Peering into the Black Hole…
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Transcript of Peering into the Black Hole…
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
1.Problem2.Phantom3.Scanner4.kV5.mA6.DECT7.SE v DE8.Dose9.Blooming
10.DE @ UW
SSR Mon 3/17/14 12:10
Peering into the Black Hole…University of Wisconsin - Madison
Ken Schreibman, PhD/MD, FACRProfessor – UW MSK Section
Sylvester Youlo, MDPGY4 – UW Orthopedic Surgery
James Brittin, MDPGY4 – UW Radiology Department
Frank Ranallo, PhD, DABRPhysicist- UW Radiology Department
Matthew Squire, MD, MSAssociate Professor, UW Orthopedic Surgery
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
1.Problem2.Phantom3.Scanner4.kV5.mA6.DECT7.SE v DE8.Dose9.Blooming
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SSR Mon 3/17/14 12:10
DisclosuresBullet Pts.
…or visit my website
I will try to cover all 10 Bullet Points in less than 10 minutes
Neither I nor my family have any financial disclosures We are members of the Disney Vacation ClubUW Radiology Department has a partnership with GE
No fancy PowerPoint animations in this talk
For fancy PowerPoint see my ePoster…
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Peering into the Black Hole…This is the problemPoor CT visualization inside
cupped femoral componentCan’t see bone-metal interface
140kVpAxial
B,W 57yoMLateralRadiograph CT: Sagittal
Can wellsee around tibial tray
?
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Pig Knee + Human Co-Cr Femoral ComponentTo simulate the bone-metal interface
within the cupped femoral component
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Implanted by Sylvester Youlo, Ortho Surg Resident
Pounding component
in place
DrillingTarget
Lesions
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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We Created Target “Erosions”
Target
Target
Target 7x7mm5mm deep
6x6mm3mm deep
14x9mm7mm deep
3D CTwithout metal
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
1.Problem2.Phantom3.Scanner4.kV5.mA6.DECT7.SE v DE8.Dose9.Blooming
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Stabilized on yardstick w/cable ties
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Placed in sealable Tupperware™Filled with water to simulate attenuation of soft tissues
surrounding the kneeSealed to eliminate
air-fluid level
CT Scout
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
1.Problem2.Phantom3.Scanner4.kV5.mA6.DECT7.SE v DE8.Dose9.Blooming
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GE 750 HD + GSI
Scanned the phantom repeatedlyvarying one parameter at a time
hok.com
WIMR
CSC
UW Medical Campus
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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First tested the effect of changing kV using conventional “Single Energy” CT
4)
600 mA, Detail0.625mm Source image
600 mA, Detail0.625mm Source image
2)
“Single Energy” Results: Comparing kV
For all images: W=3000 L=1000
Target
Target
140 kV 120 kV
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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“Single Energy” Results: Comparing kV
For all images: W=3000 L=10002)
140 kV
Target
4)
120 kV
Target
6)
100 kV
Target
Conclusion: With “SE”CT, use 140 kV
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Then, holding kV=140, varied mA“Single Energy” Results: Comparing mA
For all images: W=3000 L=10002)
140 kV 600 mA
8)
140 kV 300 mA
10)
140 kV 150 mA
Target
Target
Target
Conclusion: Don’t need to use max mA
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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Disclaimer:On this slide I am going to try to explain physics
that my physicist says I don’t understand…Here’s where things get confusing because there
are two types of “voltage”.The electricity applied into the CT tube is in volts, or kVThe energy of emitted photons in electron-volts, or keV
put kV into CT tube get keV out……but what comes out is less than what’s put in!
“Single Energy” is actually a Spectrum of Energies
Num
ber o
f X-ra
y ph
oton
s em
itted
from
CT
tube
0 20 40 60 80 100 120 140Energy of the X-ray photons (x103 electron-volts) (keV)
140kV
80kV
Applying 140kV to the CT tube yields an X-ray spectrum……nearly all with energies much less than 140keV.
(We can ignore the pointy spikes not as relevant to this discussion)Applying 80kV to the CT tube yields lower energy spectrum.With physics + math, can use the CT attenuation data,measured from these two real energy spectra,to calculate what the attenuation would look like if we
had single energy X-rays…140keV
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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“Dual Energy” is actually Single EnergyConventional “Single Energy” CT generates images from X-rays with a spectrum of energies.
