CT图像中几种少见伪影现象的分析

ＣＴ图像中几种少见伪影现象的分析ＡｎＡｎａｌｙｓｉｓｏｆＲａｒｅＡｒｔｉｆａｃｔｓｏｎＣＴＩｍａｇｅｓ张南玲暨南大学医学院附属医院医学影像科５１０６３２ＣＴ图像中经常遇到的伪影，是由Ｘ线源、信息收集、图像重建和扫描所造成的［１］。可使图像质量下降，给...     

CT图像2例伪影分析

伪影是ＣＴ机中常见的一种故障，是由Ｘ线源、数据采集处理、图像重建、显示所造成的，其主要表现多种多样，常见的有运动、异物等引起的伪影，这是ＣＴ影像固有的物理现象，可以避免，由于机器故障产生的伪影则应分析原因，进行检修，现就我院在工作当中遇到的两种伪影作...     

CT图像中射线束硬化伪影的分析

<正>影像技师是图像质量第一位质控员,也是图像质量最主要的决定者。射线束硬化伪影是由于X光子吸收不均衡,相应产生部分高能(或低能)射线,如果这种非线性衰减不加补偿,会产生条状或环状伪影[1]。本文通过分析射线束硬化伪影的产生原因,指导技师日常的扫描工作,避免此类伪影的发生。1资料与方法1.1一般资料从2015年4月12日第一次发现此伪影至17日,共发现5例患者出现此伪影,其中男3例,女2例,年     

常见CT图像伪影及原因分析

虽然理论上已证明:假若一个物体在所有角度上的投影都已知的话,则其横截面象就能由重建正确地获得。但在许多情况下,物理测量没有能够正确地获得投影数据,导致最后的重建图象失真或产生伪影。本文论述X线CT中各种伪影及其产生机理,尤其对第四代CT中常见的伪影作了较详细的叙述,分析了产生的原因,同时对维修CT,保证图象质量进行了讨论。 一、X线CT图象中常见的伪影 1.Hounsfield伪影 X光子辐射是一个随机变量,包含着统计涨落。理论和实践都证明:较小的透射率产生较大的测量误差,反映在图象上高密度物质会产生较严重的条状伪影,这种伪影称为Hounsfield伪影,这是不可消除的,只有提高光子辐射强度来提高信噪比,减少测量误差来减少它对图象的影响。管球老化,X光子辐射率下降,引起图象质量的退化,实际上也是投影数据信噪比的下降。     

三维CT图像的运动伪影

目的研究呼吸运动对三维CT成像的影响和运动伪影的规律。方法根据螺旋扫描的基本原理建立运动伪影的数学模型,分析三维图像几何形变;并采用自制体模在CT扫描仪上进行实验验证。结果静止条件下的三维图像细节清楚,失真小;运动条件下的三维图像存在明显变形,程度随螺距和运动周期的增大而减小,初始相位不同图像也有所不同。结论三维CT图像的几何形变取决于目标运动的特点和螺距、层厚等扫描参数。     

胸部低剂量CT图像噪声和伪影分析

目的 分析胸部低剂量CT扫描图像噪声与伪影的影响因素及分布特点.方法 应用组织等效胸部模型置于Philips Brilliance 64层CT机以常规剂量(管电压120 kV,管电流250 mAs)和低剂量(管电压120 kV,管电流50、30和21 mAs)分别扫描,测量、记录模型各部位CT值、CT值噪声标准差(SO),分别行方差分析.对200例肺结节患者以30或21 mAs剂量组行小范围低剂量扫描,通过卡方检验分析不同剂量扫描影像噪声和伪影严重程度与患者性别、体型的关系及在肺部的分布特点.结果 不同扫描剂量条件下测量模型各部位CT值差异均无统计学意义:肺-777.3～-758.2 HU(F=0.992,P>0.05),胸壁107.9～111.3 HU(F=2.044,P>0.05),椎骨835.6～875.3 HU(F=1.453,P>0.05);而CT值SD差异有统计学意义:肺9.5～29.0 HU(F=108.7,P<0.01),胸壁10.1～32.4 (F=84.3,P<0.01),椎骨19.2～57.1 HU(F=30.6,P<0.01),且随电流降低而增加.临床患者低剂量扫描显示,不同性别组图像噪声和伪影严重程度(男性无或轻微者74例,严重者17例;女性无或轻微者81例,严重者28例)差异无统计学意义(X~2=2.294,P>0.05),不同体型组的体质量指数[(BMI)<18.5组无或轻微者29例,严重者2例;18.5≤BMI<24.0组无或轻微者120例,严重者13例;BMI≥24.0组无或轻微者6例,严重者30例]差异有统计学意义(X~2=128.274,P<0.01).低剂量扫描图像的噪声和伪影在上肺野(无或轻微者80例,严重者38例;X~2=18.918,P<0.01)、肺野后部(无或轻微者89例,严重者33例;X~2=6.760,P<0.05)较严重.结论 低剂量CT扫描图像噪声增加,噪声和伪影在肺野后、上部较严重,可能和骨骼分布有关.应根据受检者BMI调整扫描方案(mAs值),做到扫描方案个体化.     

