XRay Operator Book 31Jan06 Bo

BASIC X-RAY MACHINE OPERATOR STUDY GUIDE

Sponsored and published by:

Florida Department of Health

Produced by:

The Center for Instructional Development and Services Florida State University

For further information, contact:

James A. Futch Environmental Administrator Department of Health Bureau of Radiation Control Radiologic Technology Program 4052 Bald Cypress Way, Bin C21 Tallahassee, Florida 32399-1741

State of Florida, Department of Health, 1998

The use of trademarks in this document is strictly for the purpose of clarity and in no way should be considered an endorsement by the Department of Education, Florida State University, or The Center for Instructional Development and Services. This publication was produced at a cost of $25 per copy to provide information in compliance with Florida Statutes Chapter 468, Part IV, the Radiologic Technologist Certification Act. The Department of Health complies with state and federal nondiscrimination policies relating to race, sex, age, and handicapping conditions.

DOH 5/0011000

BASIC X-RAY MACHINE OPERA TOR STUDY GUIDE

State of Florida Department of Health December 1986

Acknowledgments

The Department of Health (DOH) is grateful to institutions and publishers who have granted permission to include their copyrighted materials in this study guide. In addition to sources noted in the text, information and illustrations have been adapted or borrowed from the following publications: From Assisting in Radiology, by Janet Schnauze. 0 1984 by The University of Texas at Austin. Used with permission. From Basic Medical Techniques and Patient Care for Radiologic Technologists, 2nd edition, by Lillian S. Torres and Carol Morrill Moore, o 1983 by J. B. Lippincott Company. Used with permission. From Basic X-ray Operator Study Guide, 0 1983 by State of Florida, Department of Health and Rehabilitative Services, Office of Radiation Control. Used with permission. From Emergency Medical Technician, by Betty G. Hirst and J. Jerome Rohrbach, Jr. 0 1978 by Florida Department of State. From Nursing Proceduresfor the Practical Nurse. 0 1972 by Ohio State University, Instructional Materials Laboratory. Used with permission. From Nursing Skills for Allied Health Services, by Lucille A. Wood and Beverly J. Rambo. 0 1977 by The Regents of the University of California. Used with permission. Portions of this study guide have as their source the publication Medical Service: Radiologic Technology, Departments of the Air Force, the Army, and the Navy (Washington, D.C., 1974). The Department gratefully acknowledges the efforts of the following individuals who prepared many of the illustrations included in this study guide: Gary L. Tomaszewski, formerly with DOH, Tallahassee; and Vala Wagie, Broward Community College, Ft. Lauderdale. The Department also thanks the following individuals who prepared the first draft of the study guide: Gary L. Tomaszewski; Vala Wagie; Nancy Delgado, formerly with the Center for Instructional Development and Services (CIDS) at Florida State University (FSU); and Linda Cornelious, CIDS, FSU. The Department thanks the following for their time and efforts in reviewing the guide: Gary L. Tomaszewski, Richard Leverone, Vala Wagie, Louise M. Tomaszewski, Janice Leifer, Susan Bridis, William Passetti, Simon Growick, Mason Cox, Don Steiner, Danny Smock, Roxanne McCarthy, Betsy Fulford, Marvin Patterson, Rusin Van Dyke, and the entire staff of the Bureau of Radiation Control. DOH would also like to express its appreciation to the applicants who reviewed the guide and took the certification examination for a pilot study: Eileen Andreu, Cheryl Bowie, Mary Bradshaw, Mary Cairns, Ladonna Greene, Mary Guinan, Julie Hall, Michele Knisley, Geraldine

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Labrecque, Mary Lamb, Sharon Lancaster, Diane Lutzen, Jane Muse, Brenda Relstab, Brenda Reynolds, Catherine Richardson, Aimee Sallas, and Susan Shephard. Finally, the Department would like to acknowledge the project staff at the Center for Instructional Development and Services of Florida State University: Hyoja Lee, project manager and instructional designer; Frances Brock and Peggy Barlow, editors; Susan Maxwell and Betty Willard, word processors; Dan Haskin, graphic designer; Alice Fisher and Bob McCann, proofreaders; Mary Sommer, illustrator; Roberta Carpenter, copyright specialist; and Linda Cornelious, Young-Sun Yang, and Mike Lado, graduate assistants.

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Preface

Chapter 468, Florida Statutes, provides legal authority for the State Radiologic Technologist certification program and Chapter 64E-3, Florida Administrative Code, establishes necessary criteria and procedures to carry out provisions of the statute. The Radiologic Technologist Certification Act includes the following declaration of policy: It is declared to be the policy of the state that the health and safety of the people must be protected against the harmful effects of excessive and improper exposure to ionizing radiation. Such protection can in some major measure be accomplished by requiring adequate training and experience of persons who use radiation and radiation-emitting equipment in each particular case under the specific direction of licensed practitioners. It is the purpose of this part to establish standards of education, training, and experience and to require the examination and certification of users of radiation and radiationemitting equipment. Well-trained radiographers and basic x-ray machine operators who at all times fully utilize their expertise in the performance of their duties serve two important purposes: 1) they provide the best possible x-ray film images for the diagnosis of diseases and injuries; and (2) they minimize the unnecessary radiation exposure of patients, operators, and others who are in range of exposure by following appropriate safety precautions and procedures. The Radiologic Technologist Certification Act is primarily concerned with the reduction of radiation exposure by ensuring that radiologic procedures are performed by personnel knowledgeable about safety precautions and procedures. Exposure can also be reduced significantly if each procedure is accomplished correctly the first time, thereby eliminating the added exposure involved in retakes and the unnecessary exposure of vulnerable body organs that results from poor body positioning. The Radiologic Technologist Certification Act and rules provide: a. A description of persons and the conditions under which they are authorized to use radiation on human beings for medical purposes. 2. Requirements for admission to an examination. 3. Criteria for recertification and continuing education. The Department of Health provides basic x- ray machine operator examination applicants with a study guide to fulfill the study material requirement of the Radiologic Technologist Certification Act. The study guide is designed to impart a knowledge of (1) important safety precautions and procedures for radiation protection, (2) x-ray

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equipment operation and maintenance, (3) image production and evaluation, (4) radiographic procedures and positioning, and (5) patient care and management. Full understanding of the material in this manual, as indicated by successfully passing the Basic X-Ray Machine Operator certification examination, should qualify the applicant to safely operate x-ray equipment while under the direct supervision of a licensed practitioner. Any person who is interested in radiologic technology as a full-time profession or who is required to operate x-ray equipment for sophisticated diagnostic procedures must successfully complete the General Radiographer examination and receive state certification as a General Radiographer. Adapted from Basic X-Ray Operator Study Guide. Tallahassee, Fla.: Department of Health and Rehabilitative Services, Sept. 1985. Used with permission.

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Table of Contents

Preface/v Orientation to the Study Guide/ix Unit 1: Radiation Protection/1 A: Introduction to X Rays/2 B: Biological Effects of Radiation/12 C: Protection of X-Ray Operators and Patients/21 D: Radiation Monitoring/56 Unit 2: Equipment Operation and Maintenance/67 A: Electronics of X-Ray Generation and the Radiographic Tube/68 B: Identifying Equipment Failures/88 Unit 3: Image Production and Evaluation/101 A: Selection of Technical Factors/102 B: Film Processing and Quality Control/126 Unit 4: Radiographic Procedures and Positioning/155 A: Positioning Terminology /156 B: General Procedural Considerations/167 C: Positioning and Procedures/175 D: Foreign-Body Localization/257 Unit 5: Patient Care and Management/263 A: Verifying Patient Identification and the Radiographic Requisition/264 B: Transferring the Patient/271 C: Using Aseptic and Sterile Techniques/282 D: Monitoring Vital Signs/289 E: Handling Emergency Situations/301 F: Monitoring Medical Equipment/312 Posttest/327 Answers to Practice Questions/355 Answers to the Posttest/367 User-Response Sheet/373

