Set of numeric dose limits that are based on calculations of the various risks of cancer and genetic (hereditary) effects to tissues or organs exposed to radiation
Effective dose (EfD) limiting system
An EfD limiting system has been incorporated into what title of the Code of Federal Regulations, Part 20, a document prepared and distributed by the U.S. Office of the Federal Register; the rules and regulations of the Nuclear Regulatory Commission (NRC) and fundamental radiation protection standards governing occupational radiation exposure are included in this document?
Title 10 of the Code of Federal Regulations
2 resources for the revised recommendations of the concept of radiation exposure and of the associated risk of radiation-induced malignancy
National Council on Radiation Protection and Measurements (NCRP) Report No. 116 International Commission on Radiological Protection (ICRP) Report No. 60
4 major organizations responsible for evaluating the relationship between radiation EqD and induced biologic effects and are also concerned with formulating risk estimates of somatic and genetic effects of irradiation
International Commission on Radiological Protection (ICRP) National Council on Radiation Protection and Measurements (NCRP) United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) National Academy of Sciences/National Research Council Committee on the Biological Effects of Ionizing Radiation (NAS/NRC-BEIR)
Evaluates information on biologic effects of radiation and provides radiation protection guidance through general recommendations on occupational and public dose limits Considered the international authority on the safe use of sources of ionizing radiation Composed of a main commission with 12 active members, a chairman, and 4 standing committees, which include committees on radiation effects, radiation exposure, protection in medicine, and the application of its recommendations Since its inception in 1928, it has been the leading international organization responsible for providing clear and consistent radiation protection guidance through its recommendation for occupational dose limits and public dose limits Only makes recommendations, does not function as an enforcement agency; each nation must develop and enforce its own specific regulations
International Commission on Radiological Protection (ICRP)
Reviews regulations formulated by the ICRP and decides ways to include those recommendations in US radiation protection criteria; nongovernmental, non-profit The council implements this task by formulating general recommendations and publishing their recommendations in the form of various reports Not an enforcement agency, enactment of its recommendations lies with federal and state agencies that have the power to enforce such standards after they have been established
National Council on Radiation Protection and Measurements (NCRP)
4 objectives of the NCRP
Collect, analyze, develop and disseminate in the public interest information and recommendations about (a) protection against radiation (referred to herein as radiation protection) and (b) radiation measurements, quantities and units, particularly those concerned with radiation protection Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations Develop basic concepts about radiation quantities, units and measurements, about the application of these concepts, and about radiation protection Cooperate with the International Commission on Radiological Protection, the Federal Radiation Council, the International Commission on Radiation Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units and measurements and with radiation protection
Evaluates human and environmental ionizing radiation exposure and derives radiation risk assessments from epidemiologic data and research conclusions; provides information to organizations such as the ICRP for evaluation Another group that plays a prominent role in the formulation of radiation protection guidelines This group evaluates human and environmental ionizing radiation exposures from a variety of sources including radioactive materials, radiation-producing machines, and radiation accidents Uses epidemiologic data information acquired from the Radiation Effects Research Foundation and research conclusions to derive radiation risk assessments for radiation-induced cancer and for genetic (hereditary) effects
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)
Reviews studies of biologic effects of ionizing radiation and risk assessment and provides the information to organizations such as the ICRP for evaluation Another advisory group that reviews studies of biologic effects of ionizing radiation and risk assessment
National Academy of Sciences/National Research Council Committee on the Biological Effects of Ionizing Radiation (NAS/NRC-BEIR)
After radiation protection standards have been determined, responsible agencies must enforce them for the protection of the general public, patients, and occupationally exposed personnel
5 U.S. regulatory agencies
Nuclear Regulatory Commission (NRC) Agreement states Environmental Protection Agency (EPA) U.S. Food and Drug Administration (FDA) Occupation Safety and Health Administration (OSHA)
Oversees the nuclear energy industry and enforces radiation protection standards, publishes its rules and regulations in Title 10 of the U.S. Code of Federal Regulations, and enters into written agreements with state governments that permit the state to license and regulate the use of radioisotopes and certain other material within the state Federal agency that has the authority to control the possession, use, and production of atomic energy in the interest of national security; also has the power to enforce radiation protection standards Does not regulate or inspect x-ray imaging facilities; its main function is to oversee the nuclear energy industry Supervises the design and working mechanics of nuclear power stations, production of nuclear fuel, handling of expending fuel, and supervision of hazardous radioactive waste material Controls the manufacture and use of radioactive substances formed in nuclear reactors and used in research, nuclear medicine imaging procedures, therapeutic treatment, and industry Licenses users of radioactive materials and periodically makes unannounced inspections to determine whether these users are in compliance with the provisions of their licenses Writes standards that are presented as rules and regulations Has the authority to enter into written contracts with state governments; these agreements permit the contracting state to undertake the responsibility of licensing and regulating the use of radioisotopes and certain other radioactive materials within the state
Nuclear Regulatory Commission (NRC)
Enforce radiation protection regulations through their respective health departments
Facilitates the development and enforcement of regulations pertaining to the control of radiation in the environment
Environmental Protection Agency (EPA)
Conducts an ongoing production radiation control program, regulating the design and manufacture of electronic products, including x-ray equipment To determine the level of compliance with standards in a given x-ray facility, it conducts on-site inspections of x-ray equipment Compliance with standards ensures the protection of occupationally and nonoccupationally exposed persons from faulty manufacturing
U.S. Food and Drug Administration (FDA)
Functions as monitoring agency in places of employment, predominantly in industry Regulates occupation exposure to radiation
Occupation Safety and Health Administration (OSHA)
Implementation of an effective radiation safety program begins with the administration of the facility; individuals in executive positions must provide the resources necessary for creating and maintaining such a program and can do what 3 things?
Delegate operation funds in the budget Oversee the development of policies and procedures Provide the equipment necessary for starting and continuing the program
3 functions of a radiation safety committee (RSC) mandated to be established by the facility by the NRC
Provides guidance for the program Facilitates ongoing operation of the program Selects a qualified person to serve as a radiation safety officer (RSO)
2 functions of an RSO
Oversee the program’s daily operation Provide for formal review of the program each year
4 things an RSO normally is
Medical physicist Health physicist Radiologist Other individual qualified through adequate training and experience
5 responsibilities of the RSO
Specifically responsible for developing an appropriate radiation safety program for the facility that follows internationally accepted guidelines for radiation protection Must ensure that the facility’s operational radiation practices are such that all people, especially those who are or could be pregnant, are adequately protected from unnecessary exposure To fulfill their responsibility, management of the facility must grant the RSO the authority necessary to implement and enforce the policies of the radiation safety program Review and maintain radiation-monitoring records for all personnel Be available to provide counseling for individuals
3 allowable pathways for a radiation safety officer to meet training and experience requirements
Certification by one of the professional boards approved by the NRC Didactic and work experience as described in detail in the regulations Identification as an authorized user, authorized medical physicist, or authorized nuclear physicist on the licence, with experience in the types of uses for which the individual has RSO responsibilities
Duties that requires the licensee to freely provide the RSO to perform
Identify radiation safety problems Initiate, recommend, or provide corrective action Stop unsafe operations involving by-product material Verify implementation of corrective actions
3 duties required that the licensee provide the RSO
Sufficient authority Organization freedom Management prerogative to perform certain duties
Law to protect the public from the hazards of unnecessary radiation exposure resulting from electronic products and diagnostic x-ray equipment
Radiation Control for Health and Safety Act of 1968
Code that applies to complete systems and major components manufactured after its effective date
Code of Standards for Diagnostic X-Ray Equipment
6 provisions included in the standards for diagnostic x-ray equipment
Positive beam limitation Appropriate minimal filtration of the x-ray beam to ensure an acceptable level of beam quality; filtration provides significant reduction in the intensity of very "soft" x-rays that contribute only to the added patient absorbed dose Ability of x-ray units to duplicate certain radiation exposures for any given combination of kVp, mA, and time to ensure both exposure reproducibility and linearity Inclusion of beam limitation devices for spot films taken during fluoroscopy; such devices should be located between the x-ray source and patient Presence of "beam on" indicators to give visible warnings when x-ray exposures are in progress and both visual and audible signals when exposure has terminated Inclusion of manual backup timers for AEC to ensure termination of the exposure if the automatic timer fails
Automatic limitation of the radiographic beam to the IR regardless of IR size
Positive beam limitation
Consistency in output in radiation intensity for identical generator settings from one individual exposure to the next The x-ray unit must be able to duplicate certain radiographic exposures for any given combo of kilovolts at peak (kVp), milliamperes (mA), and time May be verified by using the same technical exposure factors to make a series of repeated radiation exposures and then, observing with a calibrated ion chamber, how radiation intensity typically varies
A variance of what is acceptable for exposure reproducibility?
5% or less
Consistency in output radiation intensity at a selected kVp setting when changing from one mA and time combination to another (mAs); output of radiation that comes out The ratio of the difference in mR/mAs values between two successive generator stations to the sum of those mR/mAs values
What must exposure linearity be?
Less than 0.1 (cannot exceed 10%)
The protection from radiation exposure is as low as reasonably achievable when the expenditure of further resources would be unwarranted by the reduction of exposure that would be achieved The continuation of good radiation protection programs and practices which traditionally have been effective in keeping the average and individual exposures for monitored workers well below the limit Medical imaging personnel and radiologists share the responsibility to keep occupational and nonoccupational dose limits as low as reasonably achievable EfDs and EqDs should be well below maximal allowable levels Goal can usually be achieved through the employment of proper safety procedures performed by qualified personnel Procedures should be clearly described in a facility’s radiation safety program.
As Low as Reasonably Achievable (ALARA) Concept Optimization
What is the model for the ALARA concept?
The relationship between ionizing radiation and potential risk is assumed to be completely linear and without any threshold In the interest of safety, risk of injury should be overestimated rather than underestimated
Biologic effect and radiation dose are directly proportional
Each patient should get the right imaging exam, at the right time, with the right radiation dose FDA announced "the launch of a cooperative Initiative to Reduce Unnecessary Exposure from Medical Imaging" Working in conjunction with their partners, the FDA intends to take specific action By coordinating these efforts, the FDA will be able to "optimize patient exposure to radiation from certain types of medical exams, and thereby reduce risks while maximizing the benefits of these studies"
FDA "White Paper"
Provides federal legislation requiring the establishment of minimal standards for the accreditation of education programs for people who perform radiologic procedures and certification of such people Purpose of federal act is to ensure that standard medical and dental radiologic procedures adhere to rigorous safety precautions and standards Individual states are encouraged to enact similar statutes and administer certification and accreditation programs based on the standards therein Because no legal penalty exists for noncompliance, many states, unfortunately, have not responded with appropriate legislation
Consumer-Patient Radiation Health and Safety Act of 1981
To prevent the occurrence of serious radiation-induced conditions (acute and chronic deterministic effects) in exposed persons and to reduce stochastic effects in exposed persons to a degree that is acceptable in relation to the benefits to the individual and to society from activities that generate such exposures
Goal for radiation protection
2 all-inclusive categories encompass the radiation-induced responses of serious concern in radiation protection programs
Deterministic effects Stochastic (probabilistic) effects
Biologic somatic effects of ionizing radiation that can be directly related to the dose received that exhibit a threshold dose below which the response does not normally occur and above which the severity of the biologic damage increases as the dose increases When radiation-induced biologic damage escalates, it does so because greater numbers of cells interact with the increased number of x-ray photons that are present at higher radiation exposure Typically occur only after large doses of radiation but they could also result from long-term individual low doses of radiation sustained over several years; in either instance the cumulative amounts of such radiation doses are usually much greater than those typically encountered by a patient in diagnostic radiology
3 early deterministic effects
Erythema Blood changes (decrease pf lymphocytes and platelets) Epilation Acute radiation syndrome
3 syndromes of acute radiation syndrome (far more serious early deterministic consequences of radiation sickness)
Hematopoietic syndrome Gastrointestinal syndrome Cerebrovascular syndrome
Effects that usually occur within a few hours or days after a very high-level radiation exposure to a significant portion of the body
Acute radiation syndrome
Diffuse redness over an area of skin after irradiation
Loss of hair
6 late deterministic somatic effects that may occur months or years after high-level radiation exposure
Cataract formation Fibrosis Organ atrophy Loss of parenchymal cells Reduced fertility Sterility caused by a decrease in reproductive cells
Early and late deterministic somatic effects have a high probability of occurring when entrance radiation doses exceed what?
