1 Nuclear Medicine SPECT and PET

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

3 “projection” “tracer”

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

5 reconstruction

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

7 Medical physicist diagnosticsdiagnostics: –QC camera hardware & software –Image formation, reconstruction –Image analysis –(dosimetry) therapytherapy –dosimetry researchresearch

8 Radionuclides

9  - emission 99 Mo 99m Tc 99 Tc  - emission (66 hours) isomeric transition (6 hours)   keV

10 Electron capture 

11 Electron capture (2.83 days) 0.0 MeV EC MeV MeV 0.0 MeV (stable) 11 22 RadiationfreqMeV 1 ce-K,  ce-L 1,  2 ce-K,  K  1 X-ray Auger-KLL

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

13 Radioactivity 1 mCi = 37 MBq = 37 x 10 6 events per s

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

15 Poisson noise

16 Poisson noise SNR = n 1 Poisson( 1 ) n 2 Poisson( 2 ) n 1 + n 2 Poisson( )

17 photon-electron interactions

18 Photon-electron interactionsTissue photo-electric Compton pair production Detectors

19 attenuation scatter photoelectric effect

20 water

21 Energy loss due to Compton scatter  -10% E E’

22 attenuation

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

24 attenuation

25 Data acquisition

26 Scintillation time

27 Scintillation crystals NaI(Tl)BGOLSOGSOLaBr:Ce Photons/keV decay time [ns] keV [/cm] wave length melting point transparency, ease of use...

28 Photomultiplier tube

29 Detector design Single crystalmulti- crystal

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

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

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

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 (similar to NaI(Tl))

35 Partial volume effect

36 Partial volume constant activity big pixels

37 Partial volume constant concentration finite resolution perfect resolution finite resolution Recovery Spill-over

38 Collimation

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

40 Collimator LensCollimator

41 Collimators ParallelFanbeam Cone beamPinhole

42 Collimator PSF FWHM position counts

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

44 Collimator sensitivity a T H FWHM

45 d Electronic collimation r x r psf x x d

46 PET lines of response

47 PET sensitivity R d sensitivity in center:

48 PET resolution 511 KeV 0.3 o 2.5 mm (for 1 m FOV) maxmaxmean Mevmmmm 11 C N O F Ga Rb C N O F Ga Rb

49 Coincidence detection TrueScatter SingleRandom

50 PET septa T d D  r trues: scatters: singles: randoms: efficiency:  time window: 

51 2D and 3D PET trues: scatters: singles: randoms: N rings

52 Compton scatter and energy windowing

53 Collimator, scatter, attenuation

54 Energy of scattered photons Measured Simulated primary scattered Counts

55 Scatter window subtraction Simulated primary scattered Energy KeV Counts Scatter PSF is energy dependent

56 Triple Energy Window Simulated primary scattered Energy KeV Counts C2 C1 C3 Corrected counts = C1 -  filter(C2 + C3)

57 TEW, 201 Tl cardiac phantom PeakCorrected Lower window Higher window global scale individual scale joint scale

58 Energy resolution Energy KeV Counts SPECT, SPECT, fwhm 10 % PET BGO, PET BGO, fwhm 20 % PET LSO, GSO, LYSO PET LSO, GSO, LYSO... between 10 and 20% Bentourkia, IEEE TMI 1999

59 Model based scatter correction Ollinger 1996, 3D PET S A B

60 PET scatter PSF Measured Monte Carlo Ollinger high sampling Ollinger low sampling Ollinger, Phys Med Biol 1996

61 Activity outside FOVS A B

62 CorrectionsCrystal front end electronics Collimator Computer

63 Linearity correction X Y X +  X Y +  Y Triad XLT 24 Detector

64 Energy correction

65 Uniformity correction E + L + Flood correctie Energy correction No correction E + Linearity divide by flood source image

66 Uniformity correction non-uniformity due to non-linearity dead PMT

67 head1head2 h1 h2 h1 h2h1 h2 h1 h2h1 h2 Tc-99m MDP – bone spect on dual head camera broken PMT

68 e.cam, detector 2 Broken PMT affecting high voltage

69 detector 1detector 2

70 Dead time True count rate Measured count rate 500,000 cps  = 700 ns Front end: Data processing: or

71

72 Randoms correction in PET delayed window time Det 1 Det 2 time prompt: true or random random!