Chapter 31 Quality Control

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Chapter 31 Quality Control

• Two areas of activity are designed to ensure the
  best possible image quality with the lowest
  possible exposure and minimum costs.
• Quality Assurance deals with people
• Quality Control deals with instrumentation and
  equipment.

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Ten Step Approach to Quality Assurance

• Assign responsibility
• Delineate scope of care
• Identify aspects of care
• Identify outcomes that effect the aspects of
  care.
• Establish limits of the scope of assessment.

3
Ten Step Approach to Quality Assurance

• Collect and organize data.
• Evaluate care when outcomes are reached.
• Take action to improve care
• Assess and document actions
• Communicate information to organization-wide QA
  Program

4
QA Projects

• Things that QA can evaluate includes
• Scheduling of patients
• Instructions given to patients
• Wait times in the office
• Interpretation of films
• Retake analysis
• Record accuracy

5
QA Program

• Quality Assurance deals with people and processes
  used to complete tasks.
• QA involves training and record keeping.
• As the owner of the equipment, you will be
  responsible for your radiology services.
• The State of California Department of Radiologic
  Health established the Standards of Good Practice
  that is the foundation of QA and QC in
  radiography.

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QA and QC Requirements

• Degree of requirements vary by state. California
  and New York have very tight standards for
  quality control of the radiographic and
  processing equipment.
• We are required by statue to teach QA and QC in
  the radiology program. It is covered in detail in
  9th Quarter. My textboook covers QC in detail.

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Quality Control

• An acceptable QC program has three steps
• Acceptance Testing
• Routine performance monitoring
• Maintenance

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Acceptance Testing

• The x-ray machine, cassettes and film processor
  or digital system are the largest capital expense
  you may experience.
• It makes economic sense to make sure that the
  equipment meets the performance standards.
• It is recommended that a third party such as a
  health physicist do the testing.

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Acceptance Testing

• Areas that should be tested include on the x-ray
  machine
• Shielding of Room
• Focal spot size
• Calibration of mA, timer or mAs
• Calibration of kVp
• Linearity of exposure
• Beam alignment
• Grid centering
• Collimation
• Filtration (HVL)

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Acceptance Testing

• Areas that should be tested on the x-ray
  cassettes
• Screen contact
• Screen speed
• Light leaks
• Light spectrum matching

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Acceptance Testing

• Areas that should be tested on the x-ray film
  processor
• Developer temperature
• Replenishment rates
• Travel time
• Water flow
• Hypo retention

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Quality Control

• The acceptance testing ensures that the machine
  was installed and calibrated properly.
• The performance may drift or deteriorate over
  time. Consequently, periodic testing is required
  to monitor the performance.
• With the exception of film processing most
  testing is annual or semiannual.

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Quality Control

• After a major repair, the machine should be
  retested to ensure that it was repaired properly.
• When the testing shows that the machine is not
  performing properly, service or preventive
  maintenance is required.
• Manufactures establish recommended preventive
  service schedules. When these are followed many
  repairs become unnecessary.

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Radiographic Quality Control

• Areas of concern in x-ray machine
• Focal Spot Size will impact spatial resolution
• Filtration will impact patient exposure
• Collimation will impact patient exposure
• kVp calibration will impact image quality and
  exposure.
• Exposure timer accuracy will impact image quality
  and exposure

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Radiographic Quality Control

• Areas of concern in x-ray machine
• Exposure linearity will impact exposure and image
  quality
• Exposure reproducibility will impact exposure and
  image quality.
• Alignment of tube and image receptor will impact
  exposure and image quality.

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Focal Spot Testing

• When the machine is installed or the tube is
  replaced, the focal spot size should be measured.
  Then annually thereafter.
• A pin hole camera, star test pattern or line pair
  test tool.
• As the tube ages, the focal spot tends to grow
  and spatial resolution is lost.

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Filtration

• The filtration is measured but determining the
  half value layer of the beam at specific exposure
  levels. Minimum filtration is 2.5mm aluminum.
• As a tube ages, tungsten will plate the x-ray
  port and increase filtration. This can cause
  technique problems. Inadequate filtration will
  significantly increase patient exposure.

