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For other articles and previous issues click here. August 30, 2004 Forest
or Trees? Few doubt MRI’s ability to image things
radiologists haven’t seen before. But just what do these new
findings mean to the patient? Researchers and clinicians are tackling
that important question. Many physicians worry, however, that the ability to pinpoint the body’s every minor flaw has merely multiplied the problem of incidental findings, where a test performed to identify or rule out one condition finds something else that may or may not need attention. Still, accumulating evidence of MRI’s positive predictive value (PPV) in many cases makes it more and more important for both primary and adjunct testing. Too Many Tests? In fact, a growing body of studies indicates just
how troubling the issue of false positives has become, including
the following: Breast MRI Presenting the results, leading breast cancer MRI researcher Mitchell Schnall, MD, PhD, of the Hospital of the University of Pennsylvania, recommended that all women considering surgical options get an MRI. “When evaluating surgical options for breast conservation,” he said, “physicians should be using MRI … [to determine] how widespread the tumors are and how much tissue really needs to be removed.” While breast cancer gets the most press, MRI today finds use in a remarkably varied range of imaging tests—for example, to determine internal injuries in shaken baby syndrome, track bone erosion in arthritic joints, help guide cardiac stent implantation, screen for telltale signs of cerebral palsy, and even track the neurological effects of untreated celiac disease. MRI is expected to yield nearly 15% of the $12.6 billion revenue generated in the medical imaging market in 2004, according to international market research and consulting firm Frost & Sullivan. In breast cancer prevention alone, imaging modalities to supplement mammography (including MRI, nuclear imaging, and laser tomography) totaled $22 million in 2002 and are projected to hit $64.7 million by 2010, Frost & Sullivan reported in December 2003. Improving PPV The continuing rapid evolution of MRI technology focuses largely on refining technology and techniques that emerged at the end of the 1990s. Conventional whole-body “tunnel” systems typically use magnets with Tesla (T) field ratings from 0.25T to 1.5T, but 3T scanners are already available, with vendors promising still higher-field strengths. And although open-bore designs and extremity magnet systems generally use lower-field magnets, they allow a far wider range of patient positioning, making them particularly useful for pediatric, older, severely injured, and obese patients. Perhaps most revolutionary are the “MRI suites” now being developed. These locate the magnet poles in the operating room’s ceiling and floor. The magnetic containment structure is outside the room, while inside only the patient is exposed to the primary magnetic field. The MRI suite enables the medical team to move about and move the patient as needed for a number of MRI-guided interventional procedures, including brain and orthopedic surgeries, cardiac catheterizations, and targeted chemotherapy. In addition, high-spatial-resolution imaging means physicians can acquire gigabytes’ worth of data virtually interactively. Advanced workstations running enhanced computer-aided detection/computer-aided manufacturing algorithms can now acquire and reconstruct enormous voxel data sets in real time. This rapid-fire sequencing of ever-thinner slices with high signal-to-noise ratios creates 3-D imaging while minimizing motion artifacts, truncation, or ghosting. Current and Future Research Even existing scanners can sometimes overwhelm radiographers and radiologists with information, so various trials now underway are also looking at how to revise screening protocols and revamp data processing methods to take best advantage of these technology advancements. Several are exploring how to combine the results of slower, high-resolution and fast, lower-resolution scans during a single exam—for example, to help distinguish cancerous tissue from a benign tumor. Such advances extend the borders of MRI beyond the imaging department and directly into the surgical suite. “The direction much of current research is going in … is almost [toward] the ‘one-stop’ shop, where you could put a patient in the MRI scanner and look at … all of this at one time,” notes Nancy Gillen, vice president of Siemens Medical Solutions magnetic resonance division. “The controversy to date has been [whether to emphasize] morphology, structure—which is MRI’s strong suit—or … look at perfusion data and flow dynamics,” traditionally PET’s field. “It would be a stretch to say you could put a cursor at something and say that it’s a specific type of tumor, but many things are going on in MRI to help get greater specificity … [and] give you some of that other, functional information without the use of separate imaging modalities,” she