Radiology and Oncology

Ultrasound and Mammography

Bremsstrahlung is the major influence in most x-ray tubes with the exception of x-ray tubes for mammography. The purpose of mammography is to detect small, nonpalpable lesions in the breast. This requires a much higher image quality than normal x-ray imaging with respect to contrast and spatial resolution. Since contrast and resolution are affected by scattering, mammography tubes reduce bremsstrahlung by suitable filtering. Furthermore, mammography tubes use a material (Molybdenum) that produces an almost monochrome x ray with peak energies around 17 to 19 keV. This would be unwanted in regular x-ray imaging as most—if not all—of the radiation would be absorbed and not reach the receptor. For the breast, however, the use of low-energy beams increases the contrast between the subtle differences of different tissues. Using an (almost) monochromatic beam will also reduce scatter, which again increases contrast.