双能量X线荧光数字直接成像系统及图像分离技术的实现

通过计算机主机控制 X线管电压调整、滤线板切换和图像拍摄 ,采用 2 m m铜板过滤高能 X线 ,较好地实现了高、低能量 X线能谱的分离 ,以“双千伏技术”实现了双能量 X线数字成像 ,能够在 2～ 3s内获得高、低能 X线图像 ,基本克服了两幅图像间的运动伪迹。采用简化的双能量图像分离技术获得了胸部软组织图像     

数字化X线成像系统的成像特性及其校正技术

随着一些新的Ｘ线图像处理方法的出现，对数字Ｘ互图像性能的要求将越来越高，本文从分析数字化Ｘ线成像系统的物理机制出发，提出了数字化Ｘ线成像系统的数学模型，并根据这一模型导出了Ｘ线成像的非线性规律及面不均匀性的规律，给出了对这些不利因素的校正方法，为进行数字Ｘ线图像的后续处理打下了坚实的基础。     

一种基于广谱X线条件下的双能量X线骨密度测量技术

虽然双能量Ｘ线技术的骨密度测量方法在很多方面优于传统的双光子骨密度测量方法，但由于实际Ｘ线源的广谱性，使这一方法的测量结果不可避免地带有很大误差。本文从分析实际Ｘ线系统的特性出发，提出了一种不受任何前提假设条件限制的骨密度测量方法，并通过实验对这一方法进行了验证，证明其测量结果要优于传统的双能量Ｘ线骨密度测量方法。     

双能量X线图像处理技术中射束硬化补偿算法的研究

为解决X射线在人体组织中的射束硬化效应对双能量图像分离的影响,本文作者采用与人体软组织吸收系数接近的有机玻璃测量X线的衰减系数,用二阶多项式拟合X线衰减的非线性性,求出拟合系数,在双能量X线图像减影之前对高、低能图像分别作非线性校正,取得了较好的效果.     

X射线机数字化成像

随着ＣＴ、ＭＲＩ、ＤＳＡ等数字化影像技术在临床的广泛应用，作为正在逐步取代普遍放射照像技术（增感屏／胶片系统）的数字化Ｘ线影像系统也日趋成熟。数字化Ｘ线影像系统在图像的采集、显示、后处理、管理和传送等功能方面有着传统Ｘ线成像无可比拟的优势和发展前景，它与快速发展的计算机网络技术逐步融合，使整个放射科发生着重大变化。     

数字X线成像术探测器

数字化Ｘ射线成像技术提高了图像质量，使其能够进行医学图像处理、计算机辅助诊断及远程放射成像。图象质量与从病人身上透射过来的Ｘ线信息的准确探测紧密相关，即与Ｘ线探测器的性能关系密切。数字放射成像术的探测器必须适合它们被应用的特殊的放射学过程。主要的参数有：空间分辨率、响应均匀性、对比灵敏度、动态范围、探测速度。下面将对一些适合数字Ｘ射线成像的探测器技术进行回顾，探讨用于全方位探测器的设备及适于Ｘ线扫     

数字X线成像术探测器

数字化Ｘ射线成像技术提高了图象质量，使其能够进行医学图像处理、计算机辅助诊断及远程放射成像。图象质量与从病人身上透射过来的Ｘ线信息的准确探测紧密相关，即与Ｘ线探测器的性能关系密切。数字放射成像术的探测器必须适合它们被应用的特殊的放射学过程。主要的参数有：空间分辨率、响应均匀性、对比灵敏度、动态范围、探测速度。下面将对一些适合数字Ｘ射线成像的探测器技术进行回顾，探讨用于全方位探测器的设备及适于Ｘ线扫描系统的设备。     

数字X线摄影中原发射线和散射线的实验研究

目的：探索数字X线摄影中散射线对图像质量的影响，确定散射线影响最小、图像边界清晰的窄束X射线的线束直径。方法：在2mm厚的铅板上钻0．8mm-10．0mm不同直径的小孔，获取不同直径的X射线束。以80kV管电压、50mA管电流、15em厚的有机玻璃体模，模拟临床成像条件，获取不同直径的圆形X线束图像，并在相同条件下获取不用铅板的X射线束的图像（开放野）；由ImageJ 1．36b图象处理软件获取沿圆形图像直径方向上的像素值，绘制像素值曲线图，分析X线束图像特征。结果：经2．0mm小孔准直后，散射线对X射线束图像质量的影响几可忽略，可认为X射线束图像全是由原发射线形成的的窄束X射线，图像的像素值与空气间隙大小无关。结论：根据开放野测得的总信号和2．Omm小孔测得的原发射线信号可以计算出散射线的强度，从而将散射线分离出来。     

