Philips readies MR-guided ultrasound therapy

Some time next year Philips Medical Systems plans to begin clinical tests of its MR-guided high-intensity focused ultrasound (HIFU) system. A year after that, it should be through the FDA and on the U.S. market, Jacques Coumans, Philips' vice president of global marketing for MR, told DI SCAN this week at the International Society for Magnetic Resonance in Medicine meeting in Seattle.

Philips is behind GE Healthcare and its partner InSightec, which began marketing their 1.5T MR-guided focused ultrasound system over a year ago. Since then, the duo has placed about 30 systems worldwide to ablate uterine fibroids. They are also looking into using 3T and considering the treatment of breast, bone, liver, and brain tumors.

Philips is targeting uterine fibroids and several other applications, but its system differs markedly from the competition. Rather than heating an individual point within a tumor, killing clusters of cells,and then moving on to others, the Philips system is being designed to raise the temperature of the entire tumor. The 256 elements in Philips' ultrasound transmitter focus energy on a single spot but move this spot in a spiral pattern throughout the irregular volume of the tumor, heating it evenly until the tumor as a whole reaches a lethal temperature.

"This way no tissue will be missed in the tumor," Coumans said.

Engineering tests suggest that the method is faster than the competing point-and-shoot method. And it may be safer.

"Raising the temperature of a large volume in a controlled way will allow the physician to stop before reaching lethal temperature, if there is an indication that something is not as it should be," said Joop J. van Vaals, Ph.D., Philips' director of new business for cardiac and interventional MR.

Next year's clinical tests will be done at 1.5T for ultrasound targeting and temperature mapping of the tumor. If the system passes FDA review at this field strength, the results might allow the marketing of HIFU at 3T, according to van Vaals.

"The FDA might be able to review the technology independent of the field strength, but that is not clear at this moment," he said.

Philips plans to test HIFU at 3T after some results have been obtained at 1.5T, to determine if any differences are apparent at the higher field strength. Using the technology with 3T may be especially important when addressing breast cancer, as radiologists are already expressing a preference for results obtained at this field strength.

The company is in the early stages of developing a breast-specific HIFU technology. Its engineers are also exploring the possibility of applying focused ultrasound in targeted drug therapy.

A toxic drug might be encapsulated in a heat-sensitive medium, injected into the patient, and then selectively heated using HIFU to release it. This would concentrate the effect of a drug on a tumor selectively heated, eliminating the need for an invasive procedure, while sparing the rest of the body exposure to the drug, as happens when medication is administered orally or by IV. A similar approach might also be used when administering gene therapy, Coumans said.

Current plans call for the ultrasound transmitter for doing uterine fibroid ablations to be built into the patient table. Procedures involving the breast, however, would require the transmitter to be located laterally to avoid inadvertently heating tissues in the chest.

Philips plans to use HIFU, at least initially, with its cylindrical 1.5T and 3T scanners. The surface coils for monitoring breast therapy, along with the ultrasound transmitters, are being designed to fit into a rounded body-length device that rests atop the patient table and fits inside the gantry. The company is looking into modifying the device, however, to fit into its 1T high-field open scanner, which has superconducting magnets and gradients above and below rather than encircling the patient.

The HFO scanner might be better suited to breast interventions, as it allows physician access during the procedure, Coumans said. If this is the case, the HIFU device might have to be modified, as it is currently designed to fit the curved space of a gantry, not the rectangular one of the HFO.

"It could be that customers demand devices that are compatible with not only cylindrical but also with HFO scanners," he said. "The decision to go with HFO has not been made yet, but it is an interesting opportunity."