نتایج جستجو برای: shimming
تعداد نتایج: 517 فیلتر نتایج به سال:
Introduction Curved spatially-varying magnetic fields have a strong impact on MRI, especially in the context of correcting magnetic field inhomogeneities (shimming) [1]. Conventional methods are well established, but new progress from hardware and sequence development intends to overcome certain limitations, e.g. by the use of higher-order shim coils or the application of spatially-selective dy...
Introduction: With the SENSE Shimming (SSH) approach (1) a method was introduced recently that allows for estimating B0 field inhomogeneities based on a reference image and a series of points on a single free induction decay (FID). The temporal evolution of the FID data is explained by field inhomogeneities, starting from the reference image, making use of the encoding properties of the differe...
INTRODUCTION The knowledge of the complex-valued + 1 B map generated by each channel of a phased-array RF coil has become essential for high field MRI systems operating above 7 T, a cornerstone for static or dynamic shimming techniques, whose aim is to provide a uniform excitation over any region of interest (ROI). The maps must be measured experimentally for each RF coil and each subject under...
Several methods have been proposed for overcoming the effects of radiofrequency (RF) magnetic field inhomogeneity in high-field MRI. Some of these methods rely at least in part on the ability to independently control magnitude and phase of different drives in either one multielement RF coil or in different RF coils in a transmit array. The adjustment of these drive magnitudes and phases alone t...
Introduction: The clinical implementation of high field MRI systems has introduced new challenges for body imaging with respect to B1 field nonuniformities, which can result in the generation of standing waves and signal loss particularly in abdominal imaging. Several approaches have been proposed to achieve a more homogeneous excitation and to avoid a degradation of image quality at higher mag...
Introduction Recent studies [1] revealed that balanced SSFP shows a pronounced magnetization transfer (MT) contrast, which can be altered via the RF pulse duration and thus allows for quantitative MT imaging [2]. It is thereby assumed that changes in signal intensity are due to the MT effect alone. However, elongated RF pulses entail a prolonged TR, which may introduce signal variations due to ...
The ability to predict both transmit and receive characteristics in vivo is an important and necessary tool for the development of coils especially at ultra high magnetic fields (UHF). Accurate simulation permits the virtual development of coils saving both human and material resources [1, 2]. This is especially important during this period where large arrays and complex geometries are being pr...
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