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RADS.105 - Radiation Protection

Northwestern College

Course Syllabus

DEPARTMENT:  SHS - Radiography Program        

COURSE CODE:  RADS.105

CREDIT HOURS:  3

Course Meeting Date/Times:  M/W   1:50 p.m. - 3:40 p.m.

TITLE:  Radiation Protection                                        

INSTRUCTOR:     Gary Gruenewald M.S., R.T(R)                                                                                   

PHONE:      708-237-5000  ext. 2825

EMAIL:       ggruenewald@nc.edu

COURSE DESCRIPTION:  Students are introduced to the principles of, and the reasons for, radiation protection. The responsibilities of the radiographer and protective measures for patients, personnel and the public are studied. Also covered is discussion of the sources of radiation, the units of radiation measurement, and federal and state radiation health and safety regulations.

Prerequisite:  Admission into Radiography Program

REQUIRED TEXTBOOKS:           

Statkiewicz Sherer, Mary Alice, Radiation Protection in Medical Radiography, 7th edition, Mosby Elsivier, 2014

Statkiewicz, Mary Alice, Radiation Protection in Medical Radiography Workbook, 7th edition, Mosby Elsivier, 2014

COURSE OBJECTIVES:

 At the completion of this course, the student will be able to:

               1.              recognize the need for radiation protection of

                                both the patient and radiology personnel.

               2.              discuss and implement various protective means

                                and measures used commonly in the radiology

                                department.

               3.              understand and discuss various state and federal

                                radiation protection specifications.

Units of Instruction

  1. Introduction to Radiation Protection
  2. Interaction of X-Radiation with Matter
  3. Radiation Quantities and Units
  4. Dose Limits for Exposure to Ionizing Radiation
  5. Equipment Design for Radiation Protection
  6. Management of Patient Radiation Dose During Diagnostic X-Ray Procedures
  7. Management of Imaging Personnel Radiation Dose
  8. Radiation Monitoring

Unit Objectives

Found at the beginning of each chapter of the text.

  1. Introduction to Radiation Protection                                                                          
  2. Interaction of X-Radiation with Matter                                                                        
  3. Radiation Quantities and Units                                                                                    
  4. Dose Limits for Exposure to Ionizing Radiation                                                             
  5. Equipment Design for Radiation Protection                                                                  
  6. Management of Patient Radiation Dose During Diagnostic X-Ray Procedures                  
  7. Management of Imaging Personnel Radiation Dose                                                        
  8. Radiation Monitoring                                                                                             

Chapter 1  -  Introduction to Radiation Protection

CRITICAL THINKING QUESTIONS

Why is radiation protection necessary for both patients and imaging personnel during diagnostic
x-ray procedures?

Healthy normal biologic tissue can be injured by ionizing radiation; therefore, it is necessary to protect humans against significant and continuous exposure.

Why is patient education important in medical imaging?

Through appropriate and effective communication, patients can be made to feel they are active participants in their own health care.

 Link to Flight Attendent Radiation:

http://www.youtube.com/watch?v=XpuYJ8Wnv0s

Link to Radiation Exposure on an Intercontinental Flight

http://www.youtube.com/watch?v=XuQgVGDENbU

 

POWERPOINT NOTES:

•X-Rays are a form of ionizing radiation.
 
•Ionizing radiation produces negatively and positively charged ions when passing through matter.
 

•These ions may cause injury in normal biologic tissue

Radiation protection is defined simply as effective measures employed by radiation workers to safeguard patients, personnel,

and the general public from unnecessary exposure to ionizing radiation.

Radiation exposure should always be kept at the lowest possible level for the general public.

When an illness or injury occurs, however, or when a specific imaging procedure for health screening purposes is necessary,

a patient may elect to assume the risk of the exposure to

A prime example of an examination in which the benefits of the exam outweigh the risks is mammography.

ionizing radiation to obtain essential diagnostic medical information.

The benefits of the exam must outweigh the risks.

ALARA  -  As Low As Reasonably Achievable

•An acronym synonymous with the term optimization for radiation protection (ORP).

