Picture archiving and communication systems (PACS) and quality assurance

Transcription

1 IT Guidance Documents Picture archiving and communication systems (PACS) and quality assurance Second edition Board of the Faculty of Clinical Radiology The Royal College of Radiologists

2 This guidance forms part of a series on the developments in information technology in radiology. This is a fast-moving field and developments are occurring rapidly. Consequently, this guidance will be updated regularly and readers should check regularly that they are using the most up-to-date guidance available. 2

3 This document gives radiologists essential guidance on the areas of quality assurance which need to be monitored throughout the life of picture archiving and communication systems (PACS). It includes the need to ensure consistency in image appearance, the testing of image display devices, and the issue of rejecting and analysing inadequate digital images. This document replaces BFCR(08)8 Picture archiving and communication systems (PACS) and quality assurance, which has now been withdrawn. 1. Overview 1.1 PACS quality assurance (QA) is an overarching topic that covers all aspects of system design and implementation, embracing everything from information governance to network performance. PACS QA is a core component of PACS acceptance testing, and quality of service should be maintained thereafter through regular performance monitoring. 1.2 From a clinical perspective, image quality is the major consideration for anyone using PACS for primary (diagnostic) image interpretation. PACS should support image QA through system design, and PACS training should ensure staff can acquire and manipulate images to optimise image display. Medical physicists have an important role in the acceptance testing and monitoring of acquisition modalities and medical display devices. 2. Consistent presentation of images 2.1 QA of PACS image display relies on consistent presentation of images across the enterprise, irrespective of whether images are viewed on a soft copy display device or on printed hard copy. 2.2 PACS and acquisition modality workstations can optimise image presentation by enabling users to adjust the contrast and brightness of images, and to apply spatial and graphical operations, such as user annotations, shutters, flip/rotate, display area selection and zoom. These changes can be saved with the images in the form of a Digital Imaging and Communications in Medicine (DICOM) Greyscale Softcopy Presentation State (GSPS). To ensure safe and consistent presentation of images, all PACS display devices must display these images with their saved presentation state applied. Where more than one presentation state is saved with an image, the system should ensure that one of these is the default QA presentation state for image display. 2.3 For the consistency of the perceived pixel intensity, a standard contrast curve has been defined as the DICOM Greyscale Standard Display Function (GSDF). This provides a standard against which different types of display and hard copy output devices can be calibrated. The Integrating the Healthcare Enterprise (IHE) consistent presentation of images profile requires support of both the DICOM GSPS and the DICOM GSDF. 3. QA of image display devices 3.1 All PACS display devices used for primary diagnostic image viewing should undergo formal QA acceptance testing and regular performance monitoring. In the UK, guidance on these procedures is provided by Institute of Physics and Engineering in Medicine (IPEM), 1 referencing guidance from the Medicines and Healthcare products Regulatory Agency, the American Association of Physicists in Medicine and the International Electrotechnical Commission. A summary of the 2005 IPEM guidance is given in Table In addition to the 2005 IPEM guidance, 1 it is recommended that all primary diagnostic displays meet acceptance criteria matching the minimum specification guidelines for display devices used for clinical image interpretation summarised in Table If a primary display workstation does not meet all the recommendations outlined above, a local risk assessment should be undertaken as to whether the workstation can be used for primary diagnostic clinical interpretation. PACS workstations not suitable for diagnostic use should be clearly labelled and the rationale for imposing restrictions on clinical use should be covered in PACS training. 3.4 These guidelines do not require colour image display capability for primary diagnostic displays. Colour display is desirable to support the display of a number of advanced imaging modalities and annotations. Examples include nuclear medicine, functional magnetic resonance imaging (MRI), physiological MRI/CT, dual-energy CT, computer-aided diagnosis (CAD). Historically, colour display devices have been unable to meet the recommended standards for primary diagnostic use, hence in high workflow areas, the use of monochrome displays has been preferred. Technological advances mean that colour devices which achieve the recommended greyscale performance are now available. 3.5 The calibration and display of colour is a complex topic, and beyond the scope of this document. The guidance documents cited above are themselves limited in scope to monochrome performance, and are 3

4 not intended to ensure the reproducibility of colour information. Agreed guidelines for the quality assurance of colour image reproduction on medical displays have not yet been published. Advice on the calibration and any QA required, in excess of that given in the monochrome guidance, should be sought from the manufacturer. 3.6 Due to the lack of standardised methodology for verifying medical image colour reproduction precision, radiologists reporting colour images should be aware that colour fidelity may be altered if viewed for primary diagnosis on equipment maintained to different standards to the device that created the image (for example, equipment supplied by different vendors). A risk assessment should be performed if colour shifts could be diagnostically relevant, although in the case of false-colour volume rendered images, and pseudocolour parametric maps, this is unlikely to be relevant. 3.7 Handheld portable devices (such as mobile phones, ipads and so on), which can be used for image viewing, are not included in the guidance. While they can offer sufficient resolution (if viewed under appropriate low lighting conditions) for gross image review/aide memoire purposes, they are clearly not suitable for primary diagnosis. Table 1. Summary of image display monitor guidance from IPEM Physical parameter Frequency Remedial level Image display monitor condition Daily to weekly Image display monitors should be clean, and the perceived contrast of the test pattern should be consistent between monitors connected to the same workstation. Ensure that the 5% and 95% details superimposed on the 0% and 100% squares respectively are visible Greyscale contrast ratio 3 monthly Ratio white to black <250 Distance and angle calibration 3 monthly ± 5mm ± 3 Resolution 3 monthly Grade AAPM TG18-QC resolution patterns according to the reference score (CX >4) Greyscale drift 6 to 12 monthly Black baseline ±25% White baseline ±20% DICOM greyscale calibration 6 to 12 monthly GSDF ±10% Uniformity 6 to 12 monthly U% >30% Variation between monitors 6 to 12 monthly Black baseline >30% White baseline >30% Room illumination 6 to 12 monthly >15 lux 4