GE8800CT图像中几种常见伪影的预防处理

ＧＥ８８００ＣＴ图像中几种常见伪影的预防处理武警广东总队医院ＣＴ室王成铭刘卫国（广州５１０５０７）关键词ＣＴ伪影处理预防我院使用美国ＧＥ８８００二手ＣＴ机已５ａ多,在临床实践中,对常见的伪影形态、原因以及预防处理方法有了一定的认识,现总结如下。１常见...     

Imaging Artifacts of Liquid Embolic Agents on Conventional CT in an Experimental in Vitro Model

BACKGROUND AND PURPOSE:Endovascular embolization using liquid embolic agents is a safe and effective treatment option for AVMs and dural arteriovenous fistulas. The aim of this study was to assess the degree of artifact inducement by the most frequently used liquid embolic agents in conventional CT in an experimental in vitro model.MATERIALS AND METHODS:Dimethyl-sulfoxide–compatible tubes were filled with the following liquid embolic agents (n = 10, respectively): Onyx 18, all variants of Squid, PHIL 25%, PHIL LV, and n-BCA mixed with iodized oil. After inserting the tubes into a CT imaging phantom, we acquired images. Artifacts were graded quantitatively by the use of Hounsfield units in a donut-shaped ROI using a customized software application that was specifically designed for this study and were graded qualitatively using a 5-point scale.RESULTS:Quantitative and qualitative analyses revealed the most artifacts for Onyx 18 and the least artifacts for n-BCA, PHIL 25%, and PHIL LV. Squid caused more artifacts compared with PHIL, both for the low-viscosity and for the extra-low-viscosity versions (eg, quantitative analysis, Squid 18: mean ± SD, 30.3 ± 9.7 HU versus PHIL 25%: mean ± SD, 10.6 ± 0.8 HU; P < .001). Differences between the standard and low-density variants of Squid were observed only quantitatively for Squid 12. There were no statistical differences between the different concentrations of Squid and PHIL.CONCLUSIONS:In this systematic in vitro analysis investigating the most commonly used liquid embolic agents, relevant differences in CT imaging artifacts could be demonstrated. Ethylene-vinyl alcohol–based liquid embolic agents induced more artifacts compared with liquid embolic agents that use iodine as a radiopaque component.

In addition to microneurosurgery and stereotactic radiation therapy, endovascular embolization using liquid embolic agents (LEAs) is an effective treatment mode for the therapy of cerebral AVMs or cranial dural AVFs. Depending on the type and extension of the vascular malformation, the endovascular treatment can be performed either alone or in combination with one of the other methods.¹For the treatment of such vascular malformations, several LEAs, each with different properties, are currently available on the market. The most commonly used nonadhesive material is Onyx (Medtronic), a LEA consisting of an ethylene-vinyl alcohol (EVOH) copolymer, dimethyl-sulfoxide, and tantalum powder. Numerous studies have demonstrated the effectiveness and safety of Onyx for the treatment of vascular malformations.^2,3 Another LEA, also based on EVOH and tantalum powder is Squid (Balt Extrusion), which has been commercially available since 2012, with its low-viscosity versions, Squid 18 and Squid 18 low density (LD), and its extra-low-viscosity versions, Squid 12 and Squid 12 LD. For adequate visibility during embolization, radiopacity for these 5 nonadhesive agents is induced by the admixed tantalum powder.^4,5 The difference between Onyx and Squid is that for Squid, the tantalum powder consists of a smaller “micronized” grain size, which is aimed at enhancing the homogeneity in radiopacity and improving the visibility during longer injections times.⁵ The aim of the LD variants of Squid is to reduce the radiopacity to improve the differentiation of the embolized and nonembolized parts of the malformation without influencing the embolic properties.A further commercially available LEA, which was introduced recently, is Precipitating Hydrophobic Injectable Liquid (PHIL; MicroVention) with its low-viscosity version PHIL 25% and its extra-low-viscosity version PHIL low viscosity (LV).^6,7 PHIL is a nonadhesive precipitating embolic agent that consists of 2 specific copolymers [poly(lactide-co-glycolide) and polyhydroxyethylmethacrylate] as its active ingredients and triiodophenol (an iodine compound), which is covalently bound to the copolymers, thus enabling the intrinsic radiopacity of PHIL.^8,9Before the introduction of these nonadhesive embolic agents, which are all based on the mechanism of precipitation, liquid embolization was predominantly performed with adhesive cyanoacrylates. The active component of cyanoacrylates is n-butyl cyanoacrylate (n-BCA), which is available in different chemical compositions and is normally mixed with iodized oil for adequate radiopacity. Even though the use of cyanoacrylates has decreased since the introduction of the above-mentioned nonadhesive LEAs,^10,11 n-BCA and its derivates are still used effectively in particular situations, for example, for the treatment of high-flow malformations and for specific techniques such as the pressure cooker technique.¹²A major drawback of LEAs is imaging artifacts, predominantly in CT.^13,14 Because intracranial vascular malformations are associated with an increased risk of peri- and postprocedural hemorrhage, embolization-related artifacts can represent a crucial obstacle in the detection of intracranial blood during or after embolization in CT.¹⁵ Furthermore, some vascular malformations, especially complex AVMs, cannot be completely occluded by endovascular means, requiring subsequent radiation therapy afterward.¹ The corresponding treatment-planning recordings are usually based on conventional CT imaging.¹⁶ Thus, embolization-related artifacts represent another substantial drawback for adequate and safe treatment planning of further radiation projects.^17-19Systematic data for imaging artifacts of LEAs is rare. To our knowledge, to date, only a few reports with low case numbers that investigated the imaging artifacts of the above-mentioned LEAs (Onyx versus PHIL and Onyx versus Squid) are available.^13,14 The differences in CT artifacts between Squid and PHIL, between nonadhesive LEAs and n-BCA, and imaging artifacts of the extra-low viscosity LEAs Squid 12 and PHIL LV were not the focus of research until now.The aim of the present study was the systematic assessment of artifacts of the most commonly used LEAs in conventional CT in an in vitro tube model.     

乳腺少见肿瘤影像分析

目的　评价乳腺少见肿瘤的影像学特点。方法　回顾分析经手术及病理证实 11例少见乳腺肿瘤影像学表现。结果　11例乳腺肿瘤中 ,非何杰金氏淋巴瘤 1例 ,恶性多形性腺瘤 1例 ,乳腺原发性鳞癌 1例 ,骨肉瘤 1例 ,叶状囊肉瘤 2例 ,错构瘤 5例。骨肉瘤特征表现为 :肿块中有象牙骨组织 ,恶性多形性腺瘤表现为较大肿块 ,边界清楚 ,周边血管增粗。叶状囊肉瘤为低度恶性肿瘤 ,病程长 ,肿块大 ,边界清楚 ,内有粗大钙化 ,周围有宽窄不一透亮带 ,通常无腋下淋巴结转移。错构瘤的特征表现是 :瘤体密度高度不均 ,高密度区域呈岛屿状分布 ,包膜完整。原发性乳腺鳞癌及非何杰金氏淋巴瘤无特征性表现。结论　乳腺少见肿瘤影像无明显特征性 ,需综合分析才有可能作出定性诊断     

Parallel Imaging Artifacts in Body Magnetic Resonance Imaging

Objective

To familiarize the reader with the fundamental concepts of partial parallel imaging (PPI); to review the technical aspects of PPI including calibration scan, coil geometry, and field of view (FOV); and to illustrate artifacts related to parallel imaging and describe solutions to minimize their negative impact.

Results

PPI has led to a significant advance in body magnetic resonance imaging by reducing the time required to generate an image without loss of spatial resolution. Although PPI can improve image quality, it is not free of artifacts, which can result in significant image degradation. Knowledge of these artifacts and how to minimize their effect is important to optimize the use of parallel imaging for specific body magnetic resonance imaging applications.

Conclusions

The reader will be introduced to the fundamental principles of PPI. Common imaging characteristics of PPI artifacts will be displayed with an emphasis on those seen with image-based methods, the principles behind their generation presented, and measures to minimize their negative impact will be proposed.     

Evaluation of a Metal Artifacts Reduction Algorithm Applied to Postinterventional Flat Panel Detector CT Imaging

BACKGROUND AND PURPOSE:Flat panel detector CT images are degraded by streak artifacts caused by radiodense implanted materials such as coils or clips. A new metal artifacts reduction prototype algorithm has been used to minimize these artifacts. The application of this new metal artifacts reduction algorithm was evaluated for flat panel detector CT imaging performed in a routine clinical setting.MATERIALS AND METHODS:Flat panel detector CT images were obtained from 59 patients immediately following cerebral endovascular procedures or as surveillance imaging for cerebral endovascular or surgical procedures previously performed. The images were independently evaluated by 7 physicians for metal artifacts reduction on a 3-point scale at 2 locations: immediately adjacent to the metallic implant and 3 cm away from it. The number of visible vessels before and after metal artifacts reduction correction was also evaluated within a 3-cm radius around the metallic implant.RESULTS:The metal artifacts reduction algorithm was applied to the 59 flat panel detector CT datasets without complications. The metal artifacts in the reduction-corrected flat panel detector CT images were significantly reduced in the area immediately adjacent to the implanted metal object (P = .05) and in the area 3 cm away from the metal object (P = .03). The average number of visible vessel segments increased from 4.07 to 5.29 (P = .1235) after application of the metal artifacts reduction algorithm to the flat panel detector CT images.CONCLUSIONS:Metal artifacts reduction is an effective method to improve flat panel detector CT images degraded by metal artifacts. Metal artifacts are significantly decreased by the metal artifacts reduction algorithm, and there was a trend toward increased vessel-segment visualization.

With continued technologic developments, both diagnostic and interventional neuroendovascular applications of flat panel detector CT (FDCT) have increasingly expanded. FDCT offers higher spatial resolution relative to multidetector row CT and improved visualization of clipped aneurysms and endovascular stents.¹ Imaging performed in the endovascular suite also offers rapid visualization of periprocedural complications, thus allowing faster management.² The acquired FDCT images, however, are degraded by artifacts created by radiodense cerebral endovascular and surgical implants including coils, stents, and clips, limiting the use of FDCT as a postprocedural imaging technique.Metal artifacts reduction (MAR) in CT images has been attempted by both interpolation and algebraic methods. Interpolation methods have been quite successful and, most important, require less computational power relative to algebraic methods, resulting in less computing time. One of the first interpolation-based MAR algorithms used a 1D linear interpolation for single-row CT data, which is inadequate for FDCT data.³ The MAR algorithm investigated in this work, developed by Siemens Healthcare Sector, is a modification and extension of a recently published MAR procedure by Prell et al.⁴ We present validation of the FDCT MAR prototype algorithm by using a phantom study and an objective critique by 7 clinicians.     

十二指肠壅积症的CT影像分析

目的 探讨十二指肠壅积症(DSD)的多层螺旋CT影像表现及诊断价值.方法 对17例DSD患者(实验组)及20例无症状的成年人(对照组)进行仰卧位多层螺旋CT检查,分析两组人群十二指肠和肠系膜上动脉(SMA)的CT影像表现,比较两组的影像差异.结果 DSD的CT影像包括胃十二指肠球部、降段及部分水平段扩张,SMA对十二指肠水平段造成压迹,十二指肠水平段充盈不佳、管腔狭窄等改变;实验组SMA与腹主动脉(A0)的夹角与对照组相近,两组间无显著差异(t=0.713,P＞0.20);实验组SMA与AO间距较对照组小,但两组间无显著差异(t =0.545,P＞0.25).实验组SMA与AO间距＜10 mm者有10例(58.82％)、SMA与AO夹角＜30°者有11例(64.71％),而对照组SMA与AO间距＜10 mm者7例(35％)、SMA与AO夹角＜30°者4例(20％),但两组之间SMA与AO间距及夹角的差异均不具有统计学意义(精确概率P=0.068,0.071).实验组中11例SMA与AO夹角＜30°的患者,这11例患者与实验组之间SMA与AO夹角的差异也不具有统计学意义(t=0.768,P＞0.10).结论 多层螺旋CT观察十二指肠的形态变化有利于DSD的诊断,但单纯测量SMA与AO间距和夹角是否能确诊DSD则难以定论.     

16层螺旋CT冠状动脉造影伪影分析

目的：探讨16层螺旋CT冠状动脉造影伪影表现和成因，提高冠状动脉CT血管造影质量和诊断准确性。材料和方法：回顾性分析400例16层螺旋CT冠状动脉造影中失败及假狭窄诊断的38例图像，以DSA冠状动脉造影为金标准，分析上述病例中的伪影及假狭窄的CT表现。结果：伪影分为呼吸伪影、心律不齐伪影、冠状动脉搏动伪影、上腔静脉高浓度造影剂产生假斑块伪影、冠状动脉重度钙化产生的伪影，上述各种伪影均具有独特的影像特征。结论：准确分析CT冠状动脉成像伪影的影像表现及成因，对提高CT成像质量，减少诊断失误有很大的临床意义。