XX IMEKO World Congress Metrology for Green Growth September 914, 2012, Busan, Republic of Korea COST EFFECTIVE FLEXIBLE MODULAR SYSTEM FOR ACQUISITION AND PROCESSING OF BIOLOGICAL SIGNALS BASED ON ADVANCED SIGNAL PROCESSING Linus Michaeli 1 , Ján Šaliga 1 , Ján Gálik 2 1 Dept. of Electronics and Telecom., Technical University of Košice, Letna 9, 04200 Košice, Slovak Republic Email: {linus.michaeli, jan.saliga}@tuke.sk 2 Institute of Neurobiology, Slovak Academy of Sciences, Košice, Slovak Republic Email: galik@saske.sk Abstract: Measurement of signals from biological objects usually requires complex and expensive system. This paper presents a simple, cost effective, computer controlled modular systems consisting of self developed modules and modules from a few vendors and own software developed in LabVIEW. The system enables multichannel data acquisition with sampling frequency a few kHz with nearly unlimited lengths, triggering and pretriggering records. The records are stored in signal database and processed by software in PC using various advanced digital signal processing methods for recovering distorted signal. The system was developed and has been used for biological experiments on rats focused on evoked potentials. Keywords: DAQ, biological signal, LabVIEW, digital signal processing, evoked potential, biological signal, waveform recovering. 1. INTRODUCTION Studies of physiological processes in live biological objects require also to measure electrical potentials and currents of excitable tissue. Each living cell maintains some electrical potential on its membrane, called membrane potential. This potential can vary during cellular activity; these changes are induced by currents flowing through the cell membrane. These biological potentials and currents can be measured. The most common signals recorded from biological objects in experiments as well as in clinical practice are electrical signals generated by activity of the heart (electrocardiography, ECG), the muscle (electromyography, EMG), and by the brain (electroencephalography, EEG). Depending on the study, the recorded signals can be spontaneous (ECG), or evoked by some kind of stimulus. The later signals are called evoked potentials (EPs), and they are on the main focus of our paper. Simple definition of EP is that it is response to certain stimulus. EPs are used to study integrity and function of different pathways in the body, such as visual, auditory, motor and somatosensory pathways. According to the type of studied pathways, the stimuli can have different modalities; they can be electrical, sound, visual, etc. [2]. The special type of EPs are the event related potentials, which are the responses of brain to internal or external stimuli as a direct manifestation of thinking or perception. They could be prospectively used for communication of fully paralyzed people with external world. Experimental system for the most of EPs is required to generate or activate a stimulus, which is also the trigger event for acquiring response, with following processing and archiving. Evoked potentials are used also for monitoring spinal cord function. This technique can detect acute changes of the spinal cord functions after different kinds of injury. Requirements on convenient data acquisition system are:  Sensing of very small electric potentials of micro and milivolts order that are usually deteriorated by noise and other disturbances.  Low frequency measurements with maximal frequency of spectral components in order of hundreds Hz.  Triggered acquisition by digital or analogue triggers derived from stimuli of measured object, and, optionally, generation of stimuli on trigger outputs.  Processing of acquired signals and saving them in a database for later offline processing. Professional systems are rather expensive, often also because of fulfilling various safety conditions required for experiments on human beings. These safety requirements are not needed for experiments on laboratory animals such as rats, etc. This was a challenge for the authors to design and develop a simple modular measuring system based on common, general purpose components, and advanced digital signal processing software, which can decrease hardware requirements. It would enable to perform experiments with laboratory rats at very low costs. The important novelty in this work is application of chosen methods of advanced signal processing on acquired signals from EPs electrodes, which enable better recovering of biological signal, which are heavily deteriorated by noise and other distortions. 2. EXPERIMENTAL SETUP The scheme of our experimental setup is shown in Fig. 1. The setup consists of electrodes implanted into the animal,