Metabolite-cycling at 14.1T: sequence implementation and initial explorations using SPECIAL and diffusion-weighted SPECIAL

Motivation: Water suppression leads to saturation of exchanging protons which biases metabolite concentration estimates and prevents the study of downfield resonances in the 1H spectrum. Goal(s): Apply metabolite-cycling (MC) to study these resonances with high sensitivity using the short-TE, full-intensity SPECIAL sequence at ultra-high field on an animal scanner. Approach: The MC pulse was optimized for 14.1T. MC SPECIAL and MC diffusion-weighted SPECIAL were implemented and tested in vivo. Results: Underestimation of specific upfield metabolite concentrations with water-suppressed SPECIAL compared to MC SPECIAL was observed. Downfield resonances attribution was further validated with diffusion-weighted acquisitions, uniquely showing the presence of macromolecules in the 6.5-7.5ppm region. Impact: The introduction of metabolite-cycling in the short echo-time, full intensity SPECIAL and diffusion-weighted SPECIAL 1H MRS sequences at 14.1T paves the way for in-depth exploration of the downfield resonances of the 1H spectrum with high sensitivity on animal scanners.