^1H-MR波谱评价骨骼肌细胞内脂肪含量的在体和模型研究

Evaluation of intra-cellular lipid of skeletal muscle by ^1H-MR spectroscopy： in vivo and phantom study

目的解释骨骼肌^1H—MRS中的脂峰形念及其影响因素，建立利用骨骼肌^1H-MRS评价肌细胞内脂肪的方法。方法取5名健康志愿者的小腿胫骨前肌和比目鱼肌区域行^1H—MRS检查，改变小腿纵轴与主磁场（B0）之间的角度，观察0．80～1．80ppm（×10^-6）处脂峰形态的变化。体外模型研究采用毛细玻璃管束中灌注大最油和脂肪乳液，分别模拟肌纤维细胞外、细胞内脂肪，比较脂峰随模型与B0角度变化的特征。结果小腿骨骼肌在0．80～1．80ppm处可以观察到3～4个峰，各峰相差约0．20～0．30ppm；当小腿纵轴与Bn所成角度增大时，胫骨前肌肌纤维间隙内的脂肪（EMCL）的亚甲基峰逐渐向右侧移位。体外模型很好地模拟了在体骨骼肌^1H—MRS脂峰形态，在0．80～1．80ppm处出现2组甘油三酸酯哑甲基峰和甲基峰，其中心频率相差0．20—0．30ppm，分别代表肌细胞内、外脂肪。由于骨骼肌组织肌纤维走行的高度有序性及肌细胞内、外脂肪的分子分布状态不同，两者感应的化学位移不同而表现出波峰的分离。这种肌细胞内外脂肪峰的分离在肌束与B0一致时最大，在两者夹角接近魔角（54．7°）时无法分离。结论骨骼肌^1H—MRS中肌细胞内、外脂肪发生分离，是一种无创性评价肌细胞内脂肪含量的有效方法；胫骨前肌足进行^1H—MRS检在的理想部位。

Objective To elucidate the spectrum of lipid peaks in ^1H-MRS of skeletal muscle and it＇s interpretation, to investigate the utility of ^1H-MRS in evaluating intramyocellular lipid （IMCL）. Methods ^1H-MRS was acquired in vivo on tibialis anterior muscle （TA） and soleus muscle （S） on 5 healthy volunteers. The spectrum of the lipid peak between 0. 80 and 1.80 ppm was observed with different angle between the long axis of the calf and B0. Ex vivo phantom was an cluster of capillary tubers filled with soybean oil and fat emulsion, simulating the extramyocellular lipid （EMCL） and IMCL, respectively. The spectra of the lipid peaks were compared using different angles between the phantom and B0 field. Results The lipid spectrum split to 3 to 4 peaks between 0. 80 and 1.80 ppm on calf muscles, with 0. 20 to 0. 30 ppm interval between each neighbouring peak. The methylene peak of EMCL, shifted to the right when the angle between long axis of the calf and B0 increased. The phantom could simulate the spectrum of ^1 HMRS of the muscle, presenting two peaks with 0. 20 to 0. 30 ppm chemical shift difference between 0. 80 and 1.80 ppm. They are methyl triglyceride and methylene, representing IMCL and EMCL, respectively. The peak splitting could be attributed to the high ordered muscle fibers and their chemical shift difference between iuta-and extra-cellular distribution. The interval of IMCL and EMCL peaks attenuated when the angle between the muscle fiber and B0 increased from 0 to the magic angle （ 54.7 ° ）. Conclusion On ^1H- MRS spectrum, the peak of the EMCL and IMCL splits. This indicated that ^1H-MRS is an applicable method to detect IMCL noninvasively. TA is an optimizing muscle for ^1H-MRS study.