MR扩散张量成像对脑肿瘤的初步应用研究

目的 :评价MR扩散张量成像在脑肿瘤中的应用价值。方法 :搜集经手术及病理证实的脑膜瘤和星形细胞瘤病例共 3 3例 ,行常规MRI、扩散张量成像 (DTI)检查。构建各向异性分数 (FA)图 ,并测量肿瘤及周围白质的FA值。结果 :正常白质纤维在FA图上表现为高信号。在肿瘤存在时 ,周围白质纤维可表现为受推压移位或浸润破坏 ,破坏后FA值降低 ,表现为低信号。这些表现在常规MRI上均未清楚显示。结论 :DTI可清楚显示肿瘤与周围白质纤维的解剖关系 ,指导临床制订手术方案。     

Comparison of the diagnostic performances of diffusion parameters in diffusion weighted imaging and diffusion tensor imaging of breast lesions

Purpose

To evaluate the diagnostic efficiency of the diffusion parameters measured by conventional diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) for discrimination of malignant breast lesions from benign lesions and the normal breast.

Materials and methods

The study included 52 women with 55 breast lesions (30 malignant, 25 benign). DTI and DWI were performed complementary to dynamic contrast MRI at 3T. Apparent diffusion coefficient (ADC) of DWI, mean diffusivity (MD) and fractional anisotropy (FA) values of DTI were measured for lesions and contralateral breast parenchyma in each patient. We used b factors of 0, 50, 850, 1000 and 1500 s/mm² for DWI and b 0 and 1000 s/mm² for DTI. ADC, MD and FA values were compared between malignant and benign lesions, and the normal parenchyma by univariate and multivariate analyses.

Results

Diffusion parameters showed no difference according to menopausal status in the normal breast. ADC and MD values of the malignant lesions were significantly lower than benign lesions and normal parenchyma (p = 0.001). The FA showed no statistical significance. With the cut-off values of ≤1.23 × 10⁻³ mm²/s (b 0–1000 s/mm²) and ≤1.12 × 10⁻³ mm²/s (b 0–1500 s/mm²), ADC showed 92.85% and 96.15% sensitivity; 72.22% and 73.52% PPV, respectively. With a cut-off value of ≤1.27 × 10⁻³ mm²/s (b 1000 s/mm²), MD was 100% sensitive with a PPV of 65.90%. Comparing the diagnostic performance of the parameters in DTI with DWI, we obtained similar efficiency of ADC with b values of 0,1000 and 0,1500 s/mm² and MD with a b value of 0, 1000 s/mm² (AUC = 0.82 ± 0.07).

Conclusion

ADC of DWI and MD of DTI values provide significant discriminative factors for benign and malignant breast lesions. FA measurement was not discriminative. Supported with clinical and dynamic contrast MRI findings, DWI and DTI findings provide significant contribution to the final radiologic decision.     

Characterization of white matter fiber bundles with T relaxometry and diffusion tensor imaging

In this study, diffusion tensor imaging (DTI) and T multiecho relaxometry were combined in 30 healthy subjects at 3T, with the aim of characterizing the spatial distribution of relaxation rates in white matter (WM). Region of interest (ROI) analysis was performed in 23 different fiber tracts automatically defined in standard space. Spearman rank analysis was performed on regional values of T, fractional anisotropy (FA), and radial diffusivity (RD). A strong relationship was observed between the location and direction of fiber bundles and relaxation rates, and adjacent fiber bundles with similar orientation showed very different relaxation rates. Moreover, while relaxation rates varied largely between different fiber tracts, variation of the same parameter within the same anatomical fiber bundle across individuals was remarkably limited. The rich variability of relaxation rates in WM and their complex relationship with DTI data suggested that the two techniques might be sensitive to complementary characteristics of myelin structure. This has tremendous potential to allow for a more detailed understanding of brain development and pathology, in particular in the context of age‐related cognitive decline. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Apparent diffusion coefficient and Magnetic resonance spectroscopy in grading of malignant brain neoplasms

Aim

This work aims to study the role of combined apparent diffusion coefficient (ADC) and Magnetic resonance spectroscopy (MRS) in grading malignant brain neoplasms.

