Knut E. W. Eberhardt

Combining local and remote visualization techniques for interactive volume rendering in medical applications

For a comprehensive understanding of tomographic image data in medicine, interactive and high-quality direct volume rendering is an essential prerequisite. This is provided by visualization using 3D texture mapping which is still limited to high-end graphics hardware. In order to make it available in a clinical environment, we present a system which uniquely combines local desktop computers and remote high-end graphics hardware. In this context, we exploit the standard visualization capabilities to a maximum which are available in the clinical environment. For 3D representations of high resolution and quality we access the remote specialized hardware. Various tools for 2D and 3D visualization are provided which meet the requirements of a medical diagnosis. This is demonstrated with examples from the field of neuroradiology which show the value of our strategy in practice.

MR cisternography: a new method for the diagnosis of CSF fistulae

The aim of this study was to compare a new MRI method for detecting the existence of cerebrospinal fluid (CSF) fistulae, i. e. MR cisternography, with CT cisternography. In a prospective study, 30 patients with post-traumatic CSF fistulae were examined. The MR examinations were performed with a 1.0-T whole-body MR system, using two T2*-weighted sequences, a 3D PSIF (time-inversed fast imaging with steady-state precession, FISP) and a 3D constructive interference steady-state (CISS) sequence. The results of MRI and CT cisternography were compared with the surgical findings. The sensitivity in detecting CSF fistulae with MR cisternography (PSIF: 89.9 %; CISS: 93.6 %) was higher than with CT cisternography (72.3 %). The sensitivity of CT cisternography at detecting CSF fistulae in patients with a size of dural lesion less than 2 mm or in patients with multiple dural lesions is significantly lower compared with the MR method. Although the localization of CSF fistulae always proved possible with MR cisternography, this could only be accomplished wih CT in 70 % of cases. The MR cisternography technique is a new examination method with a higher sensitivity for the detection of CSF fistulae than CT cisternography. The CISS technique is superior compared with PSIF and should be used in patients with high-flow CSF fistulas.

Clinical applications of 1H-MR spectroscopy in the evaluation of epilepsies – What do pathological spectra stand for with regard to current results and what answers do they give to common clinical questions concerning the treatment of epilepsies?

Nuclear magnetic resonance spectroscopy (1H‐MRS) is a non‐invasive method in detecting abnormal spectra of various brain metabolites containing N‐acetylaspartate (NAA), Choline (Cho), Creatine (Cr), γ‐Aminobutyric acid (GABA) and Glutamate. Technical processing of the MR‐systems, improved automated shimming methods and further development of special shim coils increase the magnetic field homogeneity and lead to a better spectral quality and spectral resolution. The handling of the systems becomes more user‐friendly and is more likely to be used in routine diagnostics. The 1H‐MRS has become a diagnostic tool for assessing a number of diseases of the central nervous system mainly including epilepsies and brain tumours. The role of 1H‐MRS in the assessment of epilepsies will probably increase in future. In the following article, the principles of 1H‐MRS and an overview of it in the evaluation and treatment of epilepsies with special regard to temporal lobe epilepsies (TLE) has been illustrated.

Fast Analysis of Intracranial Aneurysms Based on Interactive Direct Volume Rendering and CTA

The diagnosis of intracranial aneurysms and the planning of related interventions is effectively assisted by spiral CT-angiography and interactive direct volume rendering. Based on 3D texture mapping, we suggest a hardware accelerated approach which provides fast and meaningful visualization without time-consuming pre-processing. Interactive tools provide reliable measurement of distance and volume allowing to calculate the size of vessels and aneurysms directly within the 3D viewer. Thereby, the expensive material required for coiling procedures is estimated more precisely. Interactively calculated shaded isosurfaces, presented in [1] were evaluated in respect of enhanced perception of depth. Based on the integration into OpenInventor, global overview and simultaneous detail information is provided by communicating windows allowing for intuitive and user-guided navigation. Due to an average of 15–20 minutes required for the complete medical analysis, our approach is expected to be useful for clinical routine. Additional registration and simultaneous visualization of MR and CT-angiography gives further anatomical orientation. Several examples demonstrate the potential of our approach.

Three-dimensional MR myelography of the lumbar spine: comparative case study to X-ray myelography

Conventional myelography was compared with a new type of MR technique using a fat-suppressing 3D fast imaging with steady precession (FISP) sequence for diagnosis of the lumbar root compression syndrome. 80 patients with discogenic disease in the lumbar spine were examined with a 1.0-T whole-body MR system (Siemens Magnetom Impact, Erlangen, Germany). A strongly T2*-weighted 3D FISP sequence was applied in the sagittal orientation. To obtain fat suppression, a frequency-selective 1-3-3-1 prepulse was applied prior to the imaging sequence. The acquired 3D data set was evaluated using a maximum intensity projection (MIP) program. The measurement time was 7 min, 47 s. Magnetic resonance myelography has significant advantages over conventional myelography, particularly in cases of extreme spinal canal stenosis. Compared with the conventional method, this new MR technique shows comparable sensitivity in the visualization of the spinal nerve roots in the lumbar spine.

The significance of bilateral CSI changes for the postoperative outcome in temporal lobe epilepsy.

Purpose In a prospective study, we evaluated the significance of preoperative bilateral chemical shift spectroscopy imaging (CSI) changes for the prognosis of postoperative seizure outcome in the surgical treatment of patients with temporal lobe epilepsy (TLE). Method CSI using multivoxel spectroscopy was performed. Twenty-six consecutive TLE patients scheduled for epilepsy surgery were included. To evaluate the value of the CSI with respect to postoperative seizure outcome, discriminant analysis with ipsilateral and contralateral CSI was performed. Results The discriminant analysis showed that the contralateral metabolic changes alone are able to predict seizure outcome whereby 92.3% of cases were correctly classified. Upon comparison of the two groups of seizure-free and non-seizure-free patients with respect to contralateral metabolic changes, the difference proved to be highly significant (paired t test:t = −6.3, df = 24, p < 0.001). Conclusion Bilateral metabolic CSI changes have a predictive value for the postoperative outcome in patients with TLE. In patients with severe bilateral metabolic changes, poor seizure outcome is a likely result.

Magnetic resonance fiber density mapping of age-related white matter changes.

OBJECTIVES To introduce fiber density mapping (FDM) for investigation of age-related white matter (WM) changes and to compare its capabilities with conventional diffusion tensor imaging (DTI) post-processing. METHODS DTI data with 1.9 mm(3) isotropic voxels were acquired from 44 healthy volunteers (18-88 years) at 3T. FDM is a 3-step approach which includes diagonalization of the diffusion tensor, fiber reconstruction for the whole brain, and calculation of fiber density (FD) values. Maps of fractional anisotropy (FA) and mean diffusivity (MD) were additionally calculated. Voxel-based analyses were performed to determine volume clusters of significant correlation with age. Bivariate linear regression models and Hotelling-Williams tests were used to detect significant differences between correlations. RESULTS FDM detected a larger WM volume affected by age-related changes concomitant with fewer significant clusters compared to FA and MD. This indicates that WM alterations due to normal aging occur rather globally than locally. FD values showed a significant stronger correlation with age in frontal lobes (prefrontal and precentral gyrus), limbic lobes (cingulate and parahippocampal gyrus), the corpus callosum (genu) and temporal lobes. CONCLUSIONS FDM shows higher sensitivity for detection of age-related WM changes because it includes all surrounding fiber structures into the evaluation of each DTI data voxel.

MR-Spektroskopie und T2-Relaxometrie bei kryptogener Temporallappenepilepsie und postoperativer Prognose

ZusammenfassungBei der epilepsiechirurgischen Behandlung kryptogener Temporallappenepilepsien kommt neben der Lokalisation des epileptischen Fokus der Beurteilung der Prognose hinsichtlich der postoperativen Anfallskontrolle Bedeutung zu. Hierbei kann die Protonen-MR-Spektroskopie (1HMR-Spekroskopie oder Chemical Shift Imaging CSI) nützliche Informationen liefern. Technik und Befunde des CSI im Vergleich zu einem Normkollektiv werden bei Patienten mit kryptogenen Temporallapenepilepsien dargestellt. Hierbei werden Ergebnisse der 1HMR-Spekroskopie (NAA/Cholin) und der T2-Relaxometrie mit der postoperativen Anfallskontrolle verglichen. Die Ergebnisse zeigen, dass die 1HMR-Spekroskopie mit NAA/Cholin wichtige Informationen für die Prädiktion hinsichtlich der postoperativen Anfallskontrolle liefert.SummaryThe preoperative localization of pharmaco-resistent focal epilepsies before surgery and the prognosis concerning seizure outcome are both of importance. In addition to conventional MRI diagnostics for the detection of small epileptogenic lesions, proton magnetic resonance spectroscopic imaging (HMR spectroscopy) can be useful for assessing the bilaterality of pathological changes in cryptogenic temporal lobe epilepsies. The technique and findings of HMR spectroscopy are reported in patients with cryptogenic temporal lobe epilepsies. The findings indicate that chemical shift imaging (CSI) investigations of the ipsilateral and contralateral hemispheres provide important information for the prediction of seizure outcome after epilepsy surgery.

High-resolutation magnetic resonance imaging of the endolymphatic duct and sac

An anatomical study was carried out to determine the extent to which magnetic resonance imaging (MRI) could delineate inner ear structures. Anatomical preparations of human petrous temporal bone were examined and compared with the results of MRI in 20 healthy subjects to see whether the structures of the inner ear could be visualized. Imaging of the subjects was carried out in a 1.0-T MRI scanner (Siemens Magnetom Impact). Two stronglyT2*-weighted sequences were used: a 3D-PSIF sequence and a 3D-CISS sequence. The 3D data sets were postprocessed using a Maximum Intensity Projection (MIP) program. Our investigations show that it is possible to obtain accurate visualization of structures with a diameter of under 1 mm. In all 20 subjects it was possible to identify both the endolymphatic duct and the endolymphatic sac.

Schnelle interaktive 3D-Darstellung des Felsenbeins mit direktem Volume Rendering

ZusammenfassungHintergrund. Die relativ neue Methode des interaktiven “direkten Volume Renderings” (dVR) erlaubt erstmals eine schnelle, direkte 3D-Visualisierung von Spiral-CT-Datensätzen ohne manuelle, explizite Segmentierung. In dieser Studie sollte die Eignung dieses Verfahrens zur Darstellung der Felsenbeinstrukturen untersucht werden. Patienten und Methode. Bei 10 Patienten wurde eine 3D-Visualisierung der Innen- und Mittelohrstrukturen aus hochaufgelösten Spiral-CT-Daten mit dVR auf einer kommerziell erhältlichen Workstation durchgeführt. Ergebnisse. Die Kochlea und die Canales semicirculares ließen sich in guter Qualität, die Ossikel und der Fazialiskanal in den meisten Fällen in guter oder befriedigender Qualität darstellen. Die benötigte Zeit zur Visualisierung der Datensätze und Beurteilung der Zielstrukturen lag in allen Fällen <15 min. Schlussfolgerungen. Die 3D-Visualisierung der Felsenbeinstrukturen gelingt mit dVR auf Standardgraphik-Workstations in kurzer Zeit mit akzeptabler Qualität aus Dünnschicht-Spiral-CT-Datensätzen. Damit steht erstmals ein Verfahren zur Verfügung das die Integration der 3D-Darstellung von Felsenbeinstrukturen in die klinische Routinediagnostik zulässt.AbstractIntroduction. 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.