The chief reason given for nonparticipation was claustrophobia. One-quarter of the women who refused the exam, or 130 out of 512, cited claustrophobia as the reason. Ninety-three (18 percent) cited time constraints, and 62 (12 percent) cited financial concerns involving insurance. Other reasons for refusal included absence of indication for the exam, lack of interest, medical inability to tolerate MRI, reluctance to receive intravenous injection, fear of further testing or biopsy, MRI scheduling, distance and contrast agent allergies.

Among the 703 who initially agreed to participate, 55 did not undergo the exam for various reasons, including withdrawal of consent, scheduling problems and missed appointments. An additional 21 patients did not complete the exam, had unreadable results or did not meet the protocol deadline. Ultimately, only 627 or 51.6 percent of the eligible women completed a screening MRI. Participation was higher among women with very high lifetime risk of cancer than among women with intermediate risk.

For some women, particularly those at intermediate risk, such as women with extremely dense tissue and many women with a personal history of breast cancer, supplemental screening with breast ultrasound in addition to mammography may represent a viable alternative to screening MRI.

"Screening with ultrasound helps to show small invasive cancers not seen on mammography and can be used to supplement mammography in high-risk women who cannot undergo MRI screening," Dr. Berg said. "Women who are at increased risk due to intermediate family history or dense breast tissue but do not meet the recommended risk level for MRI can also consider screening with ultrasound in addition to mammography."

Source: Radiological Society of North America