多系统萎缩磁共振成像特征的研究

目的 探讨多系统萎缩(MSA)的磁共振成像特征以及各型之间的差别.方法 回顾性分析经临床诊断为MSA的32例病人常规磁共振成像资料,其中橄榄桥脑小脑萎缩(OPCA)17例,纹状体黑质变性(SND)8例,Shy-Drager综合征(SDS)7例.结果 OPCA组主要有十字征、小脑中脚高信号、小脑萎缩、小脑中脚萎缩、延髓萎缩、桥脑萎缩及四脑室扩大等7项MR表现.SND组主要有壳核边缘裂隙状高信号、壳核高信号及壳核萎缩等3项MR表现.而SDS组缺乏特征性MR表现.OPCA组与SND组比较,十字征、小脑中脚高信号、小脑萎缩、小脑中脚萎缩、延髓萎缩、桥脑萎缩、四脑室扩大、壳核边缘裂隙状高信号和壳核萎缩等9项MR表现差别有统计学意义(P<0.05).OPCA组与SDS组比较,十字征、小脑萎缩、小脑中脚萎缩、延髓萎缩、桥脑萎缩和四脑室扩大等6项MR表现差别有统计学意义(P<0.05).而SND组与SDS组比较差别有统计学意义的MR表现只有壳核萎缩和壳核边缘裂隙状高信号2项.结论 常规磁共振成像有助于MSA的诊断及各型的鉴别诊断.     

小脑及小脑中脚表观扩散系数值在鉴别多系统萎缩与帕金森病中的价值

目的 探讨小脑及小脑中脚ADC值在鉴别多系统萎缩(MSA)与帕金森病(PD)中的价值.方法 选取经临床诊断为MSA的18例患者(MSA组),其中发病较早期7例(MSA早期组),诊断为PD的19例患者(PD组)和年龄匹配的18名正常人(对照组)行常规MR和DWI扫描.DWI采用单次激发自旋回波-平面回波序列,测量ROI为两侧小脑半球、小脑中脚及顶叶白质,运用单因素方差分析对各组3个部位的ADC值进行统计学分析.结果 18例MSA中,MR表现异常11例,其中桥脑十字征8例,延髓、桥脑及小脑萎缩11例,小脑中脚萎缩10例,T2WI见壳核边缘高信号和壳核萎缩2例.MSA组及MSA早期组小脑中脚的ADC值[(0.98±0.07)×103、(0.95±0.05)×103 mm2/s]较PD组[(0.77±0.04)×103 mm2/s]和对照组[(0.78±0.04)×103 mm2/s]均明显升高,差异均有统计学意义(F值分别为91.049、55.301,P值均＜0.01),MSA组及MSA早期组ADC值分布范围[(0.86～1.13)×103、(0.86～l.02)×103 mm2/s]与PD组[(0.68～0.84)×103 mm2/s]和对照组[(0.69～0.82)×103 mm2/s]均没有交叉.MSA组及MSA早期组小脑的ADC值[(0.95±0.09)×103、(0.92±0.07)×103 mm2/s]较PD组[(0.78±0.05)×103 mm2/s]和对照组[(0.79±0.05)×103 mm2/s]均明显升高,差异均有统计学意义(F值分别为39.274、18.623,P值均＜0.01),其分布范围[(0.80～1.10)×103、(0.80～0.99)×103 mm2/s]与PD组[(0.72～0.90)×103 mm2/s]和对照组[(0.71～0.87)×103mm2/s]均有交叉.而MSA组及MSA早期组顶叶白质的ADC值与PD组和对照组差别均无统计学意义(P值均＞0.05).结论 小脑及小脑中脚的ADC值对于这两种疾病的鉴别诊断有重要意义,尤其对于发病较早期常规MR表现正常的MSA患者与PD患者的鉴别诊断有重要意义.     

