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Updated: Jul 15, 2026

Rapid Scan Electron Paramagnetic Resonance Opens New Avenues for Imaging Physiologically Important Parameters In Vivo
Published on: September 26, 2016
RF refocused echoes of J-coupled spin systems: effects on RARE-based spectroscopic imaging
Dirk Mayer1, Wolfgang Dreher, Dieter Leibfritz
1Lucas MRS Imaging Center, Department of Radiology, Stanford University, Stanford, California 94305-5488, USA. dirk.mayer@stanford.edu
Abstract:
A numerical simulation tool was developed to calculate the echo amplitudes of J-coupled resonances within a series of radiofrequency (RF) refocused echoes. The signal modulation due to J-coupling in rapid acquisition with relaxation enhancement (RARE) is suppressed only when the inverse of the pulse interval (tau) is large compared to both the chemical shift (CS) difference (Deltadelta) of the coupled spins and the coupling constant. In contrast, the echo amplitudes in ultrafast low-flip-angle RARE (U-FLARE) oscillate around a quasi-steady-state value that is greater than zero (neglecting relaxation and diffusion) even when Deltadelta > 1/tau. The flip-angle distribution over the measured slice caused by the use of Gaussian-shape slice-selective refocusing pulses further reduces the echo oscillations. When the pulse interval falls short of the fast pulse rate regime, spectroscopic U-FLARE provides an improved spatial impulse response in the phase-encoding (PE) direction compared to spectroscopic RARE.
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