Improved nuclear magnetic resonance (NMR) imaging methods based on a Carr-Purcell-Meiboom-Gill (CPMG) RF pulse sequence and pulsed magnetic field gradients applied to both multiple angle projection (MAP) imaging techniques, and to the two-dimensional Fourier transform (2DFT) or spin warp imaging techniques, are disclosed. The improved methods involve the generation of multiple spin echoes induced by a repetitive sequence of phase alternated 180.degree. nonselective pulses, wherein the resulting spin echoes are used to provide substantive improvements in the pixel signal to noise ratio, and/or to generate images which reflect substantially the transverse relaxation time T.sub.2. The improved imaging methods are particularly useful when directed to the detection and localization of various disease states of biological tissue, which exhibit altered T.sub.2 relaxation times indicative of changes at the molecular level.