T₁-independent exchange rate quantification using saturation- or phase sensitive-water exchange spectroscopy

Area of Science:

• Magnetic Resonance Spectroscopy
• Biophysical Chemistry

Background:

• Water Exchange Spectroscopy (WEX) measures labile proton exchange rates (ksw) between solutes and water.
• The T1-decay of the solvent pool can obscure valuable information in WEX measurements.

Purpose of the Study:

• To introduce Saturation-WEX (Sat-WEX) and Phase Sensitive WEX (PS-WEX) as extensions to WEX.
• To reduce T1-decay masking and improve the dynamic range of WEX measurements.

Main Methods:

• Sat-WEX reduces T1-dependence by introducing an additional RF-pulse and fixing the exchange time.
• PS-WEX utilizes phase information within the WEX signal to enhance dynamic range.
• Both methods were validated through simulations and phantom measurements.

Main Results:

• Measurements demonstrated an improved dynamic range with the new methods.
• Fixing the exchange time reduced T1-decay influence, leading to better signal curve fitting and improved fit quality.

Conclusions:

• Sat-WEX and PS-WEX offer advancements over standard WEX.
• These methods provide a less complex fit equation and, particularly for PS-WEX, an enhanced dynamic range for more accurate quantification of exchange rates.