iaea human health series publications - SEDIM

8.12. IMAGE QUALITY8.12.1. Evaluation of image quality8.12.1.1. ScopeIt is recognized that no phantom is currently available that truly mimics the complex problem of imaging thebreast. Nevertheless, it is possible to assess some key features of mammography quality by imaging a subjectivebreast phantom. This, for example, is the basis of image quality assessment in the IAEA QA programme for screenfilm mammography [34].In digital mammography, it is useful to perform routine imaging of such a phantom to confirm that there havebeen no substantial changes in imaging performance from the baseline. No particular phantom can berecommended at this time. Instead, the facility should use whatever nationally or internationally recommendedphantom is currently used for its screen film or digital mammography QC programmes.— Objective: To establish a baseline level of subjective image quality; to ensure that the overall image qualityhas not degraded from baseline performance levels.— Minimum frequency: At commissioning, annually and after changes.8.12.1.2. Instrumentation(1) Breast phantom containing structures mimicking those found in the breast.(2) Magnifying lens (4× to 5× magnification).8.12.1.3. Methodology(1) Place the phantom on the breast support positioned flush with the chest wall and centred laterally.(2) Lower the compression paddle to apply a compression force typically used clinically (e.g. 80 N). 34(3) If there is a separate AEC sensor, confirm that it is correctly located under the phantom.(4) Select the technique factors that are used in the clinical practice for a breast having characteristics equivalentto those of the phantom. Normally this is achieved by using the automatic exposure mode. Otherwise, selectthe appropriate target, filter, kV, grid, density control position and operation mode (semiautomatic orautomatic).(5) Make an exposure.(6) On the phantom image quality chart (Chart 18 in Annex II), record the exposure factors, the exposureindicator for CR systems and technique used.(7) Process the image using the algorithms that would be used clinically.(8) Compare this image with the baseline image obtained on this system. Determine if there are artefacts thatcould be confused with any of the phantom details. With the magnifying lens, carefully examine the image fornon-uniform areas, dirt or dust, lines (if the grid is used), processing artefacts or any other type of artefact.(9) If desired, evaluate the image according to the evaluation method provided by the manufacturer. 35 Note theresults on the data collection sheet.(10) Investigate the causes of any artefacts.34The actual force should be similar to the typical value used clinically, but the same value should be used for all testing. Notethat in some systems and in some modes of operation, the compressed breast thickness is utilized in an automated algorithm todetermine the technique factors; this thickness is, in turn, dependent on the degree of compression applied.35A description of how this is done for the ACR accreditation phantom is provided in the IAEA publication Quality AssuranceProgramme for Screen Film Mammography (IAEA Human Health Series No. 2) [34].134