vii

Orientation to the Study Guide

Purpose of the Guide The Basic X-RayMachine Operator Study Guide designed to help is applicants prepare for the certification examination required of basic xray machine operators and to help them acquire the knowledge and skills needed on the job. It is NOT the purpose of this guide to serve as the sole source of instruction preparation for the certification examination. You, the basic x-ray machine operator applicant, must acquire further training or instruction in an organized program such as the one offered in the Medical Assisting programs (HR 17-050300; MEA 0991) in community colleges or in area vocational-technical centers. (NOTE: Some Medical Assisting programs offer instruction for the basic x-ray machine operator.) You can also obtain further instruction from licensed physicians and from special training programs in hospitals and other qualified training facilities. Development of the Guide The certification examination for basic x-ray machine operators, developed by the American Registry of Radiologic Technologists (ARRT), is based upon tasks and content specifications identified by ARRT. This study guide is based upon the same tasks and content specifications. The practice and posttest questions, however, are not identical to the certification examination questions. In order to prepare yourself for the certification examination, YOU MUST THOROUGHLY STUDY AND FULLY UNDERSTAND THE MATERIAL IN THIS GIDDE so that you can apply your knowledge and skills to the different situations you will encounter. Hypothetical situations posed in the examination differ from those provided in the guide. Components of the Guide This study guide consists of five units: Radiation Protection, Equipment Operation and Maintenance, Image Production and Evaluation, Radiographic Procedures and Positioning, and Patient Care and Management. Each unit is composed of several sections, in which you will find the following components. The Introduction tells you what each section covers and why it is important for basic x-ray machine operator applicants to learn the topics covered in that section. The Objectives state what you should be able to do on a written test after studying that section.

ix

The Text contains information you need to know in order to achieve the objectives. Definitions of technical terms are presented either in the text or in the footnotes (terms defined in the footnotes are printed in bold face with a footnote number). The text also includes illustrations to enhance the text. The practice Questions allow you to see how well you have learned the material. After completing the Practice Questions, check your answers with the correct answers provided in the Answers to Practice Questions at the back of this guide. If you miss questions, review those parts of the text that cover the items missed. If you still have trouble understanding the material, you need to seek further instruction. The Posttest includes 140 multiple-choice items covering all five units: items 1-40 on Unit 1, 41-55 on Unit II, 56-90 on Unit III, 91-100 on Unit V, 101-120 on the chest section of Unit IV, and 121-140 on the extremity section of Unit IV. This posttest enables you to practice before you take the 140-item certification examination. Since you will be allowed three hours for the certification examination, allow yourself three hours to complete this posttest. After you have completed the posttest, check your answers in the Answers to the Posttest at the back of this guide. If you made mistakes, review the appropriate parts of the guide. If you still need explanation on the items answered incorrectly, you should seek further instruction or training. Remember, the items in the practice exercises and the posttest are not the same test items that appear in the certification examination. The Answer Keys to the practice questions and to the posttest are provided at the back of this guide. For the purpose of clarification and review, "Notes" are included in the answer keys. In addition, a recommended number of study hours for each unit is indicated on the unit cover page. This is only a suggested minimum number of study hours, which is based on the results of a field test. You will have to study as many hours as you need to in order to understand the material in the guide thoroughly. (Be sure to include in your study the names and locations of each bone of the chest and of the lower and upper extremities as shown in diagrams in Unit IV.) Reference It is recommended that you read The Handbook for State Licensing Examinees which candidates for the Basic X-ray Machine Operator Examination that you will receive from the ARRT.

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UNIT I: RADIATION PROTBC'l10N

A: Introduction to X Rays/2 B: Biological Effects of Radiation/12

c: Protection of X-Ray Machine Operators and Patients/21 D:Radiation Monitoring/56

Recommended study hours for Unit I: 24

1

Section A: Introduction to X Rays

Introduction The discovery of x rays has had a major impact in the field of medicine. With the growing use and sophistication of radiographic procedures, the need for well-trained operators has increased. The more knowledge about radiation that you as an x-ray machine operator have, the greater your ability will be to make proper job-related decisions. Such information will also help you to minimize radiation exposure to the patient and yourself, while achieving an optimum diagnostic radiograph. In this section you will be introduced to the important properties of x rays. You will learn what you need to know about the sources and types of radiation, and you will find out how x rays interact with matter and how they are produced. You will also learn terminology for the measurements used in radiology. Objectives Upon completion of this section, you should be able to do the following on a written test: 1. Identify the discoverer of x rays. 2. Describe the properties of x rays. 3. Describe the major sources of natural and man-made radiation. 4. Identify what can happen when x rays interact with matter. 5. Explain how x rays are produced. 6. Identify the major types of radiation. b. Define "exposure," "absorbed dose," and "dose equivalent," and identify the unit of radiation measurement for each. c. Given values of the absorbed dose, the quality factor, and the modifying factors, calculate the dose equivalent.

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I-A: Introduction toX Rays

Introduction to X Rays

Discovery of X Rays In 1895, German physicist Wilhelm Konrad Roentgen was operating a vacuum tube at high voltage when he noticed a glow coming from cardboard coated with a chemical, several feet away from the tube. He realized that this glow, or fluorescence, was caused by the invisible radiation leaving the vacuum tube. Since the rays were new and without a name, they were called X (for unknown) rays, and sometimes Roentgen rays, after their discoverer.

Properties of X Rays X rays are a form of electromagnetic radiation* similar to gamma radiation.* To understand how such radiation behaves, imagine a person throwing a stone into a lake. The water moves in all directions away from the stone. Radiation moves away from its source in a wavelike motion similar to the movement of the water. Although x rays are the same type of radiation as radio, or visible light waves, they have higher energy photons and a much shorter wavelength. For example, the wavelengths used in television are approximately six feet, whereas the average wavelength of medical x rays is about one-billionth of an inch. Because x rays have such short wavelengths, they can penetrate matter, whereas other types of electromagnetic radiation, such as visible light, are absorbed or reflected. When x rays are produced, they travel in straight lines at an extremely fast speed-186,000 miles per second, the speed of light. Although invisible, they can cause certain substances to fluoresce, or glow. They produce an image on a photographic film that can be made visible by processing. X rays are electrically neutral; in other words, they are neither positive nor negative. Some of the properties of x rays are listed below. X rays: are a form of electromagnetic radiation like gamma radiation have higher-energy photons and shorter wavelength than visible light penetrate most forms of matter NOTE: X rays do not readily penetrate certain dense materials such as lead. travel at the speed of light (186,000 miles per second) affect photographic film very much as light rays do

*electromagnetic radiation: the transmission of energy via photons* at the speed of light *photon: a very small bundle of electromagnetic energy *gamma radiation: electromagnetic radiation spontaneously emitted from radioactive materials

I: Radiation Protection

3

into an make certain a positive electron (or positron). The positron loses energy by electron and chemicals emit light (fluorescence) ionization until it finds anincluding and annihilates it, producing two characterisic can ionize matter, electron living tissue annihilation photons. of x rays can produce biological changes and cause NOTE: This property damage to the human body. cannot be seen, heard, or felt X-Ray Production travel in a straight line from their source, though they may be deflected by atoms they meet X rays used for diagnostic purposes(This law is discussed in Section electrons* obey the inverse square law are produced when fast-moving C of this strike a positively charged target* (the anode) in the radiographic tube and interactunit.) the atoms of the target. Electrons are produced by heating a filament with cannot be reflected (thecathode), which is a coil of tungsten wire. When a high voltage is applied, the negatively charged electrons are accelerated toward the positively charged target. (According to a rule of physics, like charges repel and unlike charges Ionizing Radiation and Its Sources attract.) Radiation is the emission of radiant energy in the form of waves or particles. When radiation interacts with radiographic tube are transformedstages, as The production of x rays in a atoms, the atoms occurs in three into electrically charged particles, called ions. This conversion of atoms to ions is called illustrated in Figure I-A-1. ionization. Since some forms of radiation ionize and some don't, the radiation (such as x-radiation) that a radiographic tubematerials to ionselectric current,* a Stage 1. The filament in converts atoms of is heated by an is called ionizing radiation. process that causes the filament to emit electrons. Ionizing radiation can be either natural (background) or man-made. Natural radiationA high voltage is applied across the radiographic and other stars in the Stage 2. comes from cosmic radiation emitted by the sun tube to accelerate outer space, electrons toward the target inside the tube. radioactive materials {uranium, thorium, etc.) in the earth, and radionuclides* deposited in the human body by the food and liquid consumed. Stage 3. As the high-speed electrons are rapidly decelerated by the target, x rays are produced. Sources of man-made radiation include radiographic and nuc1earmedicine procedures, radioactive fallout from atomic- and nuc1earweapons testing, Target television,Filament and high-voltage electronic devices.(cathode, -) (anode, +)

a.

