Quality assurance in dental radiography

explains all the relevant quality assurance measures in both conventional and digital dental radiography

1. QUALITY ASSURANCE IN DENTAL RADIOGRAPHY BY MAMMOOTTY IK

2. CONTENTS INTRODUCTION Schedule of radiographic QA procedures Daily procedures Weekly procedures Monthly procedures QA of digital radiography Conclusion References

3. INTRODUCTION Quality Assurance - steps taken to make sure that a dental office or radiologic facility will produce consistently high-quality radiographs with minimum cost and pt exposure

4. Schedule of Radiographic QA procedures Daily Tasks: For conventional set up Compare the radiographs with reference film Enter findings in retake log Replenish processing solutions Check temperature of processing solutions Make step-wedge test of processing system For digital radiography CCDs/CMOS Visual inspection of wiring and casing For phosphor plates:(CR –system) Visual inspection of any external scratches

5. Weekly For conventional set up: Replace processing solutions Clean processing equipment Clean view-boxes Review retake log Monthly For conventional set up: Check darkroom safe-lighting Clean intensifying screens Rotate film stocks Check exposure charts For digital radiography CCDs/CMOS and PSPs Checking the uniformity of the image

6. Schedule of Radiographic QA procedures Yearly Calibrate x-ray machine Check kVp accuracy Check mA accuracy Check timer accuracy Check half –value layer Check focal spot degradation Check collimator efficacy Panoramic slit alignment test

7. Daily tasks Several tasks should be performed daily to ensure excellent radiographs: Compare Radiographs with Reference Film: Simple and effective means for constant monitoring of the quality of images produced. Soon after processing solutions are replaced, mount a patients film that has been properly exposed and processed with exact time-temperature technique on a corner of the viewbox . This image with optimal density and contrast – serve as reference for radiographs made in the following days and weeks. Subsequent images are compared with the reference-if any discrepancy is identified, source determeined and corrected

8. Enter findings in Retake Log: Effective way of reducing the number of faulty radiographs Record all errors for films that were rendered undiagnostic before the retake

9. Checking the automatic x-ray processor/manual solutions: the purpose is to determine the proper freshness of developer solution and developing temperature Most usual problem is depleted developer or cold developer solution due to failure of the heating element or its temoerature control Step wedge test: Provides accurate monitoring of day to day processing conditions Measures the speed of imaging system and image contrasts-sensitive measures of the processing environment. An aluminum step wedge can be purchased or can be made using a stack of 5 lead foils from film packets Lay the step wedge on top of a film packet and expose using usual setting for an adult bitewing view. After changing to fresh solutions develop the film and save it as a base line reference film. Similarly expose a series of films and store it in the refrigerator. Everyday, one of the pre-exposed film is run through the processor or processed manually and is checked if density and contrast remain constant when compared with the baseline film.

10. If not of the same density-the solutions should be replenished or changed. developer should be replenished after 4 full mouth surveys, panoramic films, or 80 IOPAs 4 to 6 onces of fresh developer should be added 2 to 3 ounces of fixer will be need – fixer lasts twice as long as developer If problem persists, temperature should be checked; All manual processors should be maintained at 70⁰F. For replenishing/changing automatic processing solutions: Always fill the fixer solution first. Rinse out the developer solution tank in case any fixer splashed into it while filling the fixer tank. Then fill the developer tank. After filling the processor , turn it on. If the processor has a thermostat to adjust the temperature, let it reach the predetermined operating temperature.

11. WEEKLY TASKS: Clean processing equipment: Regular cleaning: necessary for optimal operation Clean the solution tanks before solutions are changed For automatic processing: For normal weekly cleaning, use warm water and non abrasive brush to clean the rollers Periodically(2-4 times in a month)use the systems cleaner recommended by the manufacturer to remove heavier build-up After cleaning with systems cleaner, one should rinse for twice as long as the manufacturer recommends Inspect the rollers, gears and turning mechanism for signs of wear and reassemble

12. Clean view-boxes: Clean view-boxes weekly to remove any particles or defects that may interfere with film interpretation. Should be of uniform luminance A difference in luminance can create confusion and may effect accurate interpretations. If a bulb or tube fails, it is best to replace all of them. Review Retake Log Review the retake record weekly. Identify any recurring problems with processing conditions or operator techniques. Use the information to educate staff or to initiate corrective actions.

