Optimization of steady-state pulsed CEST imaging for amide proton transfer at 3T MRI

To optimize a steady-state imaging sequence for maximizing the amide proton transfer effects in pulsed-CEST (pCEST) imaging.

The steady-state pCEST (SS-pCEST) sequence is a fast CEST imaging scheme that applies repetitive short RF pulses for generating CEST and acquiring MR imaging signal alternately. To maximize the obtainable amide proton transfer effects, the SS-pCEST scheme is analyzed and optimized with respect to not only the imaging parameters but also the imaging schemes of the signal acquisition part. Three imaging parameters such as the flip angle and RF power for saturation and the flip angle for imaging are selected as factors affecting the obtainable CEST effects; and 2 imaging schemes, namely, SSFP and spoiled gradient echo sequences, are analyzed and compared for numerical simulations and MRI experiments at 3 tesla.

SS-pCEST combined with SSFP could provide higher amide proton transfer effects than that with spoiled gradient echo. Furthermore, in the proposed SS-pCEST imaging with SSFP, 3 imaging parameters can be independently optimized so that the optimization complexities can be reduced.

We optimized the SS-pCEST imaging method with SSFP to maximize the amide proton transfer effects. In addition, our analysis showed the SSFP sequence was more efficient than the spoiled gradient echo sequence for SS-pCEST imaging.