Reduction of field of view for dynamic imaging

This paper describes a simple technique that improves the temporal resolution for certain dynamic imaging applications. The technique is based on the assumption that the image to image intensity changes sought in dynamic imaging studies ire sometimes localized, and a smaller field of view can be used to reduce imaging time. Technical details and experimental results are presented. Experimental results show that this technique works reasonably well for in vivo applications.     

Fast dynamic imaging using two reference images

This paper presents a fast dynamic imaging method which is characterized by the acquisition of two high-resolution reference images and a sequence of low-resolution dynamic data sets. Image reconstruction is accomplished using a generalized series based algorithm. Experimental results demonstrate that dynamic images with high temporal resolution can be obtained while maintaining excellent spatial resolution. This method will be useful for a variety of dynamic imaging applications including contrast-enhanced dynamic imaging and functional brain studies.     

K-space substitution: A novel dynamic imaging technique

A rapid dynamic imaging sequence has been developed in which only the 32 phase encoding steps that encode low spatial frequencies are collected for each dynamic image. These are substituted into a previously acquired, 128 × 128 raw data set prior to image reconstruction. In this way the dynamic information is retained while the overall appearance is improved in comparison with images obtained by zero filling to 128 × 128, leading to better qualitative evaluation. The limited k-space sampling means that the technique is most effective for large homogeneous areas of signal change since fine changes in contrast are imperfectly recorded.     

A comparison of RIGR and SVD dynamic imaging methods

Several constrained imaging methods have recently been proposed for dynamic imaging applications. This paper compares two of these methods: the Reduced-encoding Imaging by Generalized-series Reconstruction (RIGR) and Singular Value Decomposition (SVD) methods. RIGR utilizes a priori data for optimal image reconstruction whereas the SVD method seeks to optimize data acquisition. However, this study shows that the existing SVD encoding method tends to bias the data acquisition scheme toward reproducing the known features in the reference image. This characteristic of the SVD encoding method reduces its capability to capture new image features and makes it less suitable than RIGR for dynamic imaging applications.     

3.0TDCE-MRI及DTI在胶质瘤分级中的价值

目的：探讨动态增强磁共振成像(DCE-MRI)及扩散张量成像(DTI)在胶质瘤分级中的价值。方法31例胶质瘤患者行3.0T DCE-MRI 及 DTI 检查,测量定量参数包括：容量转移常数(Ktrans )、血管外细胞外间隙容积比(Ve )、速率常数(Kep )、对比剂浓度下峰面积(iAUC)及相对各向异性分数(rFA)。低级别、高级别胶质瘤组间 DCE-MRI、rFA 参数与微血管密度(MVD)、微血管结构(MVS)相关性评估采用 Spearman 相关性检验。结果胶质瘤分级与 MVD 计数和 MVS 改变呈正相关。14例低级别胶质瘤的 Ktrans 值、Kep 值、Ve 值、iAUC 值及 rFA 值分别为(0.02±0.01)min-1、1.82(0.18~8.54)min-1、0.05±0.03、2.47±1.66和0.55±0.22;17例高级别胶质瘤参数值分别为(0.11±0.02)min-1、1.31(0.12~7.58)min-1、0.28±0.10、10.84±6.46和0.28±0.08。各参数值组间除 Kep 外,其他参数差异均有统计学意义(P <0.05)。Ktrans 、Ve 、iAUC 值与 MVD 计数及 MVS 呈正相关(P <0.05),rFA 值与MVD 计数及 MVS 呈负相关(P <0.01)。结论DCE-MRI、DTI 定量参数对胶质瘤分级以及肿瘤新生血管增生、血管微结构改变都有重要的评估价值。     

Optimized parallel imaging for dynamic PC‐MRI with multidirectional velocity encoding

