CR成像中的伪影及消除方法

CR又名计算机X线成像系统（ComputedRadiography），是将X线拍摄的影像信息记录在影像板（ImagePlate）上，经过激光扫描系统凑取，由计算机系统合成为数字化图像，再由于式激光打印机打印成数字化胶片，CR可显示传统X线照相所无法达到的细节和精确性。我院使用的CR是柯达8900型，使用2a来在成像过程中经常出现的伪影以及产生伪影的原因及解决方法归纳如下：     

计算机X线摄影废弃图像产生的原因及处理对策

目的分析CR系统废弃图像产生的原因,提出处理对策。方法收集2009～2011年柯达CR900系统产生的废弃图像138例,并进行归类分析。结果 138例废弃图像产生原因有6种:X线量子噪声、饱和伪影、左右侧黑白亮度不均、IP板感光层损坏伪影、黑边框过度遮挡伪影、IP灰尘伪影。结论实施相应处理措施可以明显降低CR废弃图像的产生。     

口腔金属材料与影像学伪影的检测与比较

背景：磁共振成像是常用的临床影像检测方法,口腔金属材料在磁共振成像检查时会出现图像伪影,从而影响图像的质量以及诊断的正确性。目的：分析不同口腔金属材料在磁共振成像中产生的伪影强度以及影响伪影的因素。方法：分析9篇近10年关于口腔金属材料对磁共振成像影响的研究文献,从不同角度分析口腔常削金属材料钴铬合金、镍铬合金、钛合金、金铂合金、银铂合金以及纯钛等在磁共振影像中产生的伪影的大小,比较其影响伪影强度的因素。结果与结论：钴铬合金在磁共振图像中产生的伪影最人,并儿随着磁场强度的增强伪影增大,其中硬质钻铬合会产生的伪影强度大于软质钴铬合金产生的伪影强度,其次足镍铬合金产生的伪影,而金、银合金以及纯钛产生的伪影最小,并且磁场强度增强等外加干扰因素对伪影大小无明届影响。     

一种消除MRI拉链伪影的脉冲序列

背景:磁共振成像会产生各种类型的伪影,经常出现的有运动伪影、卷褶伪影、金属伪影、部分容积效应伪影、化学位移伪影、相位伪影和拉链伪影等,但由自旋回波序列成像过程中形成拉链伪影的控制和校正方法还未见报道.目的:通过分析自旋回波序列成像过程中拉链伪影的产生机制,探索出一种新的消除拉链伪影的脉冲序列.方法:编写标准SE序列得到标准图,编写伪影序列得到直线干扰图像和拉链伪影图,编写改进序列得到改进后的除拉链伪影图.结果与结论:5°一瞬间梯度-120°回波序列可得到直线干扰图像,90°一瞬间梯度-120°回波序列可得到拉链伪影图,而改进后序列90°-120°一瞬间梯度回波可彻底消除拉链伪影.结果提示,改进后的脉冲序列显示的图形效果彻底消除了拉链伪影.     

浅谈计算机X线摄影图像伪影形成的因素

计算机X线摄影(CR)系统以其方便、快捷、图像清晰以在各级医院广泛使用。但在实际操作应用中发现CR图像会产生形式多样的伪影,有些伪影已经直接影响图像质量,进而影响临床诊断。因此,有必要对其     

CR成像原理及临床应用

目的：探讨CR技术图像在临床应用中的价值。方法：CR成像。将X线影像信息直接记录在成像板（IP板）上构成潜影，用激光束对荧光板进行扫描，读取信息，经模／数转化后进人计算机图像处理系统处理，改善影像的细节，使图像降噪、灰阶对比度调整、影像放大、数字减影等，再将影像的特征信息图像显示在荧屏上。结果：通过数字化X线成像（CR）对3万5千多例患者检查中的应用，提高了图像信息，为诊断提供了可靠的依据，适应现代诊断的要求。结论：CR数字计算机的应用，为构建“以病人为中心的服务宗旨”奠定了基础，为我们迎接未来挑战及影像科室的发展展示出了无限的潜力。     

