The many different imaging modaliti

The many different imaging modalities-or types of imaging methods-fill different scientific and/or clinical niches. Every modality has limitations: a particular method may be low in quality, slow to acquire images, expensive, or not suitable for all patients. The set of advantages for a particular technology (e.g., high quality, faster, cheaper, or dynamic) will make it suitable in the right situations. Different modalities operate over different time or length scales and-because of the physics that underlie their operation-can measure different structures or functions. Virtually all imaging modalities are now digital; the images are acquired by a computer and are made up of individual picture elements, or pixels. Digital images can be readily processed to improve their quality, make measurements, and extract features of interest.