1. A method for non-invasively identifying and/or measuring or estimating a degree of myocardial ischemia, identifying one or more stenoses, and/or localizing and/or estimating fractional flow reserve, the method comprising:obtaining, by one or more processors, a data set associated with a plurality of wide-band gradient signals simultaneously from the subject via at least one electrode;
generating, by the one or more processors, a residue subspace data set and a noise subspace data set from the data set associated with the plurality of wide-band gradient signals;
determining, via the one or more processors, one or more coronary physiological parameters of the subject selected from the group consisting of a fractional flow reserve estimation, a stenosis value, and a myocardial ischemia estimation, based on the residue subspace data set and the noise subspace data set; and
output, via one or more of an output data set in a report and/or a display, the one or more coronary physiological parameters, wherein the output is used in the diagnosis of cardiac disease.