title: Ex-vivo cellular MRI with b-SSFP: quantitative benefits of 3T over 1.5 T.
abstract: BACKGROUND
  The use of MRI with iron-based magnetic nanoparticles for imaging cells is a rapidly growing field of research. We have recently reported that single iron-labeled cells could be detected, as signal voids, in vivo in mouse brains using a balanced steady-state free precession imaging sequence (b-SSFP) and a customized microimaging system at 1.5 T.
  
  
  METHODS
  In the current study we assess the benefits, and challenges, of using a higher magnetic field strength for imaging iron-labeled cells with b-SSFP, using ex vivo mouse brain specimens imaged with near identical systems at 1.5 and 3.0 T.
  
  
  RESULTS
  The substantial banding artifact that appears in 3 T b-SSFP images was readily minimized with RF phase cycling, allowing for banding-free b-SSFP images to be compared between the two field strengths. This study revealed that with an optimal 3 T b-SSFP imaging protocol, more than twice as many signal voids were detected as with 1.5 T.
  
  
  CONCLUSIONS
  There are several factors that contributed to this important result. First, a greater-than-linear SNR gain was achieved in mouse brain images at 3 T. Second, a reduction in the bandwidth, and the associated increase in repetition time and SNR, produced a dramatic increase in the contrast generated by iron-labeled cells.
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, London, ON, Canada. sramadan@imaging.robarts.ca
authors.forename: Soha Said
authors.initials: SS
authors.lastname: Ramadan
authors.forename: Chris
authors.initials: C
authors.lastname: Heyn
authors.forename: Lisa T
authors.initials: LT
authors.lastname: Mackenzie
authors.forename: Ann F
authors.initials: AF
authors.lastname: Chambers
authors.forename: Brian K
authors.initials: BK
authors.lastname: Rutt
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Foster
mesh_terms: D000818:Animals; D016477:Artifacts; D001921:Brain / Q000166:cytology*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007501:Iron / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods; D053768:Metal Nanoparticles; D051379:Mice; D008819:Mice, Nude
chemical_list: D007501:Iron