By Martin Berger, Qiao Yang, and Andreas Maier
The X-ray was discovered on November 8, 1895, and this discovery led to the development and evolution of the field of medical radiography as we currently know it today. When X-rays interact with the human body during a radiographic exposure, they form an image, which is generated based on how these X-rays interact with the body. The attenuation properties of bone, soft tissue, and the air inside the body are very different, resulting in the heterogeneous distribution of X-rays. Understanding the basic concepts of how X-rays are generated, emitted, and how they affect the matter they interact with are some of the building blocks of radiologic imaging.
Radiologic imaging has come a long way since its inception, and digital radiography has largely replaced film-screen analog radiography and continues to drive the growth of radiography services worldwide. Fluoroscopy has also been in clinical use since shortly after the discovery of the X-ray and is widely used in diagnostic, therapeutic, and interventional procedures, as it can provide real-time images of dynamic processes occurring within the body, especially with the use of contrast agents. Together, these modalities now exist as the backbone of modern radiologic imaging.
This book chapter will review how X-rays are generated (including information on electromagnetic radiation, photons, energy variations, cathodes, anodes, and how electrons interact with each), how photons behave when they interact with matter, which include the principles of absorption, the photoelectric effect, and scattering. Various detection methods will also be addressed including imaging intensifiers, their parts, properties, and how they function, as well as flat-panel detectors and sources and types of radiologic noise. Finally, this chapter will cover the physical principles and technical nuances of X-rays, digital radiography, fluoroscopy, and digital subtraction angiography.