High-resolution 3D-constructive interference in steady-state MR imaging and 3D time-of-flight MR angiography in neurovascular compression: a comparison between 3T and 1.5T.

BACKGROUND AND PURPOSE: High-resolution MR imaging is useful for diagnosis and preoperative planning in patients with NVC. Because high-field MR imaging promises higher SNR and resolution, the aim of this study was to determine the value of high-resolution 3D-CISS and 3D-TOF MRA at 3T compared with 1.5T in patients with NVC. MATERIALS AND METHODS: Forty-seven patients with NVC, trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia were examined at 1.5T and 3T, including high-resolution 3D-CISS and 3D-TOF MRA sequences. Delineation of anatomic structures, overall image quality, severity of artifacts, visibility of NVC, and assessment of the SNR and CNR were compared between field strengths. RESULTS: SNR and CNR were significantly higher at 3T (P < .001). Significantly better anatomic conspicuity, including delineation of CNs, nerve branches, and assessment of small vessels, was obtained at 3T (P < .02). Severity of artifacts was significantly lower at 3T (P < .001). Consequently, overall image quality was significantly higher at 3T. NVC was significantly better delineated at 3T (P < .001). Six patients in whom NVC was not with certainty identifiable at 1.5T were correctly diagnosed at 3T. CONCLUSIONS: Patients with NVC may benefit from the higher resolution and greater sensitivity of 3T for preoperative assessment of NVC, and 3T may be of particular value when 1.5T is equivocal.

Diagnosis and neurosurgical treatment of glossopharyngeal neuralgia: clinical findings and 3-D visualization of neurovascular compression in 19 consecutive patients.

Glossopharyngeal neuralgia is a rare condition with neuralgic sharp pain in the pharyngeal and auricular region. Classical glossopharyngeal neuralgia is caused by neurovascular compression at the root entry zone of the nerve. Regarding the rare occurrence of glossopharyngeal neuralgia, we report clinical data and magnetic resonance imaging (MRI) findings in a case series of 19 patients, of whom 18 underwent surgery. Two patients additionally suffered from trigeminal neuralgia and three from additional symptomatic vagal nerve compression. In all patients, ipsilateral neurovascular compression syndrome of the IX cranial nerve could be shown by high-resolution MRI and image processing, which was confirmed intraoperatively. Additional neurovascular compression of the V cranial nerve was shown in patients suffering from trigeminal neuralgia. Vagal nerve neurovascular compression could be seen in all patients during surgery. Sixteen patients were completely pain free after surgery without need of anticonvulsant treatment. As a consequence of the operation, two patients suffered from transient cerebrospinal fluid hypersecretion as a reaction to Teflon implants. One patient suffered postoperatively from deep vein thrombosis and pulmonary embolism. Six patients showed transient cranial nerve dysfunctions (difficulties in swallowing, vocal cord paresis), but all recovered within 1 week. One patient complained of a gnawing and burning pain in the cervical area. Microvascular decompression is a second-line treatment after failure of standard medical treatment with high success in glossopharyngeal neuralgia. High-resolution MRI and 3D visualization of the brainstem and accompanying vessels as well as the cranial nerves is helpful in identifying neurovascular compression before microvascular decompression procedure.

Virtual neuroendoscopy: MRI-based three-dimensional visualization of the cranial nerves in the posterior cranial fossa.

This article presents the advances of three-dimensional (3D) virtual neuroendoscopy of the cranial nerves (CN) in the posterior fossa. Interactive 3D visualizations were generated and the anatomical landmarks, such as the root entry/exit zones (REZ) and cisternal segments of the CN were evaluated. Twenty patients (M:F, 6:14) with trigeminal neuralgia (TN) underwent MRI constructive interference in steady state (MRI(CISS)) imaging and subsequent 3D visualization based on explicit segmentation of the MRI(CISS) data and interactive evaluation with direct volume rendering including implicit segmentation. The 3D topography of the interesting CN V-X were evaluated with interactive and virtual neuroendoscopy. The anatomical landmarks of the CN V-X could be visualized in all 20 cases (100%). The systematic application of virtual neuroendoscopy could be realized in all patients for the non-invasive observation of the CN without any technical difficulties. Interactive 3D visualization using explicit and implicit techniques for segmentation, and 3D direct volume rendering is demonstrated to successfully identify 3D neurovascular relations in patients with trigeminal neuralgia. It has the ability to provide a useful tool for surgeons in the pre- and intraoperative evaluation of such cases.

