Magnetic resonance imaging (MRI) is an imaging technique that uses a powerful magnetic field and radio waves to produce cross sectional images of the body. The Swiss Atlas of Healthcare contains analyses on the frequency of MRI scans of the knee, and on the frequency of MRI scans of the peripheral joints. The peripheral joints include the arm joints (including shoulder joints) and legs (including ankles). To measure the frequency, this indicator takes account of the number of images produced, where several MRI images may concern the same patient. The Swiss Atlas of Healthcare also contains a separate indicator on the number of cases for which an MRI scan was performed.