13. Monthly tasks Check dark room safelighting Film becomes fogged in the darkroom because of inappropriate safelight filters, excessive exposure to safelights Stray light from other sources. To check for light leaks in a darkroom, turn off all the lights, allow your vision to accommodate to the dark and check for light leaks, Mark light ;leaks with chalk or masking tape. Weather stripping is useful for sealing light leaks under doors

14. Penny test: Can be done monthly to evaluate for fogging caused by inappropriate safe lighting conditions: Open the packet of an exposed film and place the test film in the area where film are unwrapped and clipped on the hanger Place a penny on the film and leave it in this position- approximate time required to unwrap and mount a full mouth set of films—usually about 5 minutes Develop the test film-if image of the penny is visible ,room is not light-safe Each type of film used should be tested. Assess the integrity of safelights(GBX-2 filters with 15 watt bulb)-should be intact without cracks

15. Clean intensifying screen Clean all intensifying screens in panoramic and cephalometric film cassettes monthly. Scratches or debris – recurring light areas in the images Foam supporting the screens must be intact and capable of holding both screen closely against the film If close contact not maintained-image loses sharpness

16. Stocking films and storage of CCDs,CMOS , PSPs For conventional X-ray films: Dental x-ray film is stable when properly handled Store it in a cool, dry facility away from a radiation source. Rotate stock when new film is received – old film does not accumulate in storage. Always use the oldest film first For CCDS , CMOS,PSPs: Should be kept in a cool dry place, must be kept dust-free CCDs should be kept covered by disposable polythene cover every time an exposure is made and should be changed after every exposure

17. Check exposure charts: Each month inspect exposure tables listing the proper kVp , milliamperes ( mA ) and exposure times for making radiographs of each region. Help ensure all operators use the appropriate exposure factors Usually, mA is set at its highest setting;kVp is fixed;and exposure times is varied-patient size and area of interest. Exposure times are initially determined emprirically

18. Yearly task Calibrating the X-ray machine: X ray machines are generally quite stable and only rarely is a malfunctioning of the machine the acuse of poor radiographs. So, machines need to be calibrated only annually unless a specific problem is identified. The x-ray machine is annually tested for the following three factors relating to the x-ray- quantity, quality and collimattion .

19. Checking the quatity of the x-ray beam(output) Purpose is to verify that output of the machine has not changed since the last procedure. Quantity is mainly affected by mA circuit and mainly by exposure time To measure for quantity, set the machine at a standardised set of exposures(for eg ; 0.25 seconds, 7 or 10 mA and 65 or 70 kVp and measure the quantity of radiation being generated. Can be done using a pocket dosimeter or using an inexpensive aluminum or lead foil wedge. If the baseline(first reading) has been 180mR(say) and the present reading is the same, then no further testing of beam quantity is needed. In case of step wedge-on comparing with a baseline step wedge image with the present step wedge image is exactly similar in terms of DENSITY and CONTRAST,then the machine is functioning normal. If not, then mA circuit and timer is checked

20. Checking the timer: Procedure employed demonstrates the principle- self rectified dental x-ray machines- xrays are generated in impulses constant potential machines –x-rays are produced continuously for the selected exposure time interval. A simple brass spinning top is used in self rectifying machines where as in constant potential machines an electric timer meter is used.

21. Using spining brass top: A brass top on which there is a brass disc with a single small hole on the periphery is placed on top of an occlusal film or a panoramic film in a cassette The machine is set at 0.25 ie 15 impulses(say)(60 impulses in 1s) Central ray is directed perpendicular to the spinning top, which is in motion On the resultant image one small dark spot will be produced for each impulse. Dark spot produced should match with exposure time set

22. Checking the mA circuit: Procedure usually demonstrates the principle of mAs reciprocity Usually done in machines where there two mA settings usually 10mA and 15 mA . As long as the mAs factor remain the same for both settings and output measured with pocket dosimeter remains the same for the both settings, mA circuits are said to be operating properly Firstly, the operator sets at 70 kVp , 15mA and 1 sec(15mAs),measures the output in mR Then , the operator sets at 10 mA and 1.5 seconds(15mAs) at 70 Kvp,again measures the output in mR Both mR readings should be same, if not servicing is required.

23. Checking the quality of the X-ray beam: Quality of the x-ray photons is the function of kVp that determines the wavelength and penetrating power of the x-ray beam. These two are influenced by accuracy of Kvp setting and Focal spot size.

