title: Radiofrequency shielding of surface coils at 4.0 T.
abstract: Because radiation loss associated with a radiofrequency (RF) coil increases as roughly the fourth power of the frequency, this loss mechanism may become important in high-field studies above 2.0 T. In this study, the contribution of radiation losses at 4.0 T were determined in a rectangular surface coil using an RF shield to modify the radiation losses. The effect of this shield was determined on coil Q, B1 distribution, and signal to noise as a function of distance between the coil and the shield. Phantoms and human tissue were evaluated to characterize the loss mechanisms. The results demonstrate a large radiation loss in the unshielded surface coil. However, the radiation losses in vivo were not dominant owing to a large inductive loss occurring from dielectric currents in the body at 170 MHz.
authors: Laboratory of Cardiac Energetics National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors: K C
authors: KC
authors: Ong
authors: H
authors: H
authors: Wen
authors: A S
authors: AS
authors: Chesnick
authors: S
authors: S
authors: Duewell
authors: F A
authors: FA
authors: Jaffer
authors: R S
authors: RS
authors: Balaban
mesh_terms: D016477:Artifacts; D004867:Equipment Design; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D007866:Leg / Q000033:anatomy & histology; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008953:Models, Anatomic; D012016:Reference Values