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(12) Using a transparent flexible ruler, measure the rulers embedded in the TG18-QC image, as well as the lengthof the annotation lines. Calculate the scaling factor of the printed image (i.e. 1 cm on the detector 33 isequivalent to how many centimetres on film?).(13) Record the results on the data collection sheet.(14) Print (and process, if a wet processor is being used) a greyscale step wedge or use the TG18-QC image.(15) If a TG18-QC image is printed, use the appropriate window width and window level settings. Record thesevalues on Chart 17 in Annex II.(16) If a wet processor is being used, obtain five films, spaced out over at least 2 hours, but preferably over 5 days.The site radiographer can print the films, provided that he or she is shown how it should be done. Ensure thatthe window width and window level settings are the same each time.(17) If using the TG18-QC pattern, read and record the densities for the maximum optical density area (D max ,border of 0–5% contrast square), the mid-density box (MD, Box 8 (47.06%)), upper density box (DD1, Box 4(21.96%)), lower density box (DD2, Box 13 (78.43%)) and the base + fog (BF, border of 95–100% contrastsquare).(18) If using a greyscale step wedge, choose step numbers as follows:— Base + fog (BF) — the lightest step;— Mid-density (MD) — the step closest to but not below an optical density of 1.20, or the working opticaldensity;— Upper density (DD1) — the step closest to but less than 2.20;— Lower density (DD2) — the step closest to but not less than 0.45;— Maximum density (D max ) — the darkest step.(19) If using a wet process printer, record the density values on a daily wet process printer sensitometry targetvalues chart. If using a dry process printer, record the density values on a monthly dry process sensitometrytarget values chart. Use Chart 4 in Annex I as a template.(20) Calculate the density difference (DD) by subtracting the lower density value from the upper density value(DD = DD1 – DD2).(21) If a wet process printer is being used, record these four values (BF, MD, DD and D max ). Establish the baselinevalues of each of these four parameters by calculating their average values over the five films that have beenproduced.(22) Record the target values on the daily wet process printer sensitometry target values chart or monthly dryprocess printer sensitometry target values chart, as appropriate.8.11.1.4. Interpretation of results and conclusions(1) All density steps should be distinct, and all low contrast squares in the corners of the greyscale patches shouldbe visible. If this is the case, the density difference (contrast), maximum density and mid-density have beenset appropriately and probably meet GSDF requirements.(2) The 5% squares at both bright and dark levels must be visible when the film is placed on the radiologistmammographic viewbox.(3) All line pair patterns should be distinguishable.(4) Measured lengths of the horizontal and vertical rulers on the TG18-QC pattern should be within 5% of actualvalues.(5) Measured lengths of the horizontal and vertical annotation lines on the film should be within 5% of actualvalues.(6) At least the letters ‘QUALITY CONT’ should be discernable in the displayed pattern at all three grey levels.system.33The modified TG18 patterns represent a simulated output from the detector of each commercial digital mammography132