Synopsis
What is the origin of CEST contrast in tissues? What are the basic steps for generating CEST contrast maps including acquisition and post-processing of CEST MRI data? What are its current applications and its limits? The purpose of this talk will be to outline the basic mechanisms of CEST either through MRS or imaging. To discuss the progress of CEST imaging towards clinical practise and to highlight extraordinary developments within this field.
CEST MRI for beginners
What is the origin of CEST contrast in tissues? What are the basic steps for generating CEST contrast maps including acquisition and post-processing of CEST MRI data? What arei ts current applications and its limits? The purpose of this talk will be to outline the basic mechanisms of CEST either through MRS or imaging. To discuss the progress of CEST imaging towards clinical practise and to highlight extraordinary developments within this field. For more than a decade, indirect ‘off-resonance’ imaging of metabolites and proteins by irradiation with frequency-selective RF pulses has been introduced within MRI to enable the detection of hydrogen atoms termed labile protons belonging to various chemical groups (e.g. amines, amides or hydroxyls) (1),(2). The MR contrast that is generated is mediated by the chemical exchange between the labile protons and the free water protons. This exchange results in a reduction of the water signal associated with transfer of the labile protons’ saturated magnetization to the protons of the surrounding free water. The signal intensity depends on the rate of chemical exchange and the concentration of labile protons. Advantages of this technique include imaging of molecules with short transverse relaxation times or mapping of physiological parameters such as pH, temperature, buffer concentration and composition as this chemical exchange effect is dependent on all these parameters. The main applications of CEST methods have been for the assessment of pH changes in stroke using the endogenous CEST contrast, as the exchange rate of amides or amines is based-catalyzed (3),(4) or by using exogenous contrast agents such as iopamidol (5). Finally, other applications include measurement of protein content in tumours (6),(7) and endogenous metabolite concentration imaging e.g. glycosaminoglycan (GAG) CEST, glycogenCEST (glycoCEST) etc (2). In conclusion, while CEST is a very useful technique, chemical exchange effects are small and while very clear in high concentration and phantoms, are today barely detectable in vivo. In addition, there is a lack of specificity since many of the endogenous CEST signals overlap and much more work is needed for prober quantification and standardization of the technique.
Acknowledgements
No acknowledgement found.References
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