Traditional x-ray equipment is designed to project the rays through the entire width of the body. This requires a higher dose of radiation than a mammogram, which only needs enough x-rays to penetrate the breast instead of the thorax.
However, a mammogram is much more uncomfortable for the patient. A traditional x-ray merely requires that the patient lay down on the table. In a mammogram, the breasts literally have to be squeezed between the two plates, requiring a fair amount of pressure to hold them in place during the exposure.
In Airborne, the patient was given a mammogram to attempt to confirm breast cancer as the diagnosis.