軟エックス線拡大撮影法の研究(第35回総会)

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It is now generally accepted that clear demonstration of the morphological characteristics of malignant microcalcifications on mammography film is indispensable to obtain precise radiological diagnoses of breast cancer especially in its early stage. Those pathognonic calcifications are actually very minute, their average size are around 0.1mm in diameter. The conventional contact mammography, however, hardly depicts those microcalcifications namely, those smaller than 0.3mm in diameter were usually erazed out mainly because of the geometric blur, of the scattering x-ray and of the quantum mottles of film and intensifying screen. The x-ray exposure doses are another controversial problem in conventional contact mammography especially in the case of mass screening program. They are usually reaching around 1R. of skin dosis per single view of mammography. These high doses of x-ray exposure have been invited by the employment of low sensitivity of recording system which has been employed to avoid unsharpness of mammographic images. The main purpose of this study is to find the appropriate range of characteristics of x-ray to enhance subject contrast of such as breast gland which is consisted of the materials with extremely small x-ray absorption differences each other, and to find the way to eliminate avoidable x-ray scattering to enhance film contrast, as well as to explore the suitable size of focal spot of x-ray tube to be able to clearly demonstrate the majority of the microcalcifications without detrimental geometric blur. Also, some psychological considerations were our concern to increase the diagnostic accuracy rate which can have intimate relationship with the size of the images of microcalcifications. Fortunately, recently available high-speed fine-grain films and rare-earth intensifying screens have been providing us the chance to challenge the study to minimize x-ray exposure doses in mamography ; this circumstance should be added to the study purpose furthermore. The following results were obtained by both fundamental and clinical studies : 1. Magnification power required 2× to 2.5×, to precisely recognize the microcalcifications and other pathognomonic finding of tumor findings of early breast cancer. This range of enlargement technique significantly reduced scattering x-ray to reach films due to "Groedel's effect". 2. The effective focal spot size to be used in the abovely mentioned technique should be smaller than 0.1mm in longest diametert to avoid geometric blur. 3. For standard size of breast, 25kVp was most appropriate tube voltage to produce well contrasted pathognomonic findings. 4. Tungsten anode delivered appreciably ideal quality of x-rays for soft tissue roentgenography. 5. The combination of Lo-D film (Du Pont) and LM screen (Toshiba) showed the best results among other many currently available receptor systems. 6. Target-Film Distance at 70cm was practically most convenient. 7. The skin surface dose in average was 0.43rad. per each projection of mammography. This low range of exposure was made possible by the introduction of high-speed recording system, The graininess of this sort of film and screen was well compensated by the enlargement of images. 8. The clinical diagnosing accuracies significantly improved by the application of this particular technique, especially of the breast and thyroid malignancies.
公益社団法人日本放射線技術学会の論文
1980-03-01

著者

柴山孝行
国立名古屋病院

軟エックス線拡大撮影法の研究(第35回総会)

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