A-153 CEST (chemical exchange saturation transfer)
B. Schmitt | Friday, March 8, 16:00 – 17:30 / Room C
CEST imaging in principle relies on the chemical exchange of protons bound to solute molecules and surrounding bulk water molecules. The effect can be used for MRI because the magnetization of each solute proton, is also transferred to bulk water, and can thus be visualized via the MR signal. CEST effects can be evaluated for specific molecular groups due to their characteristic proton resonance frequencies, which provides the technique with a high intrinsic sensitivity to these groups. In healthy cartilage tissue, strong CEST effects from exchangeable protons of glycosaminoglycan (GAG) molecules can be observed. The magnitude of these effects decreases when concentration ratio between bulk water protons and GAG protons decreases, e.g. in the early stages of osteoarthritis (OA). Initial studies on patients after cartilage repair surgery with GAG-dependent CEST (gagCEST) imaging have demonstrated that it is feasible to visualize GAG loss in vivo at 7.0 Tesla. Initial reports also claim that the technique might be transitioned to the clinical field strength of 3 T. Although CEST imaging can be performed with standard clinical equipment and protocols can easily be implemented in a routine clinical workflow, the signal analysis in gagCEST imaging and the reading of gagCEST images are technically complex. For example, effects, which alter the T2 relaxation time of tissue such as high relative water concentration, can affect the magnitude of gagCEST effects although the absolute concentration of GAG is unchanged. Unless confounding effects are automatically corrected, careful analysis of images is necessary for proper interpretation of results.