Tube

Target

Interaction of X Rays with Matter When x rays enter an object, some of the x-ray photons interact with the object's atoms and some do not. When they do, radiant energy is transferred from the x rays to the atoms. This transfer of energy is called absorption. The remaining xray photons, those that do not interact with atoms, travel in straight lines and can produce an image on a film showing the size, shape, and internal composition of the object. When the object is the human body, this image on a radiographic film is used for diagnosis. X rays interact with matter in basically three different ways: photoelectric interaction, Compton interaction, and pair production. In photoelectric interaction, the x-ray photon transfers all of its energy to the electron when they interact. If that energy is sufficient to release the electron from its atomic orbit, the atom is ionized. In Compton interaction, the photon transfers only a part of its energy to the electron when they interact. The rest of the photon's energy is radiated as a lower-energy photon, which travels in a different direction, causing scatter radiation. Therefore, Compton interaction is also called Compton scatter. In pair production, the photon changes all its energy

*radionuclide: a radioactive nuclide 4 I-A: Introduction to X Rays

b.

trols the filament temperature of the radiographic tube: the higher the rn A, the greater the electron emission. Consequently, by varying the rnA, we can vary the quantity of x rays. (The relationship between exposure time and rnA is discussed in Section C of this unit.) In stage 2, the acceleration of the electrons controls the quality-that is, the penetrating power-of the x rays. The higher the voltage, the greater the speed of the electrons. The greater the speed, the higher the energy range of the photons. The higher the energy range of the photons, the greater the penetrating power of the x rays. In other words, by varying the peak kilovoltage (k Vp), we can vary the quality of the x rays. In the third stage, the rapid deceleration of the electrons produces the x rays.

Types of Radiation As the electrons interact with the atoms of the target, photons of various energies emerge from the target. Most of these photons are directed toward the object being radiographed, and a few of them are not. Those photons directed toward the object are called primary radiation, and those which are not are called leakage radiation. The primary radiation is then divided into remnant and attenuated radiation. The primary photons that pass through the object being radiographed and reach the film are the useful x-ray beam, and they are called remnant radiation. The primary photons that interact with atoms of the object are called attenuated radiation (see Figure I-A-2). When it interacts with the object, the attenuated radiation is divided into scatter radiation and absorption. Since scatter radiation and leakage radiation are not useful for radiographic procedures, they are categorized as secondary radiation. These different types of radiation can be depicted as follows:

Figure I-A-l Production of X-Radiation Inside a Radiographic Tube In stage 1, the number of electrons produced provides a means of controlling the quantity of x rays. The number of milliamperes (rn A) con-

*electron: a tiny, negatively charged particle that revolves in orbit around the nucleus of an atom *target: a block or disc made of tungsten, which has a high melting point, and high heat conductivity *current: a movement of electric charges from one place to another. Its strength is measured in am peres. I: Radiation Protection5

Scatter radiation Attenuated radiation

_Film

RadilgraPhic tube

Remnant radiation (useful x-ray beam)

Figure I-A-2 Types of Radiation6

I-A: Introduction to X Rays

Units and Quantities Roentgen (R}-Unit of Exposure. It is difficult to measure the amount of energy carried by an x-ray beam because it travels through the air. Therefore, an indirect form of measurement is used, as follows: The amount of ionization in a specified amount of air surrounding a point of interest is proportional to the energy carried by the beam at that point. To measure the amount of energy carried by the x-ray beam, therefore, you measure the amount of ionization that x-ray beam produces in that specified amount of air. This amount of ionization is called exposure, and the unit used to measure exposure is the roentgen (known as R). One roentgen represents the amount of exposure necessary to produce 1 electrostatic unit of ions or 1 charge (+ or -) per 0.001293 gram of air. An equally important and commonly used unit is the milliroentgen (rn R), which is 1/1000 of a roentgen.

The exposure rate is the number of roentgens produced by the x-ray machine per second, per minute, or per hour. In other words, it is the intensity of radiation. Exposure rate can be expressed, for example, as R/min (roentgens per minute) or R/hr (roentgens per hour). Rad-Unit of Absorbed Dose (D). The absorbed dose of radiation, known as D, is the amount of energy absorbed by a substance or object. A rad refers to a unit of the absorbed dose. A rad is 100 ergs deposited per gram of substance. As the amount of exposure (R) increases, so does the absorbed dose (D). The higher the quantity of the absorbed dose in the human body, the greater the chance of biological damage occurring. Rem-Unit of Dose Equivalent (10 . The dose equivalent, known as H, takes into account the fact that the biological effects of ionizing radiation on human body tissue are dependent not only on the absorbed dose, but also on other factors. The rem is the unit used to measure dose equivalent. The quality factor (Q) takes into account the different degrees of biological effect that can result following exposure to the same absorbed dose of different types of radiation. The quality factor for diagnostic x rays is 1, for neutrons 10, and for alpha 20. This means that neutrons can cause ten times more damage than diagnostic x rays. The modifying factor (N) is the product of all other factors. For practical purposes, N is assigned a value of 1 for all irradiations by external sources. The dose equivalent (H) is the product of the absorbed dose (D), the quality factor (Q), and any other necessary modifying factors (N). Since the quality factor (Q) of diagnostic x rays is 1, and an absorbed dose (D) of 50 rads has been received, the dose equivalent (in rems) is calculated as follows:H= DQN H = 50 rads x 1 x 1 H = 50 rems


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Another example: If an x-ray machine operator exposed to an x-ray beam received an absorbed dose of 200 rads, the dose equivalent for this operator is 200 rems becauseH = DQN H = 200 x 1 x 1 H = 200 rems

The following table lists the ionizing radiation quantities with their units of measure, the media, and the effects measured.QUANTITY UNIT OF MEASURE MEDIUM EFFECT MEASURE D

exposure absorbed dose (D)

roentgen (R) air rad any object

ionization of air amount of energy absorbed by the object biological effects

dose equivalent (H)

rem

human body tissue

Summar y

X rays are a form of electromagnetic radiation (like gamma radiation) that can penetrate and ionize matter, including human tissue. Ionizing radiation has both natural and man-made sources. X rays, a type of ionizing radiation, are produced when electrons are made to strike a positively charged target in the radiographic tube and to interact with the atoms of the target. Radiation can be categorized into two main types: primary radiation and secondary radiation. Primary radiation is the useful x-ray beam, and secondary radiation consists of leakage and scatter radiation. Three units of measurement are used in determining the amount of ionizing radiation: roentgen for radiation exposure, rad for absorbed dose, and rem for dose equivalent.

Complete the Practice Questions beginning on the following page.

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I-A: Introduction to X Rays

Practice Questions (I-A)

Directions Each of the questions or incomplete statements is followed by four suggested answers or completions. Circle the one (a, b, c, or d) which is best in each case. 1. Who discovered x rays? d. e. f. g. Curie Rothernburg Roentgen Ohms

2. Which of the following is not a property of x rays? h. They are electromagnetic in nature like gamma radiation. i. They have a shorter wavelength and higher-energy photon than visible light. j. They produce biological changes. k. They penetrate any object. l. Which basic property of x rays can cause damage to the human body? m. n. o. p. They can be refracted from the line of travel. They ionize matter. They are absorbed uniformly. They cannot be seen, heard, or felt.

q. Which of the following causes the harmful effects of radiation on the human body? r. s. t. u. ionization photons deflection refraction

5. Which of the following describes ionizing radiation? v. w. x. y. the conversion of atoms to electrically charged particles the collision of a filament with a specific target the straight-path travel of x rays radiographic fallout from nuclear-weapons testing


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6. Which of the following are sources of natural radiation? z. outer space aa. the earth bb. food cc. dd. ee. ff. 1 and 2 only 2 and 3 only 1 and 3 only 1, 2, and 3

gg. Which of the following does not represent a source of man-made radiation? hh. ii. jj. kk. nuclear medicine radiographic procedures food and drink nuclear-weapons testing

ll. When x rays interact with matter, all of the following can happenEXCEPT:

mm.The radiant energy is absorbed in the matter. nn. X-ray photons are transformed into ions. oo. X-ray photons penetrate the matter and travel in a straight line. pp. X-ray photons produce an image of the matter on a radiograhic film. 9. All of the following describe steps in x-ray production EXCEPT: qq. rr. ss. tt. Tungsten is melted to produce electrons. The heated filament produces electrons. When electrons strike a target, sudden deceleration occurs. Rapidly decelerated electrons produce x rays.

