Peering into the Black Hole…

1. Peering into the Black Hole… • University of Wisconsin - Madison • Ken Schreibman, PhD/MD, FACR • Professor – UW MSK Section • Sylvester Youlo, MD • PGY4 – UW Orthopedic Surgery • James Brittin, MD • PGY4 – UW Radiology Department • Frank Ranallo, PhD, DABR • Physicist- UW Radiology Department • Matthew Squire, MD, MS • Associate Professor, UW Orthopedic Surgery

2. Disclosures Bullet Pts. • Neither I nor my family have any financial disclosures • We are members of the Disney Vacation Club • UW Radiology Department has a partnership with GE • I will try to cover all 10 Bullet Points in less than 10 minutes • No fancy PowerPoint animations in this talk • For fancy PowerPoint see my ePoster…    …or visit my website 

3. Peering into the Black Hole… 140kVp Axial • This is the problem • Poor CT visualization inside cupped femoral component • Can’t see bone-metal interface • ? • Can wellsee around tibial tray Lateral Radiograph B,W 57yoM CT: Sagittal

4. Pig Knee + Human Co-Cr Femoral Component • To simulate the bone-metal interface within the cupped femoral component

5. ImplantedbySylvesterYoulo,OrthoSurgResident • DrillingTarget • Lesions • Pounding component in place

6. We Created Target “Erosions” Target 6x6mm 3mm deep  Target Target 7x7mm 5mm deep  14x9mm 7mm deep 3D CTwithout metal

7. Stabilized on yardstick w/cable ties

8. Placed in sealable Tupperware™ Filled with water to simulate attenuation of soft tissues surrounding the knee Sealed to eliminate air-fluid level CT Scout

9. CSC •  GE 750 HD + GSI • WIMR •  • Scanned the phantom repeatedly • varying one parameter at a time • UW Medical Campus hok.com

10. “Single Energy” Results: Comparing kV First tested the effect of changing kV using conventional “Single Energy” CT 600 mA, Detail 0.625mm Source image 140 kV 600 mA, Detail 0.625mm Source image 120 kV  Target  Target 2) 4) For all images: W=3000 L=1000

11. “Single Energy” Results: Comparing kV 140 kV 120 kV 100 kV  Target  Target  Target • Conclusion: With “SE”CT, use 140 kV 2) 4) 6) For all images: W=3000 L=1000

12. “Single Energy” Results: Comparing mA • Then, holding kV=140, varied mA 140 kV 600 mA 140 kV 300 mA 140 kV 150 mA  Target  Target  Target • Conclusion:Don’t need to use max mA 2) 8) 10) For all images: W=3000 L=1000

13. “Single Energy” is actually a Spectrum of Energies • 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 kV • The 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! 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… Number of X-ray photons emitted from CT tube 140kV  140keV 80kV 0 20 40 60 80 100 120 140 Energy of the X-ray photons (x103 electron-volts) (keV)

14. “Dual Energy” is actually Single Energy • Conventional “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! Number of X-ray photons emitted from CT tube 140kV  140keV 80kV 0 20 40 60 80 100 120 140 Energy of the X-ray photons (x103 electron-volts) (keV)

15. GE 750 HD with GSI • GSI: Gemstone Spectral Imaging • What GE calls their DECT • It’s easy to turn on DECT • Click “On” button • With DECT, the presets control the kV and mA

16. GSI generates bothSE&DE images • 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. 600 mA SE:140 kV SE:140 kV “600 mA” SECT Acquired earlier GSI: QC Generated automatically  Target  Target • Conclusion: QC equivalent to SECT 2) 11)

17. Results: SE&DE CT for Target Lesion 600 mA SE:140 kV “600 mA” DE:140 keV  Target  Target • Conclusion: DE at least as good as SE 2) 12)

18. Results: SE&DE CT for Dose • Chart of DLP (Dose Length Product) (mGy-cm) • Values calculated by the CT scanner CHANGING VOLTAGE DECT (keV) Conventional CT (kV) 140 120 100 140 600 696 1202 843 532 CHANGING CURRENT (mA) 300 701  42% lessthan 1202 150 350 • Conclusion:DECT lower dose than SE

19. Results: SE&DE Metal Blooming (Phantom) 600 mA SE:140 kV “600 mA” DE:140 keV 13mm 10mm • Conclusion:DELessMetalBlooming 2) 12) For all images: W=3000 L=1000

20. Results: SE&DE Metal Blooming (Patients) SE:140 kV DE:140 keV Can’t see if osteolysis inside femoral component CAN see osteolysis inside femoral component Metal Blooming Much Less Metal Blooming DLP=2764 DLP=1234 55% less than 2764! 630 mA, Detail 3mm Sagittal 600 mA, Detail 3mm Sagittal B,W 57yoM A,C 69yoF

21. Results: Metal Blooming +/- GE MARs • Metal Artifact Reduction software • Post-processing iterative technique • It can be applied, or not, after scanning • Only 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” DE:140 keV+MARs DE:140 keV 600 mA 600 mA Eliminates Black streak artifacts   Black streak artifacts    Target  Target? www.gehealthcare.com/ct • November 2011 page 29 • Conclusion: MARs may worsen bone-metal interface 13) 12)

22. Limitations • I’ve only worked with GE 750 HD GSI • That’s what we have at the UW • I’ve only worked with 2 TKA phantoms • Got the same results • Both times failed to see largest target! • Geometry of cupped femoral component? • We weren’t trying to minimize dose • Just wanted to see what advantages DECT offered over SECT

23. What We’re Presently Doing • Because DECT seems to be no worse than SECT in seeing bone-metal interfaces • SECT & 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.

24. What We’re Planning on Doing • Working 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! DE:140 keV 600 mA, Detail 3mm Sagittal A,C 69yoF

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