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FRCR: Physics Lectures Diagnostic Radiology Lecture 9 Quality Assurance (QA) of radiographic systems Dr Tim Wood Clinical Scientist.

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Presentation on theme: "FRCR: Physics Lectures Diagnostic Radiology Lecture 9 Quality Assurance (QA) of radiographic systems Dr Tim Wood Clinical Scientist."— Presentation transcript:

1 FRCR: Physics Lectures Diagnostic Radiology Lecture 9 Quality Assurance (QA) of radiographic systems Dr Tim Wood Clinical Scientist

2 Overview What is QA? The life cycle of X-ray imaging systems –The critical examination –Acceptance testing –Commissioning –Routine performance testing IPEM Report 91 –Recommended tests by modality – a whistle stop tour The role of Medical Physics in Diagnostic Radiology

3 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 met Merriam-Webster's Medical Dictionary, © 2007 Merriam-Webster, Inc.

4 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.’

5 What is QA? Regulation 32 also requires; –Adequate testing before entering clinical service (commissioning) –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

6 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 use –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 acceptability

7 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 IR(ME)R)

8 The life cycle of X-ray imaging systems There are essentially four stages of checks applicable to X-ray imaging systems; –Critical examination –Acceptance –Commissioning –Routine performance testing Maintenance is vital throughout

9 The life cycle of X-ray imaging systems

10 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

11 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 required

12 Commissioning 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

13 Routine testing Regular tests throughout the lifetime of the equipment Looking for changes in performance that indicates remedial action required Generally, routine are a subset of the commissioning tests

14 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 (2005) Relates primarily to imaging performance and radiation safety checks

15 IPEM Report 91 The report is split into chapters on different modalities 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)

16 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

17 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

18 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 quality

19 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 testing –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 promptly –Test equipment should be available and within calibration (annual recalibration usually required for dosemeters)

20 A whistle stop tour of IPEM 91

21 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)

22 X-ray tubes and generators (Chapter 3) Level B –Radiation output repeatability and reproducibility (larger range of settings) –Exposure time –Tube potential

23 Film/screen radiography, processors and AECs (Chapter 4) Level A –Developer temperature, fog, film speed, contrast index, replenishment, pH, silver content –Intensifying screens and darkroom checks –AEC guard timer and resulting film OD

24 Film/screen radiography, processors and AECs (Chapter 4) Level B –Only AEC tests –Consistency between chambers –Repeatability and reproducibility –Receptor dose

25 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

26 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 (NNPS) –AEC tests

27 Image display (Chapter 7) Film viewers –Level A – general condition –Level B – luminance, uniformity, variation between viewers, room illumination Monitors –Level A – general condition, greyscale and resolution with test patterns –Level B – DICOM greyscale calibration, test patterns, uniformity, variation between monitors, room illumination

28 Mammography (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

29 Mammography (Chapter 8) Example tests include; –Processing, where applicable –AEC –Limiting spatial resolution –Image quality with test phantoms –MGD to standard breast –X-ray beam alignment –Compression force –kV accuracy (specific calibrations) –Uniformity –Radiation output repeatability/reproducibility –And much more…

30 Dental Radiography (Chapter 9) Processing tests –Temperature, solutions, step- wedge, 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

31 Fluoroscopy (Chapter 10) Level A –Dose rate reproducibility under ABC/AEC –Display monitor setup –Limiting spatial resolution –Threshold contrast –Radiation/image field size

32 Fluoroscopy (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

33 Fluorography (Chapter 11) Level A –Dose per image under AEC –Limiting spatial resolution –Threshold contrast

34 Fluorography (Chapter 11) Level B –Dose per image at the input face of the detector under AEC –Limiting spatial resolution –Threshold contrast –Dynamic range

35 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 DAP > DRL

36 CT (Chapter 12) Craig to cover…

37 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

38 The role of Medical Physics in Diagnostic Radiology QA –Level B tests –Advising on QA programme and monitoring performance Radiation protection and physics advice (RPA/MPE) –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

39 The role of Medical Physics in Diagnostic Radiology Optimisation –We aren’t just here to interfere and police the regulations! –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…

40 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)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-e639Br 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): Radiat Prot Dosimetry (2012) 150(4): 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), British Journal of Radiology 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, 77-83Journal of Radiotherapy in Practice

41 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 mammography And many more…

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