The Complex-Pole Filter Representation (COFRE) for spectral modeling of fNIRS signals

TL;DR

This paper introduces COFRE, a novel spectral modeling method for biomedical signals, enabling precise frequency analysis and real-time application, demonstrated on fNIRS data to identify tinnitus-related spectral markers.

Contribution

The paper presents COFRE, a new complex-pole filter approach for spectral modeling that offers high resolution and efficiency for biomedical signal analysis.

Findings

Identified significant spectral differences in tinnitus patients at specific frequencies.

Demonstrated COFRE's effectiveness in real-time spectral analysis of fNIRS signals.

Revealed tinnitus signatures in low-frequency oscillations.

Abstract

The complex-pole frequency representation (COFRE) is introduced in this paper as a new approach for spectrum modeling in biomedical signals. Our method allows us to estimate the spectral power density at precise frequencies using an array of narrow band-pass filters with single complex poles. Closed-form expressions for the frequency resolution and transient time response of the proposed filters have also been formulated. In addition, COFRE filters have a constant time and space complexity allowing their use in real-time environments. Our model was applied to identify frequency markers that characterize tinnitus in very-low-frequency oscillations within functional near-infrared spectroscopy (fNIRS) signals. We examined data from six patients with subjective tinnitus and seven healthy participants as a control group. A significant decrease in the spectrum power was observed in tinnitus patients in the left temporal lobe. In particular, we identified several tinnitus signatures in the spectral hemodynamic information, including (a.) a significant spectrum difference in one specific harmonic in the metabolic/endothelial frequency region, at 7mHz, for both chromophores and hemispheres; and (b.) a significant differences in the range 30-50mHz in the neurogenic/myogenic band.