Diffusion tensor imaging fiber tractography for evaluating diffuse axonal injury

Patients with Diffuse axonal injury (DAI) frequently exhibit cognitive disorders chronically. Radiologic recognition of DAI can help understand the clinical syndrome and to make treatment decisions. However, CT and conventional MRI are often normal or demonstrate lesions that are poorly related to the cognitive disorders. Recently, diffusion tensor imaging (DTI) fiber tractography has been shown to be useful in detecting various types of white matter damage. The aim of this study was to evaluate the feasibility of using DTI fiber tractography to detect lesions in DAI patients, and to correlate the DAI lesions with the cognitive disorders. We investigated two patients with chronic DAI. Both had impaired intelligence, as well as attention and memory disorders that restricted their activities of daily living. In both patients, DTI fiber tractography revealed interruption of the white matter fibers in the corpus collosum and the fornix, while no lesions were found on conventional MRI. The interruption of the fornix which involves the circuit of Papez potentially correlates with the memory disorder. Therefore, DTI fiber tractography may be a useful technique for the evaluation of DAI patients with cognitive disorders.     

利用扩散张量成像及纤维跟踪技术分析 胼胝体发育不良脑内主要纤维束

目的 利用扩散张量成像(DTI)和纤维跟踪技术显示胼胝体发育不良状态下脑内纤维结构的变化。方法患者，男，9岁，头痛1周。采用SIEMENS Trio2003T完成全脑MRI和DTI数据收集和后处理。结果常规MRI显示胼胝体体中部以后缺如，半球间蛛网膜囊肿，右侧向上延伸。纤维跟踪技术显示左侧弓状纤维柬、下纵行纤维柬、扣带柬、海马及外囊等主要的连合、联合纤维走行方向与正常发育不同，有左右侧相互支援的趋势。结论DTI纤维跟踪技术能精确、直观显示先天性发育畸形的脑内白质纤维柬，有助于预后的评估。     

Diffusion tensor imaging and white matter tractography in patients with brainstem lesions

Summary Background. 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, we investigated the ability of DTI and WMT to visualize white matter tract involvement for the preoperative surgical planning and postoperative assessment of brainstem lesions. Methods. Preoperative and postoperative DTI data (echo-planar, 1.5T) were retrospectively analyzed in 10 patients with brainstem lesions (3 diffuse, 7 focal). WMT applying a tensor deflection algorithm was used to reconstruct WM tracts adjacent to the lesions. Reconstructed tracts included corticospinal tracts and medial lemnisci. The clinical and imaging follow-up data were also compared and analyzed. Findings. WMT revealed a series of tract alteration patterns including deviation, deformation, infiltration, and apparent tract interruption. WMT reconstructions showed that the major WM tracts were preserved during surgery and improved in position and appearance postoperatively. These findings correlated with the improvement or preservation of neurological function as determined by clinical assessment. Conclusions. Compared with the information provided by conventional MR imaging, DTI and WMT provided superior quantification and visualization of lesion involvement in eloquent fibre tracts of the brainstem. Moreover, DTI and WMT were found to be beneficial for white matter recognition in the neurosurgical planning and postoperative assessment of brainstem lesions.     

扩散张量纤维束示踪成像诊断无小脑病灶的多发性硬化患者共济失调

目的探讨扩散张量纤维束示踪成像诊断无小脑病灶的多发性硬化患者共济失调的价值。方法对18例有共济失调症状的MS患者(MS组)和18名健康志愿者(对照组)进行头部MR扫描,利用纤维束示踪技术追踪穿过小脑双侧齿状核和双侧丘脑白质的纤维束,计算FA值、ADC值和纤维束条数,并进行统计学分析。结果与对照组比较,MS组右侧丘脑白质纤维束FA值减低、ADC值增加(P均0.05);左侧丘脑、双侧齿状核FA值、ADC值差异均无统计学意义(P均0.05);双侧丘脑、双侧齿状核的白质纤维束条数差异均无统计学意义(P均0.05)。MS组双侧丘脑、双侧齿状核的FA值、ADC值、纤维束条数与临床扩展残疾状态量表评分、病程均无相关性(P均0.05)。结论扩散张量纤维束示踪成像诊断无小脑病灶的多发性硬化患者共济失调有一定临床应用价值。     

Diffusion tensor imaging and tractography of the sciatic and femoral nerves in healthy volunteers at 3T

Background

The aim was to clarify the normal fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the sciatic and femoral nerves at the level of the hip joint and to visualize the neural tracts with diffusion tensor imaging (DTI).

Methods

Twenty-four healthy volunteers (12 men and 12 women, age 20–29 years) underwent DTI for visualization with tractography and quantification of FA and ADC values on a 3 Tesla MRI (b value?=?800 s/mm², motion probing gradient, 11 directions, time to repeat/echo time?=?9000/72.6 ms, axial slice orientation, slice thickness?=?3.0 mm with no inter-slice gap, field of view?=?320?×?320 mm, 96?×?192 matrix, 75 slices, number of acquisitions?=?4). Regions of interest in the sciatic nerve were defined at the femoral head, the S1 root, and the midpoint levels. The femoral nerve was evaluated at 3–4 cm proximal to the femoral head level.

Results

The tractography of the sciatic and femoral nerves were visualized in all participants. The mean FA values of the sciatic nerve were increased distally from the S1 root level, through the midpoint, and to the femoral head level (0.314, 0.446, 0.567, p?=?0.001, respectively). The mean FA values of the femoral nerve were 0.565. The mean ADC values of the sciatic nerves were significantly lower in the S1 root level than in the midpoint and the femoral head level (1.481, 1.602, 1.591?×?10^?3?×?10^?3 mm²/s, p?=?0.001, respectively). The ADC values of the femoral nerve were 1.439?×?10^?3 mm²/s. FA and ADC values showed moderate to substantial inter- and intra-observer reliability without significant differences in gender or laterality.

Conclusion

Visualization and quantification of the sciatic and femoral nerves simultaneously around the hip joint were achieved in healthy young volunteers with DTI. Clinical application of DTI is expected to contribute to hip pain research.

     

Diffusion tensor tractography reveals disrupted topological efficiency in white matter structural networks in multiple sclerosis

Little is currently known about the alterations in the topological organization of the white matter (WM) structural networks in patients with multiple sclerosis (MS). In the present study, we used diffusion tensor imaging and deterministic tractography to map the WM structural networks in 39 MS patients and 39 age- and gender-matched healthy controls. Graph theoretical methods were applied to investigate alterations in the network efficiency in these patients. The MS patients and the controls exhibited efficient small-world properties in their WM structural networks. However, the global and local network efficiencies were significantly decreased in the MS patients compared with the controls, with the most pronounced changes observed in the sensorimotor, visual, default-mode, and language areas. Furthermore, the decreased network efficiencies were significantly correlated with the expanded disability status scale scores, the disease durations, and the total WM lesion loads. Together, the results suggest a disrupted integrity in the large-scale brain systems in MS, thus providing new insights into the understanding of MS connectome. Our data also suggest that a topology-based brain network analysis can provide potential biomarkers for disease diagnosis and for monitoring the progression and treatment effects for patients with MS.     

Role of diffusion tensor imaging and tractography in spinal cord injury

Spinal cord injuries pose grave medical and socioeconomic burdens warranting measures for early diagnosis, triaging, prognostication and therapeutics. Imaging has since long played a pivotal role in this regard, with continuing research and technological advancements opening newer frontiers. One such advanced Magnetic resonance (MR) technique is Diffusion tensor imaging (DTI) which assesses cord microstructure by tracking the movement of water molecules in biological tissues. DTI utilizes the principle of anisotropy exhibited by the normal compact white matter (WM) tracts of the cord, in which direction-dependent water molecular motion is seen along the axonal axis. Disruption of this complex structure in response to injury alters the movement of these molecules, interrupting anisotropy and thereby DTI metrics.Evaluation of DTI images can be done both by quantitative indices, of which fractional anisotropy (FA) and mean diffusivity (MD) are the most commonly used and by qualitative fiber tracking (tractography) methods in which three-dimensional WM tracts are reconstructed by algorithmic post-processing. Reduced FA is consistently seen at injury sites as a direct consequence of disturbance of anisotropy. Diffusivity values are however more variable with both high and low values recorded across studies. 3D tractography images allow visual assessment of cord integrity, morphology, and orientation. Significant correlation is found between DTI parameters and various spinal injury scores. Furthermore, DTI also helps in accurate lesion mapping and in assessing cord changes distant from injury epicenter providing a holistic evaluation.From its inception, consistent progress in the understanding and application of DTI has effectuated its clinical utility and impact. Incorporation into day-to-day diagnostics is however still challenging, due to suboptimal image acquisition, difficult post-processing, and lack of standardized protocols & image interpretation guidelines. Further research with technical validation, development of normative and disease data sets, and histological confirmation will help establish this novel technique in routine diagnostics.     

Diffusion tensor imaging in the cervical spinal cord

There are discrepancy between MR findings and clinical presentations. The compressed cervical cord in patients of the spondylotic myelopathy may be normal on conventional MRI when it is at the earlier stage or even if patients had severe symptoms. Therefore, it is necessary to take a developed MR technique—diffusion tensor imaging (DTI)—to detect the intramedullary lesions. Prospective MR and DTI were performed in 53 patients with cervical compressive myelopathy and twenty healthy volunteers. DTI was performed along six non-collinear directions with single-shot spin echo echo-planar imaging (EPI) sequence. Intramedullary apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in four segments (C2/3, C3/4, C4/5, C5/6) for volunteers, in lesions (or the compressed cord) and normal cord for patients. DTI original images were processed to produce color DTI maps. In the volunteers’ group, cervical cord exhibited blue on the color DTI map. FA values between four segments had a significant difference (P < 0.01), with the highest FA value (0.85 ± 0.03) at C2/3 level. However, ADC value between them had no significant difference (P > 0.05). For patients, only 24 cases showed hyperintense on T2-weighted image, while 39 cases shown patchy green signal on color DTI maps. ADC and FA values between lesions or the compressed cord and normal spinal cord of patients had a significant difference (both P < 0.01). FA value at C2/3 cord is the highest of other segments and it gradually decreases towards the caudal direction. Using single-shot spin echo EPI sequence and six non-collinear diffusion directions with b value of 400 s mm⁻², DTI can clearly show the intramedullary microstructure and more lesions than conventional MRI.     

The role of the posterior superior temporal sulcus in audiovisual processing

In this study we investigate previous claims that a region in the left posterior superior temporal sulcus (pSTS) is more activated by audiovisual than unimodal processing. First, we compare audiovisual to visual-visual and auditory-auditory conceptual matching using auditory or visual object names that are paired with pictures of objects or their environmental sounds. Second, we compare congruent and incongruent audiovisual trials when presentation is simultaneous or sequential. Third, we compare audiovisual stimuli that are either verbal (auditory and visual words) or nonverbal (pictures of objects and their associated sounds). The results demonstrate that, when task, attention, and stimuli are controlled, pSTS activation for audiovisual conceptual matching is 1) identical to that observed for intramodal conceptual matching, 2) greater for incongruent than congruent trials when auditory and visual stimuli are simultaneously presented, and 3) identical for verbal and nonverbal stimuli. These results are not consistent with previous claims that pSTS activation reflects the active formation of an integrated audiovisual representation. After a discussion of the stimulus and task factors that modulate activation, we conclude that, when stimulus input, task, and attention are controlled, pSTS is part of a distributed set of regions involved in conceptual matching, irrespective of whether the stimuli are audiovisual, auditory-auditory or visual-visual.     

Inferior temporal sulcus as a site of corticotomy: magnetic resonance imaging analysis of individual sulcus patterns

OBJECTIVE: Transcortical approaches to the inferior horn often result in quadrant hemianopsia attributable to the injury to the optic radiation. The inferior temporal sulcus (ITS) has received little attention as an entrance point for the transsulcal approach. We used the method of detecting the ITS with magnetic resonance imaging (MRI) scans and investigated the sulcus pattern of ITS, its incidence rate, and the availability of the ITS to the corticotomy for selective amygdalohippocampectomy. METHODS: The sulcus patterns of the ITS of 100 temporal lobes in 50 healthy individuals were classified according to the number of interruptions by gyral bridges, and the localization of the ITS was characterized in relation to the outer surface by means of the surface anatomy scan of MRI. RESULTS: Most of the ITS was interrupted by one to three gyral bridges (0 bridges, 8%; one bridge, 27%: two bridges, 37%; three bridges, 20%; more than four bridges or no apparent ITS, 8%). When the ITS was present, it was located 15 mm above the orbitotragus line at a point 20 mm anterior to the tragus. The number of gyral bridges was significantly larger in the left temporal lobes than in the right temporal lobes, regardless of the sex of the subject. CONCLUSION: The ITS was clearly identified in 72% of the temporal lobes by the oblique sagittal view of MRI scans; thus, in such cases, the ITS was considered to be a candidate for an entrance point of a small temporal corticotomy. The preoperative observation of the ITS in relation to the orbitotragus line by means of MRI may improve the planning of the transsulcal approaches to deeply seated mesial temporal lesions, such as hippocampal sclerosis.     

