扩散峰度张量成像在帕金森病的诊断效用

目的研究扩散峰度张量成像对帕金森病的诊断价值。材料与方法本研究病人均签署知情同意书,获得伦理委员会认可,并遵循本地法律及赫尔辛基宣言。30例原发性帕金森病病人[平均年龄(64.5±3.4)岁]及30例健康志愿者[平均年龄(65.0±5.1)岁]进行了MR扩散加权成像检查。比较两     

Microstructural changes of the corticospinal tract in idiopathic normal pressure hydrocephalus: a comparison of diffusion tensor and diffusional kurtosis imaging

Introduction

The goals of this study were to examine the usefulness of diffusional kurtosis imaging (DKI) for assessing microstructural changes in the compressed corticospinal tract (CST) among patients with idiopathic normal pressure hydrocephalus (iNPH).

Methods

Eleven patients with iNPH (mean age: 73.6 years, range: 65–84), who underwent 3-T magnetic resonance imaging, including DKI before surgery, were recruited. Six age-matched, healthy subjects (mean age: 69.8 years, range: 60–75) served as the control group. DKI and diffusion tensor imaging parameters were calculated and compared between the iNPH and the control groups using tract-specific analysis of the CST at the level of the lateral ventricle.

Results

Mean diffusional kurtosis (DK) and axial diffusion kurtosis were significantly lower in iNPH patients. However, apparent diffusion coefficient, fractional anisotropy, and axial eigenvalue (λ ₁ ) were significantly higher in the iNPH group than in the control group.

Conclusions

The mechanical pressure caused by ventricular enlargement in iNPH patients might induce formation of well-aligned fiber tracts and increased fiber density in the CST, resulting in decreased DK. DKI is able to depict both the altered microstructure and water molecule movement within neural axons and intra- or extracellular space. In addition, the investigated DKI parameters provide different information about white matter relative to conventional diffusional metrics for iNPH.     

Effects of diffusional kurtosis imaging parameters on diffusion quantification

Diffusional kurtosis imaging (DKI) is a new technique based on non-Gaussian water diffusion analysis. However, the original DKI protocol (six b values and 30 motion-probing gradient (MPG) directions) requires more than 10 min of scanning time, which is too long for daily clinical use. We aimed to find suitable b value, MPG direction, and diffusion time settings for faster DKI. Four normal healthy subjects participated in the study. All DKI data sets were acquired on a clinical 3T-MRI scanner (Philips Medical Systems) with use of three protocols of 0–7500 s/mm² b values, 6–32 MPG directions, and 23–80 ms diffusion time. There was a remarkable difference in the standard deviation (SD) of the mean DK values in the number of MPG directions. The mean DK values were significantly higher in the posterior limb of the internal capsule (p = 0.003, r = 0.924) and thalamus (p = 0.005, r = 0.903), whereas the mean DK values of the cerebrospinal fluid (CSF) (p = 0.001, r = ?0.976) were significantly lower when we used a longer diffusion time. Our results indicate that the SD of the mean DK values was higher in 15 MPG directions than in 20 MPG directions and more. Because the mean DK values of the CSF were significantly lower when we used longer diffusion times, we expect longer diffusion times to be useful for DKI. We propose the following imaging parameters for clinical use: 0, 1000, and 2000 s/mm² b values; 20 MPG directions; Δ/δ 45.3/13.3 ms.     

Mitochondrial encephalomyopathy: comparison of conventional MR imaging with diffusion-weighted and diffusion tensor imaging: case report

Summary: Conventional MR imaging, MR spectroscopy, diffusion-weighted imaging, and diffusion tensor imaging were performed in a 5-month-old male patient with mitochondrial encephalomyopathy. On conventional T2-weighted MR images, symmetric, confluent high signal intensity was found in the temporoparietal white matter. A large lactate peak and decreased N-acetylaspartate were found in this region on proton MR spectroscopic images. Diffusion-weighted imaging showed increased apparent diffusion coefficient, representing vasogenic edema. Diffusion tensor imaging revealed decreased anisotropy, consistent with injury to the oligodendro-axonal unit. A muscle biopsy specimen revealed an isolated complex III enzyme respiratory chain deficiency. Diffusion-weighted and diffusion tensor imaging are valuable techniques for the characterization of hyperintense lesions on T2-weighted MR images in cases of mitochondrial encephalomyopathy.     