5 Table 2. Summary of the PACS and Imaging Informatics Group minimum and recommended specification for primary diagnostic display devices used for clinical image interpretation. This guidance applies to all workstations where CR, DR, fluoroscopy, ultrasound, CT, MR, nuclear medicine and PET images are viewed (excluding mammography). Screen resolution b (Native pixel array) Minimum a 1280 x 1024 (~1.3 megapixels) Recommended 1500 x 2000 c (~3 megapixels) Screen size (viewable diagonal) 42 cm (~17 ) 50 cm (~ 20 ) Maximum luminance 170 cd/m2 d 500 cd/m2 Luminance ratio (maximum/minimum) 250:1 e 500:1 Greyscale calibration Within 10% GSDF Calibrated to GSDF Greyscale bit depth Video display interface 8-bit greyscale (24-bit colour) Digital (where possible) Analogue f 10-bit greyscale Digital Notes a. The minimum specification for diagnostic display devices is only appropriate if clinical image viewing is performed according to image viewing guidelines, making use of the application software zoom, pan, magnification and windowing tools. b. LCD devices should be run at their native resolution to ensure there is a 1:1 match between screen pixels and screen resolution, and therefore no loss of image quality due to screen interpolation. CRT displays can be run at a variety of resolutions with no loss of display quality; however, care should be taken that the correct aspect ratio is maintained to avoid distortion of the image. c. Displays with a variety of aspect ratios are in common usage, in both landscape and portrait orientations. The absolute values of the horizontal and vertical screen matrix dimensions are the limiting factors in the resolution of image display. The total pixel count is therefore of secondary importance. d. High fidelity displays ( 3 megapixels) are recommended in radiology and other areas where large numbers of images are reported to reduce image interpretation and reporting times, and thereby assist department workflow. e. AAPM TG18 recommendation. f. AAPM TG18 & IPEM recommendation. g. New installations should not be analogue, except where a workstation/display package is provided as a single unit by a medical device manufacturer. 4. Image rejects and reject analysis 4.1 PACS must be able to hide images that are not considered adequate for clinical image viewing. These images should not be deleted from the system, but should be retained so that they can be accessed by authorised personnel for reject analysis. It is helpful if PACS enables these images to be categorised at the time of rejection, and can collate them in a PACS reject folder to facilitate audit analysis. 4.2 PACS can support QA workflow by optionally hiding images received from modalities from general clinical viewing until the images have been quality assured on a PACS workstation. By combining PACS support for QA workflow with PACS reject analysis functionality, it should be possible to store all images acquired on PACS, without the need for a separate image archive and reject analysis package. Approved by the Board of the Faculty of Clinical Radiology: 15 June 2012 Reference 1. Institute of Physics and Engineering in Medicine. Report 91. Recommended Standards for the Routine Performance Testing of Diagnostic X-Ray Imaging Systems. London: IPEM, TestingofDiagnosticX-RayImagingSystems.aspx (last accessed 27/11/12) 5

6 The Royal College of Radiologists 38 Portland Place London W1B 1JQ Tel +44 (0) Fax +44 (0) A Charity registered with the Charity Commission No Citation details: The Royal College of Radiologists. Picture archiving and communication systems (PACS) and quality assurance, Second edition. London: The Royal College of Radiologists, Ref No. BFCR(12)15 The Royal College of Radiologists, November 2012 For permission to reproduce any of the content contained herein, please permissions@rcr.ac.uk This material has been produced by The Royal College of Radiologists (RCR) for use internally within the specialties of clinical oncology and clinical radiology in the United Kingdom. It is provided for use by appropriately qualified professionals, and the making of any decision regarding the applicability and suitability of the material in any particular circumstance is subject to the user s professional judgement. While every reasonable care has been taken to ensure the accuracy of the material, RCR cannot accept any responsibility for any action taken, or not taken, on the basis of it. As publisher, RCR shall not be liable to any person for any loss or damage, which may arise from the use of any of the material. The RCR does not exclude or limit liability for death or personal injury to the extent only that the same arises as a result of the negligence of RCR, its employees, Officers, members and Fellows, or any other person contributing to the formulation of the material.