Comparisons of regional white matter diffusion in healthy neonates and adults performed with a 3.0-T head-only MR imaging unit

PURPOSE: To evaluate the normal brains of adults and neonates for regional and age-related differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA). MATERIALS AND METHODS: Eight healthy adults and 20 healthy neonates were examined with a 3.0-T head-only magnetic resonance (MR) imaging unit by using a single-shot diffusion-tensor sequence. Trace ADC maps, FA maps, directional maps of the putative directions of white matter (WM) tracts, and fiber-tracking maps were obtained. Regions of interest-eight in WM and one in gray matter (GM)-were predefined for the ADC and FA measurements. The Student t test was used to compare FA and ADC between adults and neonates, whereas the Tukey multiple-comparison test was used to compare FA and ADC in different brain regions in the adult and neonate groups. RESULTS: A global elevation in ADC (P <.001) in both GM and WM and a reduction in FA (P <.001) in WM were observed in neonates as compared with these values in adults. In addition, significant regional variations in FA and ADC were observed in both groups. Regional variations in FA and ADC were less remarkable in adults, whereas neonates had consistently higher FA values and lower ADC values in the central WM as compared with these values in the peripheral WM. Fiber tracking revealed only major WM tracts in the neonates but fibers extending to the peripheral WM in the adults. CONCLUSION: There were regional differences in FA and ADC values in the neonates; such variations were less remarkable in the adults.     

Axial asymmetry of water diffusion in brain white matter.

The diffusion tensor (DT) is a three-dimensional (3D) model of diffusivity in biological tissues. In white matter (WM), the major eigenvector, which is the direction of greatest diffusivity, is generally assumed to align with the direction of the fiber bundles. The distribution of major eigenvectors in WM has been investigated using color-based maps and WM tractography (WMT). However, anatomical patterns in the medium and minor eigenvector directions have largely been ignored in DTI studies of the human brain. In this study, the patterns of medium and minor eigenvectors in the brain were investigated using both color-based maps and WMT. Specific WM structures, such as the corona radiata, internal and external capsules, sagittal stratum, cingulum, and superior longitudinal fasciculus, demonstrated coherent patterns in the medium and minor eigenvector directions. These patterns were consistent across subjects. The orthogonal or axial diffusion asymmetry may be explained by merging, diverging, or crossing fiber geometries. The effects of orthogonal diffusion asymmetry on WMT were also investigated. This study shows that WM axial asymmetry causes anisotropic dispersion patterns in the estimated tract trajectories. The medium and minor eigenvector patterns may be useful for elucidating the local dispersion distributions of WM tracts.     

Quantitative analysis of diffusion tensor orientation: theoretical framework.

Diffusion-tensor MRI (DT-MRI) yields information about the magnitude, anisotropy, and orientation of water diffusion of brain tissues. Although white matter tractography and eigenvector color maps provide visually appealing displays of white matter tract organization, they do not easily lend themselves to quantitative and statistical analysis. In this study, a set of visual and quantitative tools for the investigation of tensor orientations in the human brain was developed. Visual tools included rose diagrams, which are spherical coordinate histograms of the major eigenvector directions, and 3D scatterplots of the major eigenvector angles. A scatter matrix of major eigenvector directions was used to describe the distribution of major eigenvectors in a defined anatomic region. A measure of eigenvector dispersion was developed to describe the degree of eigenvector coherence in the selected region. These tools were used to evaluate directional organization and the interhemispheric symmetry of DT-MRI data in five healthy human brains and two patients with infiltrative diseases of the white matter tracts. In normal anatomical white matter tracts, a high degree of directional coherence and interhemispheric symmetry was observed. The infiltrative diseases appeared to alter the eigenvector properties of affected white matter tracts, showing decreased eigenvector coherence and interhemispheric symmetry. This novel approach distills the rich, 3D information available from the diffusion tensor into a form that lends itself to quantitative analysis and statistical hypothesis testing.     

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。     

Diffusion tensor imaging of tract involvement in children with pontine tumors

BACKGROUND AND PURPOSE: Conventional MR imaging permits subcategorization of brain stem tumors by location and focality; however, assessment of white matter tract involvement by tumor is limited. Diffusion tensor imaging (DTI) is a promising method for visualizing white matter tract tumor involvement supratentorially. We investigated the ability of DTI to visualize and quantify white matter tract involvement in pontine tumors. METHODS AND MATERIALS: DTI data (echo-planar, 1.5T) were retrospectively analyzed in 7 patients with pontine tumors (6 diffuse, 1 focal), 4 patient controls, and 5 normal volunteers. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were calculated from the diffusion tensor in 6 regions of interest: bilateral corticospinal tracts, transverse pontine fibers, and medial lemnisci. Relationships between FA and ADC values and results of the neurologic examinations were evaluated. RESULTS: The corticospinal tracts and transverse pontine fibers were affected more often than the medial lemnisci. The DTI parameters (FA and ADC) were significantly altered in all tracts of patients with pontine tumors (P < .05), compared with those values in the control groups. A marginally significant (P = .057) association was seen between the severity of cranial nerve deficit and decreased FA. CONCLUSION: DTI provided superior visualization and quantification of tumor involvement in motor, sensory, and transverse pontine tracts, compared with information provided by conventional MR imaging. Thus, DTI may be a sensitive measure of tract invasion. Further prospective studies are warranted to assess the ability of DTI to delineate tumor focality and improve risk stratification in children with pontine tumors.     

Multiple sclerosis: diffusion tensor MR imaging for evaluation of normal-appearing white matter

PURPOSE: To determine whether the normal-appearing white matter (NAWM) regions surrounding and remote from multiple sclerosis (MS) plaques have abnormal diffusional anisotropy and to compare anisotropy maps with apparent diffusion coefficient (ADC) maps for sensitivity in the detection of white matter (WM) abnormalities. MATERIALS AND METHODS: Conventional and diffusion tensor magnetic resonance (MR) imaging examinations were performed in 26 patients with MS and in 26 age-matched control subjects. Fractional anisotropy (FA) and ADC maps were generated and coregistered with T2-weighted MR images. Uniform regions of interest were placed on plaques, periplaque white matter (PWM) regions, NAWM regions in the contralateral side of the brain, and WM regions in control subjects to obtain FA and ADC values, which were compared across the WM regions. RESULTS: The mean FA was 0.280 for plaques, 0.383 for PWM, 0.493 for NAWM, and 0.537 for control subject WM. The mean ADC was 1.025 x 10(-3) mm(2)/sec for plaques, 0.786 x 10(-3) mm(2)/sec for PWM, 0.739 x 10(-3) mm(2)/sec for NAWM, and 0.726 x 10(-3) mm(2)/sec for control subject WM. Significant differences in anisotropy and ADC values were observed among all WM regions (P <.001 for all comparisons, except ADC in NAWM vs control subject WM [P =.018]). CONCLUSION: The anisotropy and ADC values were abnormal in all WM regions in the patients with MS and were worse in the periplaque regions than in the distant regions. Diffusion tensor MR imaging may be more accurate than T2-weighted MR imaging for assessment of disease burden.     

Potential of diffusion tensor MRI in the assessment of periventricular leukomalacia

AIM: To investigate magnetic resonance (MR) diffusion tensor imaging (DTI) and fibre tractography in the assessment of altered major white matter (WM) fibre tracts in periventricular leukomalacia (PVL). MATERIALS AND METHODS: Twelve children (male:female = 7:5, age range 3-10 years; mean age = 6.5 years) who had suffered PVL were included in this study. Meanwhile, Twelve age-matched normal controls (male:female = 6:6, age range 4-12 years; mean age = 7.3 years) with normal MRI findings and no neurological abnormalities were recruited for comparison. DTI was performed with 15 different diffusion gradient directions and DTI colour maps were created from fractional anisotropy (FA) values and the three vector elements. To identify alteration of WM fibre tracts in patient of PVL quantitatively, FA values on diffusion tensor colour maps were compared between the patients and controls. Quantitative analysis was performed using the regions of interest (ROI) method settled on the central part of all identifiable WM fibres, including the corticospinal tract (CST) in the brainstem, middle cerebellar peduncle (MCP), medial lemniscus (ML), anterior/posterior limb of internal capsule (ICAL/ICPL), arcuate fasciculus (AF), posterior thalamic radiation (PTR), genu of corpus callosum (GCC), splenium of corpus callosum (SCC), corona radiata (CR), cingulum (CG), and superior longitudinal fasciculus (SLF). The averaged FA value of each WM fibre was measured and summarized as the mean +/- standard deviation (SD). All data were analysed by paired Student's t-test. A p-value of less than 0.05 was considered to indicate statistical significance. RESULTS: Visual investigation of WM fibre tracts showed that the ICAL, brainstem CST, ML, MCP, and external capsule (EC) was similar in controls and subjects. However, the ICPL, AF, PTR, CR, CG, SLF and corpus callosum, were all attenuated in size. All 12 cases of PVL showed a significant mean FA reduction in the ICPL, AF, PTR, CR, CG, SLF, SCC, and GCC in comparison with the ipsilateral regions of healthy controls (p<0.05). However, there were no statistically significant differences of the ICAL, ML, MCP, and brainstem CST when analysed using a two-tailed Student's t-test for paired data (p>0.01). CONCLUSION: DTI can provide more information for understanding the pathophysiology of motor disability and associated sensory handicap in PVL.     

