Keyhole chemical exchange saturation transfer.

The keyhole technique, which involves the acquisition of dynamic data at low resolution in combination with a high-resolution reference, is developed for the purposes of chemical exchange saturation transfer (CEST) imaging, i.e., Keyhole CEST. Low-resolution data are acquired with saturation applied at different frequencies for Z-spectra, along with a high-resolution reference image taken without saturation. Three methods for high-resolution reconstruction of Keyhole CEST are evaluated using the values from quantitative high-resolution CEST maps. In addition, Keyhole CEST is applied for collection of data used for B(0) correction. The keyhole approach is evaluated for CEST contrast generation using exchanging protons in hydroxyl groups. First, the techniques are evaluated in vitro using samples of dextrose and chondroitin sulfate. Next, the work is extended in vivo to explore its applicability for gagCEST. Comparable quantitative gagCEST values are found using Keyhole CEST, provided the structure or region of interest is not limited by the low-resolution dataset.