A Double Film Technique in Mammography

Abstract

This report describes a technique in mammography for recording maximum contrast and detail over the wide range of radiographic opacity in the breast while minimising radiation to the patient. There is some difference of opinion and personal preference regarding the optimal kilovoltage, film type, positioning, and other technical factors in mammography, but most radiologists using this procedure have adopted some variation of a “low” kilovoltage (25–40) technique using a fine grain, non-screen film. After viewing over 2,000 such mammograms it was felt that in some instances all areas of the breast were not well demonstrated. The technique to be described was, therefore, adopted and may be used in conjunction with any of the “standard” low kilovoltage techniques. The variations in radiographic opacity which provide the subject contrast in mammography depend on two major factors: differences in tissue thickness due to the conical or globular contour of the breast and the differential radiation absorption of the tissues themselves (fat: atomic number about 6; and breast tissue: atomic number about 7·5; Siler, Garrett, Snyder, Laughlin and Sherman, 1962) which is greatly enhanced at low kilovoltages. These factors produce a variation in subject contrast which is too great to record on a single radiograph (Gershon-Cohen, 1960). If the areas of lesser radioopacity, fat and thinner superficial regions, are properly exposed, the areas of greater radio-opacity, glandular tissue and thicker regions near the base, are underexposed. Conversely, if the more radioopaque areas are properly exposed, those less radioopaque are overexposed (Fig. 2).