Open MR is more a perception than a technology, according to market strategists at Siemens Medical Solutions. If they're correct, Siemens is the only company in the world with a high-field open scanner.
Magnetom Espree, a 1.5T cylindrical system, has an opening more like that of a CT than an MR. The wide bore measures 70 cm (2.3 feet) in diameter, offering 30 cm of headroom from the patient to the scanner bore ceiling.
Although the bore is wide, the footprint is compact, spanning just 125 cm or about 4 feet in width, allowing 60% of exams to be completed with the patient's head outside the magnet.
"Even with the patient in the magnet, the larger bore allows much more headroom and arm room," said Dr. Jerald Pietan, chair of radiology at the Mayo Clinic in Jacksonville, FL.
The Jacksonville center began operating an Espree in mid-September. The center has seven other MR scanners, all operating at 1.5T. None of the Mayo Clinics have low- or midfield open MRs. The reason is quality, Pietan said.
"Over half the exams done on open scanners in our area are of such poor quality that we have to repeat them on our 1.5Ts under sedation or, if the patient is large, try to get them another scan," he said.
Espree promises the needed image quality and openness to accommodate just about anyone. The wide-bore system is designed to handle routine as well as advanced cases, including MR angiography; diffusion, functional, and breast imaging; whole-body scanning; and spectroscopy. The system will enter full production in February 2005.
"The large bore will also be amenable to developing MR interventional procedures, because you will be able to more freely access the patient," Pietan said. "We are looking forward to working in that area as well."
Espree is the latest MR scanner to reflect a decade-old trend of smaller footprints and wider bores in deference to patients' desire for a less closed environment. The ultimate answer is an open scanner of the type seen at low- and midfield. Five years ago, Siemens announced R&D aimed at developing a 1T open system, and three such scanners were built and placed at clinical sites. But the product line, dubbed Rhapsody, was discontinued. Espree has since emerged as Siemens' answer to the dilemma of providing a high-performance open MR.
"To make a vertical high-field magnet is expensive, and the siting costs are prohibitive," said Nancy Gillen, vice president of MR at Siemens. "But if we make a 1.5T system with a short and open bore, we give customers what they are asking for, and they can achieve the throughput they need."
Espree is roomier inside yet more compact outside than any other cylindrical MR scanner on the market. Its small footprint makes for easy siting, and the system is light enough to place on an upper floor.
Its sticker price between $1.5 million and $1.6 million puts the new system at the lower range of high-field products and well within the budget of Siemens' priority customers. The company is focusing on freestanding outpatient clinics, which tend to cater to patient demands. Espree might also find a home in hospitals as a second or third MR system for patients too claustrophobic or too large to fit into conventional cylindrical scanners.
Its advantages come with a price, however. The field-of-view is more limited than that of premium-performance 1.5T scanners, and challenges persist in field homogeneity. These disadvantages are largely offset by the integration of the company's Total Imaging Matrix, a whole-body coil technology that boosts the signal-to-noise ratio, and a table that moves the patient into multiple positions, when necessary, according to Siemens.