与IP板相关的CR图像伪影分析及对策

计算机射线照相（CR）获得的影像往往会带有各种伪影,直接影响诊断质量,伪影可能来源于整个CR系统的各个部分,如：成像板（IP）、扫描、读出、处理、擦除、激光照相机等等,而成像板作为CR系统中用于捕俘射线影像信息的传感器,其影响是最关键的,本文集中分析与IP板相关的图像伪影及应对措施。     

激光胶片静电伪影产生的原因及排除方法

在医生读片时，有时发现一些无规则散乱的树枝状伪影(图1、2)，直接影响医生对疾病的诊断。对照监视器显示的图像，没有发生任何伪影。显然，这种伪影的产生与影像采集过程无关，图像采集的过程包括：CR，MR，DSA等。在胶片成像的过程中，以上的数字成像设备图像采集直接通过     

医用(CT)X射线辐射源故障的排除

一、医用(CT)X射线辐射源最常见故障是伪影伪影是由于设备或患者造成、与扫描物体无关的影像,在图像中表现的形状各异,并会影响诊断的准确性。伪影分患者移动造成的运动伪影、金属物造成的放射状伪影、多能谱X线造成的射线硬化伪影、层厚过大引起的部分容积效应伪影等。与检定有关的伪影是由设备造成而与患者无关的伪影,也是检定过程中经常遇到的故障,一般有放射状伪影、中心低密度伪影、环状伪影、蜂窝状、海绵状伪影等。     

东芝X VISION CT伪影的诊断及相应的排除方法

CT设备在临床应用时，经常会出现各种各样的伪影，比如环形伪影、斜线伪影以及波纹伪影，伪影出现较轻的时候使得图像质量下降，影响诊断准确率。当伪影严重时，扫描出的图像根本无法诊断疾病。为提高CT的图像质量，对CT扫描中经常出现的伪影进行分析判断并加以排除，就显得尤为重要。本文只就东芝X VISION机器的伪影进行分析。     

高分辨率CT低剂量扫描在限制性通气障碍患者中的应用

目的:探讨限制性通气障碍高分辨率CT(HRCT)低剂量扫描能否达到常规扫描的诊断要求。方法:选取2013年4月-2015年3月在我院就诊的部分限制性通气障碍患者,进行低剂量以及常规HRCT扫描,对比不同扫描方案下图像质量和伪影情况。结果:27例常规HRCT扫描图像质量Ⅰ级16例,Ⅱ级8例,Ⅲ级3例,而低剂量HRCT扫描图像质量Ⅰ级18例,Ⅱ级7例,Ⅲ级2例,低剂量HRCT图像质量与常规HRCT相当(P﹥0.05);常规HRCT图像中,15例无伪影,轻度伪影5例,中度伪影4例,重度伪影3例,而低剂量HRCT图像中,16例无伪影,轻度伪影6例,中度伪影4例,重度伪影1例,低剂量HRCT图像伪影情况与常规HRCT无统计学差异(P﹥0.05)。结论:限制型通气障碍患者低剂量和常规剂量HRCT扫描图像质量及伪影情况相当,但低剂量HRCT扫描减少了病人的辐射剂量,降低对病人的辐射损伤。     

一种CT图像放射形金属伪影的校正方法（英文）

在计算机断层成像(computer tomography,CT)技术中,散射和射束硬化等因素会使CT图像出现放射状的金属伪影.这些金属伪影影响着医生对疾病的诊断同时干扰放射治疗过程中的剂量计算等.为了解决目前临床实践中广泛使用的CT扫描机成像中的金属伪影问题,本文就牙科金属材料形成的伪影问题提出了一种基于极坐标变换的校正方法.该算法通过极坐标变换将放射状伪影条纹转换为行列可分的线形伪影,并对得到的线形伪影图像进行频域滤波处理,最终得到校正后的CT图像.采用标准差和平均CT值差异等参数对11例患者CT图像数据进行量化研究,结果表明处理后的CT图像伪影条纹减少.该算法能够在一定程度上去除CT图像中放射状的伪影条纹,并且保护了图像边缘信息.     

一种改进的MRI图像刚性平移运动伪影的校正

在磁共振成像过程中由于患者的运动会在图像中造成运动伪影,从而造成图像的退化,严重影响临床诊断．本文对MRI图像刚性平移运动伪影提出了一个改进的后处理方法：首先用谱平移理论消除频率编码方向平移运动;然后建立模糊模型表示图像的背景并对其进行抑制,用数学形态学的方法确定图像的支撑域;最后以能量熵为收敛准则,用相位恢复算法对频率编码方向残余的子像素移动造成的伪影和相位编码方向的伪影进行消除．实验表明,应用本研究提出的方法能够明显地消除图像空间运动造成的伪影．     

DR静态平板去除错层伪影的方法探究

岛津D-vision平板摄影系统在多种疾病检查中具有较高的价值,但在实际应用过程中会生成错层伪影的图像,致使DR静态平板出现错层伪影的因素较多,本文从电路角度对岛津D-vision摄影系统的平板进行了改进设计,力图从源头上降低DR图像断层伪影发生率。     

