用MRI直接检测神经电磁场的研究

随着医学影像学的发展,基于脑内血氧水平变化的功能磁共振成像(fMRI)技术逐渐成为研究人脑功能的最主要的手段之一,但它的时间分辨率低.近年提出的神经电流磁共振成像(nc-MRI)是一种利用磁共振成像(MRI)技术对神经活动产生的电磁场直接成像的新方法.在原理上,nc-MRI是一种无创伤且同时具有高时间和空间分辨率特性的技术.因此,它的出现有可能会极大地推进脑功能的研究.探讨了nc-MRI信号的产生机制,包括神经磁场的理论模型和nc-MRI信号源及nc-MRI信号的模拟计算,其中包括对树突分支磁场的模拟以及nc-MRI的实验研究进展:展望了nc-MRI的未来发展方向.     

PDMS-2在儿童运动发育障碍评估中的研究进展

Peabody运动发育量表（Peabody development measurescale,PDMS）是目前在国内外康复界和儿童早期干预领域中被广泛应用的一个专门的运动功能评估量表,该量表不仅可用于运动发育迟缓的评价,也适用于脑性瘫痪的运动功能障碍的评价,并可用于儿童运动康复的评定。     

多模态MRI技术结合神经导航术中超声在枕叶视觉功能区胶质瘤手术中的应用

目的 探讨多模态MRI技术结合神经导航及术中超声在大脑枕叶视觉功能区胶质瘤手术中的应用价值。方法 回顾性分析2012年1月—2014年11月安徽医科大学附属省立医院神经外科收治的20例大脑枕叶视觉功能区胶质瘤患者手术相关资料,其中男9例、女11例,年龄27~72岁,均行神经显微手术治疗。术前利用灌注加权成像、弥散张量成像及血氧水平依赖功能MRI多模态MRI技术结合神经导航进行图像融合,重建病灶与视皮层及视辐射的3D图像位置,设计合适的手术入路、界定病灶切除范围;术中超声实时判断肿瘤切除程度,合理保护功能区和视辐射。结果 根据术后复查MRI结果,影像学全切除85.0%(17/20),大部分切除15.0%(3/20)。术后随访1~30个月,肿瘤大部分切除3例分别于术后7、13、15个月复发;与术前相比,视力视野改善与术前相比,视力视野改善60%(12/20),无明显变化40%(8/20)。结论 多模态MRI技术结合神经导航及术中超声,能够准确定位枕叶视觉功能区和视辐射的走行,制定个体化手术方案,提高了枕叶视觉功能区胶质瘤外科治疗的安全性和有效性,实现最大程度保护脑功能的同时最大范围切除肿瘤组织,提高患者术后生存质量。     

老年患者术后认知功能障碍的多模态MRI研究进展

老年人术后认知功能障碍(postoperative cognitive dysfunction,POCD)严重地影响老年人的健康和生活,造成家庭和社会的严重负担,正日益受到人们的重视。近年来,脑MRI在检测老年人POCD中的脑结构、功能及代谢变化以及探讨其发病的神经机制方面的研究日益增多。结合多模态磁共振成像技术,能同时从细微结构、功能及代谢层面对疾病进行研究,为POCD的发病机制提供新的见解,为早期诊断治疗提供新的思路。     