The frequency of occurrence of high-dose deterministic effects follows what curve?
Nonlinear, threshold curve that is sigmoidal (S-shaped) with a threshold Not proportional to the dose
Mutational, nonthreshold, randomly occurring biologic somatic changes; chances of occurrence increase with each radiation exposure
Stochastic (probabilistic) effects
Changes to somatic cells that would affect the individual when the cells divide
Changes to germ cells that would affect future generations
2 examples of stochastic (probabilistic) effects
Cancer Genetic alterations
What curves may be used to demonstrate stochastic (probabilistic) effects?
Linear and the linear-quadratic dose-response curves
What is a genetic (hereditary) effect of radiation?
Irradiation of DNA of somatic cells leading to abnormalities in new cells as they divide in that individual
2 explicit objectives of radiation protection
To prevent any clinically important radiation-induced deterministic effect from occurring by adhering to dose limits that are beneath the threshold levels To limit the risk of stochastic responses to a conservative level as weighted against societal needs, values, benefits acquired, and economic considerations (ex: cancer)
Current radiation protection philosophy is based on the assumption that what relationship exists between radiation dose and biologic response?
Linear nonthreshold relationship
Probability of injury, ailment, or death resulting from an activity
Possibility of inducing a radiogenic cancer or genetic defect
Risk, in the medical imaging industry, after irradiation
_____ minimal safe dose exists
Current method for assessing radiation exposure and associated risk of biologic damage to radiation workers and the general public Concerns the upper boundary dose of ionizing radiation that results in a negligible risk of bodily injury or hereditary damage Upper boundary limits are designed to minimize the risk to humans in terms of deterministic and stochastic effects (upper limits do not include natural background and medical exposure) Upper boundary radiation exposure limits for occupationally exposed persons are associated with risks that are similar to those encountered by employees in other industries such as manufacturing, trade, or government, which are generally considered to be reasonably safe Radiation risks are derived from the complete injury caused by radiation exposure Includes, for the determination of EqD for tissues and organs, all radiation-vulnerable human organs that can contribute to potential risk, rather than only those human organs considered critical An attempt to equate the various risks of cancer and hereditary effects to the tissues or organs that were exposed to radiation
EfD limiting system
3 ways EfD limits may be expressed
Whole-body exposure Partial-body exposure Exposure of individual organs
The sum of what exposures is considered when EfD limits are established?
Both the external and internal whole-body exposures
The benefit obtained from any diagnostic imaging procedure must always be weighed against the ______ that is taken
The occupational risk associated with radiation exposure is generally estimated to be what chance of fatal accident over an entire career?
Embryo-fetus in utero is particularly sensitive to radiation exposure; epidemiologic studies of atomic bomb survivors exposed in utero provided conclusive evidence of a dose-dependent increase in the incidence of severe mental retardation for fetal doses greater than approximately what?
0.4 Sievert (Sv)
Greatest risk for radiation-induced mental retardation occurred when the embryo-fetus was exposed how many weeks after conception?
8-15 weeks/first trimester
Any organ in the human body is vulnerable to damage from exposure to ionizing radiation Some organs are more sensitive to radiation than others Every organ is at some risk because of the assumed random nature of somatic or hereditary radiation-induced effects
Concept underlying radiation protection
Indicates the ratio of the risk of stochastic effects attributable to irradiation of a given organ or tissue (T) to the total risk when the whole body is uniformly irradiated Because various tissues and organs do not have the same degree of sensitivity to these effects, the system employed must compensate for the differences in risk from one organ to another
Tissue weighting factor (WT)
Published reports reflect the current position and recommendations of the NCRP on radiation protection standards
What is the annual EfD limit for occupational exposure?
What is the cumulative EfD (cumEfD) limit for occupational exposure?
10 mSv x age
What is the annual EqD limit for occupational exposure to the lens of the eye?
What is the annual EqD limit for occupational exposure to localized areas of the skin, hands, and feet?
What is the annual EfD limit for continuous or frequent exposure to the public (ex: radiation therapy)?
What is the annual EfD limit for infrequent exposure to the public?
What is the annual EqD limits for the public to the lens of the eye?
What is the annual EqD limits for the public to localized areas of the skin, hands, and feet?
What is the annual EfD limit for education and training exposures (students) under the age of 18 years?
What is the annual EqD limit for education and training exposures (students) to the lens of the eye?
What is the annual EqD limit for education and training exposures (students) to localized areas of the skin, hands, and feet?
What is the monthly EqD limit for embryo and fetus exposures?
What is the EqD limit for embryo and fetus exposures during the entire gestation?
What is the annual negligible individual dose?
A radiation worker's lifetime EfD must be limited to his or her age in years times 10 mSv
Cumulative effective dose (CumEfD) limit
2 sources of radiation EfD limits do not include
Radiation exposure from natural background radiation Medical procedures
2 exposures EfD limits include the possibility of
Internal exposure External exposure
The sum/total of both the internal and external equivalent doses
Effective dose (EfD)
2 deterministic effects of the embryo-fetus that are expected to be statistically negligible if the EqD remains at or below the recommended limit
Small head size Mental retardation
Provides a low-exposure cutoff level so that regulatory agencies may dismiss a level of individual risk as being of negligible risk
Negligible individual dose (NID)
Personnel dosimeter readings should be well below what of the maximum EfD limits, even for those technologists who receive the most exposure?
A tenth of the maximum EfD
Health care facilities, such as hospitals, establish their own internal limits that are set at levels far below the actual limits and are meant to trigger an investigation that should uncover the reason for any unusually high exposure
How does the lead-lined metal diagnostic-type protective tube housing 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-rays produced in the anode but not at the focal spot Photons that pass through the housing because the lead shielding around the tube for practical reasons cannot be made perfect Radiation generated in the x-ray tube that does not exit from the collimator opening but rather penetrates the protective tube housing and, to some degree, the sides of the collimator
X-rays emitted through the x-ray port tube window, or port
Useful, or primary, beam
The housing enclosing the x-ray tube must be constructed so that the leakage radiation measured at a distance of 1 m from the x-ray source does not exceed what when the tube is operated at its highest voltage at the highest current that allows continuous operation?
1 mGya/hr (100 mR/hr)
What is the radiographic examination table frequently made of?
Carbon fiber material
What is used to measure SID
A tape measure or laser
Distance indicators must be accurate to within what percent of the SID?
Centering indicators must be accurate to within what percent of the SID?
Most versatile device for defining the size and shape of the radiographic beam; most often used with multipurpose x-ray units Box shaped and contains the radiographic beam defining system
Light-localizing variable-aperture rectangular collimator
3 things that radiographic beam defining system consists of
Two sets of adjustable lead shutters mounted within the device at different levels A light source to illuminate the x-ray field and permit it to be centered over the area of clinical interest Mirror to deflect the light beam toward the patient to be radiographed
Mounted as close as possible to the tube window to reduce the amount of off-focus, or stem, radiation coming from the primary beam exiting at various angles from the x-ray tube window; reduces patient dose resulting from off-focus radiation
Upper shutters (first set of shutters)
4 x-ray beam limitation devices
Light-localizing variable-aperture rectangular collimator Aperture diaphragms Cones Cylinders
2 things x-ray beam limitation devices do
Confine the useful, or primary, beam before it enters the area of clinical interest, thereby limiting the quantity of body tissue irradiated Reduces the amount of scattered radiation in the tissue and prevents unnecessary exposure to tissues not under examination
All the radiation that arises from the interaction of an x-ray beam with the atoms of a patient or any other object in the path of the beam Compton interaction between the x-ray photons and electrons of the atoms within the attenuating object deflect x-ray photons from their initial trajectories; as a result, photons emerge from the object in all directions Greatly reduced in intensity relative to the incident beam; also quite weakened in energy and consequently in penetrability
2 benefits of restricting x-ray field size to include only the anatomic structures of clinical interest
Significant reduction in patient dose because less scatter radiation is produced by a smaller field size Improves the overall quality of the radiographic image
Mounted below the level of the light source and mirror and function to further confine the radiographic beam to the area of clinical interest Consists of two pairs of lead plates oriented at right angles to each other; each set may be adjusted independently so that an extensive variety of rectangular shapes can be selected
Lower shutters (second set of shutters)
The brightness of a surface; quantifies the intensity of a light source (i.e., the amount of light per unit area coming from its surface) Determined for measuring the concentration of light over a particular field of view Light emission
What is the primary unit of luminance?
Candela per square meter (nit)
The sum of the cross-table and along-the-table alignment differences between the x-ray and light beams must not exceed what of the SID?
Consists of electronic sensors in an IR holder that sends signals to the collimator housing; when activated, the collimators are automatically adjusted so that the radiation field matches the size of the IR May be activated with the turn of a key
Positive beam limitation (PBL)
Regulatory standards require accuracy of what of the SID with PBL?
Simplest of all beam limitation devices Consists of a flat piece of lead with a hole of designated size and shape cut in its center; the dimensions of the hole determine the size and shape of the radiographic beam Different IR sizes and SIDs require aperture diaphragms of various sizes to accommodate them Placed directly below the window of the x-ray tube and confines the primary radiographic beam to dimensions suitable for covering a given size IR at a specified SID Limits field size, and thus the area of the body irradiated,
3 shapes of aperture diaphragm openings
Rectangular Square Round
Most common shape of aperture diaphragm
3 examinations aperture diaphragms are used in
Trauma radiographic imaging systems X-ray units designed specifically for chest radiography Dental radiographic units
3 specific areas/radiographic examinations cones are used for
Head (e.g., coned-down lat projection of the sella turcica, projections of the paranasal sinuses) Vertebral column Chest
Circular metal tubes that attach to the x-ray tube housing or variable rectangular collimator to limit the x-ray beam to a predetermined size and shape
Collimating device with the diameter of the upper end smaller than the diameter of the lower end
Flared metal tube
Collimating device with the diameter the same at both the upper and lower ends
Reduces exposure to the patient's skin and superficial tissue by absorbing most of the lower-energy photons (long-wavelength or soft x-rays) from the heterogenous beam Increases the mean energy, or "quality," of the x-ray beam aka "hardening" the beam; x-rays are more penetrating
What is the effect of filtration on the absorbed dose to the patient?
Because filtration absorbs some of the photons in a radiographic beam, it decreases the overall intensity (quantity, or amount) of incident radiation The remaining photons, as a whole, are more penetrating and therefore less likely to be absorbed in body tissue Hence, the absorbed dose to the patient decreases when the correct amount and type of filtration are placed in the radiographic beam
2 types of filtration
Filtration in the tube
3 examples of inherent filtration
Glass envelope encasing the x-ray tube Insulating oil surrounding the tube Glass window in the tube housing
The inherent filtration material amounts to approximately what aluminum equivalent?
0.5 mm aluminum equivalent
The light-localizing variable-aperture rectangular collimator provides an additional what amount of aluminum equivalent to the inherent filtration (the reflective surface of the collimator mirror provides most of this aluminum equivalent)?
1 mm aluminum equivalent
What is the requirement for total filtration?
2.5 mm aluminum equivalent at above 70 kVp
Inherent filtration plus added filtration
3 examples of added filtration
Sheets of aluminum (or the equivalent) of appropriate thickness Collimators Mirror
Extra filtration located outside the glass envelope window of the tube housing above the collimator shutters Filtration below the tube
Each x-ray tube and collimator system typically has a total inherent filtration of what aluminum equivalent?
