Of course you’ve heard the claims, but do you believe them? MRI will replace x-ray angiography; MRI will supplant PET; MRI will dwarf CT. Are they facts, really, or just teasers?

The truth is this: MRI hasn’t yet overtaken any of them, but market research says it is poised to surpass them all. MRI results are often superior to those of other modalities; it has been in clinical use long enough to usurp some of their territory, and it may eventually squeeze them all off the bench.

IMV Medical Information Division in Des Plaines, Ill., says MRI markets are growing at a faster rate than radiology markets — 15 percent annually, according to various industry sources — and that MRI use in chest, vascular, breast, and cardiac procedures is increasing. In 2001, IMV found that MRI procedures in hospitals with fixed units averaged 3,300; by comparison, the average per-site volume was 5,835 for CT (2000 figure), 2,570 for fluoroscopy, and 313 for PET. If MRI continued to grow and CT didn’t, MR use would exceed CT use by 2005.

Robert Bell, president of R.A. Bell and Associates, a consulting firm in Encinitas, Calif., estimates that 18 million MR scans are performed annually in the U.S., compared with 40 million CT scans. He believes the disparity owes to factors other than quality. “They’re pretty much equivalent exams,” he says.

If so, then what delayed MRI’s wider acceptance for two decades? There are several answers. One is that MRI signals were weak compared with those in other modalities; improving signal-to-noise ratio (SNR) was critical. Another is that MRI units typically were heavy, immobile, and not exactly speedy. Some things that MRI excels at aren’t reimbursable. The user pool is limited because many people aren’t candidates for MRI — those with pacemakers, cochlear implants, aneurysm clips, or shrapnel, for example. Sometimes patients cancel exams when faced with lengthy confinement in a claustrophobic chamber bombarded by loud noise. Recent negative publicity concerning fatal MRI-related accidents didn’t boost its popularity, either.

But then there’s the good news. With its unique ability to image both anatomically and functionally, MRI has found its way into surgical planning and navigation as well as diffusion and perfusion imaging. It is being combined with other modalities to achieve image clarity not previously attainable. Once considered unreliable in cartilage imaging, it is being dusted off for assessing chondral damage and repair now that 3D MRI has the sensitivity to replace arthroscopy. The latest entrant, 3-tesla MRI, may well surpass x-ray and CT in cardiac and neuro applications and likely will relegate breath-holding to the past. Faster imaging with better temporal and spatial resolution may enable 3 T MRI to be used with spectroscopy to reduce biopsies. A total rout by MRI is now restrained only by … well, cash.

Please refer to the July 2002 issue for the complete story. For information on article reprints, contact Martin St. Denis