Nonlocal two dimensional denoising of frequency specific chirp evoked ABR single trials.

Recently, we have shown that denoising evoked potential (EP) images is possible using two dimensional diffusion filtering methods. This restoration allows for an integration of regularities over multiple stimulations into the denoising process. In the present work we propose the nonlocal means (NLM) method for EP image denoising. The EP images were constructed using auditory brainstem responses (ABR) collected in young healthy subjects using frequency specific and broadband chirp stimulations. It is concluded that the NLM method is more efficient than conventional approaches in EP imaging denoising, specially in the case of ABRs, where the relevant information can be easily masked by the ongoing EEG activity, i.e., signals suffer from rather low signal-to-noise ratio SNR. The proposed approach is for the a posteriori denoising of single trials after the experiment and not for real time applications.