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1.
非下采样Contourlet变换医学图像融合性能研究   总被引:3,自引:0,他引:3  
通过对非下采样Contourlet变换(NSCT)滤波器组合及图像融合规则性能的研究,比较了不同条件得到的融合结果,全面分析了各种融合规则对融合性能的影响。提出低通子带区域能量取大,高频子带方差加权取大和绝对值取大相结合的融合算法。相比基于传统规则的NSCT算法,所提出算法的融合质量及各项指标都有明显提高。实验结果表明,选取合适的滤波器组合和融合规则,即使分解层数较少,方向数不大,也能够获得理想的融合效果,同时还可有效减少融合算法的复杂度。  相似文献   

2.
基于小波变换医学图像融合算法的对比分析   总被引:2,自引:1,他引:1  
小波变换融合方法具有重要的应用价值,而融合规则的选取直接影响着融合效果。为了获得医学临床上实用的小波融合算法,选择标准CT/MRI图像,通过调整和组合各种小波变换低频及高频融合规则进行仿真实验,深入对比分析各种融合规则对医学图像融合性能的影响。在此基础上,提出低频能量取大与高频系数绝对值取大相结合的融合改进算法,比目前基于传统小波融合规则的融合质量及各项客观评价指标都有明显提高,在各种算法比较中最优。采用多聚焦图像和临床实际的CT/MRI图像进行对比验证,表明了方法的有效性。理论分析和实验结果证明:选取合适的融合规则对融合结果影响很大,本研究提出的算法简单有效。  相似文献   

3.
为了研究小波变换分解的尺度和融合策略对图像融合效果的影响。我们选择已配准后的多聚焦医学图像以及MRI/CT灰度图像,在提取图像的低频和高频小波系数时,分别进行单尺度和多尺度分解,融合时采取了基于独立像素点和基于邻域窗口的多种融合策略,深入对比分析各种融合规则对医学图像融合性能的影响。实验结果和性能评价表明:使用局部滤波的操作可以明显改善图像融合的效果,使图像的细节信息更加丰富,而多尺度融合能明显提高融合图像的亮度。  相似文献   

4.
医学图像融合方法可以将有用的信息整合到一张图上,提高单张图像的信息量。对多模态医学图像进行融合时,如何对图像进行有效的变换,提取到不同图像中独有的特征,并施以适当的融合规则是医学图像融合领域研究的重点。近年随着深度学习的快速发展,深度学习被广泛应用于医学图像领域,代替传统方法中的一些人工操作,并在图像表示、图像特征提取以及融合规则的选择方面显示出独特优势。本文针对基于深度学习的医学图像融合进展予以探讨,介绍了卷积神经网络、卷积稀疏表示、深度自编码和深度信念网络这些常用于医学图像融合的框架,对一些应用于融合过程不同步骤的深度学习方法进行分析和总结,最后,分析了当前基于深度学习的融合方法的不足并展望了未来的研究方向。  相似文献   

5.
医学图像的不同格式影响着图像融合性能,恰当选取合适的图像格式是医学图像融合技术的前提。本文首先选择常用的BMP、JPG、PNG图像格式,采用典型的小波变换进行小波融合,然后选用无下采样Contourlet变换(nonsubsampled contourlet transform,NSCT)进行融合对比验证。实验结果显示PNG格式图像无论在融合性能还是运行时间和存储空间都具有优势。  相似文献   

6.
目的选择已配准后的多聚焦医学图像以及MRI/CT灰度图像为实验素材,以探究不同的融合策略对图像融合效果的影响。方法在对多模态医学图像融合时,低频融合分别采取了加权平均、取极大值法、区域能量以及区域方差的对比实验。高频融合分别采取了区域能量、区域方差以及滤波后基于邻域窗口的一致性检验的对比实验。结果通过对融合图像主观(融合效果)与客观(灰度直方图、边缘提取、性能评价)对比分析,找到了多模态医学图像融合的最优融合策略。结论当低频选择局部区域方差融合,融合后的图像轮廓清晰、边缘较完整;而高频选择滤波后基于邻域窗口的一致性检验,融合后的图像更好地保留和加强了源图像的细节信息。  相似文献   

