title: Modified look-locker inversion recovery T1 mapping indices: assessment of accuracy and reproducibility between magnetic resonance scanners.
abstract: BACKGROUND
  Cardiovascular magnetic resonance (CMR) T1 mapping indices, such as T1 time and partition coefficient (λ), have shown potential to assess diffuse myocardial fibrosis. The purpose of this study was to investigate how scanner and field strength variation affect the accuracy and precision/reproducibility of T1 mapping indices.
  
  
  METHODS
  CMR studies were performed on two 1.5T and three 3T scanners. Eight phantoms were made to mimic the T1/T2 of pre- and post-contrast myocardium and blood at 1.5T and 3T. T1 mapping using MOLLI was performed with simulated heart rate of 40-100 bpm. Inversion recovery spin echo (IR-SE) was the reference standard for T1 determination. Accuracy was defined as the percent error between MOLLI and IR-SE, and scan/re-scan reproducibility was defined as the relative percent mean difference between repeat MOLLI scans. Partition coefficient was estimated by ΔR1myocardium phantom/ΔR1blood phantom. Generalized linear mixed model was used to compare the accuracy and precision/reproducibility of T1 and λ across field strength, scanners, and protocols.
  
  
  RESULTS
  Field strength significantly affected MOLLI T1 accuracy (6.3% error for 1.5T vs. 10.8% error for 3T, p<0.001) but not λ accuracy (8.8% error for 1.5T vs. 8.0% error for 3T, p=0.11). Partition coefficients of MOLLI were not different between two 1.5T scanners (47.2% vs. 47.9%, p=0.13), and showed only slight variation across three 3T scanners (49.2% vs. 49.8% vs. 49.9%, p=0.016). Partition coefficient also had significantly lower percent error for precision (better scan/re-scan reproducibility) than measurement of individual T1 values (3.6% for λ vs. 4.3%-4.8% for T1 values, approximately, for pre/post blood and myocardium values).
  
  
  CONCLUSIONS
  Based on phantom studies, T1 errors using MOLLI ranged from 6-14% across various MR scanners while errors for partition coefficient were less (6-10%). Compared with absolute T1 times, partition coefficient showed less variability across platforms and field strengths as well as higher precision.
authors.affiliation: Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, MD 20892-1182, USA.
authors.forename: Fabio S
authors.initials: FS
authors.lastname: Raman
authors.forename: Nadine
authors.initials: N
authors.lastname: Kawel-Boehm
authors.forename: Neville
authors.initials: N
authors.lastname: Gai
authors.forename: Melanie
authors.initials: M
authors.lastname: Freed
authors.forename: Jing
authors.initials: J
authors.lastname: Han
authors.forename: Chia-Ying
authors.initials: CY
authors.lastname: Liu
authors.forename: Joao A C
authors.initials: JA
authors.lastname: Lima
authors.forename: David A
authors.initials: DA
authors.lastname: Bluemke
authors.forename: Songtao
authors.initials: S
authors.lastname: Liu
mesh_terms: D003287:Contrast Media; D004719:Endomyocardial Fibrosis / Q000175:diagnosis*; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results
chemical_list: D003287:Contrast Media
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