says. Based on current Siemens participation in National Institutes of Health trials at Case Western Reserve University in Cleveland, the University of California, Los Angeles, and BrainLAB (among others), she sees MRI innovations and refinements emerging from two experimental areas in particular: interventional MRI and MRI spectroscopy. Learning Curve “Each area of medicine has its own nuances and its own requirements,” Schnall says. The scope of MRI’s role may change, he adds, although he feels that for helping detect and characterize cancers, and in following up patients after various types of treatments, MRI use will only grow along with the technology. “There are many areas where we’re working out strong applications. You have to put the caveat that the right pieces have to be in place to make the system and the process work.” — J. K. Bucsko is a freelance healthcare writer and editor based in Westville, N.J. References
Lee JM, Orel SG, Czerniecki BJ, et al. MRI before reexcision surgery in patients with breast cancer. Am J Roentgenol. 2004 Feb;182(2):473-480. Breast MRI for Detection or Diagnosis of Primary or Recurrent Cancer. Assessment Program, Volume 19, No. 1 April 2004. Available at: http://www.bcbs.com/tec/vol19/19_01.html Rothenberg B. Medical Technology as a Driver of Health Care Costs: Diagnostic Imaging, Blue Cross Blue Shield Association 2003. Available at: http://www.bcbs.com/coststudies/research_report2.html
The study Mitchell Schnall, MD, PhD, presented at this summer’s American Society for Clinical Oncology conference in New Orleans was the first to encompass multiple sites, comprising a total of 17 locations in the United States, Canada, and Germany. The study was conducted by the International Breast MRI Consortium and led by researchers from the Abramson Cancer Center of the University of Pennsylvania. For three years, researchers followed more than 1,000 patients who were being evaluated for a suspicious lesion initially detected by mammogram and physical exam. At the end of the study, they determined that MRI is more than twice as effective as mammography for detecting multiple cancers. In 428 patients, mammograms found just 17 additional tumors compared with 56 identified by MRI, and cancers were confirmed by subsequent biopsy. The findings are significant for women who have already identified tumors via mammogram, particularly those in the upper half of breast densities mammographically and whose index lesion (the lesion being treated) is greater than 1.5 to 2 centimeters large. “We already know that the likelihood of finding a previously missed cancer gets higher with bigger lesions and higher breast densities,” Schnall points out, “which doesn’t mean that we don’t find cancers [with MRI] in lower mammographic densities. In about one-third of cases, MRI-detected multicentricity occurred in patients in the lower half of breast density.” Overall, MRI discovered second lesions greater than 2 centimeters from the index lesion in approximately 18% of cases, compared with 7% detected by mammography. “Of course, you can never be sure you’ve identified all tumors, but you see more with MRI,” says Schnall. “While one or two lesions that presented as calcifications [on mammograms] weren’t seen by MRI, about 10% [of newly detected lesions] … were seen only on MRI, not mammography.” These types of results may prove crucial to women hesitating between breast conservation therapy and mastectomy because contrast-enhanced MRI is currently the only modality that can image multifocal lesions. One thing the study couldn’t do was specify just how dangerous these newly found lesions might be. “The key is the high number of false-positive findings,” he acknowledges. “In real clinical practice [vs. a controlled laboratory study], everybody’s scared to miss cancers. If you’re going to have to do … needle localization or mastectomy for these false positives, then … you might be doing a lot of harm to a lot of women for every one you might help to reduce recurrence.” The problem, notes Schnall, is that follow-up studies that may definitively answer that question remain five or 10 (or more) years in the future. So the researchers compared the surface attributes of MRI-detected lesions with those found via mammography to measure any differences. They were almost identical in size and invasiveness, says Schnall, but “when we looked at the cancer grade, if anything the grade in the MRI-only detected tumors was higher.” Given the equivalence of the types of lesions picked up, and knowing the importance of multicentricity, he says, the question becomes, “What do we do in the interim … until we have studies to confirm the critical importance of these MRI-detected lesions?” In answer, “Women with breast cancer should get an MRI of that breast if they’re considering breast conservation therapy,” Schnall states. “After diagnosis with percutaneous needle biopsy, that’s when you do the MRI.” — JKB Sources for More Information
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