X-rays have been a valuable diagnostic tool since 1896.
Plain-film radiography for diagnosing injury and pathology has been used since 1896, a year after X-rays were discovered. While technological advances have improved the quality of the X-ray images and have reduced exposure to ionizing radiation, the basic concepts of producing plain-film radiograpic imaging is unchanged. On Nov. 8, 1895, Wilhelm Conrad Roentgen discovered X-rays while working in his laboratory in Wurzburg, Germany. Within a year, Roentgen identified all of the fundamental properties of X-rays.
Definition of X-ray
X-ray is a form of man-made electromagnetic radiation with properties similar to visible light, radio waves and microwaves. X-rays are dangerous. Because of their very short wavelengths, they are capable of penetrating objects and interacting with matter at the atomic level. Because they can ionize (remove electrons from) the atoms of tissue, X-rays can cause significant tissue damage. For this reason, X-ray equipment is regularly inspected and practitioners are required to practice and document safe radiographic practices.
Plain-film Radiographic Examinations
Plain-film radiographs are used to diagnose internal injury and pathology of the skull, face, spine, bony thorax and upper and lower limbs. Other imaging modalities such as computerized tomography (CT), sonography, and magnetic resonance imaging (MRI) have replaced plain-film for diagnosing soft tissue injury and pathology. Plain-film radiographs are still considered a valuable, inexpensive, diagnostic tool.
Basic Components
The basic components of a plain-film imaging system are an X-ray source, a beam-limitation device and an image receptor (film). The X-ray source is a high-voltage glass vacuum diode tube. When energized, electrons pass through the vacuum from the cathode to the anode. X-rays are produced when the electrons slam into the anode at a high speed. The collimator (beam-limitation device) allows the operator to limit radiation exposure to only the area of interest, protecting the patient and operator. The film is both light and X-ray sensitive. It must remain enclosed in a light-tight holder called a cassette.
X-ray Interaction With Tissue
Depending on the energy level of the X-ray beam and the physical properties of the tissue, the beam will pass through the tissue, be absorbed by the tissue or be scattered by the tissue. X-rays that pass completely through tissue make the darkest areas on an X-ray film. X-rays that are stopped (absorbed) by the tissue are responsible for the white areas on the film. The gray areas on the film are due to partial transmission/absorption of the X-ray beam.
Exposing the Film to Make the Radiograph
To X-ray a patient's hand, the hand is placed on top of the X-ray film cassette. The X-ray machine is directed toward the hand on the cassette. The operator adjusts the collimator to protect the patient from unnecessary radiation. At the X-ray generating console, the operator selects the penetrating power and quantity of radiation to be used for the examination and makes the exposure. Remnant radiation that exits the patient and strikes the film forms the latent (invisible) image.
Developing the Film
Plain films go through a four-step development process to turn the latent image into the manifest (visible) image. In the developer solution, exposed silver halide crystals are turned into black metallic silver. In the fixer, unexposed crystals are removed, forming the white areas on the film. Fixer solution also contains a fixative and a preservative to maintain archival quality of the image. The film is then washed and dried.
Tags: areas film, injury pathology, absorbed tissue, beam-limitation device, cassette X-ray