橄榄桥脑小脑萎缩的临床和磁共振分析

目的：分析橄榄桥脑小脑萎缩（OPCA）的临床和MR表现。方法：回顾28例临床拟诊为OPCA并经MR证实的病例，所有病人均采用1.5T MR进行检查。获得自旋回波序列T1加权矢状面和T2、T2及质子密度加权横断面图像。结果 小脑半球28例、桥脑腹侧28例、小脑中脚28例和延髓腹侧上部26例体积缩小。在T2和质子密度加权像上常可见桥横纤维（19/28）和小脑中脚（12/28）高信号。中脑及幕上亦可见到某些异常征象。结论：OPCA的MR表现主要为小脑半球桥脑腹侧、小脑中脚和延髓橄榄的萎缩。某些异常信号，特别是桥横纤维的高信号在T2和质子密度加权像上较易观察到。     

桥脑出血或梗死继发双侧小脑中脚Wallerian变性及肥大性下橄榄核变性的MR浅析(附5例报告)

目的探讨继发于桥脑出血或梗死并同时继发双侧小脑中脚Wallerian变性(WD)及肥大性下橄榄核变性(HOD)的发病机制、MRI特征及其与原发病灶关系,以期提高对该病的认识。方法回顾性分析5例继发于桥脑出血或梗死同时继发双侧小脑中脚WD及HOD的MRI表现,同时根据MRI表现和解剖结合文献对其进行分析。5例均行MRI常规序列和DWI、SWI或T2*WI序列扫描。结果 5例中3例桥脑基底部背侧出血,均继发双侧HOD及双侧小脑中脚WD。1例桥脑右背侧出血继发右侧HOD及双侧小脑中脚WD,1例桥脑左背侧梗死继发左侧HOD及双侧小脑中脚WD。HOD表现为单侧或双侧下橄榄核体积增大,T1WI呈等或稍低信号,T2WI呈稍高或高信号,FLAIR呈等或稍高信号,DWI呈等或稍高信号,ADC图呈等或稍高信号,SWI或T2*WI呈等或稍高信号,其对原发出血病灶显示最好。双侧小脑中脚WD早期表现为对称性DWI图高信号,ADC图低信号,T2WI稍高信号,T1等信号;中后期表现为DWI图等或稍低信号,ADC图稍高信号,T1WI稍低信号,T2WI稍高信号。结论肥大性下橄榄核变性多继发于桥脑背盖部病变,并且有特定的发病部位和较为特征的MRI表现;双侧小脑中脚对称性异常信号不难发现,但当同时存在桥脑出血或梗死、HOD及双侧小脑中脚对称性异常信号时要考虑到是桥脑出血或梗死同时继发HOD及双侧小脑中脚的WD,而不要盲目的把它们误认定为是三个原发孤立病变。     

扩散加权成像在正常胎儿脑发育中的应用

目的 探讨扩散加权成像(DWI)对正常胎儿脑发育的评估价值.方法 回顾性分析40例正常胎儿脑DWI表现,孕周19～39周,平均33.6周.在ADC图上分析总结正常胎儿脑表现特征,并测量脑干、双侧小脑半球、基底节区、丘脑、颞叶白质、额叶白质、枕叶白质、半卵圆中心及顶叶白质的ADC值,分析不同部位ADC值随孕周变化的规律.结果 在ADC图上,胎儿幕上脑实质表现为信号强度不同的分层状结构,随孕周增加分层减少.双侧大脑半球间对称部位ADC值无显著性差异.幕上深部白质平均ADC值高于小脑半球、脑干及深部灰质核团,顶叶ADC值最高(1.62 ±0.17) mm/s,脑干ADC值最低(1.08±0.13) mm/s.胎儿脑干、双侧小脑半球、基底节区、丘脑、颞叶白质、枕叶白质、半卵圆中心及顶叶白质ADC值与胎龄呈负相关,小脑半球相关系数最高(r=0.78),枕叶相关系数最低(r=0.38),额叶与胎龄无线性相关(P＞0.05).小脑半球ADC值随胎龄增长下降最快(b=0.03).结论 DWI可应用于正常胎儿脑发育的评估,为胎儿脑发育的产前诊断及预后提供重要信息.     

