1. Part No...., Module No....Lesson No
Module title
RTC on RADIATION PROTECTION OF PATIENTS FOR RADIOGRAPHERS Accra, Ghana, July 2011
QA Programmes in Diagnostic Radiology
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

3. QUALITY ASSURANCE QUALITY CONTROL
An overall system which deals with quality in all its aspects, qualitative and quantitative
QUALITY CONTROL
The quantitative aspects of a quality assurance programme

4. Quality assurance programs (I)
Radiology imaging equipment should produce images that meet the needs of the radiologist or other interpreters without involving unnecessary irradiation of the patient.
Quality assurance actions contribute to the production of diagnostic images of a consistent quality by reducing the variations in performance of the imaging equipment.

5. The quality control aspects of a quality assurance program are, however, not necessarily related to the quality (information content) of the image.
They may (and often do) relate to the radiation dose to the patient

6. Quality assurance programs (II)
It has been increasingly recognized that quality assurance programs directed at equipment and operator performance can be of great value in improving the diagnostic information content, reducing radiation exposure, reducing medical costs, and improving departmental management.
Quality assurance programs thus contribute to the provision of high quality health care.

7. Quality assurance programs (III)
Several studies have indicated that many diagnostic radiological facilities produce poor quality images and give unnecessary radiation exposure.
Poor equipment performance makes a significant contribution to the high prevalence of poor image quality.

8. Effect of poor quality images
A poor quality image has three negative effects:
If the image is not of adequate quality, practitioners may not have all the possible diagnostic information that could have been made available to them, and this may lead to an incorrect diagnosis.
If the quality of the radiograph is so poor that it cannot be used, then the patient shall be exposed again, causing an increase in the cost of diagnosis.
Unnecessary radiation exposure also occurs in the production of inadequate quality radiographs.

9. Standards of acceptable image quality
Prior to the initiation of a quality control program, standards of acceptable image quality should be established.
Ideally these standards should be objective, for example “acceptability limits for parameters that characterize image quality”, but they may be subjective for example “the opinions of professional personnel” in cases where adequate objective standards cannot be defined.

10. Retake analysis
The analysis of rejected images is a basic component of the quality assurance program
Those images judged to be of inadequate quality are categorized according to cause of reject, which may be related to the competence of the technical personnel, to equipment problems or specific difficulties associated with the examination, or some combination of these elements
Examples of the main causes of retake:
Exposure faults (particularly important in mobile radiographic equipment)
Bad positioning
Equipment malfunction

11. How to start ? (I)
Look for past experience in the existing literature.
Taking into account the personnel and material available.
Define priorities if it is not possible to develop the full program.
Look for the usefulness of the actions to be done.

12. How to start ? (II)
With the “basic” quality items (image quality and patient dose).
Use criteria to decide if the results of the controls are good enough (eg. comparison with guidance levels) or if it is necessary to propose corrective actions.
Leave the more difficult items for a second step!

13. Basic advice !
Any action (quality control, corrective action, etc) should be reported and documented, and:
Should be performed within a reasonable time.
The reports should be understood and known by radiologists and radiographers.
The cost of the proposed corrective actions should be taken into account (useless actions should be avoided).

14. Test objects for objective image quality evaluation
Test for QC of monitors and laser printers
Test for QC of geometry in
fluoroscopy
Test for QC of radiography
Test for QC in mammography

15. Clinical images and quality criteria for image quality evaluation (I)
For a chest examination (P/A) projection:
Performed at full inspiration (as assessed by the position of the ribs above the diaphragm - either 6 anteriorly or 10 posteriorly) and with suspended respiration.
Symmetrical reproduction of the thorax as shown by central position of the spinous process between the medial ends of the clavicles.
Medial border of the scapulae outside the lung fields.
Reproduction of the whole rib cage above the diaphragm.

16. Clinical images and quality criteria for image quality evaluation (II)
EUR CEC 1996.
For a chest examination (cont’d):
Visually sharp reproduction of the vascular pattern in the whole lung, particularly the peripheral vessels
Visually sharp reproduction of :
a) the trachea and proximal bronchi,
b) the borders of the heart and aorta,
c) the diaphragm and lateral costo-phrenic angles
Visualization of the retrocardiac lung and the mediastinum
Visualization of the spine through the heart shadow

17. Patient dosimetry Dose indicators:
Entrance dose for simple examinations.
Dose area product and total number of images and fluoroscopy time for complex procedures.
For some complex interventional procedures, maximum skin dose.
For CT scanner, CTDI and the number of slices (also Dose Length Product DLP).

