title: Susceptibility effects in hyperpolarized (3)He lung MRI at 1.5T and 3T.
abstract: OBJECTIVE
  To compare susceptibility effects in hyperpolarized (3)He lung MRI at the clinically relevant field strengths of 1.5T and 3T.
  
  
  METHODS
  Susceptibility-related B(0) inhomogeneity was evaluated on a macroscopic scale by B(0) field mapping via phase difference. Subpixel susceptibility effects were quantified by mapping T2. Comparison was made between ventilation images obtained from the same volunteers at both field strengths.
  
  
  RESULTS
  The B(0) maps at 3T show enhanced off-resonance effects close to the diaphragm and the ribs due to susceptibility differences. The average T2 from a voxel (20 x 4 x 4) mm(3) was determined as T2 = 27.8 msec +/- 1.2 msec at 1.5T compared to T2 = 14.4 msec +/- 2.6 msec at 3T. In ventilation images the most prominent effect is increased signal attenuation close to the intrapulmonary blood vessels at higher B(0).
  
  
  CONCLUSIONS
  Image homogeneity and T2 are lower at 3T due to increased B(0) inhomogeneity as a consequence of susceptibility differences. These findings indicate that (3)He imaging at 3T has no obvious benefit over imaging at 1.5T, as signal-to-noise ratio (SNR) was comparable for both fields in this work.
authors.affiliation: Academic Radiology, University of Sheffield, Royal Hallamshire Hospital, Sheffield, UK.
authors.forename: Martin H
authors.initials: MH
authors.lastname: Deppe
authors.forename: Juan
authors.initials: J
authors.lastname: Parra-Robles
authors.forename: Salma
authors.initials: S
authors.lastname: Ajraoui
authors.forename: Steven R
authors.initials: SR
authors.lastname: Parnell
authors.forename: Matthew
authors.initials: M
authors.lastname: Clemence
authors.forename: Rolf F
authors.initials: RF
authors.lastname: Schulte
authors.forename: Jim M
authors.initials: JM
authors.lastname: Wild
mesh_terms: D000328:Adult; D003287:Contrast Media; D006371:Helium; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male
chemical_list: D003287:Contrast Media; D006371:Helium