Short-bore MRI debuts continue with Harmony and Symphony from Siemens

It wasn't unexpected, but it was impressive all the same. German multimodality vendor Siemens pulled out all the stops with the introduction of two new short-bore MRI magnets at an international press conference held Sept. 18 at its Medical Engineering Group headquarters in Erlangen, Germany. In addition to the product debuts, Siemens used the event to reassert its leadership in the global MRI market.

The introduction of new Siemens MRI scanners has been expected since this summer. News of their impending arrival hit the market as Picker International prepared for the launch of its own short-bore magnets, Eclipse and Polaris (SCAN 8/20/97). GE Medical Systems is also said to be preparing to introduce a line of short-bore magnets.

Short-bore MRI architecture has been generating interest as a more compact, easier-to-site, and less claustrophobic alternative to traditional long-bore magnets. Although short-bore systems are not as accessible as open MRI scanners, they offer many benefits, such as superconducting high-field magnets, that are not found on most open MRI systems.

In the case of Symphony and Harmony, the systems have magnet bores that are only 5 feet, 3 inches (1.6 m) long, making it possible to permit the patient's head to remain outside the scanner for many studies, such as those of the lower extremities and pelvis. The 1.5-tesla Symphony weighs 8900 pounds while the 1-tesla Harmony tips the scales at 7700 pounds, and either scanner can be sited in a room as small as 325 square feet (30 sq m). In most cases they will not need a dedicated computer room.

Siemens executives at the Erlangen news conference cited the success of the company's competition-most likely Philips-in the short-bore niche as part of the reason for their decision to develop such a product line. The company faced a number of challenges in its R&D effort, however, particularly in keeping the cost of the systems down, according to Hermann Requardt, MR division president.

"Our challenge was to maintain our quality standards and specifications with the shorter bore," Requardt said. "We didn't compromise on field homogeneity, and that was a big challenge. Another was that shortness per se is expensive, and to do that (within cost limits) was obviously a challenge."

According to Requardt, Siemens devoted more time to predevelopment than with other MRI systems, conducting customer focus sessions in the U.S., Europe, and Japan. The actual development process took 18 months. Oxford Magnet Technology of Oxford, UK, produces magnets for the systems, and the scanners are assembled in a new plant at Erlangen, with final assembly taking place at the customer site.

The scanners include a number of new design features. Their integrated panoramic array coil system is built into the tabletop and allows simultaneous scanning with up to four coils. They can remain in the table with additional coils plugged in as needed; Siemens officials said that up to 95% of studies requiring coil changes can be performed without taking the patient off the table, optimizing imaging and patient setup times.

The scanners have actively shielded three-axis gradient systems with a compact water-cooled coil and amplifier. The maximum gradient strength is greater than 20 mtesla/m and the system has rise times of 800 microseconds with the turbo-gradient system and 400 microseconds with the ultra-gradient system. The scanner's table can handle patients weighing up to 440 pounds.

Both systems will also include packages for functional MRI and cardiac imaging applications. A functional package is being developed that will be similar but not identical to the one used in Magnetom Vision, Siemens' previous 1.5-tesla offering. Cardiac applications are included in the first software version already available.

The Food and Drug Administration cleared Harmony for sale in June and Symphony in August; to date one Harmony system has been installed in the U.S., but Siemens officials declined to name the site. Around the world, six other systems have been installed, with three in Germany and one each in Switzerland, Belgium, and France. In mid-September, Siemens received its import license in Japan. It plans to install a Harmony system there in the near future.

Harmony will replace Magnetom Impact in the 1-tesla segment. The 1.5-tesla Magnetom Vision has received a faster computer workstation and has been rechristened Magnetom Vision Plus. It will be refocused as a research-oriented scanner.

Siemens deliberately chose not to develop a 0.5-tesla short-bore magnet. Siemens believes that the 0.5-tesla segment has a limited future, as the niche is being squeezed between high-field scanners like Symphony and Harmony and open-magnet scanners like the vendor's 0.2-tesla Magnetom Open Viva. Hospitals prefer high-field scanners because they can perform new applications like functional MRI and cardiac imaging, while open-magnet systems have obvious patient-access advantages. The 0.5-tesla systems are caught in the middle, according to Requardt.

In addition to introducing Harmony and Symphony, Siemens reiterated its claim to being the world market-share leader in MRI, ahead of arch-rival GE. Siemens claims to have a 30% share of the 11,600 MRI systems in operation around the world, compared with a 26% share for its Milwaukee-based competitor. Siemens executives reported that MRI market demand is estimated at 1300 systems a year.