Minimum detectable difference of MR diffusion maps in acute ischemic stroke

PURPOSE: To determine the minimum detectable difference (MDD) and investigate variability of region-of-interest (ROI) analysis of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in acute ischemic stroke. MATERIALS AND METHODS: Ten patients with acute stroke (<24 hours) and moderate-to-large infarcts were imaged using a fast diffusion tensor technique. Four observers repeated three trials, during which each of two ROI types (free-hand polygon and ellipse) were drawn in white and gray matter (WM and GM) on FA and ADC maps. Analysis-of-variance techniques examined tissue and ROI type effects as well as inter- and intraobserver variability. F-tests examined the variability differences between ROI types. RESULTS: The MDD for ADC was 0.160 x 10(-3) mm(2) s(-1) in WM and 0.212 x 10(-3) mm(2) s(-1) in GM. The FA MDD was 0.19 in WM and 0.10 in GM. Tissue but not ROI type affected the mean values for both ADC and FA maps. Intraobserver reliability was substantial, while interobserver reliability was poor-to-moderate. No variability differences were found by ROI types. CONCLUSION: The MDD for WM and GM in normal and ischemic tissue were calculated. Inter- and intraobserver variability and tissue type affect ROI analysis of ADC and FA maps.     

3．0T弥散张量成像FA值和ADC值在颅脑恶性星形细胞瘤中的运用

目的：探讨磁共振弥散张量成像FA值和ADC值在颅脑恶性星形细胞瘤中的应用价值。方法：收集经手术及组织病理学证实的恶性星形细胞瘤患者14例,术前行常规MRI平扫、DTI检查、增强扫描及1H-MRS检查,工作站自动生成各向异性指数图（FA图）及表观弥散系数图（ADC图）,定义肿瘤实质区为最高Cho／Cr和Cho／NAA比值、异常强化、T2WI信号异常区;定义瘤体边缘为Cho／Cr和Cho／NAA比值异常、无强化、T2WI信号异常区;定义瘤周水肿区为正常MRS表现、无强化、T2WI信号异常区;定义正常白质区为正常MRS表现、无强化、T2WI信号正常区（肿瘤同侧或对侧）;分别测量上述区域的FA1—4值、ADC1—4值,分析比较上述4个区FA值、ADC值有无统计学差异。结果：肿瘤实质区、瘤体边缘、瘤周水肿区及正常白质区平均FA值为FA1：0．1822±0．0583,FA2：0．2947±0．0786,FA3：0．1769±0．0942,FA4：0．6668±0．0817。肿瘤实质区、瘤体边缘、瘤周水肿区与正常自质区比较差异有高度显著性（P=0．000）,瘤体边缘与肿瘤实质区、瘤周水肿区之间差异有高度显著性（P〈0．005）,肿瘤实质区与瘤周水肿区差异无显著性（P〉0．05）;平均ADC值为ADC1：11．132±4．101,ADC2：11．175±2．983,ADCB：14．939±2．857,ADCA：7．265±0．914（单位10^-3mm^2／s）。瘤体实质部、肿瘤边缘及瘤周水肿区与正常脑白质区ADC值差异有高度显著性（P〈0．005）;瘤体实质部、肿瘤边缘与瘤周水肿区差异有高度显著性（P〈0．005）;而瘤体实质部与肿瘤边缘差异无显著性（P〉0．05）。结论：FA值和ADC值对高级别星形细胞瘤浸润范围的划定有重要价值。     

Effects of chemotherapy on the brain in childhood: diffusion tensor imaging of subtle white matter damage

Introduction

With reducing mortality in children with hematological malignancies, the survivors' quality of life regarding development of chronic neurological disturbances is important. We aimed to determine whether chemotherapy affects white matter (WM).

