基于血氧水平依赖信号fMRI的轻微型肝性脑病研究进展

【摘要】轻微型肝性脑病（MHE）是肝性脑病（HE）的早期阶段,不但降低了患者的生活质量,甚至与跌倒发生率和死亡率增加有关。血氧水平依赖功能磁共振成像（BOLD-fMRI）可以反映脑区间脑激活的差异和功能网络连接变化,有助于无创性研究MHE的脑灌注状态及神经重塑,并对疾病进行跟踪和预测。本文就BOLD-fMRI在MHE中的研究进展进行综述。     

BOLD-fMRI在视觉研究中的应用

BOLD-fMRI是利用磁共振成像技术探测大脑在不同刺激条件下,不同脑功能区神经活动相关生理变化的实验方法.它可以无创、直观地反映活体大脑功能,是研究脑功能相关视觉问题的一项新技术.对BOLD-fMRI的基本原理、技术特点及其在视觉研究中的应用做一综述.     

MRI新技术在PVL患儿脑性视觉损伤中的应用

MRI新技术的发展为神经系统疾病的诊断提供了新方法,其中BOLD-fMRI和DTI可以分别对皮质功能及白质纤维结构进行研究,本文旨在介绍BOLD-fMRI和DTI在脑室旁白质软化症患儿脑性视觉损伤早期诊断方面的应用价值和意义.     

轻微型肝性脑病患者空间工作记忆的fMRI研究

目的采用行为学和血氧依赖水平功能磁共振成像(BOLD-fMRI)方法探讨轻微型肝性脑病患者空间工作记忆损伤的脑神经机制。资料与方法从符合肝硬化诊断的40例患者中筛选出轻微型肝性脑病患者12例与正常对照者12名进行n-back任务负载下的脑fMRI扫描,以AFNI软件对fMRI数据进行定位定量分析。结果 (1)轻微型肝性脑病患者在三种任务负载下的正确率明显低于正常对照组,平均反应时间亦明显延长,两组差异具有显著性(P<0.001)。(2)fMRI结果发现,在n-back任务负载下,两组被试共同激活的脑区包括双侧前额叶(PFC),前运动区(PreMA),辅助运动区(SMA)及双侧顶叶(PA),且以右侧大脑半球优势为主。对这些感兴趣区进行定量分析发现,正常对照组这些脑区均表现出了和记忆负载相关的负载效应,而轻微型肝性脑病组只在双侧前运动区及双侧顶叶发现了这种负载效应。组间比较发现,在n-back任务负载下轻微型肝性脑病患者大部分工作记忆相关脑区的激活强度均比正常对照组小。结论轻微型肝性脑病患者存在空间工作记忆损伤,双侧前额叶、前运动区、辅助运动区及双侧顶叶功能减弱是空间工作记忆损伤的机制之一。     

肝性脑病患者基于静息态fMRI的全脑功能连接研究

目的：采用静息态功能磁共振成像研究肝性脑病患者全脑功能网络连接改变机制。方法：采集13例慢性肝硬化肝性脑病患者和17例健康志愿者的静息态血氧依赖水平功能磁共振成像（BOLD-fMRI）数据,采用自动化解剖标记（AAL）模板计算90个脑区的两两间功能连接情况。结果：肝性脑病患者有15条功能连接出现异常,其中12条功能连接显著下降（P〈0．01）,3条显著升高（P〈0．01）,且其中9条异常连接出现在皮层下区域与皮层区域之间,且改变的功能连接与神经心理学测试存在一定相关性。结论：肝性脑病患者的基底节一丘脑一皮层回路受损,功能连接的改变与肝性脑病患者认知功能的改变有关。     

肝性脑病神经影像学研究新进展

肝性脑病是由各种严重肝脏疾病引起的以代谢紊乱为基础的中枢神经系统功能失调综合征,其发生率居高不下,已成为我国一个重大公共卫生问题。近年来,神经影像学发展迅速,特别是功能磁共振成像及正电子发射型体层摄影术,从结构、功能、代谢等多方面对肝性脑病进行早期诊断和随访观察。本文就肝性脑病神经影像学研究及进展作一综述。     

基于血氧水平依赖fMRI的胎儿脑功能研究进展

应用血氧水平依赖功能成像(BOLD-fMRI)可以分析胎儿大脑的神经活动信号,以获得胎儿脑功能发育的信息。BOLD-fMRI可以检测并有助于理解胎儿脑功能发育,目前已有重要研究结果,但仍需将胎儿脑功能参数及出生后神经行为表现联系起来,以提高其预测及应用价值。大规模纵向研究、融合多模态数据、结合人工智能算法评估胎儿大脑发育有望成为未来研究热点。本综述中,笔者总结了胎儿BOLD-fMRI任务态研究、静息态功能连接及功能网络、胎儿BOLD-fMRI研究所面临的挑战。     

手运动及感觉BOLD-fMRI的研究进展

近年来随着血氧水平依赖功能性磁共振成像(BOLD-fMRI)技术在脑功能研究方面的广泛应用,为脑功能研究开辟了新领域.手运动及感觉BOLD-fMRI可对相应脑功能区进行定位,突破了既往解剖学和生理学研究状态,对手运动及感觉相应的脑活动有了新的发现和深入的理解,并在临床中得到了初步应用.     

汉语分类命名功能磁共振初步研究

目的 设计一种适合汉语分类命名的刺激任务,探索汉语词义分类命名(CF)的脑功能区分布特征.方法 对19名健康汉语志愿者进行CF语言任务刺激,同时采集血氧水平依赖性功能磁共振成像(BOLD-fMRI)数据,通过SPM8软件分析获取CF任务相关脑功能激活区位置、大小及强度.结果 任务态BOLD-fMRI图像显示汉语CF刺激在额、颞叶存在特定的激活区,主要分布于左额上回(BA8区)、右额上回(BA6区);负激活区位于右额上回(BA9区)、左颞中回(BA20区)及梭状回(BA37区).结论 利用该语言任务能有效激活汉语CF相关的脑功能区;同时BOLD-fMRI可以准确定位激活区,量化激活区的大小及激活强度,患者依从性好.此方法可适用于汉语分类联想相关脑功能疾病的研究.     

手运动及感觉BOLD-fMRI的研究进展

近年来随着血氧水平依赖功能性磁共振成像(BOLD-fMRI)技术在脑功能研究方面的广泛应用，为脑功能研究开辟了新领域。手运动及感觉BOLD-fMRI可对相应脑功能区进行定位，突破了既往解剖学和生理学研究状态，对手运动及感觉相应的脑活动有了新的发现和深入的理解，并在临床中得到了初步应用。     

A monitoring,feedback, and triggering system for reproducible breath-hold MR imaging

A technique is described that provides improved reproducibility of breath-holding for MR image acquisition by monitoring the superior-inferior (S/I) position of the diaphragm. The method incorporates detection of the level of inspiration using an MR signal, rapid display to the patient of diaphragm position to enable breath-hold adjustment, and triggering of image data acquisition once appropriate position is attained. The response time of the system is short, approximately 10 ms. Studies in six volunteers using this method demonstrate a considerable decrease in the S/I range of diaphragm position over 10 consecutive periods of suspended respiration. The mean range is 1.3 mm with the system, while it is 8.3 mm without using it is expected that this method will be of assistance in many abdominal and cardiothoracic studies that use breath-hold techniques.     

DSA功能性参数的提取与利用

本文介绍了在临床实际中利用功能性参数，对冠状动脉ＤＳＡ心肌血流灌注成像、冠状动脉血流量测定、左心室功能测定、肺动脉高压程度的评价等项目研究结果。重点讨论了提取ＤＳＡ功能性参数的一般方法，认为功能性参数在现代影像诊断学中的作用是对疾病做出程度、定量、动态及功能诊断。     

Fast imaging of phosphocreatine in the normal human myocardium using a three-dimensional RARE pulse sequence at 4 Tesla

PURPOSE: To investigate the use of a three-dimensional rapid acquisition with relaxation enhancement (RARE) pulse sequence for direct acquisition of phosphocreatine (PCr) images of the human myocardium. MATERIALS AND METHODS: A short elliptical birdcage radiofrequency (RF) body coil was constructed to produce a uniform flip angle throughout the chest cavity. In vivo images using a spectrally-selective RARE sequence with a spatial resolution of 1.2 cm x 1.2 cm x 2.5 cm (4 cm(3)) were acquired in nine minutes and 40 seconds. RESULTS: Scans of phantoms demonstrated excellent spectral selectivity. The signal-to-noise ratio in the myocardium ranged from 12.6 in the anterior wall to 5.3 in the mid septum. CONCLUSION: This study demonstrates that PCr data can be acquired using a three-dimensional RARE sequence with greater spatial and temporal resolution than spectroscopic techniques.     

RARE spiral T2-weighted imaging

Spiral imaging has a number of advantages for fast imaging, including an efficient use of gradient hardware. However, inhomogeneity-induced blurring is proportional to the data acquisition duration. In this paper, we combine spiral data acquisition with a RARE echo train. This allows a long data acquisition interval per excitation, while limiting the effects of inhomogeneity. Long spiral k-space trajectories are partitioned into smaller, annular ring trajectories. Each of these annular rings is acquired during echoes of a RARE echo train. The RARE refocusing RF pulses periodically refocus off-resonant spins while building a long data acquisition. We describe both T₂-weighted single excitation and interleaved RARE spiral sequences. A typical sequence acquires a complete data set in three excitations (32 cm FOV, 192 × 192 matrix). At a TR = 2000 ms, we can average two acquisitions in an easy breath-hold interval. A multifrequency reconstruction algorithm minimizes the effects of any off-resonant spins. Though this algorithm needs a field map, we demonstrate how signal averaging can provide the necessary phase data while increasing SNR. The field map creation causes no scan time penalty and essentially no loss in SNR efficiency. Multiple slice, 14-s breath-hold scans acquired on a conventional gradient system demonstrate the performance.     

Echo-Time-Encoded Burst Imaging (EBI): A Novel Technique for Spectroscopic Imaging

A new technique for rapid spectroscopic imaging is presented. The proposed experiment enables a complete mapping of the two-dimensional reciprocal space k_x, k_o, and thus the acquisition of a 1D spectroscopic image in a single scan. The properties of the pulse sequence, based on the use of a burst of low flip angle pulses, are analyzed in the framework of linear response theory, and it is shown that chemical shift information may be introduced into the spatially encoded echoes. First experimental results are presented demonstrating that 32 x 32 proton spectroscopic images may be acquired within less than 1 min with a conventional imaging system.     

Simultaneous multislice (SMS) imaging techniques

Simultaneous multislice imaging (SMS) using parallel image reconstruction has rapidly advanced to become a major imaging technique. The primary benefit is an acceleration in data acquisition that is equal to the number of simultaneously excited slices. Unlike in‐plane parallel imaging this can have only a marginal intrinsic signal‐to‐noise ratio penalty, and the full acceleration is attainable at fixed echo time, as is required for many echo planar imaging applications. Furthermore, for some implementations SMS techniques can reduce radiofrequency (RF) power deposition. In this review the current state of the art of SMS imaging is presented. In the Introduction, a historical overview is given of the history of SMS excitation in MRI. The following section on RF pulses gives both the theoretical background and practical application. The section on encoding and reconstruction shows how the collapsed multislice images can be disentangled by means of the transmitter pulse phase, gradient pulses, and most importantly using multichannel receiver coils. The relationship between classic parallel imaging techniques and SMS reconstruction methods is explored. The subsequent section describes the practical implementation, including the acquisition of reference data, and slice cross‐talk. Published applications of SMS imaging are then reviewed, and the article concludes with an outlook and perspective of SMS imaging. Magn Reson Med 75:63–81, 2016. © 2015 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.     

Current Status of Optical Imaging for Evaluating Lymph Nodes and Lymphatic System

Optical imaging techniques use visual and near infrared rays. Despite their considerably poor penetration depth, they are widely used due to their safe and intuitive properties and potential for intraoperative usage. Optical imaging techniques have been actively investigated for clinical imaging of lymph nodes and lymphatic system. This article summarizes a variety of optical tracers and techniques used for lymph node and lymphatic imaging, and reviews their clinical applications. Emerging new optical imaging techniques and their potential are also described.     

Dynamic bioluminescence imaging for quantitative tumour burden assessment using IV or IP administration of <Emphasis Type="SmallCaps">d</Emphasis>-luciferin: effect on intensity,time kinetics and repeatability of photon emission

Introduction In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumour imaging. d-luciferin can be administrated intraperitonealy or intravenously. This will influence its availability and, therefore, the bioluminescent signal. The aim of this study is to compare the repeatability of BLI measurement after IV versus IP administration of d-luciferin and assess the correlation between photon emission and histological cell count both in vitro and in vivo. Materials and methods Fluc-positive R1M cells were subcutaneously inoculated in nu/nu mice. Dynamic BLI was performed after IV or IP administration of d-luciferin. Maximal photon emission (PE_max) was calculated. For repeatability assessment, every acquisition was repeated after 4 h and analysed using Bland–Altman method. A second group of animals was serially imaged, alternating IV and IP administration up to 21 days. When mice were killed, PE_max after IV administration was correlated with histological cell number. Results The coefficients of repeatability were 80.2% (IV) versus 95.0% (IP). Time-to-peak is shorter, and its variance lower for IV (p < 0.0001). PE_max was 5.6 times higher for IV. A trend was observed towards lower photon emission per cell in larger tumours. Conclusion IV administration offers better repeatability and better sensitivity when compared to IP. In larger tumours, multiple factors may contribute to underestimation of tumour burden. It might, therefore, be beneficial to test novel therapeutics on small tumours to enable an accurate evaluation of tumour burden. Marleen Keyaerts is a Ph. D. fellow of the Research Foundation—Flanders (Belgium; FWO).     

Molecular imaging programs in the United States: results of a national survey

RATIONALE AND OBJECTIVES: We sought to identify and describe the characteristics of molecular imaging (MI) programs in the United States and to determine the factors considered critical for their future. MATERIALS AND METHODS: In a cross-sectional study, a validated survey was sent to members of the Society of Chairmen in Academic Radiology Departments (SCARD) in the United States, and 26 variables were studied. RESULTS: The response rate was 40.3%; 67.9% of the departments surveyed have an MI program. The main focus of 47.4% of departments is oncology. The number of radiologists working for the department was the only variable found to be significantly positively correlated with (1) number of researchers in the MI program, (2) number of MI modalities available, (3) total number of grants, and (4) having ongoing MI clinical trials. These four variables plus the number of federal grants and the space used by MI programs were independent of the geographical region, hospital size (number of beds), and department size (number of radiological examinations per year). All the MI programs received grants during 2005. Only 16.1% have no alliances with industry. Among all the departments, 82% identified staff training and recruitment as the keys for success; 78.57% considered oncology the most important future application of MI and cancer management the hospital service most affected by MI. CONCLUSION: MI programs are starting to be more widespread throughout the United States, and the trend is for more academic radiology departments to become engaged in MI activities; their development is independent of department characteristics. Radiology departments strongly agreed about the key components for success of MI initiatives and the areas that will be most affected by MI applications.