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

http://www.schreibman.info/


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10.DE @ UW

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…



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10.DE @ UW

SSR Mon 3/17/14 12:10

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

?



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10.DE @ UW

SSR Mon 3/17/14 12:10

Pig Knee + Human Co-Cr Femoral ComponentTo simulate the bone-metal interface

within the cupped femoral component



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10.DE @ UW

SSR Mon 3/17/14 12:10

Implanted by Sylvester Youlo, Ortho Surg Resident

Pounding component

in place

DrillingTarget

Lesions



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10.DE @ UW

SSR Mon 3/17/14 12:10

We Created Target “Erosions”

Target

Target

Target 7x7mm5mm deep

6x6mm3mm deep

14x9mm7mm deep

3D CTwithout metal



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10.DE @ UW

SSR Mon 3/17/14 12:10

Stabilized on yardstick w/cable ties



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10.DE @ UW

SSR Mon 3/17/14 12:10

Placed in sealable Tupperware™Filled with water to simulate attenuation of soft tissues

surrounding the kneeSealed to eliminate

air-fluid level

CT Scout



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10.DE @ UW

SSR Mon 3/17/14 12:10

GE 750 HD + GSI

Scanned the phantom repeatedlyvarying one parameter at a time

hok.com

WIMR

CSC

UW Medical Campus


http://www.hok.com/design/type/science-technology/university-of-wisconsin-madison-wisconsin-institutes-for-medical-research/


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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

“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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

“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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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!



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10.DE @ UW

SSR Mon 3/17/14 12:10

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


http://www3.gehealthcare.com/~/media/Downloads/us/Product/Product-Categories/Computed-Tomography/Discovery-CT-750-HD/GEHealthcare-Publication_Clinical_Value_Emergency_Applications_in_Musculoskeletal_CT_Imaging_June_2011.pdf?Parent=%7BDE804542-75B6-4904-95CE-C24E06EA6969%7D


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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

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.



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10.DE @ UW

SSR Mon 3/17/14 12:10

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



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10.DE @ UW

SSR Mon 3/17/14 12:10

Anyone who wants to join me in a bike ride can meet me up front as soon as we’re done


Peering into the Black Hole…

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