Journal of magnetic resonance imaging : JMRI
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J Magn Reson Imaging · Jun 2007
Insight into RF power requirements and B1 field homogeneity for human MRI via rigorous FDTD approach.
To study the dependence of radiofrequency (RF) power deposition on B(0) field strength for different loads and excitation mechanisms. ⋯ With variable phase/amplitude excitation, as a function of frequency, the peak-then-decrease relation observed in the upper axial slices of brain with quadrature excitation becomes more evident in the lower slices as well. Additionally, homogeneity optimization targeted at minimizing the ratio of maximum/minimum B(1) (+) field intensity within the region of interest, typically results in increased RF power requirements (standard deviation was not considered in this study). Increasing the number of excitation ports, however, can result in significant RF power reduction.
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J Magn Reson Imaging · Jun 2007
Rapid dark-blood carotid vessel-wall imaging with random bipolar gradients in a radial SSFP acquisition.
To investigate and evaluate a new rapid dark-blood vessel-wall imaging method using random bipolar gradients with a radial steady-state free precession (SSFP) acquisition in carotid applications. ⋯ Overall, this sequence offers a simple and effective dark-blood contrast mechanism for high-SNR SSFP acquisitions in vessel wall imaging within a short acquisition time.
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J Magn Reson Imaging · Jun 2007
Contrast-dose relation in first-pass myocardial MR perfusion imaging.
To determine the regime of linear contrast enhancement in human first-pass perfusion cardiovascular magnetic resonance (CMR) imaging to improve accuracy in myocardial perfusion quantification. ⋯ Quantitative evaluation of cardiac MR perfusion data needs to account for signal saturation in both the LV blood pool and the myocardium.