•ALARA/ORP should be a main part of every health care facility’s personnel and patient radiation control program.
 
•Radiation protection guidelines are based on a linear non-threshold concept which identifies that there is no
  safe amount of radiation to which one can be exposed.

Radiation induced cancer does not have a threshold (a dose level below which individuals would have no chance of sustaining this disease)

-A stochastic (probalistic) effect
-A stochastic event is an all or nothing response meaning that ionizing radiation could cause a disease process such as cancer.

Patients need to be aware of the specifics of the procedure that has been ordered on them.

They must also be informed of any follow-up protocols.

Through appropriate and effective communication, patients can be made to feel that they are active participants in their own health care (autonomy).

Typically, patients are more willing to accept a risk if they perceive that the potential benefit to be obtained is greater than the risk involved.

A means by which radiographers can alleviate a patient’s fear regarding radiation exposure during their exam is through the use of

the concept of Background Equivalent Radiation Time (BERT).

This method compares the amount of radiation received from an exam to that of natural background radiation per a given time frame.

BERT is based on an annual background exposure of

3 milliseiverts (300mrem) per year.

The radiation one typically encounters is one of four types: alpha radiation, beta radiation, gamma radiation,

and x radiation. Neutron radiation is also encountered in nuclear power plants and high-altitude flights and emitted

from some industrial radioactive sources.

 

Radiation

Type of Radiation

Mass (AMU)

Charge

Shielding material

Alpha

Particle

4

+2

Paper, skin, clothes

Beta

Particle

1/1836

 -1

Plastic, glass, light metals

Gamma

Electromagnetic Wave

0

0

Dense metal, concrete, Earth

Neutrons

Particle

1

0

Water, concrete, polyethylene, oil

 

Interaction of X-Radiation with Matter - PowerPoint Notes (Chapter 2)

•The processes of interaction between radiation and matter are emphasized because a basic understanding of the subject is necessary to select technical exposure factors such as

            - Peak kilovoltage (kVp)      

            - Milliampere-seconds (mAs)

 •Peak kilovoltage (kVp) controls

           -  Quality, or penetrating power, of the photons in the x-ray beam and to some degree also affects the

              quantity or number of photons in the beam   

•Milliampere-seconds (mAs) controls

            -  Quantity of radiation that is directed toward a patient during a selected x-ray exposure

                       (mA x s = mAs)

 •Radiographer

            -  Selects technical exposure factors that control beam quality and quantity

            -  Is actually responsible for the dose the patient receives during an imaging procedure

•With a suitable understanding of technical exposure factors, radiographers can select appropriate techniques that can

  minimize the dose to the patient  and produce optimal-quality images.

 •X-rays are carriers of manmade, electromagnetic energy

•When x-rays enter a material such as human tissue, they may

            -  Interact with the atoms of the biologic material in the patient

            -  Pass through without interaction

 •When x-rays interact with human tissue

            -  Electromagnetic energy is transferred from the x-rays to the atoms of the patient’s biologic

               material (absorption), and the amount of energy absorbed per unit mass is the absorbed dose (D).

•Keep the amount of electromagnetic energy transferred to the patient’s body as small as possible to minimize the
  possibility of biologic damage.

 •Without absorption and the differences in the absorption properties of various body structures, it would not

  be possible to produce diagnostically useful images in which different anatomic structures could be perceived and distinguished.

Benefit for the Radiographer When Patient Dose Is Minimal

•Less radiation is scattered from the patient
 
•Reduces the occupational hazard for the radiographer

 •Production of primary radiation

          -  A diagnostic x-ray beam is produced when a stream of high-speed electrons bombards a positively charged target in a highly evacuated glass tube.

•Target (anode) composition used in general radiography

          -  Tungsten (a metal)

          -  Tungsten rhenium (a metal alloy)

         -  Reasons tungsten and tungsten rhenium are used as target materials

                        -  High melting points

                        -  High atomic numbers

Filtration of the Diagnostic X-Ray Beam

 •Inherent filtration (built-in)

•Added filtration (a certain thickness of added aluminum to “harden” the beam)
 
•Total filtration (permanent) (removes low-energy x-ray photons thereby decreasing patient dose)
 
•All photons in a diagnostic x-ray beam do not have the same energy.
 