MRI在椎间孔镜腰椎间盘切除术治疗腰椎间盘突出症疗效评价中的应用

目的 探讨MRI在椎间孔镜腰椎间盘切除术治疗腰椎间盘突出症疗效评价中的应用价值。方法 回顾性研究。纳入2018年2月—2020年9月北京积水潭医院收治的500例腰椎间盘突出症患者的临床资料。其中男343例,女157例;年龄25~70（50.6±10.4）岁;均为单节段椎间盘突出,L_4/5273例、L₅/S₁227例。患者均行椎间孔镜术治疗。分别于手术前和手术后1、6个月行MR检查。观察指标：（1）评估手术疗效,比较术前和术后1、6个月患者的疼痛视觉模拟评分法（VAS）评分、日本骨科协会（JOA）评分;（2）测量术前和术后不同时间的椎间盘还纳值、硬膜外压痕纵轴值;（3）观察术前和术后不同时间椎间孔、侧隐窝的狭窄发生率,计算手术后不同时间患者椎间隙高度率的变化;（4）分析术后1个月硬膜外压痕纵轴值与患者疼痛VAS评分、JOA评分的相关性。结果 500例患者均顺利完成手术,术后随访1~6个月。患者术后症状均得到缓解。（1）患者术后1、6个月的VAS评分分别为（4.81±0.94）和（2.50±0.65）分,均低于手术前的（7.14±1.48）分;JOA评分分别为（20.64±3.26）和（27.03±2.45）分,均高于术前的（16.06±2.31）分,差异均有统计学意义（F=4.62、P=0.010;F=4.15、P=0.016）。（2）患者术后1、6个月的硬膜外压痕纵轴值分别为（6.37±2.47）、（6.37±2.65）mm,均低于术前的（8.45±3.21）mm,差异有统计学意义（F=92.34,P<0.001）;术后1、6个月的椎间盘还纳值分别为（5.25±2.06）、（5.30±2.34）mm,差异无统计学意义（t=0.36,P=0.720）。（3）术后1、6个月患者的椎间孔狭窄发生率分别为11.2%（56/500）、3%（15/500）,侧隐窝狭窄发生率分别为6.2%（31/500）、1%（5/500）,均低于术前的48.2%（241/500）和20.4%（102/500）,差异均有统计学意义（χ²=352.01、120.71,P值均<0.001）。术后1、6个月患者的椎间隙高度比较,差异无统计学意义（t=1.57、P=0.116）。（4）术后1个月硬膜外压痕纵轴值与患者VAS评分呈正相关（r=0.73,P=0.015）,与JOA评分呈负相关（r=-0.68,P=0.023）。结论 MRI可作为评估椎间孔镜治疗腰椎间盘突出症疗效的有效影像学方式。     

基于脑电的多模态神经功能成像新技术研究进展

神经功能成像能够实现活体脑结构与功能变化的无创(微创)检测。鉴于头皮脑电具有高时间分辨、便于操作、能直接反映大脑神经生理活动等优点,近年已逐步整合形成脑电-功能磁共振成像(EEG-fMRI)、脑电-近红外光谱(EEG-NIRS)、脑电-经颅聚焦超声(EEG-tFUS)等兼具高时空分辨优势的多模态神经功能成像新技术。从技术原理、技术特征及其在神经功能研究中的最新进展等方面,综述3种新模式的研究现状,论述存在问题与发展趋势,突出多模态神经功能成像新技术在促进脑科学发展中的意义。     

基于定量磁化率成像的脑发育及老化研究进展

铁元素和髓鞘的变化间接反映了大脑结构与功能的改变,并与多种神经退行性疾病相关。在脑发育及老化过程中,铁元素沉积和髓鞘形成与脱落的过程会引起脑组织磁化率数值的改变。定量磁化率成像（QuantitativeSusceptibility Mapping,QSM）是一种基于梯度回波（Gradient Recalled Echo,GRE）序列对磁化率进行定量的磁共振成像手段,可定量脑灰质中铁元素的沉积和脑白质中髓鞘的含量。有研究表明,可以基于QSM图像用指数和泊松函数拟合脑发育过程中铁元素与髓鞘的发展轨迹,得到与组织学等其他定量手段相似的结论。在此基础上,研究人员构建了基于QSM图像的全年龄脑图谱,为研究铁元素和髓鞘在脑老化及神经退行性疾病中的作用提供了基础。该文介绍了QSM成像原理及其在脑发育及老化定量研究中的最新进展。     

