Chapter 31 Quality Control

1. Chapter 31 Quality Control • Two areas of activity are designed to ensure the best possible image quality with the lowest possible exposure and minimum costs. • Quality Assurance deals with people • Quality Control deals with instrumentation and equipment.

2. Ten Step Approach to Quality Assurance • Assign responsibility • Delineate scope of care • Identify aspects of care • Identify outcomes that effect the aspects of care. • Establish limits of the scope of assessment.

3. Ten Step Approach to Quality Assurance • Collect and organize data. • Evaluate care when outcomes are reached. • Take action to improve care • Assess and document actions • Communicate information to organization-wide QA Program

4. QA Projects • Things that QA can evaluate includes • Scheduling of patients • Instructions given to patients • Wait times in the office • Interpretation of films • Retake analysis • Record accuracy

5. QA Program • Quality Assurance deals with people and processes used to complete tasks. • QA involves training and record keeping. • As the owner of the equipment, you will be responsible for your radiology services. • The State of California Department of Radiologic Health established the Standards of Good Practice that is the foundation of QA and QC in radiography.

6. QA and QC Requirements • Degree of requirements vary by state. California and New York have very tight standards for quality control of the radiographic and processing equipment. • We are required by statue to teach QA and QC in the radiology program. It is covered in detail in 9th Quarter. My textboook covers QC in detail.

7. Quality Control • An acceptable QC program has three steps: • Acceptance Testing • Routine performance monitoring • Maintenance

8. Acceptance Testing • The x-ray machine, cassettes and film processor or digital system are the largest capital expense you may experience. • It makes economic sense to make sure that the equipment meets the performance standards. • It is recommended that a third party such as a health physicist do the testing.

9. Acceptance Testing • Areas that should be tested include on the x-ray machine: • Shielding of Room • Focal spot size • Calibration of mA, timer or mAs • Calibration of kVp • Linearity of exposure • Beam alignment • Grid centering • Collimation • Filtration (HVL)

10. Acceptance Testing • Areas that should be tested on the x-ray cassettes: • Screen contact • Screen speed • Light leaks • Light spectrum matching

11. Acceptance Testing • Areas that should be tested on the x-ray film processor: • Developer temperature • Replenishment rates • Travel time • Water flow • Hypo retention

12. Quality Control • The acceptance testing ensures that the machine was installed and calibrated properly. • The performance may drift or deteriorate over time. Consequently, periodic testing is required to monitor the performance. • With the exception of film processing most testing is annual or semiannual.

13. Quality Control • After a major repair, the machine should be retested to ensure that it was repaired properly. • When the testing shows that the machine is not performing properly, service or preventive maintenance is required. • Manufactures establish recommended preventive service schedules. When these are followed many repairs become unnecessary.

14. Radiographic Quality Control • Areas of concern in x-ray machine • Focal Spot Size will impact spatial resolution • Filtration will impact patient exposure • Collimation will impact patient exposure • kVp calibration will impact image quality and exposure. • Exposure timer accuracy will impact image quality and exposure

15. Radiographic Quality Control • Areas of concern in x-ray machine • Exposure linearity will impact exposure and image quality • Exposure reproducibility will impact exposure and image quality. • Alignment of tube and image receptor will impact exposure and image quality.

16. Focal Spot Testing • When the machine is installed or the tube is replaced, the focal spot size should be measured. Then annually thereafter. • A pin hole camera, star test pattern or line pair test tool. • As the tube ages, the focal spot tends to grow and spatial resolution is lost.

17. Filtration • The filtration is measured but determining the half value layer of the beam at specific exposure levels. Minimum filtration is 2.5mm aluminum. • As a tube ages, tungsten will plate the x-ray port and increase filtration. This can cause technique problems. Inadequate filtration will significantly increase patient exposure.

18. Collimation • If the collimation is misaligned, intended anatomy can be missed. • It can be tested in many ways from using pennies to using test patterns. • Misalignment can not exceed ± 2% of the SID. • It is tested semiannually and after the replacement of the collimator lamp.

19. kVp Calibration • In diagnostic radiology, any change will impact patient exposure. A variation of about 3% will impact contrast and image density. • Can be tested with filtered ion chambers, filtered photodiodes or even a cassette with calibrated filters. • Tested annually.

20. Exposure Timer Accuracy • The exposure time is the responsibility of the operator. It will impact the density of the image and spatial resolution. • Tested with an ion chamber, multi-meter internally or even a spinning top. • Exposure time must be within ±5% for exposure times greater than 10 ms and ±20% less than 10 ms.

21. Exposure Linearity • Many combinations of mA and time will produce the same mAs value. The ability of the machine to produce a constant level of exposure with various combinations of mA and time is called exposure linearity. • Can be tested with a step wedge and densitometer or rate meter. • Should be within 10% for adjacent stations.

22. Exposure Reproducibility • Any exposure using the same factors should produce the same level of density and contrast on the image. • Sequential exposure should be reproducible to within ± 5% • Can be tested with a rate meter or step wedge and densitometer.

23. Performance standards for x-ray equipment

24. Darkroom and Processing • The development of the image is dependent upon the temperature of the developer, it’s concentration and how long the film is in the developer. • The film is sensitive to variations in the environment and processing from the time it is manufactured until it is processed. • Darkroom and Processor QC is the key process of Quality Control.