•The most energetic photons in the beam can have no more energy than the electrons that bombard the target.
 
•In diagnostic radiology, the energy of the electrons is expressed in kilovolts (kV). Because the voltage across the tube fluctuates,
  it is usually expressed in kilovolt peak (kVp).
 
•If an electron is drawn across an electrical potential of 1 volt, it has acquired energy of 1 electron volt (eV).
 
•100 kVp means that the electrons bombarding the target have a maximum energy of 100,000 eV, or 100 keV.
 
•The x-rays produced do not have all of the same energy x-rays of various energies are produced, but the most energetic x-ray photons can have no more energy than 100 keV.
 
•For a typical diagnostic x-ray unit, the energy of the average photon in the x-ray beam is about one third the energy of the most energetic photon. Therefore, a 100-kVp beam contains photons having energies of 100 keV or less, with an average energy of about 33 keV.

   •Direct and indirect transmission x-ray photons

      -   When an x-ray beam passes through a patient, it goes through a process called attenuation.

      -   Some primary photons will traverse the patient without interacting (direct transmission).

            These noninteracting x-ray photons reach the radiographic image receptor (e.g.,

            phosphor plate, digital radiography receptor, or radiographic film).

      -   Other primary photons can undergo Compton and/or coherent interactions and, as a result,

            may be scattered or deflected. Such photons may still traverse the patient and strike

            the image receptor (indirect transmission).

The Optimum X-Ray Image:

•Is formed when only direct transmission x-ray photons reach the image receptor.
 
•In clinical situation

              -   Scattered photons do reach the image receptor and degrade image quality.

                    Several  methods—air gaps and radiographic grids are the most common—have

                    been devised to limit effects of indirectly transmitted x-ray photons.

           •In conventional or digital radiography, the image receptor covers a broad enough area

            that x-ray photons scattered from one part of the beam might still strike the image receptor in another area.

•Result

            - The radiographic image is formed from both directly transmitted x-ray photons and indirectly

               transmitted (i.e., scattered) x-ray photons.

Effect of Scatter on Radiographic Density

•Production of radiographic fog, an undesirable, additional density

•Problem caused by radiographic fog

            -  Interferes with the radiologist’s ability to distinguish different structures in the image

•Reduction of the amount of fog produced by small-angle scatter

            -  Reducing the amount of tissue irradiated reduces the amount of fog produced by small-angle scatter.

                 Therefore, adequately collimating the x-ray beam is one way to reduce fog.

 •Interaction of photons with biologic matter is random

           -  It is impossible to predict with certainty what will happen to a single photon when it enters human tissue.

           -  It is possible to predict what will happen on the average, when a large number of

                photons enter the human body, and this is more than adequate to determine the characteristics

                of the image that results from such numerous interactions.

 •Five types of interaction between x-radiation and matter are possible.

    •Only two are important in diagnostic radiology  -  Compton and Photoelectric

Coherent Scattering:

•A relatively simple process that results no loss of energy as x-rays scatter.
 
•It occurs with low-energy photons, typically less than 10 keV.
 
•Because the wavelengths of both incident and scattered waves are the same, no net energy has been absorbed by the atom. (See Appendix E in the textbook.)
 
•Rayleigh and Thompson scattering play essentially no role in radiography.

Coherent scattering. The incoming low-energy x-ray photon interacts with an atom and transfers its energy by

causing some or all of the electrons of the atom to vibrate momentarily. The electrons then radiate energy in

the form of electromagnetic waves. These waves nondestructively combine with one another to form a scattered

wave, which represents the scattered photon. Its wavelength and energy, or penetrating power, are the same as those of the incident photon.

Compton Scattering:

Compton scattering is responsible for most of the scattered radiation produced during a radiologic procedure.