24. Checking the penetrating power of the beam: This procedure demonstrates HVL principle “50% of the x-ray photns should penetrate through a standardized thickness of a given material(usually Al) depending on kVp ” As per the standard; For machines working at max kVp of 69 or less;50% of x-ray should pass through at least 1.5mm of Al For those working at max kVp of 70+;HVL should be at least 2.5mm Al To test HVL, discs of 1.5mm or 2.5mm of Al is placed above a pocket dosimeter and the machine is set at its max kVp . The operator then compares the output readings with and without discs in place. Should be checked if the readings meet the accepted standard.

25. Checking the accuracy of kVp setting: Procedure visible demonstrates the kVp measurement. If the x-ray machine fails the HVL test, then kVp circuit must be checked A kVp meter is generally used to check the kVp circuit. The machine is set at max kVp stting and aimed at the target area on kVp meter. Exposure time should be long enough for the kVp meter to obtain a reading\ Measures the wavelength and frequency of the beam- gives an accurate read-out of actual kVp . Should be same as that of the setting If different, problem is asso with the machine itself, not the external power supply.

26. Checking the focal spot: Purpose is to evaluate the surface area of the focal spot that becomes pitted over time and enlarges. An enlarged focal spot decreases definition and increases magnification. A small focal spot size provides sharpness that is measured by resolution. Resolution is the ability to visibly separate or resolve images of small objects placed close together. Can be checked by using a test object-containing a no. of bar patterns – to test the resolution.

27. Focal spot checker: Inexpensive device – 6 inch plastic cylinder –has paired bar patterns on a lead wafer on one end and other end is open Open end centered over a occlusal film and an exposure is made by placing the end of PID against the closed end. If 11 or 12 line pairs visible on the processed film- excellent resolution 7 or less line pairs-poor resolution-focal spot need to be replaced (either by rebuilding or purchasing a new machine).

28. Checking the collimation of the x-ray beam: Purpose to ensure proper reduction of size of the x-ray beam As per standards; beam must be collimated to 2.75inches at the tip of the PID Collimation test: Operator simply places end of the PID against a rare –earth fluorescent screen or a loaded panoramic cassette-exposure time is set at 1 or 2 seconds Lights turned off-operator looks through the leaded window if the fluorescence is limited to diameter of PID Can also process the panoramic film to check if the exposed area is limited to the DM of the PID

29. Alternate test for collimation: Four no.2 dental films placed on a piece of paper in the form of cross-shaped template PID and location of each film is traced on the paper-film identified with lead numbers or small puncture holes PID is positioned to cover approx. half of each of the films Exposed using half the max. anterior exposure-processed and returned to proper order. If exposed area >2.75inches in DM-collimator opening is too large. Rarely , beam may not be centered on open end of the PID –due to faulty positioning of collimator-result in unavoidable cone-cuts-resolved by adjusting the collimator by tapping or changing the PID

30. Panoramic slit alignment test: Done to check wether the opening on the X-ray tube head is in alignment with the opening in the image receptor Procedure: Tape film packets to the top and bottom of the slit on the image receptor Mark the position of the slit on the film packetswith a ballpoint pen Expose the film Observe if the exposed portion of the film is in alignment with demarcation caused by the use of the pen Record the results Discrepancy if any should be reported to x-ray service provider for repair as soon as possible.

31. QC procedures for digital radiography Digital image quality assessment should include: Investigation of any significant deterioration in quality and instigation of appropriate corrective measures: Recording all investigations together with identified cause and action taken Regular annotation of image quality record Subjective assessment of quality of each radiograph.

32. QC of digital equipment: Solid state sensors: can be either CCDs or CMOS: They require Regular checks to ensure no evidence of cracks or damage to the cable and sensor casing Regular assessment of non-uniformity of receptor.

33. Phosphor plates: These require: Regular checks for visible scratches and dirt Being passed daily through the reader to detect scratches Regular cleaning following manufacturer's instructions Regular assessment for non-uniformity of receptor

34. Monitors These require: Regular cleaning Regular QA calibration/checks for Distortion Grey scale reproduction Limiting resolution(at both high and low contrast) Unifromity Can be done using specific test patterns designed such as TG18-QC test pattern(by AAPM)and SMPTE test patten designed by SMPTE

35. conclusion

36. REFERENCES: Oral radiology- Principles & interpretation-white & pharoah-5 th edition Essentials of dental radiography- johnson , Mcnelly,Essay (6 th edition) Essentials of dental radiology and radiography- whaite & Drago (5 th edition) Principles Of Dental Imaging- Langland,Langlaise,preece (2 nd edition)