1. Quality Control in Diagnostic Radiology

2. Factors driving Q.C. Why do we do it?
Legal Requirements
Accreditation
JCAHO
ACR
Clinical improvement
equipment performance
image quality
Medical Physicists at Work

3. Q.C. Goals Minimize dose to Optimize image quality Establish baselines
patients
staff
Optimize image quality
Establish baselines
More on this in a moment

4. Yeah, that’s what I always say.
Why is Q.C. Important?
Without a QC program the only way to identify problems is on patient images. And some problems don’t show up on images.
Yeah, that’s what I always say.

5. QC can detect Malfunctions Unpredictability
may be hard to isolate clinically
Inefficient use of Radiation
high fluoroscopic outputs
Radiation not reaching receptor
inadequate filtration
oversized collimation

6. Goals of a Q.C. Program
Obtain acceptable image with least possible radiation exposure to
patients
staff
Attempt to identify problems before they appear on patient films
without QC problems only detected on patient films

7. “Acceptable” Image
Image containing information required by radiologist for correct interpretation
goal: minimize exposure while maintaining acceptability
high exposure images often have excellent appearance
Low noise

8. Q.C. & Baselines Baselines Baselines useful for troubleshooting
quantitative data on equipment obtained during normal operations
Baselines useful for troubleshooting
isolating problem component, for example
generator
processor
Allows efficient use of engineering / repair personnel

9. X-Ray Quality Control Filtration Focal Spot Size Collimation
Maximum Fluoroscopic Output
Calibration Verification
Phototimer Performance

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

11. Half Value Layer (HVL) We don’t measure filtration We measure HVL
HVL: amount of absorber that reduces beam intensity by exactly 50%

12. Half Value Layer Depends upon Minimum HVL regulated by law
kVp HVL
(mm Al)
Depends upon
kVp
waveform (single/three phase)
inherent filtration
Minimum HVL regulated by law
Maximum HVL regulated only in mammography
Georgia State Rules &
Regulations for X-Ray

13. Radiographic HVL Setup

14. Checking HVL Compliance (Radiographic)
How much aluminum must be placed in beam to reduce intensity by exactly 50%?
90 kVp Measurements;
2.5 mm Al minimum HVL
filter mR
(mm Al)
filter mR
(mm Al)
filter mR
(mm Al)
Not OK! Must remove Al to reduce beam to exactly 50%
OK! Must add Al to reduce beam to exactly 50%
Acceptable
HVL > 2.5 mm
Marginal
HVL = 2.5 mm
Unacceptable
HVL < 2.5 mm

15. Checking HVL Compliance (Radiographic)
Is this machine legal?
2.5 mm Al minimum filtration at 90 kVp
90 kVp Measurements
filter mR
(mm Al)

16. Fluoroscopic HVL Setup

17. Fluoroscopic HVL Set desired kilovoltage manually
measure exposure rates instead of exposure
Move absorbers into beam as needed

18. Focal Spot Size We measure apparent focal spot Trade-off
smaller spot reduces geometric unsharpness
larger spot improves heat ratings
Apparent
Focal Spot
Actual

19. Focal Spot Size (cont.) Focal spot size changes with technique
Standard technique required
75 kV (typical)
50% maximum mA for focal spot at kV used
direct exposure (no screen)
NEMA Standards defines tolerances
Nominal Size Tolerance
>1.5 mm %
>0.8 and <=1.5 mm %
<0.8 mm %

20. Focal Spot Measuring Tools
Direct Measurement Pin Hole Camera
Slit Camera
Indirect Measurement of Resolving Power
Star Test Pattern
Bar Phantom

21. Direct Focal Spot Measurement
Measure focal spot directly in each direction
Use triangulation to correct for distances
formula corrects for finite tool size
two exposures required for slit
Slit
Camera
Pinhole
Camera

22. Star Test Pattern Measures resolving power measure
infers focal spot size
Dependent on focal spot energy distribution
measure
largest blur diameter (in each direction)
magnification
use equation to calculate focal spot size

23. Bar Phantom Measures resolving power
Find smallest group where you can count three bars in each direction

24. Bar Phantom Setup

25. Radiographic Collimation
X-Ray / Light Field Alignment
Beam Central Axis
should be in center of x-ray beam
Collimator field size indicators
PBL (automatic collimation)
field automatically limited to size of receptor
Bucky Alignment
Using longitudinal bucky light & transverse detent, x-ray field should be centered on bucky film

26. X-Ray / Light Field Alignment
Mark light field on table top with pennies

27. Radiographic X-Ray / Light Field Alignment

28. Fluoroscopic Collimation
image field is scale seen on monitor
expose film on table above scale
compare visual field (monitor) with x-ray field on film
must check all magnification modes

29. Fluoroscopic Collimation

30. Fluoroscopic Collimation

31. Maximum Fluoro Output put chamber in beam on tabletop
block beam with lead above chamber
fools generator into providing maximum output
10 R/min. limit for ABS fluoro

32. Maximum Fluoro Output
Lead

33. Calibration Performance Parameters
Timer Accuracy
Repeatability
Linearity/Reciprocity
Kilovoltage accuracy mA
must be measured invasively

34. Calibration 120 kVp mA time mAs mR mR / mAs (msec)
? ?
? ?
Constant mAs
mR/mAs should stay constant for all combinations of mA & kVp at any particular kVp

35. Calibration 120 kVp mA time mAs mR mR / mAs (msec)
? ?
? ?
Double mAs
Double mAs
again
mR/mAs should stay constant for all combinations of mA & time at any particular kVp

36. Phototiming (check with output or film)
Reproducibility
Density Controls
Field Placement
Field Balance
Phototiming Operation should be Predictable

37. Density Control Phototimer Density Control Settings -2 -1 1 2 41 49 62a b l e t o p
Density Control -2 -1 1 2 41 49 62 76 96

38. Phototiming Density Steps should be predictable & approximately even

39. Phototimer Field Placement / Balances u r m n f P h i F d c / B
Lead for checking field placement
Placement
cover desired field with lead
select field as indicated
Balance
no fields covered

40. Phototimer Field Placement / Balance

41. Phototiming checked with Exposure Index
kV Response
phototimer pick-up attenuation may vary with kV
phototimer must track kV response of rare-earth film
Rate Response
Check with varying
phantom (lucite) thickness mA

42. kV/Rate Response kV 70 81 90
Lucite
17.5
4.5
4.9
5.2
Depth
12.5
4.7
(cm)
7.5
4.7
kV Response
kilovoltage
Optical Density 2 4 70 81 90
Thickness Tracking 4
Optical
Density 2
17.5
12.5
7.5
Lucite Thickness

43. Any questions, you varmints?
The End
Any questions, you varmints?