Biomedical subjects

T Krings

Publications and source records attributed to T Krings.

At least 19 recordsLinked to original sources

PubMed2006

First measurement of the linear polarization of radiative electron capture transitions.

For radiative electron capture into the K shell of bare uranium ions, a study of the polarization properties has been performed. For this purpose a position sensitive germanium detector has been used as an efficient Compton polarimeter. This enabled us to measure the degree of linear polarization by analyzing Compton scattering inside the detector and to determine the orientation of the polarization plane. Depending on the observation angle and the beam energy used, the radiation is found to be linearly polarized by up to 80%. In all cases studied, the plane of polarization coincides with the collision plane. The results will be discussed in the context of rigorous relativistic calculations, showing that relativistic effects tend to lead to a depolarization of the radiation emitted.

Journal Article↗

PubMed2006

Multiple mirror-like intracranial aneurysms. Report of a case and review of the literature.

While multiple intracranial arterial aneurysms occur in 26.4% of patients with aneurysms, in our practice bilateral mirror-like aneurysms are encountered in 9.4% of patients. Multiple mirror aneurysms in the same patient are exceedingly rare. We report a case of mirror-like middle cerebral artery aneurysms associated with mirror-like posterior inferior cerebellar arteries aneurysms and discuss their significance. Although an exceptional finding, multiple mirror-like aneurysms may shed light on the vulnerability of different arterial segments to specific diseases.

Cerebellum↗

PubMed2006

Magnetic versus manual guidewire manipulation in neuroradiology: in vitro results.

INTRODUCTION: Standard microguidewires used in interventional neuroradiology have a predefined shape of the tip that cannot be changed while the guidewire is in the vessel. We evaluated a novel magnetic navigation system (MNS) that generates a magnetic field to control the deflection of a microguidewire that can be used to reshape the guidewire tip in vivo without removing the wire from the body, thereby potentially facilitating navigation along tortuous paths or multiple acute curves. METHOD: The MNS consists of two permanent magnets positioned on either side of the fluoroscopy table that create a constant precisely controlled magnetic field in the defined region of interest. This field enables omnidirectional rotation of a 0.014-inch magnetic microguidewire (MG). Speed of navigation, accuracy in a tortuous vessel anatomy and the potential for navigating into in vitro aneurysms were tested by four investigators with differing experience in neurointervention and compared to navigation with a standard, manually controlled microguidewire (SG). RESULTS: Navigation using MG was faster (P=0.0056) and more accurate (0.2 mistakes per trial vs. 2.6 mistakes per trial) only in less-experienced investigators. There were no statistically significant differences between the MG and the SG in the hands of experienced investigators. One aneurysm with an acute angulation from the carrier vessel could be navigated only with the MG while the SG failed, even after multiple reshaping manoeuvres. CONCLUSION: Our findings suggest that magnetic navigation seems to be easier, more accurate and faster in the hands of less-experienced investigators. We consider that the features of the MNS may improve the efficacy and safety of challenging neurointerventional procedures.

Catheterization↗

PubMed2006

Silent microemboli related to diagnostic cerebral angiography: a matter of operator's experience and patient's disease.

INTRODUCTION: The aim of the present investigation was to elucidate in a large consecutive patient cohort whether the level of training has an effect on the number of microemboli detected by diffusion-weighted imaging (DWI) and which additional risk factors can be identified. METHODS: A total of 107 consecutive patients in whom a diagnostic cerebral angiography had been performed were prospectively investigated with DWI; 51 angiographies were performed by experienced neuroradiologists, 56 by neuroradiologists in training. RESULTS: In 12 patients (11.1%), a total of 17 new lesions without any clinically overt neurological symptoms were identified. Of these, 12 patients, 11 (91.7%) with 16 lesions were investigated by junior neuroradiologists. In 11 of 12 patients with DWI abnormalities (91.7%), risk factors could be identified (atherosclerotic vessel wall disease, vasculitis, hypercoagulable states). Experienced neuroradiologists performed 21 of 48 angiographies (43.8%) on patients with the above-mentioned risk factors, whereas junior neuroradiologists performed 27 angiographies in this subgroup (46.2%). The rate of diffusion abnormalities in patients with risk factors was 11/48 (22.9%) - considerably higher than in patients without risk factors (1/59; 1.7%). CONCLUSION: The level of experience and the nature of the underlying disease are predictors of the occurrence of cerebral ischemic events following neuroangiography. Alternative diagnostic modalities should be employed in patients who are investigated for diseases with the highest risk of angiographic complications (i.e., vasculitis, and arteriosclerotic vessel wall disease). If diagnostic angiography remains necessary in these patients, the highest level of practitioner training is necessary to ensure good patient outcome.