利用多分辨率分析的胸部X线数字图像粗糙集滤波增强

研究采用一种分辨率分析的胸部X线双能量分离数字图像，实现粗糙集滤波增强的新算法。该方法在用多分辨率分析处理图像的基础上，根据粗糙集理论的条件属性，将每个尺度获得的图像均采用粗糙集处理算法划分为不同的子图像，然后对各个子图像分别作区域滤波和对比度增强处理，最后合成一幅高清晰度的新图像。从结果中可看出，采用这种方法处理后得到的图像效果较为理想，能给临床上的医学工作者提供较清晰的图像，同时也为后续的计算机辅助诊断提供有效的依据。     

基于边缘特征点匹配的临床X线自动全景成像研究

目的：本文提出了一种基于边缘特征点匹配的X线自动全景成像方法。方法：一,采用双正交小波变换与Canny算子相结合的算法实现X线图像的有效边缘提取,并通过矩阵计算得到特征点;二,利用Pearson相关系数和随机抽样一致算法来建立图像之间的相关性和匹配性;三,利用渐入渐出的融合算法实现X线无缝全景成像。结果：该算法可快速高质量地实现骨科临床无外部特征的X线图像序列全景拼接。结论：该算法对弱对比度的X线图像序列全景拼接具有很强的鲁棒性,允许X线图像序列之间存在较小的图像旋转和缩放差异,有助于减少X线使用剂量,具有较强的应用价值。     

Optimization of a flat-panel based real time dual-energy system for cardiac imaging

A simulation study was conducted to evaluate the effects of high-energy beam filtration, dual-gain operation and noise reduction on dual-energy images using a digital flat-panel detector. High-energy beam filtration increases image contrast through greater beam separation and tends to reduce total radiation exposure and dose per image pair. It is also possible to reduce dual-energy image noise by acquiring low and high-energy images at two different detector gains. In addition, dual-energy noise reduction algorithms can further reduce image noise. The cumulative effect of these techniques applied in series was investigated in this study. The contrast from a small thickness of calcium was simulated over a step phantom of tissue equivalent material with a CsI phosphor as the image detector. The dual-energy contrast-to-noise ratio was calculated using values of energy absorption and energy variance. A figure-of-merit (FOM) was calculated from dual-energy contrast-to-noise ratio (CNR) and patient effective dose estimated from values of entrance exposure. Filter atomic numbers in the range of 1-100 were considered with thicknesses ranging from 0-2500 mg/cm2. The simulation examined combinations of the above techniques which maximized the FOM. The application of a filter increased image contrast by as much as 45%. Near maximal increases were seen for filter atomic numbers in the range of 40-60 and 85-100 with masses above 750 mg/cm2. Increasing filter thickness beyond 1000 mg/cm2 increased tube loading without further significant contrast enhancement. No additional FOM improvements were seen with dual gain before or after the application of any noise reduction algorithm. Narrow beam experiments were carried out to verify predictions. The measured FOM increased by more than a factor of 3.5 for a silver filter thickness of 800 microm, equal energy weighting and application of a noise clipping algorithm. The main limitation of dynamic high-energy filtration is increased tube loading. The results of this study can be used to help develop an optimal dual-energy imaging system.     

A correlated noise reduction algorithm for dual-energy digital subtraction angiography

It has long been recognized that the problems of motion artifacts in conventional time subtraction digital subtraction angiography (DSA) may be overcome using energy subtraction techniques. Of the variety of energy subtraction techniques investigated, non-k-edge dual-energy subtraction offers the best signal-to-noise ratio (SNR). However, this technique achieves only 55% of the temporal DSA SNR. Noise reduction techniques that average the noisier high-energy image produce various degrees of noise improvement while minimally affecting iodine contrast and resolution. A more significant improvement in dual-energy DSA iodine SNR, however, results when the correlated noise that exists in material specific images is appropriately cancelled. The correlated noise reduction (CNR) algorithm presented here follows directly from the dual-energy computed tomography work of Kalender who made explicit use of noise correlations in material specific images to reduce noise. The results are identical to those achieved using a linear version of the two-stage filtering process described by Macovski in which the selective image is filtered to reduce high-frequency noise and added to a weighted, high SNR, nonselective image which has been processed with a high-frequency bandpass filter. The dual-energy DSA CNR algorithm presented here combines selective tissue and iodine images to produce a significant increase in the iodine SNR while fully preserving iodine spatial resolution. Theoretical calculations predict a factor of 2-4 improvement in SNR compared to conventional dual-energy images. The improvement factor achieved is dependent upon the x-ray beam spectra and the size of blurring kernel used in the algorithm.(ABSTRACT TRUNCATED AT 250 WORDS)     

