نتایج جستجو برای: radiofrequency fields

تعداد نتایج: 262715  

Journal: :Journal of magnetic resonance 2004
Daniel Topgaard Alexander Pines

A methodology for chemical shift resolved molecular self-diffusion measurements in time-independent static and radiofrequency field gradients is demonstrated. Diffusion encoding is provided by a stimulated echo sequence with additional z-storage that allows for a change of diffusion time without affecting the relaxation weighting. The signal is acquired stroboscopically between the pulses of a ...

2014
António M Ferreira Francisco Costa António Tralhão Hugo Marques Nuno Cardim Pedro Adragão

Use of both magnetic resonance imaging (MRI) and pacing devices has undergone remarkable growth in recent years, and it is estimated that the majority of patients with pacemakers will need an MRI during their lifetime. These investigations will generally be denied due to the potentially dangerous interactions between cardiac devices and the magnetic fields and radio frequency energy used in MRI...

2017
Tomoyuki Shirai Jianqing Wang Mayumi Kawabe Kanako Wake So-ichi Watanabe Satoru Takahashi Osamu Fujiwara

In everyday life, people are exposed to radiofrequency (RF) electromagnetic fields (EMFs) with multiple frequencies. To evaluate the possible adverse effects of multifrequency RF EMFs, we performed an experiment in which pregnant rats and their delivered offspring were simultaneously exposed to eight different communication signal EMFs (two of 800 MHz band, two of 2 GHz band, one of 2.4 GHz ban...

Journal: :The Journal of chemical physics 2006
Brent Pryor Navin Khaneja

In this paper, we introduce algorithms based on Fourier synthesis for designing phase compensating rf pulse sequences for high-resolution nuclear magnetic resonance (NMR) spectroscopy in an inhomogeneous B0 field. We show that using radio frequency pulses and time varying linear gradients in three dimensions, it is possible to impart the transverse magnetization of spins phase, which is a desir...

Journal: :European journal of radiology 1992
J E Brock

Many of our most sophisticated hospitals are located in urban areas where available land is at a minimum. Consequently ideal sites for diagnostic equipment like PET, medical cyclotrons, and MRI scanners are not available. These sites require special structural considerations, shielding provisions, and construction access. Due to the processes involved in PET and MRI scanning, shielding for radi...

Journal: :Radiographics : a review publication of the Radiological Society of North America, Inc 2005
Robert A Pooley

Learning the basic concepts required to understand magnetic resonance (MR) imaging is a straightforward process. Although the individual concepts are simple, there are many concepts to learn and retain simultaneously; this situation may give the illusion that learning the physics of MR imaging is complicated. It is important for the radiologist who interprets MR images to understand the methods...

Journal: :Journal of magnetic resonance imaging : JMRI 2000
F G Shellock

During an MR procedure, most of the transmitted RF power is transformed into heat within the patient's tissue as a result of resistive losses. Not surprisingly, the primary bioeffects associated with the RF radiation used for MR procedures are directly related to the thermogenic qualities of this electromagnetic field. This review article discusses the characteristics of RF energy-induced heati...

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