多模态MRI技术在激素性股骨头坏死微循环及脂肪含量病理机制研究中的应用

目的利用多模态MRI技术检测塌陷前期激素性股骨头坏死(SIONFH)患者的股骨头骨组织微循环障碍及脂肪化的情况,并探讨二者与SIONFH疾病发展的相关性。 方法纳入在广州中医药大学第一附属医院骨科确诊的SIONFH塌陷前期患者(即ARCO I期～Ⅲ期早期),运用多模态MRI技术[包括功能性磁共振非对称回波的最小二乘估算法迭代水脂分离序列(IDEAL－IQ)、体素内不相干运动磁共振扩散加权成像(IVIM-DWI)、T₁WI和T₂WI/fs]进行诊断研究。具体流程包括在采用T₁WI和T₂WI/fs实现原发灶结构定位的基础上,运用IVIM-DWI和IDEAL-IQ分别测量不同区域(坏死区、硬化区、正常区)的局部微循环(f)和脂肪含量(FF)。重点分析股骨头骨组织微循环障碍及组织脂肪化情况与ARCO分期的相关性,同时对2种病理机制之间相关性进行探讨研究。数据比较采用单因素方差分析、LSD-t检验、Pearson相关性分析。 结果SIONFH不同区域的局部微循环和脂肪含量比较,差异均有统计学意义(P值均小于0.05)。其中,在IDEAL-IQ序列中,坏死区FF值最高,硬化区FF值最低。在IVIM-DWI中,坏死区f值最低,硬化区其次,正常区最高。部微循环和脂肪含量呈负相关(r＝－0.37,P值均小于0.05)。ARCO Ⅲ期早期的f值最小,而FF值最小(P值均小于0.05),并且FF值与ARCO分期呈正相关(r＝0.72,P值均小于0.01),但f值与ARCO分期之间无明显相关性。 结论多模态MRI技术(IDEAL-IQ、IVIM-DWI、T₁WI和T₂WI/fs)定量测量得出,SIONFH在塌陷前期中局部微循环进行性障碍和组织脂肪化增加会关联性出现,并随ARCO分期的进展而逐步加重。     

实时功能性磁共振成像神经反馈的研究进展

神经反馈是一种自我调节技术,可以为个体特定的脑活动和关联行为提供反馈。实时功能性磁共振成像神经反馈(rtfMRI-nf)作为一种新型的神经反馈技术,要求参与者在训练中通过改变血氧水平依赖信号指数,以调节大脑活动。近期rtfMRI-nf在数据采集和分析方面已取得重大进展,开始出现两种新的rtfMRI-nf技术,即解码神经反馈和基于功能连接的神经反馈。介绍这两种新的rtfMRI-nf技术,总结其在内隐方案、多变量分析和连接性分析等关键方法领域的进展。综述两种rtfMRI-nf技术在知觉学习、元认知等基础研究领域以及恐惧消除、抑郁症、孤独症谱系障碍和尼古丁成瘾等临床研究领域的现状,最后讨论目前这两种rtfMRI-nf技术潜在的“一对多”关系和维度诅咒两大问题,并提出解决对策。     

新生儿窒息史对儿童神经心理发育五项功能的影响

目的：分析有新生儿窒息史儿童五项神经心理发育测查结果，了解新生儿窒息对小儿神经心理发育的影响。方法：对有新生儿窒息史儿童98例分别于6月、12月、24月进行“小儿五项神经心理发育测查”，同时选择50例无新生儿窒息史、无其它重大疾病史儿童于相同月龄进行相同测量作对照，计算测得月龄与实际月龄的相差百分比平均值作标准化对比分析。结果：轻度窒息组57例与对照组无显著性差异，重度窒息组与对照组有显著性差异。结论：新生儿重度窒息对小儿五项神经心理发育有显著性影响。     

咀嚼时局部脑活动的功能性核磁共振成像

目的：应用功能性核磁共振成像（fMRI）探测人吸嚼时的大脑功能活动。方法：要求人在无任何其它躯体活动条件下咀嚼肌以10s运动20s休息的频率进行。选用8例成人冠状切面和横轴面的头部磁共振片,观察脑功能活动情况。结果：①在咀嚼时脑的广泛区域是激活的;②在相对应的咀嚼活动中有优势半球的激活区;③第I躯体感觉区激活的方式远较第I躯体运动区多样化;④在额叶中4例年轻观察对象出现了广泛的神经元激活区,但在老年人很少出现这样的激活区。结论：咀嚼活动除了它本身的功能运动外,在维持脑的活动方面具有重要的作用。同时也说明fMRI在研究活体人脑功能活动方面是一个相当有效的方法。     

