K. Niemann

Somatotopy of human hand somatosensory cortex revealed by dipole source analysis of early somatosensory evoked potentials and 3D-NMR tomography

Somatosensory evoked potentials (SEPs) to median nerve and finger stimulation were analyzed by means of spatio-temporal dipole modelling combined with 3D-NMR tomography in 8 normal subjects. The early SEPs were modelled by 3 equivalent dipoles located in the region of the brain-stem (B) and in the region of the contralateral somatosensory cortex (T and R). Dipole B explained peaks P14 and N18 at the scalp. Dipole T was tangentially oriented and explained the N20-P20, dipole R was radially oriented and modelled the P22. The tangential dipole sources T were located within a distance of 6 mm on the average and all were less than 9 mm from the posterior bank of the central sulcus. In 6 subjects the tangential sources related to finger stimulation arranged along the central sulcus according to the known somatotopy. The radial sources did not show a consistent somatotopic alignment across subjects. We conclude that the combination of dipole source analysis and 3D-NMR tomography is a useful tool for functional localization within the human hand somatosensory cortex.

A Quantitative Approach to Spatial Variation of Human Cerebral Sulci

The surfaces and the sulci of the lateral hemispheres of 30 postmortem brain specimens were three-dimensionally measured. The coordinates of all the structures registered constitute a digital brain model. The models were scaled linearly until they fitted a defined cuboid. Then all the models within the reference volume, each represented by a set of points, were considered together. The reference volume was divided into small cubic volume elements (voxels). Two parameters of the voxels were studied: the point density of each structure per voxel and the contribution index which designates how many of the hemispheres contribute points to a certain voxel. The latter parameter may serve as an index for the presence probability of a sulcus, which means the probability with which a sulcus will be contained in a defined volume element. The presence probability of a sulcus corresponds well with its first appearance in embryological development. Spatial variation in the early developing principal sulci is far less than in those which develop in later stages. As regards some defined regions of the brain, statements about the probable location of cortical areas in relation to the commissural system can be made.

A New Method in Computer-Assisted Imaging in Neuroanatomy

A procedure is described yielding computed images of postmortem brains with high topographic accuracy. Structures of the brain are traced and registered by means of a digitizer capable of measuring coordinates three-dimensionally. The information corresponding to one brain model is stored on a flexible disk with a capacity of 256 Kbytes. According to the output desired, the resulting brain images are either completely or partially displayed on the computer screen as stereo pairs. The brain models possess a local fidelity of about 1 mm. The images are useful in simultaneously studying superficial and central parts of the brain, spatial relationships of the various structures and the projection of deep structures onto the surface of the brain. A RAM of about 100 Kbytes is necessary for a program enabling the user to perform stereo projections, three-dimensional transformations and other image manipulations. The special features of anatomical computer imaging as compared to computed tomography (CT) and nuclear magnetic resonance imaging (NMR) are outlined. A combination of these different techniques seems to improve clinical diagnosis.

Digital brain atlas for structure localization in CT combined with EEG mapping

Localization of structures and regions in the brain beyond the scope of what can be clearly visualized and identified by neuroradiological imaging is very desirable in psychiatry. Because of the enormous variation in size and shape of the human cerebrum, this aim is difficult to achieve. To overcome these obstacles, we developed an averaged brain atlas to assist structure identification in CT scans

Anatomically Guided Neuronavigation: Sample Applications of the SulcusEditor in a Clinical Setting

The clinical use of the SulcusEditor (SE) on an everyday basis for preoperative analysis of 3D MRI data sets of neurosurgical patients is reported. The SE is applied to MRI data sets of patients with tumors in the central and the temporal region of the brain in order to trace the individual sulcal pattern. This leads to a better understanding of the topographical relationships between the tumor and the surrounding tissue. Hence the operating neurosurgeon is provided preoperatively with detailed knowledge concerning the area of interest, eventually leading to a reduction of the operating trauma. Three cases of patients with tumors in the central region are shown examplarily.

A new stereotaxic multiarchitectonic atlas of the human thalamus in a 3D MRI navigation system

In the context of MRI-guided stereotaxy a new stereotaxic atlas of the human thalamus was developed in order to improve anatomical definition and precision in the prediction of the exact location of thalamic targets. It is based on multiarchitectonic parcellation (Nissl, myelin, calcium-binding proteins). Sagittal atlas data were digitized and registered together with 3D MRI data sets. In a coarse to fine strategy the atlas-to-patient transformation matrix is refined. Thus the atlas is tailored to the individual anatomy of the patient. The effects of the rigid transformation are directly monitored on the computer screen using visible anatomical landmarks as control.

Automatic Transfer from Three-Dimensional Volume Elements in the Brain to Knowledge-Based Artificial Diagrams

Imaging of the brain in psychiatry is usually part of a diagnostic decision process. As a computer already produces the images, it may be useful to integrate image processing and rendering into a more general knowledge-based system, e.g., a decision support system. Such systems have several basic features in common. The digital image data must be modeled; that means they must be structured in a suitable abstract arrangement so that both image data and data representing knowledge may be handled and brought into a relationship. Suitable plans for the acquisition and integration of knowledge have to be made. General rules for Conclusions must be designed such that they result in medical decisions. If the system contains different levels of symbolic representation or different kinds of knowledge, mechanisms of inference between the different parts have to be defined. In particular, the method of presentation of the procedural outcome is crucial. The results should not only be presented in a clear and concise way which is easy to grasp, but the decisions of the system must also be made transparent to the physician, who in the end accepts, corrects, or discards the proposed decisions.

Computer-Assisted Anatomical Localization of Cortical Areas

In the fields of cranial computed tomography (CCT) and magnetic-resonance imaging (MRI) digital Computers generate powerful pictorial representations of physical data about the living brain. Both CCT and MRI series, however, contain more three-dimensional Information than that which is usually utilized. Although image processing, including three-dimensional reconstructions of scan series, is gaining increasing popularity, literature about the Integration of anatomical know-ledge remains rather scanty.

Mitteln bei 3-D-Rekonstruktionen biologischer Objekte

Verfahren zur dreidimensionalen Rekonstruktion von Serienschnitten im Bereich Biowissenschaften haben sich zu einer solchen Vielfalt entwikkelt, das ihre kritische Wurdigung eigene Reviews rechtfertigt1). Wahrend immer aufwendigere Algorithmen immer mehr Prozessorleistung erfordern, um Einzelrekonstruktionen beliebiger Komplexitat in vertretbaren Zeiten zu erhalten, ist ein biologiespezifischer Aspekt bisher kaum berucksichtigt worden: die Vari ati on als individuell verschiedene Lage und Auspragung von Strukturen. So werden z.B. fur die Beurteilung computertomographischer Schnittserien des Gehirns als Referenz Atlanten mit zweidimensionalen Schnittserien individueller Gehirne, meist mit fester Winkelvorgabe, verwandt. Auf dem Hintergrund der zunehmend besseren Qualitat digitaler Rontgenbilder ist der Wunsch des Klinikers zu verstehen, diese fur eine genauere lokalisatorische Diagnostik verfugbar zu machen — bei gleichzeitig vertretbarer Strahlenbelastung fur den Patienten.