Radiation Protection in Digital Radiology

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Radiation Protection in Digital Radiology

• Optimisation in CR DR
• L03

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Educational Objectives

• Provide rationale for optimisation in Computed
  Radiography (CR) and Digital Radiography (DR)
• Describe components of optimisation and specific
  methods to detect, correct, and avert errors in
  CR and DR
• Identify standards and references for
  optimisation in CR and DR

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Optimisation includes

• All activities that ensure consistent, maximum
  performance from physician and imaging facility1
  
• A distinct series of technical procedures which
  ensure the production of a satisfactory product
• Four steps
• Acceptance Testing (AT)
• Establishment of baseline performance
• Diagnosis of changes in performance
• Verification of correction of deterioration

1National Council on Radiation Protection and
Measurements. (1988) Quality Assurance for
Diagnostic Imaging, NCRP Report No. 99, Bethesda,
MD
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Optimisation includes both personnel and equipment

• Identifying aspects of facility operation that
  require decisions or actions
• Establishing policies with respect to these
• Encouraging compliance through education and
  recognition
• Analyzing records at regular intervals
• Dose optimisation
• Image quality optimisation

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Whats my motivation?

• Regulatory Compliance
• International BSS
• National Regulations
• Standards of Care
• Standards established by professional societies
• Providing the highest quality medical care
• MANAGING RADIATION DOSE!!!

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Factors that affect image quality and patient dose
Factor Contrast Resolution Noise Patient Dose
Focal spot size X
Off-focus radiation x (x) x
Beam filtration x X
Voltage waveform (x) x x
kVp X (x) X
mA (x)
S X
mAs (x) X X
SID X X
Field size X X
Scatter rejection X X
X very important connection x sometimes
significant (x) sometimes noticeable
Wolbarst (1993) Table 19-1
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Quantifiable Consequences of Degraded Performance

• Loss of Contrast Sensitivity
• Loss of Sharpness/Spatial Resolution
• Loss of Dynamic Range
• Increase in Noise
• Decrease in System Speed
• Geometric Distortion
• artefacts

• Decrease in diagnostic accuracy
• Increase in observer time/fatigue
• Delay of diagnosis
• Increase in patient radiation dose
• Decrease in efficiency of imaging operation

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Inherent limitations of human operators

• Every process that depends on a human is a source
  of random errors
• Every process that automation performs
  independently is source of systematic errors.
• Human errors increase exponentially with the
  complexity of the system and operator interface.
• It is not a question of whether, but when errors
  will occur.

?
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Someone has to reconcile the checking account

• The technologist/supervisor must accept
  responsibility for appropriate delivery of all
  images to the physician.
• Processes must be in place to verify that all
  exams performed and all images acquired reach
  their intended destinations (note an image count
  of two does not necessarily mean both the PA and
  LAT views!).
• Processes must be in place to correct errors when
  detected.

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Some traditional components of optimisation

• QA Committee
• Policies and Procedures
• Reject Analysis
• Radiologist Film Critique
• Operator QC Activities
• Service Events
• Technologist In-service training
• Medical Physicist QC Activities
• Incident investigation/troubleshooting
• Error log maintenance

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Reject Analysis once considered unnecessary with
CR/DR

• Low repeat rates initially reported with DR
• DR is tolerant of incorrect exposure factor
  selection
• Criteria for improper exposure lacking
• Most DR systems include QC Workstations
• Capacity to modify non-diagnostic images before
  release
• Bad electronic DR images can disappear without a
  trace

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Conventional Reason for Repeated Exam

• Artefacts
• Mispositioning
• Over-collimation
• Patient motion
• Double exposure
• Inadequate inspiration

• Overexposed - too dark
• Underexposed - too light
• Marker missing or wrong
• Wrong exam
• Wrong patient
• Film lost in processor

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CR/DR Reason for Repeated Exam

• Overexposed - high exposure index
• Underexposed - low exposure index
• Marker missing or wrong
• Wrong exam
• Wrong patient
• Lost image
• corrupt data, cannot transfer
• deleted by operator (waste bin)
• Auto-pilot

• Artefacts
• Mispositioning
• Over-collimation
• Patient motion
• Double exposure
• Inadequate inspiration

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How does one perform reject analysis?

• Develop method for capturing rejects
• Collect data
• 3 vs. 12?
• Analyze data
• Report results to management and staff
• Implement training as indicated
• Share results with vendors

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How can electronic system accommodate reject
analysis?

• Develop codes for Radiologist exam critique
• QC Techs append critique code to patient name and
  modify Accession number, and Exam Description
  (Procedure) Fields
• None files archived as usual
• Modified exam routing tables prevent widespread
  dissemination of rejected images
• None files available for review

Some vendors implement reject analysis
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DR systems must be operated properly to make good
images!