Phase contrast MRI with multidirectional velocity encoding requires multiple acquisitions of the same k‐space lines to encode the underlying velocities, which can considerably lengthen the total scan time. To reduce scan time, parallel imaging is often applied. In dynamic phase contrast MRI using standard generalized autocalibrating partially parallel acquisitions (GRAPPA), several central k‐spaces for autocalibration of the reconstruction (autocalibrating signal lines (ACS)) are typically acquired, separately for each velocity direction and each cardiac timeframe, for calculating the reconstruction weights. To further accelerate data acquisition, we developed two methods, which calculated weights with a substantially reduced number of ACSl lines. The effects on image quality and flow quantification were compared to fully sampled data, standard GRAPPA, and time‐interleaved sampling scheme in combination with generalized autocalibrating partially parallel acquisitions (TGRAPPA). The results show that the two proposed methods can clearly improve scan efficiency while maintaining image quality and accuracy of measured flow or myocardial tissue velocities. Compared to TGRAPPA, the proposed methods were more accurate in evaluating flow velocity. In conclusion, the proposed reconstruction strategies are promising for dynamic multidirectionally encoded acquisitions and can easily be implemented using the standard GRAPPA reconstruction algorithm. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

盆腔异位肾肾动态显像前后位像GFR测定值的差异比较

目的比较分析盆腔异位肾肾动态显像前、后位像肾小球滤过率（GFR）测定值的差异。方法回顾性分析10例盆腔异位肾患者的肾动态显像GFR测定结果,分别进行前位异位单肾处理和后位双肾处理,将后位像处理所获正常肾脏GFR与前位像处理所获异位肾GFR相加,获得总肾GFR,并与后位像处理所获双肾GFR和双血浆法GFR测定结果进行比较和相关性分析,并进行了相应随访。采用配对t检验法和双变量相关分析检验法对数据进行统计学分析。结果10例盆腔异位肾患者前位像处理所获异位肾GFR[（27．48±12．24）ml／（min·1．73m^2）]较后位像处理所获异位肾GFR[（10．71±4．74）ml／（min·1．73m^2）]高出46％,二者间差异有统计学意义（t=5．481,P〈0．01）。前位像处理所获总GFR与双血浆法GFR差异无统计学意义（t=-2．238,P〉0．05）,二者的相关性较好（r=0．704,P〈0．05）;后位像处理所获总GFR与双血浆法GFR差异有统计学意义（t=4．629,P〈0．01）,二者的相关性较差（r=0．576,P〉0．05）。结论在肾动态显像中,前位像处理所获GFR较后位像更能真实地反映盆腔异位。肾的功能状况。     

MR 动态增强联合扩散加权成像对壶腹区良恶性病变的鉴别

目的：研究M R动态增强联合扩散加权成像（DWI）在鉴别壶腹区良恶性病变的价值。方法回顾性分析43例胆总管下段狭窄患者的M R动态增强及DWI的数据。其中包括32例恶性病变和11例慢性炎症。1位影像医生对壶腹周围良恶性病变的M R动态增强信号强度及DWI信号进行分析,另外2位影像医生对壶腹周围病变的M R动态增强影像以及M R动态增强联合DWI影像进行评估。应用 Logistic回归分析比较灵敏度及特异性。结果壶腹周围良恶性病变MR动态增强表现差异无统计学意义;DWI影像中,壶腹周围癌比炎症更多地表现为高信号,表观扩散系数（ADC）图表现为低信号（P＜0．001）。2位读片者在结合DWI影像后对恶性壶腹周围病变的诊断灵敏度均有提高,分别从84．4％提高到96．9％和从87．7％提高到96．6％。结论 M R动态增强联合DWI可提高鉴别壶腹周围区良恶性狭窄的诊断准确率。     

肾动态显像分次处理法定量评价肾脏局部功能

目的 :明确正常情况下及不同肾脏疾病时 ,肾脏各部分对 99m　Tc DTPA浓聚及清除速度的差别与特点 ,以定量评价肾脏各部分的局部功能状态。方法 :对 18例正常对照、74例不同肾病患者进行了肾动态显像 ,并应用常规肾动态处理软件及ROI技术分别对全肾、肾皮质、肾盂肾盏作了定量分析 ,获得肾脏各部分的Tb、C1/2及 2 0min残留率。结果 :在无肾脏疾病的正常对照组 ,全肾与肾皮质、肾盂肾盏部分之间的定量分析指标均无明显差别 ,在疾病组 ,肾脏各部分的指标则有不同程度的改变 ,尤其是在糖尿病、慢性肾炎及肾盂肾炎的患侧肾差异更明显 ,表现为肾盂肾盏部分的Tb延长。全肾、肾皮质和肾盂肾盏的Tb均值在糖尿病分别为 5 .8min、4.5min和 6.8min(P <0 .0 1) ;慢性肾炎为 7.9min、6.3min和 9.1min(P <0 .0 5 ) ;肾盂肾炎为 6.0min、4.0min和 7.6min(P <0 .0 5 ) ;在高血压病患者三者无显著差异。而在 13例有上尿路排泄不畅的患者 ,三种处理方法时 ,Tb、C1/2及 2 0min残留率均有差异 (P <0 .0 5～ 0 .0 0 1)。结论 :定量评价肾脏各部分的功能对于正确反映和认识肾功能受损程度及其部位有参考价值 ,尤其适用于尿路排泄不畅患者的肾功能估计     

