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 into which a patient region of interest (ROI) can be disposed; 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 from patient tissue when an ROI is disposed therein, 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 for a patient ROI using said tag-on and tag-off data acquisition subsequences for each of plural time to inversion (TI) intervals without using an injected contrast agent; (b) reconstruct said acquired k-space data into spatial domain tag-on and tag-off MR image data; (c) subtract said acquired tag-off and tag-on MR image data for each of plural TI intervals to produce difference image data as a function of time representing blood perfusion in said ROI having a corresponding flow time and/or relative peak blood flow magnitude, or lack thereof, for said ROI which differentiates between normal, ischemic and infarct tissues; and (d) store and/or display perfusion data of the ROI having values which are different for normal, ischemic and infarct tissues.