T-independent exchange rate quantification using saturation- or phase sensitive-water exchange spectroscopy.

Purpose: Water Exchange Spectroscopy (WEX) is a direct measurement of the exchange rate k of labile protons from a solute to water in which the exchange time is varied. However the useful information can be masked by the T-decay of the solvent pool. We propose Saturation-WEX and Phase Sensitive WEX (PS-WEX) as an extension upon the WEX approach to reduce T-masking. Additionally PS-WEX takes advantage of the phase information contained in the WEX signal to improve the dynamic range.

Methods: By introducing an additional RF-pulse and fixing the exchange time delay the T-dependence of the signal is reduced. By exploiting the phase sensitivity of the WEX pathway the dynamic range can be increased. This approach is validated using simulations as well as phantom measurements.

Results: The improved dynamic range is demonstrated in measurements. The fixed exchange time reduces the influence of the T-decay on the signal curve leading to improved fit quality.

Conclusion: Sat-WEX and PS-WEX are an extension to the well established WEX approach with a less complex fit equation and in the case of PS-WEX improved dynamic range, allowing more accurate quantification.