title: Influence of Off-resonance in myocardial T1-mapping using SSFP based MOLLI method.
abstract: BACKGROUND
  Myocardial T1-mapping methods such as MOLLI use SSFP readout and are prone to frequency-dependent error in T1-measurement. A significant error in T1 may result at relatively small off-resonance frequencies that are well within the region without banding artifacts.
  
  
  METHODS
  The sensitivity of T1-estimates based on the SSFP based MOLLI sequence to errors in center frequency are calculated by means of a Bloch simulation and validated by phantom measurements. Typical off-resonance errors following local cardiac shimming are determined by field mapping at both 1.5 and 3.0T. In vivo examples demonstrate the artifactual appearance of T1-maps in the presence of off-resonance variation.
  
  
  RESULTS
  Off-resonance varied 61.8 ± 15.5 Hz (mean ± SD, n = 18) across the heart at 1.5T and 125.0 ± 40.6 Hz (mean ± SD, n = 18) at 3.0T. For T1 = 1000 ms, the variation in T1 due to off-resonance variation was approximately 20 ms at 62 Hz, and > 50 ms at 125 Hz.
  
  
  CONCLUSIONS
  Regional variations due to the inability to completely shim the B0-field variation around the heart appear as regional variation in T1, which is artifactual.
authors.affiliation: National Heart, Lung, and Blood Institute, National Institutes of Health, DHHS, Bethesda, MD 20892, USA. kellman@nih.gov
authors.forename: Peter
authors.initials: P
authors.lastname: Kellman
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Herzka
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Arai
authors.forename: Michael Schacht
authors.initials: MS
authors.lastname: Hansen
mesh_terms: D006331:Heart Diseases / Q000175:diagnosis*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity