Quantitative chemical exchange saturation transfer (qCEST) MRI - RF spillover effect-corrected omega plot for simultaneous determination of labile proton fraction ratio and exchange rate

摘要

Chemical exchange saturation transfer (CEST) MRI is sensitive to dilute proteins and peptides as well as microenvironmental properties. However, the complexity of the CEST MRI effect, which varies with the labile proton content, exchange rate and experimental conditions, underscores the need for development of quantitative CEST (qCEST) analysis. Towards this goal, it has been shown that the omega plot is capable of quantifying paramagnetic CEST (PARACEST) MRI. However, the use of omega plot is somewhat limited for diamagnetic CEST (DIACEST) MRI because it is more susceptible to direct RF saturation (spillover) effects owing to their relatively small chemical shift. Recently, it has been found that for dilute DIACEST agents that undergo slow to intermediate chemical exchange, the RF spillover effect varies little with the labile proton ratio and exchange rate. Therefore, we postulated that the omega plot analysis can be improved if RF spillover effect could be estimated and taken into account. Specifically, simulation showed that both labile proton ratio and exchange rate derived using the spillover effect-corrected omega plot are in good agreement with simulated values. In addition, the modified omega plot was confirmed experimentally, and we showed that the derived labile proton ratio increases linearly with creatine concentration (P< 0.01), with little difference in their exchange rate (P=0.32). In summary, our study extended the conventional omega plot for quantitative analysis of DIACEST MRI.