乳腺组织MR扩散加权成像中GRAPPA技术的应用

目的：评价在乳腺磁共振扩散加权成像（DWI）中应用全自动校准部分并行采集（GRAPPA）技术对改善图像质量及乳腺组织表观扩散系数（ADC）值测量的影响。方法：分别对28例女性乳腺MR受检者进行平面回波（EPI）序列的常规DWI和GRAPPA-DWI检查。常规DWI检查时扩散梯度因子（b）值取800s／mm^2,GRAPPA-DWI检查时b值分别取800、1000s／mm^2。比较不同参数条件下的图像质量分级、信噪比（SNR）及乳腺组织ADC值,并进行统计学分析。结果：在相同b值（b=800s／mm^2）条件下,GRAPPA—DWI组图像质量明显优于常规DWI组,乳腺组织的SNR高于常规DWI组,两组差异均有显著性意义（P〈0．01）,乳腺的平均ADC值略低于常规DWI组,但两组差异无显著性意义（P〉0．05）。在GRAPPA—DWI组中,b值为800s／mm。组图像质量略优于b值为1000s／mm。组,但二者差异无显著性意义（P〉0．05）,而b值为800s／mm。组乳腺组织的SNR高于b值为1000s／mm^2组,两组差异有显著性意义（P〈0．01）,b值为800s／mm^2时乳腺组织的ADC值略高于b值为1000s／mm^2时,差异有显著性意义（P〈0．05）。结论：GRAPPA技术的应用有助于改善乳腺DWI的图像质量,提高信噪比,并且不会影响乳腺组织ADC值的测量。     

磁共振扩散加权成像在胃肠道良、恶性病变诊断中的应用价值

目的探讨MR扩散加权成像（DWI）在胃肠道良、恶性病变诊断中的价值。资料与方法对69例胃肠道病变进行常规MR平扫和DWI,扩散敏感梯度（b值）分别为0和700s／mm^2,测量病变的表观扩散系数（ADC）值,其中29例同时续行增强扫描。结果59例恶性病变的平均ADC值为（0．96±0．11）×10^-3mm^2／s,10例良性病变的平均ADC值为（1．49±0．12）×10^-3mm^2／s,两组病变之间比较差异有统计学意义（P〈0．01）。将恶性病变ADC值95％可信区间上界1．16×100mm^2／s定位为良、恶性病变鉴别的界值,诊断敏感性为86．6％,特异性为95．8％。结论DWI有助于对胃肠道良、恶性病变的诊断和鉴别。     

MR扩散加权成像在肝癌介入治疗后随访中的图像评价

目的：探讨不同扩散敏感梯度因子（b值）MR扩散加权成像（DWI）对肝癌介入治疗后随访中图像质量的影响。方法：对20例肝癌介入治疗后患者分别进行DWI检查和MRI常规扫描（T1WI和T2WI）。每次取2个扩散敏感梯度值即b=0和／或150、350、500和800s／mm^2利用固定参数组合的自旋回波-平面回波（SE—EPI）序列进行DWI检查。在各成像序列上分别计算病灶信号-噪声比（SNR）、病灶-脏信号对比噪声比（CNR）和病灶的ADC值;与肝脏CT和DSA检查结果进行对比分析,定性评价不同b值DWI对肿瘤内部坏死组织和活组织的鉴别诊断能力。结果：病灶在T2WI、DWI150、DWI350、DWI500和DWI800的SNR分别为：（69．81±18．99）、（59．33±32．66）、（59．23±32．94）、（54．25±19．71）、（39．43士11．67）,差异有统计学意义（F＝4．43,P＝0．0024）;病灶-肝脏CNR分别为（19．11±11．33）、（17．69±9．20）、（21．38±10．10）、（19．90±13．75）和（13,24±11．02）,差异无统计学意义（F=1．70,P＝0．1556）;b＝150、350、500和800s／mm^2时病灶的ADC分别为（2．35±0．80）×10^-3、（1．95±0．59）×10^-3、（1．78±0．44）×10^-3和（1．54±0．37）×10^-3mm^2／s,差异有统计学意义（F=21．96,P=0．0001）。DWI500和DWI800病灶内部坏死和活性肿瘤组织能有效区分。结论：在肝癌介入治疗后随访检查时,选择合适的扩散梯度系数能够得到较佳的信号对比度,同时也能较准确地区分坏死组织与活性肿瘤。     

