磁共振弥散张量成像和纤维束示踪技术及其在脑肿瘤诊治中的应用

磁共振弥散张量成像(diffusion tensor imaging, DTI)的概念是由Basser等在二十世纪九十年代中期提出的~[1],作为功能磁共振成像的一个重要组成部分,DTI成为近年来在弥散加权成像(diffusion weighted imaging, DWI)基础上迅速发展起来的新的核磁成像技术.     

磁共振弥散张量成像在临床诊疗中的应用

磁共振弥散张量成像(diffusion tensor imaging,DTI)作为一种功能磁共振成像(magnetic resonance imaging,MRI),在临床诊疗中发挥了重要作用.本文先介绍了DTI临床应用的各个领域,重点阐述了其在脑部疾病的应用,后指出临床应用中存在的问题,并对其前景进行了展望.     

高斯噪声对DTI参数MD和FA的影响

目的探索弥散张量成像(diffusion tensor imaging,DTI)中高斯白噪声对参数平均弥散率(mean diffusion,MD)和各向异性分数(fractional anisotropy,FA)的影响。材料和方法计算多个感兴趣区的MD和FA值,分析这两个参数随高斯噪声方差的变化趋势。结果在所研究的方差范围内,MD不受高斯噪声的影响,且图像视觉效果变化也很小;但FA参数受到高斯噪声的影响很大,图像视觉效果严重下降。结论DTI参数MD具有较强的鲁棒性,而FA受噪声的干扰较大,临床上适当折衷之后,可以允许一定噪声存在以增加图像细节。     

DWI检测超急性期兔大脑中动脉梗死模型神经血管单元损伤的初步研究

目的　评价磁共振弥散加权成像（diffused weighted imaging, DWI）对兔脑超急性期脑梗死模型中神经血管单元（neurovascular unit , NVU）损伤的诊断价值。 方法　15只健康新西兰大白兔,随机分为对照组（5只）和实验组（10只）。 其中实验组用微导丝超选择性栓塞法制作兔大脑中动脉阻塞(middle cerebral artery occlusion, MCAO)模型,并根据存活时间分为0.5 h和4 h组。所有动物行磁共振DWI扫描和T2-flair扫描并分析表观弥散系数（apparent diffusion coefficient,ADC）和相对表观弥散系数（relative apparent diffusion coefficient,rADC）,之后立即取全脑固定,切片进行尼氏染色、GFAP（glial fibrillary acidic protein, 星形胶质细胞标记物）和CD31（血管内皮标记物）染色。 结果　和对照组相比, 0.5 h组缺血区DWI成像见高信号,ADC成像见低信号,T2-Flair成像未见异常信号,尼氏染色未见异常,GFAP染色表达增加;4h组缺血区DWI成像见高信号,ADC成像见低信号,二者成像范围和强度较0.5h组扩大增强,T2-Flair成像见高信号,尼氏染色见尼氏体数目显著减少,GFAP染色表达较0.5h组显著增加。与0.5h组比,4h组缺血区的ADC值及rADC值均有显著差异（P<0.01）。实验组rADC值与GFAP荧光强度值呈负直线相关关系（r=－0.672,P<0.001）。 结论　DWI对超急性期兔脑梗死可以及时准确的进行诊断,对应时间点梗死模型的NVU损伤特点符合影像学特征。     

弥散张量成像在周围神经病变的应用及进展

弥散张量成像（diffusion tensor imaging，DTI）及纤维束示踪术（diffusion tensor tracking，Dr丌）是在常规弥散基础上发展起来的新兴技术，可通过监测水分子的随机运动和测量各向异性来提供组织的显微结构和组织架构等有价值的信息，具有常规MRI技术无法比拟的优势。目前已广泛应用于中枢神经系统多种疾病的诊断及预后评价中。近年来，DTI及DTT示踪技术已逐步应用于周围神经及肌肉病变的诊断。由于神经纤维的组织学特性，沿着神经轴突长轴方向弥散略高于垂直于它们的短轴方向，导致各向异性扩散存在差异，因此，周围神经病变适合采用DTI及DTr技术对细微结构进行评估及量化研究。     

弥散张量成像在缺陷型精神分裂症患者认知功能评估中的应用

目的:探讨弥散张量成像(diffusion tensor imaging,DTI)在缺陷型精神分裂症患者认知功能评估中的应用价值.方法:选取2019年6月至2021年6月淮安市第三人民医院缺陷型精神分裂症患者68例为研究组,另选取同期健康体检者39例为对照组.所有受检者均接受影像学检查,测定左侧大脑脚、右侧额叶、左侧内...     

基于功能磁共振成像可视化解码中医药促进脑卒中后脑功能的重塑

背景：通过功能磁共振成像可视化技术直观研究大脑重塑和神经再生机制,探讨其揭示中医药促进脑功能重塑和大脑重构的可行性和科学性,提高中医临床治疗方案修订、临床疗效和预后评估的客观性。目的：利用功能磁共振成像可视化技术解码中医药促进脑卒中后大脑重塑可行性和科学性,为探讨评价中医药治疗脑卒中的临床疗效、理论创新、疗效和预后评估提供重要依据。方法：以“功能磁共振成像、磁共振弥散张量成像、局部一致性、低频振幅、中医药、脑功能重塑、神经重塑”及“diffusion tensor imaging,blood oxygenation level dependent functional magnetic resonance imaging,regional homogeneity,amplitude of low frequency fluctuation,brain remodeling,nerve regeneration,Chinese Medicine”为主题检索词,检索中国期刊全文数据库、PubMed和万方数据库的相关文献,最终纳入63篇文献进行综述。结果与结论：(1)功能磁共振成像具有无创动...     

FSL在DTI大脑图像分析中的应用现状

随着弥散张量成像(diffusion tensor imaging,DTI)技术在大脑结构方面应用研究的增多,与之相关的数据分析软件也在增多,其中FMRIB Software Library(FSL)在示踪时使用的是基于概率性示踪的算法,在进行交叉纤维示踪和灰质连接上有很大优势。本文主要根据数据分析方式的不同对FSL包含的两个子工具(tract-based spatial statistics,TBSS和FMRIB’s diffusion toolbox,FDT)在DTI大脑图像分析方面的应用现状进行分类介绍,主要涉及老年抑郁症、精神分裂症以及认知功能等领域。本文首先简要介绍DTI原理,然后根据数据分析方式的不同,在TBSS部分分为全脑分析和感兴趣区域(region of interest,ROI)分析两方面,在FDT部分分为全脑示踪、ROI互连分析、基于连通度的分类三方面进行介绍,最后对FSL的局限性以及发展状况进行总结。     

磁共振功能成像在足月新生儿缺氧缺血性脑病中的应用

新生儿缺氧缺血性脑病(hypoxic-ischemic encephalopathy HIE)是指由围生期缺氧窒息导致的脑缺血缺氧性损伤,可出现嗜睡、肌张力异常、惊厥等一系列的临床症状。轻者可治愈,严重者可导致患儿智力低下、发育落后、脑瘫、癫痫,甚至死亡。因此,对新生儿HIE的早期诊断和预后评估方法的研究始终是国内外关注的热点。近年来,随着医学影像技术的飞速发展,磁共振弥散加权成像(diffusion-weighted imaging,DWI)、弥散张量成像(diffusion-tensor imaging,DTI)及磁共振波谱分析(magnetic resonance spectroscopy,MRS)等功能成像技术在该病的早期诊断和预后分析等方面具有明显的优势。本文就磁共振功能成像在HIE早期诊断和预后评估方面的应用进展做一综述。     

