early treated phenylketonuria and in 27 healthy volunteers, we acquired volumetric MR imaging data. Serum Phe concentrations at different times were measured as well. Semiautomatic volumetric postprocessing of the cerebellum, cerebrum (supratentorial brain tissue), hippocampus, intracranial volume, lateral ventricles, nucleus caudatus, nucleus lentiformis, pons, and thalamus, as well as the two-dimensional extension of the corpus callosum, was performed using the software BRAINS2. For each separate brain structure, the relative differences between the normal and the phenylketonuria group (delta(rel)) were calculated. RESULTS: The cerebrum, corpus callosum, hippocampus, intracranial volume, and pons were significantly smaller in patients with phenylketonuria than in healthy patients. The volume of the lateral ventricles was significantly larger in patients with phenylketonuria than in healthy ones. The most severely affected structures were the pons (delta(rel) = 16%), hippocampus (delta(rel) = 14.5%), cerebrum (delta(rel) = 13%), and corpus callosum (delta(rel) = 10%). No significant differences were found for the basal ganglia, cerebellum, and thalamus. There were no significant correlations found between the volume of any of the different brain structures and the metabolic parameters. CONCLUSION: The most severely affected brain structures in early-treated patients with phenylketonuria regarding volume loss are the cerebrum, corpus callosum, hippocampus, and pons.

Adult↗
PubMed2004

Fully automated localization of the human primary somatosensory cortex in one minute by functional magnetic resonance imaging.

A clinical functional magnetic resonance imaging (fMRI) protocol based on a fully automated tactile stimulation was optimized in 10 right-handed volunteers at 1.5 T for minimum scan time, high BOLD-signals and robust localization of the primary somatosensory cortex (S1) by systematically varying the applied block design. All volunteers had six different fMRI measurements of 5 stimulation/baseline cycles each with equal block duration that was changed between the measurements from 6 to 30 s. Data sets of 4, 3 and 2 cycles were generated post hoc resulting in a total of 240 data sets that were evaluated individually for BOLD-signal intensity (dS%), correlation to the hemodynamic reference function (r) and Euclidean coordinates (x, y, z). The protocol with 5 cycles, a block duration of 6 s and a total scan time of 66 s provided the best BOLD-signal characteristics (dS% = 1.15, r = 0.78). Compared to the mean scan time of other clinical fMRI protocols (174 s) a reduction of 62% was achieved.

Adult↗
PubMed2003

Robust localization and lateralization of human language function: an optimized clinical functional magnetic resonance imaging protocol.

An optimized clinical functional magnetic resonance imaging (fMRI) protocol with a total scanning time of 8 min is presented that localizes Broca's and Wernicke's areas robustly and determines hemispheric dominance. Language function was visualized using two different sentence generation (SG) and word generation (WG) tasks. Block designed blood oxygenation level dependent (BOLD) fMRI was applied in 14 right-handed volunteers at 1.5 T during visual stimulation. BOLD-clusters were assessed individually for anatomical localization. Reference data are provided for the maximum correlation of the measured BOLD-signal time course to the applied reference function (r(max)), for the maximum relative signal change (dS%), cluster size and Euklidian coordinates of Broca and Wernicke activation and of the anatomical homologues in the right hemispheres. Statistical means and a lateralization index (LI) were calculated. Broca activation focussed on the inferior frontal gyrus, and Wernicke activation on the superior temporal, supramarginal or middle temporal gyri. Mean BOLD-signals for Broca ranged from 1.53% (SG) to 2.56% (WG), and for Wernicke from 1.47% (SG) to 1.80% (WG). LI indicated left language dominance. The data provided further evidence for the high anatomical variability of language areas, which underlined the relevance of an individual language localization and lateralization prior to brain surgery.

Adult↗
PubMed2003

Local intra-arterial fibrinolysis of thromboemboli occurring during neuroendovascular procedures with recombinant tissue plasminogen activator.

BACKGROUND AND PURPOSE: There is a lack of systematic data regarding local intra-arterial fibrinolysis (LIF) of thromboemboli occurring during neuroendovascular procedures with the use of recombinant tissue plasminogen activator (rtPA). We report our technique for treating LIF of intracerebral thromboemboli occurring during neuroendovascular procedures. METHODS: Nine of 723 patients (1.2%) who underwent neuroendovascular procedures during the period from January 1997 to September 2002 suffered thromboembolic complications. These patients were treated by LIF with a maximum dose of 0.9 mg rtPA per kilogram body weight. Recanalization was categorized as successful (Thrombolysis in Myocardial Infarction [TIMI] grade 2 or 3) versus unsuccessful (TIMI grade 0 or 1), and clinical outcome was categorized as independent (Rankin Scale score 0 to 2) versus dependent or dead (Rankin Scale score 3 to 6). RESULTS: The minimum time between thrombus detection and beginning of LIF was 10 minutes, and the maximum time was 90 minutes. Successful recanalization was achieved in 4 of 9 patients (44%). All 9 patients suffered cerebral ischemic infarctions, and none of the patients sustained intracerebral hemorrhage. Two patients (22%) died from malignant brain infarctions. Four patients (44%) remained moderately disabled, and 3 patients (33%) were severely disabled 3 months after LIF. CONCLUSIONS: Although we used relatively high doses of rtPA, the recanalization rates and clinical outcome of LIF in our patients were not satisfactory. Strategies for the prevention of thromboemboli during neuroendovascular procedures must be improved, and novel fibrinolytic or thrombolytic techniques should be developed.

