Remaking the MRI
Weill Cornell Medicine’s Simone Winkler, Ph.D., together with her postdoctoral fellow Dr. Elizaveta Motovilova and collaborators at the Hospital of Special Surgery, has acquired R01 funding from the National Institutes of Health (NIH) to develop a liquid metal technology that may vastly improve magnetic resonance imaging (MRI). Her innovation may ultimately offer clinicians a far more precise and intimate analysis of anatomical details such as nerve damage problems in the neck, arm, and shoulder—and beyond.
MRI relies on a dense array of radiofrequency (RF) coils—the “antennae” of the machines— to obtain functional and anatomical information inside the body. Tightly fitting coil arrays boost the MRI’s imaging performance, because its signals do not have to travel to a conventional, further removed, apparatus. The challenge: most commercial RF coils are rigid, of fixed size, intentionally designed to fit the general patient population, so providing limited imaging performance such as spatial resolution or speed of acquisition.
Novel flexible and stretchable coils are now trending, as RF coil designers race to substantially refine MRI ergonomics, beyond the aforementioned imaging performance gains, with an eye to versatility and patient comfort. Toward this end, the Winkler lab is using liquid metal technology to generate unusually stretchable receive coil arrays. In particular, the lab works with non-toxic gallium-indium alloys, embedded in a stretchable polymer, to create a conformal fit for the anatomy of interest. The challenge with stretchable electronics is that their resonance frequencies depend on their size. To this end, the Winkler lab has developed a smart self-tuning geometry that offsets shifts in resonance automatically.
With this technology, the Winkler lab has begun creating adaptive coil arrays that accommodate vastly different patient anatomies—without compromising the SNR. The approach even promises to allow dynamic imaging of joints bending, an impossible feat with commercial rigid RF coils.
One such application lies in the diagnosis of brachial plexopathy, for which MRIs famously lack specificity. In brachial plexopathy, the brachial plexus (a network of shoulder nerves carrying movement and sensory impulses from spinal cord to arm and hand) has been injured either manually (resulting in the stretching or tearing of nerves away from the spinal cord), or as a result of autoimmune disease. Either way, such traumas or injuries can result in severely limited movement, paralysis, and/or lack of feeling in the arm, hand, and/or shoulder. Minor brachial plexus injuries, known as stingers or burners, are common in contact sports like football. Infants can suffer brachial plexus injuries at birth. Inflammatory conditions, tumors, or cancer therapies can impact the brachial plexus, if the most serious brachial plexus injuries generally result from vehicular accidents. All told, brachial plexopathy can lead to profound functional, psychological, and economic damage.
Dedicated peripheral nerve MRI, or MR neurography (MRN), is an important adjunct to brachial plexopathy physical exams and electrodiagnostic testing. MRN influences clinical decision-making like surgery, and thus outcomes, allowing direct visualization of individual nerves and their relationship to osseus and soft tissue structures. Too often, however, MRN offers insufficient spatial resolution (~1.0mm-isotropic) resulting from poor signal-to-noise ratio (SNR). This is largely due to the concave anatomy of the neck-shoulder junction that precludes close proximity of conventional MRI coils to the skin. The complex branching and intertwining anatomy of the brachial plexus demands the use of higher spatial resolution (~0.5 mm-isotropic) than is possible with current RF coils.
The Winkler lab has been generating a novel, non-toxic, and robust liquid metal RF coil technology that will lead to a conformal and flexible 32-channel neck-brachial plexus array. The design will ensure that coil elements conform to body contour in its entirety, and with the arm in different positions. Ultimately, the Winkler lab’s dedicated RF coil array should allow for higher spatial resolution and 3D imaging, in unprecedented detail, of patients with a variety of thoracic outlet syndromes (TOS), from neurogenic to arterial to venous. The lab has already begun systematically evaluating liquid metal coils against standard coils. Dr. Winkler believes an achievable spatial resolution will be ~0.5 mm isotropic, greater than the ~1 mm isotropic currently achieved with commercial coils, thus better depicting regional anatomy and pathology.
In the end, says Dr. Winkler and her team, her new liquid metal RF coil technology will “deliver three times higher SNR. The achievable spatial resolution should be about 0.5 mm isotropic, greater than the approximately 1 mm isotropic currently afforded by commercial coils.” All this, she concludes, will easily enable superior 3D resolution in brachial plexus magnetic resonance neurography. This will, at long last, “vastly improve both diagnosis, and non-operative and operative management of brachial plexopathy”—and eventually, it is hoped, severe nerve damage problems in other hard-to-reach areas of the body.
Research reported in this publication was supported by the National Institute of Biomedical Imaging and Bioengineering of the NIH under Award Number R01EB031820-01A1. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.