磁共振扩散张量成像与纤维束成像在脊髓型颈椎病中的应用研究

目的 :评价磁共振扩散张量成像技术(diffusion tensor imaging,DTI)对脊髓型颈椎病的诊断价值。方法 :对收集的2014年1月至2015年4月20例健康志愿者和50例脊髓型颈椎病(CSM)患者行颈髓DTI。以健康志愿者作为对照组。依据颈髓MRI平扫结果将CSM患者分A、B、C组,A组17例(单纯硬膜囊受压),B组23例(颈髓受压,信号正常),C组10例(颈髓受压,T2高信号)。分析4组颈髓的平均表观扩散系数(ADC)、平均分数各向异性值(FA)之间的差异,对所有受检者行颈髓纤维束成像。结果:对照组C_2/C_3、C_3/C_4、C_4/C_5、C_5/C_6、C_6/C_7之间ADC值及FA值差异无统计学意义(P0.05),平均ADC值为(0.875±0.096)×10~(-3)mm~2/s,平均FA值为0.720±0.051;对照组与A组比较,平均ADC值、FA值差异无统计学意义,对照组与B、C组及A、B、C组间比较,平均ADC值、FA值差异均有统计学意义。结论:颈髓DTI较常规MRI能够早期、准确地量化脊髓型颈椎病的颈髓微结构改变,颈髓纤维束成像可以反映脊髓纤维束受压损伤的范围。     

Intraoperative visualisation of language fascicles by diffusion tensor imaging-based tractography in glioma surgery

Background

For gliomas, the goal of surgery is to maximise the extent of resection (EOR) while minimising the postoperative morbidity. The purpose of this study was to evaluate the benefits of a protocol developed for the surgical management of gliomas located in language areas, where tractography-integrated navigation was used in conjunction with direct electrical stimulations (DES).

Methods and materials

The authors included ten patients suffering of gliomas located in language areas. The preoperative planning for multimodal navigation was done by integrating anatomical magnetic resonance images and subcortical pathway volumes generated by diffusion tensor imaging. Six white matter fascicles implicated in language functions were reconstructed in each patient, including fibres for phonological processing (i.e. the arcuate fasciculus), fibres for lexical-semantic processing (i.e. the inferior frontooccipital fasciculus, inferior longitudinal fasciculus and uncinate fasciculus), and two premotor fasciculi involved in the preparation of speech movements (the subcallosal medialis fasciculus and cortical fibres originating from the medial and lateral premotor areas). During surgery, language fascicles were identified by direct visualisation on tractography-integrated navigation images and by observing transient language inhibition after subcortical DES. Language deficits were evaluated preoperatively and postoperatively, and compared with the EOR.

Results

Tractography was successfully performed in all patients, preoperatively demonstrating the relationships between the tumours to resect and the language fascicles to preserve from injury. With the use of the tractography-integrated navigation system and intraoperative DES, language functions were preserved in all patients. The mean volumetric resection was 93.0?±?10.4 % of the preoperative tumour volume, with a gross total resection in 60 % of patients.

Conclusion

The intraoperative combination of tractography and DES contributed to maximum safe resection of gliomas located in language areas.     

Diffusion tensor magnetic resonance imaging of brain tumors

DTI seems to offer the possibility of adding important information to presurgical planning. Although experience is limited, DTI seems to provide useful local information about the structures near the tumor, and this seems to be useful in planning. In the future, DTI may provide an improved way to monitor intraoperative surgical procedures as well as their complications. Furthermore, evaluation of the response to treatment with chemotherapy and radiation therapy might also be possible. Although DTI has some limitations, its active investigation and further study are clearly warranted.     

Depiction of the trigeminal nerve deviated by a tumor lesion, using probabilistic diffusion tensor tractography

We attempted presurgical visualization of the trigeminal nerve deviated by tumor compression using the probabilistic diffusion tractography (PDT) technique, which is used to analyze diffusion tensor imaging (DTI) data. We acquired DTI data of 3 patients with a tumor lesion around the trigeminal nerve (2 patients with trigeminal neurinomas and 1 with epidermoid) using the 3T magnetic resonance imaging system. The DTI data was analyzed by PDT using the Diffusion Toolbox, and the software of FMRIB (FDT; www.fmrib.ox.ac.uk/fsl). In all 3 patients, PDT allowed successful visualization of the trigeminal nerve which is further distal to the trigeminal ganglion, even when heavy T2-weighted imaging and conventional fiber-tracking analysis of the DTI data revealed only the cisternal segment of the nerves. Especially in 2 cases with the tumor mainly located in the Meckel's cave, the location of the nerve was determined only by PDT. All these findings obtained by PDT were concordant with the intraoperative observation of the actual nerves. In conclusion, PDT is a useful technique for visualization of the trigeminal nerve even when it is severely deviated by tumor compression, and this technique could have potential for evaluating other cranial nerves in surgical cases with a tumor in the skull base.