Single-preparation spectroscopic exchange rate quantification using Turbo WEX and Turbo PS-WEX

The spectroscopic Water Exchange Filter (WEX) and its phase-sensitive variant PS-WEX allow quantification of the chemical exchange rate k_sw. These methods selectively sample the solute pool magnetization, utilizing only a small fraction of the total prepared magnetization for signal generation. This work introduces Turbo WEX and Turbo PS-WEX, which acquire multiple readouts corresponding to different effective mixing times following a single preparation to substantially improve acquisition efficiency.

Repeated readouts of the solute pool after a single preparation enable accelerated sampling of the exchange process. Signal models for both methods were derived to allow quantitative exchange rate estimation. The approaches were demonstrated in single-preparation spectroscopy and as a proof of principle in a spatially and spectrally resolved Turbo PS-WEX imaging experiment using a creatine and phosphocreatine phantom. The achievable acceleration is primarily limited by longitudinal relaxation of the solvent pool.

Both Turbo WEX and Turbo PS-WEX enabled accurate exchange rate quantification from single-preparation measurements in creatine samples with several pH-values. The imaging experiment yielded spatially and spectrally resolved exchange rate maps of the multi-compartment phantom.

Multi-readout turbo acquisition substantially increases the efficiency of WEX-type experiments while preserving the ability to quantify exchange rates with spectral resolution. Reusing the magnetization from a single-preparation reduces the acquisition time for the spectroscopic measurement to less than five seconds, transforming WEX from a multi-minute experiment into a rapid quantitative tool.