1.5 mm equivalent
Metal the is the most wide selected filter material in diagnostic radiology because it effectively removes low-energy (soft) x--rays from polyenergetic (heterogenous) x-ray beam without severely decreasing the x-ray beam intensity Lightweight, sturdy, relatively inexpensive, and readily available
The thickness of a designated absorber (customarily a metal such as aluminum) required to decrease the intensity of the primary beam by 50% of its initial value Measure of beam quality/effective energy of the x-ray beam
Half-value layer (HVL)
Dose reduction and uniform radiographic imaging of body parts that vary considerably in thickness or tissue composition may be accomplished by the use of these filters Partially attenuate x-rays that are directed toward the thinner, or less dense, area while permitting more x-radiation to strike the thicker, or denser area
3 materials compensating filters are constructed of
Aluminum Lead-acrylic Other suitable material
3 types of compensating filters
Wedge filter Trough, or bilateral wedge filter Boomerang
Used to provide uniform density when the foot is undergoing radiography Filter is attached to the lower rim of the collimator and positioned with its thickest part toward the toes and thinnest part toward the heel
3 examinations a trough, or bilateral wedge filter is used in
Lateral knee (patella) T-spine Dedicated chest radiographs
3 materials that may make up the grid interspaces
Aluminum Plastic Wood
Device made of parallel radiopaque strips alternately separated with low-attenuation strips; strips of lead with aluminum between them Placed between the patient and radiographic IR to remove scattered x-ray photons that emerge from the patient before they reach the film or other IR Increases patient dose, but improves quality of the recorded image Remove scattered x-ray photons
When is a grid usually used?
When the thickness of the body part to be radiographed is greater than 10 cm
The ratio of the height of the lead strips in the grid to the distance between them
2 types of grids
Focused grid Parallel grid
Grid whose lines follow divergence of beam, slanted in and meet at anode; used in diagnostic
Has straight grid lines
2 things grids significantly improve
Radiographic contrast Visibility of detail
What is the minimum SSD for mobile radiographic units?
At least 30 cm (12 inches)
What distance is generally used for mobile radiography?
100 cm (40 inches) or even 120 cm (48 inches)
Temporary image produced conventionally by ionizing radiation after x-rays pass through an anatomic area of clinical interest
Invisible/latent image must be chemically processed to make the unseen image visible; the finished radiograph that results from this process
Anatomic information collected by a computer and shown on its display
The amount of luminance of a display monitor
Shades of gray that are displayed on the image
Number of different shades of gray that can be stored in memory and displayed on a computer monitor
Changes brightness; the amount of radiation doesn't affect brightness in DR
The numeric values of the digital image are aligned in a fixed number of arrays that form many individual miniature square boxes, each of which corresponds to a particular place in the image; these individual boxes collectively constitute this
Rows and columns
Each miniature square box in a matrix that collectively produce a 2D representation of the information contained in a volume of tissue
What do the size of the pixels determine?
The sharpness of the image
Resolution is sharper when pixels are _______ and matrix is ________
2 common matrix sizes
512 x 512 1024 x 1024
What is an advantage and disadvantage of DR?
Advantage: contrast better because image can be manipulated Disadvantage: film offers better detail
IRs used in DR convert the energy of x-rays into what?
What does indirect DR use?
A scintillator, such as amorphous silicon, to convert the x-ray energy into visible light The visible light is converted into electrical signals by an array of transistors (TFTs) or an array of charge-coupled devices (CCDs)
What does direct DR use?
A photoconductor, such as amorphous selenium, to convert the x-ray energy directly into electrical signals
The CR filmless cassette contains a photostimulable phosphor made of what?
Europium-activated barium fluorohalide
Use of an image reading unit to scan the photostimulable phosphor image plate in CR uses what kind of beam?
Helium-neon laser beam
Use of an image reading unit to scan the photostimulable phosphor image plate in CR, results in the emission of violet light that is changed into an electronic signal by what?
A photomultiplier tube
Although the radiographer can manipulate the CR image of the patient's anatomy of interest to adjust image size, brightness, and contrast, this technologic flexibility does not excuse overexposing the patient Responsibility of the radiographer to minimize radiation exposure by using correct technical exposure factors the first time a patient is x-rayed If patients are overexposed by radiographers who claim the rationale that computerized images can be manipulated later on to produce a diagnostic-quality image, thereby avoiding the possibility of repeat exposures, patients are actually receiving higher radiation doses than are necessary to produce those initial images
The sensitivity of the phosphor used in CR is approximately equal to a what speed screen-film combination?
200 speed screen-film combination
CR has ________ kilovoltage flexibility than does conventional screen-film radiography
CR is _______ sensitive to scatter radiation, so a grid should probably be used more frequently except for the majority of pediatric patients
4 factors grid selection depends on
Size of the anatomic feature to be radiographed kVp selected Amount of scatter removal preferred Grid frequency (lines per cm or in)
How long does the image stay on the CR imaging plate?
4 advantages DR systems offer advantages over both CR and conventional SFSs
Lower dose Ease of use Immediate imaging results Manipulation of the image
Process in which an x-ray examination is performed that demonstrates dynamic, or active, motion images of selected anatomic structures by producing a real-time image of those structures on a television monitor that works in conjunction with an image intensification system under low-light conditions Greatest patient radiation exposure rate in diagnostic radiology Responsibility of physician to evaluate the need for the examination to make sure the benefit outweighs the risk and there is minimum patient exposure time
Traditionally, fluoroscopic imaging systems have the x-ray tube positioned _____ the x-ray examination table and the image intensifier and spot film system mounted on a C-arm and centered over the x-ray examination table
Minification gain x flux gain
3 benefits of image intensification fluoroscopy
Increased image brightness Saving of time for for the radiologist Patient skin dose reduction (scatter goes back to floor)
The x-ray image intensification system increases the overall brightness of fluoroscopic image how many times?
Because an image intensification system permits observing of the fluoroscopic image at ordinary brightness levels (regular white light) that radiologist makes use of what type of vision?
Daytime vision Photopic/cone vision
Because an image intensification system greatly increases brightness, image intensification fluoroscopy requires less mA than does old-fashioned fluoroscopy, approximately how much?
What is the input phosphor of a fluoroscopic image intensification system made of?
What is the photocathode of a fluoroscopic image intensification system made of?
What is the output phosphor of a fluoroscopic image intensification system made of?
An electronic device that receives the image-forming x-ray beam and converts it into a visible-light image of high intensity
Image intensification tube
What is the most common size of multifield image intensification tubes?
25/17/12 cm (10/6.8/4.8 in)
What is the normal viewing mode of multifield, or magnification, image intensifier tubes?
