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control limit. The upper and lower values indicating that the process is ‘out of control’ and requiring that correctiveaction be taken. It is prudent to immediately repeat the measurement to verify that the system is ‘out ofcontrol’ before taking corrective action. If the repeated measurement is ‘out of control’, then corrective actionis required immediately (or in some cases within 30 days). Synonym for action limit.D max , D min . The maximum and minimum optical density on a film. D max is the darkest area of the film, where thehighest exposure of X rays occurs. D min is the base plus fog optical density of the film.del. A physical detector element that determines the sampling aperture of the detector.densitometer. An instrument for measuring the optical density or degree of blackening of film.density difference (DD). The difference in optical density between the high density and the speed index. Thisprovides an index of contrast of the mammography film.detective quantum efficiency (DQE). DQE is a measure of the efficiency of an imaging system in transferringinformation from the X ray pattern incident on the detector to the output image. Specifically it is evaluated bydividing the square of the signal-to-noise ratio (SNR) of the output image by the square of the SNR in theincident X ray pattern. DQE ranges between 0 and 1. The only source of noise in an ideal detector results fromthe incident X ray quantum statistics. DQE is reduced if not all of the incident X rays are absorbed by thedetector and/or the noise is increased from its theoretical value due to sources of noise added by the detector.dry processing. Laser film printers that use thermal processes to produce and fix the blackness on the transparencyfilm. They use a heat sensitive development process rather than chemicals and normally have frequent selfrecalibrationto ensure stability of images.dynamic range. The range of exposures over which a detector can acquire image data in a single image. Typicaldigital systems will respond to exposures as low as 1 μGy and as high as 50 mGy outside the breast.effective resolution. The limiting spatial resolution measured with a line pair test pattern located at the level of thetop surface of the average breast. It is affected by both focal spot size and detector resolution. The effectiveresolution is typically measured in the orthogonal directions parallel to and perpendicular to theanode–cathode axis.exposure. The act of initiating and producing X radiation from an X ray unit.exposure index (EI). An index that gives an indicative relative value of the amount of radiation absorbed by a CRplate. Currently different manufacturers have different proprietary exposure indices.exposure time. The duration of primary X rays striking the breast and image receptor.fog. The unwanted signal added to an image by the exposure of the image receptor to light, radiation or heatbetween patient exposures.heel effect. Non-uniformity of the radiation field striking the image receptor caused by the geometry of the X raytarget. X ray intensity is higher toward the chest wall than toward the nipple, due to the increased path lengththrough the target and filter of X rays striking the nipple side of the image receptor.illuminance. A photometric quantity describing the light intensity per unit area falling on a surface. The SI unit forilluminance is the lux (candela-steradians per square meter).image noise. See radiographic noise.174
image quality. The overall merit of a radiographic image. Image sharpness, image contrast and image noise arethree common measures of image quality.image receptor. A device that detects and records the distribution of X rays to form an image.image sharpness. The overall impression of detail in a radiographic image.just noticeable difference (jnd). The smallest detectable difference between a starting and secondary level of aparticular sensory stimulus. Since the visual system is not linear and has varying response depending onillumination levels, the video display must be set up so that similar changes in pixel values should be equallyvisible in both the dark and light regions of an image.kilovoltage, peak (kVp). The maximum value of the potential difference (kV) between anode and cathode in anX ray tube. The kVp determines the maximum energy of X rays emitted by the X ray tube, usually measuredin kilo-electron volts (keV).linearity. System response where the output increases in direct proportion to the input signal.luminance. A photometric quantity describing the light power per unit area per unit solid angle emitted by a lightsource. The SI unit for luminance is candelas per square meter (or nit).lux. The SI unit of illuminance. One lux equals one lumen per square meter. The lumen is derived from the candelaand is the luminous flux emitted into a unit solid angle (1 steradian) by an isotropic point source having aluminous intensity of 1 candela.mean glandular dose (MGD). The energy absorbed per unit mass of fibroglandular tissue (the most radiosensitivetissue in the breast) averaged over all the fibroglandular tissue in the breast. The MGD is calculated fromvalues of entrance air kerma, the X ray beam quality (half value layer), and compressed breast thickness.modulation transfer function (MTF). A parameter that describes the transfer object contrast by the imagingsystem as a function of spatial frequency.Nyquist frequency. The highest spatial frequency that can be recorded by a digital detector. The Nyquist frequency isdetermined by the pixel pitch. The pixel pitch is determined by sampling frequency for cassette based PSPsystems and by del spacing for TFT flat panels. The