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Biological tissue characterization by magnetic induction spectroscopy (MIS): requirements and limitations
Scharfetter, Hermann; Casañas Bueno, Roberto; Rosell Ferrer, Francisco Javier
Universitat Politècnica de Catalunya. Departament d'Enginyeria Electrònica; Universitat Politècnica de Catalunya. IEB - Instrumentació Electrònica i Biomèdica
Magnetic induction spectroscopy (MIS) aims at the contactless measurement of the passive electrical properties (PEP) σ, ε, and μ of biological tissues via magnetic fields at multiple frequencies. Whereas previous publications focus on either the conductive or the magnetic aspect of inductive measurements, this article provides a synthesis of both concepts by discussing two different applications with the same measurement system: 1) monitoring of brain edema and 2) the estimation of hepatic iron stores in certain pathologies. We derived the equations to estimate the sensitivity of MIS as a function of the PEP of biological objects. The system requirements and possible systematic errors are analyzed for a MIS-channel using a planar gradiometer (PGRAD) as detector.We studied 4 important error sources: 1) moving conductors near the PGRAD; 2) thermal drifts of the PGRAD-parameters; 3) lateral displacements of the PGRAD; and 4) phase drifts in the receiver. All errors were compared with the desirable resolution. All errors affect the detected imaginary part (mainly related to σ ) of the measured complex field much less than the real part (mainly related to ε and μ). Hence, the presented technique renders possible the resolution of (patho-) physiological changes of the electrical conductivity when applying highly resolving hardware and elaborate signal processing. Changes of the magnetic permeability and permittivity in biological tissues are more complicated to deal with and may require chopping techniques, e.g., periodic movement of the object.
Peer Reviewed
Àrees temàtiques de la UPC::Enginyeria biomèdica::Electrònica biomèdica
Medical physics
Bioelectric phenomena
Biological tissues
Biomedical measurement
Electrical conductivity measurement
Magnetic permeability measurement
Measurement errors
Patient monitoring
Permittivity measurement
Brain edema
Important error sources
Detected imaginary part
Pathophysiologial changes
Magnetic permeability
Impedance spectroscopy
Iron overload
Systems requirements
Systematic errors
Chopping techinques
Periodic object movement
Magnetic induction tomography
Tissue passive electrical properties
Medicina física

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