1. Diagnostic Equipment Quality Control
George David, MS, FAAPM, FACR
Associate Professor of Radiology Augusta University
Augusta, Georgia

2. Why do Quality Control? Legal Requirements
Manufacturers regulated by federal law
Use of imaging equipment
Regulated by states --- Except ---
Mammography
Regulated by federal law

3. Why do Quality Control? Accreditation Because we make a difference
JCAHO
ACR
Because we make a difference
Equipment performance
Image quality
Patient & staff dose

4. Why is Q.C. Important?
Without a QC program the only way to identify problems is on patient images. And some problems aren’t visible on images. See?
Oversized collimation
Insufficient beam filtration

5. Our Goal
Best Possible Image
Oh yeah, dose

6. Our Goal Provide DIAGNOSTIC IMAGE at lowest dose
If both images are diagnostic, did zee patient receive benefit from additional 1.5 mSv?
Diagnostic but more noisy
Image #1 (2 mSv ESE)
Diagnostic but less noisy (prettier)
Image #2 (3.5 mSv ESE)
Dose

7. Q.C. Goals Obtain diagnostic images while minimizing dose to
patients
staff
Monitor image quality
Ensure predictable equipment operation
Establish baselines
data on properly operating equipment
assist in problem diagnosis by identifying performance changes

8. A QC program can detect Malfunctions (some) Unpredictability
may be hard to isolate clinically
Inefficient use of Radiation
high fluoroscopic outputs
Radiation not reaching receptor
inadequate filtration
oversized collimation

9. X-Ray Quality Control Filtration Focal Spot Size / System Resolution
Collimation
Radiographic Tube Leakage
Fluoroscopy
Scatter
Outputs
Calibration Verification
Phototiming

10. Filtration: Equivalent Absorber Present in Beam
A filtration of 4 mm Al means the beam spectrum is the same as if 4 mm Al were in the beam

11. Filtration Locations
inherent filtration
x-ray tube and housing

12. Filtration not in Tube
Metal sheets (usually Al) between tube & collimator or in collimator
Mirror
May be removable
If removable, must pass minimum HVL with plate removed
Added Filter
Filter

13. Why is Filtration Important?
Tube emits spectrum of x-ray energies
Filtration preferentially attenuates low energy photons
If not removed, low energy photons
expose patients
do not contribute to image
low penetration

14. Filtration: What do we measure?
Half Value Layer (HVL)
absorber (aluminum) thickness that reduces beam intensity by 50%

15. Check at single kVp value
kVp Minimum HVL
(mm Al)
Half Value Layer
HVL depends upon
Filtration
Waveform
kVp
(1 or 3 phase, medium frequency)
Minimum HVL regulated by law
Check at single kVp value
Georgia State Rules &
Regulations for X-Ray

16. Checking HVL Compliance (Radiography)
Fancy 1-shot meters can measure HVL

17. Checking HVL Compliance (Radiography)
Find aluminum thickness that reduces beam intensity 50%

18. Checking HVL Compliance (Radiographic)
What Al thickness reduces beam intensity 50%?
90 kVp, 20 mAs
2.5 mm Al HVL minimum
filter mR (mm Al)
Room #2
HVL > 2.5 mm
Room #1
filter mR (mm Al)
Room #3
HVL < 2.5 mm
filter mR (mm Al)
HVL = 2.5 mm
Marginal HVL exactly 2.5 mmAL
Must add Al to reduce beam to 50% (125)
Must remove Al to reduce beam to 50% (110)

19. Added Filtration Some collimators have selectable filtration
Check for all settings
Minimum HVL should be at minimum filtration setting
All settings should comply with state regs
Filter Selection Wheel

20. Fluoroscopic HVL Setup / ABS on (can’t turn it off)
Tabletop
Image Receptor
Filter
Absorber to protect image receptor

21. Fluoroscopic HVL Setup (ABS on)
Place all filters above chamber
Obtain desired kVp by manipulating
Absorber
SID
mag mode
Measure exposure rate
move filters from top to bottom
technique remains constant
total absorber in beam remains constant

22. Apparent Focal Spot Size (system resolution)
Trade-off
smaller spot reduces geometric unsharpness
larger spot provides improved heat ratings
Actual
Focal Spot
Apparent
Focal Spot

23. Bar Phantom Setup
Focal spot
18”

24. Bar Phantom Setup Evaluate digital image on workstation.
One image for each focal spot

25. Collimation
Radiography
Fluoroscopy

26. Radiographic Collimation
X-Ray / Light Field Alignment
Bucky Alignment
X-ray field should be centered on bucky
Beam Central Axis
should be in center of x-ray field
Collimator field size indicators
PBL (automatic collimation)
field limited to size of receptor

