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Nuclear Medicine

Nuclear Medicine

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Nuclear Medicine

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  1. Nuclear Medicine SPECT and PET

  2. a good book! SR Cherry, JA Sorenson, ME Phelps Physics in Nuclear Medicine Saunders, 2012

  3. “tracer” “projection”

  4.  (  ) d   y  I  I e   (  ) d  L  T 0 d  y   ( x ) dx e L E    (  ) d  L x y    ( x ) e dx E L CT PET SPECT

  5. reconstruction

  6. Metabolic images, • characteristics depend on • tracer specificity • tracer sensitivity • detection system

  7. Medical physicist • diagnostics: • QC camera hardware & software • Image formation, reconstruction • Image analysis • (dosimetry) • therapy • dosimetry • research

  8. Radionuclides

  9. b- emission  140 keV 99Mo 99mTc 99Tc isomeric transition (6 hours) b- emission (66 hours)

  10. Electron capture

  11. Electron capture 0.0 MeV (2.83 days) EC 0.4167 MeV g1 0.2454 MeV g2 0.0 MeV (stable)

  12. Positron or b+ emission 11C + - 511 keV positronium 511 keV 180o

  13. Radioactivity 1 mCi = 37 MBq = 37 x 106 events per s

  14. Poisson noise Chance of measuring n photons when l are expected : Poisson distribution resembles Gaussian

  15. Poisson noise

  16. Poisson noise SNR = n1 Poisson(l1) n2 Poisson(l2) n1+ n2 Poisson(l1+ l2)

  17. photon-electroninteractions

  18. Photon-electron interactions Detectors pair production photo-electric Compton Tissue

  19. attenuation scatter photoelectric effect

  20. water Photoelectric Compton Rayleigh Pair

  21. Energy loss due to Compton scatter E’ 511 q E -10% 140

  22. attenuation

  23. attenuation N(b) N(a) b a a c b Single photon Positron

  24. attenuation

  25. Data acquisition

  26. Scintillation time

  27. Scintillation crystals NaI(Tl) BGO LSO GSO LaBr:Ce Photons/keV 40 5..8 20..30 12 60..70 decay time [ns] 230 300 40 65 16..20 lin.att.coeff @ 511keV [/cm] 0.34 0.95 0.87 0.67 0.47 wave length 410 480 420 440 380 melting point651 1050 2050 1950 783 transparency, ease of use...

  28. Photomultiplier tube

  29. Detector design Single crystal multi- crystal

  30. Position and energy measurement x,y,z Electronics output current X Y

  31. Multiple events x,y,z Electronics output current All wrong

  32. Intrinsic resolution x,y,z Electronics Y X FWHM NaI(Tl): 4 mm Collimator Source

  33. Multidetector crystal

  34. Expensive alternatives • APD: avalanche photo diode • diode in reverse mode • replaces PMT, much smaller, low voltage • works in high magnetic field • Cd Zn Te detectors • direct detection of high energy photons • excellent energy resolution • high stopping power

  35. Partial volume effect

  36. Partialvolumeconstantactivitybig pixels

  37. Partialvolumeconstantconcentrationfinite resolution Recovery Spill-over perfect resolution finite resolution

  38. Collimation

  39.  (  ) d   y  I  I e   (  ) d  L  T 0 d  y   ( x ) dx e L E    (  ) d  L x y    ( x ) e dx E L CT PET SPECT

  40. Collimator Lens Collimator

  41. Collimators Parallel Fanbeam Cone beam Pinhole

  42. Collimator PSF counts FWHM position

  43. Collimator sensitivity R H a r Sens T S pMol! PSF(r) r

  44. Collimator sensitivity FWHM H a T

  45. Electronic collimation r x psf d x r d x psf

  46. PET lines of response

  47. PET sensitivity sensitivity in center: R d

  48. PET resolution max max mean Mev mm mm 11C 0.96 3.9 1.113N 1.19 5.1 1.515O 1.72 8.0 2.518F 0.64 2.4 0.668Ga 1.90 8.9 2.982Rb 3.35 17 5.9 511 KeV 2.5 mm (for 1 m FOV) 0.3o 511 KeV

  49. Coincidence detection True Scatter Single Random

  50. PET septa r T d D r efficiency:e time window:t trues: singles: randoms: scatters: