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。     

放射性核素肾动态显像弹丸注射方法的应用研究进展

肾动态显像检查需要弹丸注射显像剂,由于弹丸注射质量直接影响显像结果,因此对注射要求较高。笔者就直接弹丸注射法、三通管注射法、留置针注射法、静脉液路注射法及其他方法在核素肾动态显像中的应用作一综述,分析多种弹丸注射方式的优缺点,为提高核素肾动态显像弹丸注射的成功率提供参考。     

99Tcm-DTPA肾动态显像在根治性肾切除术中的应用价值

目的通过99Tcm-DTPA肾动态显像测定总肾及分肾肾小球滤过率（GFR）,评价其在根治性肾切除术中的应用价值。方法 60例根治性肾切除术患者术前行99Tcm-DTPA肾动态显像,定量测得总肾及分肾GFR。依据肾脏肿瘤直径大小分为≥ 4 cm组和 < 4 cm组,以了解术前患者GFR降低与肿瘤大小的相关性。采用t检验进行两组GFR水平的比较。单因素及多因素回归分析寻找术后肾功能不全的预测因子。结果肿瘤 < 4 cm组患侧平均GFR为（52.94±8.57）mL/min,≥ 4 cm组患侧平均GFR为（45.78±13.27）mL/min,两组术前患侧GFR水平的差异有统计学意义（t=2.152,P < 0.05）。术前总GFR水平、术前健侧GFR水平的差异均无统计学意义（t=1.852、1.255,均P>0.05）。术后新出现肾功能不全的比例为21.6%,单因素及多因素logistic回归分析结果发现,术前健侧GFR降低（OR=3.6,P < 0.05）、术前总肾GFR降低（OR=5.64,P < 0.05）是术后肾功能不全的独立危险因素。结论采用99Tcm-DTPA肾动态显像可以定量评价分肾和总肾GFR,对肾脏肿瘤患者术前指导及术后肾功能不全的预测有重要的临床意义。     

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.     

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。     

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。