Andre Folkers

Content-based image retrieval using Fourier descriptors on a logo database

A system that enables the pictorial specification of queries in an image database is described. The queries are comprised of rectangle, polygon, ellipse, and B-spline shapes. The queries specify which shapes should appear in the target image as well as spatial constraints on the distance between them and their relative position. The retrieval process makes use of an abstraction of the contour of the shape which is invariant against translation, scale, rotation, and starting point, that is based on the use of Fourier descriptors. These abstractions are used in a system to locate logos in an image database. The utility of this approach is illustrated using some sample queries.

Realtime bioelectrical data acquisition and processing from 128 channels utilizing the wavelet-transformation

Abstract We propose a versatile signal processing and analysis framework for bioelectrical data, and in particular for neural recordings and EEG. Within this framework the signal is decomposed into subbands using fast wavelet transform algorithms, executed in real-time on a current digital signal processor hardware platform. The decomposition is used to perform various processing and analysis tasks. Besides fast implementation of high, band, and low pass filters, the decomposition is used for denoising and lossy, as well as lossless compression. Furthermore specific electrophysiologic analysis tasks like spike detection and sorting are performed within this decomposition scheme.

Test of spike-sorting algorithms on the basis of simulated network data

Results of spike-sorting algorithms are usually compared with recorded signals which themselves underly interpretations, distortions and errors. Our approach is to provide and compare physiological extracellular potential data by a realistic cortical network simulation. For this purpose, we utilize the neural simulator GENESIS and simulate a region of rat hippocampus containing 90 cells. We are able to “record” simulated extracellular potentials from “virtual electrodes” and produce test data closely resembling multisite neuronal recordings. Our realisitic, arti8cial data are complex and almost natural in appearance; however, current spike detection schemes appear unable to reliably detect all spikes produced. c � 2002 Elsevier Science B.V. All rights reserved.

A 64(128)-channel multisite neuronal recording system.

We used a recently described all-dry silicon etch process for SOI wafers to fabricate 64-site electrode arrays in stereotrode arrangement for acute cortical recordings. The fork-like probes are connected to preamplification units by flexible, Y-shaped interconnects. This facilitates maximal experimental flexibility for simultaneously recording from all available channels from the cortex of anaesthetised rats. Preconditioned signals are amplified by a novel modular main amp, which may be software or dial controlled. Signals are 16bit digitized, recorded, analyzed, stored and processed on a DSP-based modular data acquisition system. Digital data is processed, filtered and denoised on all up to (4*32) 128 channels based on an extremely fast wavelet transformation framework.

Processing pictorial queries with multiple instances using isomorphic subgraphs

An algorithm is given for processing pictorial query specifications that consist of a query image and a similarity level that must hold between the query image and database images. The similarity level specifies the contextual similarity (how well the content of one image matches that of another) as well as the spatial similarity (the relative locations of the matching symbols in the two images). The algorithm differs from previous approaches in its ability to handle multiple instances of each object in both the query and database images by searching for isomorphic subgraphs. The running time of the algorithm is O(m 2/sup m/) in the worst case where all symbols in both the query and database image are from the same class, but falls far below this bound in the presence of spatial constraints.

TOWARDS A VERSATILE SYSTEM FOR ADVANCED NEURONAL RECORDINGS USING SILICON MULTISITE MICROELECTRODES.

1 Med. Universitat zu Lubeck, Institut fur Signalverarbeitung und Prozesrechentechnik, Seelandstr. 1a), 23569 Lubeck, Germany. * corresponding author 2 ACREO AB, 16440 Stockholm-Kista, Sweden 3 Uwe Thomas RECORDING, Giessen, Germany 4 Universitaire Instelling Antwerpen, Laboratory for Theoretical Neurobiology, 2610 Antwerp, Belgium 5 Istituto Nazionale Neurologico Carlo Besta, Neurofisiologia Sperimentale, 20133 Milano, Italy 6 Aalborg Universitet, Center for Sensory-Motor interaction, 9220 Aalborg, Denmark

NEUROSURGERY BY MULTICHANNEL ELECTROPHYSIOLOGY, 3D NAVIGATION, AND CUSTOMIZED DATABASE

Accuracy is a main issue in intracranial surgeries like e.g. the implantation of deep brain stimulators. Surgeries are planned on the basis of preoperative CTor MR-scans, thus neglecting the intraoperative brainshift. Microelectrode recordings are performed in order to enhance the accuracy. We present an all-in-one solution to assist stereotactic neurosurgeons: Our system records and analysis electrophysiological signals from 32 channels intraoperatively in realtime and presents them related to anatomical structures. Our hardware consists of DSP technology integrated into a standard PC. We wrote our own visualization and analysis software. So far, only few experienced specialists perform functional neurosurgery. By introducing a customized database into our system, we seek to shorten the “experience gap” between specialists and novices. The database holds electrophysiological signals and describing features related to an anatomical coordinate system, thus presenting the novice what he has to expect in a certain brain region.

AN INTEGRATED SYSTEM TO TRIGGER FEEDBACK-COUPLED EVENT RELATED BRAIN POTENTIALS

INTRODUCTION Long going physiological research [1], strongly suggests that the macroscopic electric (i.e. EEG) state of a subjects brain influences the responses to defined stimuli, manifested in evoked (or event-related) potentials. Since this evidence is up till now based on post-hoc evaluation of EEG data, we designed and built a data acquisition system able to fully digitally record raw EEG signals from up to 32 scalp electrodes in standard configuration over a prolonged period of time. The design was furthermore meant to evaluate the incoming signals according to user defined criteria and in succession trigger the stimulus to evoke an ERP by either of auditory, visual or sensory stimuli [4]. All these requirements have to be satisfied within the space and financial constraints given by off-the-shelve PC technology.