IAEA International Atomic Energy Agency Radiation Protection in Digital Radiology Optimisation in CR & DR L03

IAEAInternational Atomic Energy Agency

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

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 …• 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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“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 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 XWolbarst (1993) Table 19-1


X: very important connection

x: sometimes significant

(x): sometimes noticeable

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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

• 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%?

• 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.

• 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.

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"

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

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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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 …

Caught by RT before exam

Caught by RT after exam

Caught by Supervisor

Passed on to Radiologist

Errors RT – Radiography Technologist


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Which image is worse?

Reported by radiologist Subsequent image, same machine,reported by same radiologist


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3. Verify exam with physician

5."Arrive" patient in RIS

6. Escort patient to exam room

7. Explain exam to patient

8. Select and ID cassettes

9. Position patient, cassette, x-ray tube

10. Perform exam

11. Scan cassette

14. Review images at QC

15. Repeat necessary?

17. Complete exam in RIS

END

4. Schedule exam in RIS

12. Preview images

13. Repeat necessary?

18. Release patient

1. Patient arrives in imaging department

Y

Y

N

N

START

2. Is exam scheduled?

N

Y

16. Release images to PACS

QC?

QC?

QC?

QC?

QC?

QC?

QC?

QC?

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?• Don’t 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

Reason Number %mispositioned 240 53.3%artifacts 40 8.9%test images 22 4.9%nondiagnostic 20 4.4%patient motion 14 3.1%misplaced marker 10 2.2%no marker 6 1.3%under-exposed 5 1.1%inadequate contrast 4 0.9%over-exposed 2 0.4%wrong exam 2 0.4%wrong patient 2 0.4%Total 450 100.0%


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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 => Radiologist “Film” critique


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Task Allocation MatrixTask 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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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 @ 2.5 lp/mm = 17%

• CsI(Tl) is hygroscopic – columnar structure is degraded

• Both systems depicted required detector replacement

A6 QAP data y = -0.0023x + 104.85

R2 = 0.2349

15

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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

Sp

atia

l MT

F a

t 2.

5 lp

/mm

XQi C1 y = -0.0052x + 218.2

R2 = 0.8897

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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

MT

F @

2.5

lp

/mm


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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


Documents

IAEA International Atomic Energy Agency Radiation Protection in Digital Radiology Optimisation in CR & DR L03