Expanded use of imaging technology and the challenge of measuring value.

The availability of computed tomography (CT) and magnetic resonance imaging (MRI) scanning has grown rapidly, but the value of increased availability is not clear. We document the relationship between CT and MRI availability and use, and we consider potentially important sources of benefits. We discuss key questions that need to be addressed if value is to be well understood. In an example we study, expanded imaging may be valuable because it provides quicker access to more precise diagnostic information, although evidence for improved health outcomes is limited. This may be a common situation; thus, a particularly important question is how non-health-outcome benefits of imaging can be quantified.