18. Repeat Analysis
Keep a record of repeated x-rays, and understand WHY a repeat was necessary
Use in continuing education of radiographers
Especially important in digital imaging, where repeats can easily by “hidden” or not recorded

19. Routine QC Testing

20. Why QC?
In general we want best possible image quality for least necessary radiation dose
Baseline testing of new equipment
Monitor equipment performance at regular intervals, and to know when corrective action is necessary
Check compliance with any regulatory requirements
Proactive QC rather than reactive ad hoc testing

21. Protocols and Guidelines
need to be able to repeat the measurement
perform the same test the same way each time
need to be able to compare your results with others
sometimes specified in national or international (eg. IEC) Standards

22. Protocols and Guidelines
regulatory bodies may want to specify not only how a test should be performed, but what range of results is acceptable
usually obtained from national or international standards

23. What is included? General Equipment design features
Radiation safety – shielding, signage, protective clothing
Equipment design features
Operation indicators, exposure switch, control of multiple tubes, filtration, markings
Performance testing (excluding mammography)
kVp, timer, HVL, linearity, AEC, leakage, collimation, fluoroscopy parameters (resolution, dose rate, image quality, collimation)

24. Beam Half Value Layer (HVL)
Possibly the most important test
Checks whether there is sufficient filtration in the x-ray beam to remove damaging low energy radiation
Need not only a radiation detector, but also high purity (1100 grade) aluminium - most Al has high levels of high atomic number impurities eg. Cu

25. Part No...., Module No....Lesson No
Module title
Unfiltered X-Ray Spectrum (100 kVp)
Radiation
Intensity
Characteristic radiation
(related to target material)
Low energy
radiation,
damaging
to tissue
Bremsstahlung
radiation
kVp
Bremsstrahlung radiation 20 40 60 80
100
120
Energy (keV)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

26. Part No...., Module No....Lesson No
Module title
Filtered (~3mm Al) Spectrum (100 kVp)
Radiation
Intensity
characteristic
radiation
Dose
saved
Bremsstrahlung
radiation 20 40 60 80
100
120
Energy (keV)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

27. kVp Accuracy kVp should be +- 5% of set value
Should be measured at acceptance of x-ray unit, or
After a tube change, generator maintenance
As well as regularly

28. Timer Accuracy Unlikely to be a problem in recent x-ray units
Measure exposure time at commonly used time settings
Calculate error between set and actual time

29. Linearity
Checks that the radiation output per mAs remains constant as the mA is varied
Checks so-called kVp and mA “compensation”, where the extra loads on a HV generator at high mA are compensated for – kVp must not fall
If radiographers make manual exposures, they should be confident of the result of an exposure adjustment (less important when AEC used)

30. AEC
AEC should routinely be used, and is fitted to table and chest Bucky systems
Usually 3 detectors, and operator can chooses whatever combination is desired
Spine
Lungs
Remember that the centre chamber sensitivity is adjusted to
account for the increased density of the spine!

31. AEC parameters Reproducibility Variation between chambers
Minimum response time
Exposure termination limit (backup timer)

32. Resolution and the Focal Spot
Part No...., Module No....Lesson No
Module title
Resolution and the Focal Spot
Penumbra
More blur
Less blur
Appearance of image
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

33. Light Field/X-Ray Field Alignment
Radiography equipment uses a light field to show the radiographer where the x-ray field will (hopefully) be
The light field can come out of alignment and must be checked
Alignment should be with ± 1% of FFD

34. GOOD Light Field/X-Ray Field Alignment
Anode end marker
Coin shadows
X-ray Field

35. POOR Light Field/X-Ray Field Alignment
Anode end marker
Coin shadows
Alignment error
X-ray Field

36. X-Ray tube housing leakage
Tube housing has 2mm+ lead to prevent excess leakage
Can be damaged at tube change
Limit is 1 1m from tube focus, using maximum continuous rated tube factors (kVp and mA)
Measure using kVp, and exposure which will not damage tube!