[Improvement of diagnosis and treatment of glossopharyngeal neuralgia]. / Verbesserung der Diagnostik und Therapie der Glossopharyngeusneuralgie.

Differential diagnosis of neuralgias affecting the cranial nerves and of facial pain is often difficult. Glossopharyngeal neuralgia is much less common than trigeminal neuralgia and is not well known. Idiopathic neuralgia of the glossopharyngeal nerve sometimes occurs in association with neurovascular compression syndrome of the vagus and trigeminal nerves. High-resolution MRI of the brain stem with three-dimensional visualization allows a secure diagnosis of neurovascular compression and is useful in the planning of appropriate microsurgical decompression (Jannetta's operation).

Neurovascular relationship at the trigeminal root entry zone in persistent idiopathic facial pain: findings from MRI 3D visualisation.

BACKGROUND: Patients with atypical neuralgia or atypical facial pain have been surgically treated with microvascular decompression (MVD) of the trigeminal root entry zone (TREZ). There are no data regarding the sensitivity and specificity of a vessel-TREZ relationship as a cause of pain in patients with persistent idiopathic facial pain (PIFP) according to the definition given by the International Headache Society (IHS). METHODS: The TREZ was visualised by 3D CISS MRI in 12 patients with unilateral PIFP according to the IHS criteria. RESULTS: The frequency of artery-TREZ, vein-TREZ, or vessel (artery/vein)-TREZ contacts on the symptomatic and asymptomatic sides did not differ significantly. On the symptomatic side, vessel-TREZ contact was found in 58% of patients (sensitivity). On the asymptomatic side, vessel-TREZ contact was absent in 33% of patients (specificity). CONCLUSIONS: On the basis of the low sensitivity and specificity found in the present study, PIFP cannot be attributed to a vessel-TREZ contact, and therefore, pain relief after MVD cannot be expected.

Determination of the elasticity parameters of brain tissue with combined simulation and registration.

Reliable elasticity parameters describing the behavior of a given material are an important issue in the context of physically-based simulation. In this paper we introduce a method for the determination of the mechanical properties of brain tissue. Elasticity parameters Young's modulus E and Poisson's ratio nu are estimated in an iterative framework coupling a finite element simulation with image registration. Within this framework, the outcome of the simulation is parameterized with both elasticity moduli that are automatically varied until optimal image correspondence between the simulated and the intraoperative data is achieved. We calculated optimal mechanical properties of brain tissue in six cases. The statistical analysis of the obtained values showed a good correlation of the results, thus proving the value of the method. An approach combining simulation and registration for the determination of the mechanical brain tissue properties is presented. This contributes to performing reliable physically-based simulation of soft tissue movement.

Magnetic source imaging supports clinical decision making in glioma patients.

OBJECTIVE: This study addresses the potential utility of preoperative functional imaging with magnetoencephalography (MEG) for the selection of glioma patients who are likely to benefit from resective surgical treatment regarding postoperative morbidity. METHODS: One hundred and nineteen patients with gliomas adjacent to sensorimotor, visual and speech related brain areas were investigated preoperatively with a MAGNES II biomagnetometer. In each patient the pre-surgical evaluation was focussed on the visual, sensorimotor cortex and/or of the speech related brain areas. A grading system was then used according to the distance of the MEG activation sources to the nearest tumour border to determine the further treatment. The therapeutic options consisted in conservative treatment, stereotactic biopsy and/or a radiation and chemotherapy, substantial cytoreduction and the gross total removal of the lesion. RESULTS: From 119 investigated patients, 55 patients (46.2%) were not considered for surgery due to tumour invasion to functional cortex. Sixty four patients (53.8%) were chosen for resective surgery. In the surgical group only four patients (6.2%) suffered from neurological deterioration. CONCLUSIONS: Magnetic source imaging (MSI) proved to be a valuable help in the clinical decision making process of lesions adjacent to functional important brain areas. The relative high number of patients in whom MSI warns of the postoperative crippling sequelae may lead to a better selection of patients who benefit from resective surgery. This method may help to find the patients for whom conservative treatment seems to be more favourable concerning quality of life in the surviving time.

