Medical imaging is a rapidly expanding field. It started with X-rays, and the next modality, ultrasonography, took sixty years to appear. Since then, three-dimensional imaging of anatomical structures was made possible with CT and MRI scans. The most recent breakthroughs in medical imaging technology, such as fMRI, PET, and SPECT scanning, create images of body function rather than anatomy. Imaging is one of the fastest-growing areas of medical technology.