Sketches of the standard imaging modalities : different ways of creating visible contrast among tissues -- Image quality and dose : what constitutes a "good" medical image? -- The creation of two-dimensional x-ray projection maps (shadowgrams) of the body : differential attenuation of x-rays by tissues -- 20th century (analog) radiography and fluoroscopy : capturing the x-ray shadow with a film cassette or with an image intensifier tube plus electronic optical camera combination -- Radiation dose and radiogenic risk : ionization-induced damage to DNA can cause stochastic, deterministic, and teratogenic health effects and how to prevent them -- 21st century (digital) imaging : computer-based representation, acquisition, processing, storage, transmission, and analysis of images -- Digital planar imaging : replacing film and image intensifiers with solid state, electronic image receptors -- Computed tomography : superior contrast in three-dimensional x-ray attenuation maps -- Nuclear medicine : contrast from differential uptake of a radiopharmaceutical by tissues -- Diagnostic ultrasound : contrast from differences in elasticity or density across tissue interfaces -- MRI in one dimension and without relaxation : a gentle approach to a challenging subject -- MRI with T1 and T2 relaxation and in three dimensions -- Evolving and experimental modalities.