Methods

A prospective study included 40 patients who were evaluated by standard contrast enhanced MRI, diffusion weighted imaging and multivoxel spectroscopy.

Results

Statistically significant difference was found between tumoral ADC values in low grade versus high grade tumors and metastasis and also between the peritumoral ADC values in metastasis versus low and high grade tumors. Statistically significant difference is noticed between tumoral Cho/Cr ratio values in low grade versus high grade tumors and metastasis, and also peritumoral Cho/Cr ratio values in low grade and metastasis versus high grade tumors. Statistically significant difference between tumoral Cho/NAA ratio in low grade versus high grade tumors and metastasis and lastly between peritumoral Cho/NAA ratio in low grade and metastasis versus high grade tumors was found. Lipid and lactate peaks were found frequently in high grade tumors and metastasis.

Conclusion

The combination of calculated ADC values and MR spectroscopy is useful in grading of malignant brain tumors and were more useful together than each on its own.     

Replicability of diffusion tensor imaging measurements of fractional anisotropy and trace in brain

PURPOSE: To evaluate within-scanner and between-scanner reliability of fractional anisotropy (FA) and trace (sum of the diagonal elements of the diffusion tensor) as measured by diffusion tensor imaging (DTI). MATERIALS AND METHODS: Ten young healthy adults were scanned on three separate days, on two different systems made by the same manufacturer. One scan was acquired at one site, and two scans were acquired on two different occasions on another scanner at another site. Three levels of analysis were used to compare the DTI metrics: 1) a voxel-by-voxel analysis of all supratentorial brain (gray matter + white matter + cerebrospinal fluid) and of supratentorial white matter; 2) a slice-by-slice analysis of supratentorial white matter; and 3) a single-region analysis of the corpus callosum. RESULTS: The voxel-by-voxel analysis of all supratentorial brain found that FA and trace measures and correlations were equivalently and significantly higher within than across scanners. For supratentorial white matter, FA was similar within and across scanners, whereas trace demonstrated across-scanner bias. A similar pattern was observed for the slice-by-slice comparison. For the single-region analysis of the corpus callosum, within-scanner FA and trace measures were highly reproducible for FA (CV = 1.9%) and trace (CV = 2.6%), but both DTI measures showed a systematic mean bias across scanners (CV = 4.5% for FA and CV = 7.5% for trace). CONCLUSION: These estimates of measurement variation and scanner bias can be used to predict effect sizes for longitudinal and multisite studies using diffusion tensor imaging.     

扩散张量成像在脑环形强化病变中的鉴别诊断价值

目的评价 MR 扩散张量成像(DTI)在环形强化病变鉴别诊断中的应用价值。方法搜集经病理或临床证实的脑脓肿9例、胶质母细胞瘤12例、单发转移瘤10例,行常规 MR 平扫、增强扫描及 DTI 检查。构建表观扩散系数(ADC)图和各向异性分数(FA)图,并测量病灶中心及周围水肿区的 ADC、FA 值。结果脓肿腔 DTI 表现为高信号,水肿区呈等或低信号;胶质母细胞瘤和转移瘤中心坏死区呈低信号,水肿区呈等信号或稍低信号。在 ADC 图上,脓肿呈低信号,平均 ADC 值为(0.66±0.07)×10~(-3)mm~2/s,水肿区呈高信号;胶质母细胞瘤和转移瘤均呈高信号,平均 ADC 分别为(2.50±0.11)×10~(-3)mm~2/s、(2.37±0.52)×10~(-3)mm~2/s,其周围水肿区亦呈高信号。脓肿与胶质母细胞瘤、转移瘤坏死区 ADC 值差异有统计学意义(F=108.80,P<0.05)。在 FA 图上,病灶坏死区与水肿均表现为低信号,脓肿与胶质母细胞瘤、转移瘤坏死区 FA 值分别为0.15±0.04、0.07±0.01、0.06±0.01,差异有统计学意义(F=34.52,P=0.000);水肿区3组间 FA 值分别为0.15±0.01、0.20±0.05、0.13±0.04,差异有统计学意义(F=8.82,P=0.001)。结论在 DTI 上,脓肿表现为较特异的高信号,ADC 值较低,有助于和囊变、坏死性肿瘤鉴别。     