A review on brain structures segmentation in magnetic resonance imaging

Background and objectivesAutomatic brain structures segmentation in magnetic resonance images has been widely investigated in recent years with the goal of helping diagnosis and patient follow-up in different brain diseases. Here, we present a review of the state-of-the-art of automatic methods available in the literature ranging from structure specific segmentation methods to whole brain parcellation approaches.MethodsWe divide first the algorithms according to their target structures and then we propose a general classification based on their segmentation strategy, which includes atlas-based, learning-based, deformable, region-based and hybrid methods. We further discuss each category's strengths and weaknesses and analyze its performance in segmenting different brain structures providing a qualitative and quantitative comparison.ResultsWe compare the results of the analyzed works for the following brain structures: hippocampus, thalamus, caudate nucleus, putamen, pallidum, amygdala, accumbens, lateral ventricles, and brainstem. The structures on which more works have focused on are the hippocampus and the caudate nucleus. In general, the accumbens (0.69 mean DSC) is the most difficult structure to segment whereas the structures that seem to get the best results are the brainstem, closely followed by the thalamus and the putamen with 0.88, 0.87 and 0.86 mean DSC, respectively. Atlas-based approaches achieve good results when segmenting the hippocampus (DSC between 0.75 and 0.90), thalamus (0.88–0.92) and lateral ventricles (0.83–0.93), while deformable methods perform good for caudate nucleus (0.84–0.91) and putamen segmentation (0.86–0.89).ConclusionsThere is not yet a single automatic segmentation approach that can emerge as a standard for the clinical practice, providing accurate brain structures segmentation. Future trends need to focus on combining multi-atlas methods with learning-based or deformable approaches. Employing atlases to provide spatial robustness and modeling the structures appearance with supervised classifiers or Active Appearance Models could lead to improved segmentation results.     

儿童抗髓鞘少突胶质细胞糖蛋白IgG相关疾病的MRI征象分析

目的 探讨儿童抗髓鞘少突胶质细胞糖蛋白IgG相关疾病（MOGAD）的MRI特征。方法 病例系列报告。纳入2018年1月—2021年12月聊城市人民医院确诊MOGAD的10例患儿,其中男6例、女4例,年龄2~9（5.9±2.4）岁。10例患儿治疗前行颅脑MR常规扫描,9例行全脊柱MR常规扫描,4例行眼眶MR常规扫描。观察指标：（1）记录MRI对MOGAD颅脑、脊髓和视神经病变的检出情况;（2）总结颅脑MOGAD病变分布位置、形态及信号特点;（3）观察脊髓MOGAD病变部位、脊髓有无肿胀,统计长节段脊髓MOGAD病变的患儿数量;（4）观察视神经病变部位、视神经有无肿胀;（5）将患儿末次随访时复查MRI与治疗前进行对比,观察病变转归情况。结果 治疗前MRI显示：（1）颅脑病变10例,脊髓病变5例,视神经病变2例。（2）10例MOGAD颅脑病变均为多发,9例双侧、1例单侧。4例仅累及幕上,1例仅累及幕下,5例同时累及幕上和幕下。幕上病变位于皮层下白质7例,脑室周围白质7例,丘脑5例,基底节区4例,胼胝体2例,单侧皮质1例;幕下病变位于桥脑6例,同时累及小脑4例、中脑2例。病变均为非对称性。MOGAD病变形态均表现为无定形斑片状、斑点状,其中2例同时出现斑块样改变;2例病变DWI序列显示弥散受限。（3）MOGAD脊髓病变5例,均为单发、累及胸段脊髓的长节段脊髓病变,其中4例同时累及颈段脊髓,未发现腰段脊髓受累;2例出现脊髓肿胀。（4）MOGAD视神经病变2例,均为双侧,其中1例视神经全程受累、1例视神经前部受累,视交叉及视束均无受累。2例视神经均无肿胀。（5）10例患儿经治疗后均好转出院,出院后随访8~29（12.9±5.8）个月。随访期间患儿定期复查MRI,均未见复发。末次随访MRI显示,2例患儿颅脑病变完全消失,1例脊髓病变完全消失,其余7例患儿颅脑、脊髓或视神经MOGAD病变范围均减小或病灶数均减少。结论 儿童MOGAD中,颅脑病变最常见,其次为脊髓和视神经;不同部位的MOGAD MRI表现具有一定特征性,认识这些影像学特征,可以提高临床医生诊断儿童MOGAD的准确率,为早期治疗提供重要参考。     

New evidence from magnetic resonance imaging of brain changes after climbs at extreme altitude