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Collimation

• If the collimation is misaligned, intended
  anatomy can be missed.
• It can be tested in many ways from using pennies
  to using test patterns.
• Misalignment can not exceed 2 of the SID.
• It is tested semiannually and after the
  replacement of the collimator lamp.

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kVp Calibration

• In diagnostic radiology, any change will impact
  patient exposure. A variation of about 3 will
  impact contrast and image density.
• Can be tested with filtered ion chambers,
  filtered photodiodes or even a cassette with
  calibrated filters.
• Tested annually.

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Exposure Timer Accuracy

• The exposure time is the responsibility of the
  operator. It will impact the density of the image
  and spatial resolution.
• Tested with an ion chamber, multi-meter
  internally or even a spinning top.
• Exposure time must be within 5 for exposure
  times greater than 10 ms and 20 less than 10 ms.

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Exposure Linearity

• Many combinations of mA and time will produce the
  same mAs value. The ability of the machine to
  produce a constant level of exposure with various
  combinations of mA and time is called exposure
  linearity.
• Can be tested with a step wedge and densitometer
  or rate meter.
• Should be within 10 for adjacent stations.

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Exposure Reproducibility

• Any exposure using the same factors should
  produce the same level of density and contrast on
  the image.
• Sequential exposure should be reproducible to
  within 5
• Can be tested with a rate meter or step wedge and
  densitometer.

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Performance standards for x-ray equipment
24
Darkroom and Processing

• The development of the image is dependent upon
  the temperature of the developer, its
  concentration and how long the film is in the
  developer.
• The film is sensitive to variations in the
  environment and processing from the time it is
  manufactured until it is processed.
• Darkroom and Processor QC is the key process of
  Quality Control.

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Processing

• Processor densitometry is performed daily before
  the first patient is exposed.
• A sensitometer is used to produce a step wedge
  image on the film that is evaluated with a
  densitometer.
• The densitometer reads the optical density of the
  processed image.
• A digital thermometer is used to test the
  chemical temperatures in the processor.

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Processing

• Key densities on the processed film are measured
  and then graphed.
• Base plus Fog is measured on an area of unexposed
  film to check the darkroom environment.
• Speed is tested at the level of exposure that
  produces a density of 1.25OD
• Contrast is tested at the level that produced a
  density of 0.40 OD and one that produced a
  density of 2.20.

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Processing

• By monitoring these densities, problems with film
  processing can be detected before image quality
  deteriorates.
• In 9th Quarter we will cover how to perform
  processor QC and problem solve.

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Waste Records

• Since used fixer is classified as a hazardous
  waste material, it is important to maintain
  accurate records of usage and disposal.
• The extent of records vary by city, county and
  state. You are responsible for the proper
  disposal of the waste. Some regions include
  developer as hazardous waste.

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Silver Recovery

• If the silver ions are removed from the fixer, it
  may be disposed of in the normal waste when
  diluted with water.
• There are two primary types of silver recovery
  systems.
• Metallic replacement uses steel wool and can
  recover 95 of the silver in the effluent
• Electrolytic recovery passes direct current
  through the solution and nearly pure metallic
  silver is deposited on the cathode.

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Silver Recovery

• Old radiographic films and repeated films are
  retained for silver recovery. X-ray images can
  not be disposed of in normal trash.
• They also can not be used to clean the processor
  rollers.
• Waste recovery companies will either burn or
  chemically remove the silver from the film.

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Performance standards for film processor and
darkroom equipment
32
Accessory QC

• The cassettes and screens are the area of chief
  concern. Problems with either will result in
  artifacts on the images and increased retakes.
• The screens need to be properly cleaned
  frequently. Mammography screens are cleaned
  daily. California recommends monthly cleaning.

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Accessory QC

• Dirty screens produce white artifacts on the
  image.
• Multiple white artifacts indicate the need to
  replace the screens.
• Screen contact is tested semiannually. A problem
  with screens contact will cause a loss of
  resolution.
• As screens age, they loose speed so this is also
  tested.