Methods

Using brain diffusion tensor imaging, we evaluated 17 patients (15 with acute lymphoblastic leukemia, 2 with non-Hodgkin's lymphoma; 9 male, 8 female; age, 1.6–13 years) before and after chemotherapy. We measured the quantitative values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) at the regions of interest (ROIs) such as periventricular WM, corona radiata, posterior limb of the internal capsule, and corpus callosum. We assessed sensorimotor and callosal tracts by tractography.

Results

Reduction in FA and increase in ADC were significant at the ROIs of the left and right anterior periventricular WM and corona radiata and at the tract passing through the genu. A significant reduction in FA with a nonsignificant increase in ADC was seen at the ROI of the genu and at the tracts passing through the body and isthmus.

Conclusion

Chemotherapy in children with hematological malignancies predominantly affects the frontal WM. This finding might indicate a negative effect of chemotherapy on neurological development in children with hematological malignancies.     

Quantitative study of prostate cancer using three dimensional fiber tractography

AIM:To investigate feasibility of a quantitative study of prostate cancer using three dimensional（3D）fiber tractography.METHODS:In this institutional review board approved retrospective study,24 men with biopsy proven prostate cancer underwent prostate magnetic resonance imaging（MRI）with an endorectal coil on a 1.5 T MRI scanner.Single shot echo-planar diffusion weighted images were acquired with b = 0.600 s/mm²,six gradient directions.Open-source available software Track Vis and its Diffusion Toolkit were used to generate diffusion tensor imaging（DTI）map and 3D fiber tracts.Multiple 3D spherical regions of interest were drawn over the areas of tumor and healthy prostatic parenchyma to measure tract density,apparent diffusion coefficient（ADC）and fractional anisotropy（FA）,which were statistically analyzed.RESULTS:DTI tractography showed rich fiber tract anatomy with tract heterogeneity.Mean tumor region and normal parenchymal tract densities were 2.53 and 3.37 respectively（P < 0.001）.In the tumor,mean ADC was 0.0011 × 10^-3 mm²/s vs 0.0014 × 10^-3 mm²/s in the normal parenchyma（P < 0.001）.The FA values for tumor and normal parenchyma were 0.2047 and 0.2259 respectively（P = 0.3819）.CONCLUSION:DTI tractography of the prostate is feasible and depicts congregate fibers within the gland.Tract density may offer new biomarker to distinguish tumor from normal tissue.     

White matter reorganization after surgical resection of brain tumors and vascular malformations

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) and white matter tractography (WMT) are promising techniques for estimating the course, extent, and connectivity patterns of the white matter (WM) structures in the human brain. In this study, DTI and WMT were used to evaluate WM tract reorganization after the surgical resection of brain tumors and vascular malformations. METHODS: Pre- and postoperative DTI data were obtained in 6 patients undergoing surgical resection of brain lesions. WMT using a tensor deflection algorithm was used to reconstruct WM tracts adjacent to the lesions. Reconstructed tracts included corticospinal tracts, the corona radiata, superior longitudinal and inferior fronto-occipital fasciculi, cingulum bundles, and the corpus callosum. RESULTS: WMT revealed a series of tract alteration patterns including deviation, deformation, infiltration, and apparent tract interruption. In general, the organization of WM tracts appeared more similar to normal anatomy after resection, with either disappearance or reduction of the deviation, deformation, or infiltration present preoperatively. In patients whose lesions were associated with corticospinal tract involvement, the WMT reconstructions showed that the tract was preserved during surgery and improved in position and appearance, and this finding correlated with improvement or preservation of motor function as determined by clinical assessment. CONCLUSION: WMT is useful for appreciating the complex relationships between specific WM structures and the anatomic distortions created by brain lesions. Further studies with intraoperative correlation are necessary to confirm these initial findings and to determine WMT utility for presurgical planning and evaluation of surgical treatments.     

大脑胶质瘤弥散张量磁共振成像定量研究

目的:应用弥散张量磁共振成像定量分析大脑胶质瘤的特点。方法:11例经病理证实的大脑胶质瘤患者,行弥散张量磁共振成像检查,在ADC图和FA图上分别测量肿瘤周围水肿区域、肿瘤强化区域、囊变区域、脑脊液及对侧正常大脑白质ADC值和FA值。结果:肿瘤周围水肿区域的ADC值和FA值与肿瘤囊变区域、脑脊液及对侧大脑白质相比较均有显著性差异(P<0.05),而与肿瘤强化区域相比较无显著性差异。肿瘤囊变区域的ADC值及FA值与脑脊液、对侧正常大脑白质相比较有显著性差异(P<0.05);肿瘤囊变区域与肿瘤强化区域相比较,ADC值无显著性差异,FA值却有显著性差异(P<0.05)。肿瘤强化区域的ADC值及FA值与对侧大脑白质相比较具有显著性差异(P<0.05)。高、低级别胶质瘤肿瘤周围水肿区域、肿瘤强化区域、肿瘤囊变区域的ADC值及FA值均无统计学显著差异。结论:磁共振弥散张量成像对定量分析大脑胶质瘤本身及其周围脑组织具有重要价值。     