1.5T MRI平扫联合DWI在宫颈癌诊断中的价值分析

目的:探究 1.5T 磁共振(magnetic resonance imaging,MRI)平扫联合扩散加权成像(diffusion weighted imaging,DWI)在宫颈癌中的诊断价值.方法:回顾性分析 2020 年 8月至 2022年 7 月我院收治的 88 例宫颈癌患者的临床资料,所有患者均行MRI平扫及DWI检查.将病理检查结果作为诊断"金标准",对比不同病理分期下表观弥散系数(Apparent diffusion coefficient,ADC)值、转移淋巴结及非转移淋巴结的ADC值、分析MRI平扫及联合扫描在宫颈癌分期中的诊断价值.结果:不同病理分期下宫颈癌患者ADC值对比,均无统计学意义.经MRI检查共检出淋巴结 102 枚,其中转移淋巴结 41 枚,非转移淋巴结 61 枚.非转移淋巴结ADC值高于转移淋巴结(P＜0.05).MRI平扫+DWI检查Ib和IIa期灵敏度及准确度均高于MRI平扫(P＜0.05).结论:1.5T MRI平扫联合DWI在宫颈癌鉴别诊断中具有较高的临床应用价值,于各分期诊断中准确度较高.     

Diffusion tensor imaging in acquired blind humans

Retinal implants as a future possible therapy of blindness rely on an intact neural transmission from the retina to the primary visual cortex. By now it remains unknown, in how far the absence of afferent input in blindness affects also the organization of the optic radiation. Using diffusion tensor imaging (DTI), the non-invasive evaluation of large fiber tracts including the optic radiation has become possible. This method is sensitive to changes of the axonal state such as wallerian degeneration. We have compared DTI data from 6 acquired blind patients with those of a group of 11 healthy control subjects. Neither the relative anisotropy quotient of the visual fiber tract and the pyramidal tract showed a statistically significant difference between the blind patients and the control group nor did the absolute values of the relative anisotropy in the pyramidal tract and the visual fiber tract. There was no axonal degeneration of the optic radiation in late onset acquired blindness. With the optic pathways remaining intact, transmitting electric signals of retinal implants to the visual regions of the human brain seems to be possible even after decades of acquired blindness.     

Retrograde and Wallerian axonal degeneration occur synchronously after retinal ganglion cell axotomy

Axonal injury and degeneration are pivotal pathological events in diseases of the nervous system. In the past decade, it has been recognized that the process of axonal degeneration is distinct from somal degeneration and that axoprotective strategies may be distinct from those that protect the soma. Preserving the cell body via neuroprotection cannot improve function if the axon is damaged, because the soma is still disconnected from its target. Therefore, understanding the mechanisms of axonal degeneration is critical for developing new therapeutic interventions for axonal disease treatment. We combined in vivo imaging with a multilaser confocal scanning laser ophthalmoscope and in vivo axotomy with a diode-pumped solid-state laser to assess the time course of Wallerian and retrograde degeneration of unmyelinated retinal ganglion cell axons in living rats for 4 weeks after intraretinal axotomy. Laser injury resulted in reproducible axon loss both distal and proximal to the site of injury. Longitudinal polarization-sensitive imaging of axons demonstrated that Wallerian and retrograde degeneration occurred synchronously. Neurofilament immunostaining of retinal whole-mounts confirmed axonal loss and demonstrated sparing of adjacent axons to the axotomy site. In vivo fluorescent imaging of axonal transport and photobleaching of labeled axons demonstrated that the laser axotomy model did not affect adjacent axon function. These results are consistent with a shared mechanism for Wallerian and retrograde degeneration.     

锥体束行程上无症状性腔隙性脑梗死大脑脚面积及FA值变化特点

目的探讨锥体束行程上无症状性腔隙性脑梗死大脑脚面积和FA值变化特点及临床意义。方法选取经核磁共振检查检确诊为锥体束行程上无症状性腔隙性脑梗死病人54例及正常人群组105例为研究对象,54例病人的大脑脚面积及FA值按梗死灶累及侧别,分为患侧组及健侧组并与对照组的左侧和右侧大脑脚的面积及FA值进行比较,同时比较了腔梗组和对照组的大脑脚面积及FA值的不对称比。结果无症状腔隙性脑梗死组双侧大脑脚面积小于对照组(左侧F=17.104,P=0.000,右侧F=12.581,P=0.000),双大脑脚的FA值无差异(左侧P=0.894,右侧P=0.968)。腔梗组双侧大脑脚面积及FA值无差异(分别为t=0.254 P=0.8,t=0.268 P=0.790),腔梗组与对照组双大脑脚面积及FA值不对称比值无差异(分别为t=0.114 P=0.67,t=1.463 P=0.175)。结论无症状性腔隙性脑梗死对于局限性脑梗死所引起Wallerian变性而导致的大脑脚面积及FA值的改变的无影响。     

