Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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To significantly reduce the background phase effects, especially at the air-tissue interface, and to enhance the desirable local structures of veins in susceptibility-weighted imaging. ⋯ The Magnitude of Complex Filtering method successfully reduced most background phase effects without requiring additional processing or scan time.
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Lung pO2 mapping with (3)He MRI assumes that the sources of signal decay with time during a breath-hold are radiofrequency depolarization and oxygen-dependent T1 relaxation, but the method is sensitive to other sources of spatio-temporal signal change such as diffusion. The purpose of this work was to assess the use of (3)He pO2 mapping in patients with chronic obstructive pulmonary disease. ⋯ Movement of gas within the lungs during breath-hold causes regional changes in signal over time that are not related to oxygen concentration, leading to erroneous pO2 measurements using the linear oxygen-dependent signal decay model. These spatio-temporal sources of signal change cannot be reliably separated at present, making pO2 mapping using this methodology unreliable in chronic obstructive pulmonary disease patients with significant bullous emphysema or delayed ventilation.
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To introduce a new method for removing background artifacts in field maps and apply it to enhance the accuracy of susceptibility mapping. ⋯ Compared with SHARP, RESHARP removes background field artifact more effectively, leading to more accurate susceptibility measurements in iron-rich deep gray matter.
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Nonlinear spatial encoding magnetic fields result in an inhomogeneous image resolution. Within this study, this characteristic property of nonlinear encoding is investigated with regard to its potential to accelerate MRI acquisitions. ⋯ A new effect of nonlinear spatial encoding magnetic fields was found, which allows more efficient data sampling and at the same time counterbalancing the natural variation in image resolution.
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Cardiac cine balanced steady-state free precession (bSSFP) imaging uses a high flip angle (FA) to obtain high blood-myocardium signal-to-noise and contrast-to-noise ratios (CNR). Use of high FAs, however, results in substantially increased SAR. Our objective was to develop a variable FA bSSFP cardiac cine imaging technique with: (1) low SAR and blood-myocardium CNR similar to conventional constant FA bSSFP (CFA-bSSFP) or (2) increased blood-myocardium CNR compared to CFA-bSSFP with similar SAR. ⋯ aVFA-bSSFP can be used for lower SAR or higher contrast cardiac cine imaging compared to the conventional segmented CFA-bSSFP imaging.