Adolescent↗

PubMed2006

Diffusion tensor imaging in acquired blind humans.

Retinal implants as a future possible therapy of blindness rely on an intact neural transmission from the retina to the primary visual cortex. By now it remains unknown, in how far the absence of afferent input in blindness affects also the organization of the optic radiation. Using diffusion tensor imaging (DTI), the non-invasive evaluation of large fiber tracts including the optic radiation has become possible. This method is sensitive to changes of the axonal state such as wallerian degeneration. We have compared DTI data from 6 acquired blind patients with those of a group of 11 healthy control subjects. Neither the relative anisotropy quotient of the visual fiber tract and the pyramidal tract showed a statistically significant difference between the blind patients and the control group nor did the absolute values of the relative anisotropy in the pyramidal tract and the visual fiber tract. There was no axonal degeneration of the optic radiation in late onset acquired blindness. With the optic pathways remaining intact, transmitting electric signals of retinal implants to the visual regions of the human brain seems to be possible even after decades of acquired blindness.

Adult↗

PubMed2006

Delayed diagnosis of spinal dural arteriovenous fistula in the absence of pathological vessels on MRI.

The authors report on a 69-year-old man presenting with progressive leg weakness and gait ataxia over two years. A central intramedullary cord lesion ranging from T8-12 on MR imaging was misdiagnosed as a low-grade glioma and a biopsy was attempted followed by temporary clinical deterioration. Selective spinal angiography revealed a spinal dural arteriovenous (AV) fistula on the left L3 nerve root sheath despite the absence of pathological vessels on MR imaging. The fistula was successfully treated by microsurgical interruption of the arterialized intradural vein. The present case should remind us to include selective spinal angiography in our diagnostic work-up in patients predisposed for spinal dural AV fistula by male sex, advanced age and clinical presentation of slowly progressive sensorimotor symptoms with myelopathy on MR imaging, even in the absence of any pathological vascular structures.

Aged↗

PubMed2005

Hereditary hemorrhagic telangiectasia in children: endovascular treatment of neurovascular malformations: results in 31 patients.

Hereditary hemorrhagic telangiectasia (HHT) is a heterogeneous disease that can present with a variety of clinical manifestations. The neurovascular complications of this disease, especially in children, may be potentially devastating. The purpose of this article was to review the therapeutic results of endovascular treatment of neurovascular malformations in children. A total of 31 patients under the age of 16 were included in this retrospective analysis. All children were treated in a single center. Twenty children presented with 28 arteriovenous (AV) fistulae, including seven children with spinal AV fistulae and 14 children with cerebral AV fistulae (one child had both a spinal and cerebral fistulae). Eleven children had small nidus-type AV malformations. All embolizations were performed employing superselective glue injection. Follow-up ranged between 3 and 168 months (mean 66 months). A total of 115 feeding vessels were embolized in 81 single sessions, resulting in a mean overall occlusion rate of the malformation of 77.4% (ranging from 30 to 100%). Two of 31 patients (6.5%) died as a direct complication of the embolization procedure; two patients (6.5%) had a persistent new neurological deficit; eight patients (26.7%) were clinically unchanged following the procedure; in 13 patients (41.9%) an amelioration of symptoms but no cure could be achieved; and six patients (19.4%) were completely asymptomatic following the endovascular procedure. In the surviving patients morphological complete occlusion was possible in twelve patients (38.7%); therapy is still not completed in six patients. Since the natural history of neurovascular manifestations of HHT in children is associated with high morbidity and mortality, therapeutic intervention is mandatory. In most instances a morphological target can be identified; therefore, even partial and staged treatment can be performed. Our results demonstrate that in 27/31 patients these targeted interventions resulted in stabilizing the disease, ameliorating the symptoms or even complete resolution. The endovascular approach employing glue as the embolizing agent represents a safe and efficient way to control the neurovascular phenotypes of HHT.

