title: Flip angle-optimized fast dynamic T1 mapping with a 3D gradient echo sequence.
abstract: OBJECTIVE
  To analyze the flip angle dependence and to optimize the statistical precision of a fast three-dimensional (3D) T1 mapping technique based on the variable flip angle (VFA) method. The proposed single flip angle (1FA) approach acquires only a single 3D spoiled gradient echo data set for each time point of the dynamical series in combination with a longer baseline measurement.
  
  
  METHODS
  The optimal flip angle for the dynamic series can be calculated as αdyn,opt  = arccos[(2E1  - 1)/(2 - E1 )] (with E1  = exp(-TR /T1 )) by minimizing the statistical error of T1 . T1 maps of a liquid phantom with step-wise increasing concentrations of contrast agent were measured using a saturation recovery (SR) and a VFA/1FA technique with 11 flip angles. The standard deviation of the parameter maps was defined as statistical error of the 1FA measurement.
  
  
  RESULTS
  The measured statistical error of the 1FA technique as a function of αdyn agrees with the derived theoretical curve. The optimal flip angle increases from about 5° for T1  = 2629 ms to 30° for T1  = 137 ms. The relative deviation between 1FA and SR measurements varies between -2.9 % and +10.3 %. Measurements in vivo confirm the expression for the optimal flip angle.
  
  
  CONCLUSIONS
  The proposed flip angle-optimized 1FA technique optimizes the precision of T1 values in dynamic phantom measurements.
authors.affiliation: Josef Lissner Laboratory for Biomedical Imaging, Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Dietrich
authors.forename: Maximilian
authors.initials: M
authors.lastname: Freiermuth
authors.forename: Linus
authors.initials: L
authors.lastname: Willerding
authors.forename: Maximilian F
authors.initials: MF
authors.lastname: Reiser
authors.forename: Michael
authors.initials: M
authors.lastname: Peller
mesh_terms: D000465:Algorithms; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: contrast agent concentration; fast dynamic imaging; longitudinal relaxation time T1; magnetic resonance imaging