More accurate estimation of diffusion tensor parameters using diffusion kurtosis imaging

With diffusion tensor imaging, the diffusion of water molecules through brain structures is quantified by parameters, which are estimated assuming monoexponential diffusion‐weighted signal attenuation. The estimated diffusion parameters, however, depend on the diffusion weighting strength, the b‐value, which hampers the interpretation and comparison of various diffusion tensor imaging studies. In this study, a likelihood ratio test is used to show that the diffusion kurtosis imaging model provides a more accurate parameterization of both the Gaussian and non‐Gaussian diffusion component compared with diffusion tensor imaging. As a result, the diffusion kurtosis imaging model provides a b‐value‐independent estimation of the widely used diffusion tensor parameters as demonstrated with diffusion‐weighted rat data, which was acquired with eight different b‐values, uniformly distributed in a range of [0,2800 sec/mm²]. In addition, the diffusion parameter values are significantly increased in comparison to the values estimated with the diffusion tensor imaging model in all major rat brain structures. As incorrectly assuming additive Gaussian noise on the diffusion‐weighted data will result in an overestimated degree of non‐Gaussian diffusion and a b‐value‐dependent underestimation of diffusivity measures, a Rician noise model was used in this study. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

A simple isotropic phantom for diffusional kurtosis imaging

Dairy cream is shown to be a simple, inexpensive, isotropic phantom useful for testing diffusional kurtosis imaging data acquisition and postprocessing. The MR-visible protons of cream exhibit slow and fast diffusion components, attributed to the fat and water protons, respectively, which give rise to a diffusion coefficient of 1.1 μm(2)/ms and a diffusional kurtosis of 1.2. These parameter values are similar to those observed in vivo for human brain. Heating the cream is found to increase the T(2)-relaxation time of the fat protons, which facilitates the evaluation of typical diffusional kurtosis imaging protocols used in clinical settings. The diffusion coefficient and diffusional kurtosis can both be measured directly and predicted based on the corresponding diffusion parameters of the individual water and fat components, which are independently measurable due to chemical shift misregistration, thus providing an important consistency check. This phantom is proposed as a convenient calibration standard for multicenter diffusional kurtosis imaging studies.     

Assessment of tissue heterogeneity using diffusion tensor and diffusion kurtosis imaging for grading gliomas

Introduction

In this work, we aim to assess the significance of diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) parameters in grading gliomas.

Methods

Retrospective studies were performed on 53 subjects with gliomas belonging to WHO grade II (n = 19), grade III (n = 20) and grade IV (n = 14). Expert marked regions of interest (ROIs) covering the tumour on T2-weighted images. Statistical texture measures such as entropy and busyness calculated over ROIs on diffusion parametric maps were used to assess the tumour heterogeneity. Additionally, we propose a volume heterogeneity index derived from cross correlation (CC) analysis as a tool for grading gliomas. The texture measures were compared between grades by performing the Mann-Whitney test followed by receiver operating characteristic (ROC) analysis for evaluating diagnostic accuracy.

Results

Entropy, busyness and volume heterogeneity index for all diffusion parameters except fractional anisotropy and anisotropy of kurtosis showed significant differences between grades. The Mann-Whitney test on mean diffusivity (MD), among DTI parameters, resulted in the highest discriminability with values of P = 0.029 (0.0421) for grade II vs. III and P = 0.0312 (0.0415) for III vs. IV for entropy (busyness). In DKI, mean kurtosis (MK) showed the highest discriminability, P = 0.018 (0.038) for grade II vs. III and P = 0.022 (0.04) for III vs. IV for entropy (busyness). Results of CC analysis illustrate the existence of homogeneity in volume (uniformity across slices) for lower grades, as compared to higher grades. Hypothesis testing performed on volume heterogeneity index showed P values of 0.0002 (0.0001) and 0.0003 (0.0003) between grades II vs. III and III vs. IV, respectively, for MD (MK).

Conclusion

In summary, the studies demonstrated great potential towards automating grading gliomas by employing tumour heterogeneity measures on DTI and DKI parameters.