Adolescent↗

PubMed2005

Neurovascular phenotypes in hereditary haemorrhagic telangiectasia patients according to age. Review of 50 consecutive patients aged 1 day-60 years.

Hereditary haemorrhagic telangiectasia (HHT) is inherited as an autosomal dominant trait with varying penetrance and expressivity. Some of the most devastating consequences of this disease result from cerebral vascular malformations that manifest themselves in either arteriovenous fistulae (AVF), small nidus-type arteriovenous malformations (AVM) or micro-AVMs with a nidus less than 1 cm in size. The purpose of this study was to compare the phenotypes of CNS-manifestations of HHT with the age of the patient. The charts and angiographic films of 50 patients diagnosed with HHT according to the Curaçao criteria were retrospectively evaluated concerning age of onset of symptoms, or, if not applicable of first consultation. The files were reviewed for clinical presentation, family and personal history, while the patients' angiograms were analysed with respect to the number of lesions (single and multiple), the location (superficial supratentorial, deep supratentorial, infratentorial, and spinal), and type of lesion (fistulous AVM, nidus-type AVM, and micro-AVM). A total of 75 central nervous system manifestations of HHT were found. Lesions included seven spinal cord AVFs that were all present in the paediatric age group (mean age: 2.2 years), 34 cerebral AV fistulae, all but two affected patients were less than 6 years (mean age 3.0). Sixteen nidus type AVMs (mean age: 23.1 years) and 18 micro-AVMs (mean age: 31.8 years) were found. HHT displays an age-related penetrance of clinical manifestations. Since members of the same family can present with completely different phenotypes of this disease there seems to be no relationship between the type of mutation and the phenotype of the disease. Since there seems to be a continuum of vascular abnormalities (from large fistulous areas to small AVMs and micro-AVMs) associated with HHT, the most likely determinating factor of the HHT phenotype is the timing of the revealing event in relation to the maturity of the vessel. Presumably, the trigger of the quiescent genetical abnormality transforms a "dormant" disease into a morphologically and therefore clinically detectable one by impairing a specific vessel segment at a specific (more or less vulnerable) period of time. The nature of this triggering event is, however, as of yet unclear.

Adolescent↗

PubMed2005

Technical pitfalls in a porcine brain retraction model. The impact of brain spatula on the retracted brain tissue in a porcine model: a feasibility study and its technical pitfalls.

We describe technical pitfalls of a porcine brain injury model for identifying primary and secondary pathological sequelae following brain retraction by brain spatula. In 16 anaesthetised male pigs, the right frontal brain was retracted in the interhemispheric fissure by a brain spatulum with varying pressures applied by the gravitational force of weights from 10 to 70 g for a duration of 30 min. The retracted brain tissue was monitored for changes in intracranial pressure and perfusion of the cortex using a Laser Doppler Perfusion Imager (MoorLDI). To evaluate the extent of oedema and cortical contusions, MRI was performed 30 min and 72 h after brain retraction. Following the MR scan, the retracted brain areas were histopathologically assessed using H&E and Fluoro-Jade B staining for neuronal damage. Sinus occlusion occurred in four animals, resulting in bilateral cortical contusions and extensive brain oedema. Retracting the brain with weights of 70 g (n = 4) caused extensive oedema on FLAIR images that correlated clinically with a hemiparesis in three animals. Morphologically, an increased number of Fluoro-Jade B-positive neurons were found. A sequential decrease in weights prevented functional deficits in animals. A retraction pressure applied by 10-g weights (n = 7) caused a mean rise in intracranial pressure to 4.0 +/- 3.1 mm Hg, and a decrement in mean cortical perfusion from 740.8 +/- 41.5 to 693.8 +/- 72.4 PU/cm2 (P < 0.24). A meticulous dissection of the interhemispheric fissure and a reduction of weights to 10 g were found to be mandatory to study the cortical impact caused by brain spatula reproducibly.

