Quantification of unsaturated fatty acids by PRESS localized-DEPT enhanced 13C MRS and ERETIC in human skeletal muscle

摘要

Introduction: The in vivo concentration and composition of unsaturated fatty acids (UFA), which are an important source of fuel in skeletal muscle, is a valid measure to assess dietary intake [1]. Some studies have demonstrated that the fatty acid contents are tissue specific [2]. In this work, we combine DEPT (Distortionless Enhancement of Polarization Transfer) and PRESS localization on protons [3] to achieve muscle group specifc in vivo detection of UFA. ERETIC (Electric Reference To access In vivo Concentrations) is used as a reference standard for absolute quantification [4]. Methods: To compose the proton-localized carbon acquired PRESS DEPT sequence, two slice selective 180 o pulses on I spins were inserted after the first 90 o pulse to realize PRESS localization and the residual part of the DEPT sequence was implemented subsequently, as plotted in figure 1. The sequence was tested on a DMSO (Dimethyl Sulfoxide) phantom and UFA in a large muscle volume. UFA signals from different calf and thigh muscle compartments were obtained and compared among healthy subjects. UFA quantification by using ERETIC method was cross-validated against internal creatine and external reference standards on five subjects. The experiments were carried out on 3T and 7T human MRI scanner. Results: In Figure 2 PRESS acquisition, PRESS-localized DEPT and PRESS-localized DEPT with proton decoupling on a DMSO phantom and a muscle volume are compared. UFA signals obtained from different muscle compartments are shown in Figure 3. Slightly different absolute concentrations and relative ratios between mono- and polyunsaturated fatty (MUFA, PUFA) acids are found (Figure 4). The MUFA/PUFA ratios are muscle compartments dependent and the average values are related to the dietary intakes. Cross-validation results shown in Figure 5, demonstrate that UFA concentrations measured with the ERETIC method are in excellent agreement with internal creatine and external reference methods. Conclusion: The sequence which combined PRESS and DEPT was imple- mented to achieve the first in vivo results for 13 C MRS. The in vivo experiments together with ERETIC reference show its feasibility to be applied to assess UFA in specific muscle compartments.