Bilateral cingulum fiber reductions in temporal lobe epilepsy with unilateral hippocampal sclerosis

PurposeTo evaluate whether white matter tracts within the Papez circuit are altered in patients with unilateral hippocampal sclerosis (HS).MethodsTwenty patients with histologically proven unilateral HS and 20 age-matched controls were studied with a 3 T Epilepsy-dedicated MRI protocol including a MPRAGE sequence for hippocampus volumetry and a diffusion tensor imaging (DTI) sequence (61 diffusion-encoding directions, 2 × 2 × 2 mm³ voxels) for diffusion tensor tractography (DTT). An energy-based global tracking algorithm was used to calculate streamline counts (SC) and fractional anisotropy (FA) of cingulate, fornix, and mammillo-thalamic tracts, respectively.ResultsSclerotic hippocampi were significantly smaller compared to the contralateral side and to age-matched controls. Cingulum SC but not FA were reduced on the hippocampal sclerosis (258 + 81.0) and contralateral side (271 + 85.6) compared to age-matched controls (447 + 138).ConclusionFocusing on white matter tracts of the Papez circuit we showed that in patients with intractable temporal lobe epilepsy unilateral hippocampal sclerosis is associated with a bilateral reduction of cingulum association fibers projecting from the cingulate gyrus to the parahippocampal gyrus.     

Correlation of diffusion tensor imaging findings and episodic memory impairment in temporal lobe epilepsy

Purpose

Our aim was to evaluate the utility of diffusion tensor imaging (DTI) in exploration of white matter tracts microstructure changes and clarify their relation to episodic memory in temporal lobe epilepsy (TLE).

Uncinate fasciculus fiber tracking in mesial temporal lobe epilepsy. Initial findings

In temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS), ictal discharge spread to the frontal and insulo-perisylvian cortex is commonly observed. The implication of white matter pathways in this propagation has not been investigated. We compared diffusion tensor imaging (DTI) measurements along the uncinate fasciculus (UF), a major tract connecting the frontal and temporal lobes, in patients and controls. Ten right-handed patients referred for intractable TLE due to a right HS were investigated on a 1.5-T MR scanner including a DTI sequence. All patients had interictal fluorodeoxyglucose PET showing an ipsilateral temporal hypometabolism associated with insular and frontal or perisylvian hypometabolism. The controls consisted of ten right-handed healthy subjects. UF fiber tracking was performed, and its fractional anisotropy (FA) values were compared between patients and controls, separately for the right and left UF. The left-minus-right FA UF asymmetry index was computed to test for intergroup differences. Asymmetries were found in the control group with right-greater-than-left FA. This asymmetrical pattern was lost in the patient group. Right FA values were lower in patients with right HS versus controls. Although preliminary, these findings may be related to the preferential pathway of seizure spread from the mesial temporal lobe to frontal and insulo-perisylvian areas.     

Transneuronal degeneration in patients with temporal lobe epilepsy: evaluation by MR imaging

The aim of this study was to assess the MR imaging findings of transneuronal degeneration of limbic system in the patients with temporal lobe epilepsy, and to detect the influence of surgery on the anatomy of the limbic system. Axial and coronal T1- and T2-weighted MR images were retrospectively analyzed in 34 patients with temporal lobe epilepsy, focusing on transneuronal degeneration. In 17 of the 34 patients, MR images were also analyzed after selective amygdalo-hippocampectomy. Atrophy of the fornix, mamillary body, mamillothalamic tract (MTT), and thalamus ipsilateral to the epileptic focus was demonstrated on MR images in 14.7, 17.6, 8.8, and 11.8% of the 34 patients, respectively. Focal hyperintensity of the thalamus was found on T2-weighted images in 8.8% of the 34 patients. In 17 patients who were evaluated before and after surgery, transneuronal degeneration was seen more frequently after surgery: fornix (11.8 vs 29.4%), mamillary body (11.8 vs 52.9%), MTT (5.9 vs 11.8%), and thalamus (11.8 vs 11.8%). Transneuronal degeneration of the limbic system is clearly demonstrated by MR imaging in patients with temporal lobe epilepsy, and surgical intervention induces transneuronal degeneration more frequently.     

Diffusion tensor imaging (DTI) with retrospective motion correction for large-scale pediatric imaging

Purpose:

To develop and implement a clinical DTI technique suitable for the pediatric setting that retrospectively corrects for large motion without the need for rescanning and/or reacquisition strategies, and to deliver high‐quality DTI images (both in the presence and absence of large motion) using procedures that reduce image noise and artifacts.

Materials and Methods:

We implemented an in‐house built generalized autocalibrating partially parallel acquisitions (GRAPPA)‐accelerated diffusion tensor (DT) echo‐planar imaging (EPI) sequence at 1.5T and 3T on 1600 patients between 1 month and 18 years old. To reconstruct the data, we developed a fully automated tailored reconstruction software that selects the best GRAPPA and ghost calibration weights; does 3D rigid‐body realignment with importance weighting; and employs phase correction and complex averaging to lower Rician noise and reduce phase artifacts. For select cases we investigated the use of an additional volume rejection criterion and b‐matrix correction for large motion.

Results:

The DTI image reconstruction procedures developed here were extremely robust in correcting for motion, failing on only three subjects, while providing the radiologists high‐quality data for routine evaluation.

Conclusion:

This work suggests that, apart from the rare instance of continuous motion throughout the scan, high‐quality DTI brain data can be acquired using our proposed integrated sequence and reconstruction that uses a retrospective approach to motion correction. In addition, we demonstrate a substantial improvement in overall image quality by combining phase correction with complex averaging, which reduces the Rician noise that biases noisy data. J. Magn. Reson. Imaging 2012;36:961–971. © 2012 Wiley Periodicals, Inc.     

Fractional anisotropy asymmetry and the side of seizure origin for partial onset-temporal lobe epilepsy

This paper presents a fractional anisotropy asymmetry (FAA) method to detect the asymmetry of white matter (WM) integrity and its correlation with the side of seizure origin for partial onset temporal lobe epilepsy (TLE) using diffusion tensor image (DTI). In this study, FAA analysis is applied to 30 patients of partial TLE (15 left, 15 right) and 14 matched normal controls. Specifically, after registering all the images with the JHU-DTI-MNI template the average FA value of each FA skeleton section is calculated using the tract-based spatial statistics (TBSS) method. Then, FAA is calculated to quantify the WM diffusivity asymmetry of the corresponding region-pairs between the left and right hemispheres. Using FAA the regional asymmetry contributing significantly to the group differences of controls and left/right TLE, as well as the left and right TLE, is identified. As a comparison, the ROI-based average FA values for WM and corresponding FAAs are also calculated. TBSS-based analysis reflects the average of local maximal FA values along the white matter skeleton sections, and ROI-based analysis shows the average of WM FA values within each anatomical region. The FAA statistical results indicated that the FA values of anatomical region-pairs are asymmetric in the ipsilateral hemisphere with seizure origin against the contralateral hemisphere. Particularly, FAA values within the temporal lobe (superior, middle, and inferior temporal WM) are significantly different between the left and right TLE patients, consistently found from both analysis methods. The study suggests that FAA values can be potentially used to identify the seizures of origin of TLE and to help understand the relationship between fiber tracts with the side of seizure origin of TLE.     

A diffusion tensor imaging group study of the spinal cord in multiple sclerosis patients with and without T2 spinal cord lesions

Purpose

To examine the T₂‐normal appearing spinal cord of patients with multiple sclerosis (MS) using diffusion tensor imaging.

Materials and Methods

Diffusion tensor images of the spinal cord were acquired from 21 healthy subjects, 11 MS patients with spinal cord lesions, and 10 MS patients without spinal cord lesions on the T₂‐weighted MR images. Different diffusion measures were evaluated using both a region of interest (ROI) ‐based and a diffusion tensor tractography‐based segmentation approach.

Results

It was observed that the FA, the transverse diffusivity λ_?, and the ratio of the longitudinal and transverse diffusivities (λ_∥/λ _?) were significantly lower in the spinal cord of MS patients with spinal cord lesions compared with the control subjects using both the ROI method (P = 0.014, P = 0.028, and P = 0.039, respectively) and the tractography‐based approach (P = 0.006, P = 0.037, and P = 0.012, respectively). For both image analysis methods, the FA and the λ _∥/λ _? values were significantly different between the control group and the MS patient group without T₂ spinal cord lesions (P = 0.013).

