小腿骨骼肌代谢物的1H-MR波谱绝对定量研究

目的 测定3.0 T场强下,小腿骨骼肌1H-MRS中可见的代谢物分子和水分子中质子的横向弛豫时间(T1)和纵向弛豫时间(T2)值,为实现采用1H-MRS进行骨骼肌各代谢物含量的测定奠定基础,并为骨骼肌1H-MRS检查的参数优化提供依据.方法 24名志愿者,采用随机数字表将其随机分为2组,分别行小腿比目鱼肌和胫骨前肌的弛豫时间测定.采用单体素受激回波采集法进行1H-MRS数据采集,T1时间测定采用渐进饱和法,T2时间测定采用改变TE法.代谢物浓度计算采用以水为内部参照方法,经测定的T1、T2时问校正后获得.对不同肌肉的相同参数所获数据之间比较采用两独立样本均数的t检验.结果 24名健康志愿者中共得到22组数据(比目鱼肌12组,胫骨前肌10组).健康成人小腿比目鱼肌中水、肌酸-甲基3(Cr3)、三甲基胺(TMA)、肌细胞外脂肪(EMCL)、肌细胞内脂肪(IMCL)的T1值分别为(1384.0±36.9)、(1064.0±167.0)、(964.2±144.0)、(373.0±46.8)、(374.7±20.6)ms,T2值分别为(26.5±1.2)、(100.2±19.3)、(149.1±32.7)、(81.4±5.2)、(84.7±4.2)ms;胫骨前肌中水、Cr3、TMA、EMCL、IMCL的T1值分别为(1307.0±24.4)、(945.7±132.0)、(968.3±127.0)、(372.7±39.2)、(412.8±80.2)ms,T2值分别为(27.1±0.9)、(135.3±18.2)、(62.1±6.0)、(84.3±4.0)、(90.7±3.2)ms.经上述弛豫时间校正后,健康成人小腿比目鱼肌和胫骨前肌各代谢物绝对浓度Cr3为(33.1±3.7)和(31.7±3.1)mmol/kg、TMA为(35.2±3.2)和(32.9±5.2)mmol/kg、EMCL为(12.2±5.0)和(8.9±4.9)mmol/kg、IMCL为(9.0±2.4)和(3.0±0.8)mmol/kg,其中胫骨前肌IMCL含量明显小于比目鱼肌,两者的差异有统计学意义(t=8.024,P<0.01),胫骨前肌和比目鱼肌其他代谢物含量差异无统计学意义(t值分别为0.926、1.264、1.542,P值均>0.05).结论 该研究较准确地测定了骨骼肌代谢物的弛豫时间值,代谢物弛豫时间值的测定对于实现骨骼肌1H-MRS的绝对定量研究及扫描参数优化具有重要意义.

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

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. 01 ), the difference between other metabolites were not statistically significant( t = 0. 926,1. 264, 1. 542, 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.