扩散张量成像技术在体部的临床应用

（一）DTI在肝脏疾病中的应用

对于肝脏疾病的DTI检查目前正处于起步阶段。Taouli等使用和不使用并行采集技术的DTI和DWI分析10例正常志愿者肝脏的信号强度发现，使用并行采集技术的DTI和DWI的肝的信号强度优于不使用并行采集技术DWI（b＝500s/ mm2，13.0和10.1 vs 9.1，P＜0.03；b=0s/mm2，9.0和 7.6 vs 6.9，P＝0.12）。使用并行采集技术做肝脏DTI检查可以使用短的接近于肝脏的TE值，减少了回波链长，减少伪影，提高肝脏的信噪比。目前，国内外关于肝脏的DTI研究较少，技术尚不成熟，应该选择最佳的成像条件，建立正常的平均扩散系数值范围和各向异指数正常范围，为肝疾病的DTI研究奠定基础。

（二）DTI在乳腺疾病中的应用

由于乳腺腺体排列具有一定方向性，一般从后向前，并逐渐向乳头集中排列，腺体间脂肪组织被抑制，因此乳腺腺体内水分子的扩散运动在各方向会存在差异，即具有一定的各向异性，这就为乳腺DTI成像构成了一定的基础。

Partridge SC等采用b＝600 s/mm2研究正常乳腺的DTI，得出λ1＝2.51×10-3mm2/s， λ2＝1.89×10-3mm2/s，λ3＝1.39×10-3mm2/s，ADC＝（1.95±0.24）×10-3mm2/s，FA＝0.29±0.05。认为FA和ADC值在乳腺各区域间存在显著差异（P＜0.05），在中间区域具有较高的ADC值，而在后部区域具有较高的FA值（图2-3-4）。比较b＝0、600s/mm2和b＝0、1 000s/mm2时的DTI，发现ADC值具有显著差异（P＜0.001），而FA值之间无显著差异。在重复测量评价时，ADC值的个体间差异为4.5%，FA值的个体间差异为11.4%。因此在应用DTI评价乳腺病变时要充分注意乳腺区域之间的差异和b值的影响，一定要结合临床，并且最好对此技术进行标准化。

Partridge SC等研究还发现乳腺囊肿与正常腺体组织相比，DWI信号增高，ADC值无明显降低，FA值明显降低（图2-3-5）。

Baltzer PA等研究了59例乳腺患者的DTI，发现乳腺腺体内水分子的扩散大部分存在主要方向（后-前），而大部分病灶内水分子的扩散没有主要方向。其ADC值在良恶性病变之间具有显著差异（P＜0.001），用其诊断良恶性病变的ROC曲线下面积达到0.899，接近高等效能。并得出良性病变的FA值（0.14～0.24）低于恶性病变的FA值（0.21～0.35），诊断乳腺良恶性病变的ROC曲线下面积为0.751～0.770。但经过多元回归分析，在良恶性病变的鉴别诊断中，FA值并不比ADC值更有价值。最后得出结论DTI可以显示乳腺良恶性病变之间及其与乳腺实质之间的微观结构差异（图2-3-6～图2-3-8）。

而Partridge SC等的研究则认为，乳腺癌的FA值（0.24±0.07）显著低于乳腺组织（0.29±0.07；P＜0.000 1），但FA值无助于良恶性病变的鉴别诊断（图2-3-9）。因此对于DTI在乳腺病变中的应用价值尚存在争议，需要更深入细致的研究和扫描技术的改进去进一步证实。

图2-3-4 乳腺DTI研究方法

注：用T1WI（A）来区分腺体和脂肪，在腺体前、中、后部分别放置大小相同的ROI，并尽量避开脂肪。B为b＝0时DWI；C为ADC图；D为FA图
[引自：Partridge SC, Murthy RS, Ziadloo A, et al. Diffusion tensor magnetic resonance imaging of the normal breast. Magn Reson Imaging, 2010, 28(3): 320-328]

图2-3-5 34岁志愿者乳腺DTI

注：发现左乳一小囊肿。A为b＝0 DWI；B为b＝600 s/mm2 DWI；C为ADC图；D为FA图
[引自：Partridge SC, Murthy RS, Ziadloo A, et al. Diffusion tensor magnetic resonance imaging of the normal breast. Magn Reson Imaging, 2010, 28(3): 320-328]

图2-3-6 46岁患者乳腺DTI显示囊肿

注：A为b=1 000 s/mm2时DWI。B为T1WI梯度回波横轴位图像和重建的冠状位图像（E），显示等信号的腺体和高信号的脂肪解剖结构。D为FA图，其像素按照主要扩散方向进行彩色编码。亮度代表各相异性的程度（定义为0-1）。C，F为DTI与T1WI相融合的图像。除了有些伪影外，主要色彩为绿色（前-后方向），反映导管的方向。另外，绿色比红色和蓝色的亮度更高（FA更高）。注意侧方的囊肿FA明显减低
[引自：Baltzer PA, Schäfer A, Dietzel M, Diffusion tensor magnetic resonance imaging of the breast: a pilot study. Eur Radiol, 2011, 21(1): 1-10]