     

DTI在腰椎间盘退行性改变中的应用初探

目的:探讨扩散张量成像(DTI)定量指标ADC及FA值与腰椎间盘退行性改变Pfirrmann分级的相关性.方法:将105例腰腿痛患者纳入研究,所有患者行椎间盘常规MRI及矢状面DTI扫描,根据T2 WI上椎间盘的特点对525个腰椎椎间盘进行Pfirrmann(Pm)分级,观察邻近终板的退变情况,测量椎间盘髓核区的ADC值及FA值并比较各级椎间盘之间的差异,采用Spearman等级相关检验分析ADC和FA值与Pm分级的相关性,并计算2个指标对椎间盘退变(PmⅣ～Ⅴ级)的诊断效能.结果:105例共525个腰椎椎间盘中PmⅠ～Ⅴ级分别有41、112、164、141和67个.经方差分析,Pm Ⅰ和Ⅱ级椎间盘间ADC值、PmⅣ及Ⅴ级椎间盘间ADC值和FA值的差异无统计学意义(P＞0.05),其余各分级之间2个指标的差异有统计学意义(P＜0.05).经ROC分析,ADC值及FA值对PmⅣ、Ⅴ级椎间盘的诊断效能分别为0.846和0.932,两者间差异有统计学意义(P＜0.05).Spearman秩相关分析显示,椎间盘退变Pm分级与ADC值呈负相关(rs=-0.66,P＜0.05),与FA值呈正相关(rs=0.805,P＜0.05).结论:DTI作为定量MRI的一种特殊检查技术,其测量参数与Pfirrmann分级之间具有很好的相关性,可作为一种无创性的检查方法应用于椎间盘退变的研究.     

MR扩散张量成像在膝关节前交叉韧带的初步应用

目的:探讨采用3.0T磁共振对膝关节前交叉韧带进行磁共振扩散张量成像(DTI)及纤维束示踪成像(FT)的可行性.方法:对25名健康志愿者进行膝关节DTI检查,男15例,女10例,年龄21～40岁,平均34.6岁.采用单次激发自旋回波平面成像序列,在工作站进行纤维束示踪三雏模拟成像,计算前交叉韧带的纤维束长度及平均FA值、ADC值,比较不同性别的FA值及ADC值差异,并分析同一操作者在不同时间测量结果的一致性.结果:25名受检者中16例前交叉韧带显示三维纤维束结构,4例显示多束,5例未显示规则的纤维束.所显示的平均纤维长度为(13.79±1.75)～(25.43±3.37)mm..全部受试者前交叉韧带平均FA值为0.457士0.058,平均ADC值为1.419±0.289,无性别差异.比较同一测量者在不同测量时间的FA和ADC测量值,其可信度和组内相关系数均较好.结论:采用3T MR成像系统能成功完成正常前交叉韧带DTI和DTT,并可显示正常前交叉韧带的双束结构.     

扩散峰度与扩散张量成像对比评估兔周围神经急性挤压伤

目的:对比扩散峰度成像(DKI)与扩散张量成像(DTI)评估兔周围神经挤压伤的价值.方法:选取新西兰大白兔27只,于右后肢建立坐骨神经损伤与修复模型,左后肢为假手术侧.分别于术前、1、3天、1、2、4、6、8周行DTI及DKI扫描,测量各时间点定量参数,并于各时间点随机取2只兔子行电镜检查.结果:DKI参数中平均峰度(MK)值在损伤后第1天明显下降并在较低水平波动,自第2～8周逐渐上升,损伤侧与假手术侧MK值于2～8周差异均有统计学意义(P<0.05);损伤后1天各向异性分数(FADKI)值明显下降至最低点;3天～8周持续上升,各时间点差异均有统计学意义(P<0.005);径向峰度(RK)值仅在6周时双侧差异有统计学意义(P=0.018);而轴向峰度(AK)值于各时间点均无显著差异(P>0.05).DTI参数中FADTI与FADKI变化趋势一致且各时间点差异均有统计学意义(P<0.001);ADC值仅在第8周差异有统计学意义(P=0.038).结论:DKI可用于周围神经急性挤压伤的评估,但与DTI相比,DKI在评估急性周围神经损伤时可能并不能提供额外价值.     