 Compton scattering results in all-directional scatter. The scatter created may be directed onward as small-angle

scatter, backward as backscatter, and to the side as sidescatter. The intensity of radiation scatter in various

directions is a major factor in planning protection for medical imaging personnel during a radiologic examination.

Photoelectric Interaction:

Photoelectric absorption. A, On encountering an inner-shell electron in the K or L shells, the incoming

x-ray photon surrenders all its energy to the electron, and the photon ceases to exist. B, The atom

responds by ejecting the electron, called a photoelectron, from its inner shell, creating a vacancy

in that shell. C, To fill the opening, an electron from an outer shell drops down to the vacated inner

shell by releasing energy in the form of a characteristic photon. Then, to fill the new vacancy in the

outer shell, another electron from the shell next farthest out drops down and another characteristic

photon is emitted, and so on until the atom regains electrical equilibrium. There is also some probability

that instead of a characteristic photon, an Auger electron will be ejected.

Additional Process That Can Occur As a Result of Photoelectric Interactions:

 •Auger effect (pronounced “awzhay”)

             - Pierre Victor Auger discovered effect in 1925

             -   Produces an Auger electron

             -   Radiationless effect

Probability of Occurence of Photoelectric Effect:

 •Depends on

            1.  Energy of the incident x-ray photon

            2.  Atomic number (Z) of the atoms comprising the irradiated object

•Increases markedly as

            1.  Energy of the incident photon decreases

            2.  Atomic number of irradiated atom increases

Difference in Absorption Properties Between Different Body Structures:

 •Make diagnostically useful images possible.

•The less a given structure attenuates radiation, the greater its radiographic density will be.
 
•The more a given structure attenuates radiation, the less its radiographic density will be.
 
Impact of Photoelectric Absorption on Radiographic Contrast Within the Energy Range of Diagnostic Radiology:
 
•The greater the difference in the amount of photoelectric absorption, the greater the contrast in the
  radiographic image between adjacent structures of differing atomic numbers
 
•As absorption increases, so does the potential for biologic damage
 
•To ensure both radiographic image quality and patient safety

            -  Choose the highest-energy x-ray beam that permits adequate radiographic contrast

Use of Contrast Media to Ensure Visualization of Anatomic Structures:

 •If tissues or structures are similar in atomic number and mass density, use of appropriate contrast media may be

   needed to ensure visualization of those tissues or structures

•Positive contrast medium
 
•Negative contrast medium
 
Pair Production:
 
Pair production. The incoming photon (equivalent in energy to at least 1.022 MeV)
strongly interacts with the nucleus of the atom of the irradiated object and disappears.
In the process, the energy of the photon is transformed into two new particles: a negatron (electron)
and a positron. The negatron eventually recombines with any atom that needs another electron.
The positron interacts destructively with a nearby electron. During the interaction, the positron
and the electron annihilate each other, with their rest masses being converted into energy,
which appears in the form of two 0.511-MeV photons, each moving in the opposite direction.

Use of Annihilation Radiation in Positron Emission Tomography:

•Source of positrons

•Process of positron decay
 
•Formation of annihilation photons
 
•Examples of unstable nuclei used in PET scanning
 
Photodisintegration:
Photodisintegration. An incoming high-energy photon collides with the nucleus of
the atom of the irradiated object and absorbs all of the photon’s energy.
This energy excess in the nucleus creates an instability that is usually alleviated
by the emission of a neutron. Also, if sufficient energy is absorbed by the nucleus,
other types of emissions are possible, such as a proton or proton-neutron combination (deuteron),
or even an alpha particle

Chapter 3  -  Radiation Quantities and Units

Somatic Damage = biologic damage to the body of the radiation exposed individual

1st American Radiation Fatality = Clarence Madison Dally

1900 - 1930        Skin Erythema Dose

1930 - 1950        Tolerance Dose

1950 - 1977        Maximum Permissible Dose (MPD)

1977 - 1991        Effective Dose Equivalent

1991 - Present   Effective Dose (EfD)

Today's radiation standards and guidelines are based on a linear, non-threshold dose response.

RAD = radiation absorbed dose     unit of absorbed dose       SI = Gray

REM = radiation equivalent man   unit of dose equivalence   SI = Sievert

Roentgen  unit of radiation exposure in air    SI  =  C/kg

Curie  unit of radioactivity  SI = Becquerel

#RADS x Quality Factor = #Rems

Quality Factor for x-rays, gamma rays and beta particles = 1

Quality Factor for alpha particles = 20

Number of rad / 100     =  # of Gray

Number of Gray  x  100  =  # of rads

EqD = Dose   x   radiation weighing factor

radiation weighing factor:   1 - x-rays, gamma rays and electrons   20 for alpha particles

EfD = Dose   x   radiation weighing factor   x   tissue weighing factor

Chapter 9  -  Dose Limits for Exposure to Ionizing Radiation

Organizations which are responsible for evaluating the relationship between radiation EqD and induced biologic effects and

making reccomendations:

ICRP  -  International Comission of Radiological Protection

NCRP  -  National Council on Radiation Protection and Measurements

UNSCEAR  -  United Nations Scientific Committee on the Effects of Atomic Radiation

NAS/NRC-BEIR  -  National Academy of Sciences/National Research Council Committee on the Biological

                         Effects of Ionizing Radiation

U.S. Regulatory Agencies include:

NRC  -  Nuclear Regulatory Commission

Agreement States

EPA  -  Environmental Protection Agency

FDA  -  U.S. Food and Drug Administration

OSHA  -  Occupational Safety and Health Administration

The above agencies are responsible for enforcing radiation protection standards.

PowerPoint Chapter 10 - Equipment Design for Radiation Protection

State-of-the-Art Diagnostic and Fluoroscopic Equipment

 •Has been designed with many devices that radiologists and imaging personnel can use

      -  To optimize the quality of the image.

      -  To reduce radiation exposure for patients undergoing various imaging procedures.

•Many safety features are built into x-ray-producing machines by their manufacturer to ensure radiation safety.

•Some safety features are included to meet federal regulations.

RADIATION SAFETY FEATURES OF RADIOGRAPHIC EQUIPMENT, DEVICES, AND ACCESSORIES

 •Take measures to ensure that radiographic equipment operates safely to ensure radiation protection for

      -  Patients

      -  All personnel

•Every diagnostic imaging system must have a

     -  Protective tube housing

     -  Correctly functioning control panel

•A radiographic examination table and other devices and accessories must be designed to reduce patient radiation dose.

•Accessories are available to lower radiation dose for the patient.

Diagnostic-Type Protective Tube Housing

 Requirements

•A lead-lined metal diagnostic-type protective tube housing is required to protect the patient and
imaging personnel from off-focus, or leakage, radiation by restricting the emission of x-rays to the
area of the useful, or primary, beam.

X-Ray Tube Housing Construction

The housing enclosing the x-ray tube must be constructed so that the leakage radiation measured at a

distance of 1 m (3.3 feet) from the x-ray source does not exceed 100 mR/hr (2.58 x 10-5 C/kg per hour)

when the tube is operated at its highest voltage at the highest current that allows continuous operation

Control Panel

•Must be located behind a suitable protective barrier that has a radiation-absorbent window that permits observation of the
  patient during any procedure
 
•Must “indicate the conditions of exposure and must positively indicate when the x-ray tube is energized”
 
•Has visible mA and kVp meters that permit the operator to assess exposure conditions
 
•Permits an audible sound to be heard when the exposure begins and the sound stops when the exposure terminates
 
•Audible sound clearly indicates to the operator that the x-ray tube is energized and ionizing radiation is being emitted

Radiographic Examination Table

 •Must be strong

•Must adequately support the patient
 
•Frequently has a floating tabletop that makes it easier to maneuver the patient during an imaging procedure
 
•Must be of uniform thickness
 
•Must be as radiolucent as possible so that it will absorb only a minimal amount of radiation, thereby reducing the patient’s radiation dose
 
•Is frequently made of carbon fiber material
 
Source to Image Receptor Distance Indicator
 
 •Provides a way to measure the distance from the anode focal spot to the image receptor to ensure that the correct source-to-image receptor distance (SID) is maintained.
 
