1. X-Ray Generators and Ancillary Radiographic Equipment
Chapter 7
Quality Control of
X-Ray Generators and Ancillary Radiographic Equipment

2. X-ray Generators
Single Phase Generator – uses single phase of alternating current

3. X-ray Generators (cont’d)
Single Phase Generator – half-wave rectified

4. X-ray Generators (cont’d)
Single Phase Generator – full-wave rectified

5. X-ray Generators (cont’d)
Three Phase Generators – utilize 3 sources of alternating current

6. X-ray Generators (cont’d)
Three Phase Generators – 3-phase, 6-pulse

7. X-ray Generators (cont’d)
Three Phase Generators – 3-phase, 12-pulse

8. X-ray Generators (cont’d)
High Frequency Generator – increases frequency of incoming alternating current

9. X-ray Generators (cont’d)
Three main components:
Control or Operating Console
High Voltage Generator
X-ray Tube, Tube Accessories and X-ray Table

10. Quality Control for Radiographic Units
Three Components:
Visual Inspection
Environmental Inspection
Performance Testing

11. Radiation Measurement
Most performance testing performed with gas-filled chamber detectors
Three different type of these detectors:
Ion Chamber – most often used
Proportional counter
Geiger-Muller Counter

12. Performance Testing X-ray Generator
Reproducibility or Exposure
Same technical factors should always produce the same radiation output
Testing requires measuring output with detector at same technical factors
Any variation found during testing cannot exceed ± 5%

13. Performance Testing X-ray Generator (cont’d)
Radiation Output
Measures amount of radiation exposure per mAs of technique
Units are either mR/mAs or μCkg-1/mAs
Determined using radiation detector and making exposure at 10 mAs
Current and previous values are compared
All values should remain within ± 10%

14. Performance Testing X-ray Generator (cont’d)
Radiation Quality and Filtration
Measured by determining Half Value Layer (HVL)
Determined by using a radiation detector and making exposures at 80 kVp adding aluminum filters in 1 mm increments
Minimum HVL at 80 kVp is 2.3 mm aluminum equivalent

15. Performance Testing X-ray Generator (cont’d)
Kilovolt peak (kVp) Accuracy
Can be determined by using a special test cassette or a digital kVp meter
Determines whether or not the kVp value on the control console corresponds with the maximum energy of the actual x-ray beam
Variations between the stated kVp and the actual x-ray beam quality must be within ± 5%

16. Performance Testing X-ray Generator (cont’d)
Timer Accuracy
Testing can be performed by using either the spinning top test or a digital timer
The variability allowed for timer accuracy is ± 5% for exposure times greater than 10 milliseconds (ms) and ± 20% for exposures less than 10 milliseconds (ms)

17. Performance Testing X-ray Generator (cont’d)
Voltage Waveform
Visualizes voltage waveform through x-ray tube

18. Performance Testing X-ray Generator (cont’d)
Reciprocity
The same mAs should produce the same radiation output regardless of mA and time selected
Testing utilizes a radiation detector and exposures using same mAs but different mA and time stations
Any variation between exposures cannot exceed ± 10%

19. Performance Testing X-ray Generator (cont’d)
Linearity
Any sequential change in mAs should produce the same sequential change in radiation output
Testing involves making exposures of a radiation detector at mAs values that are double that of previous exposure
Any variation between exposure cannot exceed ± 10%

20. Performance Testing X-ray Tube and Tube Accessories
Focal Spot Size
Evaluated to determine if focal spot blooming has occurred
Level of blooming must not exceed NEMA standards

21. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Focal Spot Size
Testing can be performed by one of three devices:
Pinhole camera
Focal Spot Test Tool
Star or slit resolution patterns

22. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Restriction System
Light Field-Radiation Field Congruence
Assures that light field of collimator is the same area struck by x-rays
The light field must be congruent to within ± 2% of the SID
Evaluation can be performed by the use of either a collimator test tool or 8-penny test

23. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Restriction System
Image Receptor-Radiation Field Alignment
Determined with collimators equipped with Positive Beam Limitation (PBL)
Variation between the x-ray field and image receptor size must be within ± 3% of the SID

24. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Restriction System
Accuracy of the X-Y Scales
Size of field selected by collimator adjustment knobs must correspond to the actual field size to within ± 2% of SID
Can be tested with collimator test tool or 8-penny test

25. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Restriction System
Illuminator Bulb Brightness
Determined using a photometer placed tabletop at a 100 cm SID
The illumination of the light source must be at least 15 foot-candles (ft-cd) or 160 lux when measured at a 100-cm (40”) distance

26. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Alignment
X-ray beam must be mounted properly in its metal housing and aligned to the center of the bucky tray
Items to evaluate include perpendicularity and x-ray beam/bucky tray alignment

27. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Alignment
Perpendicularity
The x-ray tube must be mounted in its housing so that the x-ray beam is within 1 degree of perpendicular
Testing is performed with a commercially available beam alignment tool

28. Performance Testing X-ray Tube and Tube Accessories (cont’d)
Beam Alignment
X-ray beam/Bucky tray alignment
Also known as central ray congruency
The x-ray beam/Bucky tray alignment must be within ± 1% of SID
Testing can be performed using either a beam alignment tool or the washer or coin method

