1. A magnetic resonance imaging (MRI) system comprising: an MRI gantry having static and gradient magnet assemblies and at least one radio frequency (RF) coil defining an image volume; MRI control circuits connected to control components within said MRI gantry and configured to effect MRI data acquisition sequences of RF and gradient magnetic pulses which elicit MRI signals, to acquire and process said elicited MRI signals into MR image data in conjunction (a) with use of an initial spatially selective nuclear magnetic resonance (NMR) RF tag pulse (tag-on) in a data acquisition subsequence and (b) without use of an initial spatially selective NMR RF tag pulse (tag-off) in a data acquisition subsequence; said MRI control circuits being configured to (a) acquire multi-dimensional MR k-space data from patient tissue using multiple said tag-on and tag-off data acquisition subsequences for each of multiple time to inversion (TI) intervals without using an injected contrast agent; (b) reconstruct said acquired k-space data into a series of spatial domain tag-on and tag-off MR image data, each having different TI intervals; (c) perform an analysis of TI dependence of signal intensity based on the series of spatial domain MR image data by (1) subtracting said tag-off and tag-on MR image data for each of plural TI intervals for each of plural regions of interest (ROI) to produce difference image data, each said ROI being a multi-pixel segment representing part of a segmented region of said patient tissue and (2) generating, for each of the plural ROIs, based on combining together the difference image data for plural pixels within that ROI, a separate profile of signal intensity versus time data representing blood perfusion versus time for that ROI, the difference image data for plural pixels within that ROI being obtained by adding together, averaging, or combining pixels within the multi-pixel segment, wherein for each of the plural ROIs, a peak flow time and/or a peak blood flow magnitude, or lack thereof, of the function differentiates between normal, ischemic and infarct tissues; and (d) store and display a result of the analysis by plotting a plurality of functions, each of the plotted plurality of functions being the generated function corresponding to a respective one of the plural ROIs.