Karl-Michael Schebesch

Magnetic Resonance Imaging Diffusion Tensor Tractography: Evaluation of Anatomic Accuracy of Different Fiber Tracking Software Packages

BACKGROUND Diffusion tensor imaging (DTI)-based tractography has become an integral part of preoperative diagnostic imaging in many neurosurgical centers, and other nonsurgical specialties depend increasingly on DTI tractography as a diagnostic tool. The aim of this study was to analyze the anatomic accuracy of visualized white matter fiber pathways using different, readily available DTI tractography software programs. METHODS Magnetic resonance imaging scans of the head of 20 healthy volunteers were acquired using a Siemens Symphony TIM 1.5T scanner and a 12-channel head array coil. The standard settings of the scans in this study were 12 diffusion directions and 5-mm slices. The fornices were chosen as an anatomic structure for the comparative fiber tracking. Identical data sets were loaded into nine different fiber tracking packages that used different algorithms. The nine software packages and algorithms used were NeuroQLab (modified tensor deflection [TEND] algorithm), Sörensen DTI task card (modified streamline tracking technique algorithm), Siemens DTI module (modified fourth-order Runge-Kutta algorithm), six different software packages from Trackvis (interpolated streamline algorithm, modified FACT algorithm, second-order Runge-Kutta algorithm, Q-ball [FACT algorithm], tensorline algorithm, Q-ball [second-order Runge-Kutta algorithm]), DTI Query (modified streamline tracking technique algorithm), Medinria (modified TEND algorithm), Brainvoyager (modified TEND algorithm), DTI Studio modified FACT algorithm, and the BrainLab DTI module based on the modified Runge-Kutta algorithm. Three examiners (a neuroradiologist, a magnetic resonance imaging physicist, and a neurosurgeon) served as examiners. They were double-blinded with respect to the test subject and the fiber tracking software used in the presented images. Each examiner evaluated 301 images. The examiners were instructed to evaluate screenshots from the different programs based on two main criteria: (i) anatomic accuracy of the course of the displayed fibers and (ii) number of fibers displayed outside the anatomic boundaries. RESULTS The mean overall grade for anatomic accuracy was 2.2 (range, 1.1-3.6) with a standard deviation (SD) of 0.9. The mean overall grade for incorrectly displayed fibers was 2.5 (range, 1.6-3.5) with a SD of 0.6. The mean grade of the overall program ranking was 2.3 with a SD of 0.6. The overall mean grade of the program ranked number one (NeuroQLab) was 1.7 (range, 1.5-2.8). The mean overall grade of the program ranked last (BrainLab iPlan Cranial 2.6 DTI Module) was 3.3 (range, 1.7-4). The difference between the mean grades of these two programs was statistically highly significant (P < 0.0001). There was no statistically significant difference between the programs ranked 1-3: NeuroQLab, Sörensen DTI Task Card, and Siemens DTI module. CONCLUSIONS The results of this study show that there is a statistically significant difference in the anatomic accuracy of the tested DTI fiber tracking programs. Although incorrectly displayed fibers could lead to wrong conclusions in the neurosciences field, which relies heavily on this noninvasive imaging technique, incorrectly displayed fibers in neurosurgery could lead to surgical decisions potentially harmful for the patient if used without intraoperative cortical stimulation. DTI fiber tracking presents a valuable noninvasive preoperative imaging tool, which requires further validation after important standardization of the acquisition and processing techniques currently available.

