Myocardial T1 mapping is sensitive to changes in tissue structure and composition. The native myocardial T1 (i.e., measured without giving contrast) becomes longer with an increase of mobile water species, and/or interstitial deposition of collagen, or amyloid protein, as illustrated by the native T1 data points in the lower left corner of the illustration. If T1 mapping is performed before and after contrast administration, one can relate the changes of 1/T1 in myocardium, to the corresponding change of 1/T1 in blood to determine the so- called myocardial tissue partition coefficient for an extracellular gadolinium contrast agent. (1/T1 rather than T1 is proportional to contrast concentration.) The partition coefficient corresponds to the slope of the line going through the measured values of 1/T1. The slope increases as a result of the expansion of the extracellular volume, e.g., as a result of diffuse interstitial fibrosis. The slope generally changes much less as a result of edema, and the native T1 is therefore more widely used to detect edema.