Analysis of Variance↗

PubMed2005

Primary lymphoma of the skull base.

This case demonstrates the rare finding of a primary malignant lymphoma of the frontobasis and ethmoidal cells in a patient presenting with progressive loss of vision. Computed tomography and MRI demonstrated a homogenously enhancing tumour with extensive bony destructions of the skull base. After transsphenoidal biopsy, histology revealed a highly malignant primary B-cell lymphoma. The patient was further treated with immunochemotherapy. Tissue diagnosis is, therefore, crucial before a definitive therapy is instituted.

Biopsy↗

PubMed2005

Fifteen-year follow-up of a patient with beta thalassaemia and extramedullary haematopoietic tissue compressing the spinal cord.

A long-term follow-up of a patient with beta thalassaemia with intra- and extraspinal extramedullary haematopoietic tissue compressing the spinal cord is presented. Extramedullary haematopoietic nodules are a rare cause of spinal cord compression and should be included in the differential diagnosis, especially in patients from Mediterranean countries. Treatment with radiation therapy solely failed, giving rise to the need of surgical intervention. Surgical decompression of the spine and the removal of the culprit lesion compressing the spine were performed. Postinterventional radiation therapy was applied to the spine. A relapse had to be treated again by surgical means combined with postinterventional radiation therapy. A complete relief of the symptoms and control of the lesion could be obtained.

Adult↗

PubMed2005

Treatment of wide-necked aneurysms with balloon-expandable polyurethane-covered stentgrafts: experience in an animal model.

OBJECTIVE: Endovascular treatment of intracranial wide-necked aneurysms employing stentgrafts might constitute a promising alternative to established neurosurgical or endovascular treatment options. However, there is uncertainity concerning long-term vessel patency and biocompatibility of the covering material used for these stentgrafts. The objective of our study was, therefore, to evaluate in an animal model of wide necked aneurysms, which changes within the parent vessel wall are present after stentgraft placement using polyurethane as the covering material. METHODS: Wide-necked aneurysms were created in rabbits by distal ligation and intraluminal incubation of the right common carotid artery with elastase. All 10 animals were treated with polyurethane covered stentgrafts. Angiography and histological analyses were performed including immunohistochemical investigations for estimating the proliferation of the intima and possible inflammatory infiltration of the vessel wall after one (n = 5) and three months (n = 5) observation. RESULTS: Stentgrafts led to a complete and stable aneurysm occlusion in all but one animal in which the stent was initially misplaced. In one animal, the stentgraft was completely occluded as visible both at angiography and on histological examination. Here, old thrombus was found within the stent although the animal was on antiplatelet therapy. The other stentgrafts remained patent and demonstrated only minimal proliferative carrier vessel wall changes and no in-stent stenosis. CONCLUSIONS: In previous animal models using Dacron covered stentgrafts, a poor short term patency rate due to the limited biocompatibility was found. We found, that Polyurethane seemed to have less adverse effects upon the vessel wall. However, a longer follow-up period is necessary to exclude delayed stenosis of the parent vessels. Stentgrafts may, therefore, play a role in broad based aneurysms, dissecting aneurysms or pseudoaneurysms, however, vessel sacrifice using permanent balloon occlusion may be a safer and better established alternative compared to the use of stentgrafts.

Aneurysm↗

PubMed2005

Diffusion-weighted imaging-guided resection of intracerebral lesions involving the optic radiation.

