Lecture 9 - Quality assurance

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Transcript Lecture 9 - Quality assurance

FRCR: Physics Lectures
Diagnostic Radiology
Lecture 9
Quality Assurance (QA) of radiographic
Dr Tim Wood
Clinical Scientist
• What is QA?
• The life cycle of X-ray imaging systems
The critical examination
Acceptance testing
Routine performance testing
• IPEM Report 91
– Recommended tests by modality – a whistle stop tour
• The role of Medical Physics in Diagnostic
What is QA?
• Quality as·sur·ance
• A programme for the systematic
monitoring and evaluation of the various
aspects of a project, service or facility to
ensure that standards of quality are being
Merriam-Webster's Medical Dictionary, © 2007 Merriam-Webster, Inc.
What is QA?
• It is a requirement under the Ionising Radiations
Regulations 1999 (Reg. 32(3)-(4)) to…
– ‘… make arrangements for a suitable quality
assurance programme to be provided in respect of
the equipment or apparatus for the purpose of
ensuring that it remains capable of restricting so far
as is reasonably practicable exposure to the extent
that this is compatible with the intended clinical
purpose or research objective.’
What is QA?
• Regulation 32 also requires;
– Adequate testing before entering clinical service
– Adequate testing at appropriate intervals and after
any major maintenance procedure (routine)
– Measurements at suitable intervals to enable
assessment of representative doses to persons
undergoing medical exposures
What is QA?
• The regulations use lots of vague terms like
‘suitable’, ‘adequate’ and ‘appropriate’
– Deliberate due to range of equipment the regulations
have to cover
• The ‘Approved Code of Practice’ gives slightly
more detail
– Depends on the nature and range of equipment in
– The QA programme should specify the frequency of
any testing and appropriate actions levels
– In establishing these levels the employer should
take into account guidance established by
relevant professional bodies about criteria of
What is QA?
• In devising the QA programme, pay special
attention to equipment for;
– Children
– Health screening programmes
– High dose procedures, such as interventional
radiology, CT or radiotherapy
• The employer should consult their RPA when
devising the QA programme
• Note QA, does not just cover the equipment, but
also procedures, etc (as required under
The life cycle of X-ray imaging
• There are essentially four stages of checks
applicable to X-ray imaging systems;
Critical examination
Routine performance testing
• Maintenance is vital throughout
The life cycle of X-ray imaging
The Critical Examination
• Under IRR 99 Reg 31(2), the installer is
required to perform a critical examination of
any new installation
• The purpose of the ‘critex’ is to ensure all safety
features and warning devices work correctly
– Also includes tube leakage, total filtration, etc
• Primarily related to radiation protection features
that affect staff and visitors, but some impact on
patient safety too
• Employer must not allow the equipment to go
into clinical service until the results of the critex
are satisfactory
Acceptance testing
• Verify that the contractor has supplied all the
equipment specified and has performed
adequate tests to demonstrate specified
requirements are met
• May be a simple check list
• Mechanical and electrical safety checks also
• Set of tests performed by a representative of the
employer (usually Medical Physics), to ensure
the equipment is ready for clinical use, and to
establish baseline values against which routine
QA can be compared
• Commissioning tests may need to be repeated
during the life of the system if any major
maintenance is undertaken e.g. new X-ray tube
– New baselines may need to be established
Routine testing
• Regular tests throughout the lifetime of the
• Looking for changes in performance that
indicates remedial action required
• Generally, routine are a subset of the
commissioning tests
IPEM Report 91
• The Institute of Physics and
Engineering in Medicine (IPEM)
produce a series of reports related
to medical equipment QA
