Recognizing Anything: Past, Present, and Future

This chapter will briefly introduce you to the major imaging modalities: conventional radiography, computed tomography, ultrasound, magnetic resonance imaging, and the use of fluoroscopy. Nuclear medicine has its own online chapter (see e-Appendix A ).

In every chapter of this text, there will be a “Case Quiz” based on material in that chapter. The answer to each quiz question can be found in a special box at the end of that chapter. Don’t be concerned if you don’t know the correct answers to the quizzes—you are about to embark on learning the answers and much more.

Case Quiz 1 Question

This is a 23-year-old male with a normal chest x-ray. We know there is blood inside the heart’s muscular chambers. Why can’t we see the blood itself inside the heart? The explanation is in this chapter and the answer appears at the end of the chapter.

Past: the Discovery

In 1895, Wilhelm Röntgen (or Roentgen), working in a darkened laboratory in Würzburg, Germany, noticed that a screen painted with a fluorescent material and located in the same room a few feet away from a cathode ray tube he had energized and made light-proof started to glow (fluoresce). He also noticed that if he held his hand in front of the fluorescent screen, an image of the bones of his hand was visible. He initially thought he was hallucinating ( Fig. 1.1 ).
After repeating the experiment, he recognized that the screen was responding to the nearby production of a form of energy transmitted invisibly through the room. He named the new rays x-rays using the mathematical symbol “x” for something unknown. It didn’t take long before almost everyone was taking x-rays of almost everything imaginable (see e-Appendix E. Early History and Public Exuberance of the Discovery of X-rays ).

Present: Today’s Imaging Modalities

Conventional Radiography (CR, Plain Films)

Images produced through the use of ionizing radiation, i.e., the production of x-rays, but without added contrast material like barium or iodine, are called conventional radiographs or, more often, plain films or x-rays, as in chest x-rays.
Such images require a source to produce the x-rays (the “x-ray machine”), a method to record the image (a film, cassette, or photosensitive plate) and a way to process the recorded image (either using chemicals or a digital reader).
Conventional radiographic images were produced then, as they are today, by a combination of ionizing radiation and light striking a photosensitive surface , which, in turn, produces a latent image that is subsequently processed to become visible. For about a hundred years after the discovery of x-rays, conventional radiographic images survived their birth as a burst of ionizing radiation by relaxing comfortably on a piece of film.
At first, the processing of film was carried out in a darkroom containing trays with various chemicals and the films were then, literally, hung up to dry. The term wet reading, now replaced by the expression “ stat interpretation ,” arose because the early films were interpreted while still dripping wet from their processing chemicals and water.
The processed films were then viewed on lighted view boxes (if the image was being used as part of a movie or television show, it was almost always positioned backward or upside-down). In a few places, film is the medium still used, but it is much less common because it had some major drawbacks.
- Archiving each patient’s films required a great deal of physical storage space for their ever-growing number. Even though each film is very thin, many films in thousands of patients’ folders take up a great deal of space ( eFig. 1.1 ).

- The other drawback was that radiographic studies could physically be in only one place at a time , which was not necessarily where they might be needed to help in the care of the patient.
Eventually digital radiography came into being, in which the photographic film was replaced by a photosensitive cassette or plate that could be processed by an electronic reader, and that image could then be stored in a digital format. This electronic processing no longer required a darkroom to develop the films or a large room to store them. Countless images could be stored in the space of one, spinning, hard disk on a computer server. Even more importantly, the images could be viewed by anyone with the right to do so, anywhere in the world, at any time.
Today, imaging studies are primarily maintained on computer servers on which the images can be archived for posterity, from which they can be communicated to others and in which they can be stored. This system is called a PACS system , for Picture Archiving, Communications and Storage system.
With PACS systems (most often shortened to just “PACS”), images from all modalities can be stored and retrieved including conventional radiographs (CR) , computed tomographic scans (CT) , ultrasound images (US) , magnetic resonance imaging studies (MRI) , fluoroscopy studies, and nuclear medicine (NM) studies.

Advantages, Disadvantages, and Uses of Conventional Radiography

The major advantage of conventional radiographs is that the images are relatively quick to acquire and inexpensive to produce and can be obtained almost anywhere using portable or mobile machines. They are still the most widely obtained imaging studies.
The major disadvantages of conventional radiography are the limited range of densities it can demonstrate and its reliance on ionizing radiation.
Although conventional radiographs are produced by ionizing radiation in relatively low doses, radiation has the potential to produce cell mutations that could lead to many forms of cancer or anomalies. Public health data on lower levels of radiation vary as to their assessment of risk, but it is generally held that only medically necessary diagnostic examinations should be performed and studies using x-rays should be avoided during potentially teratogenic times, such as pregnancy (see e-Appendix C. Radiation Dose and Safety ).
Common uses for conventional radiography include the ubiquitous chest x-ray, plain films of the abdomen, and virtually every initial image of the skeletal system to evaluate for fractures or arthritis.