Transcript Radiation Protection in Digital Radiology

Radiation Protection in Digital Radiology
Optimisation in CR & DR
L03
IAEA
International Atomic Energy Agency
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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Radiation Protection in Digital Radiology
L03 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 …
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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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
Optimisation includes both personnel
and equipment
• Identifying aspects of facility operation that require
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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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“What’s 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
Focal spot size
X: very important
connection
x: sometimes
significant
(x): sometimes
noticeable
Off-focus
radiation
x
Beam filtration
x
Voltage
waveform
(x)
kVp
X
(x)
Patient Dose
x
X
x
mA
(x)
S
X
mAs
Noise
X
(x)
SID
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Resolution
x
(x)
X
X
X
X
X
Field size
X
X
Scatter rejection
X
X
Wolbarst (1993) Table 19-1
Radiation Protection in Digital Radiology
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Quantifiable Consequences of Degraded
Performance
• Loss of Contrast
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Sensitivity
Loss of
Sharpness/Spatial
Resolution
Loss of Dynamic
Range
Increase in Noise
Decrease in System
Speed
Geometric Distortion
artefacts
• Decrease in
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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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
Some traditional components of
optimisation
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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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
Conventional Reason for Repeated Exam
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Artefacts
Mispositioning
Over-collimation
Patient motion
Double exposure
Inadequate inspiration
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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
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Artefacts
Mispositioning
Over-collimation
Patient motion
Double exposure
Inadequate inspiration
• 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
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How does one perform reject analysis?
• Develop method for capturing rejects
• Collect data
• 3% vs. 12%?
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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
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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.
• 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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CRITICAL ELEMENTS
S
U
OPERATOR LEVEL
1
Has knowledge of the following status changes and how to differentiate
between them.
a. "WARNING"
b. "LOCKED"
c. "ERROR"
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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.
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Has knowledge of the correct extension to call the PACS Trouble call
line.
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.
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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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L03 Optimisation in CR and DR
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
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Subsequent image, same machine,
reported by same radiologist
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Process map
START
• Flowchart of steps
• Identify potential QC
1. Patient arrives in
imaging department
2. Is exam
scheduled?
control points
3. Verify
exam with
physician
Y
• actions to be taken
5."Arrive"
patient in RIS
• Identify “work-arounds”
• Example: What if RIS is
out-of-service?
• How to continue
N
4. Schedule exam in
RIS
6. Escort patient
to exam room
END
7. Explain exam
to patient
QC?
18. Release patient
operations?
• Don’t forget actions on
restoration of service
8. Select and ID
cassettes
QC?
17. Complete exam
in RIS
9. Position patient,
cassette, x-ray tube
16. Release images
to PACS
10. Perform exam
QC?
QC?
11. Scan cassette
QC?
12. Preview images
QC?
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QC?
N
15. Repeat
necessary?
Y
QC?
Y
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13. Repeat
necessary?
N
14. Review
images at QC
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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
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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:
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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
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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
Reason
mispositioned
artifacts
test images
nondiagnostic
patient motion
misplaced marker
no marker
under-exposed
inadequate contrast
over-exposed
wrong exam
wrong patient
T o ta l
N umb e r %
240
53.3%
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8.9%
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4.9%
20
4.4%
14
3.1%
10
2.2%
6
1.3%
5
1.1%
4
0.9%
2
0.4%
2
0.4%
2
0.4%
450 100.0%
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Step 4. Image receptor captures the
radiographic projection
• Potential errors
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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
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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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L03 Optimisation in CR and DR
Functions of the QC workstation:
sometimes integrated into acquisition station
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Modify image processing
Imprint demographic overlays
Add annotations
Apply borders or shadow masks
Flip and rotate
Increase magnification
Conjoin images
• Scoliosis
• Full leg
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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
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Exposure indicator
Processing parameters
Shutters
Annotations
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L03 Optimisation in CR and DR
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 => Radiologist “Film” critique
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L03 Optimisation in CR and DR
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.
• Radiologist’s 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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
New accommodations for testing in CR
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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
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
2
R = 0.8897
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MTF @ 2.5 lp/mm
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2/13/2002
9/1/2002
3/20/2003
10/6/2003
4/23/2004
11/9/2004
5/28/2005
12/14/2005
Date
A6 QAP data
y = -0.0023x + 104.85
R2 = 0.2349
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Spatial MTF at 2.5 lp/mm
relatively new,
manufacturers are
uncertain about
longitudinal data
• Lower limit for test is MTF
@ 2.5 lp/mm = 17%
• CsI(Tl) is hygroscopic –
columnar structure is
degraded
• Both systems depicted
required detector
replacement
y = -0.0052x + 218.2
XQi C1
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3/20/03
6/28/03
10/6/03
1/14/04
4/23/04
8/1/04
11/9/04
2/17/05
5/28/05
9/5/05
Date
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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.
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Biomedical engineering
Medical informatics / Information services
Medical Physicists
Hospital QA personnel
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Radiation Protection in Digital Radiology
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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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Radiation Protection in Digital Radiology
L03 Optimisation in CR and DR
Answer True or False
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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
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