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8.5.4. Detector ghosting8.5.4.1. ScopeIn this measurement, ghosting (sensitivity variation) or lag (residual signal) from a previous exposure isinduced in a manner similar to clinical operation and the results are quantified. For simplicity, both phenomena arereferred to in this publication as ‘ghosting’. Both qualitative and quantitative (preferred) evaluations may beundertaken, depending on the capability of the acquisition workstation. Here, a quantitative method for assessingghosting and an alternative qualitative technique are described.— Objective: To evaluate the severity of any artefact due to recent previous exposure to the detector in allsystems except photon counting systems.— Minimum frequency: Annually and after replacement of the detector.8.5.4.2. Instrumentation(1) PMMA slab, 45 mm thick.8.5.4.3. MethodologyImportant: Read through these steps and understand them before starting this test. It is important that theelapsed time between acquisition of the initial image (step 4) and the ghost measurement image (step 5) be theshortest time allowed by the mammography unit, as this will replicate the clinical situation.(1) Create a ‘patient’ study with an appropriate name.(2) Place the PMMA slab on the right half of the breast support table with the edge placed at the middle of thetable, running from the chest wall to the anterior edge such that approximately one half of the breast imagingarea is covered (Fig. 32(a)).(3) Lower the paddle so that it is in contact with the breast support plate. Note where the edge of the phantomcrosses the detector.(4) Acquire an image under manual exposure, using typical clinical exposure factors for the average breast. Thisis the ‘ghost creation’ image.(5) For CR, immediately process the cassette and retrieve the same cassette (screen) from the processing station.(6) Reposition the slab on the breast support table so that the middle of the slab is centred on the location of theedge of the uniform attenuator in the ghost creation image (Fig. 32(b)).(7) As soon after the first image is acquired that the unit allows another exposure, or as soon as the same detectorplate is available, acquire a second image using the same manual technique. This is the ‘ghost measurement’image.(8) View the ghost measurement image (the unprocessed version, if possible). Use the ROI tool (area ~4 cm 2 ) totake three measurements in two ROIs in the ghost measurement image at the locations described below:(a) The MVP in the background of the phantom on the side where no attenuator was present in the first image.In Fig. 32(b), the centre of the ROI should be ~20 mm to the left of the line marked D.(b) The MVP in the background of the phantom on the side where the uniform attenuator was present in thefirst image. Here, the centre of the ROI should be ~20 mm to the right of the line marked D.(c) The standard deviation (SD) in the background of the phantom on the side where the uniform attenuatorwas present in the first image (i.e. the same ROI as for step 8(b)).(9) Record the results on the evaluation of ghosting chart (Chart 7 in Annex II).100
Breast supportPMMA slabBreast supportPMMA slabprevious locationPMMA slabA – mean ROI 1 DB – mean ROIC – SD ROI22(a)(b)FIG. 32. Set-up for (a) ghost creation image and (b) ghost measurement image.(10) Calculate the ghost image SDNR using the equation:Ghost image SDNR = A - BC(2)where the variables are as defined in Fig. 32(b).(11) View the ‘for processing’ version of the ghost measurement image on the radiologist review workstation.(12) Using a narrow window width (without exaggerating image noise) and an appropriate window level, inspectthe central part of the image where the boundary between the two areas of exposure lies. Record the windowwidth and window level on Chart 7 in Annex II.(13) Record the presence or absence of any visually observable ghost image on Chart 7 in Annex II.8.5.4.4. Interpretation of results and conclusionsTolerance:(1) Acceptable: Ghost image SDNR ≤2.0.(2) Alternative measure: When viewing the ghost measurement image with a typical, clinically used windowsetting, there should be no visible indication of the attenuator in the ghost creation image.8.5.4.5. Recommendations and corrective action(1) If the absolute value of the ghost image SDNR is more than the tolerance value, the service person should becontacted.(2) If ghosting is visible at clinically relevant window width and window level settings, the service person shouldbe contacted.8.5.4.6. Time frame for corrective actionImmediately: Corrective action should be taken before any further patients are imaged.101
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X raysdel matrixCs scintillatorLine
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QUALITY ASSURANCE PROGRAMMEFOR DIGI
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IAEA HUMAN HEALTH SERIES No. 17QUAL
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FOREWORDThe application of radiatio
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An effective QA programme is necess
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The Integrating the Healthcare Ente
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technology. Systems containing othe
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X raysTop electrodea-Se layerCharge
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dose received by inhomogeneous real
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2.3.8.1. Soft copy displayFlat pane
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3. ELEMENTS OF HIGH QUALITY MAMMOGR
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— The ability to mask edges of ma
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Disposal orsaleNew facility(start h
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4.2.3. Radiographer (mammography te
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5.2.2. Electronic versus geometric
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To allow full utilization of the di
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5.7. ARTEFACTSWhile the incidence o
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FIG. 10. Detector crystallization.
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FIG. 13. A more subtle example of a
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FIG. 16. An example of poor collima
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7. RADIOGRAPHER’S QUALITY CONTROL
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7.1. DAILY TESTS7.1.1. Monitor insp
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7.1.3. Daily flat field phantom ima
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7.1.4. Visual inspection for artefa
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7.1.5. Laser printer sensitometry7.
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Page 73 and 74: TABLE 7. TOLERANCES FOR IMAGING WEE
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Page 85 and 86: RECORD OF DIGITAL MAMMOGRAPHY REPEA
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Page 89 and 90: 7.5. SEMI-ANNUAL TESTS7.5.1. Comput
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Page 101 and 102: (2) Stack the 20 and 25 mm PMMA sla
Page 103 and 104: TABLE 13. ACCEPTABLE AND ACHIEVABLE
Page 105 and 106: 8.5. DETECTOR PERFORMANCE8.5.1. Bas
Page 107 and 108: 8.5.2. Detector response and noise8
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Page 117 and 118: 8.6. EVALUATION OF SYSTEM RESOLUTIO
Page 119 and 120: TABLE 17. ACCEPTABLE FREQUENCIES AT
Page 121 and 122: 8.7. X RAY EQUIPMENT CHARACTERISTIC
Page 123 and 124: 8.7.2. Incident air kerma at the en
Page 125 and 126: 8.8. DOSIMETRY8.8.1. Mean glandular
Page 127 and 128: TABLE 21. ACCEPTABLE AND ACHIEVABLE
Page 129 and 130: FIG. 34. Suggested layout for ruler
Page 131 and 132: 8.10. IMAGE DISPLAY QUALITYThe accu
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Page 152 and 153: Appendix IISPECIFICATIONS OF TEST E
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[29] ALSAGER, A., YOUNG, K.C., ODUK
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Annex IRADIOGRAPHER DATA COLLECTION
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Chart 2 — DIGITAL MAMMOGRAPHY (DM
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Chart 4 LASER PRINTER SENSITOMETRY
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Chart 6 — WEEKLY DISPLAY MONITOR
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Chart 7(b) WEEKLY QC TEST OBJECT:
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Chart 9 — SAFETY AND FUNCTION CHE
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Chart 11 — LASER PRINTER ARTEFACT
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Chart 13(a) — RECORD OF DIGITAL M
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Chart 14 — CR PLATE SENSITIVITY M
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Annex IIITHE MAMMOGRAPHY EXTRACTThe
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GLOSSARYair kerma. The energy depos
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image quality. The overall merit of
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CONTRIBUTORS TO DRAFTING AND REVIEW
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