Relationship between HMO market share and the diffusion and use of advanced MRI technologies.

Background: Financial incentives associated with managed care may shift incentives associated with the adoption of new medical technologies. This study examined whether managed-care activity was associated with the adoption rate of magnetic resonance imaging (MRI) equipment during the 1990s.

Data And Methods: Data from three nationwide "censuses" of MRI sites conducted in 1993, 1997, and 1999 were used. The number of MRI sites and magnets; magnet field strength; MRI procedures; the use of contrast media; and the presence of power injectors, echoplanar imaging, cardiac MRI, and interventional MRI were measured in each of 322 metropolitan statistical areas each year. Regression analysis was used to assess the relationship between area MRI availability and overall area health maintenance organization (HMO) market share, controlling for potential confounders.

Results: Areas with higher HMO activity had markedly lower adoption and use of MRI. By 1999, high-HMO areas had about 40% fewer MRI scanners per 100,000 people than low-HMO areas (1.02 vs. 1.73, P < .01). High-HMO areas had fewer 1.5-T scanners than low areas in all 3 years and tended to use contrast media less often in 1993 and 1997 (all P < .01). There were statistically insignificant trends toward less availability of echoplanar imaging, cardiac MRI, and interventional MRI in high-HMO areas.

Conclusions: The fact that managed care is associated with the slower adoption of MRI and less availability of some of the most advanced MRI equipment suggests the need for attention to the potential for managed care to have important effects on the quality of care and health care spending by influencing technology growth.