MRI abnormalities in normal-appearing brain tissue of treated adult PKU patients

PURPOSE: To detect possible subclinical pathological brain changes a study on adult phenylketonuria (PKU) patients by using quantitative MRI methods was performed, since neuropsychological and cognitive deficits in treated patients with PKU have not yet been shown to correlate clearly with the brain lesions identified by conventional MRI. MATERIALS AND METHODS: Eight subjects, four PKU patients with well-documented dietary treatment and four age- and sex-matched adult controls, underwent MRI, including a triple echo sequence and a diffusion tensor imaging sequence. Brain maps of T2 relaxation time (T2), relative proton density (PD), and fractional anisotropy (FA) as well as apparent diffusion coefficient (ADC) were derived for each subject. T2, PD, FA, and ADC were measured in 22 predefined regions of gray matter (GM) and white matter (WM) on the corresponding maps, and compared with those of four age-matched healthy adult controls. RESULTS: In addition to a prolonged T2 value measured in affected WM, as expected, we observed a significant shortening of the T2 relaxation time and reduction of ADC in normal-appearing brain tissue and an increased proton density in both GM and WM of the patients. No differences were observed in FA values between controls and patients. CONCLUSION: Repeatedly reduced T2 relaxation time, ADC, and increased proton density without changes in FA indicate a higher cell-packing density in normal-appearing brain without changes in the directedness of fibers. These structural changes may be related to neuropsychological and cognitive deficits in treated PKU patients.     

Directional correlation characterization and classification of white matter tracts.

To study the architectural characteristics of white matter (WM) tracts, the directional correlation (DC), defined as the inner product of the major eigenvector of adjacent pixels, was used as a quantitative index to investigate directional similarity in WM tracts. A region-growing algorithm was employed to propagate an area from a seed point as a function of the DC threshold (DCt) to critically evaluate the directional properties of WM tracts. As the DCt was increased, more pixels were excluded from the propagated region as their DC fell below the DCt, and neighboring WM tracts could be distinguished as the area decreased. Taking the DC into account, a systematic classification routine for WM tracts was devised and tested on a mouse brain in vivo. The results show that individual WM tracts possess a high degree of directional similarity, and, by careful choice of the DCt value, the proposed classification algorithm can recognize all possible WM tracts in a given data set.     

3.0T磁共振扩散张量成像对高级别脑胶质瘤和脑转移瘤的鉴别诊断价值

目的探讨3.0T磁共振扩散张量成像参数中的各向异性分数(FA)值、表观扩散系数(ADC)值对高级别脑胶质瘤和脑转移瘤的鉴别诊断价值。方法分析经手术病理或临床随访证实15例高级别脑胶质瘤和19例脑转移瘤,术前行常规MRI扫描、增强扫描、DWI及DTI扫描,选取感兴趣区(肿瘤囊变区、肿瘤实质区、肿瘤边缘区、瘤周水肿区、肿瘤周围正常脑实质区),分别测量其ADC值及FA值,比较两种肿瘤不同部位ADC值及FA值的差异,采用t检验。结果高级别脑胶质瘤与脑转移瘤的肿瘤实质区(t=4.09,P=0.001)、肿瘤边缘区(t=3.34,P=0.002)的FA值差异显著(P<0.05)。两种肿瘤周围水肿区(t=4.79,P=0.000)的ADC值差异显著(P<0.05)。结论扩散张量成像可以作为高级别脑胶质瘤和脑转移瘤的鉴别诊断方法。     

Diffusion tensor imaging of the brain: effects of distortion correction with correspondence to numbers of encoding directions

