Quality Control in
Diagnostic Radiology
Factors driving Q.C.
Why do we do it?
 Legal Requirements
 Accreditation
 JCAHO
 ACR
 Clinical improvement
 equipment performance
 image quality
Q.C. Goals
 Minimize dose to
 patients
 staff
 Optimize image quality
 Establish baselines
 More on this in a moment
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.
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
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
“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
Q.C. & Baselines
 Baselines
 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
X-Ray Quality Control
 Filtration
 Focal Spot Size
 Collimation
 Maximum Fluoroscopic Output
 Calibration Verification
 Phototimer Performance
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
Half Value Layer (HVL)
 We don’t measure filtration
 We measure HVL
 HVL: amount of absorber that reduces beam intensity
by exactly 50%
Half Value Layer
 Depends upon
 kVp
 waveform (single/three
phase)
 inherent filtration
 Minimum HVL regulated
by law
 Maximum HVL regulated
only in mammography
kVp HVL
(mm Al)
30
0.3
40
0.4
49
0.5
50
1.2
60
1.3
70
1.5
71
2.1
80
2.3
90
2.5
100 2.7
110 3.0
120 3.2
130 3.5
140 3.8
150 4.1
Georgia State Rules &
Regulations for X-Ray
Radiographic HVL Setup
Radiographic
Filter
R
Tab leto p
Checking HVL Compliance
(Radiographic)
Radiographic
 How much aluminum must be placed
in beam to reduce intensity by exactly
50%?
Filter
R
Tab leto p
OK! Must
add Al to
reduce beam
to exactly
50%
90 kVp Measurements;
2.5 mm Al minimum HVL
filter
mR
(mm Al)
------------------0
250
2.5
133
filter
mR
(mm Al)
------------------0
250
2.5
125
filter
mR
(mm Al)
------------------0
250
2.5
111
Acceptable
HVL > 2.5 mm
Marginal
HVL = 2.5 mm
Unacceptable
HVL < 2.5 mm
Not OK!
Must remove
Al to reduce
beam to
exactly 50%
Checking HVL Compliance
(Radiographic)
Radiographic
 Is this machine legal?
 2.5 mm Al minimum filtration at 90
kVp
Filter
R
Tab leto p
90 kVp Measurements
filter
mR
(mm Al)
------------------0
450
2.5
205
Fluoroscopic HVL Setup
Fluoroscopic Tube Filt rat ion
( Half Value Layer)
Image
Tube
A bsorber
( t o prot ect
Image Tube)
R
Tablet op
Fi l t e r
Fluoroscopic HVL
 Set desired
kilovoltage manually
 measure exposure
rates instead of
exposure
Fluoroscopic Tube Filt rat ion
( Half Value Layer)
Image
Tube
A bsorber
( t o prot ect
Image Tube)
 Move absorbers into beam as
needed
R
Tablet op
Fi l t e r
Focal Spot Size
 We measure apparent
focal spot
 Trade-off
 smaller spot reduces
geometric unsharpness
 larger spot improves
heat ratings
Actual
Focal Spot
Apparent
Focal Spot
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
30%
>0.8 and <=1.5 mm 40%
<0.8 mm
50%
Focal Spot Measuring Tools
 Direct Measurement
Pin Hole Camera
 Slit Camera
 Indirect Measurement of Resolving Power
 Star Test Pattern
 Bar Phantom
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
Star Test Pattern
 Measures resolving power
 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
Bar Phantom
 Measures resolving
power
 Find smallest group
where you can count
three bars in each
direction
Bar Phantom Setup
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
X-Ray / Light Field Alignment
 Mark light field on table top with pennies
X-ray / Light Field Alignment
Slig ht m isal ignm ent
on this edg e
Lam p
Lig ht
Tab leto p
X-Rays
Tab leto p
Radiographic X-Ray / Light
Field Alignment
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
Image
Tube
Film
Collimator Test Tool Template
Ta bletop
Fluoroscopic Collimation
Fluoroscopic Collimation
Maximum Fluoro Output
 put chamber in beam on
tabletop
 block beam with lead above
chamber
Image
Tube
 fools generator into providing
maximum output
Lead
 10 R/min. limit for ABS fluoro
R
Tab leto p
Maximum Fluoro Output
Lead
Calibration
Performance Parameters
 Timer Accuracy
 Repeatability
 Linearity/Reciprocity
 Kilovoltage accuracy
 mA
 must be measured invasively
Calibration
120 kVp
mA
time mAs
mR
mR / mAs
(msec)
-----------------------------------------------------.1
10
240
24
Constant 100
200 .05
10
?
?
mAs
50
.2
10
?
?
 mR/mAs should stay constant for all
combinations of mA & kVp at any particular
kVp
Calibration
120 kVp
mA
Double mAs
Double mAs
again
time mAs
mR
mR / mAs
(msec)
----------------------------------------------------100
.1
10
240
24
200
.1
20
?
?
100
.4
40
?
?
 mR/mAs should stay constant for all combinations
of mA & time at any particular kVp
Phototiming
(check with output or film)
Reproducibility
Density Controls
Field Placement
Field Balance
Phototiming Operation should
be Predictable
Phototimer Density Control Settings
R
R
Tablet op
Density Control
-2
41
-1
49
0
62
1
76
2
96
Phototiming
Density Steps
should be
predictable &
approximately
even
% Step to Step Change
Change
30.0
20.0
10.0
0.0
0
-2 -1 0
1
2
0
Density Control Setting
0
Phototimer Field
Placement / Balance
 Placement
Measurement of Phot ot imer
Field Placement / Balance
 cover desired field with
lead
 select field as indicated
Lead for checking
field placement
 Balance
 no fields covered
 select field as indicated
R
R
Tablet op
Phototimer Field
Placement / Balance
Field
Covered
Left
Center
Right
L& R
Left
355
26.9
29.9
578
Field Placement
Field Selected
Center
Right
L&
23.2
29
242
25.4
24.3
610
18.3
266
Above readings in mR
R
51
25.6
56.6
354
Field Balance
15 cm Lucite, 81 kVp
Field
mR
Left
6.6
Center
4.9
Right
6.3
L& R
6.3
"Disc" units
Phototiming
checked with Exposure Index
 kV Response
 phototimer pick-up attenuation may vary with
kV
 phototimer must track kV response of rareearth film
 Rate Response
 Check with varying


phantom (lucite) thickness
mA
Measurement of Phot ot imer
kV / Rat e Response
Tablet op
Fi l m
kV/Rate Response
kV
70
81
Lucite
17.5
4.5
Depth
12.5
4.7
7.5
4.7
(cm)
4.9
90
5.2
kV Response
Optical Density
Optical
Density
Thickness Tracking
4
2
0
17.5
12.5
7.5
Lucite Thickness
4
2
0
70
81
kilovoltage
90
The End
Any
questions,
you varmints?