Rapid Parametric Mapping of the Longitudinal Relaxation Time T.sub.1 Using Two-Dimensional Variable Flip Angle Magnetic Resonance Imaging at 1.5 Tesla, 3 Tesla, and 7 Tesla

• Published in: PloS one 2014-03, Vol.9 (3), p.e91318
• Main Authors: Dieringer, Matthias A, Deimling, Michael, Santoro, Davide, Wuerfel, Jens, Madai, Vince I, Sobesky, Jan, von Knobelsdorff-Brenkenhoff, Florian, Schulz-Menger, Jeanette, Niendorf, Thoralf
• Format: Article
• Language: English
• Subjects: Brain damage; Magnetic fields; Magnetic resonance imaging; Multiple sclerosis
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0091318

Visual but subjective reading of longitudinal relaxation time (T.sub.1) weighted magnetic resonance images is commonly used for the detection of brain pathologies. For this non-quantitative measure, diagnostic quality depends on hardware configuration, imaging parameters, radio frequency transmission field (B.sub.1 .sup.+) uniformity, as well as observer experience. Parametric quantification of the tissue T.sub.1 relaxation parameter offsets the propensity for these effects, but is typically time consuming. For this reason, this study examines the feasibility of rapid 2D T.sub.1 quantification using a variable flip angles (VFA) approach at magnetic field strengths of 1.5 Tesla, 3 Tesla, and 7 Tesla. These efforts include validation in phantom experiments and application for brain T.sub.1 mapping. T.sub.1 quantification included simulations of the Bloch equations to correct for slice profile imperfections, and a correction for B.sub.1 .sup.+ . Fast gradient echo acquisitions were conducted using three adjusted flip angles for the proposed T.sub.1 quantification approach that was benchmarked against slice profile uncorrected 2D VFA and an inversion-recovery spin-echo based reference method. Brain T.sub.1 mapping was performed in six healthy subjects, one multiple sclerosis patient, and one stroke patient. Phantom experiments showed a mean T.sub.1 estimation error of (-63±1.5)% for slice profile uncorrected 2D VFA and (0.2±1.4)% for the proposed approach compared to the reference method. Scan time for single slice T.sub.1 mapping including B.sub.1 .sup.+ mapping could be reduced to 5 seconds using an in-plane resolution of (2x2) mm.sup.2, which equals a scan time reduction of more than 99% compared to the reference method. Our results demonstrate that rapid 2D T.sub.1 quantification using a variable flip angle approach is feasible at 1.5T/3T/7T. It represents a valuable alternative for rapid T.sub.1 mapping due to the gain in speed versus conventional approaches. This progress may serve to enhance the capabilities of parametric MR based lesion detection and brain tissue characterization.