Application of a BIlinear Rotation Decoupling (BIRD) filter in combination with J‐difference editing for indirect (13)C measurements in the human liver

PURPOSE: Recently, we introduced a quantum coherence based method (ge‐HSQC) for indirect (13)C‐MRS in the liver to track (13)C‐labeled lipids into the hepatic lipid pool in vivo. This approach is more robust in case of respiratory motion, however, inherently leads to a signal loss of 50% when compared with a conventional J‐difference editing technique (JDE). Here, we intend to improve the robustness of a regular JDE (STEAM‐ACED) with the use of a BIlinear Rotation Decoupling (BIRD) filter to achieve 100% higher signal gain when compared with ge‐HSQC. METHODS: To determine the efficiency of the BIRD filter (1)H‐[(13)C] lipid spectra were acquired on 3T from a peanut oil phantom, with three different MR sequences: ge‐HSQC, STEAM‐ACED, and the BIRD filter together with STEAM‐ACED (BIRD‐STEAM‐ACED). Finally, our proposed method is tested in vivo in five healthy volunteers with varying liver fat content. In these subjects we quantified the (1)H‐[(13)C]‐signal from the hepatic lipid pool and determined (13)C enrichment, which is expected to be 1.1% according to the natural abundance of (13)C. RESULTS: The application of the proposed BIRD filter reduces the subtraction artifact of (1)H‐[(12)C] lipid signal efficiently in JDE experiments, which leads to a signal gain of 100% of (1)H‐[(13)C]‐lipid signals when compared with the ge‐HSQC. Phase distortions in vivo were minimal with the use of BIRD compared with STEAM‐ACED, which enabled us to robustly quantify the (13)C‐enrichment in all five subjects. CONCLUSION: The BIRD‐STEAM‐ACED sequence is an efficient and promising tool for (13)C‐tracking experiments in the human liver in vivo.