Fast spin-echo sequence could shorten MRI exams

Rediscovering an old idea and applying state-of-the-art technologyto it has enabled a Boston research team working with GE MedicalSystems to implement a novel pulse sequence that could changethe clinical practice of magnetic resonance imaging. The experimentaltechnique--called fast spin-echo (FSE) by its developers--hasalready become a primary diagnostic tool at the four clinicalresearch sites using it.

In addition to challenging the dominance of T2-weighted spin-echosequences, the FSE method has enabled investigators to performimaging feats heretofore impossible in a clinical setting. Thisincludes the routine use of a 512 x 512-pixel matrix for bothlarge field-of-view and high-resolution imaging, breath-hold abdominalT2-weighted scanning, and thin-section, three-dimensional T2-weightedacquisitions.

Over the past six months, the FSE sequence has been used inmore than 2000 clinical cases at Yale, the University of Pennsylvaniain Philadelphia, Keio University in Tokyo, and Brigham and Women'sHospital in Boston. The bulk of the preclinical development workwas performed at Brigham and Women's Hospital by a research teamheaded by Dr. Ferenc A. Jolesz, director of MRI.

The most noticeable difference between FSE and conventionalspin-echo images obtained with equivalent parameters is that thesignal intensity of fat on the FSE images is increased. In headimages, this shows up as a bright rim of subcutaneous fat surroundingthe brain. Edges of structures are also somewhat enhanced on FSEimages, "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 supportand close collaboration with GE. The company plans to offer FSEas a product by the end of this year, said Ron Kokot, generalmanager of MR for GE Medical Systems in Milwaukee.

Although FSE made its first public appearance on panels atthe GE booth at the 1990 meeting of the Radiological Society ofNorth America, GE executives and the Brigham and Women's teamheld a joint press conference last month to formally introducethe technique.

FSE IS A VARIATION of an imaging method called rapid-acquisitionrelaxation-enhanced, or RARE. RARE was developed in 1984 by Dr.Jorgen Hennig and colleagues at the University of Freiburg inGermany. The German team implemented the technique on a clinicalsystem manufactured by Bruker. Bruker has since incorporated thesequence as a standard part of the clinical protocols availableon its scanners.

Patents for RARE were received in 1987, said Roy Gordon, marketingdirector of imaging products for Bruker.

"We have been promoting the technique, but if you don'thave the marketing muscle or the market share, people just lookat it as a curiosity," Gordon said. "To some extentit's gratifying to see that GE is justifying some of our developmentwork. If GE tells radiologists that this is what they should beusing, most radiologists will believe it."

While Bruker had improved upon Hennig's original single-shotapproach by implementing a multislice version of RARE, its usewas still largely limited to heavily T2-weighted imaging of thespine. If Jolesz and coworkers can be said to have made a breakthrough,it would be that they have modified RARE to make it flexible enoughto challenge the diagnostic dominance of virtually all conventionalT2-weighted spin-echo imaging.

"The technique will have immediate image quality benefitsfor the doctor, exam comfort benefits for the patient, and operationalefficiency benefits for the hospital. This is a true win-win-winsituation," said John Trani, senior vice president and medicalsystems group executive for GE Medical Systems.

The cost of upgrading a GE Signa high-field MRI system to functionwith FSE is not clear. Additional memory will most likely haveto be added, Kokot said. This would involve inserting at leastone 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 Advantageplatform level. GE expects the majority of its installed basein the U.S. to have reached the Advantage level by the end ofthis 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 atthe Society for Magnetic Resonance Imaging meeting in Chicago.It plans to have the sequence available to Magnetom users by theend of this year as well, according to Chris Ruebeck, MRI productmanager for Siemens in the U.S.