Fig. 1.

Exemplar whole brain rs-EPI power spectrum (red) and the power spectra of the cardiac (blue) and respiratory trace (green) from external measurements (pulse-ox at the finger and a pressure pad on the chest). The external physiological signals are sub-sampled to the EPI TR. Above the low-frequency neurovascular range ($\mathrm{\lesssim }0.1$ Hz) the EPI spectrum closely matches the physiological spectra. The cardiac spectrum shows aliases of the second and third harmonics of the dominant cardiac frequencies (according to $f_{\text{alias}}=|f_{\text{true}}-n\cdot f_{\text{sample}}|,n\in \mathrm{\mathbb{N}}$).