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

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

Research output: Contribution to journalArticle

71 Citations (Scopus)

Abstract

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 B1 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 B1 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).

Original languageEnglish (US)
Pages (from-to)197-202
Number of pages6
JournalJournal of Magnetic Resonance Imaging
Volume24
Issue number1
DOIs
StatePublished - Jul 2006

Fingerprint

Head
Computer Simulation
Water
Signal-To-Noise Ratio
Artifacts
Brain

Keywords

  • FDTD
  • High-field MRI
  • RF field focusing
  • RF field inhomogeneity
  • RF field passive shim

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

Cite this

Manipulation of image intensity distribution at 7.0 T : Passive RF shimming and focusing with dielectric materials. / Yang, Qing X.; Mao, Weihua; Wang, Jinghua; Smith, Michael B.; Lei, Hao; Zhang, Xiaoliang; Ugurbil, Kamil; Chen, Wei.

In: Journal of Magnetic Resonance Imaging, Vol. 24, No. 1, 07.2006, p. 197-202.

Research output: Contribution to journalArticle

Yang, Qing X. ; Mao, Weihua ; Wang, Jinghua ; Smith, Michael B. ; Lei, Hao ; Zhang, Xiaoliang ; Ugurbil, Kamil ; Chen, Wei. / Manipulation of image intensity distribution at 7.0 T : Passive RF shimming and focusing with dielectric materials. In: Journal of Magnetic Resonance Imaging. 2006 ; Vol. 24, No. 1. pp. 197-202.
@article{0b2078c014da42b0be67c2ccf78f299c,
title = "Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials",
abstract = "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 B1 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 B1 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).",
keywords = "FDTD, High-field MRI, RF field focusing, RF field inhomogeneity, RF field passive shim",
author = "Yang, {Qing X.} and Weihua Mao and Jinghua Wang and Smith, {Michael B.} and Hao Lei and Xiaoliang Zhang and Kamil Ugurbil and Wei Chen",
year = "2006",
month = "7",
doi = "10.1002/jmri.20603",
language = "English (US)",
volume = "24",
pages = "197--202",
journal = "Journal of Magnetic Resonance Imaging",
issn = "1053-1807",
publisher = "John Wiley and Sons Inc.",
number = "1",

}

TY - JOUR

T1 - Manipulation of image intensity distribution at 7.0 T

T2 - Passive RF shimming and focusing with dielectric materials

AU - Yang, Qing X.

AU - Mao, Weihua

AU - Wang, Jinghua

AU - Smith, Michael B.

AU - Lei, Hao

AU - Zhang, Xiaoliang

AU - Ugurbil, Kamil

AU - Chen, Wei

PY - 2006/7

Y1 - 2006/7

N2 - 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 B1 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 B1 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).

AB - 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 B1 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 B1 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).

KW - FDTD

KW - High-field MRI

KW - RF field focusing

KW - RF field inhomogeneity

KW - RF field passive shim

UR - http://www.scopus.com/inward/record.url?scp=33745700347&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33745700347&partnerID=8YFLogxK

U2 - 10.1002/jmri.20603

DO - 10.1002/jmri.20603

M3 - Article

C2 - 16755543

AN - SCOPUS:33745700347

VL - 24

SP - 197

EP - 202

JO - Journal of Magnetic Resonance Imaging

JF - Journal of Magnetic Resonance Imaging

SN - 1053-1807

IS - 1

ER -