title: Prototype phantoms for characterization of ultralow field magnetic resonance imaging.
abstract: OBJECTIVE
  Prototype phantoms were designed, constructed, and characterized for the purpose of calibrating ultralow field magnetic resonance imaging (ULF MRI) systems. The phantoms were designed to measure spatial resolution and to quantify sensitivity to systematic variation of proton density and relaxation time, T1 .
  
  
  METHODS
  The phantoms were characterized first with conventional magnetic resonance scanners at 1.5 and 3 T, and subsequently with a prototype ULF MRI scanner between 107 and 128 μT .
  
  
  RESULTS
  The ULF system demonstrated a 2-mm spatial resolution and, using T1 measurements, distinguished aqueous solutions of MnCl2 differing by 20 μM  [Mn(2+) ].
  
  
  CONCLUSIONS
  The prototype phantoms proved well-matched to ULF MRI applications, and allowed direct comparison of the performance of ULF and clinical systems.
authors.affiliation: Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Boss
authors.forename: John A B
authors.initials: JA
authors.lastname: Mates
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Busch
authors.forename: Paul
authors.initials: P
authors.lastname: SanGiorgio
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Russek
authors.forename: Kai
authors.initials: K
authors.lastname: Buckenmaier
authors.forename: Kent D
authors.initials: KD
authors.lastname: Irwin
authors.forename: Hsiao-Mei
authors.initials: HM
authors.lastname: Cho
authors.forename: Gene C
authors.initials: GC
authors.lastname: Hilton
authors.forename: John
authors.initials: J
authors.lastname: Clarke
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D010865:Pilot Projects; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: T1; phantom; proton density; spatial resolution; superconducting quantum interference device; ultralow field; ultralow field magnetic resonance imaging