Biomedical subjects
Publications and source records attributed to M G Abele.
A brief survey of the permanent magnet design techniques that are made possible by the availability of modern magnetic materials is followed by experimental results and some consideration of their practical applicability to the realization of MRI magnets.
The three-dimensional data obtained by computed tomographic (CT) scanning offer an advantage in using this imaging technique for stereotactic surgical procedures. This requires interfacing of CT image data with a stereotactic guide. In the performance of functional procedures where the surgical target must be identified from brain landmarks, such as the anterior and posterior commissures, an image reconstruction technique that presents in an image high spatial resolution structural information must be used. The description of a fully hardware- and software-interfaced CT-directed stereotactic surgical system is presented. The logic of operation and examples of images reconstructed with a high spatial resolution algorithm are illustrated. The experimentally determined measurement of an electrode tip localization with this system is within 1 pixel or +/- 0.5 mm in any direction.
A fully interfaced computerized tomographic system has been designed and constructed. A prototype Philips Medical Systems Inc. translate-rotate body scanner has been modified to accommodate a specially designed head holder and stereotactic guide. A high resolution partial scanning algorithm is used to achieve improved spatial resolution in comparison to conventional algorithms. Integration of scanning data with the geometry of the guide system is achieved with software control.
Designing gradient coils for permanent magnets requires modeling the interaction between the currents and the ferromagnetic material. We have developed and tested an iterative design approach based on the boundary element method. The power dissipated by the gradient coil is treated as a constraint of the minimization problem. The technique is illustrated on a magnet with a rectangular prismatic cavity and two ferromagnetic plates adjacent to the coil. The procedure improved the linearity of the field from 10.5% to 3.4% and reduced the power dissipation to 63% of the power of the unoptimized coil. The optimized distribution of currents has been transformed to variable locations of coil windings without loss of gradient uniformity. The new approach significantly reduces computation time and memory storage and yields practical designs of gradient coils for permanent magnets.
A technique is described for three-dimensional reconstruction of human diencephalic structures based on information contained in a widely used stereotaxic brain atlas. Various methods of graphically representing the obtained diencephalic volumes are discussed and examples are given. The anatomic information contained in the computerized atlas can be implemented with computed tomography performed under stereotaxic conditions. Volume data provided by the tomograms are used for three-dimensional "stretching" of the volumes presented in the atlas. Improved accuracy in identifying "invisible" diencephalic targets in functional stereotaxic neurosurgery is expected to result from this new technique.