Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Transverse relaxation (T2 ) mapping has many applications, including imaging of iron accumulation in grey matter. Using the typical multiecho spin-echo sequence with long echo trains, stimulated echo compensation can enable T2 fitting under conditions of variable radio frequency homogeneity arising from slice profile and in-plane radio frequency variation. Substantial reduction in the number of refocusing pulses could enable use at high magnetic fields where specific absorption rate is a major limitation, and enable multislice use with reduced incidental magnetization transfer at all field strengths. ⋯ All territories produce marginal results when using standard exponential fitting. Savings from reduced echoes can be used to substantially increase slice coverage. In multislice mode, the resulting incidental magnetization transfer decreased brain signal but had minimal effect on measured T2 values.
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Arterial spin labeling has been developed and used for the quantitative and completely noninvasive assessment of myocardial perfusion in vivo. Here we propose a novel arterial spin labeling method called cine-ASL, which is based on an electrocardiogram-gated steady-pulsed labeling approach combined with simultaneous readout over the cardiac cycle using cine-fast low-angle shot. This method led to shorter acquisition times than the previously used Look-Locker flow-sensitive alternating inversion recovery gradient-echo technique while preserving spatial resolution and robustness with respect to cardiac motion. ⋯ In one animal, physiological stress was induced with higher anesthetic concentration to evaluate the response of both methods under vasodilation. Global myocardial perfusion increased from 5.6 to 16.0 mL g(-1) min(-1) with cine-ASL and from 6.3 to 18.7 mL g(-1) min(-1) with Look-Locker flow-sensitive alternating inversion recovery. Although this original scheme requires a separate T1 measurement to be fully quantitative, it improves arterial spin labeling sensitivity while maintaining compatibility with motion constraints in cardiac MRI in small rodents.