肾上腺肿瘤不同b值DWI研究

目的：研究不同b值肾上腺肿瘤扩散加权成像（DWI）的表现,比较不同b值组表观扩散系数（ADC值）之间的差异,探讨最佳b值的选择及最佳b值组良恶性肿瘤的ADC值范围及阈值。方法：对23例经手术病理及临床证实的肾上腺肿瘤患者行平扫、DWI（b值分别取0、400、800和1000s/mm^2）,分别观察不同b值肿瘤信号的差异,同时测量不同b值肿瘤的ADC值并作统计学分析。结果：①b值为0s/mm^2时,DWI肿瘤的信号和T2WI一致,b值分别为400、800和1000s/mm^2,良性肿瘤随着b值的增高,信号逐渐减低,而恶性肿瘤随着b值的增高,信号变化不明显;②3个b值组,低b值组肾上腺肿瘤的平均ADC值最大,随着b值的增大,平均ADC值逐渐减小,并有统计学意义（F=13.543,P〈0.05）;③400～0s/mm^2b值组肾上腺良恶性肿瘤ADC值之间无统计学意义（t=-2.033,P=0.054）,而800～0s/mm^2b值组及1000～0s/mm^2b值组有统计学意义（t=-2.700,P=0.013;t=-3.529,P=0.002）;④以800～0s/mm^2b值组ADC值作为研究对象进行受试者工作特性（ROC）曲线分析,诊断阈值为0.986×10^-3mm^2/s,此阈值点对肾上腺良恶性病变诊断的敏感度为80%,特异度为78%。结论：b=800～0s/mm^2为较佳选择,此时良性肿瘤的平均ADC值为（1.138±0.180）×10^-3mm^2/s,恶性肿瘤的平均ADC值为（0.916±0.218）×10^-3mm^2/s;DWI对肾上腺肿瘤性质鉴别具有价值,是对常规MR检查有益的补充。     

DWI对胰腺癌的诊断价值

目的：探讨磁共振扩散加权成像（DWI）及表观扩散系数（ADC）对胰腺癌诊断价值。方法：搜集胰腺癌患者35例,正常对照组共32例。DWI选用b值分别为50、400、700s／mm^2,分别测量胰腺癌组织、癌周胰腺组织及正常对照组的ADC值,并进行对比分析;分别测量胰腺癌组织在T2WI,DWI（b=400s／mm^2）及磁共振增强扫描图像中病灶最大直径,并进行分析。结果：3组b值所测得ADC值统计结果示胰腺癌组织与正常对照组、癌周胰腺组织之间均有统计学意义;正常对照组与癌周胰腺组织之间均无统计学意义。胰腺癌组织在T2WI,DWI（b=400s／mm^2）及动态增强图像中最大直径测量无统计学差异。结论：DWI可以较清楚地显示胰腺癌病灶,b值为400s／mm^2时图像效果最佳,与ADC值测定共同分析对胰腺癌病灶的检出有价值。     

不同类型正常乳腺表观扩散系数值差异的研究

目的 研究不同类型正常乳腺表观扩散系数（ADC）值的差异，探讨ADC值与组织学分型之间的关系。方法 采用单次激发平面回波（EPI）技术，扩散敏感因子（b）值分别为0、500、1000s／mm^2，对62个正常乳腺（包括42例乳腺病变患者的对侧正常乳腺及10名健康志愿者20个乳腺）进行MR扫描及MR扩散加权成像（DWI）检查，计算62个正常乳腺分别在不同b值时的ADC值。将62个正常乳腺分为3型，比较3型之间ADC值的差异及不同b值时ADC值的差异。结果 42例乳腺病变患者对侧正常乳腺的DWI及ADC图与组织切片对比，不同类型乳腺组织学结构不同，其DWI及ADC图表现亦有差异。62个正常乳腺分为致密型10个，分叶斑点型42个及退化型10个。致密型和分叶斑点型乳腺随b值降低ADC值升高，而退化型乳腺随b值降低ADC值变化不明显。b=1000—0s／mm^2时，致密型、分叶斑点型、退化型乳腺ADC值分别为（1．70±0．37）、（1．93±0．46）、（1．18±0．65）×10^-3mm^2／s，3组间比较差异有统计学意义（F=12．998，P=0．000）。不同b值时每2种类型间进行单因素方差分析，致密型和分叶斑点型之间差异无统计学意义（F=2．167，P=0．147）；致密型和退化型之间、分叶斑点型和退化型之间差异均有统计学意义（F值分别为5．593、19．128，P值分别为0．029、0．000）。结论 3型正常乳腺ADC值受乳腺组织学结构的影响，致密型和分叶斑点型乳腺ADC值受b值高低的影响。     

DWI在鉴别诊断脑脓肿和坏死、囊变脑肿瘤中的影像学价值

目的研究扩散加权成像（DWI）在鉴别脑脓肿和坏死、囊变脑肿瘤中的诊断价值。资料与方法对17例脑脓肿和23例脑肿瘤（胶质瘤和转移瘤）行常规MR和DWI检查。DWI采用b=1000s/mm^2,b=0s/mm^2时进行采集,测量感兴趣区（ROI）的表观扩散系数（ADC）值,两个独立样本间行秩和检验,与常规MR比较,计算敏感性、特异性、阳性预测值、阴性预测值。结果大部分脑脓肿在DWI上为高信号,ADC值为（0.33±0.11）×10^-3mm/s,除2例外其余脑肿瘤的坏死、囊变部分在DWI上为低信号,ADC值为（2.46±0.49）×10^-3mm/s。结论DWI在鉴别脑脓肿和坏死、囊变脑肿瘤方面是十分有意义的,比常规MR有更大的优越性。     

