Metabolite cycled liver ¹H MRS on a 7 T parallel transmit system

Abstract

Introduction Single‐voxel 1 H MRS in body applications often suffers from respiratory and other motion induced phase and frequency shifts, which lead to incoherent averaging and hence to suboptimal results. Methods Here we show the application of metabolite cycling (MC) for liver STEAM‐localized 1 H MRS on a 7 T parallel transmit system, using eight transmit‐receive fractionated dipole antennas with 16 additional, integrated receive loops. MC‐STEAM measurements were made in six healthy, lean subjects and compared with STEAM measurements using VAPOR water suppression. Measurements were performed during free breathing and during synchronized breathing, for which the subjects did breathe in between the MRS acquisitions. Both intra‐session repeatability and inter‐session reproducibility of liver lipid quantification with MC‐STEAM and VAPOR‐STEAM were determined. Results The preserved water signal in MC‐STEAM allowed for robust phase and frequency correction of individual acquisitions before averaging, which resulted in in vivo liver spectra that were of equal quality when measurements were made with free breathing or synchronized breathing. Intra‐session repeatability and inter‐session reproducibility of liver lipid quantification were better for MC‐STEAM than for VAPOR‐STEAM. This may also be explained by the more robust phase and frequency correction of the individual MC‐STEAM acquisitions as compared with the VAPOR‐STEAM acquisitions, for which the low‐signal‐to‐noise ratio lipid signals had to be used for the corrections. Conclusion Non‐water‐suppressed MC‐STEAM on a 7 T system with parallel transmit is a promising approach for 1 H MRS applications in the body that are affected by motion, such as in the liver, and yields better repeatability and reproducibility compared with water‐suppressed measurements.

Proton Magnetic Resonance Spectroscopy at 3.0T in Rabbit With VX2 Liver Cancer: Diagnostic Efficacy and Correlations With Tumor Size

“…With the increase in magnetic field intensity, the signal-to-noise ratio of the static magnetic field changed with the chemical shift in a positive proportion. This allowed the quantitative measurement of MRS metabolites, such as peak amplitude and peak area ( 16 – 18 ). The accuracy relied on the stability of the spectral baseline, which could be negatively affected by respiration and intestinal disturbance ( 19 , 20 ).…”

Magnetic Resonance Spectroscopy of Hepatic Fat from Fundamental to Clinical Applications

“…Most of the visible peaks in the MRS liver spectrum obtained from the clinical MR scanner (1.5-3 Tesla) are fat and water. While water shows a single peak at approximately 4.7 ppm, fat shows multiple peaks due to its complex chemical components ( Table 2 ) [ 22 , 73 , 74 ]. Six resonances of fat are usually detected with the main lipid peak at approximately 0.9 to 2.75 ppm.…”

“…Six resonances of fat are usually detected with the main lipid peak at approximately 0.9 to 2.75 ppm. There are also unresolved fat resonances at 4.2 and 5.3 ppm from glycerol and olefinic acid, respectively ( Figure 2 ) [ 73 , 74 , 75 ]. These two peaks overlap with the water peak signal at 4.7 ppm.…”

Interleaved trinuclear MRS for single‐session investigation of carbohydrate and lipid metabolism in human liver at 7T

“…Acquisitions are usually performed using either breath-holds, respiration triggering (by MR-navigator or external monitoring), or rhythmic breathing in sync with the MR sequence. 17 Two of them were evaluated. (3) Metabolite cycling (MC) [17][18][19] has been proposed for water signal elimination with the potential to track and mitigate residual phase and frequency shifts/drifts.…”

“…17 Two of them were evaluated. (3) Metabolite cycling (MC) [17][18][19] has been proposed for water signal elimination with the potential to track and mitigate residual phase and frequency shifts/drifts. Its benefit was tested.…”