The aim of the present study was to look for anatomical changes in climbers' brains, using magnetic resonance imaging (MRI), after extremely high-altitude climbs and to relate them to possible associated risk factors. Clinical history, neurological examinations and MRI were carried out on a group of nine climbers before and after climbing to over 7500 m without the use of supplementary oxygen. None of the subjects showed any neurological dysfunctions. In five climbers MRI abnormalities (high signal areas, cortical atrophy) were observed before the expedition. After the descent, two of them showed new high intensity signal areas recorded by MRI. Both subjects suffered severe neurological symptoms during the climb. The present study suggested that the brain changes observed by MRI could be related to the severity of clinical events at high altitude. However, we do not know the exact meaning of such MRI findings or the reason for their location, predominantly in posterior regions of the brain. The new evidence that a high percentage of climbers show MRI brain abnormalities, and especially the appearance of changes after the ascent, reinforces the possibility of a potential neurological risk in high-altitude climbing.     

成人与儿童髓母细胞瘤的MRI特征分析

目的 分析成人与儿童髓母细胞瘤的MRI表现,提高对髓母细胞瘤的认识。方法 回顾性分析2009年1月—2017年12月广东省农垦中心医院经手术病理证实的髓母细胞瘤36例的影像学资料。将其分为两组:儿童组(＜18岁)25例,成人组(≥18岁)11例。36例患者术前行MRI平扫及增强扫描,观察并对比分析两组患者肿瘤的发生部位、瘤体最大径线、边界、囊变、实性部分强化程度、瘤周水肿、梗阻性脑积水、室管膜种植转移等影像学特征。结果 36例髓母细胞瘤均发生于幕下,儿童常见于小脑蚓部(21/25),成人病灶多位于小脑半球(9/11),差异有统计学意义(P=0.000)。儿童肿瘤最大径为(4.50±0.58) cm,其中17例肿瘤最大径超过4 cm;成年人瘤体最大径为(5.24±1.36) cm,其中8例肿瘤最大径超过4 cm;两者比较差异无统计学意义(Z=-0.895, P＞0.05)。成人组和儿童组囊变分别有16例和11例,瘤周水肿分别有4例和7例,差异均有统计学意义(P=0.034、0.008);而边界、梗阻性脑积水及室管膜种植转移方面组间差异均无统计学意义(P值均＞0.05)。36例患者髓母细胞瘤实性部分均表现为T₂WI及T₂WI-FLAIR稍高信号,T₁WI等偏低信号。12例做了弥散加权成像检查(5例儿童、7例成人),瘤体实性部分均表现为弥散受限;增强后,两组肿瘤实性区域均表现为轻度至中度强化。结论 儿童髓母细胞瘤好发于小脑蚓部,成人以小脑半球多见;儿童肿瘤囊变及瘤周水肿相对于成年人少。儿童与成人髓母细胞瘤均常表现为边界清楚肿块,实性区域轻度至中度强化,易发生梗阻性脑积水,可发生室管膜种植转移。     

Factors affecting perceived tumor volumes in magnetic resonance imaging

Irregularly structured brain tumors, such as glioblastomas, challenge attempts to visualize and quantify their three-dimensional structure. Magnetic resonance imaging (MRI) represents one tool for attempting to noninvasively track tumor size. MR images demonstrate widely varying perceived tumor margins. In addition, adjunct therapies, such as the administration of steroids, greatly affect the volumes perceived in images formed by certain pulse sequences. In this study tumors were grown in 15 dogs and the tumor size tracked for a period of time. The dogs were placed on dexamethasone for a week and another series of scans was obtained. No other therapies were provided. The data for visualized tumor size are provided for T₁, T₂, and proton density. Weighted images are provided and the relationships between the scans are discussed.     

Functional magnetic resonance imaging of brain activity during chewing and occlusion by natural teeth and occlusal splints

Brain imaging based on functional magnetic resonance (fMRI) is a useful tool for examination of neuronal networks and cerebral structures subserving visiospatial function. The purpose of this study was to compare the brain activity during chewing and occlusal function in centric occlusion on natural teeth or on occlusal splints. Four tasks were performed by 13 healthy, fully dentate subjects (21-32 years old, 6 female and 7 male): occlusal tap-tap movements in centric occlusion by natural teeth, after application of a maxillary occlusal splint and chewing movements on left and right sided rubberdam strips. In order to reveal which areas of the brain were more strongly activated, conjunction analyses between the different tasks were performed for each subject and for the average values of brain signal activity of all subjects. Whilst several known foci of activity were subtracted, differences of significant activity rested in areas of the sensorimotor cortex. Mainly ipsitaterality of hemispheres concerned the left and right sided chewing, whereas the conjunction between tap-tap movements on natural teeth and splint occlusion indicated only one weak, but significant activation foci. The study confirms fMRT as one of the most useful developing methods to clear up neuro-cortical effectiveness of occlusion and occlusal therapy.     

