A general approach to T1, T2, and spin-density discrimination sensitivities in NMR imaging sequences

Previous specific empirical studies and computer simulations show convincing evidence for superior sensitivity in imaging T1 differences (T1-discrimination) by the simple saturation-recovery NMR sequence above all other common sequences. This occurs under optimum conditions where system repetition time is shorter than commonly employed in most currently recommended NMR sequences. This paper presents a general theory of discrimination sensitivity; its application to the human subject shows that the specific empirical results must, in general, be true in all cases. This occurs because all functional forms entering the NMR relaxation modulations of imaged-magnetization (in the current sequences) are the same exponential-function. Moreover, density-discrimination and T2-discrimination are optimized by short repetition times just as for T1-discrimination; the lower limit is a T2-controlled data-window constraint not treated in previous descriptions. These results have significant practical consequences for NMR scanner design.