• Select the proper examination
• Properly associate demographic and exam
  information to image
• Properly manipulate the detector
• Review the image before releasing
• Know how to recover from errors without repeating
  examination
• Follow exposure factor control limits
• Select appropriate factors for paediatrics and
  young adults

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Human operators need to know what is expected of
them.
CRITICAL ELEMENTS CRITICAL ELEMENTS S U
OPERATOR LEVEL OPERATOR LEVEL
1 Has knowledge of the following status changes and how to differentiate between them.
a. "WARNING"
b. "LOCKED"
c. "ERROR"
2 Demonstrates ability to differentiate between an error "CODE" message and a "Service" message
3 Demonstrates the ability to properly identify the cassette and image plate location on the displayed pictogram when a jam occurs.
4 Has knowledge that the RESET button should never be pressed by personnel other that an AGFA service engineer.
5 Has knowledge of the correct extension to call the PACS Trouble call line.
SUPERVISOR LEVEL SUPERVISOR LEVEL
6 Demonstrates ability to clear a plate jam in the Upper Section of the ADC70 by performing the proper sequence of events.
a. Makes sure there are no cassettes protruding through the emergency slot.
b. Properly raises the top cover.
c. Locates and unlocks support rod, and secures top cover into position with support rod.
d. Properly removes any jammed cassettes or image plates.

• Vendor applications training is never sufficient.
• Local policies and practice must be developed,
  communicated, documented, reinforced, and
  enforced.
• Clinical Competency Criteria are helpful for
  standardizing and documenting basic proficiency
  training.
• Training must be tailored for technologists,
  radiologists, clinical engineers, and PACS
  personnel.
• Radiation protection training of referring
  physicians should also be considered.

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So how do you go about establishing optimization?

• Define hospital processes from scheduling patient
  to reporting diagnosis (workflow analysis)
• Define PACS components and processes that support
  hospital processes (IHE references, system
  architecture)
• For each hospital process, identify operational
  roles and responsibilities (task allocation
  matrix)
• Identify reasonable failure scenarios. Identify
  single points of failure. Minimize by
  redundancy. (failure modes and effects analysis)
• Institute performance measures that indicate when
  processes are working and detect, correct, and
  document errors. Add to the task allocation
  matrix.
• Create, document, test, and train downtime and
  recovery procedures.
• Periodically review and publicize the results of
  measurements and adjust as needed.

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Reasons for differences between CR and DR
optimisation

• CR cassette-based vs. integrated receptor DR
• Cleaning
• Physical defects
• Erasure
• Mis-identified patient, view, orientation
• Need adequate knowledge of radiographic technique
• Separation between image acquisition and
  development
• Time
• Geographic (PACS)
• Distinctions are blurring
• Poorly integrated DR
• Integrated CR

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Consider QC procedures to be a series of sieves
Errors
RT Radiography Technologist
Caught by RT before exam
Caught by RT after exam
Caught by Supervisor
Passed on to Radiologist
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Which image is worse?
Reported by radiologist
Subsequent image, same machine, reported by same
radiologist
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Process map

• Flowchart of steps
• Identify potential QC control points
• actions to be taken
• Identify work-arounds
• Example What if RIS is out-of-service?
• How to continue operations?
• Dont forget actions on restoration of service

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Step 1. Patient reports for an examination.

• The technologist verifies
• the patient is the person identified in the exam
  request
• the anatomy to be examined matches the exam
  request
• other information about the patient, such as
• Pregnancy
• Restricted motion
• Allergies
• Appliances
• QC accomplished by training or checklist

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Step 2. Technologist identifies the patient and
exam to the imaging system

• Usually occurs before, but sometimes after the
  exam is performed
• Misidentification has consequences
• incorrect information can cause image
  unavailability
• incorrect exam info can affect image development
• mis-association complicates error detection
• proliferation of digital images complicates
  correction
• Automation of association imperfect QC!
• New classes of errors

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The best image, improperly identified, is useless.

• Consequences of misidentification
• Broken studies
• Orphans
• Exceptions
• Penalty Box

• Automation of association
• RIS interfaces
• Bar code scanner augmentation
• DICOM Modality Worklist Management (MWL)
• unscheduled exams
• resource re-allocation

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Step 3. Technologist positions the patient in the
radiation field and performs the examination

• Potential errors
• mispositioning
• patient motion
• incorrect radiographic technique selection
• poor inspiration
• improper collimation
• incorrect alignment of x-ray beam and grid
• wrong exam performed
• double exposure
• QC accomplished at acquisition station?
• Image processing inadequate to correct
• Correction requires repeated exam (s)

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Results Rejects during one month
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Step 4. Image receptor captures the radiographic
projection

• Potential errors
• Inadequate erasure, lag, ghosting
• Improper compensation for non-uniform gain
• Incorrect gain adjustment
• Incorrect exposure factor selection
• artefacts
• Interference with the projected beam
• Receptor defects
• Interference with converting the captured
  projection into a digital image
• Detection possible at acquisition station?
• Correction may require repeated exam
• Can be averted by active QC

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Active QC countermeasures emphasize avoiding
vs. correcting errors

• Prophylactic erasure at start of shift
• Periodic checks of non-uniformity corrections
• Periodic gain re-calibration
• Technique guide
• Periodic checks of Automatic Exposure Control
  (AEC) calibration
• Periodic cleaning of equipment and environment
• Thorough Acceptance Testing of new receptors
• Also incidental to service events and software
  upgrades

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Step 5. Image receptor renders the captured
projection for viewing

• Potential errors
• Incorrect Exposure Field recognition incorrect
  determination of values of interest (VOI)
• Incorrect histogram re-scaling
• Incorrect gray-scale rendition
• Incorrect edge restoration
• Inappropriate noise reduction
• Incorrect reorientation
• QC possible at acquisition station?
• Correction usually possible without repeated exam

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Functions of the QC workstation sometimes
integrated into acquisition station

• Modify image processing
• Imprint demographic overlays
• Add annotations
• Apply borders or shadow masks
• Flip and rotate
• Increase magnification
• Conjoin images
• Scoliosis
• Full leg
• Modify sequence of views
• Verify exposure indicator
• Select images for archive
• Delete images

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Step 6. Acquisition station transfers the image
to the archive

• Potential errors
• Transmission failure
• Image deletion from local cache
• Information omitted from transmitted image
• Exposure indicator
• Processing parameters
• Shutters
• Annotations

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Step 7. Digital image is displayed for viewing by
a physician

• Potential errors (hard or soft copy)
• Incorrect GSDF calibration
• Inadequate matrix
• Moire (interference) patterns
• Inadequate spatial resolution
• Incorrect or missing demographics or annotations
• Inadequate viewing conditions
• Errors not filtered by previous QC
• QC gt Radiologist Film critique

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Task Allocation Matrix

Task Responsibility Frequency
Verify Patient ID and exam info Radiographer Each exam
Verify Patient Positioning Radiographer Each view
Verify Image Quality release or repeat Lead Radiographer Each image
Verify exam in PACS Lead Radiographer Each exam
Reconcile patient data/image counts in PACS Medical Informatics Incidental
Report substandard images Radiologist Incidental
Erase cassette-based image receptors Radiographer Start-of-shift
Test image receptor uniformity Radiographer Weekly
Clean cassette-based image receptors Radiographer Monthly
Compile and review reject analysis data Lead Radiographer Monthly
Verify display calibrations Clinical Engineer Quarterly
Review QC indicators QA Committee Quarterly
Verify receptor calibrations Medical Physicist Semi-Annual
Verify x-ray generator functions Medical Physicist Annual
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Get the radiologists actively involved.

• Key element to any successful optimization
  program.
• Incidental guidance valuable.
• Radiologists Film Critique more valuable.
• Codes transcribed into report
• includes availability and quality items
• documents causes and frequency of substandard
  imaging tracks improvement
• mechanism for establishing responsibility for
  quality of service

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New accommodations for testing in CR
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Value of automated self-tests

• Some manufacturers provide automated self-tests
• Should provide operator with assurance that unit
  is ready for clinical use
• Actions should be clearly indicated by faults
• Should provide longitudinal information on system
  performance

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What do you do with the QC data?

• Because systems are relatively new, manufacturers
  are uncertain about longitudinal data
• Lower limit for test is MTF _at_ 2.5 lp/mm 17
• CsI(Tl) is hygroscopic columnar structure is
  degraded
• Both systems depicted required detector
  replacement

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Commitment to optimisation

• The optimisation effort is integral to how you
  organize and perform the work.
• The cost of optimisation is trivial compared to
  the cost of inefficiency consider one bad
  patient outcome.
• Training for optimisation is professional
  development for hospital staff.
• Leverage local resources for optimisation
  expertise.
• Biomedical engineering
• Medical informatics / Information services
• Medical Physicists
• Hospital QA personnel

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Who is responsible for optimisation?(It takes a
village )

• Physician responsible for clinical service is
  ultimately responsible
• Medical Physicist oversees the program
• Radiographer makes day-to-day measurements,
  verifies post-repair integrity
• Service engineer carries out repairs, PM,
  calibrations

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Answer True or False

• Random error is a source of inherent limitation
  of human operators
• It is the responsibility of the physician to
  ensure appropriate delivery of all images to PACS
• High doses can go undetected with the use of DR
  or CR systems

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Answer True or False

• True. Every process that depends on a human
  operator is a source of random errors and every
  process that automation performs independently is
  source of systematic errors.
• False. The technologist/supervisor is responsible
  for appropriate delivery of all images to the
  PACS
• True. DR and CR have wide latitude and high doses
  can go undetected. Optimised exposure parameters
  should be used in digital systems.

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References
Comprehensive QC Plan for CR
Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR