Measured

(Siemens, 2004). In the screening programs, it is essential that low radiation dose protocols beused to reduce cancer induction by radiation to an absolute minimum, and achieve qualityhealth: the ultimate aim ofmedical services.1.2. Mammography TechniqueMammography is the most sensitive technique currently available for the early detection ofbreast lesions and therefore is the method of choice (Fahrig and Yaffe, 1994a; Simonetti et al1998). Mammography is a radiographic technique that uses X-rays produced from amolybdenum, rhodium or tungsten or combination of any two of them as anode or targetmaterials with an exit window of beryllium or glass. Some older machines have glass as exitwindow. The mammography X-ray beam is generated when high-velocity electrons from thecathode collide with the target or anode material. Only one percent of the energy of thestreams of electrons is transformed directly into X-ray energy producing bremsstrahlung andcharacteristic X-rays. The remaining ninety-nine percent of the energy of the electrons isconverted into heat and dissipated away. To avoid excessive heating ofone point of the anodematerial surface and cause irreparable damage to the anode material, most modernmammography machines have rotating anodes. The X-ray tube is mounted on tube housingwhich provides mechanical support and also serves as a container to store oil used to cool theanode during operation. The mammography machine is designed such that the generated X-ray beam is directed through a window by a primary beam restrictor and then passed through afilter l . The filter materials commonly used in mammography are molybdenum, rhodium andaluminium. The filtered beam is collimated to desired dimensions for patient imaging.1 A material insertedin the X-ray beam to alterthe qualityofthe beam by removing unwanted energy which doesnot contribute to image information but increases patientdose.3