Kazuo Noma

The first trial of phase contrast imaging for digital full-field mammography using a practical Molybdenum x-ray tube

Rationale and Objectives:The image quality of a newly developed full-field digital phase contrast mammography (PCM) system and of a conventional screen-film (SF) mammography system were compared via images of a phantom and receiver operating characteristic (ROC) analysis of clinical images. Methods:Magnified (1.75×) PCM images were scanned (sampling rate, 43.75 &mgr;m) and then reduced to original-sized, 25-micron pixel images printed on photothermographic film. Along with corresponding SF images, the phantom images were evaluated subjectively, and the clinical images of 38 patients were subjected to ROC analysis of mass and microcalcification. Results:In the image quality of a phantom, the PCM exceeded the SF. In both mass and microcalcification, the ROC analysis Az values of the PCM clinical images surpassed those of the SF images. Conclusion:The PCM provides better images than the SF. Clinical trials suggest superior detection of both mass and microcalcification by full-field digital PCM over conventional SF mammography.

An Analysis Method of Measurement of Noise Spectrum in the Ultra Low Space Frequencies of a Radiographic Film by MEM.

The noise power spectra of radiographic film have been used to analyze the graininess of radiography. Furthermore, it has recently become clear that graininess analysis, especially at low space frequencies, is needed for quantitative evaluation of a radiographic screen/film system. This paper describes a method for analysis of film at low space frequencies that is based on the maximum entropy method (MEM). This method can determine the basic order of MEM to maximize the ratio of the order to the power spectrum at low space frequencies. Experimental results confirmed that the noise power to express the radiographic influence on films can be precisely measured at ultralow space frequencies.