Comparison of localized proton NMR signals of skeletal muscle and fat tissue <i>in vivo</i>: Two lipid compartments in muscle tissue

TLDR

The study identifies two lipid compartments in muscle tissue, likely corresponding to intramuscular fat cells and intracellular lipids, both containing similar fatty acid or triglyceride composition. The authors localized in vivo 1H NMR spectra of small volumes in soleus muscle, subcutaneous fat, and bone marrow using a double spin echo PRESS technique with identical sequence timing to compare tissues. Using long echo times (TE > 200 ms), the authors achieved clear resolution of two distinct lipid signals in muscle differing by ~0.2 ppm, supported by relaxation time and line‑shape analysis.

Abstract

Abstract In vivo 1 H NMR spectra of small volumes‐of‐interest (VOI) were localized in human soleus muscle (8 ml) and compared with volume selective spectra of subcutaneous fat tissue and femoral yellow bone marrow (2 ml). All examinations were performed by the double spin echo (PRESS) localization technique. To provide comparability, spectra of different tissues were recorded using identical sequence timing. Clearly improved resolution of the lipid signals of muscle tissue was obtained using long echo times TE &gt; 200 ms. The spectra of muscle tissue exhibit lipid signals that stem from two compartments with a difference of their resonance frequencies of about 0.2 ppm (Larmor frequency difference 12‐13 Hz at 1.5 T). The existence of two fatty acid compartments is supported by measurements of the relaxation times and line shape analysis. Both compartments contain fatty acids or triglycerides with similar composition. Probably one compartment corresponds to fat cells within muscle tissue, the other compartment with lower Larmor frequency is located within muscle cells.