Research On Digital Mammography Softcopy Display Technology

Mammogram is an important imaging tool to diagnose breast cancer. Film mammogram based hard copy reading is widely replaced by digital mammogram based soft copy reading. Soft copy display has great infulence on diagnosis, so it achieves wide attention and becomes one of the most important research areas of medical image processing.In the first part of this dissertation, we introduce the classification, present research situation and performance analysis of digital mammography soft-copy display techniques. The present used soft copy display techniques didn't fully use priori knowledge of diagnosis and characters of digital mammograms, so these techniches are not good engough to confront the challenges of image presentation arrised by high resolution and low contrast of digital mammograms. The main shortcomings of present techniques include: Firstly, the breast region segementation techniques didn't satisfy the demand of high accuracy and high speed for soft copy display preprocessing. Secondly, the unsharp enhancement methods have disadvantages of over shooting and noise sensitivity, import information for diagnosis is not effectively enhanced. Thirdly, window intensity techniques have problems of low contrast and low luminosity, while histogram specification methods will either introduce unbearable information loss or cause discontinuity presentation during interactive display. At last, the most time consuming part of window intensity interactive is not optimized, so still has great space to improve the real-time capability.In order to solve those problems mentioned above, this dissertation focuses on digital mammogram soft-copy display. The main research topics are as follows:1. Thresholding method based on identified intensity planesThe features of identified intensity planes in mammogram are dominated by mammography mechanism, they are very stable and been used to calculate the threshold to segment breast region and background. After obtaining rough breast region by line segment based region growing method, a refine procedure is used to peel off the unexposed band regions. At last, pure breast region is extracted. Precision and efficiency of the method have been verified by experimental results.2. Fuzzy logic based mutiscale mammogram enhancement methodIn order to strengthen noise resistance, the original image is filtered by the hybrid low pass filter to remove out the impulse noise and Gaussian noise. Considering diagnosis information contained in different scales, the filtered image is decomposed by Laplacian pyramid. During enhancement coefficient calculation, local contrast and importance of different tissue are considered. The proposed methed overcomes over shooting and noise sensitivity, it can achieve good performance for mammogram enhancement and shows obvious advantage at both visual quality and objective indicator.3. Window parameter optimization by simulating the process of kinetic energy variationWindow parameter setting has great influence on mammogram reading. In this method, the probality intensity histogram of breast region is treated as a bumpy road and the procedures of calculating the optimal window parameters are simulated as the process of kinetic energy variation, just like a small ball rolling through the bumpy road, including up/down slope, resistance and finally stoped. The window parameters can be calculated when the kinetic energy of the small ball achieves the maximum value. The proposed mehod has good robustness; it can improve intial display luminance of breast region in mammogram.4. Window intensity display method based on dynamic range transformationWe improved window intensity display by introducing the concept of dynamic range transformation (DRT). The formal definition of DRT is presented and relative theorems are proved. DRT is a nonlinear transformation from pixel intensities to gray levels which reflects the frequency of occurences of pixel intensities and importance of different breast tissues. By using DRT, the mammogram display quality can be effectively improved. In addition, DRT doesn't cause information loss and keeps display continuity at interactive window intensity operations.5. Real-time window intensity interactive display optimizationTo avoiding calculation of pixels in background, the method uses breast region segmentation result. The feasibility of optimizing polynomial interpolation with dichotomy is proved. A fast bilinear interpolation method for image zooming is prosed. The method replaces floating-point operation by integer operation and bit-shift operators. Compared with the original method, the excuting speed increases almost 10 times and the real-time capability is obviously improved.All methods metioned above have been verified by experiments. Most of them have been intergrated into PACS which were used in dozens of hospitals and have achieved good benefits.