Tenascin-C expression during Wallerian degeneration in C57BL/Wlds mice: possible implications for axonal regeneration

Summary Schwann cells in the distal stumps of lesioned peripheral nerves strongly express the extracellular matrix glycoprotein tenascin-C. To gain insights into the relationship between Wallerian degeneration, lesion induced tenascin-C upregulation and regrowth of axons we have investigated C57BL/Wld^s (C57BL/Ola) mice, a mutant in which Wallerian degeneration is considerably delayed. Since we found a distinct difference in the speed of Wallerian degeneration between muscle nerves and cutaneous nerves in 16-week-old C57BL/Wld^s mice, as opposed to 6-week-old animals in which Wallerian degeneration is delayed in both, we chose the older animals for closer investigation. Five days post lesion tenascin-C was upregulated in the muscle branch (quadriceps) but not in the cutaneous branch (saphenous) of the femoral nerve in 16-week-old animals. In addition myelomonocytic cells displaying endogenous peroxidase activity invaded the muscle branch readily whereas they were absent from the cutaneous branch at this time. We could further show that it is only a subpopulation of axon-Schwann cell units (mainly muscle efferents) in the muscle branch which undergo Wallerian degeneration and upregulate tenascin-C at normal speed and that the remaining axon-Schwann cell units (mainly afferents) displayed delayed Wallerian degeneration and no tenascin-C expression. Regrowing axons could only be found in the tenascin-C-positive muscle branch where they always grew in association with axon-Schwann cell units undergoing Wallerian degeneration. These observations indicate a tight relationship between Wallerian degeneration, upregulation of tenascin-C expression and regrowth of axons, suggesting an involvement of tenascin-C in peripheral nerve regeneration.     

White Matter Fiber Tracking Computation Based on Diffusion Tensor Imaging for Clinical Applications

Fiber tracking allows the in vivo reconstruction of human brain white matter fiber trajectories based on magnetic resonance diffusion tensor imaging (MR-DTI), but its application in the clinical routine is still in its infancy. In this study, we present a new software for fiber tracking, developed on top of a general-purpose DICOM (digital imaging and communications in medicine) framework, which can be easily integrated into existing picture archiving and communication system (PACS) of radiological institutions. Images combining anatomical information and the localization of different fiber tract trajectories can be encoded and exported in DICOM and Analyze formats, which are valuable resources in the clinical applications of this method. Fiber tracking was implemented based on existing line propagation algorithms, but it includes a heuristic for fiber crossings in the case of disk-shaped diffusion tensors. We successfully performed fiber tracking on MR-DTI data sets from 26 patients with different types of brain lesions affecting the corticospinal tracts. In all cases, the trajectories of the central spinal tract (pyramidal tract) were reconstructed and could be applied at the planning phase of the surgery as well as in intraoperative neuronavigation.     

Bilateral middle cerebral artery thromboembolic occlusion. Could maternal hyperthermia be a detrimental factor?

We describe a six-month-old girl with microcephaly, developmental delay, truncal hypotonia, left pyramidal signs, partial seizures and myoclonic spasms, born to a feverish mother. MRI showed bilateral vascular lesions in the territory of the middle cerebral arteries, prevalent in the right hemisphere, together with hypoplasia of the posterior part of the corpus callosum and Wallerian degeneration of the cerebral peduncle. There may be many reasons for these lesions. In the reported patient the presence of maternal hyperthermia could have exacerbated cerebral thromboembolic occlusion.     

