  This article introduces the Zeffiro interface (ZI) version 2.2 for brain
imaging. ZI aims to provide a simple, accessible and multimodal open source
platform for finite element method (FEM) based and graphics processing unit
(GPU) accelerated forward and inverse computations in the Matlab environment.
It allows one to (1) generate a given multi-compartment head model, (2) to
evaluate a lead field matrix as well as (3) to invert and analyze a given set
of measurements. GPU acceleration is applied in each of the processing stages
(1)-(3). In its current configuration, ZI includes forward solvers for
electro-/magnetoencephalography (EEG) and linearized electrical impedance
tomography (EIT) as well as a set of inverse solvers based on the hierarchical
Bayesian model (HBM). We report the results of EEG and EIT inversion tests
performed with real and synthetic data, respectively, and demonstrate
numerically how the inversion parameters affect the EEG inversion outcome in
HBM. The GPU acceleration was found to be essential in the generation of the FE
mesh and the LF matrix in order to achieve a reasonable computing time. The
code package can be extended in the future based on the directions given in
this article.
