Retinal fundus photographs are employed as standard diagnostic tools in ophthalmology. Serial photographs of the flow of fluorescein and indocyanine green (ICG) dye are used to determine the areas of the retinal lesions. For objective measurements of features, the registration of the images is a necessity. In this paper, we employ optimization techniques for registration with the help of 2-parameter translational motion model of retinal angiograms, based on non-linear pre-processing (Wiener filtering and morphological gradient) and computation of the similarity criteria for the alignment of the two gradient images for any given rigid transformation. The optimization methods are effectively employed to minimize the similarity criterion.
The presence of noise, the variations in the background and the temporal variation of the fluorescence level pose serious problems in obtaining a robust registration of the retinal images. Moreover, local search strategies are not robust in the case of ICG angiograms, even if one uses a multiresolution approach.
The present work makes a systematic comparison of different optimization techniques, namely the minimization method derived from the optical flow formulation, the Nelder-Mead local search and the HCIAC ant colony metaheuristic, each optimizing a similarity criterion for the gradient images. The impact of the resolution and median filtering of gradient image is studied and the robustness of the approaches is tested through experimental studies, performed on macular fluorescein and ICG angiographies.
Our proposed optimization techniques have shown interesting results especially for high resolution difficult registration problems. Moreover, this approach seems promising for affine (6-parameter motion model) or elastical registrations. 相似文献
The carpal regions of ten cadaver extremities were imaged by CT. The images were combined into a 3-dimensional model of the
carpus using a technique based on a dynamic programming algorithm to find an optimal estimate of the location of the bone
boundaries in the CT images. The resulting set of surface points on each bone was used to compute volumes and principal and
antipodal axes for the bones. A spatial coordinate system was established based on the positions of the centroids of three
bones in the distal carpal row. The angular orientations of all carpal bones were determined with respect to this system.
The principal axes for the same bone among ten wrist specimens proved to be more widely dispersed than the antipodal axes
for the same bones. The antipodal axes also correspond more closely to an intuitive notion of the “longest axis” of the bones.
We conclude that the antipodal axis is a more reliable and useful measure of bone orientation than the principal axis. 相似文献
The authors present an improvement to a sigma-filter extrapolation method for the reconstruction of magnetic resonance (MR) images from symmetric discrete Fourier data. By making use of the phase information in the image data, the proposed method can overcome the data inconsistency problem of the original method for handling MR image data with large phase variations, such as those obtained in gradient-echo pulse sequences. Reconstruction results show that its performance is comparable with that of the modified complex sigma-filter method proposed previously to handle the inconsistency problem. However, the new approach has the advantage of reducing computation time by a factor of two with use of a sigma filter applied to real instead of complex images. It is expected that this method will be more practical for use in clinical MR imaging systems. 相似文献
A series of 8 rat and 16 mouse invasive bladder carcinomas were investigated for the presence of silverstained nucleolar organizer regions (AgNORs) to clarify whether this parameter is applicable to the estimation of their invasive character. With regard to number of AgNORs per cell, neither rat nor mouse carcinomas showed any difference between invasive and noninvasive sites within the same tumor. However, the frequency of cancer cells bearing bizarre dots, irregular in size and shape, was significantly higher at sites of actual invasion. Quantitative data generated using an image analyzer revealed significantly lower values for NOR roundness and significantly larger NOR size in invasive sites than in noninvasive sites in all groups. Double staining for the proliferation marker proliferating cell nuclear antigen (PCNA) and AgNORs was performed on eight rat carcinomas and a close correlation between the two was confirmed. Thus the number of AgNORs in PCNA-positive cells was significantly greater than in PCNA-negative cells. Furthermore, a particularly strong correlation was observed for incidences of PCNA-positive cells and bizarre dots (P<0.01). The quantitative data also demonstrated significant differences in size and shape of dots. It is concluded that AgNORs have diagnostic value for the invasive character of bladder carcinomas. 相似文献
Objectives To develop a simple image viewer that utilizes image files in general-purpose formats that are written from the original 3DX
volume data.
Methods We used FLASH MX2004 for Macintosh to develop a simple image viewer. In developing the software for the simple image viewer,
we decided that the viewer should provide the following features: (1) be available to both Windows OS and Mac OS, (2) allow
interlocking of the 3D images, (3) display image enlargement, and (4) allow distance measurements. The accuracy of the distance
measurements was evaluated.
Results The procedure was as follows: (1) write 3D images in jpeg format to a folder on i-VIEW; (2) place the folder containing the
3D images into the directory of the simple image viewer software on a PC; (3) start the software and open the window to input
the folder name containing the 3D images; and (4) display the 3D images. Our viewer had features such as image enlargement,
interlocking 3D images, drawing, and distance measurements. No significant differences were shown between the measurements
made by our simple viewer and the actual values of the images in any direction.
Conclusions Our image-viewing software for 3DX is beneficial for clinical use. 相似文献
An image processing system for application to studies of the temporal and spatial parameters of movement during swallowing
and speech is described. Image sequences from videotape are digitized for computerized manipulation and analysis in an attempt
to improve on conventional visual inspection. The system is “interactive” or “event-driven”: after executing a function, the
computer waits for guidance from the user who controls the program through keyboard and mouse input, selecting options from
menus and responding to prompts. The analyst alters image clarity by the application of filters and heightens contrast through
video enhancement. A technique called “remapping” reduces head motion and provides uniform spatial scaling. Animated sequences
of images are used, as opposed to frame-by-frame analysis, to preserve temporal context and increase efficiency of measurement.
Low cost off-the-shelf personal computer hardware is used along with original software tailored to the application. 相似文献
A new technique for multistep phase-contrast image processing is presented. The N-step method consists of simply forming the linear average of the N — 1 adjacent phase-difference signals. It has similar noise reduction properties as other multistep techniques, but the simplicity of the noise variance of the N-step technique allows intuitive insight into phase-difference phase-contrast processing and noise reduction, which can aid in the design of efficient and improved phase-contrast imaging sequences. As well, the computational simplicity of the N-step phase-difference technique compared with any other known multistep technique is advantageous. Like other multistep techniques, it has far more efficient noise reduction properties than simple two-step, multiple average phase-contrast imaging, even when normalized for total scan time. A three-step phase-difference velocity image has 50% less variance than an image acquired with two steps and two scans averaged but is obtained in 25% less scan time. Given its advantages, it should now be the chosen technique for increasing velocity-to-noise and contrast-to-noise ratios in all phase-difference phase-contrast clinical applications. 相似文献