Simultaneous acquisition of multiple resolution images for dynamic contrast enhanced imaging of the breast.

An imaging technique is described that allows the reconstruction of a series of images at high temporal rates, while simultaneously providing images at high spatial resolution. The method allows one to arbitrarily choose from among several combinations of temporal/spatial resolutions during postprocessing. This flexibility is accomplished by strategically interleaving multiple undersampled projection reconstruction datasets (or subapertures), in which each set can be used to reconstruct a high temporal resolution image. Images with increasingly higher spatial resolutions can subsequently be formed by combining two or more subaperture datasets. The technique is demonstrated in vivo to assess the kinetics of contrast enhancement and to visualize the architectural features of suspicious breast lesions.     

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.     

Functional tumor imaging with dynamic contrast-enhanced magnetic resonance imaging

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is the acquisition of serial MRI images before, during, and after the administration of an MR contrast agent. Unlike conventional enhanced MRI, which simply provides a snapshot of enhancement at one point in time, DCE-MRI permits a fuller depiction of the wash-in and wash-out contrast kinetics within tumors, and thus provides insight into the nature of the bulk tissue properties. Such data is readily amenable to two-compartment pharmacokinetic modeling from which parameters based on the rates of exchange between the compartments can be generated. These parameters can be used to generate color-encoded images that aid in the visual assessment of tumors. DCE-MRI is used currently to characterize masses, stage tumors, and noninvasively monitor therapy. While DCE-MRI is in clinical use, there are also a number of limitations, including overlap between malignant and benign inflammatory tissue, failure to resolve microscopic disease, and the inconsistent predictive value of enhancement pattern with regard to clinical outcome. Current research focuses on improving understanding of the meaning of DCE-MRI at a molecular level, evaluating macromolecular and targeted contrast agents, and combining DCE-MRI with other physiologic imaging techniques such as positron emission tomography. Efforts to standardize DCE-MRI acquisition, analysis, and reporting methods will allow wider dissemination of this useful functional imaging technique.     

Temporal frequency analysis of dynamic MRI techniques.

Dynamic imaging strategies often involve updating certain areas of k-space (i.e., the low spatial frequencies) more frequently than others. However, important dynamic signal changes may occur anywhere in k-space. In this study, a dynamic k-space sampling analysis method was developed to determine the energy error associated with specific dynamic sampling strategies. The method uses the temporal power spectrum of k-space signals to determine the level and k-space locations of sampling errors. The proposed method was used to compare two dynamic sampling strategies (full sequential and keyhole) for a dynamic first-pass bolus simulation and a continuous heart imaging study. The error analysis agreed well with the errors in the reconstructed images. The technique can be used to determine the minimum sampling frequency for any location in the k-space, and may ultimately be used to optimize dynamic sampling strategies. Magn Reson Med 45:550-556, 2001.     

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     

Kalman filter techniques for accelerated Cartesian dynamic cardiac imaging

In dynamic MRI, spatial and temporal parallel imaging can be exploited to reduce scan time. Real‐time reconstruction enables immediate visualization during the scan. Commonly used view‐sharing techniques suffer from limited temporal resolution, and many of the more advanced reconstruction methods are either retrospective, time‐consuming, or both. A Kalman filter model capable of real‐time reconstruction can be used to increase the spatial and temporal resolution in dynamic MRI reconstruction. The original study describing the use of the Kalman filter in dynamic MRI was limited to non‐Cartesian trajectories because of a limitation intrinsic to the dynamic model used in that study. Here the limitation is overcome, and the model is applied to the more commonly used Cartesian trajectory with fast reconstruction. Furthermore, a combination of the Kalman filter model with Cartesian parallel imaging is presented to further increase the spatial and temporal resolution and signal‐to‐noise ratio. Simulations and experiments were conducted to demonstrate that the Kalman filter model can increase the temporal resolution of the image series compared with view‐sharing techniques and decrease the spatial aliasing compared with TGRAPPA. The method requires relatively little computation, and thus is suitable for real‐time reconstruction. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Multiecho time‐resolved acquisition (META): A high spatiotemporal resolution dixon imaging sequence for dynamic contrast‐enhanced MRI

Purpose

To evaluate a new dynamic contrast‐enhanced (DCE) imaging technique called multiecho time‐resolved acquisition (META) for abdominal/pelvic imaging. META combines an elliptical centric time‐resolved three‐dimensional (3D) spoiled gradient‐recalled echo (SPGR) imaging scheme with a Dixon‐based fat‐water separation algorithm to generate high spatiotemporal resolution volumes.

Materials and Methods

Twenty‐three patients referred for hepatic metastases or renal masses were imaged using the new META sequence and a conventional fat‐suppressed 3D SPGR sequence on a 3T scanner. In 12 patients, equilibrium‐phase 3D SPGR images acquired immediately after META were used for comparing the degree and homogeneity of fat suppression, artifacts, and overall image quality. In the remaining 11 of 23 patients, DCE 3D SPGR images acquired in a previous or subsequent examination were used for comparing the efficiency of arterial phase capture in addition to the qualitative analysis for the degree and homogeneity of fat suppression, artifacts, and overall image quality.

Results

META images were determined to be significantly better than conventional 3D SPGR images for degree and uniformity of fat suppression and ability to visualize the arterial phase. There were no significant differences in artifact levels or overall image quality.

Conclusion

META is a promising high spatiotemporal resolution imaging sequence for capturing the fast dynamics of hyperenhancing hepatic lesions and provides robust fat suppression even at 3T. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Accelerated dynamic MR imaging with a parallel imaging technique for hypervascular hepatocellular carcinomas: usefulness of a test bolus in examination and subtraction imaging

PURPOSE: To assess the impact of the accelerated dynamic MR imaging (ADMRI) approach using parallel imaging for detecting hypervascular hepatocellular carcinomas (HCCs) and to evaluate the usefulness of a test bolus in examination and subtraction imaging in this setting. MATERIALS AND METHODS: Thirty patients with 135 HCCs underwent ADMRI using a two-dimensional gradient-recalled echo sequence with parallel imaging. Seventeen patients were evaluated without a test bolus and 13 patients with a test bolus. The detectability of HCCs was calculated between the groups with and without a test bolus. ADMRI was evaluated regarding the signal-to-noise ratio (SNR) of the lesion and the liver, the contrast-to-noise ratio (CNR) of the lesion vs. the liver, and the feasibility of subtraction images. RESULTS: ADMRI with and without a test bolus had almost equal sensitivity (92.5% and 92.6%). No significant difference was seen in the SNR of lesions and the CNR of lesions vs. livers between both groups. With a test bolus, ADMRI could depict the peak enhancement of nodules on the 2nd or 3rd dynamic phases and optimized the timing of peak lesion enhancement. Subtraction images could be obtained regarding minimal slice misregistration. CONCLUSION: ADMRI had high detectability of HCCs with and without a test bolus.     

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.