As many as 42 percent of women who are at intermediate or high risk of getting breast cancer decide not to get recommended MRI screening, even if it is offered for free, U.S. researchers said on Tuesday.

A quarter of the women in the study who were offered the free screening test decided not to get it because they feel claustrophobic in the tunnel-like scanners. But many also said they declined because of costs involved if the test reveals something that needs to be followed up.

Some said they simply could not spare the time.

"Very early on we were surprised to notice that very few women would accept that invitation, even though it would be no cost to them," said Dr. Wendie Berg, a breast imaging specialist at American Radiology Services in Lutherville, Maryland, and Johns Hopkins University, whose study appears in the journal Radiology.

Her team studied the reasons why high-risk women who are recommended for the more sensitive MRI breast screening test do not get it.

Magnetic resonance imaging, or MRI, can help identify early breast cancer in high-risk women who tend to develop cancer earlier than women at average risk.

For the study, they identified 1,215 women who were at intermediate or high risk for breast cancer and were taking part in larger clinical trial.

All of the women were at increased risk for breast cancer, but even in a group of high risk women, who have a 25 percent greater lifetime risk of breast cancer because of they have known or suspected genetic mutations in the BRCA1 or BRCA2 genes, the willingness to undergo a breast MRI was limited.

"About 20 percent of our patients fall into that category," Berg said. "We would have expected virtually 100 percent participation in the study."

Berg said the chief reason women gave for not wanting a breast MRI was because they feel claustrophobic in the tunnel-like machines.

"That has been a common issue in MRI of the breast and other areas as well. It is usually something that can be overcome with sedation but it is still an issue," she said.

Of the 512 women who declined, 25.4 percent refused because of claustrophobia, 18.2 percent cited time constraints, 12 percent cited financial concerns if the tests identifies any cancers or has false-positive results, 9.2 percent said their doctor would not refer them and 7.8 percent said it was because they were not interested.

Women who are at high risk for breast cancer currently are recommended to get a yearly mammogram and an MRI test.

Berg said the study points to the need for alternative ways of screening high-risk women, including training more experts in breast ultrasound, a quicker, more convenient test.

More than 400,000 women in the world die from breast cancer each year.