25. Processing • Processor densitometry is performed daily before the first patient is exposed. • A sensitometer is used to produce a step wedge image on the film that is evaluated with a densitometer. • The densitometer reads the optical density of the processed image. • A digital thermometer is used to test the chemical temperatures in the processor.

26. Processing • Key densities on the processed film are measured and then graphed. • Base plus Fog is measured on an area of unexposed film to check the darkroom environment. • Speed is tested at the level of exposure that produces a density of 1.25OD • Contrast is tested at the level that produced a density of 0.40 OD and one that produced a density of 2.20.

27. Processing • By monitoring these densities, problems with film processing can be detected before image quality deteriorates. • In 9th Quarter we will cover how to perform processor QC and problem solve.

28. Waste Records • Since used fixer is classified as a hazardous waste material, it is important to maintain accurate records of usage and disposal. • The extent of records vary by city, county and state. You are responsible for the proper disposal of the waste. Some regions include developer as hazardous waste.

29. Silver Recovery • If the silver ions are removed from the fixer, it may be disposed of in the normal waste when diluted with water. • There are two primary types of silver recovery systems. • Metallic replacement uses steel wool and can recover 95% of the silver in the effluent • Electrolytic recovery passes direct current through the solution and nearly pure metallic silver is deposited on the cathode.

30. Silver Recovery • Old radiographic films and repeated films are retained for silver recovery. X-ray images can not be disposed of in normal trash. • They also can not be used to clean the processor rollers. • Waste recovery companies will either burn or chemically remove the silver from the film.

31. Performance standards for film processor and darkroom equipment

32. Accessory QC • The cassettes and screens are the area of chief concern. Problems with either will result in artifacts on the images and increased retakes. • The screens need to be properly cleaned frequently. Mammography screens are cleaned daily. California recommends monthly cleaning.

33. Accessory QC • Dirty screens produce white artifacts on the image. • Multiple white artifacts indicate the need to replace the screens. • Screen contact is tested semiannually. A problem with screens contact will cause a loss of resolution. • As screens age, they loose speed so this is also tested.

34. Accessory QC • The other important accessory is the gonad protection devices and lead aprons. • Improper care of the apron can result in cracks and holes in the lead that reduces their effectiveness. • Aprons and shields are tested semiannually. The easiest was to test them is with video-fluoroscopy but film can be used.

35. Performance Standards for Accessories

36. Failed Lead Apron Test

37. Record keeping • All electromechanical devices need periodic service. • There are three types of maintenance. • Scheduled maintenance such as processor monthly or weekly service. It includes observing moving parts and lubrication. • Preventive maintenance is planned service and replacement of parts at regular intervals before they fail at inopportune times.

38. Record keeping • Non-scheduled maintenance is the worst type of service because it impacts patient service. It may also be very expensive. • With proper scheduled and preventive maintenance, non-scheduled service can be minimized. • All service schedules should meet manufacture recommendations. • All service should be documented as part of the quality assurance program.

39. Retake Analysis • Required part of a QA program in California. • Evaluation includes • View repeated • Cause of the repeat • Rate of retakes should be less than 5%. • Information can be gathered from the log that the state mandates for patients being exposed to radiation.

40. Retake Analysis • Done every three months using a relatively large sample of data to see trends in: • Type of examination being repeated. • Reasons for the repeated films. • Determine if additional training or review is needed. • Determine if equipment service might be required.

41. Repeat Analysis • Your patient log can be designed to capture both films usage and repeated films. • Data is gathered from log for analysis • Repeated films can be put into two main categories: • X-ray Personnel Errors • Equipment malfunctions

42. X-ray Personnel Errors • Failure to measure patient. • Use of improper technical factors (mAs, kVp or distance) • Incorrect positioning • Improper Collimation • Improper use of accessories such as cassettes, grids or filters

43. X-ray Personnel Errors • Improper handling of exposed or unexposed films. • Failure to clearly communicate to the patient breathing instructions and to remain still. • Failure to observe patient during exposure.

44. X-ray Equipment and Accessory Failure or Malfunctions • Inaccurate calibration of kVp and mA. • Inaccurate timer calibration • Dirty or damaged cassettes • Improperly labeled or damaged grids • Malfunctioning collimator • Improper film storage or processor function.

45. Reasons for Retake Films • Over or under exposure accounts for over 50% of retakes nationally. • Errors in positioning (25%) • Patient motion 11% • Processing errors 6% • Wrong view, beam alignment,cassette screen or grid errors and artifacts.

46. Retake Films by Region • Cervical Spine Exams = 7% • Thoracic Spine Exams = 17% • Lumbar and Abdominal X-rays = 40% • Skull, Chest,Lower Extremities = 15% • Majority or retake results in unnecessary exposure to gonads or blood forming organs of the body.

47. Daily Log Design • Most regulatory agencies will require a log of patients having radiation exposure. • Columns can be added to capture film usage, repeats, views repeated and reason. • This data can be gathered and analyzed.

48. Retake Analysis • In this example, most of the retakes were of the T-spine. Potential reasons include: • Improper use of filters • Incorrect measurements • Faulty technique chart

49. Retake Analysis • The reason of each retake is recorded and percentages are computed to determine the overall rate and rate by reason. • Less than 5% is ideal.

50. Quality Assurance and Digital Radiography Information gathered for this lecture came from American College of Radiology Practice Guidelines for Digital Radiography 10/10/07 “Quality Management in The Imaging Sciences “ Jeffrey Pap Mosby 1998