Modified iterative model based on data extrapolation method to reduce Gibbs ringing.

An iterative algorithm that involves image filtering and data replacement (as suggested by Constable and Henkelman) is investigated for reducing the Gibbs artifact in magnetic resonance imaging. The image is processed with an edge-preserving filter to estimate the height and location of a set of model elements (delta functions or boxes) for generating the missing high-frequency information. Filtering was performed in the complex image domain to account for discontinuities in phase as well as magnitude. The process is repeated after each data replacement to handle varying degrees of contrast. The convergence and signal-to-noise characteristics of the algorithm are investigated by means of simulated and clinical examples. The results indicate that the algorithm performs reasonably well in reducing ringing artifacts due to nearby edge contrast seen in most of the homogeneous, isointense regions. Nevertheless, it may generate some spurious thickening of structures that do not match the assumed step-edge models.     

Fast,interactive algorithm for segmentation of a series of related images: Application to volumetric analysis of MR images of the heart

Magnetic resonance (MR) cine images of the beating heart have excellent spatial and temporal resolution. Extracting the boundaries of the heart from MR images for volumetric measurements is of considerable interest; however, since the number of images involved is large, tracing the boundaries by hand is tedious and prohibitively time consuming. The authors have developed an interactive method of boundary detection that uses the correlation between the cardiac boundaries on temporally or spatially adjacent images to increase the speed of the process and reproducibility of the measurement. A simulated cine MR study of a phantom (total of 155 images) and cardiac cine studies of two patients (192 images each) were analyzed by two independent observers. Analysis of the phantom data was completed in 5.6 minutes (2.16 seconds per image) by observer 1 and 6.3 minutes (2.4 seconds per image) by observer 2. The percent measurement errors for 31 phantom volumes (30-120 mL) were 0.96% and 0.83% for observers 1 and 2, respectively. The observers analyzed the patient studies in 14-23 minutes (4.4-7.2 seconds per image), with interobserver variabilities of 5.8% and 3.7% for the two patients, respectively. The authors conclude that their flexible, semiautomatic, interactive algorithm allows rapid and reproducible detection of structural boundaries.     

Pulsatile flow artifacts in two-dimensional time-of-flight MR angiography: Initial studies in elastic models of human carotid arteries

Initial experimental and numerical analysis of artifacts due to pulsatile flow in two-dimensional time-of-flight (2D-TOF) magnetic resonance (MR) angiography are presented. The experimental studies used elastic models of the carotid artery bifurcation cast from fresh cadavers and accurately reproducing the twisting and tapering of the human blood vessels, allowing direct comparison of images with and without flow. Prominent image artifacts, including periodic ghosts and signal loss, were produced by pulsatile flow even though flow-compensated gradient waveforms were used. The dependence of artifacts due to partial saturation on pulse sequence parameters (TR and flip angle) was investigated theoretically for a simple pulsatile velocity profile and compared with experimental results from a model of a normal carotid artery. Signal reduction was observed proximal and distal to the stenosis in a model with a 70% internal carotid artery (ICA) stenosis and a model with 90% stenoses in both the ICA and the external carotid artery. Although this study deals exclusively with 2D-TOF imaging, the methods can also be applied to evaluate other MR angiography techniques.     

A Comparison of Two Commercial Volumetry Software Programs in the Analysis of Pulmonary Ground-Glass Nodules: Segmentation Capability and Measurement Accuracy

Objective

To compare the segmentation capability of the 2 currently available commercial volumetry software programs with specific segmentation algorithms for pulmonary ground-glass nodules (GGNs) and to assess their measurement accuracy.

Materials and Methods

In this study, 55 patients with 66 GGNs underwent unenhanced low-dose CT. GGN segmentation was performed by using 2 volumetry software programs (LungCARE, Siemens Healthcare; LungVCAR, GE Healthcare). Successful nodule segmentation was assessed visually and morphologic features of GGNs were evaluated to determine factors affecting segmentation by both types of software. In addition, the measurement accuracy of the software programs was investigated by using an anthropomorphic chest phantom containing simulated GGNs.