印刷品自动光学检测伪缺陷去除方法

目的 为了解决使用差影法进行印刷品表面缺陷自动光学检测存在伪缺陷从而造成误检的问题,提出一套通过提高配准精度和空间滤波来减少伪缺陷的方法。方法 使用连续域蚁群算法求全局最优解,改进基于轮廓的模板匹配算法配准精度,减少伪缺陷的产生;配准时的仿射变换会产生轮廓伪影,根据伪影的分布特点将图像切分成轮廓区和非轮廓区。分别使用不同的空间滤波方法削弱伪缺陷,再使用阈值分割将其剔除。结果 在实验环境中,连续域蚁群算法改进的基于轮廓的模板匹配配准方法,可精确到亚像素级,配准率为92%;使用空间滤波剔除伪缺陷后进行缺陷检测,缺陷误检率为0,漏检率为3%;印刷品表面缺陷平均检测时间为1.05 s,最长时间小于1.5 s。结论 该研究改善了差影法在自动光学检测中的效果,方法快速、有效、易于实现;在降低了缺陷误检率的同时不会造成大量漏检;满足在线检测的要求,可用于实际工业生产。     

基于相位恢复和直方图修正法校正ghost伪影

EPI(Echo Planar Imaging)技术基于方向相反的频率读出梯度交替采集MR信号的奇、偶回波.但是,由于成像物体的磁敏感性、化学位移及磁场B0不均匀性等因素的影响会导致奇、偶回波之间产生相位移动,因而会产生ghost伪影.提出了基于相位恢复和直方图修正的ghost伪影消除方法,首先以最小熵为约束条件运行迭代算法直到得到满意的图像,然后用直方图规定化修正直方图,从而建立相位恢复后的图像和目标图像的灰度映射关系.运用该方法能够明显地降低ghost伪影.实验证明这种方法是可行的.     

1140例计算机X线摄影(CR)照片常见问题研讨

我们曾经对190例计算机X线摄影(CR)照片问题进行综合分析研究(文章发表于本刊2004年第4期),本文是对该项研究的继续,重点是介绍CR照片的测试方法、评价依据、评价内容,并在此基础上在对1140例CR照片质量进行分类、分项分析,进一步探讨CR照片常见问题产生的原因及解决方法,以求提高照片质量。     

IP板研究现状与前景展望

CR技术是数字射线检测技术中的非胶片射线照相检验技术,具有强大的图像后处理功能。本文系统阐述了CR系统的组成和工作原理,并对其主要组成部分——IP板的结构、功能、工作原理和优点做了详细介绍。     

Complete erasing of ghost images on computed radiography plates and role of deeply trapped electrons

Computed radiography (CR) plates made of europium-doped Ba(Sr)FBr(I) were simultaneously exposed to filtered ultraviolet light and visible light in order to erase ghost images, i.e., latent image that is unerasable with visible light (LIunVL) and reappearing one, which are particularly observed in plates irradiated with a high dose and/or cumulatively over-irradiated. CR samples showing LIunVLs were prepared by irradiating three different types of CR plates (Agfa ADC MD10, Kodak Directview Mammo EHRM2, and Fuji ST-VI) with 50 kV X-ray beams in the dose range 8.1 mGy—8.0 Gy. After the sixth round of simultaneous 6 h exposures to filtered ultraviolet light and visible light, all the LIunVLs in the three types of CR plates were erased to the same level as in an unirradiated plate and no latent images reappeared after storage at 0 °C for 14 days. With conventional exposure to visible light, LIunVLs consistently remained in all types of CR plates irradiated with higher doses of X-rays and latent images reappeared in the Agfa M10 plates after storage at 0 °C. Electrons trapped in deep centers cause LIunVLs and they can be erased by simultaneous exposures to filtered ultraviolet light and visible light. To study electrons in deep centers, the absorption spectra were examined in all types of irradiated CR plates by using polychromatic ultraviolet light from a deep-ultraviolet lamp. It was found that deep centers showed a dominant peak in the absorption spectra at around 324 nm for the Agfa M10 and Kodak EHRM2 plates, and at around 320 nm for the Fuji ST-VI plate, in each case followed by a few small peaks. The peak heights were dose-dependent for all types of CR samples, suggesting that the number of electrons trapped in deep centers increases with the irradiation dose.     