In this paper we report our experience with diffusion-weighted imaging (DWI) for optic radiation (OR) visualization during resection of tumors. We hypothesize that intraoperative OR visualization helps to maintain patients' visual fields. DWI studies were performed together with T1-weighted postcontrast magnetic resonance imaging (MRI) in four patients with lesions in or adjacent to the OR (glioblastoma, oligo-astrocytoma, cavernoma, and metastasis; n = 1 each). The OR was identified from one of six DWI data acquisitions, segmented and reconstructed three-dimensionally. The image data were neuronavigationally transferred into the operative field, and provided the neurosurgeon with information on lesion site and adjacent OR localization. Preoperative and postoperative neuroophthalmological testing included, among others, perimetry to define the value of diffusion-weighted image guidance during OR lesion resection. Three lesions were removed completely. In one case, low-grade tumor parts infiltrating the OR were intentionally left. No persistent visual field deficits were induced. In one patient, a transient homonymous hemianopia attributable to postoperative swelling completely resolved under steroid medication. The authors conclude that intraoperative OR visualization, realized by neuronavigationally displayed DWI data, might prove to be helpful to maintain patients' visual fields.

Affect↗

PubMed2005

Interneuronal systems of the cervical spinal cord assessed with BOLD imaging at 1.5 T.

The purpose of this study was to investigate if functional activity with spinal cord somatosensory stimulation can be visualized using BOLD fMRI. We investigated nine healthy volunteers using a somatosensory stimulus generator. The stimuli were applied in three different runs at the first, third, and fifth finger tip of the right hand, respectively, corresponding to dermatomes c6, c7, and c8. The stimuli gave an increase of BOLD signal (activation) in three different locations of the spinal cord and brain stem. First, activations could be seen in the spinal segment corresponding to the stimulated dermatome in seven out of nine volunteers for c6 stimulation, two out of eight for c7, and three out of eight for c8. These activations were located close to the posterior margin of the spinal cord, presumably reflecting synaptic transmission to dorsal horn interneurons. Second, activation in the medulla oblongata was evident in four subjects, most likely corresponding to the location of the nucleus cuneatus. The third location of activation, which was the strongest and most reliable observed was inside the spinal cord in the c3 and c4 segments. Activation at these spinal levels was almost invariably observed independently of the dermatome stimulated (9/9 for c6, 8/8 for c7, and 7/8 for c8 stimulation). These activations may pertain to an interneuronal system at this spinal level. The results are discussed in relation to neurophysiological studies on cervical spinal interneuronal pathways in animals and humans.

Adult↗

PubMed2005

Clinical applications of 2-D dynamic contrast-enhanced MR subtraction angiography in neurosurgery -- preliminary results.

OBJECTIVES: Advances in MR hardware performance and imaging techniques have enabled us to perform sub-second frame rate contrast enhanced MR angiographies as a clinical routine, resulting in subtraction angiographies with temporal resolutions similar to those obtained by conventional DSA. In this manuscript, we describe the technique of 2-D dynamic contrast-enhanced MR subtraction angiography and its possible applications in neurosurgery. METHODS: A T (1)-weighted gradient-echo sequence with short TR and TE values was performed during the intravenous bolus application of MR contrast media. This sequence had a temporal resolution of up to 0.34 seconds per image and was performed in 28 patients harbouring arteriovenous malformations (n = 12), dural AV fistulas (n = 3), meningiomas (n = 8), glomus tympanicum or jugulare tumours (n = 3), and haemangioperizytomas (n = 2). Arterial digital subtraction angiography (DSA) was performed in all patients and compared to the MRA sequences with respect to differentiation into early, late arterial and venous phases, detectability of normal vessels, detection of the pathology, feeding arteries, capillary blush, early draining veins, and hyper-vascularization. RESULTS: In all 28 investigated cases and all pathological entities separation of early and late arterial phases, capillary phases, early and late venous phases was possible. The proximal portions of the major cerebral arteries, the capillary blush and the venous anatomy including the tributaries to the large sinuses could be well defined and correlated well with the gold standard, i. e. DSA. CONCLUSIONS: Dynamic contrast enhanced MR angiography will prove helpful in 1) the follow-up of AVMs since early venous drainage can be visualised; 2) the demonstration of dural AVF, which can be recognised as an early filling of a dural sinus during the early arterial phase; and 3) the characterisation of the degree of vascularisation of brain tumours.

