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Coincidence to Image: PET Imaging

Coincidence to Image: PET Imaging. Jennifer White Marketing Manager SNS Workshop October 13, 2003. The PET Mission. “ Disease is a biological process and PET is a biological imaging technique that uses molecular probes .” -Michael Phelps

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Coincidence to Image: PET Imaging

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  1. Coincidence to Image: PET Imaging Jennifer White Marketing Manager SNS WorkshopOctober 13, 2003

  2. The PET Mission “Disease is a biological process and PET is a biological imaging technique that uses molecular probes.” -Michael Phelps The CPS mission is to utilize CPS’ unique foundation of knowledge and experience in molecular imaging technology to manage disease better through earlier detection and more complete diagnosis.

  3. The Image Dedicated PET Brain Imaging Fused PET CT Image Cardiac Image PET CT and PET

  4. PET Principles 18-F-FDG most common nuclide 18O(p,n)18F Other PET Radionuclides 11C 13N 15O 82Rb

  5. Annihilation Reaction Positron scatters in tissue losing energy e+ Positron emission 511 keV -ray e- 511 keV -ray Annihilation

  6. Detector Block PET Principles LSO PROCESSING ELECTRONICS

  7. PET Principles ECAT System Schematic Rotating Rod Converter Formatter & Motion Translator Coincidence Processor Acquisition Memory Acquisition Disk Optical data link Sorter VSB bus Singles Events VMEbus Serial line Real Time CPU Gantry Controller Ethernet Gantry Workstation Detectors Detector Electronics Ethernet

  8. PET Principles Types of Events Detected Prompt True Random Scatter Line of Response is Defined by connecting Pairs in Coincidence Event

  9. Event Detection

  10. Detector Detector t = 12ns t = 12ns Constant Constant Delay Fraction Fraction Discrim Discrim t>>12ns AND Event Detection Collection of Events

  11. Sinogram Formation A sinogram is formed by placing the projection for the angle 0 at the top of a matrix and the other angles in ascending order. EXACT, ART, Accel: 192 x 192 elements. HR+: 288 x 288 elements Data is collected as the integral of the activity along parallel rays for each angle from 0 to 180 degrees.

  12. PET Principles PROMPT EMISSION SINOGRAM Random Subtraction TRUE EMISSION SINOGRAM acquisition time and decay correction calibration/branching fraction correction deadtime correction detector efficiency normalization scatter subtraction ring geometry rebinning attenuation correction IMAGE

  13. B A PET Imaging • Attenuation Corrections • Correction made for number of detection lost • Scatter (Compton or Rayleigh interactions) • Absorption (photoelectric interaction) • Significance of Attenuation • The reconstruction algorithms are not valid without AC. • The emitter distribution is distorted. • Quantification is not possible. Scattered Unattenuated Absorbed Absorbed

  14. PET Principles Image Quality Considerations Uncorrected Corrected

  15. PET Attenuation Correction Blank scan Emission scan Transmission scan Methods of Attenuation Correction: ROD SOURCE 4–8 min 1 hour 2–4 min Measure rod intensity with no object present. Measure emission from object. Measure transmission through the object. Smooth and take the ratio. Blank/Transmission = ACF Correct the emission data. Etrue = Emeas x ACF

  16. PET Attenuation Correction Methods of Attenuation Correction: CT ~70 keV 511 keV bone soft tissue

  17. Corrected Sinogram to Image FBP Sinogram OSEM measured N = 3 N = 1

  18. PET Images FBP MI projection Plane 66 Plane 71 Plane 76 OS-EM 7.1 Plane 66 Plane 71 Plane 76 Plane 66 Plane 71 Plane 76 OS-EM 7.2 (prototype) Reconstruction Methods vs Image Quality

  19. -map Transmission scan Blank scan Attenuationcorrection Emission scan Normalization Putting it all together Image

  20. PET Image Reconstruction: multiple bed positions 25 yr old male, melanoma, 71 kg, 178 cm, 16.9 mCiFDG Data courtesy of NCPIC, Sacramento, CA

  21. Case Study

  22. PET Analysis Measured Activity Weight Volume Injected Activity SUV =  • Partial volume effect (Resolution dependent) • Size of ROI • Size of lesion • Resolution • Scanner • Reconstruction parameter • Filter/ Noise • Glucose concentration before injection • Metabolism • Pathologic • Stress • Time after injection • Uptake time • Scan length (to reach ROI) • Scanner calibration • Weight only used as substitute for blood/ water volume! • Measuring error (esp. when patient estimate) • Tissue/ fat/ bone composition/ distribution • Measuring error • Cross-calibration

  23. Analysis Packages PMOD Technologies www.pmod.com

  24. Case Study Coronal Series Multi-Planar Fused Sagittal, Coronal, Transaxial

  25. Case Study Sub-cm nodes detected with PET localized with CT Patient with history of Breast Cancer evaluated for treatment follow-up. Small 7 mm nodes detected by examination on PET/CT

  26. Thank you

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