IMAGING MODALITIES
Diagnostic X-Ray
About
X-ray imaging is one of the fastest and easiest ways for a physician to view the internal organs and structures of the body. X-ray imaging has been available for 100 years and is an excellent tool for assessing skeletal trauma (e.g. broken bones), for diagnosing the gastro-intestinal system (digestive tract), for high resolution diagnostic imaging of the breasts (mammography), and for comprehensive imaging of the thoracic cavity including the lungs and heart. A host of other applications for x-ray imaging are also available including imaging the kidneys, teeth and jaws, and the fine structures of the ear, nose and throat. X-ray diagnostic imaging still comprises a majority of all diagnostic procedures done on a worldwide annual basis.
Conventional x-ray imaging encompasses a wide range of techniques and applications. However, in general, x-ray imaging is broken into two major categories:
1. Radiographic imaging where a "still image" is made of a bone or organ and shown on film or on a computer screen. A radiograph may be likened to taking a picture with a 35 mm camera.
2. Fluoroscopic imaging where a "movie" is made of an organ (for example, swallowing) and viewed on a TV monitor or computer screen.
What To Expect
X-rays are also referred to as radiographs or roentgenograms (after W.C. Roentgen). Conventional x-ray imaging has evolved over the past 100 years, but the basic principal is still the same as in 1895. An x-ray source is turned on and x-rays are radiated through the body part of interest and onto a film cassette positioned under or behind the body part. A special phosphor coating inside the cassette glows and exposes the film. The resulting film is then developed much like a regular photograph. It is the special energy and wavelength of the x-rays which allow them to pass through the body part and create the image of the internal structures like bones of the hand. As the x-rays pass through the hand, for instance, they are attenuated (weakened) by the different density tissues they encounter. Bone is very dense and absorbs or attenuates a great deal of the x-rays. The soft tissue around the bones is much less dense and attenuates or absorbs far less x-ray energy. It is these differences in absorption and the corresponding varying exposure level of the film that creates the images which can clearly show broken bones, clogged blood vessels, cancerous tissues and other abnormalities.
The principals of fluoroscopy are much the same as with film x-ray (called radiography) described above. However, fluoroscopic imaging yields a moving x-ray picture or movie. The original "fluoroscopes" consisted of an x-ray system and a fluorescent screen which registered the x-rays and emitted glowing light. The doctor could watch the fluorescent screen and see a dynamic (moving) image of the patient's body (for example the beating heart). Fluoroscopic technology improved greatly with the addition of television cameras and fluoroscopic "image intensifiers".
Today, many conventional x-ray systems have the ability to switch back and forth between the radiographic and fluoroscopic modes. The latest x-ray systems have the ability to acquire the radiograph or fluoroscopic movie using digital (computerized) acquisition. This gives the radiologist additional control over image quality and interpretation and can allow lower doses of radiation. Digital imaging allows the final image to be networked to various locations for additional consultation or interpretation.
Patient Preparation
While there are differences, most conventional x-ray procedures are basically similar:
1. Patient preparation involves removing any articles of clothing or jewelry that might interfere with the creation of the x-ray image. The patient is positioned by the technologist so that the anatomy of interest is in the proper field of view between the x-ray tube and film or image intensifier.
2. The technologist leaves the room. For many types of x-ray, for example chest x-ray or bone x-ray, the patient is asked to hold their breath and/or remain perfectly still for a few moments while the technologist makes the x-ray picture.
3. Some x-rays (like upper gastro-intestinal series) will require the patient to drink a barium solution immediately before the x-rays are taken (to help delineate the internal structures).
4. The technologist will ask you to get dressed and wait while the x-ray images are reviewed (either on computer or TV monitor).
Common Uses for the Test
Probably the most common use of bone radiographs is to assist the physician in identifying and treating fractures. X-ray images of the skull, spine, joints and extremities are performed every minute of every day in hospital emergency rooms, sports medicine centers, orthopedic clinics and physician offices. Images of the injury can show even very fine hairline fractures or bone chips, while images produced after treatment ensure that a fracture has been properly aligned and stabilized for healing. Bone x-rays are essential tools in orthopedic surgery, such as spinal repair, joint replacements or fracture reductions.
X-ray images can be used to diagnose and monitor the progression of degenerative diseases such as arthritis. They also play an important role in the detection and diagnosis of cancer, although usually computed tomography (CT) or MRI is better at defining the extent and the nature of a suspected cancer. Severe osteoporosis can be visible on regular x-rays, but bone density determination for early loss of bone mineral is usually done on specialized, more sensitive equipment.
Risks and Benefits
Benefits:
X-ray imaging is useful to diagnose bone and joint injury and disease, such as fractures, infections, arthritis and cancer.
Because x-ray imaging is fast and easy, it is particularly useful in emergency diagnosis and treatment.
Risks:
X-rays are a type of invisible electromagnetic radiation and create no sensation when they pass through the body. Modern x-ray techniques use only a fraction of the x-ray dose that was required in the early days of radiology.
Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