•Frequently a simple device such as a tape measure is attached to the collimator or tube housing so that the radiographer can manually measure the SID.
 
•Lasers are also sometimes used to measure SID.
 
•“The indicator must be accurate to within 2% of the indicated SID.”
 
X-Ray Beam Limitation Devices
 
•The primary x-ray beam must be adequately collimated so that it is no larger than the size of the image receptor being used for the examination.
 
•Accomplished by providing the x-ray unit with a light-localizing variable-aperture rectangular collimator to adjust the size and shape of the beam either automatically or manually.
 
•Light-localizing variable-aperture rectangular collimator is currently the most popular x-ray beam limitation device.
 
•Types of x-ray beam limitation devices

     -  Light-localizing variable-aperture rectangular collimator

       -  Aperture diaphragms

       -  Cones

       -  Cylinders

•All of these devices confine the useful, or primary, beam before it enters the area of clinical interest,

thereby limiting the quantity of body tissue irradiated.  This also reduces the amount of scattered radiation

in the tissue, preventing unnecessary exposure to tissues not under examination.

•Benefit of restricting x-ray field size to include only the anatomic structures of clinical interest

     -  Significant reduction in patient dose because less scatter is produced

     -  Improves the overall quality of the radiographic image

Light-Localizing Variable-Aperture Rectangular Collimators

•Construction

-  Reduction of off-focus, or stem, radiation

-  Confinement of the  radiographic beam

•Skin sparing

-  Minimizing skin exposure to electrons produced by photon interaction with the collimator

•Luminance
•Coincidence between the radiographic beam and the localizing light beam
•Positive beam limitation (PBL)
•Alignment of the x-ray beam

 Light-Localizing Variable-Aperture Rectangular Collimators

•Positive Beam Limitation (PBL)

     -  The radiographer must ensure that collimation is adequate by collimating the radiographic beam so that it is no larger than

          the image receptor.

 Aperture Diaphragm

•Simplest of all beam limitation devices
 
 Cones
•Sometimes used for radiographic examinations of specific areas such as the head
 
•Flared metal tubes and straight cylinders
 
•Beam-defining cones used in dental radiography
 
Filtration
 
•Purpose of radiographic beam filtration
 
•Effect of filtration on the absorbed dose to the patient
 
•Types of filtration

       -  Inherent

       -  Added

•Total filtration = Inherent  + Added

Filtration for Mammographic Equipment

•Metallic elements such as molybdenum and rhodium are commonly employed as filters.
 
•These filtration materials facilitate adequate contrast in the radiographic
image over the clinical extent of compressed breast thickness by preferentially selecting
a particular range or window of energies from the x-ray spectrum emerging from the x-ray tube target.
 

Filtration for General Diagnostic Radiology

•Aluminum is the metal most widely selected as a filter material because it effectively removes low-energy
(soft) x-rays from a polyenergetic (heterogeneous) x-ray beam without severely decreasing the x-ray beam intensity.
 
•A diagnostic x-ray beam must always be adequately filtered.
 
•Half-value layer (HVL) of the beam must be measured to verify this. A radiologic physicist should obtain this
measurement at least once a year and also after an x-ray tube is replaced or repairs have been made on the
diagnostic x-ray tube housing or collimation system.
 
•HVL is expressed in millimeters of aluminum.
 
•HVL is a measure of beam quality, or effective energy of the x-ray beam; a certain minimal HVL is required at a given kVp.
 

Compensating Filters

•Made of aluminum, lead-acrylic, or other suitable materials

 
•Used to accomplish dose reduction and uniform imaging of body parts that vary considerably in thickness or
tissue composition
 
•Partially attenuates x-rays that are directed toward the thinner, or less dense, area while permitting
more x-radiation to strike the thicker, or more dense, area
 
•Types of compensating filters

      -  Wedge filter

      -  Trough, or bilateral wedge filter

 Exposure Reproducibility
•Consistency in output in radiation intensity for identical generator settings from one
individual exposure to subsequent exposures.
 
•Variance of 5% or less is acceptable.
 
•Reproducibility may be verified by using the same technical exposure factors to make a
series of repeated radiation exposures and then observing how radiation intensity typically varies.
 
 Exposure Linearity
•Consistency in output radiation intensity at selected kVp settings when settings are changed
from one mA and time combination to another.
 
•Linearity is the ratio of the difference in mR/mAs values between two successive generator settings
to the sum of those mR/mAs values. It must be less than 0.1.
 
•When settings are changed from one mA to a neighboring mA station, the most that linearity can vary is 10%.
 
Screen Film Combinations
 
•Value of intensifying screens in patient dose reduction

 -  Rare-earth screens

•Effect of faster screen-film systems on patient dose

 -  Availability of relative speeds from 200 to 1200

 -  400-speed system standard for use in general radiography

 -  Reduction in radiation dose for patients

•Effect of kilovoltage on screen speed and patient dose

•Selection of film-based image receptor systems

 -  Comparing use of slower rare-earth film-screen image receptor systems with faster rare-earth film screen image receptor systems

 -  Quantum mottle effect

•Benefits of rare-earth intensifying screens

•Use of carbon as a front material in a radiographic cassette

•Use of asymmetric film emulsion and intensifying screen combinations

Radiographic Grids

 Construction, Purpose, Technical Value and Impact of a Radiographic Grid on Patient Dose

•Placement of a grid in relation to the patient and the image receptor
•Determining when to use a grid in accordance with body part thickness

Function of a Radiographic Grid

Grid Ratio and Patient Dose

Minimal Source to Skin Distance for Mobile Radiography

 Requirement

•Minimum source-skin distance
•Distance generally used for mobile radiography

Effect of Source-Skin Distance on Patient Entrance Exposure

Use of Mobile Units

RADIATION SAFETY FEATURES OF DIGITAL IMAGING EQUIPMENT, DEVICES, AND ACCESSORIES

 Digital Imaging

•Use of the computer in almost all imaging modalities

•Conventional radiography: Analog image

-  Process of producing the conventional radiographic image

-  Disadvantages to the use of this technology

•Digital radiography (DR)

-  Process of producing a digital radiographic image

-  Components of the digital image

-  Resolution (detail) of the digital radiographic image

-  Composition and function of digital radiography image receptors

-  Function of charge-coupled devices (CCDs)

-  Access of DR images

 Retake Rates in Digital Radiography

•DR eliminates the need for almost all retakes required because of improper technical selection
because image contrast and overall brightness may be manipulated after image acquisition.
 
•Retake rates for mispositioning will not be affected.
 
•Mispositioning retakes should be monitored by an independent quality control technologist
at a separate monitor, or a quality control system should be used, whereby the number of
images per examination is compared with the number ordered for each technologist.
 

Computed Radiography (CR)

•Process of producing a computed radiographic image
•Use of conventional radiographic equipment, traditional patient positioning, and standard technical exposure factors
•CR cassette
•Use of an image-reading unit to scan the photostimulable phosphor image plate with a helium-neon laser beam
•Function of a photomultiplier tube
•Digital image display monitor
 
•Avoiding overexposure of the patient

-  Responsibility of the radiographer to use correct technical exposure factors the first time a patient is x-rayed to minimize radiation exposure

-  Phenomenon known as “dose creep”

