Cardiac R2*Values Are Independent of the Image Analysis Approach Employed

Purpose: 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 (similar to 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. Conclusion: 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. (C) 2013 Wiley Periodicals, Inc.