Image fusion of MR images and real-time ultrasonography: evaluation of fusion accuracy combining two commercial instruments, a neuronavigation system and a ultrasound system

SummaryObjective. The aim of our study was to evaluate MRI/Ultrasonography fusion accuracy depending on three ultrasonographic parameters. Method. An ultrasonography and MRI compatible model was created, consisting of a plastic box, which contained 3 objects. MRI scans were performed with 128 sagittal slices. The objects were segmented and 3D reconstructions were created. A special ultrasound adapter with 3 reflective markers was fixed to the ultrasound probe. Thus, the probe could be tracked by the navigation system (Vector Vision2, BrainLab, Heimstetten, Germany) and the segmented shape of the 3D-objects obtained from the MR images were overlaid onto the ultrasound display (Elegra, Siemens, Erlangen, Germany). The dependency of fusion accuracy on different depth of ultrasound display, different distances between probe and objects and different angles between the axis of the ultrasound probe and the centre of the spheres was evaluated. 435 single measurements were performed. Findings. Overall fusion accuracy was 1.08 mm±0.61 mm (mean ± standard deviation) for spheres and 1.6 mm±1.1 mm for arrow heads. If the ultrasound probe was directed more tangentially to the surface of the spheres the fusion became increasingly inaccurate (P<0.05). Fusion accuracy decreased the more distant the US probe was held to the object (P<0.05). Different depth of ultrasound display had no significant effect on fusion accuracy. Conclusions. Highly accurate fusion of MR images and real-time ultrasonography could be achieved. However, careful interpretation of the fused data is necessary, when different angles and distances of the US probe to the object are concerned.

ICAM-1 and VCAM-1 Expression following Aneurysmal Subarachnoid Hemorrhage and Their Possible Role in the Pathophysiology of Subsequent Ischemic Deficits

Background: The pathophysiology of ischemic cerebral lesions following aneurysmal subarachnoid hemorrhage (SAH) is poorly understood. There is growing evidence that inflammatory reactions could be involved in the pathogenesis of such delayed occurring ischemic lesions. The aim of this study was to evaluate adhesion molecules with regard to these lesions following SAH. Methods: Serum and cerebrospinal fluid (CSF) samples were taken daily from 15 patients up to day 9 after SAH and evaluated for intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1). Results: CSF and serum samples correlated well during nearly the whole time course (p < 0.0001). A secondary increase in ICAM-1 and VCAM-1 in the serum and CSF correlated with an increase in flow velocity in the transcranial Doppler (p > 0.0001 and p < 0.007) but not to a delayed lesion in the CT scan. Conclusion: We believe that inflammatory processes are involved in the pathogenesis of cerebral vasospasm but they might only be a part of a multifactorial pathogenesis.

Levetiracetam compared to phenytoin for the prevention of postoperative seizures after craniotomy for intracranial tumours in patients without epilepsy

Anticonvulsant drugs are frequently given after craniotomy. Phenytoin (PHT) is the most commonly used agent; levetiracetam (LEV) is a new anticonvulsant drug with fewer side effects. To compare the incidence of seizures in patients receiving either prophylactic PHT or LEV perioperatively, 971 patients undergoing a craniotomy were analysed retrospectively during a 2-year period. PHT was used routinely and LEV was administered when PHT was contraindicated. Seizures documented during the first 7 days after craniotomy were considered. A total of 235 patients were treated with an antiepileptic drug: 81 patients received LEV, and 154 patients, PHT. Two patients receiving LEV (2.5%) and seven receiving PHT (4.5%) had a seizure despite this treatment. No patient had a documented side effect or drug interaction. The data show that LEV may be an alternative option in patients with contraindications to PHT.

A mechanism for the rapid development of intracranial aneurysms: a case study.

BACKGROUND:Despite technical and diagnostic progress there are still open questions in the understanding of the pathophysiology of intracranial aneurysms. OBJECTIVE:Within 44 days we observed the de novo genesis and rupture of an aneurysm of the basilar artery in a patient. We performed computational fluid dynamics on 3-dimensional (3D) models of the inconspicuous vessel and the same vessel with aneurysm. Based on the simulations we propose a mechanism of genesis of fast-growing aneurysms. METHODS:Three-dimensional mesh models were built using computed tomography-angiography slices. Flow was modeled as a non-Newtonian blood model with shear-dependent dynamic viscosity. We investigated flow velocity, wall pressure, impingement point, wall shear stress (WSS), and asymmetric flows in 3D models of the vessel tree of the basilar artery. RESULTS:Impingement point and wall pressure had no clear relation to the origin of the aneurysm. The impingement point faded away during aneurysm growth. Instead we found an area of permanently low WSS in the original basilar artery. This location corresponded to the origin of the later developing aneurysm. Aneurysm growth was facilitated by an increasing overall expansion of the basilar tip and a constant decrease of WSS. CONCLUSION:Assuming a preexisting reduced resistibility of the vessel wall to pressure changes and an area of permanently low WSS, an increase in pressure induces geometrical changes. These cause changes of intravascular flow distribution, lowering the already low WSS in specific locations. This leads to endothelial damage in this area and to a decreasing stability of the vessel wall, causing aneurysm development, growth, and rupture.

Accuracy of core temperature measurement in deep hypothermic circulatory arrest

Deep hypothermia is an effective technique for neuroprotection in cardiac surgery. However, standard body temperature measurement may deviate from actual brain temperature. Therefore, we simultaneously measured brain and core temperatures during neurosurgical interventions in hypothermic circulatory arrest to determine its accuracy. Between 1994 and May 2007, 26 patients (12 female, mean age 46+/-14 years), with complex intracranial aneurysms, underwent resection or clipping applying closed chest cardiopulmonary bypass and hypothermic circulatory arrest via inguinal cannulation. During surgery, temperature probes were positioned in the brain, tympanum, bladder, rectum and pulmonary artery. Mean cardiopulmonary bypass time was 147+/-39 min, mean circulatory arrest time was 28+/-8 min. Brain temperatures were best reflected by bladder and tympanum probes (Pearsons correlation coefficients: bladder=0.83; tympanum=0.80; pulmonary artery=0.63; rectum=0.37; P<0.05). Mean deviations from brain temperature were +0.2+/-2.7 degrees C at the tympanum, -0.8+/-2.6 degrees C in the bladder, -0.7+/-2.6 degrees C in the pulmonary artery and -1.8+/-4.4 degrees C in the rectum. In conclusion, temperature monitoring in the bladder and tympanum reliably reflects brain temperature. Temperature measurements in the pulmonary artery and rectum are less optimal.

Normal values of volume flow in the internal carotid artery measured by a new angle-independant Doppler technique for evaluating cerebral perfusion

SummaryBackground. Cerebral blood flow is an important parameter when monitoring critically ill patients. Blood flow volume within the internal carotid artery (ICA) was shown to be correlated with the cerebral blood flow. The aim of our study was to provide normal values of the internal carotid artery volume flow using this new technology (QuantixND, Cardiosonix Ltd., Israel).Method. The QuantixND System is an angle-independant Doppler system that employs two digital high resolution ultrasound heads within one probe in an defined angle to each other. Thus several flow velocities within the vessel and the vessel diameter can be measured. 77 healthy patients (41 women, 36 men) were included and divided into age groups of ten-year intervals (mean age 48.9 years). Internal carotid artery flow was evaluated as well as physiological and hematological parameters (hematocrit, arterial blood pressure etc).Findings. We found that the blood flow volume in the ICA decreased significantly with age. No side-to-side effects as well as no gender-related differences could be observed. There was no influence of hemoglobin, hematocrit and blood pressure in this healthy population.Conclusions. There is an age-related decrease in blood flow volume with age that can be easily and exactly determined by the use of the new angle-independant doppler technique.

