Firm develops small MRI coils for cardiac imaging applications

Coils could put MRI on even footing with cardiac cath

Real-time images of the heart and surrounding vasculature, at resolutions down to 100 microns, could be possible with a new breed of radio-frequency coils under development at a Columbia, MD, start-up called Surgi-Vision.

Surgi-Vision is developing the coils based on research done at Johns Hopkins Medical Institutions in Baltimore. Private investors have stoked this one-year-old company with about $10 million in seed capital. Its first product, designed for transesophageal use, is scheduled for submission to the FDA in spring. Commercial release could come within two years.

Inserted through the nose and down the esophagus, Surgi-Vision’s RF coil will come within several centimeters of the aorta. That’s close enough to deliver resolution of 300 microns, the company has discovered in preliminary clinical tests, according to Ergin Atalar, associate professor of radiology at Johns Hopkins. Atalar has been a key developer of the coil technology, which has applications outside cardiac imaging.

“We don’t have to look only at the aorta, because there are other organs close to the probe,” Atalar said. “One is the heart. There is also the esophagus, where we will be looking for cancer.”

The TE probe could also be modified for endorectal use to visualize the prostate, Atalar said. There are additional possibilities. Research done at Johns Hopkins, with a prototype intravascular RF coil developed by Atalar, has visualized plaque on the lumen of vasculature, documenting the size of the plaque and the space it occupies in the vessel.

Surgi-Vision’s coils have a radius of 0.035 inches and are small enough to fit inside vascular catheters that can be guided into the heart or coronary vessels. These coils promise to deliver diagnostic information equivalent to or better than can be achieved with conventional cardiac catheterization, according to Dr. Joao A.C. Lima, a Hopkins cardiologist doing research with the technology. This information would be gained during procedures strikingly similar to cardiac cath exams. But, rather than serving as conduits for x-ray opaque dyes, these catheters would serve as vascular highways for MR coils.

The coils work in tandem with standard surface coils. They generate data from the inside out; surface coils provide data from the outside in. The combination provides full high-resolution coverage of the region of interest, Atalar said.

Usually, coils must be individually tuned to work with each other. This is not a problem when using Surgi-Vision’s coils in combination with surface coils, however. The probes are so small that they do not interfere with surface coils, he said.

The effectiveness of miniature coils in visualizing inside patients depends on circumstances. Resolution of about 100 microns is possible in real-time on tissues within 1 cm of the miniature coil. Resolution falls off with increasing distance. For example, resolution of 300 microns can be achieved on tissue about 4 to 5 cm from the probe, Atalar said.

These images are achieved by using the coil to boost signal-to-noise ratios during the short acquisition periods that accompany real-time imaging. MR images obtained at 10 frames per second have relatively low resolution, Atalar said. This is unacceptable when doing interventional MR to support vascular procedures.

“You would not know where you are with respect to the especially small vessels,” he said. “We think that our technology is a solution to this problem.”

The coil technology boosts the signal-to-noise ratio by a factor of several hundred, Atalar said. But image quality is critically dependent on the power of the scanner with which the coil is used. Miniature coils cannot deliver 100-micron resolution if the scanner itself is not powerful enough to support that resolution, Atalar said.

Research leading to the development of prototype coils now in the hands of Surgi-Vision engineers was done on MRI equipment tweaked for research applications at Johns Hopkins. Typically this equipment can deliver 1-mm resolution without the use of minimally invasive coils, twice the resolution of just a few years ago.

Surgi-Vision’s coils are being designed for use in diagnosis as well as interventional guidance. Atalar and his colleagues envision a range of products, including some tailored specifically to cardiovascular applications. These probes might be threaded into blood vessels in much the same way as catheters are used in x-ray-based cardiac procedures.

In addition, Hopkins researchers are investigating the possibility of doing electrophysiology procedures inside an MRI magnet. These could include ablations to correct heart arrhythmias.

“In the future, (cardiac cath) x-ray machines are going to be in museums,” Lima said. “With MR, you have tissue signatures that you can exploit in many more ways than you can with x-ray technology.”

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