Effects of B 1 inhomogeneity correction for three-dimensional variable flip angle T 1 measurements in hip dGEMRIC at 3 T and 1.5 T

摘要

Delayed gadolinium-enhanced MRI of cartilage is a technique for studying the development of osteoarthritis using quantitative T 1 measurements. Three-dimensional variable flip angle is a promising method for performing such measurements rapidly, by using two successive spoiled gradient echo sequences with different excitation pulse flip angles. However, the three-dimensional variable flip angle method is very sensitive to inhomogeneities in the transmitted B 1 field in vivo. In this study, a method for correcting for such inhomogeneities, using an additional B 1 mapping spin-echo sequence, was evaluated. Phantom studies concluded that three-dimensional variable flip angle with B 1 correction calculates accurate T 1 values also in areas with high B 1 deviation. Retrospective analysis of in vivo hip delayed gadolinium-enhanced MRI of cartilage data from 40 subjects showed the difference between three-dimensional variable flip angle with and without B 1 correction to be generally two to three times higher at 3 T than at 1.5 T. In conclusion, the B 1 variations should always be taken into account, both at 1.5 T and at 3 T.