DWI与DCE-MRI联合应用对乳腺良恶性病变鉴别诊断价值的Meta分析

目的 运用Meta分析方法研究近几年在最新技术条件下扩散加权成像(DWI)与动态对比增强磁共振成像(DCE-MRI)联合应用对乳腺良恶性病变的鉴别诊断价值.方法 检索PubMed、EMbase、Web of Science、Cochrane图书馆、中国期刊网(CNKI)的英文和中文文献,按照Cochrane协作网推荐的诊断试验纳入标准筛选文献,提取纳入研究的特征信息.文献评价采用诊断研究评价工具QUADAS-2.数据分析采用Meta-DiSc1.4软件,检验异质性,并根据异质性结果选择相应的效应模型.对所有研究进行加权定量合并,计算汇总灵敏度(Se)、汇总特异度(Sp).绘制汇总受试者工作特征曲线(SROC),并计算曲线下面积(AUC).结果 纳入28项研究,共1 707例患者、1 857个病灶.28项研究存在异质性,按照随机效应模型计算汇总Se、汇总Sp分别为93％、88％,SROC的AUC为0.96.结论 DWI与DCE-MRI联合应用对乳腺良恶性病变的鉴别诊断具有很高的灵敏度和特异度,是一种诊断效能较高的检查方法.     

注射速率及时间分辨率对胶质瘤动态增强的影响

目的：探讨对比剂注射速率和序列时间分辨率对脑胶质瘤动态增强(DCE)的影响。方法收集行 MRI 检查并有颅脑占位性病变疑是胶质瘤的患者58例,分为2组,常规组41例,优化组17例。采用西门子 Verio3.0T 磁共振,8通道相阵控头部线圈,均行头部常规扫描、DCE-MRI 扫描。常规组对比剂注射速率3 mL/s,DCE 序列时间分辨率5.36 s,优化组对比剂注射速率4 mL/s, DCE 序列时间分辨率4 s 左右。2组病例应用 Tofts 模型进行后处理分析,对动脉输入函数(AIF)的曲线形态做优、中评估,2组计数资料行卡方检验。结果优化组 AIF 曲线形态明显优于常规组(P <0.05),差别有统计学意义。结论提高对比剂注射速率和DCE 序列时间分辨率对改进胶质瘤 DCE 图像质量是有意义的。     

Parallel MRI with extended and averaged GRAPPA kernels (PEAK-GRAPPA): optimized spatiotemporal dynamic imaging

Purpose

To evaluate an optimized k‐t‐space related reconstruction method for dynamic magnetic resonance imaging (MRI), a method called PEAK‐GRAPPA (Parallel MRI with Extended and Averaged GRAPPA Kernels) is presented which is based on an extended spatiotemporal GRAPPA kernel in combination with temporal averaging of coil weights.

Materials and Methods

The PEAK‐GRAPPA kernel consists of a uniform geometry with several spatial and temporal source points from acquired k‐space lines and several target points from missing k‐space lines. In order to improve the quality of coil weight estimation sets of coil weights are averaged over the temporal dimension.

Results

The kernel geometry leads to strongly decreased reconstruction times compared to the recently introduced k‐t‐GRAPPA using different kernel geometries with only one target point per kernel to fit. Improved results were obtained in terms of the root mean square error and the signal‐to‐noise ratio as demonstrated by in vivo cardiac imaging.

