Each of the PV(t) signals, from a ROI or a pixel in the coarse grid, is presented in one of the following ways in this paper:PVraw(t) no processing other than spatial averaging over ROI or coarse grid cell; PVAC(t) the mean over time of PVraw(t) is subtracted (= PVraw(t) minus DC); or PVBP(t) band-pass filtered PVraw(t) signal.
Fast Fourier transforms (“FFT“ in Matlab®) on PV(t) signals were performed to determine the power and phase spectra for PV(t). Zero padding of PV(t) prior to the Fourier transform was used to allow for a finer discretization of the frequency. We will refer to an nth order zero padding if the original signal was expanded on both sides with a 0 signal of length n times the original time span.
Plethysmographic signals are sometimes presented inverted to render the intensity proportional to blood pressure or volume. In this communication, all signals will be presented directly: a higher signal corresponds to a higher reflectance and smaller blood volume. Although we will indicate how pixel values (the basic measurement unit) relate to reflectance, all signals will be presented in pixel values.
Fast Fourier transforms (“FFT“ in Matlab®) on PV(t) signals were performed to determine the power and phase spectra for PV(t). Zero padding of PV(t) prior to the Fourier transform was used to allow for a finer discretization of the frequency. We will refer to an nth order zero padding if the original signal was expanded on both sides with a 0 signal of length n times the original time span.
Plethysmographic signals are sometimes presented inverted to render the intensity proportional to blood pressure or volume. In this communication, all signals will be presented directly: a higher signal corresponds to a higher reflectance and smaller blood volume. Although we will indicate how pixel values (the basic measurement unit) relate to reflectance, all signals will be presented in pixel values.
