Accuracy of proton T1 calculated by approximations from image signals

In proton magnetic resonance imaging, T1 calculation from two measurements is simplified by using an approximation algorithm that assumes equilibrium recovery of longitudinal magnetizations or one that ignores refocusing 180 degrees pulses used. Errors in calculated T1 arising from either approximation are evaluated using signal expressions that presume neither approximation. The approximation error depends on T1, sequence parameters, and the simplifying algorithm. The computed relation can be used to correct for the approximation error. The correction reduces calculated-T1 errors, but does not eliminate them, since other significant or potentially significant sources of the error are unaccounted for. These sources relate to ever-present stochastic noises, proper signal expressions, various instrumental factors, exponential compared with nonexponential nature of tissue proton relaxations, and tissue movements. The problem of quantitative T1 measurement from image signals is briefly discussed.