Deriving blood-oxygen-level-dependent contrast in MRI with T2*-weighted, T2-prepared and phase-cycled SSFP methods: theory and experiment.

The objectives of this work were: 1) to perform a comparative evaluation of the oxygen-sensitive contrast (OC) derived from the phase-cycled steady-state free precession (SSFP PC) method against T*2-weighted gradient recalled echo (GRE) and T2-prepared (T2-prep) methods with theoretical simulations and imaging studies using an ischemic leg cuff model at 1.5T and 3.0T; and 2) to investigate the dependence of SSFP PC-based OC on imaging parameters. Results showed that the SSFP PC method (repetition time (TR) = 6.3 ms; flip angle (alpha) = 90 degrees ) provides significantly higher OC compared to T2-prep (at both field strengths) and GRE (3.0T) (P < 0.05). The OC of low TR SSFP (TR = 3.5 ms at 1.5T; TR = 4.5 ms at 3.0T; alpha = 90 degrees ) was significantly lower compared to GRE (P < 0.05) at 1.5T and 3.0T and to T2-prep methods at 1.5T (P < 0.05). In summary, the findings from this study are the following: 1) SSFP-based OC is directly dependent on TR and alpha at 1.5T and 3.0T; and 2) OC derived with SSFP PC can be increased above GRE and T2-prep methods with an appropriate choice of imaging parameters.