脑桥径线测量随年龄变化规律及其在橄榄脑桥小脑萎缩中的诊断价值

目的 探讨脑桥随年龄变化规律及脑桥测量在橄榄脑桥小脑萎缩(OPCA)诊断中的价值.方法 253例正常人(21~80岁)按每10岁为1个年龄组共分6组,13例OPCA患者为病人组.在MRI正中矢状位T1WI图像上,分别测量脑桥上下径(A线)、脑桥腹侧凸度(B线)、脑桥中部前后径(C线)、中脑前后径(D线),将测得结果进行OPCA组和正常各年龄组间的比较.结果 AD线均随年龄增大有逐渐下降趋势,各径线正常各年龄组与OPCA组的差别均有显著统计学意义(P<0.05).脑桥腹侧凸度(B线)正常人女性均＞7.0 mm,男性均＞8.0 mm,而OPCA患者均低于上述两值;而A、C、D线OPCA组和正常对照组间测量值有一定的重叠.结论 脑桥体积在20~40岁时达到顶峰,之后随年龄增长脑桥体积逐渐变小.脑桥腹侧凸度女性＜7.0 mm,男性＜8.0 mm时诊断OPCA意义较大.     

橄榄桥脑小脑萎缩SPECT脑显像和MRI对比研究

目的 评价SPECT脑血流灌注显像在橄榄桥脑小脑萎缩（OPCA）诊断中的价值。方法 对20例OPCA患者行SPECT脑血流灌注显像和头颅MRI检查,并对各项检查结果进行比较。结果 OPCA患者的SPECT显像异常表现为脑局部血流低灌注,以脑干、脑小及基底节为主,也可累及大脑各叶;与MRI比较,SPECT显示病变范围更广泛;SPECT和MRI的异常率分别为95％和75％。结论 SPECT脑血流灌注显像为诊断OPCA提供了新方法,灵敏度优于MRI;SPECT与MRI相结合,有助于提高OPCA诊断的准确性。     

DWI在脐动脉多普勒正常的迟发型宫内生长受限胎儿脑中的研究

目的 探讨扩散加权成像对脐动脉多普勒正常的迟发型宫内生长受限胎儿脑的诊断价值。方法 回顾性分析58例经产前超声诊断脐动脉多普勒血流参数正常的迟发型宫内生长受限胎儿,同时选取与其胎龄相匹配的33例正常胎儿作为对照组。所有胎儿均接受产前常规MRI和DWI检查。分析胎儿脑表现特征,测量额叶白质、顶叶白质、枕叶白质、基底节、桥脑和小脑半球的ADC值,计算额叶/枕叶ADC比值和额叶/小脑半球ADC比值。比较上述参数在两组间的差异。结果 所有胎脑常规MRI检查形态和信号均未见异常。与对照组相比,宫内生长受限组胎儿脑枕叶白质ADC值下降,额枕比显著增加,差异具有统计学意义(P<0.05)。结论 ADC值对检测潜在脑损伤较敏感,有助于诊断脐动脉多普勒正常的迟发型宫内生长受限,但ADC值改变的意义和远期预后需要进一步的研究。     

腕管综合征的3.0T扩散张量成像与电生理的对照研究

目的 评估常规MRI和DTI对腕管综合征(CTS)的诊断价值,评价其在CTS分级中的作用.方法 对16名志愿者32个腕关节及21例患者31个腕关节进行常规MRI、DTI扫描及神经电生理检查.测量不同层面正中神经的MRI数据,计算膨胀率(MNSR)、扁平率(MNFR)、弯曲率(BR);测量平均FA值及ADC值.分别对患者和志愿者的MRI数据以及其与电生理结果进行统计学分析.结果 CTS患者的MNSR、MNFR及BR值较志愿者明显增大;正中神经T2WI信号均有不同程度的增高.患者平均FA值显著低于志愿者(t=15.05,P＜0.01).患者平均FA值与神经电生理的严重程度呈负相关(r=-0.69,P＜0.001).轻度组的平均FA值明显高于中-重度组(t=4.14,P＜0.01).结论 常规MRI和DTI不仅能从形态上反映已经发生病变的神经,且对CTS的分级诊断具有一定的价值.     