白血病脑实质浸润的弥散张量成像应用研究

目的探讨1．5T磁共振弥散张量成像（diffusiontensorimaging,DTI）,部分各向异性（fractionalanisotropy,FA）和表观扩散系数（apparentdiffusioncoefficient,ADC）及弥散张量纤维束成像（diffusiontensortractography,DTT）在成人白血病脑实质浸润的应用价值。方法回顾性分析经临床证实的8例白血病脑实质浸润病例DTI之ADC、FA参数图,分别测量病变、水肿及健侧相应部位FA值和ADC值;观察各例在DTT图的变化。结果白血病脑实质浸润的肿瘤实质部分FA值8例全部较健侧降低,ADC值5例减低,3例增高;周围水肿区FA值全部降低,ADC值全部增高;脑白质纤维束DTT显示有中断、移位、浸润。结论DTI对脑侵犯神经纤维束损伤具有独特诊断价值;DTI的参数变化能够量化神经纤维受压后微细结构的变化,DTT图像重建能直观显示脑白质纤维束的完整性及损伤程度,DTI联合DTT可更加准确地评估白血病脑侵犯的损害程度。     

磁共振弥散张量成像在脑肿瘤放射治疗中的应用

弥散张量成像（diffusion tensor imaging，DTI）利用水分子弥散运动描述大脑空间结构，获得脑肿瘤的浸润破坏情况，使得疾病的诊断方式实现从宏观至微观、从形态学上升至形态与代谢并重，为脑肿瘤的诊疗研究带来新的机遇。在这篇综述中，概述了DTI技术的理论基础及目前的局限性，并对其在脑肿瘤放射治疗及其疗效预判中的应用价值进行全面讨论。DTI为脑肿瘤的放疗方案制定提供重要的影像学信息。     

Diffusion tensor tractography as a supplementary tool to conventional MRI for evaluating patients with myelopathy

Purpose

The aim of this study was to assess the clinical utility of DTI including apparent diffusion coefficient (ADC), fractional anisotropy (FA), in patients with symptoms of spinal cord myelopathy.

Patients and methods

Fifteen subjects with clinical symptoms of acute (n = 3) or slowly progressive (n = 12) spinal cord myelopathy and 11 healthy volunteers were prospectively selected. They all underwent magnetic resonance imaging of the spine at 3.0 T machine. In addition to conventional MRI, DTI was performed; maps of the apparent diffusion coefficient and of fractional anisotropy were reconstructed. Diffusion tensor tractography was used to visualize the morphological features of normal and impaired white matter at the level of the pathological lesions in the spinal cord. The patients were divided into two groups according to the signal intensity on T2WI (group A with no change in signal intensity and group B with high signal intensity).

Results

There were no statistically significant differences in the apparent diffusion coefficient and fractional anisotropy values between the different spinal cord segments of the normal subjects. All of the patients in group B had increased apparent diffusion coefficient values and decreased fractional anisotropy values at the lesion level compared to the normal controls. However, there were no statistically significant diffusion index differences between group A patients and the normal controls.

Conclusion

Diffusion tensor imaging is a reliable method for the evaluation of the diffusion properties of normal and compressed spinal cords. Furthermore, this technique can be used as an important supplementary tool to conventional MRI for the quantification of fiber damage in spinal cord compression, thus has the potential to be of great utility for treatment planning and follow up.     

Glucocorticoid treatment of brain tumor patients: changes of apparent diffusion coefficient values measured by MR diffusion imaging

Glucocorticoids (GCC) generally are administered to patients with brain tumors to relieve neurological symptoms by decreasing the water content in a peritumoral zone of edema. We hypothesized that diffusion imaging and apparent diffusion coefficient (ADC) values could detect subtle changes of water content in brain tumors and in peritumoral edema after GCC therapy. The study consisted of 13 patients with intra-axial brain tumor, and ADC was measured in the tumor, within peritumoral edema, and in normal white matter remote from the tumor before and after GCC therapy. ADC also was measured in normal white matter in four control patients with no intracranial disease who were treated with GCC for other indications. Conventional MR images showed no visually evident interval change in tumor size or the extent of peritumoral edema in any subject after GCC therapy, which nonetheless resulted in a decrease in mean ADC of 7.0% in tumors (P<0.05), 1.8% in peritumoral edema (P>0.05, not significant) and 5.8% in normal white matter (P<0.05). In patients with no intracranial disease, GCC therapy decreased mean ADC in white matter by 5.4% (P<0.05). ADC measurement can demonstrate subtle changes in the brain after GCC therapy that cannot be observed by conventional MR imaging. Measurement of ADC proved to be a sensitive means of assessing the effect of GCC therapy, even in the absence of visually discernible changes in conventional MR images.     

