Polarizacija elektrod pri meritvah bioimpedance

BRODNIK, LUKA (author), Kos, Bor (mentor)

V magistrski nalogi je predstavljena definicija pojma polarizacijske impedance, ki se pojavi na stiku elektroda – tkivo in nam lahko na videz dokaj enostavno meritev zelo pokvari. Predstavljene so obstoječe rešitve za zmanjšanje oz. izločitev njenega vpliva in meritve oz. rezultati naloge. Napisan je bil program za zajem meritev in sicer v programu LabVIEW. Meritve so bile izvedene na šestih parih elektrod, 7 različnih koncentracijah raztopine elektrolita, 9 napetostnih amplitudah ter v frekvenčnem območju 20 Hz – 100 kHz. Narejena je bila primerjava rezultatov z visokoznanstvenimi članki in predstavitev rezultatov z matematičnim modelom. Z uporabo metode matematične aproksimacije je bil vpliv polarizacijske impedance v celoti izločen. V prvem poglavju je predstavljena teoretična razlaga polarizacijske impedance elektrod, skupaj s predlaganimi rešitvami za njegovo odpravo. Drugo poglavje opisuje uporabo meritev bioimpedance v praksi in pri procesu elektroporacije. Tretje poglavje navede pomembne podatke uporabljenega merilnega instrumenta, opiše pripravo merilnega sistema, napisan program za zajem meritev in izbiro ustrezne merilne posode. Četrto poglavje prikazuje rezultate, kjer vsako podpoglavje analizira odvisnost polarizacijske impedance od drugega parametra. Parametri so koncentracija raztopine, amplituda merilnega signala, vrsta elektrode, debelina elektrode, dolžina elektrode ter merilna čaša. Rezultati so prikazani v grafični obliki in nazorno pokažejo, pri katerih parametrih je vpliv polarizacijske impedance najmanjši. Prikazani so grafi upornosti R, kapacitivnosti C ter izračunane absolutne impedance |Z|. V nadaljevanju se zaradi lažjega razumevanja pojem absolutne impedance velikokrat nadomesti s pojmom impedance Z. Peto poglavje rezultate meritev analizira z matematičnim modelom. Narejena je primerjava parametrov matematičnega modela za več različnih koncentracij elektrolita in amplitude merilnega signala. Opravljen je poizkus matematične aproksimacije za izločitev polarizacijske impedance iz meritev prevodnosti. Šesto poglavje povzema ugotovitve magistrske naloge. Poleg tega našteje vse omejitve, naredi primerjavo z visokoznanstvenim člankom ter komentira rezultat matematične aproksimacije. Naštete so možne izboljšave oz. nadgradnje magistrske naloge. Zadnje poglavje podaja zaključke naloge. Ugotovitev naloge je, da je polarizacijska impedanca odvisna od velikega števila parametrov in jo lahko z uporabo pravilnega matematičnega modela iz meritve uspešno odpravimo.

• Language: Slovenian
• Keywords: Polarizacija elektrod, Zmanjšanje polarizacijske impedance, Meritve bioimpedance, Biomedicinska tehnika
• Work type: Master's thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2019
• PID: 20.500.12556/RUL-108526
• Publication date in RUL: 05.07.2019

Secondary language

• Language: English
• Title: Electrode polarization in bioimpedance measurements

Abstract

Master's thesis presents definition of polarization impedance, which is present on contact electrode – tissue and can spoil our mesaruemnt. Known solutions for its reducement are presented and measurements with results are provided. Measurements program was written in LabVIEW. Measurements were conducted on 6 pairs of electrodes, 7 different concentrations of the electrolyte solution, 9 voltage amplitudes and in frequency range of 20 Hz – 100 kHz. Comparison with scientific articles was made and results were presented using mathematical model. With usage of mathematic approximation, polarization impedance impact was completely excluded. In first chapter, theoretical explanation of electrode polarization impedance is presented, together with suggested solutions for it's reducement. In second chapter, bioimpedance measurement usage in clinical applications and electroporation processes is presented. Third chapter presents data of used measurement instrument, measurement system preparation, written program for measurements and choice of appropriate measurement cup. In fourth chapter, results are shown. Every subchapter analyzes polarization impedance dependency of particular parameter. Parameters are concentration of solution, voltage amplitude, electrode type, electrode thickness, electrode length and measuring cup. Results are shown in graphic form, so it is clear to determine where polarization impedance impact is the lowest. Charts of resistance R, capacitance C and calculated absolute impedance |Z| are shown. For clearer understanding, term of absolute impedance is generally replaced with term of impedance Z during thesis. In fifth chapter, results are analyzed using mathematical model. Comparison of mathematical model's parameters is made for multiple concentrations of electrolyte solutions and voltage amplitudes. Experiment of mathematical approximation is made to reduce polarization impedance impact from conductivity measurements. In sixth chapter, thesis findings and limits are presented. Comparisons with scientific articles are made and results of mathematic approximation are commented. Possible improvements and upgrades of thesis are suggested. In last chapter, conclusions of master's thesis are given. Thesis finding: polarization impedance is dependent of many parameters and can be successfully excluded from measurement using corect mathematical model.

• Keywords: Electrode polarization, Reduction of electrode polarization, bioimpedance measurements, biomedical engineering