基于DTI分析小脑上脚及其交叉各向异性分数和ADC值的差异性

目的 :应用DTI定量评估小脑上脚和小脑上脚交叉的各向异性分数(fractional anisotropy,FA)与ADC值,并比较小脑上脚与小脑上脚交叉数值之间的差异性。方法:回顾性分析100例在我院行颅脑MRI检查患者的DTI图像数据,由2名专家运用ROI功能在FA图和ADC图上分别测量小脑上脚交叉和两侧小脑上脚的FA值和ADC值。计量资料比较采用配对样本t检验。结果:100例中,平均FA值两侧小脑上脚为0.710±0.049,明显高于小脑上脚交叉0.514±0.042,差异有统计学意义(t=37.165,P=0.000)。小脑上脚和小脑上脚交叉的平均ADC值分别为(759.59±30.87)×10-6 mm2/s和(723.86±36.33)×10-6 mm2/s,差异有统计学意义(t=8.128,P=0.000)。结论:小脑上脚交叉的FA值和ADC值均低于小脑上脚,说明两者的微细结构存在差异性。FA图可以区分小脑上脚和小脑上脚交叉。     

扩散张量成像导出量对扩散时间依赖关系的实验研究

目的研究扩散张量导出量与扩散时间的关系。方法保持扩散敏感梯度磁场强度不变，使用8个不同的扩散时间对11名被试者进行扩散张量成像扫描得到脑部的各向异性与各向同性信息，计算出各个感兴趣区的平均扩散率与各向异性分数后进行比较。结果不同扩散时间对应的平均扩散率有显著性差异（P〈0．05），而各向异性分数无显著性差异（P〉0．05）。结论扩散时间对扩散张量成像导出量中的各向异性分数无影响，对平均扩散率有影响。原因是细胞内外水分子扩散性质不同。     

The tensor distribution function

Diffusion weighted magnetic resonance imaging is a powerful tool that can be employed to study white matter microstructure by examining the 3D displacement profile of water molecules in brain tissue. By applying diffusion‐sensitized gradients along a minimum of six directions, second‐order tensors (represented by three‐by‐three positive definite matrices) can be computed to model dominant diffusion processes. However, conventional DTI is not sufficient to resolve more complicated white matter configurations, e.g., crossing fiber tracts. Recently, a number of high‐angular resolution schemes with more than six gradient directions have been employed to address this issue. In this article, we introduce the tensor distribution function (TDF), a probability function defined on the space of symmetric positive definite matrices. Using the calculus of variations, we solve the TDF that optimally describes the observed data. Here, fiber crossing is modeled as an ensemble of Gaussian diffusion processes with weights specified by the TDF. Once this optimal TDF is determined, the orientation distribution function (ODF) can easily be computed by analytic integration of the resulting displacement probability function. Moreover, a tensor orientation distribution function (TOD) may also be derived from the TDF, allowing for the estimation of principal fiber directions and their corresponding eigenvalues. Magn Reson Med 61:205–214, 2009. © 2008 Wiley‐Liss, Inc.     

Effects of osmotically driven cell volume changes on diffusion-weighted imaging of the rat optic nerve

The apparent diffusion coefficient (ADC) of the rat optic nerve was measured In vitro, using magnetic resonance imaging, to determine the effects of changes in cellular volume fraction on the diffusion of tissue water. Nerve ADC was determined under conditions of cell membrane depolarization and (i) increased intracellular volume, (ii) decreased intracellular volume, and (iii) negligible volume change. Depolarization alone had little affect on ADC, whereas volume changes produced strong, reversible effects. Increased cell volume decreased ADC and vice versa. These results are consistent with the view that changes in the extracellular space are the major source of ADC changes in brain tissue.     

Echo-Planar Diffusion Spectroscopic Imaging

High-speed diffusion spectroscopic imaging based on an echo-planar technique is presented. A pair of diffusion gradients is applied prior to a rapidly oscillating magnetic field gradient which encodes both chemical shift and spatial information. By applying this technique to a phantom consisting of acetone and water, a diffusion spectroscopic image is obtained in about 15 min, about 64 times faster than the time required in the conventional method. The measured diffusion coefficients show good agreement with previously reported values. This kind of diffusion spectroscopic imaging is expected to provide a way to observe more specific metabolism.     

