Positive chemical exchange contrast in MRI using Refocused Acquisition of Chemical Exchange Transferred Excitations (RACETE)

Abstract

Purpose: A new chemical exchange MRI method is proposed which allows for direct detection of exchanging solute protons with concurrent water background suppression.

Methods: The proposed method, RACETE (Refocused Acquisition of Chemical Exchange Transferred Excitations), is based on a stimulated-echo-technique, where the first two excitation pulses are replaced by a train of N solute-selective excitation-transfer modules. This excitation cycle is then followed by a stimulated echo acquisition via selective refocusing of exchanged solute protons now present in the solvent pool.

Results: The obtained magnitude and phase phantom images demonstrate that with only one RACETE-imaging experiment two different chemical exchange active substances with mMol-concentrations can be detected and distinguished simultaneously.

Conclusion: The proposed RACETE-approach allows for true positive chemical exchange contrast imaging with the proven ability to exploit magnitude as well as phase image data.

Keywords: CEST; Chemical exchange; MRI; Positive exchange contrast.