Chapter 1

Most musculoskeletal injuries occur as a result of either trauma or overuse. Following a thorough evaluation by a qualified health-care professional, most patients are usually required to have a basic radiographic (x-ray) examination of the injured area to assist in confirming the diagnosis. Many of these individuals, however, will require the use of an advanced imaging modality such as ultrasound, computed tomography (CT), and/or magnetic resonance imaging (MRI) to increase the accuracy in diagnosing the specific nature of the injury. The purpose of this chapter will be to provide a basic understanding of the four major imaging modalities used in diagnosing injuries: x-ray, ultrasound, CT, and MRI. It will also review pertinent terminology, common imaging applications, and important safety precautions.

### Historical Overview

Using an x-ray tube to produce x-rays and a sheet of x-ray film or image receptor placed in a specially designed cassette to capture the energy of the x-ray beam image is the most commonly used method of taking a radiograph. Since its beginning in the late 1800s, diagnostic radiography, also known as x-ray, has seen several technologic advancements in the design of the x-ray tube, x-ray film, and cassette. Advancements made in image receptor technology have evolved from glass plates, which were used initially, to polyester-base material, which is used currently. Film emulsions have experienced considerable change since they were first introduced. Historically, the x-ray image was produced by the direct exposure of the x-ray beam to the x-ray film. Today, the x-ray image is produced when the x-ray beam interacts with special phosphor crystals within intensifying screens located inside the film cassette. When x-rays interact with the phosphor crystals, a light of a specific wavelength is produced and exposes the x-ray film. This method reduces the amount of radiation necessary to create an x-ray image.

The latest technology incorporates the use of computer technology in what may be referred to as computed radiography or digital radiography. Digital radiography introduces a moving away from the traditional film-screen (hard copy) method of taking an x-ray to producing a digital (soft copy) image that is presented on a high-quality monitor. Digital images, once recorded, can be manipulated just like CT images. The density and contrast scale of the images can be adjusted to demonstrate the anatomy such as bone or soft tissue. The images can be magnified to better visualize small structures. Another advantage of digitally formatted images is that they can be reviewed using high-quality monitors located throughout the hospital in such locations as the emergency room, operating rooms, and patient floors. Soft-copy images can also be sent to other health-care professionals in other health-care settings on a compact disc (CD). Finally, the storage of soft-copy images requires less space than the traditional hard-copy film jacket. The patient's images are stored and maintained on a picture archive and communication system (PACS) for an indefinite period of time.

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