A reanalysis of the ventrolateral input in slow and fast pyramidal tract neurons of the cat motor cortex

In deeply anesthetized cats the temporal characteristics of ventro-lateral (thalamic) excitatory postsynaptic potentials (EPSPs) induced in pyramidal tract cells were studied with an averaging technique. Stimulation of the ventrolateral thalamus induced EPSPs in all pyramidal tract neurons at latencies of 1–5 ms. It was found that there was a positive relationship between the latency and rise time of stimulation-induced EPSPs and the latency of antidromic invasions of pyramidal tract neurons. In response to two closely spaced shocks the second EPSP had the same latency and amplitude as the first one in both slow and fast pyramidal tract neurons. Moreover, the span of antidromic latencies of ventrolateral thalamic relay cells to motor cortex stimulation showed that these thalamic neurons had the necessary conduction velocities to account for the distribution of EPSP latencies recorded in pyramidal tract neurons. From these electrophysiological results, it has been concluded that slow and fast pyramidal tract neurons receive a monosynaptic input from neurons in the ventrolateral thalamus. We also report morphological evidence, obtained at the electron-microscopic level, supporting this conclusion. Terminal degeneration induced by a lesion in the ventrolateral thalamus was found on the apical dendrite of a slow pyramidal tract neuron that had been injected with horseradish peroxidase.It is proposed that the matching between the latencies of EPSPs evoked from the ventrolateral thalamus and the latencies of antidromic invasions of pyramidal tract neurons may reflect a matching between the conduction velocity of thalamocortical and cortico-spinal neurons and/or it may be due to the electrotonic properties of the apical dendrites.     

Extensive piano practicing has regionally specific effects on white matter development

Using diffusion tensor imaging, we investigated effects of piano practicing in childhood, adolescence and adulthood on white matter, and found positive correlations between practicing and fiber tract organization in different regions for each age period. For childhood, practicing correlations were extensive and included the pyramidal tract, which was more structured in pianists than in non-musicians. Long-term training within critical developmental periods may thus induce regionally specific plasticity in myelinating tracts.     

Axonal regeneration proceeds through specific axonal fusion in transected C. elegans neurons

Functional neuronal recovery following injury arises when severed axons reconnect with their targets. In Caenorhabditis elegans following laser‐induced axotomy, the axon still attached to the cell body is able to regrow and reconnect with its separated distal fragment. Here we show that reconnection of separated axon fragments during regeneration of C. elegans mechanosensory neurons occurs through a mechanism of axonal fusion, which prevents Wallerian degeneration of the distal fragment. Through electron microscopy analysis and imaging with the photoconvertible fluorescent protein Kaede, we show that the fusion process re‐establishes membrane continuity and repristinates anterograde and retrograde cytoplasmic diffusion. We also provide evidence that axonal fusion occurs with a remarkable level of accuracy, with the proximal re‐growing axon recognizing its own separated distal fragment. Thus, efficient axonal regeneration can occur by selective reconnection and fusion of separated axonal fragments beyond an injury site, with restoration of the damaged neuronal tract. Developmental Dynamics 240:1365–1372, 2011. © 2011 Wiley‐Liss, Inc.     

Assessing optic nerve pathology with diffusion MRI: from mouse to human

The optic nerve is often affected in patients with glaucoma and multiple sclerosis. Conventional MRI can detect nerve damage, but it does not accurately assess the underlying pathologies. Mean diffusivity and diffusion anisotropy indices derived from diffusion tensor imaging have been shown to be sensitive to a variety of central nervous system white matter pathologies. Despite being sensitive, the lack of specificity limits the ability of these measures to differentiate the underlying pathology. Directional (axial and radial) diffusivities, measuring water diffusion parallel and perpendicular to the axonal tracts, have been shown to be specific to axonal and myelin damage in mouse models of optic nerve injury, including retinal ischemia and experimental autoimmune encephalomyelitis. The progression of Wallerian degeneration has also been detected using directional diffusivities after retinal ischemia. However, translating these findings to human optic nerve is technically challenging. The current status of diffusion MRI of human optic nerve, including imaging sequences and protocols, is summarized herein. Despite the lack of a consensus among different groups on the optimal sequence or protocol, increased mean diffusivity and decreased diffusion anisotropy have been observed in injured optic nerve from patients with chronic optic neuritis. From different mouse models of optic nerve injuries to the emerging studies on patients with optic neuritis, directional diffusivities show great potential to be specific biomarkers for axonal and myelin injury.