7.
目的:针对传统的图像增强算法中存在弱边缘增强效果差、同时噪声抑制较弱等问题,本文提出的一种无抽样方向滤波器组,并将其用在医学图像增强中.方法:首先,将一维低通滤波器转换成二维低通滤波器,此滤波器再经平移、旋转等操作得到其他多方向无抽样频域滤波器,并将各频域滤波器转化成空间模板,便于使用;其次,将多尺度分析方法与无抽样方向滤波器组结合对图像进行分解得到各子带图像,对各子带图像进行统计特性分析,确定图像的强边缘、弱边缘和噪声;最后,对此三类信息不同的线性变换分别进行处理,获得增强后的图像.结果:由于无抽样方向滤波器能够较好的捕获图像的方向信息,多尺度分析能够较好区分不同的边缘信息,所以该方法的结果很好的保护了图像的边缘及细节.同时有效的去除了图像的噪声,层次结构清晰,视觉效果有了显著改善.结论:将无抽样方向滤波器与多尺度分析结合,并根据不同纹理信息的特点,对各类信息采用不同的处理,是一种行之有效的图像增强方法.  相似文献   

8.
基于小波包变换的医学图像融合方法   总被引:6,自引:0,他引:6  
为满足医学图像临床辅助诊断和治疗的需要,将小波包变换和自适应算子相结合,提出一种新的医学图像融合算法.算法首先对已配准的医学图像进行小波包分解,并采用自适应算子对小波系数及分解子图像进行处理,通过小波包重建,获得高质量的医学融合图像.该方法克服了小波变换不能兼顾图像高频成分的缺陷,并且可以根据不同的医学图像自动调整融合规则的权重系数,有效避免了设置固定权重系数造成的融合误差.实例融合仿真验证了算法的有效性和先进性.  相似文献   

9.
医学图像信息融合技术的发展   总被引:6,自引:0,他引:6  
医学图像信息融合是医学图像处理、放射医学及医学影像学领域近几年兴起的一种新技术。应用医学图像信息融合技术 ,可以把不同模态的医学图像有机地结合起来 ,为临床诊断和治疗提供更完善的图像信息 ,从而使医学图像能更好地为现代医学服务。本文对医学图像信息融合技术及其研究现状作了详细的介绍和综述 ,并对其研究前景作了预测。  相似文献   

10.
人脑MRI和PET图像的融合方法   总被引:4,自引:0,他引:4  
目的:研究MRI和PET医学图像融合的方法并且应用在人脑神经解剖中。方法:以Chamfer matching为基本配准方法和以模糊数学为理论基础的融合方法。结果:使得融合后图像有很强的抗配准偏差能力,并且能极大程度地保留原来解剖性信息图像和功能性图像的信息。能根据融合算子的不同组合,得到倾向于不同检查仪器结果的图像。结论:通过本文方法得出的融合后图像,能在人脑解剖结构上显示出该区域的功能状态,对于了解该结构的存在、变异、病变提供了很大的便利。对人脑神经解剖学研究和临床应用都有很大的理论和实践意义。  相似文献   

11.
We present an analysis of different filter banks for the compression of magnetic resonance (MR) images of the human brain using wavelet packets based on biorthogonal filters. Initially, peak signal to noise ratio (PSNR) and normalized root mean square (RMS) error criteria are calculated for a series of images compressed with a 33:1 ratio, using filter banks based on biorthogonal wavelet packets. The results lead us to choose a few of these filter banks as optimal for image compression. One of these filters is employed to compress several images at four different compression ratios: 12.5:1, 25:1, 37.5:1 and 50:1. The quality of these images was evaluated by visual analysis by a group of seven experts who graded image quality on a 0-7 scale. Results show that using these filters, we can compress images to a rate of around 30:1 without introducing noticeable differences. Other applications for these filters are currently under study and include the compression/fusion of MR image stacks in order to obtain even better reductions in the amount of data needed to reconstruct complete MRI studies.  相似文献   

12.
New nonlinear image processing techniques, in particular smoothing based on the understanding of the image, may create computerized tomography (CT) images of good quality using less radiation. Such techniques may be applied before the reconstruction and particularly after it. Current CT scanners use strong linear low-pass filters applied to the CT projections, reducing noise but also deteriorating the resolution of the image. The method in this study was to apply a weak low-pass filter on the projections, to perform the reconstruction, and only then to apply a nonlinear filter on the image. Various kinds of nonlinear filters were investigated based on the fact that the image is approximately piecewise constant. The filters were applied with many values of several parameters and the effects on the spatial resolution and the noise reduction were evaluated. The signal-to-noise ratio of a high-contrast phantom image processed were compared with the nonlinear filter, with the SNR of the phantom images obtained with the built-in CT linear filters in two scanning modes, the normal and the ultra high resolution modes. It was found that the nonlinear filters improve the SNR of the image, compared to the built-in filters, about three times for the normal mode and twice for the UHR scanning mode. The most successful filter on low-contrast phantom image was applied and it also seems to lead to promising results. These results seem to show that applying nonlinear filters on CT images might lead to better image quality than using the current linear filters.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