Tumor extension in high-grade gliomas assessed with diffusion magnetic resonance imaging: values and lesion-to-brain ratios of apparent diffusion coefficient and fractional anisotropy

Purpose: To determine whether the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) can distinguish tumor-infiltrated edema in gliomas from pure edema in meningiomas and metastases.

Material and Methods: Thirty patients were studied: 18 WHO grade III or IV gliomas, 7 meningiomas, and 5 metastatic lesions. ADC and FA were determined from ROIs placed in peritumoral areas with T2-signal changes, adjacent normal appearing white matter (NAWM), and corresponding areas in the contralateral healthy brain. Values and lesion-to-brain ratios from gliomas were compared to those from meningiomas and metastases.

Results: Values and lesion-to-brain ratios of ADC and FA in peritumoral areas with T2-signal changes did not differ between gliomas, meningiomas, and metastases (P = 0.40, P = 0.40, P = 0.61, P = 0.34). Values of ADC and FA and the lesion-to-brain ratio of FA in the adjacent NAWM did not differ between tumor types (P = 0.74, P = 0.25, and P = 0.31). The lesion-to-brain ratio of ADC in the adjacent NAWM was higher in gliomas than in meningiomas and metastases (P = 0.004), but overlapped between tumor types.

Conclusion: Values and lesion-to-brain ratios of ADC and FA in areas with T2-signal changes surrounding intracranial tumors and adjacent NAWM were not helpful for distinguishing pure edema from tumor-infiltrated edema when data from gliomas, meningiomas, and metastases were compared.     

Q-ball imaging.

Magnetic resonance diffusion tensor imaging (DTI) provides a powerful tool for mapping neural histoarchitecture in vivo. However, DTI can only resolve a single fiber orientation within each imaging voxel due to the constraints of the tensor model. For example, DTI cannot resolve fibers crossing, bending, or twisting within an individual voxel. Intravoxel fiber crossing can be resolved using q-space diffusion imaging, but q-space imaging requires large pulsed field gradients and time-intensive sampling. It is also possible to resolve intravoxel fiber crossing using mixture model decomposition of the high angular resolution diffusion imaging (HARDI) signal, but mixture modeling requires a model of the underlying diffusion process.Recently, it has been shown that the HARDI signal can be reconstructed model-independently using a spherical tomographic inversion called the Funk-Radon transform, also known as the spherical Radon transform. The resulting imaging method, termed q-ball imaging, can resolve multiple intravoxel fiber orientations and does not require any assumptions on the diffusion process such as Gaussianity or multi-Gaussianity. The present paper reviews the theory of q-ball imaging and describes a simple linear matrix formulation for the q-ball reconstruction based on spherical radial basis function interpolation. Open aspects of the q-ball reconstruction algorithm are discussed.     

In vivo generalized diffusion tensor imaging (GDTI) using higher‐order tensors (HOT)

Generalized diffusion tensor imaging (GDTI) using higher‐order tensor (HOT) statistics generalizes the technique of diffusion tensor imaging by including the effect of nongaussian diffusion on the signal of MRI. In GDTI‐HOT, the effect of nongaussian diffusion is characterized by higher‐order tensor statistics (i.e., the cumulant tensors or the moment tensors), such as the covariance matrix (the second‐order cumulant tensor), the skewness tensor (the third‐order cumulant tensor), and the kurtosis tensor (the fourth‐order cumulant tensor). Previously, Monte Carlo simulations have been applied to verify the validity of this technique in reconstructing complicated fiber structures. However, no in vivo implementation of GDTI‐HOT has been reported. The primary goal of this study is to establish GDTI‐HOT as a feasible in vivo technique for imaging nongaussian diffusion. We show that probability distribution function of the molecular diffusion process can be measured in vivo with GDTI‐HOT and be visualized with three‐dimensional glyphs. By comparing GDTI‐HOT to fiber structures that are revealed by the highest resolution diffusion‐weighted imaging (DWI) possible in vivo, we show that the GDTI‐HOT can accurately predict multiple fiber orientations within one white matter voxel. Furthermore, through bootstrap analysis we demonstrate that in vivo measurement of HOT elements is reproducible, with a small statistical variation that is similar to that of diffusion tensor imaging. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.