25 cm (10 in)
When magnification in the fluoroscopic image is needed and the viewing mode is changed to the 17-cm mode (6.8 in) or even less (12 cm [4.8 cm]), the focal point of the electrons move to a _________ from the output phosphor
Greater distance away
Fluoroscopy mA _________ automatically with magnification; the use of smaller-diameter modes results in increased pt dose Quality of the magnified image is somewhat _________ (new digital systems can magnify without increasing dose)
Involves manual or automatic periodic activation of the fluoroscopic tube by the fluoroscopist, rather than lengthy continuous activation
Intermittent, or pulsed, fluoroscopy
2 things intermittent/pulsed fluoroscopy does
Practice significantly decreases patient dose, especially in long procedures Helps extend the life of the tube
Feature that allows the fluoroscopist to see the most recent image without exposing the patient to another pulse of radiation; reduces patient dose
What is the kVp range for adults, depending on the body area being examined during fluoroscopy; mA range varies
The SSD should not be less than what for stationary fluoroscopes?
38 cm (15 inches)
Percentage of kVp decrease for children as compared to an adult should be as much as what?
Position of the input phosphor surface of the image intensifier in relation to the patient should be maintained as ________ as is practical to reduce the patient’s entrance exposure rate
With image intensification systems, a total aluminum equivalent filtration of what may be preferred?
3.0 mm aluminum equivalent or greater
Patient does decreases by how much during fluoroscopic procedures when aluminum filtration increases from 1-3 mm aluminum
In standard image intensification fluoroscopy, a HVL of what is considered acceptable when kVp ranges from 80 to 100?
3 to 4.5 mm aluminum
What is the minimum SSD for mobile fluoroscopes?
No less than 30 cm (12 inches)
Resettable device that times the x-ray beam-on time and sounds an audible alarm or temporarily interrupts the exposure after the fluoroscope has been activated for 5 minutes
What is the current federal standard limit for entrance skin exposure rates of general-purpose intensified fluoroscopic units?
Maximum of 100 mGya per minute (10 R/min)
A primary protective barrier of what lead equivalent is required for a fluoroscopic unit?
2-mm lead equivalent
The fluoroscopic exposure control switch must be of what type?
Patient-image intensifier distance should be as _______ as possible to reduce entrance dose (puts tube further)
With the C-arm x-ray tube positioned _______ the patient, scatter radiation is less intense
The lines composing the image are progressively scanned to provide the picture that appears on a monitor during a brief period of time The x-ray beam is turned off while the image is being scanned, thereby decreasing patient dose, and then pulsed back on for the next image
Pulsed progressive system
Treating the patient as a whole person rather than just the area of concern
An interaction that produces a satisfying result through an exchange of information
2 benefits of effective communication
Alleviates the patient’s uneasiness Increases the likelihood for cooperation and successful completion of the imaging procedure
2 ways radiographers limit the patient’s exposure to ionizing radiation
Employing appropriate radiation reduction techniques; lowest mAs, highest kV, lowest grid ratio Using protective devices that minimize radiation exposure
Unconscious actions or body language
2 types of patient motion
Voluntary motion Involuntary motion
Motion controlled by will
Motion caused by muscle groups (digestive organs or heart)
How can the radiographer compensate for involuntary motion?
Shortening the length of exposure time with an appropriate increase in mA to maintain sufficient mAs for useful radiographic density/brightness and using very-high-speed IRs
4 areas of the body that should be selectively shielded from the useful beam whenever possible
Lens of the eye Breasts Reproductive organs Thyroid
Gonadal shielding should be used on patients during diagnostic x-ray procedures to protect the reproductive organs from exposure to the useful beam when these organs are in or within approximately what distance of a properly collimated beam?
Female reproductive organs receive about how many times more exposure during a given radiographic procedure involving the pelvic region than do the male reproductive organs, because the female reproductive organs are located within the pelvic region?
A 1-mm lead flat contact shield for the female reduces exposure by about what percent?
A 1-mm lead contact shield for the male patient reduces exposure by about what percent?
When a male patient is in the supine position what anatomical landmark can be used to guide shield placement over the testes?
When a female patient is in the supine position the shield should be placed approximately how far medial to each palpable anterior superior iliac spine (ASIS) to protect the ovaries?
2.5 cm (1 inch)
4 basic types of gonadal shielding devices
Flat contact shields Shadow shields Shaped contact shields Clear lead shields
Shield made of lead strips or lead-impregnated materials 1 mm thick Can be placed directly over the patient's reproductive organs Most effective when they're used as protective devices for patients having AP or PA while in a recumbent position; not suited for nonrecumbent positions or projections other than AP or PA
Flat contact shields
If the flat contact shield is used during a typical fluoroscopic examination, it must be placed _____ the patient to be effective because the x-ray tube is located under the radiographic table
Shield made of radiopaque material and is suspended from above the radiographic beam-defining system, these shields hang over the area of clinical interest to cast a shadow; sterile field
Shields containing 1 mm of lead and are contoured to enclose the male reproductive organs Disposable or washable athletic supporters or jockey-style briefs function as carriers for these shields Not recommended for PA projections because it only covers the anterior and lateral surfaces
Shaped contact shields
Shields made of transparent lead-acrylic material impregnated with approximately 30% lead by weight Ex: full spinal scoliosis examination
Clear lead shields
Recorded detail in the radiographic image
Blotchy radiographic image that results when an insufficient quantity of x-ray photons reaches the IR
7 technical exposure factor considerations
Mass per unit volume of tissue of the area of clinical interest Effective atomic numbers and electron densities of the tissues involved Type of IR SID Type and quantity of filtration employed Type of x-ray generator used (single phase, three phase, or high frequency [lowest dose]) Balance of radiographic density or brightness and contrast required
What is the voltage ripple of a single phase generator?
What is the voltage ripple of a 3 phase 6 pulse generator?
What is the voltage ripple of a 3 phase 12 pulse generator?
What is the voltage ripple of a high frequency generator?
Product of x-ray electron tube current and the amount of time in seconds that the x-ray beam is on
To ensure standardization in the processing of both film and digital images, it is absolutely essential that every imaging department establish a program that includes regular monitoring and maintenance of all processing and image display equipment in the facility, to ensure the production of optimal-quality images
Quality control program
As an alternative procedure instead of using a radiographic grid for reducing scattered radiation during certain examinations (e.g., cross-table lateral c-spine and areas of chest radiography) Technique that removes scatter radiation by using an increased OID which improves radiographic image contrast A complementary increase in SID may be made The scattered x-rays are disseminated in many directions at acute angles to the primary beam when the radiographic exposure is made Because of the increased distance between the anatomic structures being imaged and the IR, a higher percentage of the scattered x-rays produced is then less likely to strike the IR
To perform an air gap technique, the IR is placed how far from the patient, and the x-ray tube is placed approximately how far away from the IR?
10-15 cm (4-6 in) 300-366 cm (10-12 ft)
In general, the use of an air gap technique requires the selection of technical exposure factors are comparable to those used with what ratio grid?
8:1 ratio grid
Over what kVp is the air gap techniques for the most part not as effective?
Over 90 kVp
For chest radiography using what kVp range can the air gap technique be successful?
At less than what kVp are air gap techniques more useful?
Less than 90 kVp
Any image that must be performed more than once because of human or mechanical error during the production of the initial image; increases patient dose
If the patient's gonads were included in the repeated imaged area, then the gonads would have received this
By determining the number of repeats and the reasons for producing unacceptable radiographic images, existing problems and conditions in an imaging department will be identified
Repeat analysis program
3 benefits of a repeat analysis program
Increases awareness among staff and student radiographers of the need to produce optimal-quality recorded images Radiographers generally become more careful in producing their radiographic images because they are aware that the images are being reviewed When it identifies problems or concerns, in-service education programs covering these specific topics may be designed for imaging personnel
3 things analysis of the department's repeats rate does
Provides valuable information for process improvement Helps minimize patient exposure Improves the overall performance of the department
The responsibility for ordering a radiologic examination lies with who?
The referring physician must determine whether the benefit to the patient in terms of medical information gained sufficiently justifies subjecting the patient to the risk of the absorbed radiation resulting from the procedure
6 unnecessary radiologic procedures
Chest x-ray examination on scheduled admission to the hospital Chest x-ray as part of a preemployment physical Lumbar spine examination as part of a preemployment physical Chest x-ray or other unjustified examination as part of a routine health checkup Chest x-ray examination for mass screening for tuberculosis (TB) Whole-body multislice spiral computed tomography (CT) screening
3 ways the amount of radiation received by a patient from diagnostic imaging procedures may be specified
Entrance skin exposure (ESE) (includes skin and glandular) Bone marrow dose Gonadal dose
Most frequently reported patient radiation amount because it is the simplest to determine
Entrance skin exposure (ESE)
Sensing devices most often used to measure skin dose directly
Thermoluminescent dosimeter (TLD)
What is the sensing material in TLDs?
Lithium fluoride (LiF)
Absorbed dose to the most superficial layers of the skin
Most superficial layers of the skin
5 layers of the epidermis
Horny/outer Translucent/clear Granular Prickle cell Germinal/basal
In diagnostic radiology, the relatively low gonadal dose for a single human is considered ____________; however, when the low gonadal dose is applied to the entire population, the dose becomes far more ____________
The EqD to the reproductive organs that, if received by every human, would be expected to bring about an identical gross genetic injury to the total population, as does the sum of the actual doses received by exposed individual members of the population The consequences of substantial absorbed doses of gonadal radiation become significantly less when averaged over an entire population rather than applied to just a few of its members The average EqD to members of the population who are of childbearing age
Genetically significant dose
What is the estimated GSD for U.S. population?
0.20 mSv (20 mrem)
Dose of radiation delivered to the bone marrow; the average radiation dose to the entire active bone marrow
Bone marrow dose Mean marrow dose
The practice of using fluoroscopy to determine the exact location of the central ray before taking a radiographic exposure Not condoned by the American Society of Radiologic Technologists (ASRT)
Fluoroscopically guided positioning (FGP)
3 benefits of fluoroscopically guided positioning (FGP)
Faster than having a repeat exposure Reduced the number of repeat exposures Provides less radiation exposure to the patient
Positioning using the radiographer's skill and anatomic landmarks, without repeat exposure; provides the patient with the lowest dose
What unit is x-ray output usually determined in?
Milligray per mAs at 100 cm (40 in) SID
Most medical procedures result in fetal exposures of less than what?
Less than 0.01 Gy
2 types of exposure effective dose does not include
Personal medical exposure Natural background exposure
Product of the average absorbed dose (D) in a tissue or organ in the human body and its associated radiation weighting factor chosen for the type and energy of the radiation in question for radiation workers
Equivalent dose (EqD)
4 imaging procedures that increase the radiographer's risk of exposure
General fluoroscopy (diagnostic) Mobile examinations C-arm fluoroscopy General radiographic procedures
2 ways for radiologists and radiographers to keep EfD and EqD doses well below their allowable maximal limits
Whenever applicable, applying the basic principles of time, distance, and shielding Always adequately collimating the radiographic beam
At a 90-degree angle to the primary x-ray beam, at a distance of 1 m, the scattered x-ray intensity is generally approximately what the intensity of the primary x-ray beam?
2 types of secondary radiation
Scatter radiation Leakage radiation
What is the minimum thickness protective aprons can be during fluoroscopy?
0.5 mm of lead equivalent
Maternity protective aprons consist of what lead equivalent over their entire length and width and also have an extra what mm lead equivalent protective panel?
0.5-mm lead equivalent 1 mm lead equivalent
Most effective means of protection from ionizing rdiation
The intensity of radiation is inversely proportional to the square of the distance from the source Expresses the relationship between distance and intensity (quantity) of radiation and governs the dose received As the separation between the radiation source and measurement point increases, the quantity of radiation measured at the more distant position decreases by the square of the ratio of the original new distance from the source; this decrease in radiation intensity physically occurs because the area, which the same flux of x-rays at the original location now covers at the new location, has increased by the square of the relative distance change When the distance from a point source of radiation is doubled, the radiation at the new location spans an area four times larger than the original area; however, the intensity at the new distance is only one fourth the original intensity
Inverse square law (ISL)
What is the formula for the inverse square law?