10. To control the quantity of x rays, what should you adjust? uu. kilovoltage at peak vv. milliamperes ww.target xx. filament 11. To control the quality of x rays, what should you adjust? yy. peak kilovoltage zz. milliamperes aaa.target bbb.filament ccc.Which of the following is the useful x-ray beam that contributes to the formation of the radiographic image? ddd.scatter radiation eee.remnant radiation fff. absorbed radiation ggg.leakage radiation I-A: Introduction to X Rays

1 0

hhh.Which of the following is dispersed in all directions by the object being radiographed? iii. scatter radiation jjj. remnant radiation kkk.absorbed radiation lll. leakage radiation 14. Which of the following describes exposure? mmm.the degree to which atoms are ionized nnn.the amount of collision that occurs after ionization ooo.the degree to which electrons are neutralized through diagnostic x rays ppp.the amount of ionization that occurs in a specified volume of air 15. What is the unit for measuring exposure in air? qqq.roentgen rrr. rad sss. rem ttt. quality factor 16. What is the unit for measuring the absorbed dose? uuu.roentgen vvv.rad www.rem xxx.quality factor 17. What is the unit that takes into account the biological effects? yyy.quality factor zzz.roentgen aaaa.rad bbbb.rem 18. Dose equivalent is the product of all of the following EXCEPT: cccc.absorbed dose dddd.quality factor eeee.ionizing factor ffff.modifying factor gggg.When the absorbed dose is 100, the quality factor is 2, and the modifying factor is 1, what is the dose equivalent? hhhh.50 rems iiii. 100 rems jjjj. 200 rems kkkk.400 rems

Now check your answers with the correct ones provided in the Answers to Practice Questions (I-A) at the back of this Guide. I: Radiation Protection 1 1

Section B: Biological Effects of Radiation

Introduction In Section A, we discussed the fact that x rays ionize when they interact with atoms. Human body tissues are composed of atoms. Therefore, when x rays penetrate body tissue, ionization occurs. This ionization can result in molecular change, which can cause cellular damage. Cellular damage can result in the abnormal functioning or the loss of cells, which may result in organic damage. When organic damage occurs, biological effects of radiation, such as cataracts or leukemia, appear in the living organism. In other words, biological effects occur at three levels: molecular, cellular, and organic. This section deals with the effects of radiation at these three levels and in the two categories, genetic and somatic. Objectives Upon completion of this section, you should able to do the following on a written test: llll. Describe the three levels at which biological effects of radiation occur. 2. Identify the most radiosensitive cells. 3. Identify three characteristics of DNA. mmmm.Identify the genetic and somatic effects of radiation. nnnn.Identify the three types of the acute radiation syndrome. oooo.Identify four types of long-term somatic effects of radiation on the human body. 7. Describe the linear and sigmoid dose-response curves.

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I-B: Biological Effects of Radiation

Biological Effects of Radiation

The Cells and Their Radiosensitivity The human body is composed of various types of cells that perform many different functions. Every mature human cell is highly specialized, having a specific function to perform. The cell's specialized function is determined by the structure of the cell's molecules. Most of these cells can be damaged by ionizing radiation, because ionization can change the structure and chemical balance of the cell's constituent molecules. This molecular change, then, changes the cellular functions. Different types of cells can be exposed to different amounts of radiation before damage occurs, since the degree of their radiosensitivity differs. The lower the cells' degree of specialization and the faster their division, the greater their radiosensitivity. Immature cells, which are nonspecialized and which undergo rapid cell division, are more radiosensitive than mature cells, which are specialized in function and which divide slowly or have ceased to divide. Lymphocytes (white blood cells) are among the most radiosensitive of the blood cells. Female and male reproductive cells (ova and spermatogonia) are very radiosensitive. The cells that become the linings and covers of body organs (epithelial cells) have moderately high sensitivity. Muscle and nerve cells, which are highly specialized and do not divide, have low sensitivity.

Three Levels of Biological Effects The biological effects of radiation occur at three levels: the molecular, the cellular, and the organic. Molecular Effects of Radiation. Damage to the human body caused by ionizing radiation begins with damage at the molecular level. A couple of theories attempt to explain how biological damage occurs: the direct-hit theory and the indirect-hit theory. These refer to the way radiation interacts with a cell at the molecular level. Cells are composed mainly of water and biologic macromolecules such as DNA (deoxyribonucleic acid) which, as the genetically active part of the genes, transmits the hereditary pattern. So, when ionizing radiation interacts with a cell, the radiation interacts directly with macromolecules such as DNA or with water. When the interaction occurs directly with DNA, the resulting ions may break a chemical bond and change the DN A molecular structure. This is called the direct-hit theory because the damage to the DNA molecules occurs directly. When the radiation interacts with water and ionizes it, water molecules break down into ions and free radicals. These free radicals can then cause damage to biologic macromolecules such as DNA. This is called the indirect-hit theory because the damage to the DNA molecules takes place indirectly.


1 3

Cellular Effects of Radiation. The effects of radiation at the cellular level can result in the following: instant death, when a dose of about 100,000 rads is absorbed in a period of a few minutes reproductive death (the cell loses its reproductive capacity), when a dose of about 100 to 1000 rads is absorbed genetic death (the cell dies after a few divisions), even when a small dose of radiation is absorbed NOTE: Genetic death is also called mitotte= death. interference with cellular function, permanently or temporarily chromosome breakage, when ionizing radiation interacts directly with a DNA macromolecule Organic Effects of Radiation. The cellular effects of radiation can result in organic damage, causing problems such as cataracts and leukemia. The degree of damage generally depends upon the following: the quantity of ionizing radiation the ionizing ability of the radiation the body part exposed to radiation (because some body parts are more radiosensitive than others) the amount of body area exposed to radiation

Two Categories of Biological Effects The biological effects of ionizing radiation can be considered in two categories: genetic effects and somatic effects. Genetic Effects. Molecular damage to DNA molecules in the sperm or ova can cause biological damage in offspring. Though these effects may not show up for years or for generations after the exposure is received, they may be passed on from one generation to another. Because the radiation dose at the gonads (ovaries and testes-where egg and sperm, respectively, are manufactured and stored) is genetically significant, it is called the genetically significant dose (GSD). Gonadal shielding (discussed in the next section) is important to minimize the amount of radiation received by the male or female gonads. NOTE: Symptoms of genetic effects are also called genetic dose indicators. Somatic Effects. Forms of biological damage that affect the individual but that are not passed on to the offspring are called somatic effects. These effects can be either short-term or long-term depending upon the length of time between the exposure and the appearance of symptoms of the damage.NOTE: Symptoms of somatic effects are also called somatic dose

indicators.