图2-3-7 50岁患者乳腺增强扫描显示——分叶状早期不均匀增强肿块

注：F，C为强化后的减影图像和冠状重建图像；A为b=0时DWI，显示分叶状肿块呈高信号；B为b=1 000 s/mm2时DWI图像，显示病灶信号明显丢失，在相应ADC图（E）上呈高信号；D为彩色编码的FA图显示病灶FA值显著降低，没有明显的扩散方向。这些是纤维腺瘤的典型表现，并已经组织病理学证实。在12:00处还有一类似病灶
[引自：Baltzer PA, Schäfer A, Dietzel M, Diffusion tensor magnetic resonance imaging of the breast: a pilot study. Eur Radiol, 2011, 21(1): 1-10]

图2-3-8 46岁患者乳腺增强扫描显示——不均匀早期增强肿块（箭）

注：F，C为强化后的减影图像和冠状重建图像。A和B分别为b=0和b=1 000 s/mm2时DWI图像，显示腺体的扩散信号丢失比病灶更明显。因此在ADC图上病灶信号更低。彩色FA图显示病灶（箭头）比乳腺组织（*）信号更低一点，并且没有主要扩散方向。这些是浸润性乳腺癌的典型表现，并已经组织病理学证实（浸润性导管癌，G2）
[引自：Baltzer PA, Schäfer A, Dietzel M, Diffusion tensor magnetic resonance imaging of the breast: a pilot study. Eur Radiol, 2011, 21(1): 1-10]

图2-3-9 2例恶性病灶均表现为低FA和ADC值

注：A～C为57岁患者，D～F为49岁患者。两者在右乳均发现一直径为1.3cm浸润性导管癌。A、D为增强后T1WI，B、E为DWI图像，C、F为彩色FA/ADC阈值图（用研究中诊断恶性肿瘤的最佳临界ADC和FA值作为阈值
[引自：Partridge SC, Ziadloo A, Murthy R, et al. Diffusion tensor MRI: preliminary anisotropy measures and mapping of breast tumors. J Magn Reson Imaging, 2010, 31(2): 339-347]

（三）DTI在前列腺的应用

随着MR设备的更新和技术的发展，DTI技术也可以用于前列腺的检查，一般要求在场强1.5T以上的扫描仪上进行。目前有多家研究在进行，都证实了前列腺DTI的可行性，但所测得数据存在一定差异。

与DWI结果相似，DTI检查所测得平均ADC值在正常前列腺中央带和外周带之间、前列腺增生和正常腺体之间以及前列腺外周带癌和正常外周带之间均具有统计学意义上的差异，尽管各家所测得数值不尽相同。Gurses B等用3.0T磁共振扫描仪对28名健康志愿者进行DTI检查，所得前列腺中央带和外周带的FA值分别为0.26×10-3mm2/ s和0.16×10-3mm2/s，具有显著差异。王锡臻等用1.5T对20名健康志愿者行DTI检查，得出了相类似的结果。Sinha S等和Manenti G等则得出正常前列腺外周带和中央带极为相近的FA值（分别为0.46×10-3mm2/s和0.40×10-3mm2/s、0.47×10-3mm2/ s和0.41×10-3mm2/s）。Sinha S等还得出前列腺中央带和外周带的纤维束成像方向均以上下方向为主要方向。Manenti G等研究还提示前列腺外周带癌的FA值（0.27±0.05）明显低于正常外周带和中央带的FA值；外周带主要纤维走行方向为顶-底，而中央带则不是；纤维失踪成像（DTT）不但可以很好的显示前列腺的轮廓和内部结构，还可以显示肿瘤的延伸及包膜浸润。

Takayama Y等对9例穿刺证实的前列腺外周带癌患者行碳离子放疗前后分别进行DTI检查，研究得出碳离子放疗后前列腺癌区的平均ADC值明显升高，而正常外周带和中央带的平均ADC值无明显变化，碳离子放疗前癌区和正常外周带和中央带的平均ADC值存在显著差异，放疗后差异消失。但是FA值却没有上述明显变化。DTT还显示放疗后癌区的各向异性主要方向有变化。

Piotr K等还比较了DTI和动态增强扫描（DCE MRI）（图2-3-10）以及两者联合诊断前列腺癌的诊断效能，认为两者联合（ROC曲线下面积0.96）要比任何一种方法（ROC曲线下面积0.92和0.87）单独诊断前列腺癌的诊断效能都高。

从以上研究结果得出，前列腺DTI检查是可行的，DTI既可以显示前列腺解剖结构，又可以反映正常组织及前列腺癌内部水分子运动差异，但由于研究尚处于起步阶段，样本量较小，所得结果尚存争议，需要进一步更细致、大样本研究来证实。

图2-3-10 前列腺肿瘤患者与正常被试对比

注：上面一行图为经穿刺证实为右后周围带前列腺癌的67岁患者（PSA = 7.1 ng/ml）的T2WI 、平均ADC图、FA图、Ktrans图和Ve图，下面一行图为穿刺证实为正常的69岁患者（PSA = 4.6 ng/ml）。可以看出，T2WI、ADC图和Ktrans图都能明显显示右后周围带的肿瘤，但在FA图和Ve图中却难以显示。虽然在某些中央带区域的Ktrans值与肿瘤一样高，但群体研究中肿瘤区的平均Ktrans值要显著高于中央带
[引自：Kozlowski P, Chang SD, Meng R, et al. Combined prostate diffusion tensor imaging and dynamic contrast enhanced MRI at 3T -quantitative correlation with biopsy. Magnetic Resonance Imaging 2010, 28(5):621–628]

（王光彬 王翠艳 王 静 张新娟 朱向玉）

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