TABLE 3.

Summary of signal variance in rs‐fMRI explained by PPG‐derived signals

Coefficient of determination (r 2)	PPG	HRV	SDPPG	PIR
Lateral ventricles	0.14 ± 0.01	0.14 ± 0.01	0.09 ± 0.01	0.15 ± 0.01
3rd ventricle	0.13 ± 0.01	0.12 ± 0.01	0.10 ± 0.01	0.12 ± 0.01
Gray matter	0.13 ± 0.01	0.15 ± 0.01	0.09 ± 0.01	0.16 ± 0.02
White matter	0.12 ± 0.01	0.15 ± 0.01	0.09 ± 0.01	0.15 ± 0.02
Arteries	0.12 ± 0.01	0.12 ± 0.01	0.08 ± 0.01	0.13 ± 0.01
Veins	0.14 ± 0.01	0.15 ± 0.02	0.08 ± 0.01	0.15 ± 0.01
Aqueduct	0.12 ± 0.01	0.11 ± 0.01	0.10 ± 0.01	0.12 ± 0.01

Note: The frequency range of interest is 0.05–0.15 Hz. These frequencies are derived from the weighted average of the ridge frequencies extracted from the cross‐spectrograms. In general, each PPG‐derived parameter exhibits a distinct coherent frequency with rs‐fMRI data.