Figure 8. A short (echo time (TE)=20 ms) (top) and long (TE=135 ms) (bottom) single voxel 1H-MR spectrum (repetition time (TR)=1500 ms in both cases) from a locally advanced rectal cancer. The principal resonances are labelled and include "choline" (due to trimethylamine protons -N+(CH3)3) a marker of cell membrane turnover and the methyl (-CH2-) and methylene (-CH3) resonances of saturated lipid. The long T2 of the "choline" species compared with that of the lipids explains the relatively greater persistence of the "choline" peak over that of lipids in the long echo time spectrum (bottom left). The three orthogonal T1 localizer images are shown on the right and demonstrate the voxel sited within the confines of the tumour. Reproduced with permission, John Wiley & Sons, Inc.