一种快速实现X辐射图像分离的方法

通过改变入射的Ｘ射线能谱,从而得到物体内部不同密度成分的分布图像的方法。是Ｘ辐射成像领域的一个重要课题,本文提出了一种新的图像分离方法,即通过影响灰度进行密度分布图像重建,从本质上对这种算法进行了探讨,证明了这种算法的可行性,并且进行了两种成分的图像分离实验,取得了较好的结果,这种方法的突出特点是减少了运算量和运算时间,可以快速实现图象分离,有一定的实用性。     

Dual-energy contrast-enhanced breast tomosynthesis: optimization of beam quality for dose and image quality

Dual-energy contrast-enhanced breast tomosynthesis is a promising technique to obtain three-dimensional functional information from the breast with high resolution and speed. To optimize this new method, this study searched for the beam quality that maximized image quality in terms of mass detection performance. A digital tomosynthesis system was modeled using a fast ray-tracing algorithm, which created simulated projection images by tracking photons through a voxelized anatomical breast phantom containing iodinated lesions. The single-energy images were combined into dual-energy images through a weighted log subtraction process. The weighting factor was optimized to minimize anatomical noise, while the dose distribution was chosen to minimize quantum noise. The dual-energy images were analyzed for the signal difference to noise ratio (SdNR) of iodinated masses. The fast ray-tracing explored 523?776 dual-energy combinations to identify which yields optimum mass SdNR. The ray-tracing results were verified using a Monte Carlo model for a breast tomosynthesis system with a selenium-based flat-panel detector. The projection images from our voxelized breast phantom were obtained at a constant total glandular dose. The projections were combined using weighted log subtraction and reconstructed using commercial reconstruction software. The lesion SdNR was measured in the central reconstructed slice. The SdNR performance varied markedly across the kVp and filtration space. Ray-tracing results indicated that the mass SdNR was maximized with a high-energy tungsten beam at 49 kVp with 92.5 μm of copper filtration and a low-energy tungsten beam at 49 kVp with 95 μm of tin filtration. This result was consistent with Monte Carlo findings. This mammographic technique led to a mass SdNR of 0.92 ± 0.03 in the projections and 3.68 ± 0.19 in the reconstructed slices. These values were markedly higher than those for non-optimized techniques. Our findings indicate that dual-energy breast tomosynthesis can be performed optimally at 49 kVp with alternative copper and tin filters, with reconstruction following weighted subtraction. The optimum technique provides best visibility of iodine against structured breast background in dual-energy contrast-enhanced breast tomosynthesis.     

临床影像设备下的X射线相干散射成像

进行在临床影像设备条件下X射线相干散射成像的研究.通过改进影像设备的准直、聚焦设备,实现更加清晰的成像.经过后期的图像处理,获得确定的光子能量空间分布的图像和曲线,进一步深化了实验研究结果.通过对影像设备的改造,获得了更具有实验说服力的实验图像,经过对实验图像的算法分析,可以肯定临床CR影像设备上进行成像是可行的,面向临床应用的X射线相干散射成像将是进一步的研究目标.在普通X射线影像设备上的X射线相干散射成像研究,是这种成像方式向应用发展的关键步骤.通过对实验设备的优化和改造,达到了预期的成像精度.     

