MRI is increasingly being used by radiologists to confirm diagnoses and perform operative procedures of the breast. MRI's contrast between soft tissues in the breast is many times greater than that obtained by plain-film mammography. As opposed to x-rays, which are known to cause damage to cellular DNA, the magnetic fields and radiowaves used with MRI are not known to have any long-term biologic effect. MRI of the breast requires intravenous injection of a contrast agent, which helps highlight breast abnormalities. The American Cancer Society has advised women at high risk for breast cancer to have an MRI.