Conclusion

Our results suggest that the spinal cord may still be affected by MS, even when lesions are not detected on a conventional MR scan. In addition, we demonstrated that diffusion tensor tractography is a robust tool to analyze the spinal cord of MS patients. J. Magn. Reson. Imaging 2009;30:25–34. © 2009 Wiley‐Liss, Inc.

     

Diffusion tensor imaging and tractography of the human language pathways: Moving into the clinical realm

The functional correlates of anatomical derangements are of interest to the neurological clinician. Diffusion tensor tractography (DTT) is a relatively new tool in the arsenal of functional neuroimaging, by which to assess white matter tracts in the brain. While much import has been given to tracking corticospinal tracts in neurological disease, studying language pathway interconnections using DTT has largely remained in the research realm. Hardware and software advances have allowed this tool to ease into clinical practice, with several radiologists, neurologists, and neurosurgeons now familiar with its applications. DTT images, although visually appealing, are founded in mathematical equations and assumptions, and require a more than basic understanding of principles and limitations before they can be integrated into routine clinical practice. Cognitive pathways like that of language, that are normally hard to assess and especially more so when pathologically affected, have been at the receiving end of several opposing and often controversial hypotheses, and the past decade has seen the clarification, validation or rejection of several of these by the in vivo charting of functional connectivity using DTT. The focus of this review is to illustrate DTT of the language pathways with emphasis on practical considerations, clinical applications, and limitations. J. Magn. Reson. Imaging 2014;40:1041–1053 . © 2013 Wiley Periodicals, Inc.     

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.     

颞叶癫痫的功能MRI研究进展

颞叶癫■（TLE）是癫■中最常见的难治性类型,临床上对于药物难以控制的癫■,手术切除致■灶具有良好的治疗效果。随着MRI技术的迅速发展,功能磁共振成像（fMRI）在癫■研究中的优势越来越显著,尤其在癫■灶的定侧、定位方面明显优于常规MRI,具有更好的临床应用价值。fMRI对TLE脑网络、认知功能的研究,及在TLE病因、病理生理机制、治疗预后等方面的应用取得了诸多进展。     

Oblique proton chemical shift imaging for the presurgical localization of mesial temporal epilepsy

Precise localization of the epileptogenic zone in patients suffering from mesial temporal lobe epilepsies is a prerequisite for surgery. For this purpose, a scheme for selecting the volume of interest in an oblique plane covering the head, body, and tail of the hippocampal formation (HF) was implemented in a water-suppressed proton chemical shift imaging (CSI) acquisition. This approach, evaluated by consecutively acquired CSI spectra of both temporal lobes, demonstrates that it can potentially be a routine technique for clinical diagnosis. Since the method produces localized spectral detail of the HF, it facilitates a convenient comparison of CSI lateralization to that assessed by HF atrophy (due to sclerosis) using the MRI-volumetry technique.     

难治性颞叶癫痫海马和同侧前颞叶MRI特征及其与临床相关性

目的：探讨难治性颞叶癫痫海马硬化（HS）与同侧前颞叶 MRI特征及其与临床的相关性。方法：搜集经影像学或病理诊断为难治性颞叶癫痫 HS的34例患者的临床和影像资料,其中25例行手术治疗。34例中女15例,男19例,平均年龄（22．4±8．2）岁。观察海马及同侧前颞叶 MRI征象,根据海马及前颞叶 MRI 征象将34例分为同侧前颞叶正常组与前颞叶异常组,后者再分为同时出现灰白质分界模糊和颞叶萎缩组与仅出现一种征象组两亚组,比较各组间临床特征的差异。结果：34例中,22例（64．7％）出现 HS及同侧前颞叶异常,12例同侧颞叶正常。前颞叶异常组首次癫痫发作年龄低于前颞叶正常组（t＝－3．438,P＝0．002）,病程时间比前颞叶正常组长（t＝2．453,P＝0．020）。前颞叶同时出现灰白质分界模糊和颞叶萎缩组与仅存在一种征象组间临床特征无统计学差异。结论：难治性颞叶癫痫伴有前颞叶异常的颞叶癫痫多数首次发病年龄小,病程长,MRI特征与临床病情具有紧密的相关性,对于手术侧别选择意义重大。     

