Absolute quantification of calf muscle metabolites by proton 1H-MR spectroscopy

Abstract

Objectiye To measure longitudinal (T1) and transverse (T2 ) relaxation time of metabolites in m. soleus (SOL) and m. tibialis anterior TA of healthy volunteers at 3.0 T through 1H-MRS and optimize measurement protocols. Methods Altogether 24 healthy volunteers were recruited in the study. All subjects signed a letter of informed consent. After divided into 2 groups randomly by the table of random number, 1H-MRS measurements with stimulated echo acquisition mode (STEAM) sequence were undertaken in SOL and TA separately. Progressive saturation method was used for T1 measurement. Spectra with 8 different TRs (770,900,1000, 1100,1200,1500,2000 and 3000ms ) were acquired with TE=20 ms.T2 time was measured by changing TE. Altogether 8 TEs (20,30,45,60,90,135,200 and 270 ms) were used with TR = 3000 ms. Metabolites' concentration was calculated through T1 and T2 correction using water as internal reference. The t test was used for statisties. Results Altogether 22 groups of data were gained ( 12 for SOL, 10 for TA ) . T1 value of water, Creatine-CH3 ( Cr3 ), Trimethyl amonium ( TMA ),extramyocellular lipid (EMCL) and intramyocellular lipid (IMCL) in SOL were ( 1384. 0 ± 36. 9 ),( 1064. 0 ± 167.0), (964. 2 ± 144. 0 ), ( 373.0 ± 46. 8 ), ( 374. 7 ± 20. 6) ms respectively and T2 value were (26.5 ±1.2), (100.2±19.3), (149. 1 ±32.7), (81.4±5.2), (84.7±4.2) ms. InTA T1 value of water, Cr3, TMA, EMCL, and IMCL were ( 1307. 0 ± 24.4), (945.7 ± 132. 0), (968.3 ± 127. 0),(372. 7 ± 39. 2), (412. 8 ±80. 2) ms respectively and T2 value were (27. 1 ± 0. 9), (135.3 ± 18. 2 ),(62.1 ± 6. 0), ( 84. 3 ± 4. 0 ), ( 90. 7 ± 3.2 ) ms. After corrected by the calculated relaxation times, the concentrations of Cr3 in SOL and TA were (33. 1 ± 3.7) and (31.7 ± 3. 1 ) mmol/kg respectively, TMA (35.2±3.2) and (32.9 ±5.2) mmol/kg, EMCL (12.2 ±5.0) and (8.9 ±4.9) mmol/kg, IMCL (9. 0 ± 2. 4) and (3.0 ± 0. 8 ) mmoL/kg. IMCL in TA was much lower than SOL with statistical significant ( t = 8. 044, P 0. 05 ) . Conclusions Accurate relaxation time was measured at 3.0 T of the metabolites in skeletal muscles of healthy adult human. After corrected by the relaxation times, the absolute concentrations calculated were consistent with the reported results. Quantitative knowledge of muscle NMR relaxation time was a prerequisite for absolute quantification of metabolites using the 1H-MRS and also was useful for optimizing measurement protocols. Key words: Magnetic resonance spectroscopy; Muscle,skeletal; Fats