Dynamic dual-energy chest radiography: a potential tool for lung tissue motion monitoring and kinetic study

Dual-energy chest radiography has the potential to provide better diagnosis of lung disease by removing the bone signal from the image. Dynamic dual-energy radiography is now possible with the introduction of digital flat-panel detectors. The purpose of this study is to evaluate the feasibility of using dynamic dual-energy chest radiography for functional lung imaging and tumor motion assessment. The dual-energy system used in this study can acquire up to 15 frames of dual-energy images per second. A swine animal model was mechanically ventilated and imaged using the dual-energy system. Sequences of soft-tissue images were obtained using dual-energy subtraction. Time subtracted soft-tissue images were shown to be able to provide information on regional ventilation. Motion tracking of a lung anatomic feature (a branch of pulmonary artery) was performed based on an image cross-correlation algorithm. The tracking precision was found to be better than 1 mm. An adaptive correlation model was established between the above tracked motion and an external surrogate signal (temperature within the tracheal tube). This model is used to predict lung feature motion using the continuous surrogate signal and low frame rate dual-energy images (0.1-3.0 frames per second). The average RMS error of the prediction was (1.1 ± 0.3) mm. The dynamic dual energy was shown to be potentially useful for lung functional imaging such as regional ventilation and kinetic studies. It can also be used for lung tumor motion assessment and prediction during radiation therapy.     

扇形束CT局部成像的Lambda优质重建

在CT扫描过程中,由于电离辐射作用会导致病人产生癌症或者基因损伤,所以发展低剂量的成像算法正成为热点研究。作为局部成像算法之一的Lambda成像技术,具有减少剂量与快速成像的优点,但由于奇异值的必然存在,从而降低了成像质量。基于Wang Ge局部成像算法框架,提出利用高斯核函数及卷积性质来构建新的Lambda精确成像技术,并对高斯函数的参数选择进行分析。实验结果表明,应用新算法可确保得到高质量的重建图像,其特点是消除了图像中奇异点处微分不存在的现象,使得重建图像更加连续和光滑,尤其是在重建结果中加入了抑制灰度值平均的调节项,使得图像的分辨率和对比度大大提高,更加有利于临床的诊断。     

Quantification techniques for dual-energy cardiac imaging

We have previously reported a motion immune dual-energy subtraction technique in which x-ray tube voltage and x-ray beam filtration are switched at 30 Hz between 60 kVp (2.0-mm Al filter) and 120 kVp (2.0-mm Al + 2.5-mm Cu filtration). In this paper we consider the suitability of these dual-energy images for quantitative measurements of iodine thickness and volume. Optimized iodine signal-to-noise ratio (S/N) was measured as a function of phantom thickness. Using a fixed mAs, the S/N of the dual-energy images was found to decrease by sevenfold as lucite thickness increased from 10 to 25 cm. For the same increase in lucite thickness S/N for time subtraction images decreased by fivefold. Image quality in two human volunteers was subjectively judged to be good. In order to quantitate physiological parameters such as ejection fraction and left ventricular volume, energy dependent corrections for scatter and veiling glare, beam hardening, detector nonuniformity, heel effect, and uncanceled bone signals were developed. Since the dual-energy technique does not completely cancel bone, a preinjection dual-energy subtraction image was used to estimate integrated bone contributions to iodine volume measurements. In a phantom measurement simulating exercise ventriculography, the known (Vk) and videodensitometrically measured (Vm) volumes of 19 mg/cm3 solution of iodine were related by Vm = 0.95 Vk + 1.50 cm3 (r greater than 0.99).     

Dual-energy digital mammography utilizing stimulated phosphor computed radiography

Dual-energy subtraction is a radiographic technique for the acquisition of a material selective image by the weighted subtraction of low- and high-energy digital X-ray images. This is achieved by exploiting the energy dependence of the X-ray attenuation components in the image. This can allow the removal of background morphology to enhance the presentation of otherwise obscured details. The detection of microcalcifications in a mammogram by dual-energy techniques has previously been investigated. These investigations indicated that, using dual-energy techniques, small microcalcifications could be extracted from the background breast morphology with sufficient signal to noise ratio (SNR) to be full visualized. The authors present the extension of a theoretical dual-energy model to incorporate practical considerations and then compare the results with experimentally derived data using a commercially available computed radiography system. In particular the extended model now takes into account the energy dependent detective quantum efficiency of a system. This is thought to be a major factor in reducing the efficiency of dual-energy mammography. The theoretical model predicts that dual-exposure dual-energy mammography, utilizing HRIII image plates, could not provide a detail SNR of five for calcifications smaller than 470 mu m. The experimental results verify this and indicate that dual-energy subtraction mammography, utilizing computed radiography, is currently not a viable technique for the detection of clinically significant microcalcifications. Further advances in X-ray image detector efficiency will be required if the full potential of this technique is to be achieved.