•Computed radiography phosphor sensitivity

•CR imaging kilovoltage flexibility

•X-ray beam collimation and centering of body part on CR cassette
 
•Use of radiographic grids in CR

 Fluoroscopic Procedures

-  Patient radiation exposure rate

-  Dynamic images of selected anatomic structures

-  Greatest patient radiation exposure rate in diagnostic radiology

-  Responsibility of physician to evaluate the need for the examination

-  Benefit versus risk

-  Minimizing patient exposure time

 Fluoroscopic Procedures

•Brightness of the fluoroscopic image
 
•Use of photopic or cone vision to view fluoroscopic image
 
•Milliamperage required and effect on patient dose
 
•Multifield, or magnification, image intensifier tubes

-  Size

-  Normal viewing mode

-  Components

-  Method of operation

-  Image quality

-  Patient dose considerations

 Fluoroscopic Procedures

-  Intermittent, or Pulsed, Fluoroscopy

     -  Effect on patient dose

            -  Last-image-hold feature

-  Limiting Fluoroscopic Field Size

     -  Benefit of fluoroscopic field size limitation

    -  Fluoroscopic beam length and width limitation

 Fluoroscopic Procedures

-  Technical Exposure Factors

     -  Selection of technical exposure factors for adult patients

           -  kVp range

           -  Source-to-skin distance (SSD)

           -  Position of the input phosphor surface of the image intensifier in relation to the patient

-  Selection of Technical Exposure Factors for Children

          -  Percent of kVp decrease compared to an adult

          -  Lowering of technical exposure factors

 Fluoroscopic Procedures

-  Filtration

      -  Purpose and requirements

    -  Half-value layer

-  Source-to-Skin Distance

     -  Requirement

-  Cumulative Timing Device

     -  Requirement

      - Function

- Exposure Rate Limitation

     - Federal standard limit for entrance skin exposure rates

            - General-purpose intensified fluoroscopic units

            - Fluoroscopic units equipped with high-level control (HLC)

- Primary Protective Barrier

- Fluoroscopic Exposure Control Switch

 Mobile C-Arm Fluoroscopy

•Portable x-ray unit that is C-shaped.
 
•Has an x-ray-tube attached to one end of its arm and an image intensifier
attached to the other end.
 
•Frequently used in the operating room for orthopedic procedures, cardiac imaging,
interventional procedures, and other potentially lengthy tasks.
 
•Use of C-arm in fluoroscopy procedures carries the potential for a relatively large
patient radiation dose.
 
•C-arm operator could also receive a significant increase in occupational exposure if
standing close to the patient.
 
•All C-arm operators must have appropriate education and training to ensure that they will
follow guidelines for safe operation and also meet radiation safety protocols essential to patient
and personnel safety.

 Mobile C-Arm Fluoroscopy

•Requirements

     - Source-to-end of collimator assembly distance

     -  Patient-image intensifier distance

•Patient dose reduction

     - Entrance dose

     - Position of C-arm x-ray tube

 Mobile C-Arm Fluoroscopy

•With the C-arm x-ray tube positioned under the patient, scatter radiation is less intense.
 
•When the C-arm x-ray tube is positioned over the patient, scatter radiation becomes more
intense, and radiation exposure of personnel increases correspondingly.

Cinefluorography

•Film size for dose reduction

•High-dose-rate procedures
 
•Film frame rate
 
•Inference of patient dose from tabletop exposure levels
 
•Collimation
 
•Dose-reduction techniques
 
•Patient dose determined by procedure
 

Digital Fluoroscopy

•Use of pulsed progressive systems for dose reduction

     - Methods for dose reduction

•Use of last-image-hold feature for dose reduction

High-Level-Control Interventional Procedures

•Justification for use of high-level-control interventional procedures
 
•Public health advisory about the danger of overexposure of patients and exposure rate limits
 
•Procedures involving extended fluoroscopic time
 
 High-Level-Control Interventional Procedures
•Radiogenic skin injuries such as erythema or desquamation are deterministic effects
in which the severity of the disorder increases with radiation dose.
 

High-Level-Control Interventional Procedures

•Use of fluoroscopic equipment by nonradiologist physicians

     - Need for ongoing education and training

    - Reasons for high radiation exposures during interventional procedures

    - Need for  monitoring and documenting procedural fluoroscopic time

    - Responsibility for documentation

    - Guidelines to assist physicians in developing strategies that will enable them to fulfill their

interventional clinical objectives while controlling patient radiation dose and minimizing exposure

to occupationally exposed personnel and other assisting personnel

 

 

 

 

 

 

 

 

 

 

 

 

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