An introduction to key physical principles applied to medical diagnostics, imaging and radiation therapy. Topics include: electrophysiology, electrocardiogram and encephalogram; biomagnetism, magnetocardiogram and magnetoencephalogram; atomic and nuclear physics, ionizing radiation, radioactivity, nuclear medicine; theory of image formation and analysis, X- and gamma-ray imaging, positron emission tomography; lasers, optical light-matter interactions, optical imaging and therapy; physics of ultrasound, Doppler scanning and imaging with ultrasound; principles of nuclear magnetic resonance, contrast in magnetic resonance imaging.