增感屏牙片成像效果不佳的原因分析

目的 通过对比测试，探讨增感屏牙片成像效果不佳的原因，以便更好地使用增感屏牙片。方法 将增感屏牙片和常规无增感屏牙片各1000张，以常规分角线投照技术完成照片，用以测试两种牙片在影像清晰度、颗粒性、伪影等成像指标方面的差异。结果 增感屏牙片明显比无增感屏牙片成像效果差，从成像效果来看，部分是受了伪影的影响。结论 增感屏的荧光扩散、屏胶接触不良、X线斜射效应、屏结构斑点、摄片技术及暗室操作方式等，是引起增感屏牙片影像清晰度降低、颗粒性变差、伪影增多等成像效果不佳的主要原因。     

CR伪影分析及质量控制的探讨

目的通过对计算机X线摄影图像的分析,以减少甚至消除CR图像的伪影。随机抽取了3000幅CR图像,通过显示器进行图像质量评价,分析伪影形成的因素及解除方法。     

DR影像伪影的原因分析与对策

目的探讨引起产生伪影的原因与解决对策。材料与方法收集了我院2005年5月至2006年5月中数字化摄影显示有影像伪影的照片756例,按人为因素与客观因素分组,再与采取对策前后相同时间所引起产生伪影的人为因素与客观因素进行对比分析。结果对策前所引起产生伪影的人为因素与客观因素比值58B%;采取对策后所引起产生伪影的人为因素与客观因素比值为15?%。结论分析证实,减少人为因素产生的伪影是提高影像质量的关键。     

高场磁共振成像常见伪影与消除165例分析

随着MR临床应用的普及,高质量的MR影像对疾病的诊断越发显得重要。MR成像中,对各种原因产生的伪影常会干扰医生对病变的客观判断,导致误诊或漏诊,尤其对于高场磁共振成像系统,在其分辨率、信噪比提高同时,伪影产生也相对增多,因此识别和消除伪影是提高MR图像质量的重要环节。1临床资料1.1一般资料收集具有不同程度伪影的165例患者MR图像资料。其中,男90例,女75例,年龄3~82(平均50.2)岁。头部扫描55例,脊髓扫描47例,胸、腹部35例,骨关节28例。1.2方法采用Siemens Avanto1.5T超导磁共振扫描仪,线圈包括头、颈、体32通道线圈,扫描序列为S…     

ACS和BLADE序列在上腹部T2WI中的应用价值对比

目的：比较ACS(AI-assisted Compressed Sensing)序列和BLADE序列在上腹部T2WI的应用价值。方法：对61例磁共振上腹部检查患者分别行BLADE-T2-FSE序列和ACS-T2-FSE序列扫描。由两位医师分别对两组图像中呼吸运动伪影、卷褶伪影、胃肠道蠕动伪影、图像错层情况、胆管和病灶显示清晰度、整体图像质量进行评分；测量并计算两组序列中病灶与肝实质信号强度对比率(Contrast Ratio,CR),并进行统计学分析。结果：ACS序列检查时间10秒,而BLADE序列62秒左右。61例患者共检出75例病灶,其中肝细胞肝癌36例,胆管细胞癌6例,肝血管瘤16例,肝囊肿17例。ACS-T2-FSE序列中各类病灶与肝实质信号的CR均高于BLADE-T2-FSE序列(P均<0.05)；两位医师对图像评分一致性良好,ACS-T2-FSE序列中呼吸运动伪影、卷褶伪影、图像错层情况、胆管和病灶显示清晰度与整体图像质量评分均高于BLADE-T2-FSE序列(P均<0.05)；胃肠道蠕动伪影评分ACS-T2-FSE序列较BLADE-T2-FSE序列略低,但不具有统计学意义(P=0.128)。结论：与常规BLADE-T2-FSE序列相比,ACS技术大幅缩短扫描时间,减少了呼吸运动伪影和图像错层,提高了图像诊断质量,值得推广。     

