This project is intended to provide computational resources to users of Dipole Source Localization (DSL) methods to allow them to decide whether or not their DSL results are distorted by certain errors called model misspecification errors. These errors are essentially due to incorrect weighing constants in the computation of the relationship between source dipole parameters and the surface potential. Such errors occur when head model simplifications are used, such as a one-shell as contrasted to a more realistic 3-shell model, and when a spherical model is employed instead of a more realistic head model. Errors in single dipole localization are magnified when multiple dipoles are required to model the sources of brain potentials. A relatively simple method for estimating misspecification errors has been devised (called the AB-plane technique) and examined using simulated data for models using one or two dipoles. The method permits the identification of models that are insufficiently accurate to produce valid DSL, and to compare models for their relative accuracy. In order to use the method on real (as contrasted to simulated) data in which the contributions of each dipole is unknown an extension of the AB-plane estimation technique called the EF-plane method is proposed. Although accurate definition of the EF plane is not possible, since the variables that define it are unknown, it is proposed that a close enough estimate might be obtained using singular value decomposition. It is indicated that even if this approach is not entirely accurate, that it will nevertheless be sufficiently close to the AB-plane estimate to disclose model misspecification errors.
| Zhang, Z (1995) A fast method to compute surface potentials generated by dipoles within multilayer anisotropic spheres. Phys Med Biol 40:335-49 |