Diffusion tensor imaging and fiber tractography of C6 rat glioma

PURPOSE: To apply diffusion tensor images using 30 noncollinear directions for diffusion-weighted gradient schemes to characterize diffusion tensor imaging (DTI) features associated with C6 glioma-bearing rat brains, and ideally visualize fiber tractography datasets. MATERIALS AND METHODS: Fiber tractographies of normal male Fischer 344 rat brains were constructed from DTI datasets acquired with a 30 noncollinear diffusion gradient scheme. Cultured C6 cell were intracranially injected into the cortex of male Fischer 344 rats. The time course of the tumor growth was monitored with DTI and fiber tractography using diffusion-weighting gradients in 30 noncollinear directions. RESULTS: Fiber tractographies through the corpus callosum (CC) were easily visualized with the 30-direction gradient scheme, and the fiber trajectories of the motor cortex and striatum were well represented in normal rats. Fiber tractography indicated that the neuronal fibers of the CC were compressed or disappeared by growing C6 glioma, which affected surrounding brain tissue. CONCLUSION: We have demonstrated in this study that fiber tractography with the 30 noncollinear diffusion gradient scheme method can be used to help provide a better understanding regarding the influence of a tumor on the surrounding regions of normal brain tissue in vivo.     

Diffusion tensor tractography demonstration of partially injured spinal cord tracts in a patient with posttraumatic Brown Sequard syndrome

The authors report the utility of diffusion tensor tractography in demonstrating the partially severed spinal cord tracts on one side with normal, intact, distally traceable tracts on the opposite side in a patient with posttraumatic Brown Sequard syndrome. A 30-year-old man presented with typical clinical features of a hemisection injury of the thoracic spinal cord, 2 months after he had sustained a back stab injury. Routine MRI showed T2 hyperintense zones in the thoracic spinal cord at the level of T5. We did axial single shot echo planar diffusion tensor imaging with a 1.5 Tesla MR machine. Tractography effectively depicted the injured spinal cord tracts on the left side with normal intact tracts on the right side, which could be traced distally. The fractional anisotropy and apparent diffusion coefficient values showed significant changes at the level of injury. Tractographic demonstration of human spinal cord injury is reported for the first time.     

Diffusion tensor magnetic resonance imaging of glial brain tumors

Aim

To evaluate the author's experience with the use of diffusion tensor magnetic resonance imaging (DTI) on patients with glial tumors.

Methods

A retrospective evaluation of a group of 24 patients with glial tumors was performed. There were eight patients with Grade II, eight patients with Grade III and eight patients with Grade IV tumors with a histologically proven diagnosis. All the patients underwent routine imaging including T2 weighted images, multidirectional diffusion weighted imaging (measured in 60 non-collinear directions) and T1 weighted non-enhanced and contrast enhanced images. The imaging sequence and evaluation software were produced by Massachusetts General Hospital Corporation (Boston, MA, USA). Fractional anisotropy (FA) maps were calculated in all patients. The white matter FA changes were assessed within the tumorous tissue, on the tumorous borderline and in the normally appearing white matter adjacent to the tumor. A three-dimensional model of the white matter tract was created to demonstrate the space relationship of the tumor and the capsula interna or corpus callosum in each case using the following fiber tracing parameters: FA step 0.25 and a tensor declination angle of 45 gr. An additional assessment of the tumorous tissue enhancement was performed.

Results

A uniform homogenous structure with sharp demargination of the Grade II tumors and the wide rim of the intermedial FA in all Grade III tumors respectively, were found during the evaluation of the FA maps. In Grade IV tumors a variable demargination was noted on the FA maps. The sensitivity and specificity for the discrimination of low- and high-grade glial tumors using FA maps was revealed to be 81% and 87% respectively. If the evaluation of the contrast enhancement was combined with the evaluation of the FA maps, both sensitivity and specificity were 100%.

Conclusion

Although the evaluation of the fractional anisotropy maps is not sufficient for glioma grading, the combination of the contrast enhancement pattern and fractional anisotropy maps evaluation improves the possibility of distinguishing low- and high-grade glial tumors. Three-dimensional models of the white matter fibers in the corpus callosum and the internal capsule may be used in the presurgical planning.