2 most common materials used for structural protective barriers
4 accessory protective devices made of lead-impregnated vinyl (devices provide protection when not behind a stationary barrier)
Aprons Gloves Thyroid shields Protective eyeglasses
3 factors the effectiveness of shielding material depends on
Atomic number Density Thickness
Prevent direct, or unscattered, radiation from reaching personnel or members of the general public on the other side of the barrier Located perpendicular to the undeflected/primary line of travel of the x-ray beam Ex: wall behind wall bucky
Primary protective barrier
2 specifications for a primary barrier at 130 kvp
Consists of 1.6 mm (1/16 inch) lead Extends 2.1 m (7 feet) upward from the floor of the x-ray room when the x-ray tube is 1.5 to 2.1 m (5 to 7 feet) from the wall in question
Radiation that has been deflected from the primary beam Made of leakage from the tube housing and scatter (primarily from the patient) radaition
Protects against secondary radiation (leakage and scatter radiation) Any wall or barrier that is never struck by the primary x-ray beam (this does not mean that secondary radiation cannot hit primary barriers as well) Walls that are not in the direct line of travel of the primary beam
Secondary protective barriers
2 specifications of secondary protective barriers
Should overlap the primary protective barrier by approximately 1.27 cm (1/2 inch) Consists of 0.8 mm (1/32-inch) of lead
Protects the radiographer from secondary radiation (leakage and scatter) Located in x-ray rooms housing permanent or nonportable radiographic equipment To ensure maximal protection during radiographic exposures, personnel must remain completely behind the barrier Exposure cord must be short enough that the exposure switch can be operated only when the radiographer is completely behind the control-booth barrier
2 specifications of the control-booth barrier
Must extend 2.1 m (7 feet) upward from the floor Must be permanently secured to the floor
Diagnostic x-rays should scatter a minimum of how many times before reaching any area behind the control-booth barrier?
The observation window in the control-booth barrier typically consists of what lead equivalent?
1.5-mm lead equivalent
With appropriate lead equivalent in the control-booth barrier, exposure of the radiographer will not exceed a maximum allowance of how much radiation per week; in actual practice in a well-designed facility, exposure should not exceed how much radiation per week?
1 mSv (100 mrem) 0.02 mSv (2 mrem)
Contains clear lead-acrylic material impregnated with approximately 30% lead by weight Permits a panoramic view, allowing diagnostic imaging personnel to observe the patient more completely
Clear lead-acrylic secondary protective barrier
3 specifications of modular x-ray barriers
Shatter resistant Can extend 2.1 m (7 feet) upward from the floor Available in lead equivalency from 0.3 to 2 mm
Clear lead-acrylic overhead protective barriers can be used as overhead x-ray barrier to provide an open view during special procedures and cardiac catheterization; shielding typically offers what lead equivalency protection?
0.5-mm lead equivalency
For 100 kVp, an apron must be equivalent to at least what thickness of lead?
Protective gloves must have what lead equivalent?
0.25-mm lead equivalent
What is the minimum lead equivalent for thyroid neck shields?
0.5-mm lead equivalent
What is the minimal lead equivalent protective level for protective eyeglasses
A spot film device protective curtain, or sliding panel, should have a minimum of what lead equivalent and should normally be positioned between the fluoroscopist and the patient to intercept scattered radiation above the tabletop?
0.25-mm lead equivalent
A bucky slot shielding device should have at least what lead equivalent and must automatically cover the bucky slot opening in the side of the x-ray table during a standard fluoroscopic examination when the bucky tray is positioned at the foot end of the table which protects radiologist and radiographer at gonadal level ?
0.25-mm lead equivalent
For mobile x-ray units that are non-remote-controlled, the cord leading to the exposure switch must be long enough to permit the radiographer to stand at least how far from the patient, the x-ray tube, and the useful beam (permits use of ISL)?
2 m (approximately 6 feet)
Radiographer should attempt to stand how to the x-ray beam–scattering object (the patient) line (when protection factors of distance and shielding have been accounted for, this is the place at which the least amount of scattered radiation is received)?
At a right angle (90-degrees)
During c-arm fluoroscopy, the exposure rate caused by scatter near the entrance surface of the patient (the x-ray tube side) ________ the exposure rate caused by scatter near the exit surface of the patient; the location of the _______ potential scatter dose is on the side of the patient away from the x-ray tube (i.e., the image intensifier side)
In most facilities room doors have attenuation for diagnostic energy x-rays equivalent to that provided by how much lead?
0.8 mm (1/32 inch) of lead
8 radiation-absorbent barrier design considerations
The mean energy of the x-rays that will strike the barrier Whether the barrier is of a primary or secondary nature The distance from the x-ray source to a position of occupance 0.3 m from the barrier Workload of the unit Use factor of the unit Occupancy factor behind the barrier Intrinsic shielding (e.g., tube housing attenuation) of the x-ray unit Whether the area beyond the barrier is "controlled" or "uncontrolled"
3 categories of radiation sources generated in an x-ray room
Primary radiation Scatter radiation Leakage radiation
Emerges directly from the x-ray tube collimator and moves without deflection toward a wall, dorr, viewing window, and so on Energy has not been degraded by scatter, and substantial portions of the initial beam may not have been attenuated
Primary radiation Direct radiation
Must be posted in any room or area where radioactive materials or radiation sources are used or stored Should be obvious and easy to read The word caution usually appears at the top of the sign, followed by the conventional three-blade radiation symbol and then specific words such as radiation area, high radiation area, or very high radiation area to make persons approaching the area aware of the radiation hazard Required to have the radiation symbol colored magenta, purple, or black on a yellow background
Atoms that have the same number of protons within the nucleus but have different numbers of neutrons
Some isotopes have too many neutrons or protons; because of this, such isotopes spontaneously undergo changes or transformations to rectify the understandable arrangement
Unstable and therefore radioactive isotope of the element iodine Prostate tracers are permanently implanted for prostate radiation therapy
For a patient with thyroid cancer, it is desirable to strongly irradiate any residual thyroid tissue not removed by surgery using this isotope
How thick are rolling lead shields?
Positron emission tomography
What is the dose limit suggested by the EPA during an emergency situation for individuals engaged in nonlifesaving activities?
50 mSv per event
What is the dose limit suggested by the EPA during an emergency situation for individuals engaged in lifesaving activities?
250 mSv per event