Purpose  The aim of the study was to estimate the effect of distortion correction with correspondence to numbers of encoding directions to acquire diffusion tensor imaging (DTI) of improved quality. Materials and methods  Ten volunteers underwent DTI of the head using echo planar imaging with 6, 13, 27, and 55 encoding directions. Fractional anisotropy (FA) maps and apparent diffusion coefficient (ADC) maps were created before and after distortion correction. Regions of interest were placed in the corpus callosum on each map, and standard deviations of FA and ADC were calculated. FA maps were also evaluated visually by experienced neuroradiologists. Results  Dispersion of standard deviations tended to be reduced after distortion correction, with significant differences found in FA maps with 6 encoding directions, ADC maps with 6 directions, and ADC maps with 13 directions (P < 0.001, P < 0.005, and P < 0.05, respectively). Visual image quality was improved after distortion correction (P < 0.01 for all of the visual comparisons). Conclusion  Distortion correction is effective in providing DTI of enhanced quality, notwithstanding the number of encoding directions. This article was presented at a Japan Radiological Society meeting in 2002     

In vivo DTI evaluation of white matter tracts in rat spinal cord

PURPOSE: To determine whether differences in specific spinal cord white matter (WM) tracts can be detected with in vivo DTI. MATERIALS AND METHODS: In vivo DTI was performed on six rats at the lower thoracic region using a 4.7T magnet. Axial diffusion images were obtained with diffusion gradients applied in six independent directions, with low and high b-values equal to 0 and 692 seconds/mm(2), respectively. Regions of interest (ROIs) were selected corresponding to the major spinal cord tracts, including the dorsal cortical spinal tract (dCST), fasciculus gracilis (FG), rubrospinal tract (RST), vestibulospinal tract (VST), and reticulospinal tract (ReST). RESULTS: ANOVA demonstrated overall differences between tracts for all of the DTI parameters, including fractional anisotropy (FA), trace diffusion (Tr), longitudinal diffusivity (EL = lambda(1)), and transverse diffusivity (ET = (lambda(2) + lambda(3))/2). Similarly to previous ex vivo analyses, the spinal cord tract with the largest and most widely spaced axons (VST) had the largest EL and ET. CONCLUSION: The principal diffusivities appear to reflect axon morphologic differences between the WM tracts that are not as well appreciated with FA and Tr.     

Contribution of diffusion tensor imaging to delineation of gliomas and glioblastomas

PURPOSE: To determine if the diffusion tensor imaging (DTI) parameters fractional anisotropy (FA) and mean diffusivity (MD) can differentiate between accompanying edema and tumor cell infiltration of white matter (WM) beyond the tumor edge as defined from conventional MRI in low- and high-grade gliomas. MATERIALS AND METHODS: We examined 12 patients with high-grade gliomas/glioblastomas and eight patients with low-grade gliomas and compared them to 10 patients with meningiomas, in which no tumor infiltration is expected. The tumor was defined as the enhancing area in glioblastomas and meningiomas and as the area of increased T2-signal in low-grade gliomas. FA and MD were measured in the center of the tumor and in the adjacent WM. The contralateral WM and internal capsule were used as an internal standard. RESULTS: Comparing the WM areas of increased T2-signal adjacent to meningiomas and glioblastomas, we saw a trend (without significance) towards a reduction of FA, but not of MD, in glioblastomas. We found no changes of FA and MD in the WM adjacent to low-grade gliomas (without T2-signal increase) compared to the WM of the contralateral hemisphere. In meningiomas and high-grade gliomas/glioblastomas, a narrow rim of significantly (P < 0.01) increased FA and decreased MD values around the enhancing tumor area was seen, whereas in low-grade gliomas, such a rim could not be defined. There was no contribution of FA or MD to grading of gliomas. CONCLUSION: In glioblastomas, a reduction of FA in the edematous area surrounding the tumor may indicate tumor cell infiltration, but a reliable differentiation between infiltration and vasogenic edema is not yet possible on the basis of DTI. The additional finding of a narrow rim of increased FA and decreased MD at the edge of glioblastomas (as well as in meningiomas) may be caused by com-pressed WM fibers and/or increased vascularity, but does not contribute to exclude peripheral cellular infiltration.     

正常成人大脑白质纤维磁共振弥散张量成像的定量研究

目的:运用弥散张量成像(DTI)定量研究正常成人脑白质不同解剖部位的各向异性特点.方法:对60名正常成人按年龄分成四组,均行DTI检查,分析其表面弥散系数(ADC)图及各向异性分数(FA)图的特点,并对不同解剖部位的脑白质进行ADC值及FA值的定量分析,通过统计学分析得出其弥散系数和各向异性特点.结果:不同年龄组间相同解剖部位脑白质ADC值及FA值的差异无统计学意义;不同解剖部位间FA值及ADC值的差异具有显著性.结论:DTI可清晰显示脑内白质的走行及方向,FA能准确定量分析正常成人不同部位脑白质纤维的各向异性程度.