Application of phase rotation to STRESS localization scheme at 3 T

Purpose: Application of phase rotation to the STRESS (=STEAM+PRESS) localization scheme, to shorten echo time, minimize J-coupling dephasing and estimate B ₁₊ inhomogeneity. STRESS (=STEAM + PRESS) simultaneously refocuses and acquires the double spin echo (SE ₁₂₃) and stimulated echo (STE _-) pathways, combining PRESS-like signal with lower chemical shift displacement as in STEAM. Phase rotation effectively separates coherence pathways, allows reduction of spoiling gradients moments leading to reduction in echo time. Implementing it in STRESS allows one to individually phase-correct SE ₁₂₃ and STE _- prior to combination. Moreover, B ₁₊ inhomogeneity can be assessed by comparing the measured ratio of resonance intensities of SE ₁₂₃ and STE _- pathways to the simulated one. Methods: In vivo spectra were acquired from a single voxel placed in the sensory-motor cortex of 10 healthy volunteers, using phase rotation-STRESS/PRESS/STEAM sequences at 3 T scanner. The phases of each slice-selective pulse were incremented by Δϕ _1/2/3 = 22.5°/ - 45°/45°. Results: Phase rotation-STRESS showed quantification accuracy (% Cramer Rao lower bounds) and reproducibility (% coefficients of variation) comparable to PRESS and STEAM, in both phantoms and in vivo study. Minimal echo time achieved was 13 ms. Conclusion: Phase rotation complements STRESS by reducing echo time, allowing processing of each pathway individually prior to addition and providing B ₁₊ estimation in single voxel proton magnetic resonance spectroscopy. Magn Reson Med 79:2481–2490, 2018.