¹H MRS of intramyocellular lipids in soleus muscle at 7 T: Spectral simplification by using long echo times without water suppression

The popular short echo time ¹H MR spectroscopy acquisition method for detection of intramyocellular lipids suffers from spectral overlap due to the large, broad, and asymmetric extramyocellular lipid signals, the time-consuming practice of selecting "lean" voxels for spectroscopy, and the overlap of the extramyocellular lipid signal with the creatine methyl ¹H signal at ∼3 parts per million (ppm), commonly used as an internal standard. Using an alternative acquisition strategy, spectra with well-resolved intramyocellular lipids resonances were acquired from large volumes (10 to 15 mL) of human soleus muscle in less than 5 min by single-voxel 7-T ¹H MR spectroscopy, using an echo time of 280 ms. From the high-resolution spectra, an average intramyocellular lipid concentration of 7.7 ± 3.5 mmol/kg muscle was found for 25 healthy subjects (male/female 17/8; age 29.4 ± 6.6 years). Since water suppression was not required, the ¹H signals from unsaturated intracellular triglycerides at about 5.3 ppm were easily detected, which, in combination with the well-determined - (CH₂)_n- /CH₃ intensity ratio at long echo time, enabled assessment of the composition of triglycerides in the intramyocellular lipids compartment. Long-echo single-voxel spectroscopy at 7 T offers rapid and convenient acquisition of high-resolution spectra from human soleus muscle.