PMC

The evolution time (t₁) was increased with 1 ms every step and started at 4.2 ms. Due to the ¹³C-¹³C couplings in the tracer, the signal now decays rapidly with increasing t₁.

(A and B) In A, the results for the 1D ge-HMQC are shown, while in B, the outcome of the 1D ge-HSQC sequence is presented. The evolution time (t₁) was increased with 1 ms every step and started at, respectively, 7.6 and 4.2 ms. It is apparent that the signal acquired with the ge-HMQC decays rapidly with an increasing t₁.

(A and B) The result from the conventional quantum coherence sequences. In both cases, the ¹³C chemical shift evolution during the t₁ period resulted in phase distortions in the spectrum. Addition of the ¹³C inversion pulse led to nonphase distorted lipid spectra, in which both CH₂ and CH₃ signals were observable. (C and D) Both relative and absolute signals were higher in the 1D ge-HSQC (heteronuclear single quantum coherence) as compared with the 1D ge-HMQC (heteronuclear multiple quantum coherence).

(A and B) Typical example of the total lipid spectrum, acquired with STEAM (stimulated echo acquistion mode) ¹H-MRS, and the concomitant ¹³C-edited lipid spectrum, acquired with the ge-HSQC (heteronuclear single quantum coherence) sequence. As no decoupling was applied, two lipid CH₂ peaks are visible, which are separated by approximately 127 Hz. (C) The total IHL (intrahepatic lipid) pool (g/kg ww) for both lean (n = 5) and obese (n = 6) subjects at 1,5, 3.0, 4.5, and 6.0 hours after a high-fat meal. Total IHL did not change after the meal (repeated-measures ANOVA, P = 0.35). (D) The absolute concentration of ¹³C lipids (g/kg ww) in the liver is plotted in time, showing retention of ¹³C-labeled fatty acids after the meal (repeated-measures ANOVA, P < 0.01).

(A) The 1D ge-HMQC (heteronuclear multiple quantum coherence) sequence is shown. The HMQC block was placed after PRESS (point resolved spectroscopy) localization. Two additional ¹³C inversion pulses were used to refocus the ¹³C chemical shift evolution. Minimum evolution time (t₁) was 7.6 ms. In contrast to the conventional ge-HMQC sequence, 5 gradients were used for coherence selection. Gradients were applied in a ratio of 1:–1:–1:1:1. (B) The 1D ge-HSQC (heteronuclear single quantum coherence) sequence, based on STEAM (stimulated echo acquistion mode) localization. The inversion pulse during the t₁, which was used on the ¹H channel previously, was now applied on the ¹³C channel to again refocus ¹³C chemical shift evolution. Minimum t₁ was 4.2 ms, and gradients were applied in a 2:–2:1 ratio. In both sequences, 1/2J_CH was chosen as 3.95 (J = 127 Hz for CH₂ lipids). No decoupling was applied.