*mitotic: a type of cell-division process

1 4


Short-term somatic effects are relatively severe and begin a short time after a person has received a large amount of radiation over his or her body within a short period of time. These injurious effects, also known as the acute radiation syndrome, occur in four stages: pppp.The initial stage, which begins within 48 hours after radiation expo sure, includes nausea, fatigue, loss of appetite, and other symptoms. qqqq.The latent stage occurs next and lasts about a week. During this latent period, the early symptoms disappear and the person feels better. However, changes are taking place within the blood-forming and other organs; symptoms of these changes will not show up until the next stage. rrrr.During the manifest illness stage the patient exhibits fever, infec tion, diarrhea, hemorrhage, nausea, vomiting, disorientation, shock, and other symptoms resulting from the damage. Death may follow these symptoms. ssss.If the dose was not lethal, body tissue starts to heal and the recovery stage begins. Full recovery may take many weeks. There are three types of acute radiation syndrome in most mammals: central nervous system syndrome, gastrointestinal syndrome, and hema topoietic syndrome. Central nervous system (CNS) syndrome will occur after very high doses, exceeding several thousand rems. Death, occurring within hours after exposure, is apparently due to the breakdown of the neurological and cardiovascular systems. Gastrointestinal syndrome will occur at lower doses, but at doses usually above 600 rems. Death, occurring within 15 to 30 days, is as sociated with the destruction of the gastrointestinal linings. Hematopoietic syndrome, also known as bone-marrow syndrome, will occur at even lower doses, but at doses greater than 100 rems. Death may occur because of damage to the blood-forming organs. -

Long-term somatic effects appear after months or years have elapsed following exposure. There are generally four types of long-term somatic effects: cataractogenesis, life-span shortening, carcinogenesis, and embryological effects. Cataractogenesis is the formation of a cataract on the lens of the eye. Radiation causes the normally transparent lens to become opaque, that is, to develop a cataract. The result may be a loss of vision. Human evidence for radiation cataractogenesis is derived pri marily from a relatively small number of workers inadvertently ex posed to large doses of radiation to the eye, from patients exposed to therapeutic radiation, and from Japanese atomic-bomb survivors. Life~ shortening occurs when the average life span is shortened because of radiation received. Several studies have been made of the longevity of radiologists (physicians who specialize in radiology), and although all the statistics do not agree, there seems to be some evi1 5


dence of life-span shortening. This effect has been confined mainly to those who practiced during the early years of x-ray use, when occupational exposure among radiologists was much higher than today Carcinogenesis, the production of cancer, is a greater risk following radiation exposure. Such cancers as leukemia (of the blood) and breast cancer can be caused by radiation. Evidence indicating that radiation is a carcinogen comes from radium-dial painters who in gested radioactive material, early radiologists and dentists, and uranium miners

Embryological effects are the effects of radiation on the embryo or fetus during its development. These effects vary in severity during each of the three major periods, or trimesters, of gestation. As the pregnancy progresses, radiosensitivity decreases. The most severe effects occur during the first trimester. Exposure to xradiation during the first six weeks often causes death or abnormalities. Between the second and sixth week of the first trimester, during organogenesis (when major organs are developing), the fetus is extremely susceptible to radiation-caused abnormalities. Radiation sensitivity decreases during the second and third trimes ters. Even at these stages, however, abnormalities and disorders can result from radiation exposure. Dose-Response Curves. Also known as dose-effect curves, these graphic representations show what can happen to cells in response to certain dosages of radiation. Two types of dose-response curves are the linear and sigmoid curves (see Figures I-B-l and I-B-2). The linear curve indicates that the biological response to radiation is directly pro portional to the dose received; the greater the dose, the greater the biological effects. The sigmoid curve indicates that there is a threshold at which a biological response to radiation first occurs, and a plateau at which the maximum biological effects level off.

w(j )

w

2B fa:

z

2B fa:THRESHOLD

z

(j)

DOSE

DOSE

Figure I-B-l Linear Dose-Response Curve 1 6

Figure 1-B-2 Sigmoid Dose-Response Curve I-B: Biological E ffects of Radiation

Summar y

Different types of cells have different degrees of radiosensitivity. The most radiosensitive cells include the blood-forming cells and the reproductive cells. Ionizing radiation can result in biological damage to the human body at the molecular, cellular, and organic levels. The damage can be either genetic or somatic. Genetic effects damage the offspring of an individual exposed to radiation, whereas somatic effects damage only the individual exposed. Generally short-term somatic effects, known as acute radiation syndrome, are of three types: central nervous system syndrome, gastrointestinal syndrome, and hematopoietic syndrome. Long-term somatic effects, which appear long after exposure, consist of cataractogenesis, life-span shortening, carcinogenesis, and embryological effects.

Complete the Practice Questions beginning on the following page.


1 7

Practice Questions (I-B)

Directions Each of the questions or incomplete statements is followed by four sug gested answers or completions. Circle the one (a, b, c, or d) which is best in each case. tttt. Biological damage caused by ionizing radiation begins at which level? uuuu.biological level vvvv.molecular level wwww. cellular level xxxx.organic level 2. Which of the following are most radiosensitive, in general? yyyy.blood-forming cells zzzz.nerve cells aaaaa. reproductive cells bbbbb. muscle cells ccccc. 1 and 3 only ddddd. 1 and 4 only eeeee. 2 and 3 only fffff.1, 2, and 4 only 3. Which of the following is not a characteristic of DNA? ggggg. It is the genetically active part of the genes. hhhhh. It transmits the heredity pattern. iiiii.It breaks down into ions when interacting with water. jjjjj.It is the biologic macromolecules in cells. kkkkk. The cellular effects of radiation can result in all of the following EXCEPT: lllll.organic damage mmmmm. molecular effects nnnnn. genetic death ooooo. reproductive death 5. All of the following affect the degree of organic damage EXCEPT: ppppp. the quantity of ionizing radiation qqqqq. the ionizing ability of the radiation rrrrr.the gender of the person exposed to radiation sssss.the body part exposed to radiation

1 8


6. Which of the following best describes genetic effects? ttttt.They affect only the patient's DNA. uuuuu.They mayor may not show up for generations after radiation exposure. vvvvv.They become noticeable only in the implantation stage. wwwww.They promote the risk of cancer. 7. What is the radiation dose received by the gonads called? xxxxx.ionizing radiation yyyyy.genetically significant dose zzzzz.somatically significant dose aaaaaa.gonadal dose bbbbbb.Which of the following is not a symptom of short-term somatic effects? cccccc.cataracts dddddd.nausea eeeeee.vomiting ffffff.fever gggggg.Acute radiation syndrome includes all of the following types EXCEPT: hhhhhh.central nervous system syndrome iiiiii.bone-marrow syndrome jjjjjj.cataractogenesis syndrome kkkkkk.gastrointestinal syndrome 10. Which of the following best describes long-term somatic effects? llllll.short-term adverse effects on animals mmmmmm.adverse effects on individuals and their offspring nnnnnn.adverse effects on an individual that appear long after exposure oooooo.long-term adverse effects on a patient's offspring 11. Which of the following are long-term somatic effects? pppppp.lif e-span shortening qqqqqq.cataracts rrrrrr.nausea ssssss.1 and 2 only tttttt.2 and 3 only uuuuuu.1 and 3 only vvvvvv.1, 2, and 3 wwwwww.The fetus is most sensitive to x-radiation during which period of a pregnancy? xxxxxx.first three months (first trimester) yyyyyy.second three months (second trimester) zzzzzz.last three months (third trimester) aaaaaaa.last month


1 9

bbbbbbb.A dose-response curve is a graph representing which of the following? ccccccc.the potential damage to cells when they respond to different doses of radiation ddddddd.the probable damage to DNA molecules once they become ionized eeeeeee.the interaction between DNA and other structures fffffff.a damaged DNA molecule 14. Which of the following describes the linear curve? ggggggg.There are a threshold and a plateau in the curve. hhhhhhh.The biological response to radiation occurs within a short period of time. iiiiiii.The biological response to radiation is not directly proportional to the absorbed dose. jjjjjjj.The biological response to radiation is greater if the absorbed dose is greater.

Now check your answers with the correct ones provided in the Answers to Practice Questions (I-B) in the back of this Guide.

20


Section C: Protection of X-Ray Machine Operators and Patients

Introduction As discussed in Section A, people are exposed to both natural and manmade radiation. Among the various sources of radiation exposure to the public, radiographic procedures are considered the largest single source of man-made radiation. Since secondary radiation (scatter and leakage radiation) produced during a radiographic exposure can be harmful to both patients and x-ray machine operators, you should employ all methods and devices to minimize secondary radiation. Effective measures include keeping the exposure time short; maintaining a considerable distance from the radiographic tube; using shielding devices, a collimator, and filter; selecting appropriate exposure factors; and using appropriate radiographic accessories. This section focuses on how these factors can reduce secondary radiation and how you can protect patients and yourself during radiographic procedures.

