Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Exciting multiple slices at the same time, "controlled aliasing in parallel imaging results in higher acceleration" (CAIPIRINHA) and "phase-offset multiplanar" have shown to be very effective techniques in 2D multislice imaging. Being provided with individual rf phase cycles, the simultaneously excited slices are shifted with respect to each other in the FOV and, thus, can be easily separated. For SSFP sequences, however, similar rf phase cycles are required to maintain the steady state, impeding a straightforward application of phase-offset multiplanar or controlled aliasing in parallel imaging results in higher acceleration. ⋯ Steady state properties and shifted banding behavior of the new phase cycles were investigated using simulations and phantom experiments. Moreover, the concept was applied to perform whole heart myocardial perfusion SSFP imaging as well as real-time and cine SSFP imaging with increased coverage. Showing no significant penalties in SNR or image quality, the results successfully demonstrate the general applicability of the concept.
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A major difference between arterial-spin-labeling MRI and gold-standard radiotracer blood flow methods is that the compartment localization of the labeled spins in the arterial-spin-labeling image is often ambiguous, which may affect the quantification of cerebral blood flow. In this study, we aim to probe whether the spins are located in the vascular system or tissue by using T2 of the arterial-spin-labeling signal as a marker. We combined two recently developed techniques, pseudo-continuous arterial spin labeling and T2-Relaxation-Under-Spin-Tagging, to determine the T2 of the labeled spins at multiple postlabeling delay times. ⋯ By fitting the experimental data to a two-compartment model, we estimated gray matter cerebral blood flow, arterial transit time, and tissue transit time to be 74.0 ± 10.7 mL/100g/min (mean ± SD, N = 10), 938 ± 156 msec, and 1901 ± 181 msec, respectively. The arterial blood volume was calculated to be 1.18 ± 0.21 mL/100 g. A postlabeling delay time of 2 s is sufficient to allow the spins to completely enter the tissue space for gray matter but not for white matter.
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In this work, two pharmacokinetic modeling techniques, population arterial input function model, and reference region model, were applied to dynamic contract-enhanced MRI data, to test the influence of a change in heart rate on modeling parameters. A rat population arterial input function was generated by dynamic contrast-enhanced computed tomography measurements using the MR contrast agent gadolinium diethylenetriamine penta-acetic acid. Then, dynamic contract-enhanced MRI was used for treatment monitoring in two groups of hepatocellular carcinoma bearing rats. ⋯ For group 1, good correlation and agreement was found between the models showing no difference in K(trans) and v(e) (ΔK(trans): 4 ± 19% and Δv(e): 4 ± 12%, P = 0.2). In contrast, for group 2, a bias in parameter values for the population arterial input function model was detected (ΔK(trans): -45 ± 7% and Δv(e): -31 ± 7%, P ≤ 0.001). The presented work underlines the value of the reference region model in longitudinal treatment monitoring and provides a straightforward approach for the generation of a rat population arterial input function.