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Accessory QC

• The other important accessory is the gonad
  protection devices and lead aprons.
• Improper care of the apron can result in cracks
  and holes in the lead that reduces their
  effectiveness.
• Aprons and shields are tested semiannually. The
  easiest was to test them is with
  video-fluoroscopy but film can be used.

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Performance Standards for Accessories
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Failed Lead Apron Test
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Record keeping

• All electromechanical devices need periodic
  service.
• There are three types of maintenance.
• Scheduled maintenance such as processor monthly
  or weekly service. It includes observing moving
  parts and lubrication.
• Preventive maintenance is planned service and
  replacement of parts at regular intervals before
  they fail at inopportune times.

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Record keeping

• Non-scheduled maintenance is the worst type of
  service because it impacts patient service. It
  may also be very expensive.
• With proper scheduled and preventive maintenance,
  non-scheduled service can be minimized.
• All service schedules should meet manufacture
  recommendations.
• All service should be documented as part of the
  quality assurance program.

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Retake Analysis

• Required part of a QA program in California.
• Evaluation includes
• View repeated
• Cause of the repeat
• Rate of retakes should be less than 5.
• Information can be gathered from the log that the
  state mandates for patients being exposed to
  radiation.

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Retake Analysis

• Done every three months using a relatively large
  sample of data to see trends in
• Type of examination being repeated.
• Reasons for the repeated films.
• Determine if additional training or review is
  needed.
• Determine if equipment service might be required.

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Repeat Analysis

• Your patient log can be designed to capture both
  films usage and repeated films.
• Data is gathered from log for analysis
• Repeated films can be put into two main
  categories
• X-ray Personnel Errors
• Equipment malfunctions

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X-ray Personnel Errors

• Failure to measure patient.
• Use of improper technical factors (mAs, kVp or
  distance)
• Incorrect positioning
• Improper Collimation
• Improper use of accessories such as cassettes,
  grids or filters

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X-ray Personnel Errors

• Improper handling of exposed or unexposed films.
• Failure to clearly communicate to the patient
  breathing instructions and to remain still.
• Failure to observe patient during exposure.

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X-ray Equipment and Accessory Failure or
Malfunctions

• Inaccurate calibration of kVp and mA.
• Inaccurate timer calibration
• Dirty or damaged cassettes
• Improperly labeled or damaged grids
• Malfunctioning collimator
• Improper film storage or processor function.

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Reasons for Retake Films

• Over or under exposure accounts for over 50 of
  retakes nationally.
• Errors in positioning (25)
• Patient motion 11
• Processing errors 6
• Wrong view, beam alignment,cassette screen or
  grid errors and artifacts.

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Retake Films by Region

• Cervical Spine Exams 7
• Thoracic Spine Exams 17
• Lumbar and Abdominal X-rays 40
• Skull, Chest,Lower Extremities 15
• Majority or retake results in unnecessary
  exposure to gonads or blood forming organs of the
  body.

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Daily Log Design

• Most regulatory agencies will require a log of
  patients having radiation exposure.
• Columns can be added to capture film usage,
  repeats, views repeated and reason.
• This data can be gathered and analyzed.

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Retake Analysis

• In this example, most of the retakes were of the
  T-spine. Potential reasons include
• Improper use of filters
• Incorrect measurements
• Faulty technique chart

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Retake Analysis

• The reason of each retake is recorded and
  percentages are computed to determine the
  overall rate and rate by reason.
• Less than 5 is ideal.

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Quality Assurance and Digital Radiography

• Information gathered for this lecture came from
  American College of Radiology Practice Guidelines
  for Digital Radiography 10/10/07
• Quality Management in The Imaging Sciences
  Jeffrey Pap Mosby 1998

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The Digital Radiography Advantage

• Digital Radiography offers many advantages over
  film based radiography.
• Film response to radiation follows a sigmoid
  response curve while digital response is linear.
  This results in a much wider dynamic response to
  exposure. The advantages include
• Reduced retakes due to exposure factors.
• Improved contrast resolution.
• Improved latitude.