Effects of temporary clipping during aneurysm surgery

Abstract Objective: Intraoperative aneurysm rupture is associated with a high morbidity and mortality. Temporary vessel occlusion is an integral part of aneurysm clipping to avoid intraoperative hemorrhage. The information concerning the role of temporary occlusion regarding the development of cerebral vasospasm is sparse. The aim of this study was to provide more information in this field. Methods: We operated on 292 patients suffering from cerebral aneurysms. The data were reviewed from a prospectively collected databank, which includes information about the severity of subarachnoid hemorrhage, as well as transcranial Doppler data and surgical data such as temporary occlusion. Results: In 50% of our patients, temporary occlusion was performed during surgery. Twenty-nine percent showed an ischemic lesion in the CCT post-operatively, and in 58% of these patients, temporary occlusion was performed (versus 47% without temporary occlusion, p=0.09). The mean occlusion time was longer in patients with radiologic signs of infarction. Furthermore, patients having unfavorable outcome showed a longer temporary occlusion time. Thirty-four percent of patients who underwent temporary vessel occlusion developed vasospasm postoperatively (versus 20% without temporary occlusion, p<0.006). Temporary occlusion time correlated to the development of vasospasm as defined by transcranial Doppler flow velocity. Forty-eight percent of the patients treated using temporary occlusion suffered from middle cerebral artery aneurysm (versus 22% without temporary occlusion, p<0.0001). An increased blood flow velocity was mostly seen in this region (p<0.003). Conclusion: According to our results, it seems to be the possible that temporary vessel occlusion is an additional factor in aggravating vasospasm after aneurysmatic subarachnoid hemorrhage.

Fluorescein Sodium-Guided Surgery of Malignant Brain Tumors: History, Current Concepts, and Future Project.

Fluorescein sodium (FL)-guided resection has become an important and beneficial treatment method for malignant brain tumors. FL-guided resection improves the rate of gross total resection in high-grade gliomas (HGG) and cerebral metastases (CM). FL sensitively visualizes the disruption of the blood-brain barrier in the area surrounding malignant lesions, similar to contrast-enhanced T1-weighted MR sequences. This review of the current literature summarizes the history of FL in neurosurgery from 1946 until today. We discuss the molecular mechanism of FL accumulation in cerebral malignant tumors and provide an overview of the current practice of using FL and applying a dedicated surgical microscope filter. Additionally, we outline and discuss ongoing trials and future projects.

Neuromonitoring in carotid surgery: are the results obtained in awake patients transferable to patients under sevoflurane/fentanyl anesthesia?

Background Diagnostic accuracy studies of neuromonitoring devices during carotid endarterectomy in awake patients are limited by the question of the transferability to anesthetized patients. This study was designed to compare the different neuromonitoring parameters in patients under regional and general anesthesia with stump pressure as the primary endpoint and the courses of cerebral blood flow velocity (Vmca) measured by transcranial Doppler sonography, regional cerebral oxygen saturation (rSO2) measured by near-infrared spectroscopy, and the amplitude of somatosensory evoked potentials (SEP) as the secondary endpoints. Materials and Methods Ninety-six patients undergoing carotid endarterectomy were randomized to regional (n=48) or sevoflurane/fentanyl anesthesia (n=48) group. Absolute and relative changes of Vmca and rSO2 and the SEP amplitude were recorded at baseline, during carotid artery clamping, and after declamping. Intergroup differences (ß) were calculated by generalized estimation equations and linear regression analysis. Results Mean arterial pressure (P<0.001) and heart rate (P<0.001) were significantly higher in the regional anesthesia group. SP did not differ between both the groups (ß=−1.6; P=0.71). Vmca (ß=9.2; P<0.01) and rSO2 (ß=4.1; P<0.01) values were higher in the awake patients. After adjustment for mean arterial pressure, the differences of Vmca remained consistent (ß=9.3; P<0.01) whereas these of rSO2 during clamping (ß=2.9; P=0.105) and during reperfusion (ß=2.7; P=0.095) disappeared. No significant differences were found for Vmca(%) (ß=−1.0; P=0.80), rSO2(%) (ß=−1.4; P=1.8) and SEP (ß=−2.6; P=0.29). Conclusion Carotid artery clamping leads to similar results of stump pressure and similar relative changes of transcranial Doppler sonography, near-infrared spectroscopy, and SEP monitoring in patients under regional and sevoflurane/fentanyl anesthesia.