The methods of the invention exploit the capabilities of manganese-enhanced MRI (MEMRI), which provides viability-specific biological contrast agent through the intracellular accumulation of Mn2+. A typical contrast agent utilizes non-chelated Mn2+ in combination with Ca2+, e.g. as calcium gluconate. Active intracellular accumulation of Mn2+ generates high signal from the viable cells in normal tissue, or normal regions of heterogeneous tissue no signal from the non-viable cells and intermediate signal from viable but injured cells. The intermediate signal defines a “gray zone” of potentially salvageable cells.