Propagation Imaging in the Demonstration of Common Shear Wave Artifacts

In this article, we describe our experience with shear wave propagation imaging (SWPI) as an adjunct to 2‐dimensional (2D) shear wave elastography (SWE) in a cohort of patients being evaluated for diffuse liver disease. Two‐dimensional SWE has been extensively studied in previous publications; however, 2D SWE using propagation images has not been widely described in the literature to date. We observed that when certain artifacts occurred on the color elastograms, highly characteristic changes to shear wave propagation contours were seen, which can help clarify the cause of the artifacts. To our knowledge, the use of SWPI to explain the etiology of artifacts has never been published before. The artifacts described in this article include the capsule reverberation artifact, penetration limitation or dropout artifact, artifact due to blood vessels, shadowing artifact, tissue motion artifact, and near‐field distortion/precompression artifact. Hence, the purpose of this article is to show examples of common artifacts seen on 2D SWE as depicted on corresponding SWPI to demonstrate that both types of image displays are complementary to each other.     

低场永磁型MR图像质量控制探讨分析

目的对影响低场MRI设备图像质量的常见原因进行分析,以达到图像质量控制的目的。材料与方法对400例行MRI检查的病例进行图像质量分析和评价,主要是空间分辨率(SR),信号噪声比(SNR)图像对比度及对比噪声比(CNR),有无设备的卷褶伪影、化学位移伪影、截断伪影、磁化敏感伪影及运动伪影、金属伪影。据此将图像按优、良、差三级分类。结果 400例中图像质量优的为280例,良为100例,差为20例。其中20例图像较差,原因为:(1)患者配合不佳;(2)MR成像中的伪影及MRI质量参数控制处理不当;(3)机器故障。结论低场永磁型MRI要想获得好的图像,就必须重视图像质量的提高。     

A novel iterative reconstruction algorithm allows reduced dose multidetector-row CT imaging of mechanical prosthetic heart valves

Multidetector-row CT is promising for prosthetic heart valve (PHV) assessment but retrospectively ECG-gated scanning has a considerable radiation dose. Recently introduced iterative reconstruction (IR) algorithms may enable radiation dose reduction with retained image quality. Furthermore, PHV image quality on the CT scan mainly depends on extent of PHV artifacts. IR may decrease streak artifacts. We compared image noise and artifact volumes in scans of mechanical PHVs reconstructed with conventional filtered back projection (FBP) to lower dose scans reconstructed with IR. Four different PHVs (St. Jude, Carbomedics, ON-X and Medtronic Hall) were scanned in a pulsatile in vitro model. Ten retrospectively ECG-gated CT scans were performed of each PHV at 120 kV, 600 mAs (high-dose CTDI_vol 35.3 mGy) and 120 kV, 300 mAs (low-dose CTDI_vol 17.7 mGy) on a 64 detector-row scanner. Diastolic and systolic images were reconstructed with FBP (high and low-dose) and the IR algorithm (low-dose only). Hypo- and hyperdense artifact volumes were determined using two threshold filters. Image noise was measured. Mean hypo- and hyperdense artifact volumes (mm³) were 1,235/5,346 (high-dose FBP); 2,405/6,877 (low-dose FBP) and 1,218/5,333 (low-dose IR). Low-dose IR reconstructions had similar image noise compared to high-dose FBP (16.5 ± 1.7 vs. 16.3 ± 1.6, mean ± SD, respectively, P = 1.0). IR allows ECG-gated PHV imaging with similar image noise and PHV artifacts at 50% less dose compared to conventional FBP in an pulsatile in vitro model.     