Correlation of sensorimotor activation with functional magnetic resonance imaging and magnetoencephalography in presurgical functional imaging: a spatial analysis.

In this study we investigated the spatial heterotopy of MEG and fMRI localizations after sensory and motor stimulation tasks. Both methods are frequently used to study the topology of the primary and secondary motor cortex, as well as a tool for presurgical brain mapping. fMRI was performed with a 1.5T MR system, using echo-planar imaging with a motor and a sensory task. Somatosensory and motor evoked fields were recorded with a biomagnetometer. fMRI activation was determined with a cross-correlation analysis. MEG source localization was performed with a single equivalent current dipole model and a current density localization approach. Distances between MEG and fMRI activation sites were measured within the same anatomical 3-D-MR image set. The central region could be identified by MEG and fMRI in 33 of 34 cases. However, MEG and fMRI localization results showed significantly different activation sites for the motor and sensory task with a distance of 10 and 15 mm, respectively. This reflects the different neurophysiological mechanisms: direct neuronal current flow (MEG) and secondary changes in cerebral blood flow and oxygenation level of activated versus non activated brain structures (fMRI). The result of our study has clinical implications when MEG and fMRI localizations are used for pre- and intraoperative brain mapping. Although both modalities are useful for the estimation of the motor cortex, a single modality may err in the exact topographical labeling of the motor cortex. In some unclear cases a combination of both methods should be used in order to avoid neurological deficits.

Local and remote visualization techniques for interactive direct volume rendering in neuroradiology.

The increasing capabilities of magnetic resonance (MR) imaging and multisection spiral computed tomography (CT) to acquire volumetric data with near-isotropic voxels make three-dimensional (3D) postprocessing a necessity, especially in studies of complex structures like intracranial vessels. Since most modern CT and MR imagers provide limited postprocessing capabilities, 3D visualization with interactive direct volume rendering requires expensive graphics workstations that are not available at many institutions. An approach has been developed that combines fast visualization on a low-cost PC system with high-quality visualization on a high-end graphics workstation that is directly accessed and remotely controlled from the PC environment via the Internet by using a Java client. For comparison of quality, both techniques were applied to several neuroradiologic studies: visualization of structures related to the inner ear, intracranial aneurysms, and the brainstem and surrounding neurovascular structures. The results of pure PC-based visualization were comparable with those of many commercially available volume-rendering systems. In addition, the high-end graphics workstation with 3D texture-mapping capabilities provides visualization results of the highest quality. Combining local and remote 3D visualization allows even small radiologic institutions to achieve low-cost but high-quality 3D visualization of volumetric data.

[Rapid interactive 3-D imaging of the temporal bone with "direct volume rendering"]. / Schnelle interaktive 3D-Darstellung des Felsenbeins mit "direktem Volume Rendering".

INTRODUCTION: For the first time, the relatively new method of interactive direct volume rendering (dVR) allows for a fast and direct three-dimensional visualization of spiral CT data without any manual, explicit segmentation. This study was performed to prove whether dVR is capable of providing a meaningful three-dimensional visualization of the structures within the temporal bone. PATIENTS AND METHODS: In ten patients a three-dimensional visualization of the structures of the inner and middle ear was performed from spiral CT data on a commercially available graphics workstation. RESULTS: The cochlea and semicircular canals were visualized in good quality in all patients. The ossicles and bony facial canal were visualized in good or fair quality in most cases. The time needed for the visualization of the data and all target structures was less than 15 min in all cases. CONCLUSIONS: Three-dimensional visualization of the structures within the temporal bone from high-resolution spiral CT data using dVR is easily performed in a very short time on standard graphics workstations. This allows integrating three-dimensional visualizations into routine clinical work.

