磁共振扩散加权成像在超急性期脑梗死诊断中的应用

目的 评价磁共振扩散加权成像（DWI）对超急性期脑梗死诊断的准确性。方法 对卒中样起病且发病时间在6h以内、临床高度怀疑脑梗死的21例患者进行DWI和常规MRI扫描。结果 DWI诊断脑死16例，其最终临床诊断均为急性脑梗死，DWI阴性5例，其最终临床诊断为短暂性脑缺血发作；DWI所见高信号区域的同一部位在以后的CT和（或）MRI随访中均有脑梗死病灶；DWI诊断超急性期脑梗死的敏感度和特异度均为100％，常规MRI诊断超急性期脑梗死的敏感度为25％，特异度为100％。结论 DWI对超急性期脑梗死的诊断高度准确，其敏感度明显高于常规MRI。     

低场MR弥散加权成像在超急性期脑梗死诊断中的应用

目的：评价低场MR扩散加权成像（DWI）在超急性期脑梗死（HCI）诊断中的应用价值。方法：对起病时间6h内临床拟诊脑梗死的16例患者使用0．35T磁共振仪行DWI和常规MRI扫描。结果：DWI诊断HCI12例，DWI阴性4例；常规MRI扫描3例符合脑梗死诊断，9例不符合，最终临床诊断为HCI12例。DWI所见异常高信号区在以后的CT或MR随访中均见明显梗死病灶。结论：低场DWI在HCI诊断中能得到成功运用，且诊断高度准确。能在最短时间内确定患者梗塞部位，为进一步治疗赢得时间。     

低场磁共振弥散加权成像诊断急性脑梗死的可行性

目的探讨低场磁共振弥散加权成像（DWI）在急性期脑梗死诊断中的可行性。方法对临床疑诊或确诊为脑梗死的116例患者包括11例超急性期（发病后6h内），35例急性期（发病后6-24h）及70例亚急性期（发病后2～7d）进行DWI和常规MRI检查，对超急性、急性、亚急性期的MRI表现进行分析，总结病变演变规律。结果DWI较常规MRI序列显示梗死灶更有明显优势，对超急性期脑梗死灶的敏感度为100％。急性期脑梗死灶在DWI序列上为异常高信号，且信号强度随b值升高而增强，各期脑梗死灶在DWI中异常信号强度由低逐渐增高。弥散全方向比单方向DWI成像显示病变效果好。结论低场磁共振弥散加权成像技术，通过精心调整扫描技术参数，对急性期脑梗死能作出诊断，尤其对超急性期脑梗死的诊断及治疗可提供可靠依据。     

低场MR扩散加权成像在超急性期脑梗死诊断中的应用

目的 :评价低场MR扩散加权成像 (DWI)在超急性期脑梗死 (HCI)诊断中的应用价值。方法 :对起病时间 6h内临床拟诊脑梗死的 12例患者使用 0 .2T磁共振仪行DWI和常规MRI扫描。结果 :DWI诊断HCI 8例 ,DWI阴性 4例 ;常规MRI扫描 2例符合脑梗死诊断 ,10例不符合 ,最终临床诊断为HCI 8例。DWI所见异常高信号区在以后的CT或MR随访中均见明显梗死病灶。结论 :低场DWI在HCI诊断中能得到成功运用 ,且诊断高度准确。     

磁敏感加权成像在脑梗死出血性转化的临床应用价值

目的探讨磁敏感加权成像（SWI）技术在脑梗死出血性转化的价值及其临床相关性。方法选择45例临床和影像明确的脑梗死出血性转化的患者作为研究对象,进行CT、常规MRI（T1WI、T2WI、DWI序列）和SWI序列扫描的自身对比研究,CT和MR检查的间隔不超过12h,MRI序列和SWI序列同时进行。结果45例脑梗死出血性转化的患者,SWI诊断脑出血45例,常规MRI序列诊断29例,CT诊断35例,阳性预测值分别为100％、64．4％、77．8％。结论SWI诊断脑梗死出血性转化比常规MR及CT具有更好的临床应用价值,可作为急性脑梗死及溶栓治疗后常规复查方法。     

MR DWI及ADC值在急性脑梗死诊断中的应用价值

目的评价磁共振扩散加权成像（DWI）和表观扩散系数（ADC）在急性脑梗死诊断中的临床价值。方法选取临床上拟诊为脑梗死患者186例进行常规MR扫描及DWI检查,根据发病时间分成超急性期（〈6h）、急性期（6～72h）、亚急性期（3～7d）3个组。测定各组梗死灶ADC值及健侧ADC值,并计算相对ADC（rADC）。结果超急性期、急性期、亚急性期梗死灶ADC值均低于健侧相应区域（配对t检验,P〈0．01）;超急性期、急性期及亚急性期病例之间rADC有统计学差异（单因素方差分析,F=7．663,P=0．001）。结论DWI在脑梗死超急性期、急性期、亚急性期均具有很高的敏感性,各期梗死灶rADC值有时间相关性,对脑梗死的准确分期有重要价值。     

