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No female breast tissue is identical, so MRIs that detect and monitor cancer should not treat them the same way.
Without a way to prove that a new MRI technique is safe for all women, clinical MRIs have not been able to track the latest advances in MRI research. More informative cancer detection is possible with stronger magnetic fields that, unfortunately, also increase the risk of tissue heating during a screening.
Researchers at Purdue University have simulated how more than 20 different breast tissue ratios respond to the heat released by MRIs at higher fields than those available in current hospitals.
The simulations would allow advanced MRI techniques to demonstrate that they meet the safety limits set by entities such as the US Food and Drug Administration and to undertake clinical trials for actual use.
On the other hand, using knowledge about the amount of radio frequency energy that each breast tissue ratio can process, new techniques might one day target the heat produced by an MRI on the tumors to kill them.
The published results are presented in the journal Magnetic resonance in medicine, and the software code for simulations is freely available to the scientific community via Github.
The work aligns with Purdue's milestone celebration, in recognition of the university's global advancements in health, space, artificial intelligence, and sustainability as part of Purdue's 150th anniversary. These are the four themes of the year-long Ideas Festival, designed to portray Purdue as an intellectual center solving real-world problems.
Despite the limitations of clinical field strengths, annual MRI screening is still recommended for women at higher than average breast cancer risk because it is more sensitive than standard mammography.
"We are starting to develop field-intensive techniques that could immediately monitor how tumors respond to treatment. So we do not want tissue heating problems to hinder such a powerful tool, "said Joseph Rispoli, Purdue Assistant Professor of Biomedical Engineering and Electrical and Computer Engineering.
A woman's breast density determines the amount of radiofrequency energy of an MRI that the breast will absorb as heat, defined as the Specific Absorption Rate (SAR). The more fibroglandular tissue in the breast than in adipose tissue, the higher the breast density and SAR.
But not all women have the same relationship between fibroglandular tissue and adipose tissue. This makes it more difficult for researchers to show that a potentially life-saving MRI technique is safe for every woman, even though the risk of overheating tissues is generally low.
"In hospitals, the strengths of the MRI field are currently up to 3 tesla, the tesla unit being the unit we use to measure the strength of the magnetic field," Rispoli said. "Many techniques would be well above 7 tesla. This would represent a five-fold increase in SAR, but would also double the sensitivity of MRI. "
The researchers demonstrated in their simulations that a five-fold increase could remain within the FDA limits for most tissue ratios, even at 7 tesla.
To carry out these simulations, the team had to overcome several public health obstacles, the first being that there are far fewer computer models, or "ghosts", of the female body than of the male body. Researchers can test their techniques on computer ghosts, typically generated from MRI or CT images, before the techniques are clinically approved for use on real humans.
The National Institute of Information and Communication Technologies, for example, has developed the "Hanako" model to represent the average Japanese woman and the Swiss Foundation for Information Technology Research within of the society.
Other existing ghosts lie behind a paywall; All were developed standing or standing, even if a woman was lying down for an MRI, and none has been successfully combined with mammalian ghosts to accurately predict SAR.
Purdue researchers merged 36 breast phantoms at different densities, according to the Atlas of Reporting Systems and Imaging Data from the American College of Radiology, with full Hanako and Ella models. They then simulated the behavior of each merged ghost in response to 7 tesla MRI coils.
The simulations help other researchers adapt their techniques to the ratio of each breast tissue. The power should be limited somewhat, for example, for those who have more fibroglandular tissue.
"We want to facilitate the most cutting-edge breast MRI techniques at all sites in the world," said Rispoli. "At the end of the day, a woman will be able to intervene, do a fast, low-powered anatomical MRI, and then the computer will be able to quickly simulate on the fly what the SAR would be like in this patient."
Rispoli is part of a working group with the International Society for Magnetic Resonance Medicine that will use simulations to inform best practices in safety testing of experimental radiofrequency material. This effort will also facilitate these investigations in hospitals and research sites.
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