Adult↗
PubMed2003

Craniofacial duplication (diprosopus): CT, MR imaging, and MR angiography findings case report.

Diprosopus is one of the rarest malformations in humans. In addition to the facial structures, the cerebral frontal lobes were duplicated in this case. Three pairs of anterior cerebral arteries were detected, and the rostral parts of the superior sagittal sinus were duplicated. Computed tomography, magnetic resonance (MR) imaging, and MR angiography allowed study of the degree of duplicative changes in diprosopus, especially for planning cosmetic correction.

Cranial Sinuses↗
PubMed2003

Small-vessel stents for intracranial angioplasty: in vitro comparison of different stent designs and sizes by using CT angiography.

BACKGROUND AND PURPOSE: Our purpose was to evaluate whether CT angiography is a suitable alternative to conventional angiography in the evaluation of small-vessel stents for intracranial angioplasty. METHODS: CT angiographic appearances of 23 stents of different designs and sizes (2.0, 3.0, and 4.0 mm) were investigated after they were filled with a solution of 0.9% NaCl or diluted contrast medium. For each stent, artificial lumen narrowing (ALN) was measured, and the difference in the number of pixels with a Hounsfield value below 200 HU between the two filling states, DIFF(HU<200), was calculated to provide an objective indicator of the size of the evaluable stent diameter. RESULTS: With a window width of 1500 HU at a window level of 400 HU, ALN ranged from 66.8% to 97.7% in the group of 2.0-mm stents and from 38.6% to 66.8% in the groups of 3.0- and 4.0-mm stents. For the 2.0-mm stents, DIFF(HU<200) was zero. In the groups of 3.0- and 4.0-mm stents, DIFF(HU<200) ranged from 0.3 to 6.7, corresponding to a diameter of 0.13-3.0 mm, when the pixel size was presupposed to be 0.449 mm. CONCLUSION: CT angiographic evaluation of small-vessel patency after stent placement is considerably impaired by ALN. Stent manufacturers should be aware of potential artifacts caused by their stents during noninvasive diagnostic studies such as CT angiography.

Angioplasty, Balloon↗
PubMed2002

Multimodal functional imaging of prolonged neurological deficits in a patient suffering from familial hemiplegic migraine.

The case of a patient with familial hemiplegic migraine (FHM) suffering from prolonged right sided hemiparesis and aphasia that persisted for more than 10 days is reported. The symptoms were accompanied by slowing of the magnetoencephalogram over the left hemisphere, which normalized parallel to the clinical improvement. Positron emission tomography obtained on the 6th day revealed glucose-hypometabolism (hemispheric difference > or =10%) in left hemisphere's fronto-basal cortex, caudate nucleus, and thalamus. In contrast, magnetic resonance imaging including perfusion and diffusion weighted imaging was normal and did not show significant alterations of cortical perfusion or water mobility during the episode. We hypothesize that this finding provides evidence for a primary neuronal dysfunction causing the prolonged neurological deficits in FHM.

Adult↗
PubMed2002

An automated method for volumetric quantification of magnetization transfer of the brain.

Cerebral white matter damages can be detected and characterized using magnetization transfer (MT) imaging. In this study a fully automated method of measuring and analyzing the MT of the whole human brain is presented and assessed. A 3D-FLASH sequence with off-resonance RF pulse was optimized for fast, volumetric MT measurements. The postprocessing software developed for this purpose includes a SPM99-based segmentation algorithm, a visualization tool, and a histogram-based MT parameter analysis. The reproducibility of the method was tested with phantom measures and in studies on nine healthy volunteers. Small variances (0-1.6%) and therefore, a high reproducibility of MT parameter measurements were found in vitro, slightly higher variances in volunteer investigations (0.7-4.0%). With our technique, we expect to be able to better recognize and follow up the progression of white matter diseases. Due to the high reproducibility, this volumetric approach is specifically suitable for longitudinal MT studies.

Adult↗
PubMed2001

The value of magnetic resonance imaging in the diagnosis of orbital floor fractures.

The value of MRI in the diagnosis of acute orbital floor fractures has not been clearly defined. We therefore compared MR findings with CT findings in patients with orbital trauma. In 30 patients with isolated orbital trauma both coronal CT and coronal MRI were used to examine the orbits and the adjacent paranasal sinuses. Visualization of anatomical landmarks, the kind and extent of traumatic lesions, as well as artifacts were scored. The scores were compared using the Wilcoxon matched-pairs signed-rank test. Interexamination agreement between the two methods was calculated using a kappa analysis. All examinations had diagnostic quality: 30 fractures of the orbital floor (9 right and 21 left orbital floor fractures) were identified. In addition, CT showed fractures of the medial orbital wall in 19 patients (63.3%), of the lateral wall in 10 patients (33.3%), of the zygomatic arch in 2 patients (6.7%), and of the maxillary sinus in 4 patients (13.3%). Soft tissue herniation was shown in 13 patients (inferior rectus muscle twice, orbital fat in 11 cases). Magnetic resonance imaging demonstrated soft tissue herniation in 21 patients: muscle in 4, orbital fat in 17 cases. Magnetic resonance imaging is able to demonstrate orbital floor fractures as sensitively as CT, but CT is superior to MRI in showing small and associated fractures; therefore, CT remains in orbital fractures the imaging modality of choice. Magnetic resonance imaging is superior to CT in showing soft tissue herniations; therefore, MRI may have a role as an adjunct to CT if soft tissue entrapment remains unclear.

Adolescent↗