Diagnostic Imaging
July 2003

OVERREAD

MR and CT for Crohn's stay in two different worlds

Europe validates MR for small bowel disease, but the U.S. remains loyal to MDCT

By: C.P. Kaiser

Several presenters at the European Congress of Radiology meeting touted the benefits of using MRI to image small bowel disease. In the U.S., however, the standard of care is CT, recently reinforced by the introduction of 16-slice scanners.

At the ECR, German researchers reported that TrueFISP sequences improved the delineation of bowel wall thickening and peri-intestinal inflammation compared with conventional sequences. Italian researchers found good correlation with MR findings obtained with T1- and T2-weighted sequences and the corresponding pathologic specimens in patients with Crohn's disease of different severity. And several studies validated MR enteroclysis as promising compared with conventional enteroclysis.

Dr. Jeffrey C. Weinreb, chief of MR at Yale University School of Medicine, said that some literature on MRI for Crohn's disease suggests it is more accurate than CT in determining location and extent of bowel involvement and in identifying complications such as fistulas. But these studies are limited.

Generally, U.S. radiologists argue that if they can do it cheaper and faster with CT and get the same results as with MR, they will stick with CT. In Europe, the attitude is if they can do it with nonionizing MR, then they should do it with MR rather than CT, Weinreb said.

"I do not know who is right, but there is room here for two points of view. MRI may be better for bowel disease than CT, but it has yet to be proven," he said.

Dr. Gabriele Masselli, a radiologist at UCSC Agostino Gemelli University Hospital in Rome, agrees that CT plays an important role in the diagnosis of small bowel disease, but mainly in patients with intestinal obstruction. He suggests that MRI and MR enteroclysis have a major role in patients with Crohn's disease for several reasons:

  • more accurate visualization of fistulas;

  • multiplanar imaging with direct coronal plane acquisition;

  • more contrast resolution (MR can visualize edema of the wall), including the use of fat-saturation sequences and MR angiography; and

  • no radiation, a particularly important point for the large young population with Crohn's.

    Radiologists at Johns Hopkins University routinely use CT for a range of small bowel applications including staging tumors, evaluating Crohn's disease, and looking at extended bowel disease, disease activity, and complications.

    "CT has always been state of the art for small bowel disease, and now with CTA, it's better than ever," said Dr. Elliot K. Fishman, director of diagnostic imaging and body CT at Johns Hopkins. "To my knowledge, there are no small bowel indications that MR can image better than CT."

    Radiologists at Hopkins do almost no enteroclysis-whether with CT or MR. Enteroclysis is invasive and requires sedation, and the same information can be obtained with a dedicated CT scan, according to Fishman.

    "I've yet to see anyone show on a one-to-one comparison that a CT enteroclysis picks up more information than a 3D CT," he said.

    Besides the lack of studies, Weinreb listed other reasons why MR gets short shrift in the U.S. for imaging the small bowel:

  • Limited access: MR scanners are so busy doing high-volume (and high-income) neuro and bone work that radiologists are reluctant to add cases that can be done just as well-or better-with high-speed CT.

  • Limited experience: Body MR expertise is thin in the U.S., and very few residents are being adequately trained. Both radiologists and clinicians have years of experience using CT with this indication and are comfortable with it. Without a compelling reason to change-and Wienreb doesn't see one yet-they will likely stick with it.

  • Limited reproducibility: Although MR scans are sometimes impressive, the image quality has not been as reproducible as CT.

    Weinreb suggests that several large nonbiased studies from respected academic institutions published in respected journals would go a long way in convincing clinicians and radiologists to change from CT to MR for Crohn's disease.