Self-gated MRI motion modeling for respiratory motion compensation in integrated PET/MRI

Accurate localization and uptake quantification of lesions in the chest and abdomen using PET imaging is challenged by respiratory motion occurring during the exam. This work describes how a stack-of-stars MRI acquisition on integrated PET/MRI systems can be used to derive a high-resolution motion model, how many respiratory phases need to be differentiated, how much MRI scan time is required, and how the model is employed for motion-corrected PET reconstruction. MRI self-gating is applied to perform respiratory gating of the MRI data and simultaneously acquired PET raw data. After gated PET reconstruction, the MRI motion model is used to fuse the individual gates into a single, motion-compensated volume with high signal-to-noise ratio (SNR). The proposed method is evaluated in vivo for 15 clinical patients. The gating requires 5–7 bins to capture the motion to an average accuracy of 2 mm. With 5 bins, the motion-modeling scan can be shortened to 3–4 min. The motion-compensated reconstructions show significantly higher accuracy in lesion quantification in terms of standardized uptake value (SUV) and different measures of lesion contrast compared to ungated PET reconstruction. Furthermore, unlike gated reconstructions, the motion-compensated reconstruction does not lead to SNR loss.     

纹理分析在MRI动态增强扫描鉴别肾细胞癌亚型中的应用研究

目的探讨动态增强MRI三维纹理分析鉴别透明细胞肾细胞癌(clear cell renalcell carcinoma,ccRCC)、乳头状肾细胞癌(papillary renal cell carcinoma,pRCC)和嫌色肾细胞癌(chromophobe renal cell carcinoma,ChRCC)的价值。材料与方法回顾性分析经病理证实的74例ccRCC、22例pRCC和17例ChRCC患者资料,分别提取肾皮髓质期、实质期及延迟期增强T1WI上肿瘤三维纹理特征,筛选后应用原始数据分析、主成分分析、线性判别分析和非线性判别分析方法进行分类分析,计算诊断准确率、敏感度、特异度及受试者工作特征曲线下面积(area under the curve,AUC)。结果动态增强MRI三维纹理分析鉴别ccRCC与pRCC的诊断准确率、敏感度、特异度达88.54%、91.89%、77.27%(AUC=0.846);鉴别ccRCC与ChRCC的诊断准确率、敏感度、特异度达95.60%、97.30%、88.24%(AUC=0.928);鉴别pRCC与ChRCC的诊断准确率、敏感度、特异度达79.49%、72.73%、88.24%(AUC=0.805)。非线性判别分析方法均获得较高的诊断效能(AUC 0.707~0.928)。结论 DCE-MRI三维纹理分析有助于鉴别ccRCC、pRCC和ChRCC。     

Numerical methods and software tools for simulation,design, and resonant mode analysis of radio frequency birdcage coils used in MRI

Design of magnetic resonance imaging (MRI) radiofrequency (RF) coils using lumped circuit modeling based techniques begins to fail at high frequencies, and therefore more accurate models based on the electromagnetic field calculations must be used. Field calculations are also necessary to understand the interactions between the RF field and the subject inside the coil. Furthermore, observing the resonance behavior of the coil and the fields at the resonance frequencies have importance for design and analysis. In this study, finite element method (FEM) based methods have been proposed for accurate time‐harmonic electromagnetic simulations, estimation of the tuning capacitors on the rungs or end rings, and the resonant mode analysis of the birdcage coils. Capacitance estimation was achieved by maximizing the magnitude of the port impedance at the desired frequency while simultaneously minimizing the variance of RF magnetic field in the region of interest. In order for the proposed methods to be conveniently applicable, two software tools, resonant mode and frequency domain analyzer (RM‐FDA) and Optimum Capacitance Finder (OptiCF), were developed. Simulation results for the validation and verification of the software tools are provided for different cases including human head simulations. Additionally, two handmade birdcage coils (low‐pass and high‐pass) were built and resonance mode measurements were made. Results of the software tools are compared with the measurement results as well as with the results of the lumped circuit modeling based method. It has been shown that the proposed software tools can be used for accurate simulation and design of birdcage coils. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 13–32, 2015