نتایج جستجو برای: shimming
تعداد نتایج: 517 فیلتر نتایج به سال:
Introduction: It has been shown that the B1 inhomogeneities in high field systems (e.g.7T) can severely compromise image quality. B1 inhomogeneities are still significant at 3T, but generally do not destroy the ability to image. However, the variations in flip angle (and hence contrast) across the field of excitation can still cause significant problems, particularly with applications where abs...
Introduction: Coronary vessel wall imaging with MR has the ability to obtain vessel wall thickness and lumen d invasively (1,2,3). Apart from cardiac and respiratory motion, a major challenge of coronary vessel wall imaging is th small thickness (0.5-2mm) and thus the need for high resolution. With the wider spread availability of high field 3T clin higher resolution coronary vessel wall imagin...
There are several means of generating circularly polarized light. The use of an electromagnetic helical device is very popular for the experiments using lower photon energy radiation. An advantage of the electromagnetic device is the capability of fast switching of polarization. However, due to its complicated structure and a limited maximum current, construction of a shorter period (< 100 mm) ...
Introduction: In the human brain, both white matter and gray matter contain significant amounts of bound water. Although the bound water is not directly seen in conventional MRI experiments, due to its very short T2, the effects of RF pulses on the bound water can influence the free water signal through proton exchange. This effect is known as magnetization transfer (MT) [1], and when MT effect...
The purpose of this study was to explore the feasibility of assessing quality of diffusion tensor imaging (DTI) from multiple sites and vendors using American College of Radiology (ACR) phantom. Participating sites (Siemens (n = 2), GE (n= 2), and Philips (n = 4)) reached consensus on parameters for DTI and used the widely available ACR phantom. Tensor data were processed at one site. B0 and ed...
A challenge in functional magnetic resonance imaging (fMRI) is to develop imaging methods that are highly sensitive to microscopic field inhomogeneities [the blood oxygenation level-dependent (BOLD) effect] and minimally sensitivity to macroscopic fields. z-Shimming compensates for the through-plane dephasing that arises in gradient-echo images due to magnetic field inhomogeneities. To date, an...
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