Adult↗

PubMed2004

Spontaneous regression of two supraophthalmic internal cerebral artery aneurysms following flow pattern alteration.

We report on a patient with fibromuscular dysplasia who presented with a right-sided giant calcified cavernous internal carotid artery (ICA) aneurysm and two additional supraophthalmic ICA aneurysms. Endovascular closure of the right ICA using detachable balloons was performed with collateralisation of the right hemisphere via the right-sided posterior communicating and the anterior communicating arteries. Repeat angiography after 6 months demonstrated spontaneous complete regression of the two supraophthalmic aneurysms, although the parent vessel was still perfused. In comparison to the former angiography, the flow within the parent vessel was reversed due to the proximal ICA balloon occlusion. MRI demonstrated that the aneurysms were not obliterated by thrombosis alone, but showed a real regression in size. This case report demonstrates that changes in cerebral hemodynamics potentially lead to plastic changes in the vessel architecture in adults and that aneurysms can be flow-related, even if not associated with high flow fistulas or arteriovenous malformations, especially in cases with an arterial wall disease.

Aged↗

PubMed2004

Are the configuration and neck morphology of experimental aneurysms predictable? A technical approach.

Aneurysm configuration and neck morphology are important factors in the decision for cerebral aneurysm therapy, i.e., clipping versus coiling. The aim of our study was to create various aneurysm configurations in a predictable and reproducible way in an animal model. In our recently proposed endovascular approach to produce bifurcation aneurysms in the rabbit, the right common carotid artery (CCA) is surgically exposed and distally ligated, and a sheath is advanced retrogradely into the CCA, the base of which is proximally occluded using a Fogarty balloon. Subsequently, elastase is injected via a microcatheter that is placed directly distal to the balloon and allowed to incubate for 20 min. After removal of the sheath, saccular aneurysms begin to form within 2 weeks. For greater variability in aneurysm size and neck morphology, we modified two parameters of this formerly established elastase-induced aneurysm model--the distance between the balloon and sheath and the level of balloon position--before the elastase was endoluminally incubated in 15 rabbits. Three weeks after aneurysm induction, the size and configuration of the aneurysms were controlled using DSA. Our results confirm that balloon occlusion in the brachiocephalic trunk results in broad-based aneurysms, whereas balloon occlusion in the CCA gives rise to circumscribed aneurysm necks. By increasing the distance between the balloon and sheath, the rabbits developed significantly larger aneurysms. The balloon-sheath distance and the level of balloon occlusion proved to be parameters whose modifications result in predictable and reproducible aneurysm variants that can be used for the testing of endovascular devices.

Animals↗

PubMed2004

Detection of intracranial aneurysms with multislice CT: comparison with conventional angiography.

We assessed the diagnostic accuracy of multislice CT in detection of intracranial aneurysms in patients presenting with subarachnoid or intracranial haemorrhage. Multislice CT and multiplanar digital subtraction angiography (DSA) images were obtained in 50 consecutive patients presenting with subarachnoid (SAH) and/or intracranial haemorrhage and reviewed by three neuroradiologists for the number, size and site of any aneurysms. The CT data were assessed using multiplanar reformats (MPR), maximum-intensity projections (MIP), surface-shaded display (SSD) and volume-rendering (VRT). In conventional angiography 51 aneurysms were detected in 41 patients. CT angiography (CTA) showed up to 48 aneurysms in 39 patients, depending on the observer. The overall sensitivity of multislice CT was 83.3% for small (< 4 mm), 90.6% for medium-size (5-12 mm) and 100% for large (> 13 mm) aneurysms. The sensitivity of multislice CTA to medium-size and large intracranial aneurysm is within the upper part of the range reported for helical single-slice CT. However, as small aneurysms may not be found, DSA remains the standard technique for investigation of SAH.

Angiography, Digital Subtraction↗