• The most useful for Diagnostic
Radiology is IPEM Report 91
– Recommended standards for the
routine performance testing of
diagnostic X-ray imaging systems
• Relates primarily to imaging
performance and radiation safety
IPEM Report 91
• The report is split into chapters on different
• Each chapter starts with a summary table of;
– The physical parameter to be tested
– Frequency – varies from daily to three yearly
– Priority – level 1 is essential for ‘good practice’; level
2 is not essential, but considered ‘best practice’
– Level of expertise required – level A applies to
frequent and relatively basic tests performed by
Radiographers; level B tests are less frequent, but
require greater expertise and more complex
equipment (Medical Physics tests)
– Action levels – split into ‘Remedial’ and ‘Suspension’
(see later)
IPEM Report 91
• Each test is then described briefly,
with appropriate references to other
documents, such as the IPEM Report
32 series
– These are a series of reports that give
much greater detail on the method for
testing systems e.g. X-ray tubes and
generators, fluoroscopy, CT, etc
IPEM Report 91
• Remedial Level:
– A level of performance at which remedial
action is required, but the unit may continue to
be used in the mean-time
– The action will be based on a risk assessment
of the equipments performance and the risk
arising should it continue to be used
– Following assessment, a timescale must be
agreed and restrictions on its use followed
IPEM Report 91
• Suspension Level:
– A level of performance at which it is
recommended the equipment is removed from
clinical use immediately
– Not all tests have suspension levels set due
to the subjective nature of the test e.g. image
IPEM Report 91
• IPEM 91 also emphasises that;
– A senior radiography or other suitable person should
be appointed to supervise the QA programme
– Time should be allocated to staff and equipment for
– All QA tests should be documented as part of the
QA programme – may be required as evidence
presented to the HSE inspectors
– Results and remedial actions must be followed up
– Test equipment should be available and within
calibration (annual recalibration usually required for
A whistle stop tour of IPEM 91
X-ray tubes and generators
(Chapter 3)
• Level A
– X-ray/light beam alignment and centring
– Light beam/bucky centring
– Field size calibration
– Distances and scales
– Radiation output repeatability and
reproducibility (small range of settings)
X-ray tubes and generators
(Chapter 3)
• Level B
– Radiation output repeatability and
reproducibility (larger range of settings)
– Exposure time
– Tube potential
Film/screen radiography,
processors and AECs
(Chapter 4)
• Level A
– Developer temperature, fog, film speed,
contrast index, replenishment, pH, silver
– Intensifying screens and darkroom checks
– AEC guard timer and resulting film OD
Film/screen radiography,
processors and AECs
(Chapter 4)
• Level B
– Only AEC tests
– Consistency between chambers
– Repeatability and reproducibility
– Receptor dose
CR and DR
(Chapters 5 and 6)
• Level A:
– Detector dose indicator monitoring
– Uniformity
– Condition of image plates (CR only)
– Low contrast sensitivity
– Limiting spatial resolution
CR and DR
(Chapters 5 and 6)
• Level B: (in conjunction with IPEM 32 Part VII)
DDI repeatability and reproducibility
Measured uniformity
Threshold contrast detail detectability
Erasure cycle efficiency (CR only)
Limiting spatial resolution
Scaling errors
Dark noise
Modulation transfer function (MTF)
Normalised noise power spectrum
– AEC tests
Image display
(Chapter 7)
• Film viewers
– Level A – general condition
– Level B – luminance, uniformity,
variation between viewers, room
• Monitors
– Level A – general condition,
greyscale and resolution with test
– Level B – DICOM greyscale
calibration, test patterns, uniformity,
variation between monitors, room
(Chapter 8)
• See also IPEM Report 89 ‘The commissioning
and routine testing of mammographic X-ray
systems’ and the latest NHSBSP reports
• NHSBSP Equipment Report 0604 for full field
digital testing
• Lots of testing required!
