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Annex IVEXPOSURE INDICES FOR MAMMOGRAPHYThe wide dynamic range of a digital imaging system will allow images produced by a wide range of detectordoses to be displayed with similar greyscale appearance. Consequently, changes to the detector dose may not bereadily observed unless an exposure index (EI) is provided giving an indication of the previous dose. Without suchan index it is possible that breast doses may drift from the optimum; this is a particular concern if they increasemarkedly above the level deemed sufficient for diagnosis.Fortunately, most digital radiography (DX) systems provide a direct indication of breast dose, based on theexposure parameters and the compressed breast thickness. These values are all carried in DICOM tagsaccompanying the image. In contrast, computed radiography (CR) systems are not able to provide the exposureparameters unless specific hardware and software are employed to transfer the details from the mammographyX ray unit to the CR reader. Additionally, they are unable to calculate an estimate of the breast dose. However, theydo provide an EI that is indirectly related to the detector dose. In all instances the relationship between the EI(Table IV–1) and the detector dose should be clearly specified in the manufacturer’s documentation along with thecalibration conditions. The conditions for general radiographic systems [A–1] differ substantially from those formammography systems. Developing a universal EI for mammography would be useful.TABLE IV–1. EXPOSURE INDICES FOR COMPUTED RADIOGRAPHY SYSTEMS IN MAMMOGRPHYManufacturer Exposure index Calibration equation Calibration conditionsAgfaSAL, SALlogor PVIlogSAL = 253·÷KSALlog = 10 000·log 10 (K) + 8 581PVIlog = 13 287.7·log 10 (K) + 23 824Agfa suggest using 28 kVp, Mo/Mo with 2 mm Alfiltration.Carestream EI EI = 1000 · log 10 (K) + 1000 28 kVp, Mo/Mo with 2 mm Al filtrationFuji s value s value = 2400/K 25 kVp, Mo/Mo with no paddleKonica s value s value = 2400/K No specific advice offered by manufacturer —use of Fuji calibration conditions is suggestedPhilips s value See Fuji entry See Fuji entryNote: K is the air kerma incident on the plate, in mR (1 mR = 8.76 μGy).REFERENCE FOR ANNEX IV[A–1] AMERICAN ASSOCIATION OF PHYSICISTS IN MEDICINE, An Exposure Indicator for Digital Radiography: Report ofAAPM Task Group 116, AAPM Rep. 116, AAPM, New York (2009),http://www.aapm.org/pubs/reports/RPT_116.pdf172
GLOSSARYair kerma. The energy deposited per unit mass in air. The unit used to measure air kerma is the gray (Gy). ForX rays with energies less than 300 kilo-electron volts (keV), the magnitude of air kerma and absorbed dose inair are equivalent.amorphous selenium (a-Se, or a-Se). Amorphous selenium layers have the same structure as single crystals overshort distances, but are less ordered over larger distances. As a result, amorphous selenium layers provideuniform X ray detection over the large areas needed by flat panel X ray detectors. When X rays are absorbedin a-Se, electron–hole charge pairs are created and these can be collected under an electric field appliedbetween the two faces of the detector to form the signal. The a-Se can be deposited onto amorphous siliconTFT arrays to provide readout of the signal.amorphous silicon (a-Si, or a-Se). A type of silicon which has the same structure as single silicon crystals overshort distances but is less ordered over larger distances The ability to produce relatively large areas ofamorphous silicon at a cost that is very much lower than that for single crystal silicon has enabled fabricationof flat panel TFT arrays large enough to be used as the readout structure for all flat panel X ray detectors.artefact. Any structure or pattern visible in the image that is not part of the object being imaged.automatic exposure control (AEC) systems.Fully automatic AEC. A device designed to determine the spectrum (target material, filtration material andkV) and/or the exposure (mAs) needed to produce an adequately penetrated X ray image. This istypically done by sampling the X ray intensity after it passes through the patient and image receptor.Automatic exposure time (photo timing). The beam quality parameters are selected manually and the exposuretime is controlled automatically.bit depth. The number of bits used to digitize the detector signal, giving rise to the number of digital signal levels(greyscale). For a bit depth of n, the number of possible grey levels is equal to 2 n (i.e. 12 bits = 4096 shades ofgrey). Bit depth cannot be changed after equipment is purchased and is a vendor specific system characteristic.cassette. A light-tight case usually made of thin, low X ray absorption plastic, for holding intensifying screens andfilm or the CR plate. The screen stores the latent image and requires further processing to produce a visibleimage.compression device. A plastic paddle used to flatten and immobilize the breast. Compression helps reduce motionblurring in the breast, separates structures within the breast, and decreases the thickness of breast tissue. Thisminimizes the amount of radiation required and the amount of scattered radiation reaching the image receptor.Ideally, the compression device is made of rigid, thin plastic and has a flat bottom surface that is parallel to theplane of the image receptor, with edges perpendicular to the plane of the image receptor to assist in movingbreast tissue away from the chest wall and into the field of view.contrast resolution. The smallest relative exposure change that can be usefully imaged by a system. Ultimately,contrast resolution is limited by the dynamic range and the quantization (number of bits per pixel) of thedetector. Increased contrast resolution is considered one of the major advantages of digital receptors and tendsto counteract the lower spatial resolution of many digital systems.control chart. A graphical means of displaying data in which the variable of interest is plotted on the vertical axisas a function of time on the horizontal axis. The control chart allows for easy and rapid review of the data todetermine whether the process is within the desired control limits (‘in control’).173
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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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Page 135 and 136: 8.10.1.5. Interpretation of results
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Page 139 and 140: TABLE 22. MONITOR PERFORMANCE TOLER
Page 141 and 142: FIG. 38. Measurement of illuminatio
Page 143 and 144: 8.11. LASER PRINTER8.11.1. Laser pr
Page 145 and 146: 8.11.1.5. Recommendations and corre
Page 147: 8.12.1.4. Interpretation of results
Page 150 and 151: iopsies are performed, a sink is of
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
Page 158 and 159: FIG. 43. The left hand image is par
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: Annex IIITHE MAMMOGRAPHY EXTRACTThe
Page 187 and 188: image quality. The overall merit of
Page 189: CONTRIBUTORS TO DRAFTING AND REVIEW
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