Results

The successful nodule segmentation rate was significantly higher in LungCARE (90.9%) than in LungVCAR (72.7%) (p = 0.012). Vascular attachment was a negatively influencing morphologic feature of nodule segmentation for both software programs. As for measurement accuracy, mean relative volume measurement errors in nodules ≥ 10 mm were 14.89% with LungCARE and 19.96% with LungVCAR. The mean relative attenuation measurement errors in nodules ≥ 10 mm were 3.03% with LungCARE and 5.12% with LungVCAR.

Conclusion

LungCARE shows significantly higher segmentation success rates than LungVCAR. Measurement accuracy of volume and attenuation of GGNs is acceptable in GGNs ≥ 10 mm by both software programs.     

Incidence and precipitating factors of delirium after coronary artery bypass grafting

Objective. To analyze large contemporary patient population, undergoing on-pump coronary artery bypass grafting at our institution, and identify the prevalence and precipitating factors of delirium development. Design. Baseline demographics, operative data and postoperative outcomes of 1367 consecutive patients were recorded prospectively and analysed using multivariate logistic regression analysis, to determine independent predictors of postoperative delirium development. Results. Delirium was detected in 42 (3.07%) patients. Eight factors: age more than 65 years, peripheral vascular disease, Euroscore≥5, preoperative IABP support, postoperative blood product usage and postoperative low cardiac output syndrome were independently predicting delirium development after coronary artery bypass procedures. Postoperative delirium was associated with significantly higher mortality rate (16.6% vs. 3.9%, p=0.013), prolonged mechanical ventilation time (9.2±3.1 vs. 5.05±7.6, p=0.04) and increased length of intensive care unit stay (6.8±4.9 vs. 2.0±2.7 days, p=0.001). Conclusions. Delirium is a dangerous complication, prolonging intensive care unit stay and postoperative mortality. Factors associated with delirium development are advanced age, peripheral vascular disease, diminished cardiac function and blood product usage.     

64层螺旋CT冠状动脉成像图像质量的相关影响因素分析(心脏体模模拟实验)

目的采用心脏动态体模，对64层螺旋CT冠状动脉成像图像质量的相关影响因素进行分析。方法采用GE Light speed64层螺旋CT，以心脏扫描的模式对心脏动态体模进行扫描。心脏动态体模由3部分组成：动力部分、解剖结构模拟部分和控制部分组成。心率设置为40、45、50、55、60、65、70、75、80、85、90、95、100、105、110和115次／min，X线管转速设置为每转0．35、0．40和0．45S，分别对不同心率下的心脏动态体模进行冠状动脉成像扫描。所有扫描数据在R-R间期90％时相分别进行单扇区和多扇区重组。重组数据传至AW4．2工作站后处理成像。后处理方法采用容积重组（VR）、多平面重组（MPR）模式。分别对不同重组图像进行评分。统计学处理采用多元线性回归模型。结果（1）心率对图像质量的影响有统计学意义（P〈0．01），随着心率的增加，图像质量评分呈下降趋势。多元线性回归分析显示心率每增加1次，图像质量评分平均减低0．046；（2）重组算法对图像质量的影响有统计学意义（P〈0．01），在同一条件下多扇区重组算法较单扇区重组算法能增加图像质量评分0．5。（3）X线管转速在0．35、0．40和0．45S下对图像质量的影响无统计学意义（P〉0，05），在40-115次／min心率时的重组图像，得到的最高评分时X线管转速分别为0．35和0．45S。（4）心率、重组算法与图像质量间具有多元线性回归关系（标准化回归系数分别为-0．824和0．194）。结论心脏动态体模评价64层螺旋CT冠状动脉成像图像质量的影响因素，能够为其临床应用和基础研究提供帮助。