Objectives Upon completion of this section, you should be able to do the following on a written test: 1. Identify three basic radiation protection measures. kkkkkkk.Explain the inverse square law and compute radiation intensity (or exposure rate), using the formula for the inverse square law. lllllll.Identify shielding accessories and primary and secondary protective barriers. 4. Identify means for protecting patients from overexposure. 5. Describe beam restriction (collimation) and filtration. mmmmmmm.Identify the types of patients and the body parts requiring gonadal shielding. nnnnnnn.Identify and explain the three primary exposure factors: kVp, rnA, and time. ooooooo.Explain radiographic accessories-radiographic film, film holders, intensifying screens, grids, autotimer, and immobilization devicesin terms of their roles in patient protection. ppppppp.Explain why pediatric patients especially must be protected from ionizing radiation. qqqqqqq.Explain the 10-day rule and the reason female patients of childbearing age must be protected from radiation.


21

Protection of X-Ray Machine Operators

(I-C-l)

As a basic x-ray machine operator, you will be exposed to radiation from several sources: Three Basic Protection Measures The radiation exposure you receive as a result of your occupation is called occupational exposure. You can minimize occupational exposure by practicing basic radiation protection measures. These measures involve time, distance, and shielding accessories. Time. Keep the time of exposure as short as possible. The quantity of radiat ion received by an individual is directly related to the amount of exposure time. If the exposure time is doubled, the dose is doubled. By the same accounting, cutting the time in half will cause the exposure to be reduced by 50 percent. Distance. Maintain a considerable distance between yourself and the radiographic tube, the source of radiation. As the distance from the source of the x-ray beam increases, the intensity of the radiation (also called exposure rate) beam decreases. Thus, the greater the distance, the smaller the radiation intensity. If the distance is doubled, the intensity is decreased to 1/4 the original exposure. A distance in creased by three times will reduce the radiation intensity to 1/9 the original exposure. This relationship is known as the inverse square law, which states that the radiation intensity is inversely proportional to the square of the distance. The formula is=

radiation from accidental exposure to the primary x-ray beam-when, for example, you hold a patient scatter radiation from patients scatter radiation from other surfaces, such as walls, floor, and x-ray table leakage radiation from the radiographic tube

Where: 11 is the exposure at the original distance 12 is the exposure at the new distanceDl is the original distance from the radiographic source D2

is the new distance from the radiographic source

2 2

I-C: Protection of X-Ray Machine Operators and Patients

For example, if an x-ray machine operator receives an exposure of 100 R/hr at a distance of 20 inches, the exposure rate (radiation intensity) at a distance of 40 inches is 25 R/hr, because: 100 R/hr=

(40)2(20)2

x100 R/hr=

4 1 (Invert and multiply)

x

100 R/hr

x = 25 R/hr

4xAs Figure I-C-1 and this example show, when the original distance (0 1) is doubled (0 2), the radiation is spread over an area four times larger, but the exposure rate, or radiation intensity, is reduced, to 1/4 of the original exposure.

D2

Figure l-C-l Inverse Square Law

NOTE:The distance from the source of radiation to the film is called target to rum distance (TFO), source to image detector (SID), or focal r u m distance (FFD). These three terms are used interchangeably.I: Radiation Protection

23

Other Radiation Protection Sbiel@!g Accessories. Use protective shielding routinely. Shielding refers Methods c. to radiopaque* materials inserted between the source of radiation and the In addition to those protective measures as protective barriers, aprons, and individual. Shielding accessories such for which the x-ray machine operator is responsible, protection is afforded both operator and patient through builtgloves are generally made of lead. in features wherever an x-ray machine is in use. While activating radiographic equipment, you should stand behind the Radiographic Room Design . Aa protective lead apronthe gloves, aspa tient protective lead barrier or wear radiographic room and or adjoining shown rooms are I-C-2. in such a way that the placement of the x-ray machine in Figure designed will direct as little radiation as possible toward the adjoining areas (see Figure I-C-3).

Bucky slot cover

Pigure I-C-2 Protecting Yourself from Radiation Using ShieldingReproduced by permission from: Statkiewicz, M. A., and Ritenour, E. R.: Radiation Protection for Student Radiographers, Denver, 1983, Multi-Media Publishing Co.; copyrighted by the C. V. Mosby Co., St. Louis.

NOTE: The National Council on Radiation Protection and Measurements

(NCRP) recommends that the thickness of the lead in shielding accessories be as follows: lead aprons lead gloves Bucky slot cover .5 mm Pb (lead or equivalent) . 25 m m Pb (lead or equivalent) . 25 mm Pb (lead or equivalent)

NOTE: The Bucky tray receives the cassette during radiographic procedures. The slot (see Figure I-C-3) has a protective cover to minimize the radiation

that would otherwise be directed through this opening.

*radiopaque: having the capacity to absorb (rather than transmit) a relatively large amount of the x rays passing through24


Leaded

Overhead radiographic tube ----

Figure I-C-3 Examples of Radiographic Room and Protective DevicesReproduced by permission from: Bushong, Stewart C.: Radiologic Science for Technologists, ed. 3, St. Louis, 1984, The C. V. Mosby Co.

Primary Protective Barriers . When a chest radiographic unit is placed on a wall and a patient stands in front of the unit, the primary beam is directed to the patient's chest, and thus toward the wall. Lead-bonded wall covering is used on these walls to eliminate the passage of radia tion into an adjoining room. This lead-bonded wall is designated as a primary protective barrier because it is designed to protect areas from primary radiation. Secondary Protective Barriers . Barriers designed to shield areas from secondary radiation are called secondary protective barriers. The lead used in secondary barriers is thinner than that used in primary protec tive barriers. However, most common building materials such as con crete sufficiently absorb and reduce secondary radiation to an accept able level. Most control booths are secondary protective barriers. NOTE: Following are some NCRP specifications for protective barriers:


25

primary barrier secondary barrier lead glass in control booth control panel (behind secondary barrier) Summary

1.5 mm Pb (1/16 inch lead) .75 mm Pb (1/32 inch lead) 1.5 mm Pb (1/16 inch lead) 1. 5 m m Pb (1/16 inch lead)

The basic measures that the x-ray machine operator can take to protect against occupational exposure to radiation involve three factors: time, distance, and shielding. Even with the proper exposure time, TFD, shielding accessories, and protective barriers, you and other persons can be exposed to radiation unnecessarily if you are not careful. The following state what you should and should not do when making an exposure: Stand behind the protective barrier. Wear protective lead apron and gloves. Never stand in the primary beam. Never allow a pregnant female to hold the patient, since she may be exposed to radiation and the embryo or fetus may be damaged. When another person restrains the patient during an exposure, have that person wear protective lead apron and gloves and never allow that person to stand in the primary beam. Make sure to remove all unnecessary persons from the area where they can be exposed to radiation.

Never hold the patient or touch accessories during exposure. Keep the time of exposure as short as possible. Keep as great a distance as possible between you and the source of radiation.

Before continuing to Patient Protection, complete the Practice Questions beginning on the following page.

26


Practice Questions (I~ ) -1

Directions Each of the questions or incomplete statements is followed by four suggested answers or completions. Circle the one (a, b, c, or d) which is best is in each case. rrrrrrr.All of the following are basic radiation protection measures for operators EXCEPT: sssssss.Keep exposure time as short as possible. ttttttt.Keep the distance between yourself and the radiographic tube as great as possible. uuuuuuu.Use only a safelight. vvvvvvv.Use shielding accessories routinely. wwwwwww.To minimize your occupational exposure, how should you keep the distance between you and the x-ray table? xxxxxxx.short yyyyyyy.close zzzzzzz.medium aaaaaaaa.long3. What is the inverse square law?

bbbbbbbb.kVp is inversely proportional to the square of rnA. cccccccc.rnA is inversely proportional to the square of kVp. dddddddd.Exposure time is inversely proportional to the square of the TFD. eeeeeeee.Intensity of radiation is inversely proportional to the square of the TFD. ffffffff.If the length of exposure time is increased from 5 to 10 seconds, the amount of exposure will do what? gggggggg.double hhhhhhhh.be the same iiiiiiii.triple jjjjjjjj.decrease kkkkkkkk.If you receive an exposure of 100 R/hr at a distance of 50 inches, how much will you receive if the distance is decreased to 25 inches? llllllll.400 R/hr mmmmmmmm.200 R/hr nnnnnnnn.50 R/hr oooooooo.25 R/hr


