Comparison of double and zero quantum NMR editing techniques for in vivo use

Several multiple quantum editing techniques for in vivo proton NMR are discussed and compared using simulated and experimental data. Extensions of these techniques for improved editing are given. Relative S/N ratios, modulation characteristics, metabolite selectivity, B0 and B1 inhomogeneity and motion effects are considered. Frequency selective read pulses can be used for signal enhancement and lipid suppression. Extra suppression of undesired signals can be obtained with a two-shot t1 cycle which gives good results for both the zero and double quantum sequences. These sequences give at most 50% signal intensity and lipid suppression factors of ca 2000 and 7000, respectively. A sequence which selects zero and double quantum coherences yields 100% signal intensity but only gives a good lipid suppression factor (7000) in combination with phase cycling. It is shown that the multiple quantum modulation can be used to obtain specific metabolite editing. Corrections can be made for the effects of B0 inhomogeneity on the multiple quantum coherences; B1 inhomogeneity affects the investigated multiple quantum sequences in about the same way and decreases the volume of interest. In vivo measurements show the good performance of the proposed zero and double quantum sequences for lactate.