超声伪像.ppt

Ultrasound artifacts and control methods超声伪像及控制方法Definition 定义定义 Artifacts can be defined as any structure in an ultrasound image that does not have a corresponding anatomic tissue structure.伪像被定义为在超声图像中显示出任何非解剖组织结构的图像 Artifacts are a common occurrence in an ultrasound display since they are often the result of the physical properties of ultrasound itself.伪像是在超声显示中一种常见的现象，是由超声本身的物理特性所导致Recognizing artifacts is essential to proper ultrasound interpretation,as not identifying an artifact as such may lead to unwarranted clinical intervention or concern.认识伪像是超声诊断必不可少的，不确定的伪像可能导致不必要的临床干扰和判断。为了得到理想的图像，超速仪器是这样设定的：1.发射声束呈理想状态沿直线传播2.超声声束穿过组织的平均速度为1540m/s3.各组织衰减系数相同，利用DGC得到均匀一致的图像 由于这些条件不能满足人体结构的复杂性，所以超声伪象是普遍存在的。1.Refractory 分辨率 2.Attenuation 衰减 Axial Resolution 横向分辨力 Shadowing 声影 Lateral Resolution 纵向分辨力 Enhancement 后方回声增强 Partial volume effect 部分容积效应 Refractory Shadowing 侧方声影 3.Propagation Path 传播途径 Reverberation 混响伪像 Ringdown 振铃伪像（内部混响）Refraction 折射伪像 Mirror Image 镜像伪像 Side Lobe 旁瓣伪像Reverberation 混响伪像混响伪像Reverberation artifact is defined as equally spaced,bright linear echoes resulting from repeated reflections from specular-type interfaces.混响伪像被定义为声波在界面之间来回反射形成的等距的，明亮的线性回声。Frequently this artifact is seen in the near field on a sonographic image.伪像常常发生在超声图像的近场。Reverberatory artifact is produced when the transmitted pulse of ultrasound energy strikes the interface between the transducer and the skin.伪像是由在超声能量冲在换能器表面和反射界面之间来回反射撞击形成的。Ringdown 振铃伪像振铃伪像When ultrasound strikes a strong interface such as gas or bone,one of two responses may be reproduced:当超声撞击强界面，例如气体或骨骼时，可能产生两种结果：either there is no sound conduction through the area(resulting in shadowing),要么没有任何声束通过该地区（产生阴影），or numerous secondary reverberations are produced.These secondary reverberations can cause a series of parallel echogenic lines extending into the tissues.It is also called Comet tail 或产生众多的二次回响。这些二次回响可引起一系列平行强回声线延伸进入组织。它也被称为彗尾征。using the intra uterine comet tail sign can identify the presence of metal IUD利用宫腔内彗尾征可以识别金属节育环的存在 Shadowing 声影声影 Because of strong reflection and attenuation structure is very large,so that the ultrasonic energy weakened sharply 由于具有强反射或声衰减甚大的结构存在，使超声能量急剧减弱resulting in ultrasound can not reach the area at the rear,called acoustic shadow 以致在该结构的后方出现超声不能达到的区域，称为声影区胆囊结石的WES征（囊壁、结石、声影三联征）Refractive shadow 折射声影折射声影Acoustic shadow sometimes on both side walls of the spherical structure behind the emergence of a narrow,called the refractive shadow.有时在球形结构的两侧壁后方会各出现一条细狭的声影，称为折射声影This is because the ultrasonic irradiation to the edge of the sphere,due to refraction between them so that there is a plot behind the loss of radiation,no echo caused这是因为超声照射到球体的边缘，因折射关系，使后方有一小区域失照射，没有回声所致注意注意折折射声影射声影只是从只是从超声物理的角度提示超声物理的角度提示病灶（或脏器）具有声速较高的外壁，病灶（或脏器）具有声速较高的外壁，多为致密的纤维组织组成多为致密的纤维组织组成，但不，但不能推能推断该病灶的性质（液性或实质，良性断该病灶的性质（液性或实质，良性或恶性）。