The introduction and evaluation of MRI in Japan.

Not only is the number of computed tomography (CT) units relative to population in Japan the highest in the world, that of magnetic resonance imaging (MRI) units is second only to the United States. This study examines the diffusion pattern of MRI in Japan, as well as the factors that influence it. The number of MRI units has increased sharply, closely following CT, as has been the case in the United States. This pattern of diffusion in Japan was determined mainly by the following factors: the technological attributes of MRI; the market situation of the medical engineering industry; the reimbursement system of health insurance; and Japan's sociocultural background. However, the introduction of MRI in Japan was not linked to any formal assessment of its efficacy or effectiveness.