Nyquist frequency is half the number of pixels per millimetre.A digital system with a pixel density of 10 pixels/mm would have a Nyquist frequency of 5 line pairs/mm.phantom. A test object that simulates some aspect of <strong>human</strong> anatomy. A breast phantom simulates a typical breastin terms of size, composition and X ray attenuation, and may contain test objects that simulate anatomy in thebreast.pixel. A ‘picture element’, or pixel, is the smallest element represented in a digital image.polymethyl methacrylate (PMMA). Also known by the generic name acrylic and the trade names Plexiglas,Acrylate, Lucite and Perspex.radiographic noise. Fluctuations in image optical density due to the discrete nature of X ray photons and theresulting random fluctuations in the number of photons contributing to the image at each location. Also calledquantum noise or quantum mottle, radiographic noise increases with increasing X ray fluence, but less rapidlythan the radiographic signal.reference operating level (ROL). The central value about which day to day measurements are expected tofluctuate, for example, the empirically determined speed index on a sensitometric film.175
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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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7.1.6. Image plate erasure (CR syst
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FIG. 19. Modified TG18-QC pattern w
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FIG. 21. Radiologist workstation wi
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7.2.1.6. Time frame for corrective
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7.2.3. Weekly quality control test
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Note: It is not necessary to view t
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TABLE 7. TOLERANCES FOR IMAGING WEE
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7.2.4.4. Interpretation of results
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7.3.1.5. Recommendations and correc
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artefacts are typically best seen w
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7.3.3.5. Recommendations and correc
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7.4.1.3. Methodology(1) Annotate th
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RECORD OF DIGITAL MAMMOGRAPHY REPEA
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(3) Including examinations of at le
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7.5. SEMI-ANNUAL TESTS7.5.1. Comput
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8. MEDICAL PHYSICIST’S QUALITY CO
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8.1. NOTE ON IMAGE NAMING CONVENTIO
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(16) On any randomly selected patie
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FIG. 30. Positioning of bathroom sc
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(6) The target, filter, kV, grid, d
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(2) Stack the 20 and 25 mm PMMA sla
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TABLE 13. ACCEPTABLE AND ACHIEVABLE
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8.5. DETECTOR PERFORMANCE8.5.1. Bas
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8.5.2. Detector response and noise8
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the service engineer responsible fo
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(13) Using the annotation tool on t
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Breast supportPMMA slabBreast suppo
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(10) Place the thinner test object
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8.6. EVALUATION OF SYSTEM RESOLUTIO
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TABLE 17. ACCEPTABLE FREQUENCIES AT
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8.7. X RAY EQUIPMENT CHARACTERISTIC
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8.7.2. Incident air kerma at the en
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8.8. DOSIMETRY8.8.1. Mean glandular
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TABLE 21. ACCEPTABLE AND ACHIEVABLE
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FIG. 34. Suggested layout for ruler
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8.10. IMAGE DISPLAY QUALITYThe accu
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FIG. 35. Modified TG18-QC test patt
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Page 143 and 144: 8.11. LASER PRINTER8.11.1. Laser pr
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Page 152 and 153: Appendix IISPECIFICATIONS OF TEST E
Page 154 and 155: TABLE 24. SPECIFICATIONS OF TEST EQ
Page 156 and 157: FIG. 40. Image acquired with a unif
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Page 160 and 161: FIG. 45. A TG18-QC test pattern dis
Page 162 and 163: [29] ALSAGER, A., YOUNG, K.C., ODUK
Page 165 and 166: Annex IRADIOGRAPHER DATA COLLECTION
Page 167 and 168: Chart 2 — DIGITAL MAMMOGRAPHY (DM
Page 169 and 170: Chart 4 LASER PRINTER SENSITOMETRY
Page 171 and 172: Chart 6 — WEEKLY DISPLAY MONITOR
Page 173 and 174: Chart 7(b) WEEKLY QC TEST OBJECT:
Page 175 and 176: Chart 9 — SAFETY AND FUNCTION CHE
Page 177 and 178: Chart 11 — LASER PRINTER ARTEFACT
Page 179 and 180: Chart 13(a) — RECORD OF DIGITAL M
Page 181 and 182: Chart 14 — CR PLATE SENSITIVITY M
Page 183 and 184: Annex IIITHE MAMMOGRAPHY EXTRACTThe
Page 185: GLOSSARYair kerma. The energy depos
Page 189: CONTRIBUTORS TO DRAFTING AND REVIEW
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