BACKGROUND: Cardiac magnetic resonance (CMR) T1 mapping has been used to 
characterize myocardial diffuse fibrosis. The aim of this study is to determine 
the reproducibility and sample size of CMR fibrosis measurements that would be 
applicable in clinical trials.
METHODS: A modified Look-Locker with inversion recovery (MOLLI) sequence was 
used to determine myocardial T1 values pre-, and 12 and 25min 
post-administration of a gadolinium-based contrast agent at 3 Tesla. For 24 
healthy subjects (8 men; 29 ± 6 years), two separate scans were obtained a) with 
a bolus of 0.15mmol/kg of gadopentate dimeglumine and b) 0.1mmol/kg of 
gadobenate dimeglumine, respectively, with averaged of 51 ± 34 days between two 
scans. Separately, 25 heart failure subjects (12 men; 63 ± 14 years), were 
evaluated after a bolus of 0.15mmol/kg of gadopentate dimeglumine. Myocardial 
partition coefficient (λ) was calculated according to (ΔR1myocardium/ΔR1blood), 
and ECV was derived from λ by adjusting (1-hematocrit).
RESULTS: Mean ECV and λ were both significantly higher in HF subjects than 
healthy (ECV: 0.287 ± 0.034 vs. 0.267 ± 0.028, p=0.002; λ: 0.481 ± 0.052 vs. 442 
± 0.037, p < 0.001, respectively). The inter-study ECV and λ variation were 
about 2.8 times greater than the intra-study ECV and λ variation in healthy 
subjects (ECV:0.017 vs. 0.006, λ:0.025 vs. 0.009, respectively). The estimated 
sample size to detect ECV change of 0.038 or λ change of 0.063 (corresponding to 
~3% increase of histological myocardial fibrosis) with a power of 80% and an 
alpha error of 0.05 for heart failure subjects using a two group design was 27 
in each group, respectively.
CONCLUSION: ECV and λ quantification have a low variability across scans, and 
could be a viable tool for evaluating clinical trial outcome.