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Dipolar coupling and ordering effects observed in magnetic resonance spectra of skeletal muscle

2001; Wiley; Volume: 14; Issue: 2 Linguagem: Inglês

10.1002/nbm.684

1099-1492

Chris Boesch, Roland Kreis,

Advanced Neuroimaging Techniques and Applications

Abstract Skeletal muscle is a biological structure with a high degree of organization at different spatial levels. This order influences magnetic resonance (MR) in vivo —in particular 1 H‐spectra—by a series of effects that have very distinct physical sources and biomedical applications: (a) bulk fat (extramyocellular lipids, EMCL) along fasciae forms macroscopic plates, changing the susceptibility within these structures compared to the spherical droplets that contain intra‐myocellular lipids (IMCL); this effect leads to a separation of the signals from EMCL and IMCL; (b) dipolar coupling effects due to anisotropic motional averaging have been shown for 1 H‐resonances of creatine, taurine, and lactate; (c) aromatic protons of carnosine show orientation‐dependent effects that can be explained by dipolar coupling, chemical shift anisotropy or by relaxation anisotropy; (d) limited rotational freedom and/or compartmentation may explain differences of 1 H‐MR‐visibility of the creatine/phosphocreatine resonances; (e) lactate 1 H‐MR resonances are reported to reveal information on tissue compartmentation; (f) transverse relaxation of water and metabolites show multiple components, indicative of intra‐, extracellular and/or macromolecular‐bound pools, and in addition dipolar or J‐coupling lead to a modulation of the signal decay, hindering straightforward interpretation; (g) diffusion weighted 31 P‐MRS has shown restricted diffusion of phosphocreatine; (h) magnetization transfer (MT) indicates that there is a motionally restricted proton pool in spin‐exchange with free creatine; reduced availability or restricted motion of creatine is particularly important for an estimation of ADP from 31 P‐MR spectra, and in addition MT effects may alter the signal intensity of creatine 1 H‐resonances following water‐suppression pulses; (i) transcytolemmal water‐exchange can be studied in 1 H‐MRS by contrast‐agents applied to the extracellular space; (k) transport of glucose across the cell membrane has been studied in diabetes patients using a combination of 13 C‐ and 31 P‐MRS; and (l) residual quadrupolar interaction in 23 Na MR spectra from human skeletal muscle suggest that sodium ions are bound to ordered muscular structures. Copyright © 2001 John Wiley & Sons, Ltd. Abbreviations used: ADC apparent diffusion coefficient BMS bulk magnetic susceptibility CK creatine kinase Cr creatine Cr/PCr creatine and/or phosphocreatine CSA chemical shift anisotropy EMCL extramyocellular lipids IMCL intramyocellular lipids MQF multi‐quantum‐filtering MRI Magnetic resonance imaging MRS magnetic resonance spectroscopy MT magnetization transfer PCr phosphocreatine.