27. Radiography X-Ray/Light Field Alignment
Alignment requires correct:
collimator position on tube
mirror tilt

28. Central Beam Alignment Check
Do 2 holes in centering tool line up?
Central beam misalignment can cause distortion
Centering Tool (small hole in bottom & top)

29. Bucky Alignment (use one image for both x-ray/light & bucky alignment)
Center tube to bucky using
longitudinal bucky light
transverse & SID detents
Collimate smaller than receptor

30. Field Size Indicator Accuracy
Use correct SID scale

31. Positive Beam Limitation aka PBL & Automatic Collimation
Goal
Constrain x-ray field to size of receptor
Unit senses receptor size
Limits beam size to receptor
Receptor
Receptor

32. Positive Beam Limitation aka PBL & Automatic Collimation
Receptor in bucky
Check
Multiple cassette sizes
Cassette orientation
Fixed digital receptor
Beam no larger than receptor

33. Fluoroscopic Collimation
X-ray field should not exceed imaged field by more than
3% of SID (sum 1 direction)
4% of SID (sum both directions)
Check all magnification modes
Bad
Good
Image
Receptor
Image
Receptor

34. Why is Fluoroscopic Collimation Important?
Additional scatter
Degrades image
Substantially increases radiation to operator
Bad
Good
Image
Receptor
Image
Receptor

35. Fluoroscopic Collimation

36. Fluoroscopic Collimation
SID ~ 20”
3% SID = 0.6” 4% SID = 0.8”
Field Edges
Compare with numbers seen on monitor

37. Radiographic Tube Leakage
Regulatory limit
100 1 meter at maximum continuous kVp & mA

38. Fluoroscopic Scatter Use "patient equivalent" phantom
Water jug
Typical clinical protocol
Measure at appropriate points around room
Post diagram
Image
Receptor
Phantom
Tabletop

39. Fluoroscopic Scatter

40. Fluoroscopic Scatter

41. Maximum Fluoro Output 10 R/min limit for ABS fluoro center chamber
lead between chamber & image receptor
Drives output to maximum
measurement point
conventional fluoro
Table top
C-arms / specials
30 cm from image receptor
Image
Receptor
Lead
Lead R

42. Image Receptor Entrance Exposure Rate
Check all mag modes

43. Image Receptor Entrance Exposure Rate
Entire probe must be in x-ray field to get valid reading

44. Fluoro Outputs Verification of proper auto brightness operation
Baseline techniques / outputs
Check at several absorbor thicknesses
Check various
mag modes
Pulse rates
Fluoro “flavors”
Low dose
High dose

45. Calibration Performance Parameters
Timer Accuracy
Repeatability
Linearity/Reciprocity
Kilovoltage accuracy

46. Performance Parameters
Repeatability
within 5%
Linearity
constant mR/mAs for all mA
Set kV
Set distance

47. Timer Operation Accuracy Deadman function with auto reset
exposure ends immediately when switch released
full exposure must follow prematurely aborted exposure

48. Kilovoltage Accuracy kV Measurement +/- 2 kV constancy desirable
Waveform represented by single number
Non-invasive & invasive kV may not match
+/- 2 kV constancy desirable 87

49. Phototiming check with output or exposure index
Reproducibility
Density Control
ESE
Field Placement
Field Balance
Phototiming Operation should be Predictable

50. Phototiming Density Steps should be predictable & approximately even
Phototimer Density Control Settings
Phototiming Density Steps should be predictable & approximately even

51. Optical Density or Exposure Indexb l e t o p
Typical Phototimer Doses
Optical Density or Exposure Index
Phantom
kVp
Time (ms)
Meas.
FS-probe
FS-"Skin"
ESE mR
(in)
O.D.
Chest
117 7
14.22 56 63 11
1.56
Abd 77
16.5
141.1 26 31 99
1.14
Spine 81
21.5
184.6
130
1.17
Skull
13.4
112.7 32 74
1.2
Ext. 60
5.2
19.8 36 10
1.15

52. Phototimer Field Placement / Balance
Fields should be approximately the same
Some manufacturers purposely set center field differently than outer fields

53. Phototiming check with exposure indexa b l e t o p M s u r m n f P h i k V / R
Phototiming check with exposure index
kV response
Thickness / Rate Response
Vary phantom thickness
Receptor