Introduction

This chapter introduces the nature of electromagnetic and particulate radiation. Students may wonder why it is necessary for the radiographer to understand the entire spectrum of radiation. This question can be answered both broadly and specifically. In general, it is the radiographer’s role to be familiar with the different types of radiation to which patients may be exposed and to be able to answer questions and educate patients. The radiographer should consider him or herself as a resource for the public and should be able to dispel any myths or misconceptions about medical imaging in general. Both ends of the electromagnetic spectrum are used in medical imaging. Radiowaves are used in conjunction with a magnetic field in magnetic resonance imaging (MRI) to create images of the body. X-rays and gamma rays are used for imaging in radiology and nuclear medicine, respectively. One difference between the “ends” of the spectrum is that only high-energy radiation (x-rays and gamma rays) has the ability to ionize matter. This property is explained in this chapter. More specifically, the radiographer should be able to explain to a patient the nature of ionizing radiation as well as any risks and benefits, and should be an advocate for the patient in such discussions with other professionals. He or she should also understand the nature of radiation well enough to safely use it for medical imaging purposes. With this rationale in mind, the electromagnetic spectrum is discussed first, followed by a discussion of particulate radiation.

Electromagnetic Radiation

In the latter half of the 19th century, the physicist James Maxwell developed his electromagnetic theory, significantly advancing the world of physics. In this theory he explained that all electromagnetic radiation is very similar in that it has no mass, carries energy in waves as electric and magnetic disturbances in space, and travels at the speed of light (Figure 3-1). His work is considered by many to be one of the greatest advances of physics. Electromagnetic radiation may be defined as “an electric and magnetic disturbance traveling through space at the speed of light.” The electromagnetic spectrum is a way of ordering or grouping the different electromagnetic radiations. All of the members of the electromagnetic spectrum have the same velocity (the speed of light or 3 × 10⁸ m/s) and vary only in their energy, wavelength, and frequency. The members of the electromagnetic spectrum from lowest energy to highest are radiowaves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays. The wavelengths of the electromagnetic spectrum range from 10⁶ to10^-16 meters (m) and the frequencies range from 10² to 10²⁴ hertz (Hz). Wavelength and frequency are discussed shortly. The ranges of energy, frequency, and wavelength of the electromagnetic spectrum are continuous—that is, one constituent blends into the next (Figure 3-2).

Electromagnetic radiation is a form of energy that originates from the atom. That is, electromagnetic radiations are emitted when changes in atoms occur, such as when electrons undergo orbital transitions or atomic nuclei emit excess energy to regain stability. Unlike mechanical energy, which requires an object or matter to act through, electromagnetic energy can exist apart from matter and can travel through a vacuum. For example, sound is a form of mechanical energy. The sound from a speaker vibrates molecules of air adjacent to the speaker, which then pass the vibration to other nearby molecules until they reach the listener’s ear. In the absence of the intervening air molecules, no sound would reach the ear. With electromagnetic radiation, it is the energy itself that is vibrating as a combination of electric and magnetic fields; it is pure energy. In fact, energy and frequency of electromagnetic radiation are related mathematically. The energy of electromagnetic radiation can be calculated by the following formula:

E=hf

In this formula, E is energy, h is Planck’s constant (equal to 4.15 × 10^-15 eV-sec), and f is the frequency of the photon. The energy is measured in electron volts (eV). The physicist Max Planck first described the direct proportionality between energy and frequency; that is, as the frequency increases, so does the energy. Planck theorized that electromagnetic radiation can only exist as “packets” of energy, later called photons. The constant, h, which is named for Planck, is a mathematical value used to calculate photon energies based on frequency. The energy of the electromagnetic spectrum ranges from 10^-12 to 10¹⁰ eV.

Electromagnetic radiation exhibits properties of a wave or a particle depending on its energy and in some cases its environment. This phenomenon is called wave-particle duality, which is essentially the idea that there are two equally correct ways to describe electromagnetic radiation. Conceptually we can talk about electromagnetic radiation based on its wave characteristics of velocity, amplitude, wavelength, and frequency. As previously stated, the velocity for all electromagnetic radiation is the same: 3 × 10⁸ m/s. The amplitude refers to the maximum height of a wave. Wavelength

Related posts:

Additional Equipment The X-ray Tube Image Intensified Fluoroscopy Automatic Exposure Control Radiographic Exposure Technique Image Characteristics

Stay updated, free articles. Join our Telegram channel

Join