title: High-permittivity thin dielectric padding improves fresh blood imaging of femoral arteries at 3 T.
abstract: OBJECTIVE
  Fresh blood imaging (FBI) is a useful noncontrast magnetic resonance angiographic (MRA) method for the assessment of peripheral arterial disease, particularly for imaging patients with poor renal function. Compared with 1.5 T, 3 T enables higher signal-to-noise ratio and/or spatiotemporal resolution in FBI. Indeed, previous studies have reported successful FBI of the calf station at 3 T. However, FBI of the thigh station at 3 T has been reported to suffer from signal void in the common femoral artery of 1 thigh only because of the radial symmetry in transmit radiofrequency field (B1+) variation. We sought to increase the signal of femoral artery in FBI at 3 T using high-permittivity dielectric padding.
  
  
  METHODS
  We performed FBI and B1+ mapping of the thigh station at 3 T in 13 human subjects to compare the following 3 dielectric padding settings: no padding, commercially available thick (approximately 5 cm) dielectric padding, and high-permittivity thin (approximately 2 cm) dielectric padding. We characterized the radial symmetry in B1+ variation as well as its impact on the FBI signal at baseline and how dielectric padding improves B1+ and FBI. We evaluated the quality of 3 FBI MRA acquisitions using quantitative (ie, contrast-to-noise ratio of femoral arteries) and qualitative (ie, conspicuity of femoral arteries) analyses.
  
  
  RESULTS
  With the subjects positioned on the magnetic resonance table in feet-first, supine orientation, the radial symmetry in B1+ variation attenuates the signal in the right common femoral artery. The signal void can be improved partially with commercial padding and improved further with high-permittivity padding. Averaging the results over the 13 subjects, the mean B1+, contrast-to-noise ratio, and conspicuity scores for the right common femoral artery were significantly higher with high-permittivity padding than with commercial padding and baseline (P < 0.001).
  
  
  CONCLUSIONS
  Our study shows that high-permittivity dielectric padding can be used to increase the signal of femoral artery in FBI at 3 T.
authors.affiliation: From the *Department of Physics, and †Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT; and ‡Center for Biomedical Imaging, New York University School of Medicine, New York, NY.
authors.forename: Marc D
authors.initials: MD
authors.lastname: Lindley
authors.forename: Daniel
authors.initials: D
authors.lastname: Kim
authors.forename: Glen
authors.initials: G
authors.lastname: Morrell
authors.forename: Marta E
authors.initials: ME
authors.lastname: Heilbrun
authors.forename: Pippa
authors.initials: P
authors.lastname: Storey
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hanrahan
authors.forename: Vivian S
authors.initials: VS
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D001512:Bedding and Linens; D001783:Blood Flow Velocity; D017097:Electric Impedance; D004574:Electromagnetic Fields; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D005263:Femoral Artery / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation; D018810:Magnetic Resonance Angiography / Q000295:instrumentation*; D008297:Male; D058729:Peripheral Arterial Disease / Q000473:pathology* / Q000503:physiopathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity