Clinical teleradiology and PACS QA

Full text: The conversion of medical imaging to exclusively electronic formats is accelerating. The traditional role of medical physics in ensuring optimal image quality at the lowest achievable dose continues. However we no longer can satisfy ourselves with examining image quality on film alone. Rather, physicists must become familiar with teleradiology and picture archive and communications system (PACS) operation, their constituent equipment and related standards. Medical physicists must become involved in teleradiology and PACS quality assurance. Medical physicists should understand all aspects of the acquisition, transmission, display and storage of medical images. It is essential that one knows the fidelity of the images stored and displayed on a PACS or teleradiology system. Responsibilities can include assessment of system design and workflow, evaluation of operational parameters, and evaluation of physical performance. The latter, which includes display and laser printer QC, will most commonly occupy the majority of a physicist's time. Medical display workstations are a major part of PACS. Display quality has a fundamental importance in the overall effectiveness of a diagnostic imaging practice. Unfortunately, display quality degrades over time. Degradation occurs both in luminance and in resolution characteristics of the display, two major performance indicators. Thus, it is vitally important to ensure that utilization of these devices does not compromise image quality, as suggested by a number of studies. Display testing in the form of acceptance testing or routine quality control provides a means by which any user can be assured that the display quality is adequate and is maintained throughout the useful life of the device. It will also determine when a display device should be decommissioned. A comprehensive PACS display QC programme will insure the consistency and integrity of image presentations in the broad electronic imaging practice. Display quality assessment is relatively new. A number of investigations have begun to address the quality control aspects of electronic displays, and the DICOM Grayscale Standard Display Function working group has recently provided recommendations for the grayscale of soft copy displays. However, the assessment of many critical medical display characteristics has not been standardized, the recommended methods have been either too complicated or too subjective, and the methods have not been endorsed by the medical community. The professional guidelines of the American Association for Physicists in Medicine (AAPM) assert that the assessment of performance for electronic display devices in health care institutions falls within the professional responsibilities of medical physicists. The monthly or quarterly routine QC procedures may be performed by a trained QC technician under the direct supervision of a medical physicist, while the more extensive inspections involved in acceptance testing and annual tests can be performed by the physicist. An AAPM Task Group (TG18) recently completed work to address acceptance testing and quality control of medical electronic display devices. The TG18 report provides standard guidelines for performing display evaluations by practising medical physicists, engineers, and display investigators, in order to assure adequate display performance for clinical tasks, and to facilitate inter- and intra-institutional comparisons. The scope of the effort is limited to devices for displaying monochrome radiological images. The performance characteristics considered include luminance response, luminance uniformity, resolution, noise, veiling glare, ambient light response, color uniformity, and geometrical distortions. Based on the current standard of practice, suggestions have been made for the acceptable ranges of display performance with limited impact on diagnostic efficacy. Under the AAPM TG18 protocol, display testing can be undertaken at several levels depending upon whether they are for acceptance testing or quality control. New display devic es should be evaluated via acceptance testing procedures, which are generally more extensive and more quantitative than routine QC evaluations and might take 1-2 hours. Annual display inspections consist of a large subset of the acceptance testing procedures taking about an hour, while the monthly/quarterly inspection relies more heavily on testing procedures that are less time consuming (∼20 minutes). Daily QC recommended to be performed by the actual user of the display device is visual and should take less than one minute to complete. For testing any given display quality characteristic, three types of testing may be used: visual, quantitative, and advanced. The latter is more appropriate for laboratory and research related evaluations. The visual and quantitative tests are used in the acceptance testing and quality control procedures. In evaluating the performance of a display device, it is also important to take into account the intended purpose of the device. In clinical practice today, display devices are often used in two capacities: as primary, so-called diagnostic, displays and as secondary, so-called clinical, displays. The former devices are used for diagnostic interpretation of medical images leading to the generation of an interpretation report, while the latter are used for clinical review of images for which the official interpretations are already rendered. The performance criteria are usually less stringent for secondary class display devices. A summary, a comprehensive PACS QA programme, including display QC, is an integral part of a medical physicist's duties in this electronic age. An appropriate programme includes acceptance testing and ongoing QC evaluations. When combined with proper QC methods for the acquisition devices in a PACS, display QC will ensure that image quality is optimized. (author)