Rediscovering an old idea and applying state-of-the-art technology to it has enabled a Boston research team working with GE Medical Systems to implement a novel pulse sequence that could change the clinical practice of magnetic resonance imaging. The experimental technique--called fast spin-echo (FSE) by its developers--has already become a primary diagnostic tool at the four clinical research sites using it.
In addition to challenging the dominance of T2-weighted spin-echo sequences, the FSE method has enabled investigators to perform imaging feats heretofore impossible in a clinical setting. This includes the routine use of a 512 x 512-pixel matrix for both large field-of-view and high-resolution imaging, breath-hold abdominal T2-weighted scanning, and thin-section, three-dimensional T2-weighted acquisitions.
Over the past six months, the FSE sequence has been used in more than 2000 clinical cases at Yale, the University of Pennsylvania in Philadelphia, Keio University in Tokyo, and Brigham and Women's Hospital in Boston. The bulk of the preclinical development work was performed at Brigham and Women's Hospital by a research team headed by Dr. Ferenc A. Jolesz, director of MRI.
The most noticeable difference between FSE and conventional spin-echo images obtained with equivalent parameters is that the signal intensity of fat on the FSE images is increased. In head images, this shows up as a bright rim of subcutaneous fat surrounding the brain. Edges of structures are also somewhat enhanced on FSE images, "making them very nice to look at," said Dr. Mitchell Schnall, an MRI fellow at the University of Pennsylvania.
Development of the sequence was expedited by technical support and close collaboration with GE. The company plans to offer FSE as a product by the end of this year, said Ron Kokot, general manager of MR for GE Medical Systems in Milwaukee.
Although FSE made its first public appearance on panels at the GE booth at the 1990 meeting of the Radiological Society of North America, GE executives and the Brigham and Women's team held a joint press conference last month to formally introduce the technique.
FSE IS A VARIATION of an imaging method called rapid-acquisition relaxation-enhanced, or RARE. RARE was developed in 1984 by Dr. Jorgen Hennig and colleagues at the University of Freiburg in Germany. The German team implemented the technique on a clinical system manufactured by Bruker. Bruker has since incorporated the sequence as a standard part of the clinical protocols available on its scanners.
Patents for RARE were received in 1987, said Roy Gordon, marketing director of imaging products for Bruker.
"We have been promoting the technique, but if you don't have the marketing muscle or the market share, people just look at it as a curiosity," Gordon said. "To some extent it's gratifying to see that GE is justifying some of our development work. If GE tells radiologists that this is what they should be using, most radiologists will believe it."
While Bruker had improved upon Hennig's original single-shot approach by implementing a multislice version of RARE, its use was still largely limited to heavily T2-weighted imaging of the spine. If Jolesz and coworkers can be said to have made a breakthrough, it would be that they have modified RARE to make it flexible enough to challenge the diagnostic dominance of virtually all conventional T2-weighted spin-echo imaging.
"The technique will have immediate image quality benefits for the doctor, exam comfort benefits for the patient, and operational efficiency benefits for the hospital. This is a true win-win-win situation," said John Trani, senior vice president and medical systems group executive for GE Medical Systems.
The cost of upgrading a GE Signa high-field MRI system to function with FSE is not clear. Additional memory will most likely have to be added, Kokot said. This would involve inserting at least one additional memory board into the scanner array processor.
The upgrade will be accomplished primarily through new software, although Signa users would have to be upgraded to the Advantage platform level. GE expects the majority of its installed base in the U.S. to have reached the Advantage level by the end of this year, Kokot said.
Other MRI vendors can be expected to jump on the RARE/FSE bandwagon. Siemens will be showing RARE images next month at its booth at the Society for Magnetic Resonance Imaging meeting in Chicago. It plans to have the sequence available to Magnetom users by the end of this year as well, according to Chris Ruebeck, MRI product manager for Siemens in the U.S.
