Effects ofB1 inhomogeneity correction for three-dimensional variable flip angleT1 measurements in hip dGEMRIC at 3 T and 1.5 T

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Delayed gadolinium-enhanced MRI of cartilage is a technique for studying the development of osteoarthritis using quantitativeT1 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 transmittedB1 field in vivo. In this study, a method for correcting for such inhomogeneities, using an additionalB1 mapping spin-echo sequence, was evaluated. Phantom studies concluded that three-dimensional variable flip angle withB1 correction calculates accurateT1 values also in areas with highB1 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 withoutB1 correction to be generally two to three times higher at 3 T than at 1.5 T. In conclusion, theB1 variations should always be taken into account, both at 1.5 T and at 3 T.

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