Since 1895 when the x-ray was discovered, x-ray imaging has been performed with absorption contrast. Somenkov and co-workers have reported that refraction of x-ray improves sharpness of x-ray images by edge effect due to phase contrast. Since this discovery, phase contrast imaging has been studied intensively with coherent x-ray from synchrotron radiation and micro-focus x-ray tubes. We have created a methodology of phase contrast imaging with incoherent x-ray from a practical medical x-ray tube of a small focal spot such as 0.1mm. In this paper, theoretical background of this phase contrast imaging is described for design of digital phase contrast mammography system, and the pixel size for printing of digital mammogram is also discussed.

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A noise reduction method with preserving the contrast of linear shadows on x-ray fluorography, such as guide wires and catheters in IVR procedure, is proposed. In the method, the direction of the linear shadow (θ) and the strength of its directivity (ζ) are calculated locally, then a space-variant filter is applied. The value of θ and ζ on a local area are obtained by the calculation of two principal components of the density distribution on an x-ray image. When an obvious linear shadow is running on an area, the strong value of ζ is obtained by calculating the difference between two eigen values of principal components, and the θ is the same direction of the eigen vector. In this case, the kernel of the spatial filter is also directive, which averages the pixels in the direction of θ. Inversely, when no linear shadow is running, zero or weak ζ is obtained and the isotropic low-pass filter is applied to reduce noise. This method is tested on a fluoroscopic image with the incident dose of 5μR. The result shows significant reduction of the background noise with keeping wire contrast, the SNR of a wire (0.25mm in diameter) improved by around 120%.

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We have been developing a computer-aided diagnosis (CAD) system for mammograms and have reported our evaluation studies. The purpose of this study is to evaluate the potential effectiveness of the system in detecting masses and clustered microcalcifications by comparing 142 doctors' and the CAD system's detection results with 200 mammograms for 100 patients employed in doctors' short training course. The sensitivity in the detection of mass was 85% with 2.1 false positives (FPs) per image and that of clusterd microcalcifications was 100% with 0.8 FPs per image for this database. We analyzed the data based on the interpretation experiences of the doctors. We found that our CAD system was able to detect some of the candidates which were missed by some doctors. Especially, the system shows the possibility of the stable assistance in detection for the physicians with less experience of the reading. In conclusion, these results imply that our CAD system has a potential to improve the accuracy of the image interpretation.

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We developed a new physical evaluation system for medical displays using a high-resolution single-lens reflex type digital camera. This system was designed for easy and precise measurements of the modulation transfer function, the luminance response and the noise power spectrum of the liquid crystal display and the cathode-ray tube display. Each of the measurements was achieved by one-time photographing of a test pattern with the optimized data processing. Simple composition (a digital camera and a computer only) was very suitable for measurement in medical settings. Actual measurements were performed to three medical displays, and the high reproducibility and easy operability of this system were demonstrated.

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