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) over bar) derived from the phase-cycled steady-state free precession (SSFPPC) method against T-2*-weighted gradient recalled echo (GRE) and T-2-prepared (T-2-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 SSFPPC-based (OC) over bar on imaging parameters. Results showed that the SSFPPC method (repetition time (TR) = 6.3 ms; flip angle (alpha) = 90 degrees) provides significantly higher (OC) over bar compared to T-2-prep (at both field strengths) and GRE (3.0T) (P < 0.05). The <(OC)over bar> 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 T-2-prep methods at 1.5T [P < 0.05). In summary, the findings from this study are the following: 1) SSFP-based M is directly dependent on TR and a at 1.5T and 3.0T; and 2) (OC) over bar derived with SSFPPC can be increased above GRE and T2-prep methods with an appropriate choice of imaging parameters.