27

pppppppp.If the exposure rate is 90 R/hr at a distance of 20 inches from the source of radiation, what will be the exposure rate at a new distance of 60 inches? qqqqqqqq.10 R/hr rrrrrrrr.25 R/hr ssssssss.50 R/hr tttttttt.200 R/hr uuuuuuuu.When the exposure rate exceeds 5 mR/hr, which of the following should you wear? vvvvvvvv.white gown wwwwwwww.rubber gloves xxxxxxxx.lead apron yyyyyyyy.a lot zzzzzzzz.What is the NCRP recommended thickness for the lead in protective gloves?aaaaaaaaa.0.25 mm bbbbbbbbb.0.5 mm ccccccccc.2.5 mm ddddddddd.5.0 mm

eeeeeeeee.Which of the following is required to reduce exposure to the waiting room directly behind the upright chest unit? fffffffff.first barrier ggggggggg.primary barrier hhhhhhhhh.secondary barrier iiiiiiiii.scatter barrier jjjjjjjjj.What is the recommended thickness of the lead in a primary protective barrier? kkkkkkkkk.1/4 inch lllllllll.1/8 inch mmmmmmmmm.1/16 inch nnnnnnnnn.1/32 inch ooooooooo.To minimize your occupational exposure, you should do all of the following EXCEPT: ppppppppp.hold the patient during the exposure qqqqqqqqq.stand behind the lead barrier while activating x-ray equipment rrrrrrrrr.stand outside of the primary beam sssssssss.wear lead apron and lead gloves Now check your answers with the correct ones provided in the Answers to Practice Questions U-C-l) at the back of this Guide.

2 8


d.

Patient Protection (J-C-2) Collimators. A collimator is the best device for restricting the primary beam. The collimator is attached to the tube housing of the x-ray ma chine. It has two sets of lead shutters that can be adjusted to restrict the size of the radiation field to no larger than the film size (see Figure I-C-5). The overexposure of the patient to radiation during a radiographic examination Anode (+) can be reduced by several means: by preparing and positioning the patient focal spot properly, by restricting the primary beam (collimation), by using a filter in front of the radiographic tube opening, by providing gonadal shields, by selecting appropriate exposure factors, and by using radiographic accessories.

Patient Preparation and Positioning Patient preparation requires having the patient remove clothing or other items that might interfere with the examination and instructing the patient in how to breathe correctly. Patient positioning requires ensuring that the parts of the body to be radiographed are clearly visible, centered in the field of the radiograph, and immobilized during the exposure. To prevent the patient from moving voluntarily, you may need to use an immobilization device. Failure to do procedures correctly can mean having to repeat the radiograph. A needless repeat gives the patient an additional 100 percent radiation exposure. NOTE: This topic is discussed in more detail in Unit!y. Beam Restriction In order to minimize secondary radiation, the primary x-ray beam should be limited to the body part being radiographed, and the radiation field size (size of the beam or size of the field exposed) should never be larger than the film. 1be smaller the field size, the smaller the amount of scatter radiation there will be. A Diaphragms, 2Yli~ and Cones. Nonadjustable diaphragms, cylinders, and cones--early devices used to restrict the area of the primary beam-no longer meet the State of Florida's legal requirements for restriction of the primary beam (see Figure I-C-4).

Simple lead diaphragm with aperture

TICone SIde view of cone Cylinder Side view of cylinder

Figure 1-C-4 Nonadjustable Beam Restriction Devices: Diaphragm, Cylinder, and Cone I: Radiation Protection

2 9

X-ray tube window (port)

Radiation field (light source projectio on film) Film carrierB

Figure I-C-S Exterior (A) and Interior (B) of Collimator

A: Courtesy Machlett Labs, Inc., Stamford, Connecticut. B: Reproduced by permission from: Statkiewicz, M. A., and Ritenour, E. R.: Radiation Protection for Student Radiographers, Denver, 1983, Multi-Media Publishing Co.; copyrighted by the C. V. Mosby Co., St. Louis.

One set of shutters is adjusted to reduce the amount of off-focus radia tion coming from the primary beam and exiting from the radiographic tube housing. The other set of shutters is adjusted to confine the radio graphic beam to the body part radiographed. For protection against exposure, the surface of the patient's skin should be at least 15 centi meters below the collimator. Most x-ray machines manufactured be fore August 1974 had manually adjusted collimators. By manually adjusting the collimator, an xray machine operator can use a radiation field smaller than the size of the cassette, thus reducing unnecessary radiation to the patient.

3 0


Since 1974, the federal government has required that every radiographic machine have a positive beam limitation (PBL) device. The PBL device automatically adjusts the collimator so that the radiation field size is no larger than the film. Figure I-C-6 shows a properly collimated radiographic beam, which minimizes scattered radiation, and an improperly collimated radiographic beam, which results in extra scattered radiation.

Figure I-C-S Proper (A) and Improper (B) CollimationReproduced by permission from: Statkiewicz, M. A., and Ritenour, E. R.: Radiation Protection for Student Radiographers, Denver, 1983, Multi-Media Publishing Co.; copyrighted by The C. V. Mosby Co., St. Louis.

Collimators are equipped with a light and mirror assembly, known as the light localizer, which projects a light field through the collimator opening onto the patient's body and shows the size and location of the x-ray beam. Because the light localizer enables the machine operator to see the actual location of the xray beam prior to making the exposure, the operator can project the light source onto the film and accurately place the radiation field (see Figure I-C5).Filtration Filtration reduces radiation exposure to the patient's skin by absorbing lower energy photons (or soft radiation). A metal (usually aluminum) filter placed in front of the radiographic tube opening (see Figure I-C-5) accomplishes this purpose. An x-ray beam includes many low-energy xray photons that contribute nothing to the formation of the radiographic image because they have insufficient energy to penetrate the patient and reach the film. These photons increase the patient's radiation exposure, nevertheless, because the skin absorbs the radiation. Removing these low-energy x rays decreases the dose that the patient


31

receives. Tbe NCRP recommends 2.5 millimeters of aluminum equivalent filtration. In most new radiographic equipment, the necessary amount of filtration is installed and requires no operator adjustment. Older models may have a "filter wheel, tI requiring the operator to manually adjust the filtration prior to making an exposure.NOTE: In addition, x-ray machines must allow no appreciable radiation

leakage outside the primary beam. A radiation physicist decides the filtration's effectiveness and leakage radiation during machine inspection. If the amount of filtration is reduced, the patient's exposure rate will be increased.

Shielding for Patients Gonadal Shields. A gonadal shield is a radiopaque material placed between the x-ray source and the gonads (female ovaries or male testes) to reduce the radiation dose. Its main purpose is to protect the gonads from exposure to the primary x-ray beam when the gonads are within range of the properly collimated beam. Gonadal shielding should be used in addition to and not instead of proper beam limitation for all patients-adults and children-with reproductive potential. Techniques for testicular shielding are better established than for ovarian shielding. The anatomical location of the testes is such that covering them with a shield usually does not obscure needed clinical information. On the other hand, the location of the ovaries often interferes with the visualization of other structures. Two basic kinds of gonadal shields are available today: the shadow shield and the contact shield. The shadow shield, a device made of radiopaque material, is suspended from the radiographic tube. The operator may move the shield in and out of the light field, so that it casts a shadow on the patient. The shield should be positioned over the gonadal region (see Figure I-C-7).

Figure 1-C-7 Shadow ShieldCourtesy Nuclear ASSOCiates, Carle Place, New York.

3 2


The contact shield, also made of radiopaque material (usually containing lead), is placed directly on the patient. The most common kind is the flat contact sbield. These shields are pieces of lead-impregnated rubber in various shapes. A contact shield is placed on the patient above the gonads. Since flat contact shields are difficult to secure in place, they are best suited to recumbent projections and to anteroposterior (AP) or posteroanterior (P A) views (these terms are defined in Unit IV). Another type of contact shield is the shaped contact shield. These radiopaque shields surround the testes. Shaped contact shields are contained within various carriers such as disposable or washable athletic supporters and jockey-style briefs. The carrier, which has a pouch into which the shield is inserted, is designed to hold the shield comfortably in position over the scrotum and penis, whether the patient is recumbent or upright. Since the patient can put on this garment by himself, effective shielding can be provided with a minimum of embarrassment to the patient (see Figure I-C-8).

Figure I-C-l Shaped Contact ShieldsCourtesy Nuclear ASSOCiates. Carle Place, New York.