DWI诊断外伤性椎体压缩骨折优化b值的初步研究

目的 应用1.5T磁共振采用不同b值对骨折椎体行扩散加权成像（DWI）检查,通过数据分析优选最佳b值。方法 根据外伤时间,按T〈7天、14天≤T〈30天将患者分为二组,每组20例,共40例。所有入组病例均行DWI检查,采用单次激发自旋回波平面成像序列,b值分别取200、300、400、500、600、700、800、900、1 000s/mm^2,测量骨折椎体表观扩散系数（ADC）值并对比不同b值下椎体扩散加权成像（DWI）图像质量,应用ROC曲线分析不同b值下ADC值对不同时间段椎体压缩骨折的诊断价值。结果 40例受检者骨折椎体DWI图像,随着b值由200s/mm^2升高至1 000s/mm^2,图像信噪比逐渐降低,b值为300s/mm^2时图像对比噪声比最高;b值为200、300、400、500、600、700、800、900、1000s/mm^2时不同时间段压缩骨折ADC值的差异均有统计学意义（P〈0.01）;b值为300s/mm^2时诊断新近压缩骨折（T〈7天）价值最大,其诊断敏感度、特异度分别为86.76%、81.87%。结论 b值为300s/mm^2时,椎体DWI图像质量佳,所获得的ADC值诊断效能相对较高。     

MR扩散加权成像鉴别颅内囊性病变的价值

目的探讨MR扩散加权成像（DWI）在颅内囊性病变中的鉴别诊断价值。方法对76例经临床及手术病理证实的颅内囊性病变患者，行常规MR、DWI及增强MR检查，其中脑脓肿19例，原发性脑胶质瘤20例，小脑血管母细胞瘤4例，脑转移瘤10例，蛛网膜囊肿7例，表皮样囊肿16例。回顾性分析颅内囊性病变的DWI信号特征，定量测定囊性变区表观扩散系数（ADC）值。结果DWI上19例脑脓肿呈高信号；34例脑肿瘤患者中，除3例脑胶质瘤呈高信号、1例呈等信号，1例脑转移瘤呈高信号外，其余29例均呈低信号。各种病变ADC值分别为：脑脓肿（0．62±0．15）×10^-3 mm^2／s、脑胶质瘤（2．39±0．78）×10^-3 mm^2／s、脑血管母细胞瘤（2．68±0．40）×10^-3 mm^2／s、脑转移瘤（2．79±0．79）×10^-3 mm^2／s。脑脓肿与脑胶质瘤、脑血管母细胞瘤、脑转移瘤的囊变坏死区ADC值比较，差异均有统计学意义（P〈0．01）；脑胶质瘤与脑血管母细胞瘤、脑转移瘤的囊变坏死区ADC值比较，差异均无统计学意义（P〉0．05）。7例颅内蛛网膜囊肿的DWI呈低信号；16例表皮样囊肿DWI呈明显高信号。颅内蛛网膜囊肿和表皮样囊肿的ADC值分别为（2．96±0．36）×10^-3 mm^2／s和（0．94±0．13）×10^-3 mm^2／s，二者之间差异有统计学意义（P〈0．01）。结论DWI及ADC值对鉴别脑脓肿和囊性或坏死性脑肿瘤具有重要的价值，DWI表现为低信号的颅内囊性病变可除外脑脓肿。     

MR扩散加权成像对乳腺良恶性疾病的应用研究

目的探讨MR扩散加权成像（DWI）的技术方法及表观扩散系数（ADC）值对乳腺良、恶性疾病的诊断及鉴别诊断价值。资料与方法经病理证实的乳腺病变50例,58个病灶,其中恶性32个,良性26个。检查使用Siemens1.5T磁共振仪、专用双穴乳腺表面线圈。所有病例采用单次激发自旋回波-回波平面成像（SE-EPI）序列行DWI,扩散敏感系数（b值）取0、400、600、800、1000s/mm^2。以恶性病变ADC值95%可信区间的上界作为诊断病变良、恶性的界值,所得结果与病理结果比较。结果DWI显示92.3%（24/26）的良性病变和96.9%（31/32）的恶性病变,敏感性为94.8%（55/58）。各b值良性组、恶性组和正常组之间的ADC值差异均有统计学意义（P〈0.05）。取b=1000s/mm^2,以恶性病变ADC值95%可信区间的上界1.4276×10^-3mm/s为界诊断良、恶性的敏感性为90.6%,特异性为84.6%,准确性为87.9%。结论（1）DWI对乳腺疾病的敏感性非常高。（2）ADC值是诊断和鉴别诊断乳腺良、恶性疾病的有价值的参数。（3）b=1000s/mm^2时对乳腺疾病的诊断最有价值。     

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.