Optimization of Keyhole Imaging Parameters for Glutamate Chemical Exchange Saturation Transfer MRI at 7.0 T.

Purpose: To evaluate the effects of a reference image and keyhole factor (K) selections for high-frequency substitution on keyhole imaging technique for applications in glutamate chemical exchange saturation transfer (GluCEST) imaging.

Procedures: The CEST data were obtained using a 7.0 T MRI scanner. We used varied K ranges that constituted from 16.67 to 75 % of the full k-space. The reference image was respectively selected for - 3 and + 3 ppm images that associated with the GluCEST calculation and the unsaturated image. The zero-padding algorithm was applied for the missing k-space lines in the low-frequency data collected to compare the results obtained from using the keyhole imaging technique. All the techniques were evaluated using a healthy rat group and extended to the status epilepticus rat group to explore their applicability and usability.

Results: The calculated GluCEST signals and visually inspected results from the reconstructed GluCEST maps indicated that the combination of unsaturated image as a reference image, and over 50 % of K showed consistent signals and image quality compared with the fully sampled CEST data.

Conclusions: Combining the keyhole imaging technique with GluCEST imaging enables stable image reconstruction and quantitative evaluation, and this approach is potentially applicable in various CEST imaging applications.