Whole-brain N-acetylaspartate spectroscopy and diffusion tensor imaging in patients with newly diagnosed gliomas: a preliminary study

BACKGROUND AND PURPOSE: Glial cancer cells can be found well beyond the MR imaging T2 signal-intensity hyperintensity. To quantify the extent of the diffuse microstructural tissue damage possibly due to the presence of these satellite tumor cells, we investigated the relationships between global metabolic and microstructural abnormalities in the normal-appearing brain regions of patients with newly diagnosed glioma. MATERIAL AND METHODS: Ten patients (6 men, 4 women) with radiologically suspected untreated supratentorial glial tumors and 9 healthy controls (5 men, 4 women) were studied with T1- and T2-weighted MR imaging, diffusion-weighted echo-planar MR imaging, and whole-brain N-acetylaspartate (WBNAA) proton MR spectroscopy. The relationship between the WBNAA concentration, the mean diffusivity (MD), and fractional anisotropy (FA) values in a large contralateral normal-appearing white matter (NAWM) brain region was investigated with the Spearman rank correlation test. RESULTS: WBNAA values were significantly lower (P < .001) in patients (9.7 +/- 1.7 mmol/L) than controls (13.1 +/- 1.1 mmol/L). MD values were higher (P = .0001) in patients (0.95 +/- 0.07 mm(2)s(-1)) than in controls (0.61 +/- 0.04 mm(2)s(-1)). FA values did not differ between patients (0.42 +/- 0.08) and controls (0.43 +/- 0.041). A strong inverse correlation between WBNAA and MD (r = -0.88, P = .0008) was found in the patients but not in controls (r = 0.012, P = .975). CONCLUSION: The correlation between the WBNAA and MD in the contralateral NAWM suggests that the microstructural damage possibly related to the presence of infiltrative tumor cells contributes to WBNAA decline in these patients.     

Effect of cerebral spinal fluid suppression for diffusional kurtosis imaging

Purpose:

To evaluate the cerebral spinal fluid (CSF) partial volume effect on diffusional kurtosis imaging (DKI) metrics in white matter and cortical gray matter.

Materials and Methods:

Four healthy volunteers participated in this study. Standard DKI and fluid‐attenuated inversion recovery (FLAIR) DKI experiments were performed using a twice‐refocused‐spin‐echo diffusion sequence. The conventional diffusion tensor imaging (DTI) metrics of fractional anisotropy (FA), mean, axial, and radial diffusivity (MD, D_‖, D_?) together with DKI metrics of mean, axial, and radial kurtosis (MK, K_‖, K_?), were measured and compared. Single image slices located above the lateral ventricles, with similar anatomical features for each subject, were selected to minimize the effect of CSF from the ventricles.

Results:

In white matter, differences of less than 10% were observed between diffusion metrics measured with standard DKI and FLAIR‐DKI sequences, suggesting minimal CSF contamination. For gray matter, conventional DTI metrics differed by 19% to 52%, reflecting significant CSF partial volume effects. Kurtosis metrics, however, changed by 11% or less, indicating greater robustness with respect to CSF contamination.

Conclusion:

Kurtosis metrics are less sensitive to CSF partial voluming in cortical gray matter than conventional diffusion metrics. The kurtosis metrics may then be more specific indicators of changes in tissue microstructure, provided the effect sizes for the changes are comparable. J. Magn. Reson. Imaging 2013;37:365–371. © 2012 Wiley Periodicals, Inc.

     

Estimation of the orientation distribution function from diffusional kurtosis imaging

The Orientation Distribution Function (ODF) is used to describe the directionality of multimodal diffusion in regions with complex fiber architecture present in brain and other biological tissues. In this study, an approximation for the ODF of water diffusion from diffusional kurtosis imaging (DKI) is presented. DKI requires only a relatively limited number of diffusion measurements and, for the brain, b values no higher than 2500 s/mm². The DKI‐based ODF approximation is decomposed into two components representing the Gaussian and non‐Gaussian (NG) diffusion contributions, respectively. Simulations of multiple fiber configurations show that both the total and the NG‐ODF are able to resolve the orientations of the component fibers, with the NG‐ODF being the most sensitive to profiling the fibers' directions. Orientation maps obtained for in vivo brain imaging data demonstrate multiple fiber components in brain regions with complex anatomy. The results appear to be in agreement with known white matter architecture. Magn Reson Med 60:774–781, 2008. © 2008 Wiley‐Liss, Inc.     

