Purpose: To characterize the effects of water T2 relaxation time in the glycosaminoglycan chemical exchange saturation transfer method (gagCEST) and compare them between 3T and 7T as well as between various saturation schemes. Methods: Simulations and a phantom experiment were conducted at 3T and 7T in a range of water T2 values and GAG concentrations using various saturation schemes. For both simulations and MRI measurements, unsaturated signal as well as the saturated Z-spectrum were generated, and the magnetization transfer ratio asymmetry at 1 parts per million was used as a measure of the gagCEST effect size. Results: The simulations and phantom experiment results showed a clear GAG concentration and T2 dependence of the gagCEST effect size. Whereas the gagCEST effect size was much larger at 7T, the impact of the T2 bias was more pronounced at 3T. The saturation train length, duty cycle, and average B1 all had clear impact on both the gagCEST effect size and T2 bias. Conclusion: The water T2 relaxation is important to consider in gagCEST, especially at 3T. The T2 differences can introduce a pronounced bias, which may obscure the gagCEST effect when using low duty cycles and long saturation trains.
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