磁共振弥散张量和波谱成像在缺血性脑小血管疾病中的应用研究

目的探讨磁共振弥散张量成像(diffusion tensor imaging,DTI)联合磁共振波谱成像(magnetic resonance spectroscopy,MRS)对于缺血性脑小血管疾病(small vessel disease,SVD)的影像评估价值。材料与方法对42例缺血性SVD患者进行常规MRI、DTI和MRS扫描,测量病灶及健侧对称正常脑白质区域的平均弥散系数(average diffusion coefficient,DCavg)值、各向异性分数(fractional anisotropy,FA)值,测量病灶及其周围正常脑白质区域的N-乙酰天门冬氨酸(N-acetyl aspartic acid,NAA)、胆碱(choline,Cho)、肌酸(creatine,Cr)、肌醇(myo-inositol,MI)等生化代谢物的浓度值,并计算NAA/Cho、NAA/Cr、Cho/Cr、MI/Cr的比值。将42例SVD患者的缺血性病灶按照影像学显示分组,并对各组上述测量指标进行统计学分析。结果选取42例缺血性SVD患者的42个病灶并分成慢性缺血组(30例)和慢性期梗死灶组(12例)。SVD病灶的DCavg值和FA值分别较健侧镜像区正常脑白质的增高和降低(P0.01),而两组间SVD病灶的DCavg值和FA值差异无统计学意义(P0.05)。SVD病灶的NAA、Cho和Cr的均数都小于周围正常白质(P0.01),而两组间的各项MRS代谢值差异均无统计学意义(P0.05)。Pearson相关性分析,正常脑白质的DCavg值与FA值(r=-0.383,P=0.012)呈负相关,FA值与NAA/Cho(r=0.420,P=0.006)、NAA/Cr(r=0.382,P=0.012)之间均呈正相关,而在SVD病灶组无上述相关性。Spearman相关分析,SVD病灶组的DCavg与高血压呈正相关(r=0.338,P=0.029)。结论对于缺血性SVD,DCavg、FA、NAA、Cho和Cr等检测指标能够共同反映神经髓鞘结构的微观变化及其功能的破坏,联合应用DTI和MRS成像技术对缺血性SVD疾病进行研究,有助于其临床诊断及病理机制的研究。

The application research of diffusion tensor imaging and magnetic resonance spectroscopic imaging in ischemic cerebral small vessel disease

Objective: To investigate the medical imaging evaluative value of diffusion tensor imaging combined with magnetic resonance spectroscopy in ischemic cerebral small vessel disease. Materials and Methods: Forty-two cases of ischemic SVD were imaged with conventional MRI, DTI and MRS. Average diffusion coefficient (DCavg) and fractional anisotropy (FA) were measured symmetrically, which in the lesion regions and the contralateral normal white matter area. Then the absolute metabolite concentrations of N-acetylaspartate (NAA), total cholines (Cho),total creatines (Cr) and myo-inositol (MI) in SVD lesion regions and the normal white matter regions around the lesions were detected, and the ratios of NAA/Cho, NAA/Cr, Cho/Cr, MI/Cr were calculated. To divide the 42 lesions of ischemic SVD into groups according to the imaging display, all the indexes above mentioned of each group were statistically analyzed. Results: The 42 lesions of ischemic SVD were divided into chronic ischemic focus group (30 cases) and chronic lacunar infarction group (12 cases). The DCavg values of SVD lesions significantly raised compared with those of the contralateral normal white matter area (P<0.01), while the FA values of SVD lesions reduced (P<0.01). Neither DCavg nor FA values between chronic ischemic focus group and chronic lacunar infractions group were significantly different (P>0.05). The mean values of NAA, Cho and Cr of the SVD lesions were all less than those of the normal white matter regions around the lesions (P<0.01), but there was no significant difference of MRS metabolic values between chronic ischemic focus group and chronic lacunar infarctions group (P>0.05). Pearson correlation analysis showed that there was a negative correlation between DCavg value and FA (r=-0.383, P=0.012) in normal white matter, the FA value was positively correlated with NAA/Cho (r=0.420, P=0.006), NAA/Cr (r=0.382, P=0.012), but there was no correlation in the SVD lesions. The DCavg value was actively associated with hypertension in SVD lesions by Spearman correlation analysis (r=0.338, P=0.029). Conclusion: For the ischemic SVD, the values of DCavg, FA, NAA, Cho and Cr can reflect the micro variations and the functional damages of nerve neurolemma. Combined application of DTI and MRS could have a great contribution to clinical diagnose and pathological mechanism in ischemic SVD.