Unlike general radiography, nearly monochromatic x-ray is used for mammography. Molybdenum is used as the target material for the x-ray tube. The bremsstrahlung radiation is suppressed and filtration with Mo, W, Rd, and Al produces a characteristic x-ray spectrum with a single very strong peak. The monochromatic beam allows Photoelectric Effect (PE) to occur, resulting in a very large contrast between the dense, high attenuation calcified tissue and normal breast tissue.
What this unusual x-ray radiation means is that the x-rays used for mammography are not absorbed or filtered in the same way as wide-spectrum x-rays used in general radiography. This monochromatic effect must be considered when choosing materials and designs for mammographic shielding or grids. How much scatter radiation is generated in mammography? The creation of scatter radiation depends on the tube voltage and thickness of the breast. Scatter radiation is increased because breasts are normally compressed to 4cm or less for the exam.
How do you eliminate scatter radiation? Similar to conventional radiography, anti-scatter grids are used in mammography to trap scattered radiation that would create fog or noise in the image. Scattered radiation in mammography is generated from breasts compression to less than 4cm thickness, so that the breast tissue itself dose does not absorb the scattered radiation. In early applications of anti-scatter grids, the image artifacts and lines created when using a grid were regarding as a serious obstacle in reading the images. These problems were reduced with the introduction of oscillating bucky devices. At present, anti-scatter grids that are used in most mammography are between 30 to 100 lp/cm. Most are between 30 to 41 lp/cm. 100 lp/cm grids are mostly used for breast tomosynthesis. Grid ratios range from 3:1 to 5:1.