Deriving blood‐oxygen‐level‐dependent contrast in MRI with T 2 * ‐weighted, T 2 ‐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 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 SSFP PC ‐based OC on imaging parameters. Results showed that the SSFP PC method (repetition time (TR) = 6.3 ms; flip angle (α) = 90°) provides significantly higher OC compared to T 2 ‐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; α = 90°) 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 OC is directly dependent on TR and α at 1.5T and 3.0T; and 2) OC derived with SSFP PC can be increased above GRE and T 2 ‐prep methods with an appropriate choice of imaging parameters. Magn Reson Med 59:561–570, 2008. © 2008 Wiley‐Liss, Inc.