13.
Speckle噪声是造成超声医学图像质量下降的最主要原因。我们通过修改形态学重构算法-Downhill算法的初始条件,使其适用于超声医学图像的去噪处理。首先在掩模图像中确定标记图像作为算法的初始化和开始区域,再使用改进的Downhill算法对超声医学图像进行滤波处理。实验结果表明,与其他3种传统滤波方法相比,该方法能快速有效地去除心脏腔室内的Speckle噪声同时保留图像的轮廓细节信息。  相似文献   

14.
In this paper, a 3-channel wavelet transform method is introduced to recover palm print images following serious deformation. The deformation processing is actually a kind of digital re-sampling. A filter bank consisting of three filters is implemented for wavelet decomposition of the palm print image, and then a procedure of binary interpolation is performed after the image is reconstructed by another filter bank consisting of another three filters. The design of multi-channel wavelet filter bank is based on the Quadrature Mirror Filter (QMF) method. Because the noise is caused by the Morie stripe, the images are further de-noised after the geometry deformation is addressed. Acceptable results have been obtained.  相似文献   

15.
In this paper, a 3-channel wavelet transform method is introduced to recover palm print images following serious deformation. The deformation processing is actually a kind of digital re-sampling. A filter bank consisting of three filters is implemented for wavelet decomposition of the palm print image, and then a procedure of binary interpolation is performed after the image is reconstructed by another filter bank consisting of another three filters. The design of multi-channel wavelet filter bank is based on the Quadrature Mirror Filter (QMF) method. Because the noise is caused by the Morie stripe, the images are further de-noised after the geometry deformation is addressed. Acceptable results have been obtained.  相似文献   

16.
Image filtering for improved dose resolution in CT polymer gel dosimetry   总被引:3,自引:0,他引:3  
X-ray computed tomography (CT) has been established as a feasible method of performing dosimetry using polyacrylamide gels (PAGs). A small density change occurs in PAG upon irradiation that provides contrast in PAG CT images. However, low dose resolution limits the clinical usefulness of the technique. This work investigates the potential of using image filtering techniques on PAG CT images in order to reduce image noise and improve dose resolution. CT image noise for the scanner and protocol used for the gel images is analyzed and found to be Gaussian distributed and independent of the contrast level in the images. As a result, several filters for reducing spatially invariant noise are investigated: mean, median, midpoint, adaptive mean, alpha-trimmed mean, sigma mean, and a relatively new filter called SUSAN (smallest univalue segment assimilating nucleus). All filters are applied, using 3x3, 5x5, and 7x7 pixel masks, to a CT image of a PAG irradiated with a stereotactic radiosurgery dose distribution. The dose resolution within 95% confidence (D(delta)95%) is calculated and compared for each filtered image, as well the unfiltered image. In addition, the ability of the filters to maintain the spatial integrity of the dose distribution is evaluated and compared. Results clearly indicate that the filters are not equal in their ability to improve D(delta)95% or in their effect on the spatial integrity of the dose distribution. In general, increasing mask size improves D(delta)95% but simultaneously degrades spatial dose information. The mean filter provides the greatest improvement in D(delta)95%, but also the greatest loss of spatial dose information. The SUSAN, mean adaptive, and alpha-trimmed mean filters all provide comparable, but slightly poorer dose resolution. In addition, the SUSAN and adaptive filters both excel at maintaining the spatial distribution of dose and overall are the best performing filters for this application. The midpoint filter, normally useful for Gaussian noise, is poor all-round, dramatically distorting the dose distribution for masks greater than 3x3. The median filter, a common edge preserving noise reduction filter, performs moderately well, but artificially increases high dose gradients. The sigma filter preserves the spatial distribution of dose very well but is least effective at improving dose resolution. In summary, dose resolution can be significantly improved in CT PAG dosimetry through postprocessing of CT images using spatial noise reduction filters. However, such filters are not equal in their ability to improve dose resolution or to maintain the spatial integrity of the dose distribution and an appropriate filter must be chosen depending on clinical demands of the application.  相似文献   

