PubMed · 5643585
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A G Fingerhut. 1968. A self-contained radiographic unit.. https://doi.org/10.1148/90.5.1030
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Dense regions in digital mammographic images are usually noisy and have low contrast, and their visual screening is difficult. This paper describes a new method for mammographic image noise suppression and enhancement, which can be effective particularly for screening image dense regions. Initially, the image is preprocessed to improve its local contrast and the discrimination of subtle details. Next, image noise suppression and edge enhancement are performed based on the wavelet transform. At each resolution, coefficients associated with noise are modelled by Gaussian random variables; coefficients associated with edges are modelled by Generalized Laplacian random variables, and a shrinkage function is assembled based on posterior probabilities. The shrinkage functions at consecutive scales are combined, and then applied to the wavelets coefficients. Given a resolution of analysis, the image denoising process is adaptive (i.e. does not require further parameter adjustments), and the selection of a gain factor provides the desired detail enhancement. The enhancement function was designed to avoid introducing artifacts in the enhancement process, which is essential in mammographic image analysis. Our preliminary results indicate that our method allows to enhance local contrast, and detect microcalcifications and other suspicious structures in situations where their detection would be difficult otherwise. Compared to other approaches, our method requires less parameter adjustments by the user.
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Synchrotron radiation imaging with the refraction-enhancement mode visualized structural inhomogeneities in phantoms used for image quality control of mammography. Eight phantoms were examined, all of which were manufactured in the United States and approved by the American College of Radiology as dedicated phantoms. In addition to fiber- and mass-mimicking test objects, each phantom has 5 groups of calcification specks of various sizes. Synchrotron radiation (SR) imaging was performed at Spring-8, a synchrotron radiation facility in Japan. Images were obtained with monochromatic 20-keV x-ray beams, a radiation field of 15 mm X 26 mm at a sample plane, a CCD camera with a resolution of 6 micrometers as a detector, and a sample-to-detector distance of 10 to 11 m. Two hundred and forty specks were evaluated in total in the SR images, and the surrounding area of each speck was also included. Evaluation of the images showed that 14 crack-like structures were depicted near specks, and there were 62 specks with attached void(s) or air bubble(s). Refraction-enhanced SR imaging sensitively detected structural inhomogeneities and abnormalities in phantoms which were implicitly agreed to have a homogeneous matrix and test objects without foreign substances. A possible manufacturing-dependent quality issue was identified. The effect of inhomogeneities detected by SR imaging on visual scoring of specks could not be identified in the tested phantoms; this should be assessed on images of other phantoms in a future study.