Scope of Diagnostic Imaging
For almost half a century following the discovery of x-rays by Roentgen in 1895, radiologic imaging was mainly based on plain and contrast-enhanced radiography. Those images were created by exposing film to an x-ray beam attenuated after penetrating the body. In the recent half century, diagnostic radiology has undergone dramatic changes and developments. Conventional angiog-raphy, nuclear medicine, ultrasonography, and computed tomography (CT) were developed between 1950 and 1970. Magnetic resonance (MR) imaging, interventional radiology, and positron emission tomography (PET) were developed later. Conventional radiology, including contrast-enhanced radiography and CT, uses ionizing radiation created from x-ray equipment. Nuclear medicine uses ionizing radiation that is emitted from injected or ingested radioactive pharmaceuticals in various parts of the body. Ultrasonography and MR imag-ing modalities use sound waves and magnetism, respectively, rather than ionizing radiation.
Radiologic subspecialties have been developed based on organ systems, modalities, and specific fields. Organ-oriented subspecialties of radiology include musculoskeletal, breast, neurologic, abdominal, thoracic, cardiac, gastrointestinal, and genitourinary imaging. Modality-oriented subspecialties com-prise nuclear medicine, interventional, ultrasonography, and MR imaging. Specific field subspecialties include pediatric and women’s imaging. Functional and metabolic imaging methods are now being used clinically, with genetic and molecular marker imaging expected in the future.