Presentation during QIBA COPD Lung Density Reference and Consistency
Standards Work Group Call
Philip F. JudyJune 8, 2011
COPDGene Reference Standard Model 2
COPDGene Model 25mm B31f
-1000
-950
-900
-850
-800
-750
-700
-650
-600
60 80 100 120 140 160
Tube Potential
CT
Num
ber Foam 1
Foam 2
Foam 2
Lung
Spectral effects200 mAs – B31f – 5mm – Varied tube potential
COPDGene Model 2 - Subtract CT Number at 120 kV200 mAs 5mm B31f
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
60 80 100 120 140 160
Tube Potential
CT N
umbe
r Diff
eren
ce
Foam1
Foam 2
Foam3
Lung
COPDGene Model 2 - Subtract CT Number at 120 kV200 mAs 5mm B31f
Added Inside Air and Water to plot
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
60 80 100 120 140 160Tube Potential
CT N
umbe
r Diff
eren
ce Foam1
Foam 2
Foam3
Lung
Inside Air
Water
COPDGene Model 2 - Subtract CT Number at 120 kV200 mAs 5mm B31f
-30
-25
-20
-15
-10
-5
0
5
10
60 80 100 120 140 160
Tube Potential
CT N
umbe
r Diff
eren
ce Foam1
Foam 2
Foam3
Lung
Inside Air
Water
Acrylic
Observations
• CT numbers inside the phantom of foams identified by NIST are sensitive to spectral differences
• CT number air inside the phantom is less sensitive to spectral differences than foams identified by NIST
• CT number of acrylic inside phantom may useful characterizing the spectral effects on CT number inside the phantom
Variation of CT numbers of foams in the Gammex Boxes
Foam1 - Phantom 1ROI Mean
-687
-686
-685
-684
-683
-682
-681
-540 -530 -520 -510 -500 -490 -480
Slice Location [mm]
CT
Num
ber
Mean -684.5Stdev 0.64
120kv 200mAs B31f 0.75mm
Gammex 1 Gammex 2 Gammex 3 Gammex 4ROI Mean StDev ROI Mean StDev ROI Mean StDev ROI Mean
Phantom 1 -684.5 0.64 -770.6 0.44 -849.2 0.39 -905.3 0.34Phantom 2 -678.4 1.72 -769.7 0.49 -846.9 0.40 -905.6 0.34Phantom 3 -692.1 0.28 -769.1 0.44 -845.7 0.37 -907.8 0.41Phantom 4 -684.9 1.18 -769.7 0.43 -851.0 0.41 -905.4 0.89Phantom 5 -680.5 1.11 -769.6 0.38 -849.1 0.52 -908.4 0.40
-684.1 -769.7 -848.4 -906.55.26 0.55 2.10 1.48
120kv 200mAs B31f 0.75mm
Gammex Boxes StackedCompare 200mAs and 50mAs
-1-0.8-0.6-0.4-0.2
00.20.40.60.8
1
-1000 -900 -800 -700 -600Average Foam CT Number
Diffe
renc
e Fo
am C
T Nu
mbe
r
Gammex Boxes StackedCompare B31f and B45f
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-1000 -950 -900 -850 -800 -750 -700 -650 -600
Average Foam CT Number
Diffe
renc
e
Stack Gammex - 200 mAs - 0.75 mm - 120 kVpDifference - Between 31f andB35f
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
-1000 -950 -900 -850 -800 -750 -700 -650 -600
Average
Diff
eren
ce
Observations:Gammex Stack
• Substantial variation CT number of densest foam (-684) from sample to sample.
• Variation caused by mAs and reconstruction kernel less than 1 HU
• Limitation: Variation could be associated with spatial variation
• Unexplained effect at lowest foam density
Scanned each box is same location
Comparison - Stack with Single
y = 0.9991x + 1.2375R2 = 0.9999
-1000
-950
-900
-850
-800
-750
-700
-650
-600
-1000 -950 -900 -850 -800 -750 -700 -650 -600
Foam CT Number - Single Phantom
Foam
CT
Num
ber -
Pha
ntom
Sta
ck
Differences between stack and single measurements
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
-1000 -950 -900 -850 -800 -750 -700 -650 -600
Average
Diffe
renc
e
Observations: Comparison scan of stack with scan
of single phantom• Still is substantial variation CT number of
densest foam (-684) from sample to sample.
• Systematic effect observed.• Limitation: Effect could be associated with
difference reconstruction field of view.