Collecting image data from 2 single energy spectra simultaneously is called “Dual Energy.”
Dual Energy allows generation of images… …as if the X-rays were of a single energy!
Num
ber o
f X-ra
y ph
oton
s em
itted
from
CT
tube
0 20 40 60 80 100 120 140Energy of the X-ray photons (x103 electron-volts) (keV)
140kV
80kV140keV
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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GE 750 HD with GSIGSI:Gemstone
Spectral Imaging
What GE calls their DECT
It’s easy to turn on DECTClick “On” button
With DECT, the presets control the kV and mA
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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Since it takes several minutes to generate DE images, GSI first yields SE Quality Check (QC) images For technologists to check for
coverage, etc. GE recommends discarding
these images. I found they looked as good as
the best SE images we got with high kV and mA.We archive them.
GSI generates both SE & DE images“600 mA”
11)
SE:140 kVGSI: QCGenerated automatically
Target
600 mA
2)
SE:140 kVSECTAcquired earlier
Target
Conclusion: QC equivalent to SECT
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Results: SE & DE CT for Target Lesion600 mA
2)
SE:140 kV “600 mA”
12)
DE:140 keV
Target
Conclusion: DE at least as good as SE
Target
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Results: SE & DE CT for DoseChart of DLP (Dose Length Product) (mGy-cm)
Values calculated by the CT scanner
140 120 100Conventional CT (kV)DECT (keV)
CHANGING VOLTAGE
140600300150
CHANGINGCURRENT
(mA)
1202 843 532696
42% lessthan 1202
701350
Conclusion: DECT lower dose than SE
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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Results: SE & DE Metal Blooming (Phantom)600 mA
2)
SE:140 kV
For all images: W=3000 L=1000
“600 mA”
12)
DE:140 keV
Conclusion: DE Less Metal Blooming
13mm 10mm
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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Results: SE & DE Metal Blooming (Patients)
B,W 57yoM630 mA, Detail3mm Sagittal
SE:140 kV
A,C 69yoF600 mA, Detail3mm Sagittal
DE:140 keV
MetalBlooming
DLP=2764 DLP=1234
Can’t see if osteolysis inside femoral component
Much LessMetal
Blooming
CAN see osteolysis inside femoral component
55% less than 2764!
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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Results: Metal Blooming +/- GE MARsMetal Artifact Reduction softwarePost-processing iterative techniqueIt can be applied, or not, after scanningOnly available on GE scanners with GSI“MARs helps significantly in the reduction of artifacts from high density metal implants and allows the accurate visualization of the underlying bone and adjacent soft tissue”
www.gehealthcare.com/ct • November 2011 page 29
600 mA
12)
DE:140 keV 600 mA
13)
DE:140 keV + MARs
Black streak artifacts
EliminatesBlack streak artifacts
Target?
Target
Conclusion: MARs may worsen bone-metal interface
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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LimitationsI’ve only worked with GE 750 HD GSIThat’s what we have at the UWI’ve only worked with 2 TKA phantomsGot the same resultsBoth times failed to see largest target!Geometry of cupped femoral component?We weren’t trying to minimize doseJust wanted to see what advantages
DECT offered over SECT
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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What We’re Presently DoingBecause DECT seems to be no worse than
SECT in seeing bone-metal interfacesSECT & DECT found/missed same targets
and because DECT metal blooming is less…and because DECT dose is lower…
UW MSK Policy is now this:For patients getting bone/joint CT scans,whenever there is metal in scanning FOV,we recommend using DECT with 140keV.
If DECT not available, use 140kV SECT.
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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What We’re Planning on DoingWorking with our
physicists to optimize the DECT protocols so we can continue to get great images with minimum dose.
Develop body part specific protocols
Hopefully share all of this with all of you at SSR 2015! A,C 69yoF
600 mA, Detail3mm Sagittal
DE:140 keV
© 2014 Ken L Schreibman, PhD/MDwww.schreibman.info
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TKA: Single vs Dual Energy CT
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Anyone who wants to join me in a bike ride can meet me up front as soon as we’re done