Constrained optimized water suppression for H MR spectroscopy.

Purpose: Water suppression is a necessary component to standard MR spectroscopy experiments due to the approximately 5000-10 000-fold higher water concentration and signal intensity compared with that of the metabolites and macromolecules of interest. Here, a novel algorithm referred to as constrained optimized water suppression (COWS) was developed, which enables generation of effective water suppression modules with an arbitrary number of radiofrequency (RF) pulses, and flexibly accommodates minimum durations between pulses, minimum total module duration, and maximum flip angles.

Methods: We use the COWS algorithm to create a water-suppression module with seven pulses, the same number of RF pulses as typical VAPOR7, at a reduced module duration of 236 ms, referred to as COWS(7;236), as well as one at the typical VAPOR duration but with an increased number of RF pulses, referred to as COWS(12;626). Experimentally, both COWS schemes were compared with variable power radio frequency pulses with optimized relaxation delays (VAPOR) using single-voxel spectroscopy in the prefrontal cortex, the posterior frontal lobe, and the occipital lobe from data collected from 10 participants on a 3T Siemens MRI scanner.

Results: We found that both COWS(7;236) and COWS(12;626) perform similar to VAPOR7 for metabolites, whereas COWS(7;236) had improved performance than VAPOR for macromolecules at a reduced 236-ms duration.

Conclusion: COWS can be used to develop flexible study-specific water suppression that can perform similarly for metabolite spectra or with improved performance for macromolecule spectra compared with VAPOR7, at a lower module duration.