Ultrasound segmentation-guided edge artifact reduction in diffuse optical tomography using connected component analysis

Ultrasound (US)-guided diffuse optical tomography (DOT) has demonstrated potential value for breast cancer diagnosis and treatment response assessment. However, in clinical use, the chest wall, poor probe-tissue contact, and tissue heterogeneity can all cause image artifacts. These image artifacts, appearing commonly as hot spots in the non-lesion regions (edge artifacts), can decrease the reconstruction accuracy and cause misinterpretation of lesion images. Here we introduce an iterative, connected component analysis-based image artifact reduction algorithm. A convolutional neural network (CNN) is used to segment co-registered US images to extract the lesion location and size to guide the artifact reduction. We demonstrate its performance using Monte Carlo simulations on VICTRE digital breast phantoms and breast patient images. In simulated tissue mismatch models, this algorithm successfully reduces edge artifacts without significantly changing the reconstructed target absorption coefficients. With clinical data it improves the optical contrast between malignant and benign groups, from 1.55 without artifact reduction to 1.91 with artifact reduction. The proposed algorithm has a broad range of applications in other modality-guided DOT imaging.     

Off-frequency tuning error artifact in steady-state free precession cine imaging due to adjacent air-filled bowel.

Identification of common cardiovascular magnetic resonance (CMR) artifacts is important to optimal image acquisition quality and the avoidance of mistaken clinical diagnosis. We describe an off-frequency tuning error artifact observed during rapid steady-state free precession acquisitions in three patients and resulting in a dramatic appearance within the right and left ventricles. These artifacts were associated with large, adjacent air pockets within a loop of bowel or stomach and were eradicated by retuning of the magnetic resonance scanner's frequency. Awareness of this artifact, its cause and correction, should improve diagnostic image quality and avoid clinical diagnostic confusion. This report also heightens the need for a more robust shimming sequence for cardiac studies.     

Mirror image artifacts of color Doppler images causing misinterpretation in carotid artery stenoses.

A knowledge of mirror image artifacts in color-coded duplex sonography is important as they can lead to diagnostic problems in the morphologic evaluation of stenoses and plaques. Mirror image artifacts were detectable in stenosed vessels when strongly reflecting plaques on the wall of the vessel distant from the transducer head were insonated obliquely. The artifacts were revealed in regions that were hypoechoic or anechoic on B-mode scans. Depending on the angle of insonation and the surface structure of the plaque, the mirror image artifact could be linked with the vessel lumen and thus imitate ulcerations or branches. The artifact appeared in both the longitudinal and the transverse projections and also occurred in the power Doppler and in pulsed Doppler sonographic modes. Mirror image artifacts with linkages to the vessel lumen that could result in a misinterpretation were seen in 2.5% of the stenosed vessels.     

Color Doppler twinkling artifacts from gallstones: in vitro analysis regarding their compositions and architectures

The purpose of our study was to investigate the relationship between a twinkling artifact and the biochemical compositions of gallstones in phantom experiments. Fifty-two gallstones surgically extracted from 26 patients (26 cholesterol, 12 brown pigment and 14 black pigment stones) were included in the phantom study. Color Doppler sonography was performed to evaluate the occurrence of a twinkling artifact behind the stones. The artifacts were graded from grade 0 (no artifact) to grade 3 (very strong artifact). Micro computed tomography (CT) images were obtained to analyze the internal architecture and external surface of the stones. A total of 20 of 26 cholesterol stones (77%) produced grade 2 or 3 artifacts, whereas almost all the black pigment stones and more than half of the brown pigment stones produced no artifacts or grade 1 artifacts (p = 0.0010). The sensitivity and specificity of grade 2 or greater artifacts for cholesterol stones were 76.9% and 76.9%, respectively. The composition of the stones was strongly correlated with the internal shape on the micro CT image. Cholesterol stones with rough surfaces did not show stronger intensities of the artifacts than those with smooth surfaces (p > 0.05). In conclusion, most of the prominent artifacts arose from cholesterol stones having radial or radial-concentric internal architectures, whereas the black pigment stones mostly produced little artifact.     

