Transcript QC Tests
QC Tests Darkroom Film processor V.G.Wimalasena Principal School of Radiography QC tests on film darkroom Safelight evaluation test Evaluation of white light leakage and processing area condition View box quality control test Evaluation of image duplicators Safelight test Load a film into a cassette in complete darkness Expose the cassette with step wedge on it , using appropriate exposure factors Take the film out in the darkroom and keep it on the darkroom bench. Cover one half of the film with a cardboard. Switch on the safe light and wait for 2 minutes Process the film and observe for a defined line which divide the image into two halves. If there is a fog, measure the optical densities and find the maximum fog (should be < 0.05) Image of step wedge showing safelight fog Light leakage testing and processing area condition Turn on all the lights surrounding darkroom. Enter the darkroom and switch off all the lights. After eyes adapt to the dark, check for white light leaks Turn on overhead light and inspect for foreign objects, dampness etc. on counter tops & film feed tray Check the film storage conditions and processing chemical tanks. Check the room temperature. Recommended conditions Film boxes should be stored vertically Temperature 14-24 0C Relative Humidity 30% - 60% Chemicals must be stored in a well-ventilated area with a temperature 5-30 0C. (for longer periods < 21 0C) and under low lighting. Films and chemicals should not be stored together. (radioactive isotope of potassium-40 is present in the chemicals and can fog the films) For films the background radiation should not exceed 7 µR/hr. Viewbox QC Should be cleaned weekly Intensity should be checked once a year (weekly for mammography) Use a photometer to measure the brightness. ( luminance or illuminance.) The standard luminance is 1700 nit. For mammography 3500 nit. (Illuminance should be above 5000 lux) The colour temperature should be 5400-10,000 0K (standard 6250 0K) Check for uniformity of the brightness compared to the centre (should be within + 10%). Film Copier QC Copy a sensitometer film and compare for density difference( + 0.02). Should be done weekly Make a copy of the wire mesh image to check the sharpness level. Should be done monthly For digital images copy a test pattern image and compare the densities from the similar areas.(+ 0.02) Processor Quality Control 1. Solution temperature Developer temperature should be checked periodically through out the day. Should not vary + 0.30C Fixer temperature should not vary + 30C from that of the developer to avoid reticulation marks. Use a digital thermometer with a remote probe or a glass, alcohol- filled thermometer 2. Processing time Change of processing time affect the image contrast, density and the visibility of recorded detail similar to that by the change of temperature. Should be maintained within + 2% to + 3% Should be checked daily. Use a stopwatch or digital timer 3. Replenishment rate If the solutions are not adequately replenished the image contrast and the optical density decreases. Excessive replenishment has the opposite effect to some extent. The rate should be + 5% of the recommended values. A film and a graduated cylinder can be used to measure the rate. Place the cylinder under the opening of the replenisher line. With the cover of the processor open, feed a 18 x 24 cm film lengthwise, collect the chemical in to the cylinder and measure the volume. Divide the volume by 24 to get the rate in milliliters per centimeter. 4 .Solution pH Developer solutions function in a pH range of 10 to 11.5. Fixer solutions should have a pH between 4 and 4.5 pH should be checked daily by using a digital pH meter or pH paper. 5. Specific gravity & proper mixing The chemicals should be mixed to recommended concentrations. This is given by the specific gravity. Use a hydrometer to measure the specific gravity Developer – range from 1.07 to 1.1 and should not vary by more than + 0.004 Fixer – range from 1.077 to 1.11 and should not vary by more than + 0.004 6. Processor cleaning procedures Dirty processors cannot function properly and is the cause of breakdown. Proper cleaning procedures should be performed: Daily – clean all roller racks and look for malfunctioning parts Monthly - drain the processing tanks, wash inside Quarterly – drain replenishment tanks and clean Yearly – use system cleaners to cleen the replenisher and circulation systems 7. Processor maintenance A proper maintenance schedule must be maintained to ensure continued operation of the film processor. A log of any maintenance procedures should be kept for documentation. Three types of maintenance Scheduled:- observations, adjustments and replacement performed daily, weekly, monthly Preventive:- regular replacement of certain parts Nonscheduled:- required when a system failure occurs. 8. Processor monitoring This is accomplished with the performance of daily sensitometric tests which evaluate the performance of processor systems and the chemicals. Equipment required Sensitometer or (step wedge and x-ray machine) Densitometer Control chart/graph paper Film Processor monitoring equipment procedure Expose the film in the sensitometer Process the film Measure and record the densities. Establish the following indicators of the processor performance. Base+Fog (BF) – optical density of the clear portion Speed indicator (or mid-density point) (MD)– optical density 1 above the base+fog and that step number Minimum density (or lower density) (Dmin)– density & step number closest to 0.25 above B+F. …….Procedure continued Maximum density (or high density) (Dmax) - the density and the step closest to 2 above B+F density Contrast indicator or relative density difference (DD) = (Dmax - Dmin ) Plot these values on a control chart. Repeat the procedure daily and measure the densities of the same step numbers established on the first day Look for variations and trends. Processor QC trouble shooting