title: Simultaneous variable flip angle-actual flip angle imaging method for improved accuracy and precision of three-dimensional T1 and B1 measurements.
abstract: A new time-efficient and accurate technique for simultaneous mapping of T(1) and B(1) is proposed based on a combination of the actual flip angle (FA) imaging and variable FA methods. Variable FA-actual FA imaging utilizes a single actual FA imaging and one or more spoiled gradient-echo acquisitions with a simultaneous nonlinear fitting procedure to yield accurate T(1)/B(1) maps. The advantage of variable FA-actual FA imaging is high accuracy at either short T(1) times or long repetition times in the actual FA imaging sequence. Simulations show this method is accurate to 0.03% in FA and 0.07% in T(1) for ratios of repetition time to T1 time over the range of 0.01-0.45. We show for the case of brain imaging that it is sufficient to use only one small FA spoiled gradient-echo acquisition, which results in reduced spoiling requirements and a significant scan time reduction compared to the original variable FA method. In vivo validation yielded high-quality 3D T(1) maps and T(1) measurements within 10% of previously published values and within a clinically acceptable scan time. The variable FA-actual FA imaging method will increase the accuracy and clinical feasibility of many quantitative MRI methods requiring T(1)/B(1) mapping such as dynamic contrast enhanced perfusion and quantitative magnetization transfer imaging.
authors.affiliation: Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Hurley
authors.forename: Vasily L
authors.initials: VL
authors.lastname: Yarnykh
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Johnson
authors.forename: Aaron S
authors.initials: AS
authors.lastname: Field
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Alexander
authors.forename: Alexey A
authors.initials: AA
authors.lastname: Samsonov
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity