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Physics CLRS 344

Single Photon Emission Tomography SPECT. Physics CLRS 344. Anger Gamma Camera. X. Y. Positional Circuit. Z. Gate. Output. Collimator. Collimators. Tomography. Shows position and relationship of objects in 3D. Planar Imaging Resolution is depth dependent

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Physics CLRS 344

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  1. Single Photon Emission Tomography SPECT Physics CLRS 344

  2. Anger Gamma Camera X Y Positional Circuit Z Gate Output Collimator

  3. Collimators

  4. Tomography • Shows position and relationship of objects in 3D. • Planar Imaging • Resolution is depth dependent • Single Photon Emission Computed Tomography • Resolution is independent on depth • Resolution is inferior to Planar • Reconstruction magnifies noise • Signal-to-noise ratio is less than planar for the same number of acquired counts

  5. Single Photon Emission Computed TomographySPECT Acquire multiple planar views

  6. SPECT Acquisition • Linear Sampling • d  1 note: max is the max obs. frequency (2max) Nyquist Frequency • Angular Sampling • Number of views = D/2d • D: Diameter of view • d: linear sampling distance

  7. SPECT Acquisition Sampling Point Actual signal, 9 Hz False signal, 1 Hz

  8. SPECT Acquisition

  9. SPECT Acquisition Angular sampling Minimum acquisition: 1800

  10. Spatial Frequency Line pair (# lines per unit distance)

  11. Modulation Transfer Function Low spatial Frequency Counts Pixel-distance Counts High spatial Frequency Pixel-distance

  12. Modulation Transfer Function Low spatial Frequency Counts MTF= cout()/cin() = 1 Pixel-distance High spatial Frequency Counts MTF= cout()/cin() = 0.33 Pixel-distance

  13. Modulation Transfer Function ideal Collimator-source distance MTF= cout()/cin() 2.5 cm 10 cm Spatial Frequency (cm-1)

  14. Spatial Frequency Spatial Domain Frequency Domain Amplitude Counts Frequency pixel

  15. Spatial Frequency Frequency Domain Amplitude Frequency

  16. Reconstruction Algorithms • Filter Backprojection • Easy to implement • Computational fast • Iterative reconstruction • Number of iterations: hard to determine • Computational intense

  17. Reconstruction Algorithms g4=f1+f2+f3 g5=f4+f5+f6 g6=f7+f8+f9 Radon Equation g2=f2+f5+f8 g1=f3+f6+f9 g3=f1+f4+f7

  18. Reconstruction Algorithms Radon Equation g4 Backprojection Operator g5 Filtered Backprojection g6 g3 g2 g1

  19. Transverse Image 60 60 60 60

  20. Backprojection 120 120 counts counts 120 60 60 120 120 60 60 120 counts 120 120 counts

  21. Backprojection 120 120 counts 20 20 20 20 20 20 20 20 20 20 20 20

  22. Backprojection 120 120 counts counts 40 40 120 40 80 80 40 40 80 80 40 120 40 40 120 40 80 80 40 40 80 80 40 120 40 40 40 40 counts 120 120 counts

  23. Backprojection 40 40 40 80 80 40 40 80 80 40 40 40 40 80 80 40 40 80 80 40 40 40 40 40

  24. Backprojection 80 80 80

  25. RampBackprojection 80 80 80 80 80 80 80 Amp Spatial Freq.

  26. Filter High Freq Noise Resultant freq Low Freq

  27. Filter Amp Cut-off frequency Nyquest Freq Spatial Freq. Smoothing function Butterworth- Low Pass Metz Wiener Parzen Amp Amp Spatial Freq. Spatial Freq.

  28. Filter Backprojection Amp Amp X Spatial Freq. Spatial Freq. Amp Spatial Freq.

  29. Filter Backprojection

  30. Filter Backprojection

  31. Filter Backprojection standard 0.5 mCi 1.0 mCi 6.0 mCi

  32. Iterative Reconstruction x x x Recon Image Initial

  33. Iterative Reconstruction y y y y x Recon Image Initial

  34. Iterative Reconstruction 45 45 y 45 45 x Recon Image Initial

  35. Reconstruction Algorithms Iterative Methods 10 6 5 11 0 0 7 9 8 8 8 8

  36. standard 6mCi/FBP 6mCi/Iterative

  37. Filtered Backprojection Iterative Reconstruction Reconstruction Algorithms Scan Time 7 min 5 min 3 min

  38. Filtered Backprojection Iterative Reconstruction Reconstruction Algorithms

  39. Reconstruction Algorithms

  40. Attenuation Correction • Uniform attenuation • First Order Attenuation Correction • Chang’s Method • Measured (Transmission Image) • Point source Measured Attenuation • Point source Segmented Attenuation

  41. Attenuation Correction • Chang’s Method d1 Contour d2 Assume: uniform  Transverse slice Note: Only good for Brain imaging

  42. Attenuation Correction • Transmission Method (point source) • Geometric Mean I0 I2 I1 d2 d1 D

  43. Attenuation Correction • Transmission Method (Measured) For each Line of response (LOR) Obtain; 1, 2, 3, etc

  44. Attenuation Correction • Transmission Method (Measured) Low statistics Poor Image quality Require long transmission scans

  45. Attenuation Correction • Transmission Method (Segmented) Option: Group attenuation factors into 3 groups; Lung, Tissue, and Bone lung tissue bone

  46. Attenuation Correction • Segmented Attenuation Correction Measured Segmented

  47. Attenuation Correction • Segmented Attenuation Correction MEASURED SEGMENTED 3 Minutes 2 Minutes 1 Minute

  48. SPECT Corrections • Partial Volume Concentration: Counts/ROI nCi/cc

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