Quantification of Lipids in 1H MR spectra recorded at 3.0 T? Improvements in metabolic studies

Purpose: From a clinical and public health standpoint, determination of amount and distribution of different lipid compartments in humans has become a very important tool in the research of pathogenesis of insulin resistance and diabetes mellitus. Besides ectopic fat (subcutaneous and visceral lipid stores), further compartments as intrahepatic lipids (IHL) or intramyocellular lipids (IMCL) seem to be involved in the development of the disease. Quantification of IMCL? which is aggravated by the overlapping signals of extramyocellular lipids (EMCL) at common field strength of 1.5 T? might make a large profit of higher field strength due to the improved spectral dispersion and the higher signal gain. Furthermore, composition of triglycerides can be studied in more detail, as for example determination of the ratio between saturated and unsaturated triglycerides is feasible, as the signals of double bonds at 5.3 ppm are less affected by water suppression pulses. Method and materials: Examinations were performed on a 1.5 T whole body imager (Magnetom Sonata, Siemens, Erlangen, Germany) and on a 3.0 T whole body imager (Magnetom Trio, Siemens, Germany). Spectra were recorded in the tibialis anterior muscle (TA), the soleus muscle (SOL), and the medial gastrocnemius muscle (GM) applying a standard single voxel STEAM technique with TE=10 ms, TM=15 ms, TR=2s. Circularly polarized extremity coils were used as combined transmitter/receiver coil. Subjects were in supine position with the most extended part of the right calf in the center of the coil. Voxel size (VOI) was chosen to 20×20×20 mm3 on both units and the number of acquisitions was 256 in order to depict the small signals of histidine protons of carnosine (Cs) at 7.0 ppm and 8.0 ppm. Results: Spectral patterns show distinct differences between 1.5 T and 3.0 T. Separation between IMCL and EMCL compartments is improved in all muscle groups as line width of IMCL is clearly smaller at 3.0 T even in spectra with large dimensions of the VOI. However, due to increasing susceptibility effects, the EMCL-signal remains with a broad and asymmetrical line shape depending on the orientation of the muscle fibers in relation to the static magnetic field B0. Double bonds of EMCL and IMCL can be clearly separated at 3.0 T. Further effects occurring due to the pennation angle of the muscle fibers are observed in TA with a splitting of the TMA-complex (including choline, carnitine, and taurine). This effect is less pronounced