DTI常用扫描序列原理及比较

磁共振弥散张量成像技术是利用水分子的弥散各向异性进行成像,可用于脑白质纤维研究,常用扫描技术包括单次激发平面回波成像(EPI),线阵扫描弥散成像,导航自旋回波弥散加权成像(LSDI),半傅立叶探测单发射快速自旋回波成像等。每种成像技术各有其优缺点,EPI扫描时间短,图像信噪比高,但存在化学位移伪影、磁敏感性伪影、几何变形;LSDI精确度高,几乎无伪影及变形,但扫描时间过长;导航自旋回波弥散加权成像运动伪影少,但扫描时间长;半傅立叶探测单发射快速自旋回波成像扫描时间短,但图像模糊。综合比较,单次激发平面回波成像是用于临床研究较适宜的方法。     

正常人颈髓扩散张量成像最佳参数研究

目的：比较不同 b 值、不同数量扩散梯度方向（NDGDs）3．0T 磁共振（MRI）扩散张量成像（DTI）对正常人颈髓成像的影响;探讨颈髓最佳 DTI 参数。方法：随机选取健康志愿者20例,进行颈髓矢状面 DTI 扫描,选用 b 值分别为0、200、400、600、800、1000 s/mm2,NDGDs 选择6、12、20。分别在不同 b 值、不同 NDGDs 条件下,分析图像质量以及颈髓各向异性（FA）值、表观扩散系数（ADC）值。结果：当 NDGDs 不变（20）,随 b 值增加图像信噪比及质量指数递减（F ＝28．694、30．272,P ＜0．05）,且不同 b 值条件下 FA、ADC 值无组间差异性（F ＝0．495、0．359,P ＞0．05）。当 b 值不变（600 s/mm2）,随 NDGDs 增加图像质量评分递增（F ＝11．927,P ＜0．05）,不同 NDGDs 条件下 FA、ADC 值无组间差异性（F ＝0．08、0．583,P ＞0．05）,但 NDGDs 为20与6、12分别两两比较,FA 值之间差异有统计学意义（P ＜0．05）。结论：使用西门子3．0T 磁共振 DTI 技术,选取 b 值为600 s/mm2,NDGDs 为20的条件下,得到最佳的颈髓 DTI 图像。     

Microstructural changes in patients with progressive supranuclear palsy: A diffusion tensor imaging study

Purpose:

To determine whether progressive supranuclear palsy (PSP) is associated with specific diffusion tensor imaging (DTI) patterns of diffusivity, anisotropy, and coherence in functionally relevant brain areas.

Materials and Methods:

In all, 17 PSP patients and 17 controls were scanned using a 3 T magnetic resonance imaging (MRI) scanner. Patients were assessed in the off‐medication condition using the Hoehn and Yahr staging and the United Parkinson's Disease Rating Scale, motor subscale (UPDRS‐III). Diffusion information were analyzed in relation to disease severity and subtypes.

Results:

Numerous changes in diffusion properties were identified in the subcortical areas. In the midbrain, fractional anisotropy (FA) decreased and MD (mean diffusivity) increased with disease progression. UPDRS‐III scores correlated positively with both FA in the caudate and MD in the pons. DTI analysis of disease subtypes demonstrated significant differences between PSP‐Parkinsonism and Steele‐Richardson‐Olszewski syndrome in axial diffusivity values in the putamen and globus pallidus, as well as in intervoxel diffusion coherence values in the middle cerebellar peduncle.

Conclusion:

Our findings, cautiously interpreted, demonstrate the advantage of using a functional imaging technique to aid in the specificity of defining more precisely the pathological processes taking place in white and gray matter regions in PSP. J. Magn. Reson. Imaging 2010;32:69–75. © 2010 Wiley‐Liss, Inc.