The definition of open MRI has changed recently with the debut of higher field strength magnets that allow a more open experience for patients and more powerful exam for care-givers. But at the same time, traditional open MRI systems have gained speed and clinical utility, offering a full menu of brain, neurologic, spinal, musculoskeletal and abdominal imaging and MR angiography - studies that a few years ago would not have been considered on an open system. And most important, image quality is earning clinical confidence.
Could it be that the definition of an open MRI scanner resides in the eye of the beholder?
There's a debate raging in the world of magnetic resonance imaging about what constitutes the definition of an open MRI system. Traditionalists believe that the only open scanners are those that do not resemble a cylindrical shape in the least, but feature a design that employs either a four-poster design such as the Toshiba America Medical Systems Ultra Open 0.35 Tesla scanner, or a wide open two-sided design like the Philips Medical Systems Panorama 0.1 Tesla, or the 0.7 Tesla SIGNA OpenSpeed system by GE Healthcare.
On the other side of the equation, clinicians who use the Siemens Medical Solutions MAGNETOM Espree 1.5 Tesla Open Bore that provides heads-out and feet first scans for most patients, would argue that this cylindrical machine qualifies as an open scanner by virtue of its 70 cm bore that is 125 cm in length from cover to cover. Some clinicians have found this feature has eliminated the sensation of being confined within an enclosed space for those patients with fears around those matters.
But that's not the only discussion occurring within the MR community these days. While open systems are immensely popular with patients because they provide maximum comfort for those who may be larger in size or who suffer from claustrophobia, clinicians are unsure that those issues outweigh the longer scan times and diminished quality of images produced by the lower field strength magnets as compared to conventional high-field scanners. Meanwhile, manufacturers of the lower field strength machines have worked diligently to overcome the problems created by the physics of the original designs to insure that those concerns become less pronounced. And image quality in recent years has improved greatly.
Open in a traditional sense
Original open MR systems used resistive or permanent magnets, which were by their nature lower field strength machines because, built of iron, they became heavier and bulkier the higher the field strength. An additional reality governed by the laws of physics involved increases in sensitivity to vibration as the field strength gained power, leading to site challenges that would maintain imaging capabilities regardless of the heavy truck that drove by the hospital, or the elevator shaft that was located adjacent to the MR scanner.
Those issues were coupled with additional drawbacks of lower field strength scanners including reduced image quality while scan times were longer. The typical 0.2 and 0.3 Tesla machines are not well suited to fat suppression imaging. This becomes important in evaluating tumors that are surrounded by adipose tissue. Without fat suppression techniques, the mass appears the same as surrounding fatty structures, and borders of the tumor are more difficult to discern.
On the positive side, many of the lower field magnets are quite sufficient for a number of studies, and they certainly come in at a lower price point and weigh significantly less than their more powerful cousins. This coupled with manufacturers' efforts to enhance performance of the lower field strength equipment has improved their utility and acceptance.
Rik Baier, CMPE, executive director of M &M Orthopedics in Downers Grove, Ill., describes their 18-physician practice as comprised of five clinics in the Western suburbs of Chicago. Following an extensive review of available MR systems, they employed a "hands on" approach for determining the best imaging quality for their purposes. Baier served as a test "patient" who was scanned on existing functioning systems they were evaluating, and he brought the films back to the practice for comparison.
After evaluation, the practice chose the Toshiba Ultra Open 0.35 Tesla system that features a four-post design to minimize vibration effects and a superconducting magnet to permit a more stable field as well as advanced gradient technology that enables shorter