17.
In this work, a Monte Carlo code was used to investigate the performance of different x-ray spectra in digital mammography, through a figure of merit (FOM), defined as FOM = CNR2/(ˉ)D(g), with CNR being the contrast-to-noise ratio in image and [Formula: see text] being the average glandular dose. The FOM was studied for breasts with different thicknesses t (2 cm ≤ t ≤ 8 cm) and glandular contents (25%, 50% and 75% glandularity). The anode/filter combinations evaluated were those traditionally employed in mammography (Mo/Mo, Mo/Rh, Rh/Rh), and a W anode combined with Al or K-edge filters (Zr, Mo, Rh, Pd, Ag, Cd, Sn), for tube potentials between 22 and 34 kVp. Results show that the W anode combined with K-edge filters provides higher values of FOM for all breast thicknesses investigated. Nevertheless, the most suitable filter and tube potential depend on the breast thickness, and for t ≥ 6 cm, they also depend on breast glandularity. Particularly for thick and dense breasts, a W anode combined with K-edge filters can greatly improve the digital technique, with the values of FOM up to 200% greater than that obtained with the anode/filter combinations and tube potentials traditionally employed in mammography. For breasts with t < 4 cm, a general good performance was obtained with the W anode combined with 60 μm of the Mo filter at 24-25 kVp, while 60 μm of the Pd filter provided a general good performance at 24-26 kVp for t = 4 cm, and at 28-30 and 29-31 kVp for t = 6 and 8 cm, respectively.  相似文献   

18.
This paper investigates the use of morphology-based nonlinear filters, and performs deterministic and statistical analysis of the linear combinations of the filters for the image quality enhancement of B-mode ultrasound images. The fact that the structuring element shape greatly influences the output of the filter, is one of the most important features of mathematical morphology. The present reported work comparatively evaluates the structuring elements for morphological liver image enhancement and verifies the hypothesis that the speckles visible in US images are short, slightly ‘banana-shaped’ white lines. Initially, five different liver images were morphologically filtered using 10 different structuring elements and then the filtered images were assessed quantitatively. Image quality parameters such as peak signal-to-noise ratio, mean square error and correlation coefficient have been used to evaluate the performance of the morphological filters with different structuring elements. To endorse the observation of the quantitative analysis, the filtered images were then evaluated qualitatively, based on the image features looked into by the medical fraternity. The evaluation parameters have been taken on the basis of the suggestions made by a group of radiologists. The results of the processed images were then evaluated by a different group of radiologists. A multi-point rank order method has been used to identify small differences or trends in observation. The subjective analysis by radiologists indicates that morphological filter using line shaped structuring element with length 2 performs better than the other structuring elements. These observations were found to be in line with the observations of quantitative analysis.  相似文献   

19.
OBJECTIVE: So far there is no ideal speckle reduction filtering technique that is capable of enhancing and reducing the level of noise in medical ultrasound (US) images, while efficiently responding to medical experts' validation criteria which quite often include a subjective component. This paper presents an interactive tool called evolutionary speckle reducing anisotropic diffusion filter (EVOSRAD) that performs adaptive speckle filtering on ultrasound B-mode still images. The medical expert runs the algorithm interactively, having a permanent control over the output, and guiding the filtering process towards obtaining enhanced images that agree to his/her subjective quality criteria. METHODS AND MATERIAL: We employ an interactive evolutionary algorithm (IGA) to adapt on-line the parameters of a speckle reducing anisotropic diffusion (SRAD) filter. For a given input US image, the algorithm evolves the parameters of the SRAD filter according to subjective criteria of the medical expert who runs the interactive algorithm. The method and its validation are applied to a test bed comprising both real and simulated obstetrics and gynecology (OB/GYN) ultrasound images. RESULTS: The potential of the method is analyzed in comparison to other speckle reduction filters: the original SRAD filter, the anisotropic diffusion, offset and median filters. Results obtained show the good potential of the method on several classes of OB/GYN ultrasound images, as well as on a synthetic image simulating a real fetal US image. Quality criteria for the evaluation and validation of the method include subjective scoring given by the medical expert who runs the interactive method, as well as objective global and local quality criteria. CONCLUSIONS: The method presented allows the medical expert to design its own filters according to the degree of medical expertise as well as to particular and often subjective assessment criteria. A filter is designed for a given class of ultrasound images and for a given medical expert who will later use the respective filter in clinical practice. The process of designing a filter is simple and employs an interactive visualization and scoring stage that does not require image processing knowledge. Results show that filters tailored using the presented method achieve better quality scores than other more generic speckle filtering techniques.  相似文献   

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