An interleaved sampling strategy for MR spectroscopy in vivo: Applicationson human calf musculature

Assessment of relaxation times, magnetization transfer rates, or apparent d iffusion coefficients' by volume selective H-1 MR spectroscopy requires dat a from several single spectra with variable sequence parameters. Unintentio nal movements during the examination lead to inaccuracies, especially if th e spatial distribution of concentrations is inhomogeneous. Improved compara bility of the single spectra in a series recorded in vivo were obtained usi ng a modified spectroscopic technique with INTerleaved ACquisiTion of multi ple SPECtra (INTACTSPEC). INTACTSPEC series of spectra from the tibialis an terior muscle (m. tib. ant.), soleus muscle (m. soleus), and tibial bone ma rrow of 20 healthy volunteers were analyzed. Transverse relaxation times T- 2 of methylene signals in muscular lipid stores ranged from 77 ms (intramyo cellular methylene component in m. tib. ant.) to 88 ms (intramyocellular me thylene component in m; soleus) and were similar to those from yellow tibia l bone marrow (T-2 = 84 ms). Echo time-dependent signal intensities of chol ine and creatine deviated markedly from a monoexponential behavior in m. ti b. ant., but were nearly exponential in m. soleus. Results from water diffu sion measurements parallel and perpendicular to the axis of the lower leg s howed significant differences between m. tib. ant; and m. soleus, probably due to the spatial orientation of the muscle fibers. Apparent diffusion coe fficients along the leg axis were found to be higher in m. tib. ant. (2.10 +/- 0.08 x 10(-3) mm(2)/s) compared to m. soleus (1.78 +/- 0.11 x 10(-3) mm (2)/s), but m. soleus showed less restricted diffusion in perpendicular ori entation (1.59 +/- 0.19 x 10(-3) mm(2)/s versus 1.20 +/- 0.08 x 10(-3) mm(2 )/s in m. tib. ant.). Magnetization transfer experiments with various RF pr eparation pulse amplitudes led to very similar results for m. tib. ant. and m. soleus. (C) 2000 Elsevier Science Inc. All rights reserved.