title: T1 mapping of the myocardium: intra-individual assessment of the effect of field strength, cardiac cycle and variation by myocardial region.
abstract: BACKGROUND
  Myocardial T1 relaxation time (T1 time) and extracellular volume fraction (ECV) are altered in the presence of myocardial fibrosis. The purpose of this study was to evaluate acquisition factors that may result in variation of measured T1 time and ECV including magnetic field strength, cardiac phase and myocardial region.
  
  
  METHODS
  31 study subjects were enrolled and underwent one cardiovascular MR exam at 1.5 T and two exams at 3 T, each on separate days. A Modified Look-Locker Inversion Recovery (MOLLI) sequence was acquired before and 5, 10, 12, 20, 25 and 30 min after administration of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist) at 1.5 T (exam 1). For exam 2, MOLLI sequences were acquired at 3 T both during diastole and systole, before and after administration of Gd-DTPA (0.15 mmol/kg Magnevist).Exam 3 was identical to exam 2 except gadobenate dimeglumine was administered (Gd-BOPTA; 0.1 mmol/kg Multihance). T1 times were measured in myocardium and blood. ECV was calculated by (ΔR1myocardium/ΔR1blood)*(1-hematocrit).
  
  
  RESULTS
  Before gadolinium, T1 times of myocardium and blood were significantly greater at 3 T versus 1.5 T (28% and 31% greater, respectively, p < 0.001); after gadolinium, 3 T values remained greater than those at 1.5 T (14% and 12% greater for myocardium and blood at 3 T with Gd-DTPA, respectively, p < 0.0001 and 18% and 15% greater at 3 T with Gd-BOPTA, respectively, p < 0.0001). However, ECV did not vary significantly with field strength when using the same contrast agent at equimolar dose (p = 0.2). Myocardial T1 time was 1% shorter at systole compared to diastole pre-contrast and 2% shorter at diastole compared to systole post-contrast (p < 0.01). ECV values were greater during diastole compared to systole on average by 0.01 (p < 0.01 to p < 0.0001). ECV was significantly higher for the septum compared to the non-septal myocardium for all three exams (p < 0.0001-0.01) with mean absolute differences of 0.01, 0.004, and 0.07, respectively, for exams 1, 2 and 3.
  
  
  CONCLUSIONS
  ECV is similar at field strengths of 1.5 T and 3 T. Due to minor variations in T1 time and ECV during the cardiac cycle and in different myocardial regions, T1 measurements should be obtained at the same cardiac phase and myocardial region in order to obtain consistent results.
authors.affiliation: Radiology and Imaging Sciences and Molecular Biomedical Imaging Laboratory, National Institute of Biomedical Imaging and Bioengineering, Bethesda, MD, USA.
authors.forename: Nadine
authors.initials: N
authors.lastname: Kawel
authors.forename: Marcelo
authors.initials: M
authors.lastname: Nacif
authors.forename: Anna
authors.initials: A
authors.lastname: Zavodni
authors.forename: Jacquin
authors.initials: J
authors.lastname: Jones
authors.forename: Songtao
authors.initials: S
authors.lastname: Liu
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Sibley
authors.forename: David A
authors.initials: DA
authors.lastname: Bluemke
mesh_terms: D000328:Adult; D003287:Contrast Media; D005260:Female; D005355:Fibrosis; D005682:Gadolinium; D019786:Gadolinium DTPA; D006331:Heart Diseases / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008536:Meglumine / Q000031:analogs & derivatives; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000473:pathology*; D009942:Organometallic Compounds; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; C064572:gadobenic acid; D008536:Meglumine; D005682:Gadolinium; D019786:Gadolinium DTPA