Shields for Other Radiosensitive O r g a .nOther organs in the body besides s the gonads are particularly radiosensitive. Two of these are the eyes and the thyroid. The eyes can be protected by glasses that have been impregnated with lead or by eye cups that fit over the eyes during some procedures. The thyroid can be protected by a device called the thyroid collar. The collar, made of a lead-impregnated material, fits around the neck. Regular use of these shields should be implemented for an effective shielding program. Any patient who undergoes radiographic examinations on a regular basis should have some sort of shielding to protect his or her body from unnecessary exposure to radiation. ExpOSlU'e Factors

Other techniques for exposure reduction are related to technical factors, which fall into two groups: exposure factors and radiographic accessories.


3 3

e.

Faetors. The factors that control the quantity and Signal -tight quality {ienetra ting power) of the radiation produced are called primary exposure factors. These factors affect how much radiation will reach the film and how energetic the radiation will be to penetrate the patient and reach the film. The three primary factors are kilovoltage peak (kVp), milliamperage (m t Major Minor mA Exposure timer A), and exposurekVp selector time (s), Exposure kVp selector selector selectorThree Prim~ ~ure

o o o o

B

The kUoyoltage peak (kVp) is the energy of the electron beam inside the radiographic tube at its peak value. The Line voltage kVp selected amount of affects radiation exposure by determining the energy of the x-ray compensation photons, which in turn determines the penetrating power of the x-ray control knob beam. That is, the amount of kVp selected determines the amount of force that will be used to accelerate the electrons from the filament to the target. With a higher kVp, the force with which the electrons strike the target will be greater. The greater the force, the more penetrating the energy of the x rays will be. In other words, the higher the kVp, the higher the quality of the beam.

switch

0G] ~Phototimer

The amount of mi11iamperage (rnA)selected controls the rate at which electrons are emitted from the heated filament. The higher the rnA, the hotter the filament and the more electrons emitted. Therefore, the amount of rnA selected controls the quantity of radiation produced.

The length of exposure time (s) selected also affects the quantity of radiation. The longer the exposure time, the higher the quantity of radiation produced. The combination of these two exposure factors, exposure time and rnA, is known as milliamperes per second (mAs). With all other factors remaining constant, an increase in the TFD will result in a decrease in the quantity of x rays striking the film, while a decrease in the TFD will result in an increase in quantity. As discussed in the previous section, this is the principle of the inverse square law.Selection of Exposure Factors. Since each patient is different in size and condition and since different body parts are of different sizes, the operator must be able to adjust exposure factors on the machine to produce the appropriate radiographic beam for every situation. In accomplishing this purpose, you should use the three basic controls (kVp, rnA, and exposure time) on the x-ray machine control panel (see Figure I-C-9).NOTE: Since distance is standardized for each radiographic examination,

Summar y

you usually do not adjust distance to alter radiographic exposure.

To set the kVp, use the kVp selector knob or buttons on the control panel, To select the appropriate kVp, take into consideration how much penetration the body part being radiographed requires. For example, the femur is much heavier than the bones of the hand; therefore, the kVp required to radiograph the femur is higher than that required for the hand. To select the appropriate rnA, adjust the rnA control knob or buttons for the particular radiographic examination, as shown on the technique chart you are using. (The use of technique charts is discussed in Unit m .) By doubling the rnA, you double the amount of x rays produced.

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0kVp meter mA meter Main _power switch

Figure I-C-S The X-ray Control Panel Since a high kVp produces a more penetrating x-ray beam and a high mAs produces more radiation, a combination of higher kVp and lower mAs reduces the patient's radiation dose. For the proper selection of these exposure factors, use the standardized technique charts. To determine bow long x-ray production will take place, set the timer on the control panel. Through the selection of time and rnA (rnAs), you can control the quantity of x rays, and you can select the fastest time possible without changing the quantity. For example: If you use 100 rnA for 1 second, you are using 100 mAs, because 100 rnA x 1 second = 100 mAs. If you use 200 rnA for 1/2 second, you are still using 100 mAs, because 200 rnA x 1/2 second = 100 mAs.

To protect patients from overexposure to radiation, you should do the following: Instruct patients to remove clothing and jewelry before the exposures and to breathe properly and remain immobile during the exposures.


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Use aeoUimator to restrict the beam to the area to be radiographed. (Remember, the smaller the field size, the less scatter radiationprodueed.)

Adjust filter. Use gonadal shields over male and female reproductive organs prior to taking radiographs, when indicated. Place protective shields (protective lenses, eye cups, or thyroid collars) over radiosensitive organs when repeated examinations or high dosage levels are required. Select the appropriate kVp and rn As, using technique charts. Generally, a combination of higher kVp and lower mAs reduces the patient's radiation dose.

Before continuing to study about radiographic accessories, complete the Practice Questions beginning on the following page.

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Praetiee Questions Which of the following is a device that projects a light vvvvvvvvvv. (I-C-2) field through the collimator to enable the machine operator to see the actual location of the x-ray beam before the exposure? Direetionswwwwwwwwww. an aluminum filter xxxxxxxxxx. a radiographic tube window yyyyyyyyyy. a set of shutters zzzzzzzzzz. a light localizer Each of the questions or incomplete statements is followed by four suggested answers or completions. Circle the one (a, b, c, or d) which is best in each case.What is the main purpose of filtering an x-ray beam? 7. aaaaaaaaaaa. to reduce radiation exposure from radiation EXCEPT: ttttttttt.All of the following provide protectionto patient's skin uuuuuuuuu.filtration reduce radiation exposure to bbbbbbbbbbb. to patient's gonads vvvvvvvvv.collimation (beam restriction) ccccccccccc. to increase the wwwwwwwww.ionization quality of radiation ddddddddddd. to increase the quantity of radiation 8. Onxxxxxxxxx.shielding should gonadal shields be used? which of the following eeeeeeeeeee. pregnant patients only yyyyyyyyy.The patient and the x-ray machine operator receive fffffffffff. all female exposure unnecessary radiationpatients from which of the following? ggggggggggg. all male patients hhhhhhhhhhh. all radiographic examination zzzzzzzzz.a limitedpatients with reproductive potential aaaaaaaaaa.a repeat radiographic examination due to technical error 9. Which of the following would you use for male patients? or carelessness bbbbbbbbbb.beam limitation and filtration techniques used when iiiiiiiiiii. shadow shield making an exposure jjjjjjjjjjj. flat contact shield cccccccccc.a high-quality radiograph produced on the first exposure kkkkkkkkkkk. shaped contact shield lllllllllll. lead shield dddddddddd.The x-ray beam should be collimated so that which of the following is true? 10. Which of the following does not require special shielding? eeeeeeeeee.The radiation field size is larger than the film holder. mmmmmmmmmmm. the eyes ffffffffff.The beam is restricted to the body part being radiographed. nnnnnnnnnnn. the thyroid gggggggggg.The beam is no larger than the film. ooooooooooo. the gonads ppppppppppp. the femur hhhhhhhhhh.1 and 2 only iiiiiiiiii.1 and 3 only 11. Alljjjjjjjjjj.2 and 3 only primary exposure factors EXCEPT: of the following are kkkkkkkkkk.1, 2, and 3 qqqqqqqqqqq. kVp rrrrrrrrrrr. rnA llllllllll.What does an automatic collimator allow the x-ray machine sssssssssss. shielding operator to do? ttttttttttt. exposure time mmmmmmmmmm.use a film holder larger than the radiation field uuuuuuuuuuu. When you increase the kVp and then decrease the mAs nnnnnnnnnn.adjust the amount of radiation produced for a accordingly, what happens to skin exposure? specific radiographic examination oooooooooo.remove the low-energy photons of x rays vvvvvvvvvvv. It the film accurately and consistently pppppppppp.placeis increased. wwwwwwwwwww. It is decreased. xxxxxxxxxxx. It is unchanged. qqqqqqqqqq.An improperly collimated radiographic beam will do yyyyyyyyyyy. It is multiplied. which of the following?

rrrrrrrrrr.minimize scattered radiation ssssssssss.result in extra scattered radiation tttttttttt.limit the beam to the area of radiation uuuuuuuuuu.reduce the amount of absorbed radiation

38Radiation Protection I:


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XRay Operator Book 31Jan06 Bo

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Transcript of XRay Operator Book 31Jan06 Bo