Patients with PMD have blood drawn for testing and also undergo functional magnetic resonance imaging (fMRI) to look at how the brain functions while the subject performs a specific task. MRI uses a strong magnetic field and radio waves to obtain images of body organs and tissues. During the scan, the subject lies on a table that can slide in and out of the scanner, a metal cylinder. The scan lasts about 60 to 90 minutes, during which the subject may be asked to lie still for up to 10 minutes at a time and to perform tasks, such as identifying the gender of faces shown on a screen.