PointResolved

PointRESolved, commonly referred to as Point-RESolved Spectroscopy (PRESS), is a proton magnetic resonance spectroscopy localization technique used to obtain spectra from a defined voxel within tissue, most often the brain. It localizes signal by applying three orthogonal, slice-selective radiofrequency pulses that excite and refocus spins in the intersection of three planes, creating a finite three-dimensional voxel. The standard PRESS implementation uses a 90-degree excitation pulse followed by two 180-degree refocusing pulses, with gradients directing each pulse to a separate anatomical axis. The echo time and repetition time are determined by the timing of these pulses, influencing spectral quality and metabolite visibility.

PRESS is widely used in clinical and research MRS due to its relatively high signal-to-noise ratio and robust voxel localization. Typical acquisitions employ voxel sizes ranging from a few cubic centimeters to several cubic centimeters, with TE commonly in the range of about 30 to 35 milliseconds and TR around 1.5 to 2 seconds, though parameters vary with field strength and study goals. To minimize lipid contamination from the scalp, outer-volume suppression or lipid-suppression techniques are often combined with PRESS.

Advantages include higher SNR compared to STEAM, straightforward implementation, and strong localization accuracy for brain studies. Limitations involve sensitivity to B0 inhomogeneities, which can distort localization near sinuses or air-filled cavities, and chemical-shift displacement effects that become more pronounced at higher field strengths. Also, TE selection influences the visibility of J-coupled metabolites. PRESS is frequently used for measuring metabolites such as N-acetylaspartate, choline, creatine, myo-inositol, and glutamate/glutamine in clinical and research contexts, and can be complemented by edited or advanced sequences for specific metabolite targets.