Journal of magnetic resonance imaging : JMRI
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To evaluate the impact of data quality on the localization of brain activation in functional magnetic resonance imaging (fMRI) and to explore whether the temporal contrast-to-noise-ratio (CNR) provides a quantitative parameter to estimate fMRI quality. ⋯ Calculating the CNR using an adaptive low-pass filter gives similar results to a GLM-based approach and could be advantageous for cases in which the hemodynamic response function (HRF) differs significantly from common assumptions. The CNR can be used to identify and exclude runs with suboptimal CNR, and to identify sessions with insufficient data quality. The CNR may serve as a quantitative and intuitive parameter to assess the performance and quality of clinical fMRI investigations, including information on both functional performance (contrast) and data quality (noise caused by the system and physiology).
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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
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.
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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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The noninvasive assessment of lung function using imaging is increasingly of interest for the study of lung diseases, including chronic obstructive pulmonary disease (COPD) and asthma. Hyperpolarized gas MRI (HP MRI) has demonstrated the ability to detect changes in ventilation, perfusion, and lung microstructure that appear to be associated with both normal lung development and disease progression. ⋯ Clinical investigations using HP MRI to study asthma, COPD, cystic fibrosis, pediatric chronic lung disease, and lung transplant are reviewed. Recent advances in polarization, pulse sequence development for imaging with Xe-129, and prototype low magnetic field systems dedicated to lung imaging are highlighted as areas of future development for this rapidly evolving technology.