Radiofrequency shielding of surface coils at 4.0 T.
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.
Ong
K C
KC
Laboratory of Cardiac Energetics National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Wen
H
H
Chesnick
A S
AS
Duewell
S
S
Jaffer
F A
FA
Balaban
R S
RS
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