37. Fluoroscopy QC
Fluoroscopy equipment must have normal tests for kVp, field alignment, and HVL
Image quality is tested with a “phantom”
Also need to check maximum and typical radiation dose rates to the patient

38. Control Charts An essential tool for detecting changes in performance
A plot of a parameter over time, with permissible limits
Easy to see when a parameter is likely to become unacceptable, before it actually does so

41. Part No...., Module No....Lesson No
Module title
DR, CR and DF – Extra QC
Routine QC interval will depend on system – not less than annually
Extra tests needed
Dose Calibration
Low Contrast (contrast to noise ratio)
Uniformity
Artifacts
Spatial Linearity
AEC will most likely need to be reset after change from film
There are general QC tests that are performed on CR readers….Dose calibration, Resolution, Contrast, Uniformity, and Spatial Linearity.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

42. Patient Dose in Digital Imaging
Because of the very wide dynamic range of digital detectors, DR/CR can reduce radiation exposure
DO NOT simply use the same exposure parameters as for film/screen
Because higher dose gives less image noise, “exposure creep” is a real problem
“A digital image without a little noise is a bad image” – Joel Gray

43. Special Requirements for CR QC
In film screen systems the film is changed for every image
With CR the IP is read up to 10,000 times
Almost all plates suffer from wear artifacts
If you are suspicious about an artifact in a patient image, take another exposure using the same plate and no patient
Make sure there is a QC program to detect wear before you see it clinically
Hammerstrom et al
J Digital Imaging :226

44. CR Plate Problems – Clinical Image
Part No...., Module No....Lesson No
Module title
CR Plate Problems – Clinical Image
Let’s begin with Agfa IPs.
On this clinical image, there appears to be two artifacts that are prominent and two others along the edges that are less obvious. But, there are more artifacts visible. In fact about 12 more. When the flat-field image is examined it is apparent that the small white line densities in the clinical image are not due to patient anatomy but are in fact artifacts caused by scratches on the phosphor surface. It is interesting to note that the two prominent artifacts do not appear on the flat-field radiograph and may be artifacts caused by something on or in the patient. The scratches were all visible visually.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

45. CR Plate Problems (Fuji IP)
Part No...., Module No....Lesson No
Module title
CR Plate Problems (Fuji IP)
Artifacts observed around the periphery of Fuji flat-field radiographs was most often caused by yellowing of the phosphor. Yellowing is caused when the physical integrity of the IP edge is compromised and moisture oxidizes the halides in the phosphor. For example from iodine to iodate.
Yellowing (oxidising) of phosphor halides
Wear of plate phosphor edge
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

46. Part No...., Module No....Lesson No
Module title
CR Plate Problems
Dust
Scratches
Lastly, we will look at Kodak IPs.
The phosphor surface of several large IPs were observed to have a slightly darker hue along one edge and it wasn’t until the phosphor surface was gently wiped with a gloved fingertip that it became apparent that the hue was really a dusting of very fine aluminum particulates. The magnified areas in the radiograph show the areas where the dust was removed from the phosphor surface.
Scratches were also apparent both radiographically and visually and were most often found in this location on large IPs and were oriented in the direction of IP travel.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

47. Part No...., Module No....Lesson No
Module title
CR QC Recommendations
Quality Control (QC) - perform monthly
Inspection – cassette and IP
Visual
Radiographic
CR Cassette cleaning
CR IP cleaning
Benefits
Fewer image artifacts and repeated exposures
Increased life cycle of cassettes, IPs, and readers
Compliance with vendor warranties
I would strongly encourage anyone using CR to perform regular quality control on your CR cassettes and imaging plates. Look at them, radiograph them, and clean them on a regular basis.
The primary goal of such a program is to reduce the number of artifacts visualized and the number of repeats performed. Other benefits include an increased life cycle of your CR equipment and compliance with vendor warranties.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

48. Calibration of Displays
Part No...., Module No....Lesson No
Module title
Calibration of Displays
Software generates grey scale levels
Photometer measures the luminance output at each level and adjusts video card output to obtain a perceptually linear gradation between grey scale levels
Calibrates display to DICOM standard grey scale display function (GSDF)
To calibrate the displays, a photometer is held against the display surface while software generates gray-scale intervals from black to white. The luminance at each gray-scale level is measured by the photometer and adjustments are made to the video card output to obtain a perceptually linear gradation between gray-scale levels.
I calibrate approximately 180 primary and secondary displays in the VCHA. Primary displays at LGH and STS are calibrated by a Rad. Service engineer whose office is at LGH.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

49. Film Processing

50. Film Processing QC Why ? How ?
Sometimes the most crucial part of imaging
“Most photo labs. have better processor QC than X-Ray departments”
How ?
sensitometry (measurement of the film response)
densitometry (measurement of the film density)
darkroom fog, film/screen contact, chemical tests

51. Film Processor QC

52. Not this!!!

53. Film Processor QC Most important QC features : proper film storage
cassette and screen care
processor chemical care
sensitometry
artifacts
processor cleanliness