29. Performance Testing X-ray Tube and Tube Accessories (cont’d)
SID Indicator
The SID indicator must be installed so that it is accurate to within ± 2% of the SID
Testing can be performed with a tape measure or the triangular method

30. Performance Testing Overload Protection
The overload protection mechanism should not permit an exposure that exceeds 80% of the tube capacity for a single exposure
Testing involves selecting technical factors that would exceed limit and then depress rotor/prep button on control panel
If rotor engages and ready light appears, system fails

31. Performance Testing (cont’d)
X-ray Tube Heat Sensors
Usually found on 3-phase equipment
Heat sensors should provide a warning when anode heat reaches 75% of the maximum

32. Automatic Exposure Control
Consists of two main components:
Detectors – also known as sensors, cells or chambers. Actual devices can be either photodetectors, ion chambers or solid state detectors
Comparator – receives signal sent by detectors and terminates exposure when a specific amount of radiation has been measured

33. Automatic Exposure Control Testing (cont’d)
Backup, or Maximum Exposure Time
The backup timer should terminate the exposure within 6 seconds or 600 mAs, whichever comes first
Testing involves placing a lead apron tabletop over sensors and seeing if exposure terminates within specified values

34. Automatic Exposure Control Testing (cont’d)
Consistency of Exposure with Varying mA
System should maintain exposure level with any changes in mA
Testing involves making a series of exposures of a homogenous phantom at different mA stations. Images should all be the same.
Any variation cannot exceed ± 10%

35. Automatic Exposure Control Testing (cont’d)
Consistency of Exposure with Varying kVp
System should maintain exposure with any changes in kVp
Testing involves making a series of exposures of a homogenous phantom at different kVp values
All images should be similar

36. Automatic Exposure Control Testing (cont’d)
Consistency of Exposure with Varying Part Thickness
System should be able to compensate for changes in part thickness
Testing involves a series of exposures of a homogenous phantom of varying thickness values
Images should be similar

37. Automatic Exposure Control Testing (cont’d)
Consistency of Exposure with Varying Field Sizes
System should be able to compensate for any changes in the x-ray field size
Testing involves a series of exposures of a homogenous phantom at different field sizes
Images should be similar

38. Automatic Exposure Control Testing (cont’d)
Consistency of AEC Detectors
Each detector or sensor should function identically to all other detectors
Testing involves exposures of a homogenous phantom at each of the sensors available on unit
Images should be similar

39. Automatic Exposure Control Testing (cont’d)
Reproducibility
Exposures made at the same kVp and mA stations of the same phantom thickness should produce the same exposure
Testing involves a series of exposures of a homogenous phantom at the same kVp and mAs
Images should be similar

40. Automatic Exposure Control Testing (cont’d)
Density Control Function
Density selector should allow for changes in radiation exposure of 25% to 30% for each increment
Testing involves a series of exposures of a homogenous phantom at each of the density selector options
Each setting should produce an image 25% to 30% greater than the previous setting

41. Conventional Tomographic Systems
Used to create “slices” of the body to remove superimposition and improve contrast in area of interest
Two basic types are linear (sometimes called rectilinear) and pluridirectional (sometimes called multidirectional)

42. Quality Control of Tomographic Systems (cont’d)
Section Level
Requires specialized test tool
The level of the section indicated on the equipment and the actual level should be the same or within ± 5 mm (some manufacturers suggest ± 1 mm for pluridirectional units)

43. Quality Control of Tomographic Systems (cont’d)
Section Thickness
Evaluation is made with special test tool

44. Quality Control of Tomographic Systems (cont’d)
Level Incrementation
Requires testing with specialized test tool
A ruler should be constructed so that changing from one tomographic section to the next is accurate to within ± 2 mm

45. Quality Control of Tomographic Systems (cont’d)
Exposure Angle
Testing involves specialized test tool
The value indicated on the equipment and the actual angle are the same or within ± 5 degrees for units operating at angles greater than 30 degrees and within ± 2 degrees for units operating less than 30 degrees

46. Quality Control of Tomographic Systems (cont’d)
Spatial Resolution
Testing involves imaging a test tool with a mesh pattern containing different size holes
Units should be able to resolve at least 40 holes per inch

47. Quality Control of Tomographic Systems (cont’d)
Section Uniformity and Beam Path
Radiation output should be consistent throughout exposure
Any variation for uniformity should be within optical density value of ± 0.3
Path closure in pluridirectional units should be within ± 10% of the path length for beam path

48. Quality Control of Tomographic Systems (cont’d)
Patient Exposure
Patient exposure for tomographic image should not exceed two times the non-tomographic exposure for the same part in the same position

49. Grid Testing Grid Uniformity
Lead strips in grid must be uniformly spaced
Image of homogenous phantom is made and optical density of the center and center of each quadrant is made
Readings should be within ± 0.10 for proper uniformity

50. Grid Testing (cont’d) Grid Alignment
Center of grid must be aligned with the detent lock position of the x-ray tube
Testing requires imaging a special test tool

51. Portable and Mobile X-ray Generators
Portable Generator – small enough to be carried by one person
Mobile Generator – pushed on wheels
Direct Power Unit
Capacitor Discharge
Cordless
High Frequency