New Siemens and GE scanners put interventional MRI on the map

November 17, 1993

There may be a cure for MRI sales depression: Take two aspirinsand expand applications. With routine MRI procedure volume saggingin the U.S., vendors are scurrying to move the modality into newrealms, such as interventional MRI. Cutting-edge

There may be a cure for MRI sales depression: Take two aspirinsand expand applications. With routine MRI procedure volume saggingin the U.S., vendors are scurrying to move the modality into newrealms, such as interventional MRI.

Cutting-edge interventional MRI systems will take center stageat this month's Radiological Society of North America meeting.These machines will for the first time offer the promise of practicalMRI-guided therapy and biopsy.

Siemens and GE will present works-in-progress MRI scannersusing radical new designs to overcome previous technical limitations.By taming the interventional frontier, vendors will open up newmarkets for MRI that could pull the modality out of the doldrums.

"The MR industry has to very quickly offer more applicationsin order to make the market turn back upward," said ThomasMiller, group manager of MRI for Siemens Medical in Erlangen,Germany. "That's exactly what we are trying to do throughoffering such things as interventional MR systems. The only waythe market is going to go up is if you have an MR machine thatcan do more procedures better than the other guys' machines."

To implement interventional MRI, manufacturers must dispensewith the traditional cylinder-shaped magnets that prevent physiciansfrom reaching patients easily while they are being scanned. BothSiemens and GE systems accomplish this through novel magnet designs.

The Siemens scanner, dubbed Magnetom Open, is a 0.2-tesla resistive-magnetscanner that is open-ended to give physicians access to patients.The magnet is shaped like a giant C-arm, with the patient lyingbetween the ends of the C in the scanner's vertical magnetic field,according to Miller.

The magnet was designed by Oxford Magnet Technology, an MRImagnet supplier majority-owned by Siemens. It can be disassembledinto three pieces, permitting installation in a hospital withoutrequiring special site construction.

Siemens opted for a magnet with low field strength becauseof cost considerations. The company wants to price the scannerunder $1 million, which will keep it below most state certificate-of-need(CON) thresholds. But the combination of low field strength andthe magnet's flat design presented a potential problem. Such designsoften suffer from eddy currents when running the types of fastscanning protocols required for interventional imaging, Millersaid.

Siemens solved the problem by designing flat actively shieldedgradient coils, with a peak strength of 10 millitesla/

meter. Miller described the coils as a design breakthrough thatenables fast scanning without eddy currents.

"Flat actively shielded gradients are not easy to do,"he said.

Magnetom Open also has an "instant field off" function,which enables clinicians to shut off the scanner's magnetic fieldwithin seconds should a patient develop complications and requiremedical equipment to be brought into the MRI suite.

The first Magnetom Open is being installed at the Universityof California at Los Angeles, at the newly formed Center for InterventionalMRI. Dr. Robert B. Lufkin, an associate professor of radiology,and Dr. Keith Black, a neurosurgeon who serves as head of neuro-oncology,are co-directors of the center.

GE's interventional MRI offering, Signa MRT (MR Therapy) takesa slightly different tack. The physical appearance of the 0.5-teslasuperconducting magnet is closer to that of traditional scanners.But the middle third of the magnet has been removed to createa gap that allows physician access to the patient. The systemlooks like two CT gantries connected to each other.

The design is made possible by the magnet's very low cryogenrequirements, according to GE. Helium is used, but the refrigerationsystem has been designed to minimize boil-off.

"Basically, the users of this system can consider it acryogenless unit," said Brian Johnson, project manager formarketing and communications at GE Medical Systems.

Like Siemens, GE designed gradient and RF coils that don'tinterfere with access to the patient. The system's workstationis also configured for interventional procedures. GE has developeda technique that allows physicians to track interventional devicesas they are introduced into the patient's body by moving the scanner'sfield-of-view to follow the device.

"You just put the system into real-time mode and tellit to follow," said Rob Newman, manager of applications developmentfor advanced products at GE. "It allows you to see what youare doing as you are doing it."

As expected, both vendors have adopted different approachesin developing niches for their scanners.

At the UCLA Center for Interventional MRI, Lufkin and colleaguesplan to use Magnetom Open for MRI-guided radio-frequency thermalablation of primary and metastatic brain tumors. The procedureis performed under local anesthesia, with MRI used to guide andmonitor the delivery of the tumor-killing thermal energy througha 2-mm burr hole in the patient's skull. The MRI approach eliminatesa $20,000 to $30,000 craniotomy, along with associated hospitalizationand patient morbidity.

Siemens' marketing plans for Magnetom Open will not be limitedto luminary sites like the UCLA center, however. The vendor intendsto market Open as an affordable and patient-friendly scanner thatcan pay for itself with conventional procedures when interventionaltechniques are not being conducted.

"We would like to see this unit purchased not only bybig hospitals for interventional use but by smaller hospitalsfor routine use," Miller said. "It's not a dedicatedinterventional machine, which will live or die on intervention."

GE's image-guided therapy (IGT) program will initially useSigna MRT to concentrate on focused ultrasound surgery of breastlesions in a procedure roughly similar to Siemens' work on braintumors. GE has integrated focused ultrasound into the scannertable setup (SCAN 8/25/93).

Which company will be first to get an interventional MRI scanneron the market? Siemens has applied for Food and Drug Administrationapproval for Magnetom Open and expects to begin shipping in July.GE declined to state when it will have Signa MRT on the market.

Siemens will have a mockup of Magnetom Open on the RSNA exhibitfloor, while GE will use video and panels to display Signa MRT.Both expect to have units installed at clinical sites by the endof the year.

Regardless of who wins the race to market, interventional MRIcould benefit the entire field of MRI by unequivocally demonstratingan ability to contain, rather than expand, the cost of medicaltreatment.

MRI's superior visualization meshes well with the trend towardminimally invasive surgery. Interventional MRI could prove tobe a cost-saving proposition that will deflect some of the heatthe modality is experiencing from health-care reform advocates.

"If we can replace more invasive surgical or treatmentprocedures with less invasive and less expensive interventionalMRI, it could be the most cost-effective application of MRI inmedicine yet," Lufkin said.