No. 13 - Eric Elzenheimer

Eric Elzenheimer: Analyse stimulationsevozierter Muskel- und Nervensignale mithilfe elektrischer und magnetischer Sensorik

Shaker-Verlag, 2022

Commission

• Prof. Dr.-Ing. Gerhard Schmidt
  (first reviewer)
• Priv.-Doz. Dr. med. Helmut Laufs
  (second reviewer)
• Univ.-Prof. Dr.-Ing. Daniel Baumgarten
  (third reviewer)
• Prof. Dr.-Ing. Michael Höft
  (examiner)
• Prof. Dr.-Ing. Eckhard Quandt
  (head of the examination board)

Abstract

The prevalence of polyneuropathies (PNPs), neurological diseases, in people over 50 years old is 5.5 %. Such systemic diseases of the peripheral nerves can be categorized into inherited metabolic, acquired metabolic, immune-mediated, and toxic forms. Medical doctors must be able to differentiate among these forms to determine which type of therapy is needed. The burden on patients and the costs to health care providers may vary considerably, depending on the therapy administered. Motor nerve conduction studies assess compound muscle action potentials (CMAPs) by using neurography, from which neurophysiological variables are derived. These are used in addition to clinical evaluations to distinguish between the different etiologies. Despite the existing applications of neurography, current analytical strategies for PNP differentiation are inadequate for differential diagnostics, and improvements are needed. To overcome these problems, digital signal processing methods and approaches that can support medical doctors making clinical decisions are presented in this thesis. The focus of these efforts was to quantitatively describe pathological CMAP signal differences without additional effort so that diagnoses can be made in a timely manner. In this context, a system-theoretical signal model was also developed to describe various physiological and pathological processes in human nerves. This model enables realistic insights into the pathophysiology of polyneuropathies.

In principle, electrode-based neurography can be complemented by magnetic detection. The use of novel magnetic field sensors would require a more precise inspection in the field of neurophysiology. These sensors facilitate contactless data acquisition, advantageous when compared with conventional methods, which require electrodes. However, the pilot measurements of nerves and muscles presented in this study revealed some limitations, specifically for non-cryogenic magnetic field sensors. The observed disadvantages mainly resulted from the measurement bandwidth they were able to support and the available detection limit. Consequently, the use of these magnetic field sensors my be more suitable for other medical applications, for example cardiology is particularly noteworthy here since the signal with the highest field amplitude originates from the human heart. Finally, in a dedicated field study, the magnetic equivalent of a human R-wave was successfully detected within one minute for the first time by using a magnetoelectric ME sensor. This affirms the hypothesis that ME sensors are valuable in magnetic diagnostics, promoting further development of this particular sensor type. Finally, sensor-specific advancements combined with digital readout techniques could advance magnetic detection in neurophysiology.

In this collaborative engineering and neuroscience work, the research methods utilized provide a in-depth assessment of nerves and may therefore be valuable for performing diagnostic tests in the long term. The experiments and results presented in this research represent the foundation of technical concepts and analytical procedures necessary for a semiautomated disease classification system in clinical practice. An interdisciplinary team of researchers and an international manufacturer of neurography equipment have already joined forces to make such a system a reality in the form of a diagnostic tool.