Motion artifact recognition and quantification in coronary CT angiography using convolutional neural networks

Excellent image quality is a primary prerequisite for diagnostic non-invasive coronary CT angiography. Artifacts due to cardiac motion may interfere with detection and diagnosis of coronary artery disease and render subsequent treatment decisions more difficult. We propose deep-learning-based measures for coronary motion artifact recognition and quantification in order to assess the diagnostic reliability and image quality of coronary CT angiography images. More specifically, the application, steering and evaluation of motion compensation algorithms can be triggered by these measures. A Coronary Motion Forward Artifact model for CT data (CoMoFACT) is developed and applied to clinical cases with excellent image quality to introduce motion artifacts using simulated motion vector fields. The data required for supervised learning is generated by the CoMoFACT from 17 prospectively ECG-triggered clinical cases with controlled motion levels on a scale of 0–10. Convolutional neural networks achieve an accuracy of 93.3% ± 1.8% for the classification task of separating motion-free from motion-perturbed coronary cross-sectional image patches. The target motion level is predicted by a corresponding regression network with a mean absolute error of 1.12 ± 0.07. Transferability and generalization capabilities are demonstrated by motion artifact measurements on eight additional CCTA cases with real motion artifacts.     

Simultaneous multi slice (SMS) balanced steady state free precession first-pass myocardial perfusion cardiovascular magnetic resonance with iterative reconstruction at 1.5 T

Background

Simultaneous-Multi-Slice (SMS) perfusion imaging has the potential to acquire multiple slices, increasing myocardial coverage without sacrificing in-plane spatial resolution. To maximise signal-to-noise ratio (SNR), SMS can be combined with a balanced steady state free precession (bSSFP) readout. Furthermore, application of gradient-controlled local Larmor adjustment (GC-LOLA) can ensure robustness against off-resonance artifacts and SNR loss can be mitigated by applying iterative reconstruction with spatial and temporal regularisation. The objective of this study was to compare cardiovascular magnetic resonance (CMR) myocardial perfusion imaging using SMS bSSFP imaging with GC-LOLA and iterative reconstruction to 3 slice bSSFP.

Methods

Two contrast-enhanced rest perfusion sequences were acquired in random order in 8 patients: 6-slice SMS bSSFP and 3 slice bSSFP. All images were reconstructed with TGRAPPA. SMS images were also reconstructed using a non-linear iterative reconstruction with L1 regularisation in wavelet space (SMS-iter) with 7 different combinations for spatial (λ_σ) and temporal (λ_τ) regularisation parameters. Qualitative ratings of overall image quality (0?=?poor image quality, 1?=?major artifact, 2?=?minor artifact, 3?=?excellent), perceived SNR (0?=?poor SNR, 1?=?major noise, 2?=?minor noise, 3?=?high SNR), frequency of sequence related artifacts and patient related artifacts were undertaken. Quantitative analysis of contrast ratio (CR) and percentage of dark rim artifact (DRA) was performed.

Results

Among all SMS-iter reconstructions, SMS-iter 6 (λ_σ 0.001 λ_τ 0.005) was identified as the optimal reconstruction with the highest overall image quality, least sequence related artifact and higher perceived SNR. SMS-iter 6 had superior overall image quality (2.50?±?0.53 vs 1.50?±?0.53, p?=?0.005) and perceived SNR (2.25?±?0.46 vs 0.75?±?0.46, p?=?0.010) compared to 3 slice bSSFP. There were no significant differences in sequence related artifact, CR (3.62?±?0.39 vs 3.66?±?0.65, p?=?0.88) or percentage of DRA (5.25?±?6.56 vs 4.25?±?4.30, p?=?0.64) with SMS-iter 6 compared to 3 slice bSSFP.

Conclusions

SMS bSSFP with GC-LOLA and iterative reconstruction improved image quality compared to a 3 slice bSSFP with doubled spatial coverage and preserved in-plane spatial resolution. Future evaluation in patients with coronary artery disease is warranted.