– Radiographer testing daily, weekly, monthly
– Physics testing every 6 months
(Chapter 8)
• Example tests include;
Processing, where applicable
Limiting spatial resolution
Image quality with test phantoms
MGD to standard breast
X-ray beam alignment
Compression force
kV accuracy (specific calibrations)
Radiation output repeatability/reproducibility
And much more…
Dental Radiography
(Chapter 9)
• Processing tests
– Temperature, solutions, stepwedge, light proofing
• X-ray/detector tests
– Tube voltage, exposure time,
collimation, dose at collimator tip
for IO, DAP for OPG, detector
condition, clinical image quality
compared with reference
(Chapter 10)
• Level A
– Dose rate reproducibility under ABC/AEC
– Display monitor setup
– Limiting spatial resolution
– Threshold contrast
– Radiation/image field size
(Chapter 10)
• Level B
– Dose rate at the entrance surface of a
phantom under ABC/AEC
– Dose rate at the input face of the detector
under ABC/AEC
– Limiting spatial resolution
– Threshold contrast
(Chapter 11)
• Level A
– Dose per image under AEC
– Limiting spatial resolution
– Threshold contrast
(Chapter 11)
• Level B
– Dose per image at the input face of the
detector under AEC
– Limiting spatial resolution
– Threshold contrast
– Dynamic range
Patient dose measurements
(Chapter 13)
• Perform dose audits and/or QA measurements
– Individual radiographic exposures
• Entrance surface dose or DAP > Diagnostic Reference Levels (DRLs)
– Complete examinations
• DAP > DRLs
– Mammography
• MGD to standard breast >2.5 mGy per film
• MGD to patients >3.5 mGy per film
– Dental Radiography
• IO dose at collimator tip > DRL
• OPG dose > DRL
– Fluoroscopy
• Dose at entrance surface of phantom > 50 mGy/min
(Chapter 12)
• Craig to cover…
QA is important because…
• QA is important because…
Can identify equipment deterioration
Can be used to achieve ALARP
Ensures patient (and staff) safety
Ensures legislative compliance
• Final thought…
– Although it’s not your responsibility to check
equipment, you should ensure that the X-ray sets you
use have been checked for your own safety, as well
as the patient’s
The role of Medical Physics in
Diagnostic Radiology
• QA
– Level B tests
– Advising on QA programme and monitoring performance
• Radiation protection and physics advice
– Ensuring compliance with relevant regulations e.g. risk
assessments, controlled areas, dose monitoring, etc
– IRR and IR(ME)R audits – make sure we’re ready if the
inspector calls!
– New installations shielding, testing, etc
– Notification of incidents to the CQC, HSE, EA, Police, etc
• Education
– FRCR, Update Training, etc
The role of Medical Physics in
Diagnostic Radiology
• Optimisation
– We aren’t just here to interfere and police the
– Significant part of the Radiation Physics groups work
is looking at how we can get the most out of our X-ray
imaging systems
– Rely on feedback and co-operation from Radiology to
ensure we are optimising exposures
– We’re here to help…
Recent publications
A Beavis, J Saunderson, J Ward , WE-G-BRA-06: Calibrating an
Ionisation Chamber: Gaining Experience Using a Dosimetry ‘flight
Simulator’, Med. Phys. 39, 3970 (2012)
CS Moore, G Avery, S Balcam, L Needler, A Swift, AW Beavis, JR
Saunderson , Use of a digitally reconstructed radiograph based computer
simulation for the optimisation of chest radiographic techniques for
computed radiography imaging systems , Br J Radiol 2012;85 e630-e639
TJ Wood, AW Davis, CS Moore, AW Beavis & JR Saunderson ,
Validation of a Large-Scale Audit Technique for CT Dose Optimisation
, Radiat Prot Dosimetry (2012) 150(4): 427-433
CS Moore, GP Liney, AW Beavis, JR Saunderson, A method to produce
and validate a digitally reconstructed radiograph-based computer simulation
for optimisation of chest radiographs acquired with a computed radiography
imaging system, British Journal of Radiology, 84 (2011), 890-902
ML Wilson, WP Colley & AW Beavis , The effect of the carbon fibre insert
for the Varian Exact™ couch on the attenuation and build-up of high energy
photon beams, Journal of Radiotherapy in Practice (2011) 10, 77-83
Current Projects
• Further development of our dose audit software
• CT AEC optimisation with a custom built phantom
• Development of a high skin dose reporting system
for interventional procedures
• Development of a new test object for routine
image quality assessment in digital
• And many more… www.hullrad.org.uk