工业CR技术最新动态

概述工业计算机射线照相(CR)技术的最新进展,包括CR成像板荧光体结构的改进,信噪比和分辨率的提高,激光扫描器的多成像板同时输入、扫描和数字图像输出,使得对射线照相质量和灵敏度有较高要求、且对检测速度和周期也要兼顾的承压设备焊缝检测,有了稳定可靠的新基础。EN和ASME有关CR标准的推出,又为焊缝实施CR检测提供了法定技术依据。本文旨在为国内承压设备加速推广应用CR检测起推波助澜作用。     

Gait recognition: highly unique dynamic plantar pressure patterns among 104 individuals

Everyone''s walking style is unique, and it has been shown that both humans and computers are very good at recognizing known gait patterns. It is therefore unsurprising that dynamic foot pressure patterns, which indirectly reflect the accelerations of all body parts, are also unique, and that previous studies have achieved moderate-to-high classification rates (CRs) using foot pressure variables. However, these studies are limited by small sample sizes (n < 30), moderate CRs (CR ≃ 90%), or both. Here we show, using relatively simple image processing and feature extraction, that dynamic foot pressures can be used to identify n = 104 subjects with a CR of 99.6 per cent. Our key innovation was improved and automated spatial alignment which, by itself, improved CR to over 98 per cent, a finding that pointedly emphasizes inter-subject pressure pattern uniqueness. We also found that automated dimensionality reduction invariably improved CRs. As dynamic pressure data are immediately usable, with little or no pre-processing required, and as they may be collected discreetly during uninterrupted gait using in-floor systems, foot pressure-based identification appears to have wide potential for both the security and health industries.     

Objective analysis and bit rate analysis of HEVC compressed 4D-fMRI images

Medical imaging and clinical diagnostics are complementary to one another since their analysis is typical and contains critical information. The growing volume of data has become one of the biggest challenges, as the acquisition of medical modalities is currently having high resolution from the improved and efficient machines (3 to 7 T or more). Moreover, image and video compression is a need with the consideration that there should not be any gap for losing the important information. Less bitrate requirement with high compression ratio without sacrificing important detail is a challenge these days. The current study, is dealing with the compression of 4D-functional medical resonance images (fMRI) with a codec, that is, high-efficient video coding (HEVC/H.265) and its objective analysis along with its predecessor that is advanced video coding (AVC/H.264) and with VP8 (WebM Project of Google) reported here. Further, the bit rate analysis that has been conducted, also accounts in conjunction with the bitrate investigation, which is an imperative perspective vital for the telemedicine field. The simulation results reported here represents the compression ratio (CR = 118.23:1) with HEVC/H.265 codec over the compression ratio (CR = 20.52:1) provided by AVC/H.264 and VP8 (CR = 78.29:1). There has been significant improvement observed in alignment of the peak signal-to-noise ratio (APSNR), structural similarity (SSIM), and mean squared error (MSE) metrics. Overall, the performance of the anticipated technique is satisfactory for the forthcoming telemedicine or clinical use.     

一种基于小波子带熵的遥感图像压缩算法

提出了一种使用小波子带熵进行比特分配的遥感图像压缩算法.对遥感图像进行小波提升分解后,分析了各高频子带能量百分比及其熵的变化趋势,在此基础上提出了一种新的快速比特分配方法-使用子带熵进行比特分配.然后对各个高频子带进行均匀量化,量化后的数据采用比特平面编码.对最高比特平面只记录该比特平面中非零系数的坐标,其它比特平面采用行程编码和Huffman编码方法进行压缩.实验结果表明,纹理复杂以及相对平坦的遥感图像使用该算法压缩后都可以获得很好的重构图像质量,峰值信噪比均大于34dB,而压缩比则与图像的复杂程度有关.     

CR在危急重症患者胸部床旁摄影的临床应用

【目的】:探讨计算机X线摄影(CR)在危急重症患者胸部床旁摄影的临床应用价值。【材料与方法】:收集整理289例急危重胸部床旁CR片及相关资料,根据曝光条件参数,运用计算机图像后处理技术对影像清晰度、对比度及病灶边缘密度细微调整、统计、归纳和分析。并且与普通屏片组合床旁照片233例相比较。【结果】:CR床旁优片213份,占74%;一般片63份,占22%。病变显示炎症145例,占50%;心功能不全86例,占35%;外伤85例,占31%;心脏术后46例,占16%。【结论】:CR床旁急危重胸部片对比度与清晰度良好,废片率低,病变显示清晰,诊断准确、及时,为抢救病人生命赢得了时间。     

A hybrid contextual compression technique using wavelet and contourlet transforms with PSO optimized prediction

Contextual compression is an essential part of any medical image compression since it facilitates no loss of diagnostic information. Although there are many techniques available for contextual image compression still there is a need for developing an efficient and optimized technique which would produce good quality images at lower bit rates. This article presents an efficient contextual compression algorithm using wavelet and contourlet transforms to capture the fine details of the image, along with directional information to produce good quality at high Compression Ratio (CR). The 2D discrete wavelet transform, which uses the simplest Daubechies wavelets, db1, or haar wavelet, is chosen and used to get the subband coefficients. The approximate coefficients of the higher subbands undergo contourlet transform employing length N ladder filters for capturing the directional information of the subbands at different scale and orientations. An optimized approach is used for predicting the quantized and the normalized subband coefficients resulting in improved compression performance. The proposed contextual compression approach was evaluated for its performance in terms of CR, Peak Signal to Noise Ratio, Feature SIMilarity index, Structure SIMilarity Index, and Universal quality (Q) after reconstruction. The results clarify the efficiency of the proposed method over other compression techniques.