Validation of bioelectric and biomagnetic measurement and analysis method with the help of physical phantoms

 

Overview

Figure 1: Front view of the physical torso phantom

Source reconstruction is a widely used method to estimate the location, orientation, and strength of bioelectrical sources from surface potential measurements or from magnetic field measurements. It is extensively used in the localization of neuronal activity in the brain, but it is also used to localize electrophysiological activity in the heart and in other biomedical research areas. Source reconstruction comprises the computation of bioelectric and biomagnetic fields due to given sources (the forward problem) and the source parameter estimation based on given measurements (the inverse problem).

Inverse bioelectric and biomagnetic problems are computationally complex and don’t have unique solutions. Consequently, validation should be an inherent part of development and application of data analysis procedures. Validation approaches in general include simulations, phantom measurements, in vitro and in vivo measurements.

Physical phantom measurements provide a unique means to assess to performance of source localization techniques. Unlike simulations, they take into account the real world influences, such as for example environmental noise or 3D positioning errors, thus giving an error estimate of the entire source reconstruction procedure. Unlike in vivo measurements, no physiological uncertainties exist and the ground truth in terms of source position, strength, orientation, and extent is known.

Figure 2: The torso phantom with a bulk of anisotropic skeins (red lines) and a current dipole (blue, below the bulk of anisotropic skeins). At the surface of the phantom the electrodes (blue) are displayed. The 195 magnetic sensors (red) above the phantom are arranged in triplets (vectorial field measurement, Argos 200 System). POS1 and POS2 indicate the set-ups for the more lateral and more inferior dipole position, respectively. The artificial current dipole is rotated with the help of the mechanical construction indicated in blue. We provide open data for a dipole localization benchmark problem and an extended source reconstruction problem (the latter was accepted as TEAM Workshop benchmark 31).
Figure 3: Normalized signal strengths over the angle between anisotropy orientation and dipole direction. Results for POS2 of the dipole (see Figure 2 above) are displayed. For the different experiments, the signal strength was reduced between 17% and 43% for different dipole positions when comparing the parallel alignment of dipole orientation and anisotropy direction with the orthogonal alignment.

Project partners

Project partners were not deposited.

Publications & patents

  • Haueisen J, Dietzel A, Liehr M, Weiser T, Elsarnagawy T, Bellemann ME.: Bioelectric and biomagnetic measurements are differentially sensitive to spiral currents. Biomedizinische Technik, 56(5): 283-289, 2011
  • Höfner,N., Albrecht,H.-H., Cassará,A.M., Curio,G., Hartwig,S., Haueisen,J., Hilschenz,I., Körber,R., Martens,S., Scheer,H.-J., Voigt,J., Trahms,L., Burghoff,M.: Are brain currents detectable by means of Low-Field NMR? - a phantom study. Magnetic Resonance Imaging, 29(10):1365-73, 2011
  • Sander, TH., Knösche, T.R., Schlögl, A., Kohl, F., Wolters, CH., Haueisen, J., Trahms, L.: Recent advances in modeling and analysis of bioelectric and biomagnetic sources. Biomedizinische Technik, 55:65-76, 2010
  • Wetterling,F., Liehr,M., Schimpf,P., Liu,H., Haueisen,J.:The localization of focal heart activity via body surface potential measurements: tests in a heterogeneous torso phantom. Physics in Medicine and Biology, 54:5395-5409, 2009
  • Sengül,G., Liehr,M., Haueisen,J., Baysal,U.: An experimental study on the effect of the anisotropic regions in a realistically shaped torso phantom. Annals of Biomedical Engineering, 36(11): 1836-43, 2008
  • Liehr,M., Haueisen,J.:  Influence of anisotropic compartments on magnetic field and electric potential distributions generated by artificial current dipoles inside a torso phantom. Physics in Medicine and Biology, 53:245–254, 2008
  • Dutz,S., Bellemann,M.E., Leder,U., Haueisen,J.: Passive vortex currents in magneto- and electrocardiography: comparison of magnetic and electric signal strengths. Physics in Medicine and Biology, 51(1):145-51, 2006 
  • Liehr,M., Haueisen,J., Görnig,M., Seidel,P., Katila,T., Nenonen,J.: Vortex shaped current sources in a Physical Torso Phantom. Annals of Biomedical Engineering, 33(2): 240–247, 2005
  • Brauer,H., Ziolkowski,M., Haueisen,J., Tenner,U., Nowak,H.: Verification of extended sources reconstruction techniques using a torso phantom. COMPEL, 20(2), 595-606, 2001
  • Brauer,H., Ziolkowski,M., Haueisen,J.: Evaluation of Inverse Field Solutions with Biomedical Applications. COMPEL, 20(3), 665-675, 2001
  • Brauer,H., Haueisen,J., Ziolkowski,M., Tenner,U., Nowak,H.: Reconstruction of extended current sources in a human body phantom applying biomagnetic measuring techniques. IEEE Transactions on Magnetics, 36, 1700 – 1705, 2000
  • Ziolkowski,M., Haueisen,J., Nowak,H., Brauer,H.: Equivalent Ellipsoid  as an interpretation tool of extended current distributions in biomagnetic inverse problems. IEEE Transactions on Magnetics, 36, 1692 – 1695, 2000
  • Tenner,U., Haueisen,J., Nowak,H., Leder,U., Brauer,H.: Source Localization in an Inhomogeneous Physical Thorax Phantom. Physics in Medicine and Biology, 44, 1969 - 1981, 1999
  • Hagner,T., Eiselt,M., Giessler,F., Hansen,E., Haueisen,J., Nowak,H.: Multichannel MEG recordings with small volume phantom - high resolution biomagnetic investigation. Biomedical Engineering, 44(3), 38 - 45, 1999

Sponsorship

Sponsors were not deposited.