或恶性）。产生的条件产生的条件圆形病灶圆形病灶病灶周围有纤维包膜（声速较软组织病灶周围有纤维包膜（声速较软组织高）高）入射角大于临界角时产生全反射入射角大于临界角时产生全反射Enhancement of behind echo 后方回声增强后方回声增强When the sound attenuation lesion or tissue very small,it will be stronger than the posterior echo around the same depth,called the posterior echo enhancement.当病灶或组织的声衰减甚小时，其后方回声将强于同等深度的周围回声，称为后方回声增强。Partial volume effect 部分容积部分容积效应效应Caused by the beam width,which is the ultrasonic tomographic slice thickness is wider,the echo structure together with the adjacent target as shown in the graph伪象由声束宽度引起，也就因为超声断层图的切片厚度较宽，把邻近靶区结构的回声一并显示在声像图上超声所获得的图像代表声束容积内回声信息在厚度上的叠加图像部分容积效应使膀胱后壁显示不清 此类此类伪象常发生于伪象常发生于小型的液性病灶小型的液性病灶胆总管的部分容积效应此征常见于较大的结石Side lobe artifact 旁瓣伪像旁瓣伪像Caused by the sidelobe echo ultrasonic beam,dog ear on both sides of the stone strong echo(dog ear)like graphics旁瓣伪象由超声束的旁瓣回声造成，在结石等强回声两侧出现“狗耳（dog ear）”样图形Mirror-image artifacts 镜像伪像镜像伪像Mirror-image artifacts are produced when an object is located in front of a highly reflective surface at which near total reflection takes place.当物体在一个高反射界面前方时，声束发生了完全反射而形成镜像伪象。Mirror image of left kidneyDoppler Artifacts 多普勒超声伪像Pulse wave Doppler artifacts misrepresent the change in transmit and received frequency caused by motion(Doppler shift).Artifacts typically disappear with corrective measures.脉冲波多普勒伪像是由运动所造成的发射和接收的频率改变形成（即多普勒频移）。通过正确的方法，典型的伪像会消失。1、Aliasing 混叠伪像混叠伪像 The color of the image will be suddenly flip the stack,that color reversal,and show the opposite flow direction 混叠时图像的颜色将突然翻转，即彩色逆转，并显示相反的血流方向 彩色血流混叠伪象 频谱多普勒混叠伪象2、Flash 闪烁伪像A sudden burst of color Doppler extending beyond the region of blood flow caused by tissue or transducer motion由于组织或传感器的运动所造成的一阵突然的彩色多普勒血流区域，延伸超出血管范围3、Mirror Image 镜像伪象Duplication of a Doppler shift on the opposite side of a strong reflector在强反射体对面形成多普勒频移的复制影像Twinkling artifact 快闪伪像快闪伪像The twinkling artifact is the color Doppler flow imaging in reflective material rear display color signal red and blue fast changing phase block.快闪伪像是彩色多普勒血流显像中，强反射物质后方显示快速变化的红蓝相嵌的彩色信号 强回声界面的光滑与否是产生快闪伪像的关键，研究发现胆囊内胆固醇沉着其后方均产生彩色多普勒伪像，而形态光滑的结石多在两侧边缘产生快闪伪像，胆囊内充满型结石也是部分出现快闪伪像。伪象的形成与结石的成分也有关系，某些结构疏松易产生多重散射的物质就容易产生快闪伪像胆固醇沉着伴闪烁伪像Methods of Overcoming Doppler Artifacts控制多普勒超声伪像的方法AliasingIncrease the pulse repetition frequency(scale)增加的脉冲重复频率（尺度）Increase the Doppler angle 提高多普勒角Decrease operating frequency 降低操作频率Decrease depth of sample volume(sample gate)降低取样容积的深度Change to continuous wave Doppler 改变为连续波多普勒超声FlashIncrease the scale 扩大扫查范围Decrease the color Doppler gain 减少彩色多普勒增益Increase filtering of low flow velocities 提高对低速血流的滤过Mirror ImageDecrease the color Doppler gain 减少彩色多普勒增益Use a different acoustic window 使用不同的声窗Understanding the physics of pulse wave Doppler ultrasound is essential.Adjusting the ultrasound system controls and acoustic window typically corrects Doppler artifacts.了解脉冲波多普勒超声的物理本质。可以通过调节超声波系统的控制和声学窗口来纠正多普勒伪像。谢谢观看