title: High permittivity pads reduce specific absorption rate, improve B1 homogeneity, and increase contrast-to-noise ratio for functional cardiac MRI at 3 T.
abstract: OBJECTIVE
  To improve image quality and reduce specific absorption rate in functional cardiac imaging at 3 T.
  
  
  METHODS
  Two high permittivity dielectric pads on the anterior and posterior sides of the thorax were numerically designed and implemented using an aqueous suspension of barium titanate. The effects on the average transmit efficiency, B(1) homogeneity, reception sensitivity, and contrast-to-noise ratio were verified in vivo on a dual-transmit system with the body coil driven in conventional quadrature and radiofrequency-shimmed mode.
  
  
  RESULTS
  Statistically significant improvements in average transmit efficiency, B(1) homogeneity, and contrast-to-noise ratio were measured in healthy volunteers (n = 11) with body mass indices between 20.3 and 34.9. Simulations show that no radiofrequency hot spots are introduced by the dielectric material.
  
  
  CONCLUSIONS
  High permittivity pads are shown to reduce specific absorption rate, improve B(1) homogeneity, and increase contrast-to-noise ratio in functional cardiac magnetic resonance at 3 T. The results presented in this work show that the current approach is more effective than dual-channel radiofrequency shimming.
authors: Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, The Netherlands.
authors: Wyger M
authors: WM
authors: Brink
authors: Andrew G
authors: AG
authors: Webb
mesh_terms: D000042:Absorption; D000328:Adult; D016477:Artifacts; D004553:Electric Conductivity; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008297:Male; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011835:Radiation Protection / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio
keywords: 3 T; B1 inhomogeneity; cardiac; contrast-to-noise ratio; dielectric; specific absorption rate