A CEST-FISP pulse sequence was developed on a Bruker Biospec 7.0T MRI scanner (Bruker Biospin, Billerica, MA) by combining a train of spectrally-selective CEST excitation pulses with a FISP acquisition scheme (Figure 1 ). The CEST preparation was developed with a train of 120 spectrally-selective Gaussian saturation pulses (BWRF = 75 Hz, TauRF = 36 ms). Gradient spoilers were applied following each CEST pulse to avoid unintended buildup of transverse magnetization. These conditions resulted in a total CEST preparation period of approximately 5 seconds immediately prior to the imaging readout (18 (link)). This CEST pulse train was developed to provide a flexible CEST preparation sensitive to glycogen exchange in order to evaluate the fundamental characteristics of the CEST-FISP technique. As such, this CEST preparation was not optimized for this specific application.
The CEST preparation above was coupled with a conventional FISP acquisition to acquireall lines of k-space following a single CEST preparation. A FISP acquisition was used instead of a True FISP acquisition to avoid well-known banding artifacts resulting from B0 inhomogeneities at 7.0T (16 ,17 ). For all in vitro experiments, the imaging parameters were FISP Repetition Time = 2ms, echo time = 1 ms, matrix = 128×92, FOV = 6×4 cm, slice thickness = 2 mm (single-slice), flip angle = 60°, and readout bandwidth = 600 kHz. Ten dummy scans were utilized to limit artifacts from the approach to steady-state. The total duration of the dummy scans was < 30ms and centric encoding was implemented for the FISP acquisition to minimize the loss of CEST sensitivity following the CEST preparation.
The CEST preparation above was coupled with a conventional FISP acquisition to acquire
