碘对比剂在下肢深静脉CT成像中的应用和技术要点

目前,CT扫描技术已成为诊断下肢深静脉血栓的重要影像手段。由于下肢静脉独特的解剖学特点,获得高质量静脉CT血管影像尚有一定难度,目前临床应用的间接静脉法、直接静脉法及双向法等多种CT检查技术亦均有其各自的局限性。因此,如何安全、合理使用碘对比剂,以提高下肢深静脉管腔内对比剂浓度的同时减少伪影,并通过降低碘对比剂的用量防止对比剂急性肾损害的发生,一直是临床上关注的热点问题。现就不同CT检查方法的技术要点以及碘对比剂用量、注射流率、浓度及温度等参数的应用策略予以综述。     

基于图像质量增强的大螺距重建技术及其应用

目的评价基于大螺距原始投影数据的图像质量增强重建(IQE)技术的图像质量。方法①采集头颅标本原始数据,分别以传统方式和IQE方式进行重建并评价图像伪影。②选择60例于16排CT接受头颅检查患者,其中30例采用螺距1∶1.75,另30例采用螺距1∶1.375,管电压及管电流均为120kVp、200 mAs,重建层厚和重建间隔均为0.625mm。对1∶1.75螺距采样原始数据分别采用常规技术和IQE技术进行重建,评价不同螺距、不同重建方式图像质量的差异,并获取图像噪声标准差(SD)值进行定量分析。结果①头颅模型数据显示,采用IQE重建较传统重建图像中的风车状伪影明显减少。②临床图像数据显示,螺距为1∶1.75时,采用IQE重建图像的伪影明显少于传统技术重建图像;IQE图像质量优于传统重建(P0.05)。传统重建技术和IQE重建图像的SD值分别为27.42±3.70和20.11±4.20(t=4.913,P0.05)。结论采用IQE技术进行大螺距扫描可获得满意的图像质量,并降低图像噪声。     

计算机X射线摄影系统的性能检测与质量控制

计算机X线摄影（Computed Radiography,CR）是一种比较先进和成熟的医学成像技术,它采用IP影像板（Imaging Panel）代替传统X线摄影技术,是第一种真正意义上实现X射线普通摄影的数字化技术。CR在各基层医院有着广泛的使用,本文就如何对CR系统的荧光板背景噪声,激光束功能,空间分辨率等几个参数进行检测做详细介绍,以达到安装验收,性能检测,质量控制的目的,并对CR系统的日常维护做简要讨论。     

Quantitative Effects of Contrast Enhanced CT Attenuation Correction on PET SUV Measurements

Purpose The presence of contrast materials on computed tomography (CT) images can cause problems in the attenuation correction of positron emission tomography (PET) images. These are because of errors converting the CT attenuation of contrast to 511-keV attenuation and by the change in tissue enhancement over the duration of the PET emission scan. Newer CT-based attenuation correction (CTAC) algorithms have been developed to reduce these errors. Methods To evaluate the effectiveness of the modified CTAC technique, we performed a retrospective analysis on 20 patients, comparing PET images using unenhanced and contrast-enhanced CT scans for attenuation correction. A phantom study was performed to simulate the effects of contrast on radiotracer concentration measurements. Results There was a maximum difference in calculated radiotracer concentrations of 5.9% within the retrospective data and 7% within the phantom data. Conclusion Using a CTAC algorithm that de-emphasizes high-density areas, contrast-enhanced CT can be used for attenuation mapping without significant errors in quantitation.     

Enhanced segmentation of gastrointestinal polyps from capsule endoscopy images with artifacts using ensemble learning

BACKGROUNDEndoscopy artifacts are widespread in real capsule endoscopy (CE) images but not in high-quality standard datasets.AIMTo improve the segmentation performance of polyps from CE images with artifacts based on ensemble learning.METHODSWe collected 277 polyp images with CE artifacts from 5760 h of videos from 480 patients at Guangzhou First People’s Hospital from January 2016 to December 2019. Two public high-quality standard external datasets were retrieved and used for the comparison experiments. For each dataset, we randomly segmented the data into training, validation, and testing sets for model training, selection, and testing. We compared the performance of the base models and the ensemble model in segmenting polyps from images with artifacts.RESULTSThe performance of the semantic segmentation model was affected by artifacts in the sample images, which also affected the results of polyp detection by CE using a single model. The evaluation based on real datasets with artifacts and standard datasets showed that the ensemble model of all state-of-the-art models performed better than the best corresponding base learner on the real dataset with artifacts. Compared with the corresponding optimal base learners, the intersection over union (IoU) and dice of the ensemble learning model increased to different degrees, ranging from 0.08% to 7.01% and 0.61% to 4.93%, respectively. Moreover, in the standard datasets without artifacts, most of the ensemble models were slightly better than the base learner, as demonstrated by the IoU and dice increases ranging from -0.28% to 1.20% and -0.61% to 0.76%, respectively.CONCLUSIONEnsemble learning can improve the segmentation accuracy of polyps from CE images with artifacts. Our results demonstrated an improvement in the detection rate of polyps with interference from artifacts.     

Diagnostic problems in two-dimensional shear wave elastography of the liver

Two-dimensional shear wave elastography (2D-SWE) is used in the clinical setting for observation of the liver. Unfortunately, a wide spectrum of artifactual images are frequently encountered in 2D-SWE, the precise mechanisms of which remain incompletely understood. This review was designed to present many of the artifactual images seen in 2D-SWE of the liver and to analyze them by computer simulation models that support clinical observations. Our computer simulations yielded the following suggestions: (1) When performing 2D-SWE in patients with chronic hepatic disease, especially liver cirrhosis, it is recommended to measure shear wave values through the least irregular hepatic surface; (2) The most useful 2D-SWE in patients with focal lesion will detect lesions that are poorly visible on B-mode ultrasound and will differentiate true tumors from pseudo-tumors (e.g., irregular fatty change); and (3) Measurement of shear wave values in the area posterior to a focal lesion must be avoided.     

Reduction of MRI signal distortion from titanium intracavitary brachytherapy applicator by optimizing pulse sequence parameters

PurposeTo demonstrate that optimized pulse sequence parameters for a T2-weighted (T2w) fast spin echo acquisition reduced artifacts from a titanium brachytherapy applicator compared to conventional sequence parameters.Methods and materialsFollowing Institutional Review Board approval and informed consent, seven patients were successfully imaged with both standard sagittal T2w fast spin echo parameters (voxel size of 0.98 × 0.78 × 4.0 mm³; readout bandwidth of 200 Hz/px; repetition time of 2800 ms; echo time of 91 ms; echo train length of 15; 36 slices; and imaging time of 3:16 min) and an additional optimized T2w sequence (voxel size of 0.98 × 0.98 × 4.0 mm³; readout bandwidth of 500 Hz/px; repetition time of 3610 ms; echo time of 91 ms; echo train length of 25; 18–36 slices; and imaging time of 1:15–2:30 min), which had demonstrated artifact reduction in prior phantom work. Visualized intracavitary tandem was hand-segmented by two of the authors. Three body imaging radiologists assessed image quality and intraobserver agreement scores were analyzed.ResultsThe average segmented volume of the intracavitary applicator significantly (p < 0.05) decreased with the experimental pulse sequence parameters as compared to the standard pulse sequence. Comparison of experimental and standard T2w sequence qualitative scores for each reviewer showed no significant differences between the two techniques.ConclusionsThis study demonstrated that pulse sequence parameter optimization can significantly reduce distortion artifact from titanium applicators while maintaining image quality and reasonable imaging times.