Introduction to Radiographic Equipment

Introduction to Radiographic Equipment

This chapter introduces the useful x-ray beam, discusses the equipment found in a typical x-ray room, and provides some fundamentals of radiation safety. Many of these topics are covered in greater detail later in the text, but it will be helpful for you at this point to have an orientation to the equipment and safety considerations that are central to your work as a limited x-ray operator.

Primary X-Ray Beam

The source of x-rays is the x-ray tube. The internal structure and function of the tube are discussed in Chapter 5. X-rays are formed within a very small area inside the tube. From this point, the x-rays diverge into space. The x-ray tube is surrounded by a lead-lined tube housing. Some of the scattered x-rays are absorbed by the tube housing. X-rays that are created exit the housing through an opening called the tube port. These x-rays form the triangular-shaped x-ray beam (Fig. 2-1). The radiation that leaves the tube is called primary radiation. The squared area of the x-ray beam that strikes the patient and x-ray table is called the radiation field. An imaginary line in the center of the x-ray beam and perpendicular to the long axis of the x-ray tube is called the central ray. The central ray is important in positioning the patient because this point is used to align the x-ray tube to the body part to be imaged.

During a radiographic exposure, x-rays from the tube are directed through the patient to the image receptor (IR) (Fig. 2-2). As the x-rays pass through the patient, some of them are absorbed by the patient and others are not. Anatomic structures that have greater tissue density (mass), such as bone, will absorb more radiation than less dense tissue, such as muscle. This results in a pattern of varying intensity in the x-ray beam that exits on the opposite side of the patient. This radiation, called remnant radiation or exit radiation, then passes through to the IR. The IR now contains an “unseen” image called a latent image. This image remains stored in the IR phosphors until it is processed. Processing will convert the latent image into a visible image.

Scatter Radiation

When the primary x-ray beam strikes matter, such as the patient or the IR, a portion of its energy is absorbed within the matter. Absorption of the x-ray beam is called attenuation. Attenuated x-rays can be totally absorbed within the body, reduced in energy, or scattered outside of the body. The patient is the primary source of scatter. This scatter radiation generally has less energy than the primary x-ray beam, but it is not as easily controlled. It travels out from the absorbing matter in all directions, causing unwanted exposure to the IR and to anyone who is in the room. This is an important reason why the study of radiation safety is so essential to the limited operator. Radiation safety is discussed briefly at the end of this chapter and more extensively in Chapter 11. The unwanted image exposure caused by scatter radiation is called scatter radiation fog. The production of scatter radiation and the control of the fog it produces are addressed in Chapter 9.

See Box 2-1 for a summary of primary, remnant, and scatter radiation.

Image Receptor System

The IR system consists of a cassette that contains a phosphor imaging plate. In the radiology department today, the IR is part of the digital imaging system. One component is a cassette (Fig. 2-3, A). The cassette contains a plate with special phosphors that store the x-ray image until it is processed. The cassette protects the plate’s phosphors from damage and dirt. IR plates come in standard sizes. The most common sizes are listed in Table 2-1. They are manufactured in both English and metric sizes, with most sizes stated in English. In the radiology department, the terms cassette and plate are often used to mean IR.

Mar 7, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Introduction to Radiographic Equipment
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