Clinical applications of diffusion tensor imaging

Directionally-ordered cellular structures that impede water motion, such as cell membranes and myelin, result in water mobility that is also directionally-dependent. Diffusion tensor imaging characterizes this directional nature of water motion and thereby provides structural information that cannot be obtained by standard anatomic imaging. Quantitative apparent diffusion coefficients and fractional anisotropy have emerged from being primarily research tools to methods enabling valuable clinical applications. This review describes the clinical utility of diffusion tensor imaging, including the basic principles of the technique, acquisition, data analysis, and the major clinical applications.     

Prediction of motor outcome in ischemic stroke involving the pyramidal tract using diffusion tensor imaging

Background and purpose

Early evaluation of the pyramidal tract is a prerequisite in patients with ischemic stroke in order to decide the optimal treatment or to assess appropriate rehabilitation. The aim of this study was to predict motor outcome using quantitative and qualitative diffusion tensor parameters and their correlations with severity of stroke as defined by the National Institutes of Health Stroke Scale (NIHSS).

Materials and methods

Twenty-one patients presenting with ischemic stroke were studied with DTI. All patients had diffusion measurements such as FA values of the affected and unaffected regions and the FA ratio between them. Color FA maps of the pyramidal tract were constructed and the degree of infarctions was classified into groups according to the involvements of the pyramidal tracts. The motor performance of the upper and lower extremities was assessed using the NIHSS on the day of patients’ admission and discharge. The motor outcomes were correlated with the FA values of the pyramidal tract.

Results

The FA values of the affected pyramidal tracts were significantly lower as compared with the unaffected side (p-value <0.01). The reduction in the FA values of the affected side was significantly correlated (r = 0.41 and p-value <0.001) with the degree of pyramidal tract involvements that were significantly correlated with the motor outcome on patients’ discharge day.

Conclusions

Quantitative (FA values) and qualitative (the diffusion tensor tractography) diffusion parameters have potential to predict motor outcome in patients with ischemic stroke.     

颅脑磁共振弥散张量成像应用进展

磁共振弥散张量成像技术是利用水分子的弥散运动各向异性进行成像,是目前唯一反映人体活体组织空间组成信息及病理状态下各组织成分之间水分子交换功能状况的检查方法,可以从细胞及分子水平来研究疾病状况。本文回顾DTI的原理和潜在的临床应用,如脑缺血性疾病、脑发育、脑肿瘤、外伤性脑损伤和癫痫、多发性硬化、代谢性疾病等。     

扩散张量成像在颅内肿瘤周围白质区的应用

目的：评价MR扩散张量成像技术在不同级别胶质瘤、脑膜瘤及转移瘤周围正常脑白质区的应用价值。方法：对43例颅内肿瘤患者行常规MRI及扩散张量成像检查,其中高级别胶质瘤12例,低级别胶质瘤10例,脑膜瘤12例、转移瘤9例。测量瘤周正常脑白质的FA值及对侧相应解剖部位正常脑白质的FA值,行组间统计学分析。结果：高级别胶质瘤瘤周正常脑白质FA值低于对侧正常脑白质FA值,差异有统计学意义（P〈0.05）;低级别胶质瘤、脑膜瘤及转移瘤FA值的差异无统计学意义。高级别胶质瘤瘤周正常脑白质FA值与低级别胶质瘤、脑膜瘤、转移瘤瘤周正常脑白质之间差异有统计学意义,后三者之间的差异比较无统计学意义。结论：MR扩散张量成像技术有助于颅内肿瘤的定性诊断及推测肿瘤细胞的浸润范围。     

