Presentation during QIBA COPD Lung Density Reference and Consistency Standards Work Group Call

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

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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

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-1

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Tube Potential

CT N

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Foam1

Foam 2

Foam3

Lung

COPDGene Model 2 - Subtract CT Number at 120 kV200 mAs 5mm B31f

Added Inside Air and Water to plot

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60 80 100 120 140 160Tube Potential

CT N

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ce Foam1

Foam 2

Foam3

Lung

Inside Air

Water

COPDGene Model 2 - Subtract CT Number at 120 kV200 mAs 5mm B31f

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0

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Tube Potential

CT N

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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

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-686

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-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

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00.20.40.60.8

1

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Diffe

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am C

T Nu

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Gammex Boxes StackedCompare B31f and B45f

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-0.8

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Average Foam CT Number

Diffe

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Stack Gammex - 200 mAs - 0.75 mm - 120 kVpDifference - Between 31f andB35f

-0.1

-0.08

-0.06

-0.04

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0

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Average

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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

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Foam CT Number - Single Phantom

Foam

CT

Num

ber -

Pha

ntom

Sta

ck

Differences between stack and single measurements

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Average

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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.