磁共振扩散张量成像在评价儿童脑内部分皮质脊髓束发育中的应用

目的 应用磁共振扩散成像技术探讨儿童皮质脊髓束年龄和性别差异及其变化规律。 方法 90例无中枢神经系统症状及体征且颅脑磁共振检查正常的儿童（年龄5d～18岁）。按年龄分为5组: 婴儿组（组1,≤1岁）,幼儿组（组2,＞1～3岁）,学龄前组（组3,＞3～6岁）,学龄组（组4,＞6～12岁）,青春发育期组（组5,＞12～18岁）。每个年龄组内再按性别分为男、女2组。各组儿童分别行头部扩散张量成像, 根据感兴趣法选取皮质脊髓束感兴趣区并重建,测量重建的皮质脊髓束的扩散张量参数并进行统计学分析。 结果 各年龄组的表观扩散系数(ADC)值、分数各向异性(FA)值、纤维示踪平均长度、体积以及示踪的纤维束数量不完全相同（P<0.01）;组间的两两比较间发现,1组与2组间ADC值、FA值及示踪纤维平均长度差异具有统计学意义;2组与3组间FA值差异具有统计学意义;3组与4组间ADC值、FA值、示踪纤维平均长度、纤维束数目及体积差异均具有统计学意义。ADC值与年龄间呈负相关,余参数与年龄间呈正相关。结论 儿童皮质脊髓束发育具有阶段性,且具有阶段性特征;磁共振扩散张量技术可用于观测儿童皮质脊髓束,评价其发育状况。     

In utero eyeball development study by magnetic resonance imaging

The aim of this study was to measure fetal ocular development and to determine a growth curve by means of measurements in utero. Fetal ocular development was recorded by analysis of the results of magnetic resonance imaging (MRI). An anatomic study allowed definition of the best contrasted MRI sequences for calculation of the ocular surface. Biometric analysis of the values of the ocular surface in the neuro-ocular plane in 35 fetuses allowed establishment of a linear model of ocular growth curve in utero. Evaluation of ocular development may allow the detection and confirmation of malformational ocular anomalies such as microphthalmia.     

Functional magnetic resonance imaging of the human brain: data acquisition and analysis

It is now feasible to create spatial maps of activity in the human brain completely non-invasively using magnetic resonance imaging. Magnetic resonance imaging (MRI) images in which the spin magnetization is refocussed by gradient switching are sensitive to local changes in magnetic susceptibility, which can occur when the oxygenation state of blood changes. Cortical neural activity causes increases in blood flow, which usually result in changes in blood oxygenation. Hence changes of image intensity can be observed, given rise to the so-called Blood Oxygenation Level Dependent (BOLD) contrast technique. Use of echo-planar imaging methods (EPI) allows the monitoring over the entire brain of such changes in real time. A temporal resolution of 1–3 s, and a spatial resolution of 2 mm in-plane, can thus be obtained. Generally in a brain mapping experiment hundred of brain image volumes are acquired at repeat times of 1–6 s, while brain tasks are performed. The data are transformed into statistical maps of image difference, using the technique known as statistical parametric mapping (SPM). This method, based on robust multilinear regression techniques, has become the method of reference for analysis of positron emission tomography (PET) image data. The special characteristics of functional MRI data require some modification of SPM algorithms and strategies, and the MRI data must be gaussianized in time and space to conform to the assumptions of the statistics of Gaussian random fields. The steps of analysis comprise: removal of head movement effects, spatial smoothing, and statistical interference, which includes temporal smoothing and removal by fitting of temporal variations slower than the experimental paradigm. By these means, activation maps can be generated with great flexibility and statistical power, giving probability estimates for activated brain regions based on intensity or spatial extent, or both combined. Recent studies have shown that patterns of activation obtained in human brain for a given stimulus are independent of the order and spatial orientation with which MRI images are acquired, and hence that inflow effects are not important for EPI data with a TR much longer than T1.