The effect of concomitant gradient fields on diffusion tensor imaging

Concomitant gradient fields are transverse magnetic field components that are necessarily present to satisfy Maxwell's equations when magnetic field gradients are utilized in magnetic resonance imaging. They can have deleterious effects that are more prominent at lower static fields and/or higher gradient strengths. In diffusion tensor imaging schemes that employ large gradients that are not symmetric about a refocusing radiofrequency pulse (unlike Stejskal–Tanner, which is symmetric), concomitant fields may cause phase accrual that could corrupt the diffusion measurement. Theory predicting the error from this dephasing is described and experimentally validated for both Reese twice‐refocused and split gradient single spin‐echo diffusion gradient schemes. Bias in apparent diffusion coefficient values was experimentally found to worsen with distance from isocenter and with increasing duration of gradient asymmetry in both a phantom and in the brain. The amount of error from concomitant gradient fields depends on many variables, including the diffusion gradient pattern, pulse sequence timing, maximum effective gradient amplitude, static magnetic field strength, voxel size, slice distance from isocenter, and partial Fourier fraction. A prospective correction scheme that can reduce concomitant gradient errors is proposed and verified for diffusion imaging. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

扩散张量成像技术及各指标的初步应用与评价

目的　探讨正常脑组织及脑肿瘤的扩散张量 (DTI)成像技术及各种评价指标的变化规律及临床应用价值。方法　 10例正常志愿者和 19例脑肿瘤患者进行常规MRI和DTI扫描并重建参数图 ,测量正常志愿者脑组织各主要白质束和神经核团的部分各向异性值 (FA)、各向同性值 (Iso)、衰减指数值 (ExAt)和容积比异向性值 (VrA) ,肿瘤患者测量受累白质束及对侧正常白质束的上述各参数 ,取值并进行统计学分析 ,包括配对t检验 ,相关性分析及方差分析。结果　DTI图上 ,正常脑组织FA、Iso、ExAt、VrA值按组织结构呈规律分布 ;脑肿瘤病例则清楚显示肿瘤对周围结构的破坏、占位效应及水肿所致的改变。各指标中 ,患、健侧间差异有显著性意义 (FA组 :t=9 12 5 ,P <0 0 0 1;Iso组 :t= 5 5 37,P <0 0 0 1;ExAt组 :t=7 16 8,P <0 0 0 1;Vra组 :t=7 12 8,P <0 0 0 1) ,FA与VrA的患侧测量值之间相关性较高 (r=0 92 2 ,P <0 0 0 1) ,其他各指标间无显著相关性 ,单因素方差分析 4种指标变化幅度 [|(患侧 -健侧 ) |/健侧 ) ]的差异具有显著性意义 (F =2 0 4 30 ,P <0 0 0 1) ,FisherLSD检验显示Vra的变化幅度与另 3种指标间差异有显著性意义 (P <0 0 0 1)。另外 ,FA与Iso比较 ,P =0 0 0 6 ,其他无显著性意义。结论　DTI能清楚     

Role of standardized and study‐specific human brain diffusion tensor templates in inter‐subject spatial normalization

Purpose:

To investigate the effect of standardized and study‐specific human brain diffusion tensor templates on the accuracy of spatial normalization, without ignoring the important roles of data quality and registration algorithm effectiveness.

Materials and Methods:

Two groups of diffusion tensor imaging (DTI) datasets, with and without visible artifacts, were normalized to two standardized diffusion tensor templates (IIT2, ICBM81) as well as study‐specific templates, using three registration approaches. The accuracy of inter‐subject spatial normalization was compared across templates, using the most effective registration technique for each template and group of data.

Results:

It was demonstrated that, for DTI data with visible artifacts, the study‐specific template resulted in significantly higher spatial normalization accuracy than standardized templates. However, for data without visible artifacts, the study‐specific template and the standardized template of higher quality (IIT2) resulted in similar normalization accuracy.

Conclusion:

For DTI data with visible artifacts, a carefully constructed study‐specific template may achieve higher normalization accuracy than that of standardized templates. However, as DTI data quality improves, a high‐quality standardized template may be more advantageous than a study‐specific template, because in addition to high normalization accuracy, it provides a standard reference across studies, as well as automated localization/segmentation when accompanied by anatomical labels. J. Magn. Reson. Imaging 2013;37:372–381. © 2012 Wiley Periodicals, Inc.