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Optimization of Flip Angle and RF Pulse Phase in MP-SSFP for MRI in Inhomogeneous Magnetic Fields
Naoharu Kobayashi1 and Michael Garwood1
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States
Flip angle and RF phase in MP-SSFP were numerically optimized. The optimal RF setting improved SNR under the fixed SAR conditions and provided strong image contrasts in brain tissues with linear gradient inhomogeneous fields at 3T.
Figure 5. Brain MP-SSFP images with 1.5-mm isotropic resolution. Images acquired with αstd = 6º, optimal flip angle and even phase (A) provided stronger image contrasts between gray and white matter as compared to those with αstd=20º, optimal flip angle and odd phase (B), but as predicted in simulation and phantom experiments, the noise level is noticeably higher in the images acquired with αstd=6º.
Figure 3. Brain MP-SSFP images acquired with αstd=6º (A) and 20º (B). With αstd=6º, strong image contrasts between gray and white matters were detected, which is consistent in even and odd RF phase images. With αstd=20º, odd RF phase provided stronger image contrasts in brain tissues than even RF phase. Although SNR increased along with an increase of NMP, image contrasts were consistent in each RF pulse setting.