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The Digital Radiography Advantages

• Much of the quality assurance for film based
  radiography is to assure proper photographic
  processing of the image. This is eliminated
  unless a film printer or multi-format camera is
  used.
• Less space and perhaps less staff is required
  because of reduced storage space requirements.
  Images can be stored on a hard disk or CD.

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The Digital Radiography Advantages

• If the images are left in digital format, no
  darkroom or darkroom personnel is needed.
• No film, processing chemistry and waste recovery
  costs.
• Computed Radiography can be added to existing
  equipment. Direct Digital requires a total
  replacement of the image receptor.

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Computed Radiography and Quality Control

• Computed radiography still uses conventional
  radiographic equipment so basic radiography
  quality control testing is still needed. This
  would include
• Calibration of the generator
• Collimation
• Beam Alignment
• Collimation
• Linearity of exposure
• Spatial resolution (focal spot)

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Computed Radiography and Quality Control

• Calibration of the generator.
• The linear dose response can be a double edged
  sword. It can mask calibration problem that can
  result in higher patient exposure.
• Over exposed images really look good so this has
  resulted in dose creep.
• Collimation Beam Alignment
• Collimation is critical for the computer to
  determine the proper contrast and density scale.
• Spatial resolution (focal spot)
• Film can record greater spatial resolution than
  digital radiography so resolution should be
  monitored more often than film based systems.

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Computed Radiography and Quality Control

• We have discussed much of the radiographic
  quality control earlier.
• The end product in radiography is the image and
  accurate report of findings.
• Therefore for film, the processor function,
  screen contract and artifact avoidance was
  critical.
• With digital radiography the computer monitor,
  image transfer and image receptor plate become
  the critical areas for quality assurance.

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Monitor Testing

• The acquisition workstation and secondary
  displays should be tested frequently using a
  standard image test pattern.
• The SMPTE RP-133 (Society of Motion Picture and
  Television Engineers) or AAPM TG-18 QC test
  patterns are suitable.

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Using the SMPTE Test Pattern

• As a image fidelity test, the test pattern data
  files should be sized to occupy the full area
  used to display images.
• The overall SMPTE image appearance should be
  inspected to assure that absence of gross
  artifacts.

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Using the SMPTE Test Pattern

• There should be no blurring or bleeding of bright
  display areas into dark areas or aliasing of the
  spatial imaging patterns.
• All monitors used for interpretation should be
  tested at least monthly.

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Using the SMPTE Test Pattern

• For the dynamic range test, both the 5 and 95
  contrast areas should be visible and distinctly
  different than the adjacent 0 and 100 areas.
• Therefore

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Using the SMPTE Test Pattern

• The brightness and contrast of the monitor is
  adequate if the 5 squares at both ends of the
  gray scale are visible.
• The gray scale is shown as a series of squares in
  the center of the image that range from black
  (0) to white (100).

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Using the SMPTE Test Pattern

• It may be difficult to get the monitor to show
  both of these inner squares perfectly.
• Most monitors do better showing the 95 square
  than the 5 square.
• However, you might try adjusting the ambient
  light to improve the visibility of the 5 square.

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Spatial Resolution Aliasing

• The spatial resolution (linearity) and aliasing
  (distortion) of the monitor are within acceptable
  limits if the high contrast bar patterns in the
  test image are distinct as simple black and white
  pairs.

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Spatial Resolution Aliasing

• In each corner and the very center of the image,
  inspect the six squares filled with varying
  widths of alternating black/white horizontal and
  vertical lines.

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Spatial Resolution Aliasing

• You should be able to differentiate all the lines
  from fat to narrow (6 pixels, 4 pixels and 2
  pixels) and both horizontally and vertically.

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BWH Pattern

• The BWH pattern is a test of the continuous gray
  scale from the center to outside of the pattern.
• It was developed at the Brigham Women's Hospital
  Radiology Department.

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BWH Pattern

• No concentric ring like features should be
  present in the image.
• If they are present, the images displayed on your
  system will be of less than optimum quality.

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New TG-18 Monitor QC

• The TG-18 Monitor QC test pattern combines
  features of the SMPTE pattern with resolution
  tests.
• New patterns with chest, breast and knee images
  are coming available soon.

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End of Lecture