Conclusion

Using a uniform kernel geometry for weight estimation with the properties of uncorrelated noise of different acquired timeframes, optimized results were achieved in terms of error level, signal‐to‐noise ratio, and reconstruction time. J. Magn. Reson. Imaging 2008;28:1226–1232. © 2008 Wiley‐Liss, Inc.     

磁共振动态增强定量灌注成像方法对子宫良恶性病变的鉴别作用

目的 探讨磁共振动态增强定量灌注成像方法在子宫良恶性病变鉴别诊断中的价值.方法 回顾性分析首诊经病理证实为子宫恶性肿瘤18例(恶性病变组),良性肿瘤或肿瘤样病变22例(良性病变组),及正常子宫肌层25例(正常对照组).均行3.0T磁共振动态增强扫描,并使用SIEMENS TISSUE 4D软件进行图像后处理,采用Tofts药代模型,分别测得感兴趣区的容积定量灌注参数值:容量转移常数(Ktrans)、速率常数(Kep)、血管外细胞外间隙容积比(Ve)值.对3组的定量灌注参数值进行单因素方差分析,多个样本均数的两两比较.结果 3组的灌注参数平均值:Ktrans值分别是恶性病变组(0.178±0.068)min-1、良性病变组(0.182±0.096)min-1、正常对照组(0.263±0.111)min-1;Kep值分别是(0.4±0.101) min-1、(0.378±0.185) min-1、(0,451±0.166) min-1;Ve值分别是0.477±0.143、0.589±0.176、0.613±0.146.恶性病变组平均Ve值比良性病变组低(P=0.037);恶性病变组平均Ktrans及Ve值均较正常对照组低,且两两比较差异有统计学意义(P=0.003、P=0.004).良性病变组平均Ktrans值较正常对照组低,且差别有统计学意义(P=0.011).结论 磁共振定量动态增强参数Ktrans及Ve值对子宫良恶性病变鉴别诊断具有一定的意义.     

Using UNFOLD to remove artifacts in parallel imaging and in partial-Fourier imaging.

In dynamic MRI, it is often difficult to achieve the acquisition speed required to resolve or freeze the temporal variations of the imaged object. Several MRI methods aim at speeding up the image acquisition process. Through assumptions and/or prior knowledge, these dynamic MRI methods allow part of the needed data to be calculated instead of acquired. For example, partial-Fourier imaging assumes that phase varies smoothly within the object, and parallel imaging (e.g., simultaneous acquisition of spatial harmonics (SMASH) and sensitivity encoding (SENSE)) uses prior knowledge about receiver-coil sensitivity. While these methods accelerate acquisition, they can introduce artifacts or amplify noise in doing so. The present work aims at accelerating image acquisition significantly, while introducing almost no artifacts or noise amplification. It is shown here that new, extra information is gained if dynamic MRI methods are modified so that the sampling function changes in specific ways from time-frame to time-frame. In other words, the set of k-space locations that are acquired (instead of calculated) changes with time. The present temporal strategy, based on the UNaliasing by Fourier-encoding the Overlaps in the temporaL Dimension (UNFOLD) method, can be incorporated into common dynamic MRI methods. Results with partial-Fourier, SMASH, and SENSE imaging are presented here, where UNFOLD's contribution is to very significantly reduce the artifact and/or amplified noise content. Used in this way, UNFOLD contributes indirectly, rather than directly to the improvement in image acquisition speed, as it allows companion methods to operate properly at greater acceleration settings than would otherwise be feasible.     

Application of reduced-encoding imaging with generalized-series reconstruction (RIGR) in dynamic MR imaging

Dynamic MRI has proven to be an important tool in studies of transient physiologic changes in animals and humans. High sensitivity and temporal resolution in such measurements are critical for accurate estimation of dynamic information. Fast imaging, often involving expensive hardware, has evolved for use in such cases. We demonstrate herein the possibility of accelerated data acquisition schemes on conventional machines using standard pulse sequences for dynamic studies. This is achieved by combining reduced-encoded dynamic data (typically 30 to 40 phase encodings) with a priori high-resolution data via a novel constrained image reconstruction algorithm. Such an approach reduces image acquisition time significantly (by a factor of 3 to 4 in the examples described here) without loss in the accuracy of information.     