低场磁共振扩散加权成像在超急性期脑梗死的应用

目的：评价低场磁共振的扩散加权成像（DWI）在超急性期脑梗死诊断上的应用价值。方法：用低场磁共振扩散加权成像诊断超急性期脑梗死36例,分析不同时间的影像学特点,并与常规 MRI 平扫进行比较。结果：低场磁共振DWI 能显示所有患者超急性脑梗死病灶,而有11例患者在常规 MRI 平扫上未发现异常,其中7例为发病2 h 内,4例为2～4 h。此外,DWI 还可发现发病1 h 内的脑梗死高信号灶,而且 DWI 显示的病灶范围较常规 T2 WI 显示的范围更大、信号更高。结论：颅脑低场强磁共振扩散成像可以诊断超急性期脑梗死,比 T2 WI、T2 FLAIR 平扫能更早显示病变,在发现病变、确定病变部位、病变范围具有较高的价值,可为临床早期治疗提供可靠的诊断依据。     

比较低场磁共振DWI、T_2WI、FLAIR序列在脑梗死分期诊断中的优势

目的比较低场磁共振弥散加权成像（DWI）、常规T2加权像（T2WI）及液体衰减反转恢复（FLAIR）序列对各期脑梗死的诊断优势。方法 465例脑梗死患者包括超急性期（发病后6h内）13例,急性期（发病后6～24h）175例,亚急性早期（发病后1～3d）106例,亚急性晚期（发病后4～14d）93例以及慢性期（发病后15d以上）78例,均经DWI、T2WI及FLAIR序列扫描。对上述不同成像序列诊断各期脑梗死的优势进行了对比性分析。结果 DWI对超急性期、急性期及亚急性早期脑梗死的诊断高度敏感,检出率达100%,但对亚急性晚期的检出率低于T2WI和FLAIR序列。然而,T2WI和FLAIR序列对慢性脑梗死的诊断高度敏感,检出率达100%,且能检出DWI扫描未发现的梗死灶。结论合理应用DWI、T2WI及FLAIR序列,有助于鉴别新旧脑梗死灶和进行术前分期,尤其能为选择治疗方案提供可靠依据。     

灌注成像在脑梗死中的应用

常规CT和MRI检查在急性期脑梗死（发病后6～72h）的诊断中发挥了重要作用,但对超急性期脑梗死（发病6h以内）的诊断敏感性低,而且不能提供梗死区的血液动力学和代谢改变信息[1,2]。近年来,随着设备的不断进步和新技术的发展,如脑CT灌注（CT perfusion）、磁共振弥散加权成像（MR diffu-sion-weighted imaging,DWI）、磁共振灌注加权成像（MP,perfu-sion-weighted imaging,PWI）,使得影橡学检查对脑梗死进行更早期、快速、准确的诊断,并获得相关的血液动力学参数和代谢改变信息成为可能。     

扩散加权成像对脑干中脑脚间区急性梗死的诊断价值

目的 探讨扩散加权成像(DWI)诊断中脑脚间区急性脑梗死的临床价值.方法 对49例中脑脚间区急性脑梗死和51例健康受检者(中脑脚间区在DWI上呈高信号)的常规MRI及DWI资料进行回顾性分析.由两名神经放射学专家共同进行两次评价,第一次仅对DWI和表观扩散系数(ADC)图像进行评价,第二次对常规MRI、DWI和ADC图进行综合评价.计算并比较两次诊断中脑脚间区急性脑梗死的一致性(Kappa值)以及敏感性、特异性、准确性、阳性预测值和阴性预测值.结果 与最终诊断结果比较,第一次和第二次评价的一致性分别为低度(K =0.363)和高度(K=0.940).两次诊断中脑脚间区急性脑梗死的敏感性分别为79.6％和100％(P=0.001),特异性分别为56.9％和94.1％ (P=0.000),准确性分别为68.0％和97.0％ (P=0.000),阳性预测值分别为63.9％和94.2％ (P=0.000),阴性预测值分别为74.4％和100％ (P=0.001).结论 DWI序列诊断中脑脚间区急性脑梗死需与正常扩散高信号鉴别,结合常规MRI可显著提高诊断中脑脚间区急性脑梗死的一致性、敏感性、特异性、准确性、阳性预测值和阴性预测值.     

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。     

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.     

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.     

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.     

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.     

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).     

Temporal resolution improvement in dynamic imaging

In some dynamic imaging applications, only a fraction, 1/n, of the field of view (FOV) may show considerable change during the motion cycle. A method is presented that improves the temporal resolution for a dynamic region by a factor, n, while maintaining spatial resolution at a cost of √n in signal-to-noise ratio (SNR). Temporal resolution is improved, or alternatively, total imaging time is reduced by reducing the number of phase encodes acquired for each temporal frame by 1/n. To eliminate aliasing, a representation of the signal from the static outer portion of the FOV is constructed using all the raw data. The k-space data derived from this representation is subtracted from the original data sets, and the differences correspond to the dynamic portion of the FOV. Improved resolution results are presented in phantom studies, and in vivo phase contrast quantitative flow imaging.