54. Film Processor QC - Film Storage
Film should be stored in cool, dry conditions
< 26° C, 30-60% relative humidity
Too low humidity allows static discharge
Storage period must not be too long
Stack film boxes vertically to avoid pressure on films (causes pressure marks)

55. Film Processor QC - Cassette and Screen Care
Clean screens regularly to avoid dust shadows and scratches
Use manufacturer’s recommended cleaning solutions
An ultraviolet light (“Black Light”) can show up dust

56. Film Processor QC - Processor Chemical Care
Chemicals (developer and fixer) degrade with time and use
Developer in particular will oxidize (go brown) and cause poor, dirty films
Fixer will change pH and lose emulsion hardener

57. Film Processor QC - Processor Chemical Care
Chemicals must be replaced or replenished (continual automatic replacement) regularly
Use manufacturer’s recommendations
Check the developer temperature daily - processing is very sensitive to temperature

58. Sensitometry Sensitometer and densitometer required
Essential to keep the process under control
To be performed daily
Main parameters investigated:
base + fog
speed
contrast

59. Sensitometry (1)
Use a sensitometer to expose a film to light and insert the exposed side into the processor first
Before measuring the optical densities of the step-wedge, a visual comparison can be made with a reference strip to rule out a procedure fault, like exposure with a different colour of light or exposure of the base instead of the emulsion side

60. Sensitometry (2)
From the characteristic curve (the graph of measured optical density against the exposure by light) the values of base and fog, maximum density, speed and mean gradient can be derived.

61. Densitometer

62. Sensitometric strip A method of exposing film by means of a
sensitometer and assessing the response
of film to exposure and development 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

63. Characteristic curve of a radiographic film
Optical
Density (OD)
Saturation
Saturation
Saturation D1 D1
Visually invaluable
range of densities
 = (D2 - D1) / (log E2 - log E1)
 = (D2 - D1) / (log E2 - log E1)
 = (D2 - D1) / (log E2 - log E1)  
The  of a film : the gradient of the straight line portion of the characteristic curve D2 D2 D2
Normal range
of exposures
Base
+ fog E1 E1 E1 E1 E2 E2 E2 E2
Log Exposure (mR)

64. Film sensitometry parameters
Base + fog: The optical density of a film due to its base density plus any action of the developer on the radiographically unexposed emulsion
Sensitivity (speed): The reciprocal of the exposure value needed to achieve a film net optical density of 1.0
Gamma (contrast): The gradient of the straight line portion of the characteristic curve
Latitude: Steepness of a characteristic curve, determining the range of exposures that can be transformed into a visually invaluable range of optical densities

65. Sensitometry Limiting value : base + fog: £ 0.20 OD
contrast: Mean Grad:
speed: reference to baseline value 10%
Frequency : Daily
Equipment : Sensitometer and densitometer

66. Film Processor QC - Artifacts
Anything on the film which is not related to the x-ray image
Examples :
dust marks, static discharge
fixer stains (poor washing)
film storage problems
processor problems (roller marks, scratches)

67. Film Processor QC - Processor Cleanliness
All processors will eventually get dirty
Strip down and thoroughly clean processor at least every 6 months
Daily cleaning of entrance trays

68. Darkroom light leakage (I)
Remain in the darkroom for a minimum of five minutes with all the lights, including the safelights, turned off
Ensure that adjacent rooms are fully illuminated
Inspect all those areas likely to be a source of light leakage

69. Darkroom light leakage (II)
To measure the extra fog as a result of any light leakage or other light sources, a pre-exposed film of about 1.2 OD is needed
Always measure the optical density differences in a line perpendicular to the tube axis to avoid influence of the heel effect

70. Darkroom light leakage (III)
Open the cassette with pre-exposed film and position the film (emulsion up) on the (appropriate part of the) workbench
Cover half the film and expose for four minutes.
Position the cover also perpendicular to the heel effect to avoid the influence of this inhomogeneity in the measurements

71. Darkroom safelight (I)
Perform a visual check that all safelights are in good working order (filters not cracked)
To measure the extra fog as a result of the safelights, repeat the procedure for light leakage but with the safelights on
Make sure that the safelights were on for more than 5 minutes to avoid start-up effects

72. QC Summary QC is meant to help take good radiographs
The best radiographer in the world will still take bad x-rays if the equipment is not working properly
More importantly, the patient will get higher and unnecessary radiation doses, as will the staff
You will also waste money on x-ray film