| Two-dimensional magnetic resonance spectroscopy has shown the promise to detect more metabolites of low concentrations and resolve overlapping resonances in the one-dimensional counterpart. However, besides a longer acquisition time, there are other tradeoffs including an intrinsic signal loss of above half and a broad peakshape due to the effects of the mixing pulse in some correlation techniques. When the mixing pulse is replaced by an isotropic mixing module as used in total correlation or homonuclear Hartmann-Hahn spectroscopy, higher sensitivity and resolution can be achieved. However, the implementations of such a module commonly require a train of high-power radiofrequency pulses which deposits a large amount of energy within a short period of time, heating body tissues up to a temperature beyond the safety threshold. The current study aims at reducing the power deposition while retaining the similar effects of such mixing module by a universal swap (SWAP) quantum logic gate. The SWAP module can be implemented in magnetic resonance using only seven pulses, including two slice-selective pulses. By appending the module to a slice-selective excitation pulse and introducing some incremental delays, a volume-localized, two-dimensional sequence is developed. This novel quantum logic sequence earns a new name called PAWS for achieving power abatement with SWAP. Theoretical analyses suggest that PAWS spectra have intrinsically higher signal gains or even full signal recovery for some spin systems, and have better peakshapes due to improved phase characteristics. Moreover, a series of phantom experiments demonstrates some special features of PAWS. For examples, dominant singlets in water and N-acetylaspartate resonances can be reduced in the N-type region but preserved in the P-type region within the same spectrum. Coupled-spin signals in alanine and lactate can be withdrawn from their diagonals and deposited back into their cross peaks while the dominant lipid signals are preserved. Fine structures of the well-known methylene singlet in creatine resonances can be readily resolved even in an isotropic solution. Furthermore, spatially imbedded product operator (SIMPO) formalism, developed here based on the popular product operator formalism, makes the theoretical expositions more concise and efficient for the practitioners in the field of biomedical magnetic resonance. |
