title: A USPIO doped gel phantom for R2* relaxometry.
abstract: OBJECTIVE
  This work describes a phantom containing regions of controlled R2* (1/T2*) values to provide a stable reference object for testing implementations of R2* relaxometry commonly used for liver and heart iron assessments.
  
  
  METHODS
  A carrageenan-strengthened gadolinium DTPA doped agarose gel was used to enclose nine gels additionally doped with ultra-small superparamagnetic iron oxide. R2* values were determined at 1.5 T using multi-echo GRE sequences and exponential regression of pixel values from a region of interest against echo time using non-linear regression algorithms. We measured R2*, R2 and R1 values and the inter-scan and inter-operator reproducibility.
  
  
  RESULTS
  The phantom reliably demonstrated R2* values in seven steps between 22.4 s-1(SE 1.98) and 441.9 s-1(SE 6.76), with an R2* relaxivity (r2*) of 792 (SE 5.6) mM-1s-1. The doped gels displayed a concentration-dependent R2' component of R2* phantom, indicating superparamagnetic enhancement effects. We observed no significant change in relaxivity (r2*) over 12 months, and estimate a useful life of 3 years. Detailed descriptions of the production process and calculators are been provided as Online Resources.
  
  
  CONCLUSIONS
  The phantom provides a durable test object with controlled R2* relaxation behaviour, useful for a range of R2* relaxometry reference work.
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Building 57, St Lucia, QLD, 4072, Australia. Greg.Brown@cai.uq.edu.au.
authors.forename: Gregory C
authors.identifier: http://orcid.org/0000-0001-7994-2743
authors.initials: GC
authors.lastname: Brown
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Building 57, St Lucia, QLD, 4072, Australia.
authors.forename: Gary J
authors.identifier: http://orcid.org/0000-0002-3400-3109
authors.initials: GJ
authors.lastname: Cowin
authors.affiliation: Translational Research Centre, The University of Queensland, St Lucia, Australia.
authors.forename: Graham J
authors.identifier: http://orcid.org/0000-0002-0805-2775
authors.initials: GJ
authors.lastname: Galloway
mesh_terms: D000465:Algorithms; D001369:Axons / Q000473:pathology*; D002138:Calibration; D002351:Carrageenan / Q000737:chemistry; D003198:Computer Simulation; D003287:Contrast Media / Q000737:chemistry; D038524:Diffusion Magnetic Resonance Imaging; D005290:Ferric Compounds / Q000737:chemistry; D005782:Gels; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007501:Iron / Q000737:chemistry*; D008099:Liver / Q000000981:diagnostic imaging* / Q000473:pathology; D009682:Magnetic Resonance Spectroscopy; D019047:Phantoms, Imaging; D012044:Regression Analysis; D015203:Reproducibility of Results; D012685:Sepharose / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D003287:Contrast Media; D005290:Ferric Compounds; D005782:Gels; D014867:Water; C000499:ferric oxide; D002351:Carrageenan; D012685:Sepharose; D007501:Iron
keywords: Calibration; MRI; Phantom imaging; Quantitative evaluation