title: Cardiac R2* values are independent of the image analysis approach employed.
abstract: OBJECTIVE
  To determine whether systematic differences were present between myocardial R2* values obtained with two different decay models: truncation and exponential + constant (Exp-C).
  
  
  METHODS
  Single-center cohorts were used to compare black and bright blood sequences separately, and a multicenter cohort of mixed bright and black blood studies was used to assess the generalizability. Truncated exponential estimates were calculated with CMRtools, which uses a single region of interest (ROI) method. Exp-C estimates were calculated using a pixelwise approach.
  
  
  RESULTS
  No differences could be distinguished based upon whether a white or black blood sequence was examined. The two fitting algorithms yielded similar R2* values, with R-squared values exceeding 0.997 and a coefficient of variation of 3% to 4%. Results using the pixelwise method yielded a small systematic bias (∼3%) that became apparent in patients with severe iron deposition. This disparity disappeared when Exp-C fitting was used on a single ROI, suggesting that the use of pixelwise mapping was responsible for the bias. In the multicenter cohort, the strong agreement between the two fitting approaches was reconfirmed.
  
  
  CONCLUSIONS
  Cardiac R2* values are independent of the signal model used for its calculation over clinically relevant ranges. Clinicians can compare results among centers using these disparate approaches with confidence.
authors.affiliation: CMR Unit, Fondazione G. Monasterio CNR-Regione Toscana and Institute of Clinical Physiology, Pisa, Italy; Division of Cardiology, Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, California, USA.
authors.forename: Antonella
authors.initials: A
authors.lastname: Meloni
authors.forename: Hugh Young
authors.initials: HY
authors.lastname: Rienhoff
authors.forename: Amber
authors.initials: A
authors.lastname: Jones
authors.forename: Alessia
authors.initials: A
authors.lastname: Pepe
authors.forename: Massimo
authors.initials: M
authors.lastname: Lombardi
authors.forename: John C
authors.initials: JC
authors.lastname: Wood
mesh_terms: D000465:Algorithms; D016477:Artifacts; D005260:Female; D006331:Heart Diseases / Q000473:pathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult; D017086:beta-Thalassemia / Q000473:pathology*
keywords: cardiac R2*; cardiovascular magnetic resonance; image analysis; iron overload