Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials.

Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. Research Abstract Details 

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Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. Abstract Text:

Qing X Yang,Weihua Mao,Jinghua Wang,Michael B Smith,Hao Lei,Xiaoliang Zhang,Kamil Ugurbil,Wei Chen,

PURPOSE: To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach. MATERIALS AND METHODS: The intensity distribution changes of gradient-recalled-echo (GRE) and spin-echo (SE) images of a human head acquired with water pads (dielectric constant = 78) placed in specified configurations around the head at 7.0 T were evaluated and compared with computer simulation results using the finite difference time domain (FDTD) method. The contributions to the B(1) field distribution change from the displacement current and conductive current of a given configuration of dielectric padding were determined with computer simulations. RESULTS: MR image intensity distribution in the human head with an RF coil at 7.0 T can be changed drastically by placing water pads around the head. Computer simulations reveal that the high permittivity of water pads results in a strong displacement current that enhances image intensity in the nearby region and alters the intensity distribution of the entire brain. CONCLUSION: The image intensity distribution in the human head at ultra-high field strengths can be effectively manipulated with high permittivity padding. Utilizing this effect, the B(1) field inside the human head of a given RF coil can be adjusted to reduce the B(1) field inhomogeneity artifact associated with the wave behavior (RF passive shimming) or to locally enhance the signal-to-noise ratio (SNR) in targeted regions of interest (ROIs; RF field focusing).

Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. Publishing Authors By Initials

QX Yang,W Mao,J Wang,MB Smith,H Lei,X Zhang,K Ugurbil,W Chen,

For similar natural sciences: physics: radiation: radiation, nonionizing: radio waves research abstracts see: natural sciences: physics: radiation: radiation, nonionizing: radio waves research

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MEDLINE DATE:

Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. Journal Published:

PUBLICATION TYPE: Research Support, N.I.H., Extr

Journal: Journal of magnetic resonance imaging : JMRI

VOLUME: 24

Page Numbers: 197-202

Journal Abbreviation:

ISSN: 1053-1807

DAY: 3

MONTH: Jul

YEAR: 2006

Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. Information

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LANGUAGE: eng

NlmUniqueID: 9105850

Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials. Keywords Mesh Terms:

KEYWORDS: Radio Waves

MESH TERMS: methods

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Grant and Affiliation Information for Manipulation of image intensity distribution at 7.0 T: passive RF shimming and focusing with dielectric materials.

AFFILIATION: Center for NMR Research, Department of Radiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA. qyang@psu.edu

Country: United States

AGENCY: United States NIBIB

GRANT: R01EB000454

ACRONYM: EB

MEDLINETA: J Magn Reson Imaging

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