Conventional X-ray equipment(automatic x ray film processor) was initially employed for breast cancer imaging with industrial (thick) emulsion film, or portal imaging film for use in radiation therapy as the image receptor in order to visualize the small microcalcifications, prior to, as late as 1970s. The breast entrance dose of this imaging process exceeded well over 85 mGy per film (10 R per film) and the radiographic techniques were typically in the range of 45–55 kVp, and 1000 mAS with a radiation beam quality of half-value layer (HVL)?1.0– 1.5mm of aluminum (mmAl) (8). The X-ray beam spectrum produced by a conventional X-ray tube, equipped with tungsten anode, is not necessarily optimized for breast cancer detection.
The mammography images obtained in thismanner had the desired spatial resolution (20 lp mm 1), but had a less than desirable radiographic contrast. This combination of "high entrance dose" with "low radiographic contrast" was not an acceptable approach. The radiology community was searching for a new breast imaging solution. In the 1970s, xeromammography imaging plates provided the much needed improvement in image quality and lowered the breast entrance dose by a factor of two thirds to one half compared to using the thick emulsion industrial type film (9).
Figure 1. Geometric arrangement of conventional radiography. The portable x-ray machine system, the anatomy of interest, and the screen-film cassette are centered and aligned for exposure.
Due to its unique patient positioning of breast imaging, the geometrical arrangement of dedicated mammography units should be pointed out. As shown in Fig. 1, with the range of 50–60 kVp. Breast tissues contain no high attenuation anatomy, such as bones, a lower tube potential (<35 kVp) would be more suitable for breast imaging (11). Use of lower tube potential has a potential benefit of taking advantage of the photoelectric effect in differentiating the subtle differences of breast tissues.