Intraoperative compensation for brain shift.

BACKGROUND: Tumor removal, brain swelling, the use of brain retractors, and cerebrospinal-fluid drainage all result in an intraoperative brain deformation that is known as brain shift. Thus, neuronavigation systems relying on preoperative image data have a decreasing accuracy during the surgical procedure. Intraoperative image data represent the correct anatomic situation, so their use may compensate for the effects of brain shift. METHODS: In a series of 16 brain tumor patients, we used intraoperative magnetic resonance (MR) imaging to obtain 3-D data, which were then transferred to the microscope-based neuronavigation system. With the help of bone fiducial markers these images were registered intraoperatively, updating the neuronavigation system. RESULTS: In all patients the updating of the neuronavigation system with the intraoperative MR data was successful. It led to reliable neuronavigation with high accuracy; the mean registration error of the update procedure in all patients was 1.1 mm. The updating procedure added about 15 minutes to the operation time. In all patients the area suggestive of remaining tumor was reached and the additional tumor could be resected, resulting in a complete tumor removal in 14 patients. In the remaining patients extension of the tumor into eloquent brain areas prevented a complete excision. CONCLUSIONS: The update of a neuronavigation system with intraoperative MR images reliably compensates for the effects of brain shift. This method allows completion of tumor removal in some difficult brain tumors.

Quantification of, visualization of, and compensation for brain shift using intraoperative magnetic resonance imaging.

OBJECTIVE: Modern neuronavigation systems lack spatial accuracy during ongoing surgical procedures because of increasing brain deformation, known as brain shift. Intraoperative magnetic resonance imaging was used for quantitative analysis and visualization of this phenomenon. METHODS: For a total of 64 patients, we used a 0.2-T, open-configuration, magnetic resonance imaging scanner, located in an operating theater, for pre- and intraoperative imaging. The three-dimensional imaging data were aligned using rigid registration methods. The maximal displacements of the brain surface, deep tumor margin, and midline structures were measured. Brain shift was observed in two-dimensional image planes using split-screen or overlay techniques, and three-dimensional, color-coded, deformable surface-based data were computed. In selected cases, intraoperative images were transferred to the neuronavigation system to compensate for the effects of brain shift. RESULTS: The results demonstrated that there was great variability in brain shift, ranging up to 24 mm for cortical displacement and exceeding 3 mm for the deep tumor margin in 66% of all cases. Brain shift was influenced by tissue characteristics, intraoperative patient positioning, opening of the ventricular system, craniotomy size, and resected volume. Intraoperative neuronavigation updating (n = 14) compensated for brain shift, resulting in reliable navigation with high accuracy. CONCLUSION: Without brain shift compensation, neuronavigation systems cannot be trusted at critical steps of the surgical procedure, e.g., identification of the deep tumor margin. Intraoperative imaging allows not only evaluation of and compensation for brain shift but also assessment of the quality of mathematical models that attempt to describe and compensate for brain shift.

Virtual labyrinthoscopy: visualization of the inner ear with interactive direct volume rendering.

Computed tomography (CT) is the modality of choice for detailed imaging of the bony labyrinth. Usually, information about the complex three-dimensional anatomic structures of the inner ear is presented as two-dimensional section images. Interactive direct volume rendering is a powerful method for visualization of the labyrinth. Unlike other visualization methods, direct volume rendering enables direct visualization of the bony labyrinth without explicit segmentation prior to the visualization process. Direct volume rendering was applied to visualization of the structures of the temporal bone in five patients without pathologic conditions and four patients with pathologic conditions. In all cases, clear representations of the bony labyrinth and the facial canal were provided. Because standard CT examinations combined with interactive visualization based on direct volume rendering are used, the method is fast and flexible. Therefore, this approach is applicable in routine clinical work. Problems occur in patients with effusion in the temporal bone because adjustment of imaging parameters for proper delineation of the target structures is difficult in this situation. However, direct volume rendering can produce meaningful images of high quality even in these problematic cases. The term virtual labyrinthoscopy is suggested for visualization of the labyrinth by using direct volume rendering.