Temporal filtering effects in dynamic parallel MRI

Autocalibrated parallel MRI methods such as TSENSE or k‐t SENSE have been presented for dynamic imaging studies as they are able to provide images with high temporal resolution. One key element of these techniques is the temporal averaging of the undersampled raw data to obtain an unaliased image. This image represents the temporal average (also known as direct current, DC) and is used to derive the reconstruction parameters. In this work, we show that aliasing artifacts can be introduced in the DC signal obtained from the undersampled raw data. These artifacts lead to undesired temporal filtering effects when the DC signal is used for coil sensitivity calibration or when the DC signal is subtracted from the raw data. It is demonstrated that the temporal filtering effects can be reduced significantly by filtering the DC signal. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

卡托普利介入99mTc-双半胱氨酸肾动态显像对肾血管性高血压患者的价值

目的研究卡托普利介入^99mTc-双半胱氨酸（^99mTc-EC）肾动态显像对高血压患者的肾血管性原因的诊断准确性,并评价其对肾血管性高血压（RVH）患者血管成型术后肾功能改善的预测价值。方法55例临床疑似RVH的患者,口服卡托普利50mg,60min后进行^99mTc-EC肾动态显像,结果异常患者次日再进行基线水平肾动态显像。按照显像结果将RVH的诊断分为高度可能组、不确定组和低度可能组。结果高度可能组的22例患者中20例有肾动脉狭窄（RAS）;不确定组10例中的5例有RAS;低度可能组23例均证实没有RAS。如果将不确定诊断组和低度可能组归为阴性,诊断RAS的灵敏度为80%,特异度为93.3%,阳性预测值为90.9%,阴性预测值为84.8%;如果将高度可能组和不确定诊断组归为阳性,则灵敏度、特异度、阳性预测值和阴性预测值分别为100%、77.7%、78.7%、100%。22例RVH患者进行介入治疗,高度可能组的18例患者中16例治疗有效,不确定组中3例无效、1例有效。结论卡托普利介入^99mTc-EC肾动态显像是诊断RVH的有效手段,同时能预测患者血管成形术治疗效果。     

乳腺肿块动态增强及高分辨MRI表现与病理相关性研究

目的:探讨动态增强和高分辨MRI中乳腺良、恶性病灶的形态学及血液动力学特点,并与病理结果对照,研究其相关性。方法:31例女性患者,年龄21~66岁,平均44.6岁。所有病例均行动态增强和高分辨MRI扫描,用高压注射器,注射速率2.5ml/s。评价病灶增强图像形态学特点,并进行血流动力学分析。结果:31例患者MRI共发现51个病灶。其中恶性12例20个病灶,良性19例31个病灶。以形态不规则、毛刺征、环形强化作为诊断乳腺癌标准,敏感性分别为60%、70%、80%,特异性83.9%、100%、93.5%,准确率74.5%、88.2%、88.2%。纤维腺瘤或纤维腺瘤样增生特征性表现有分叶状、压脂T2WI及增强后低信号分隔,敏感性分别为68%、60%、72%,特异性分别为92.3%、92%、96.2%,准确率80.4%、76.5%、84.3%。早期增强率和时间信号百分比曲线类型分布在良恶性病灶之间的差异有显著性意义(P<0.05)。以Ⅱ型、Ⅲ型曲线作为诊断乳腺癌的标准,敏感性90%,特异性86.6%,诊断准确率88%。结论:乳腺癌的特征性表现有形态不规则、环形强化和毛刺征。纤维腺瘤特征性表现有分叶状、T2WI及强化后可见低信号间隔。动态增强扫描中乳腺病变的时间-信号强度百分比曲线对鉴别良、恶性病变有较大意义,但是部分良、恶性病灶的曲线有重叠表现。     

Small animal imaging with high resolution single photon emission tomography

Molecular imaging of small animals in vivo is vital in the study of mouse and rat models of human diseases, and will provide important clues to the pathogenesis, progression and treatment of many disorders. Functional imaging of small animals using ultra-high resolution single photon emission tomography (SPECT) should be a valuable tool in the molecular imaging armamentarium. SPECT has been used to study cerebral binding sites, to image the expression of reporter genes, and in applications in cardiology and oncology. In this review, we summarize the most recent developments in SPECT imaging of small animals, with particular reference to the types of systems available, their application, and some of the potential limitations.