More patient dose is exposed in cone beam CT compared with former systems. If we reduce patient dose, the reconstruction images are significantly degranded by the quantum noise. It is necessary to improve these degranded images to satisfy the requirements of high image quality in modern medical diagnosis. In this paper, we propose the denoising method using the wavelet transform and sobel filter for 2D CT projection images. The results show that the proposed method can be reduced the patient dose to 10% original dose and removed the noise preserving edge.

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The control of exposure dose in mammography and its evaluation are important factors in quality control. Tanaka et al. measured the glandular composition of each pixel by using a digital mammogram, and suggested the method to estimate an average glandular dose from the mean measurement value (average glandular composition) by using a formula of Sobol. Their suggestion was regarded as excellent and epoch-making. However, this measurement method has not been popular in the area of radiological technology because of the complicated procedure of getting the average glandular dose from a mammogram. In this study, we improved the method used by Tanaka et al. and developed a new method, which makes it possible to analyze glandular dose more easily and precisely. We performed an imaging of glandular composition and a histogram analysis of glandular dose, and made clear the validity of our new method. Furthermore, we studied this method's weak points.

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The method using a medial axis model, which we proposed before, extracted aorta areas from multi-slice chest CT images properly. In principle, a pulmonary artery area can be extracted by the same method. However the modification was needed in the process to determine the initial model location and to restore the shape when the method applied to the extraction of a pulmonary artery. The modified method was applied to 29 patient cases and we confirmed its effectiveness from the results.

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