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

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

The CEST data were obtained using a 7.0 T MRI scanner. We used varied K_f 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.

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_f showed consistent signals and image quality compared with the fully sampled CEST data.

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.