SPECT handout - Nuclear Nuclear Medicine Imaging Zhenghong...

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uclear Nuclear Medicine Imaging Zhenghong Lee, Ph.D. Case Western Reserve University epartment of Biomedical Engineering Department of Biomedical Engineering University Hospitals Case Medical Center Nuclear Medicine, Department of Radiology
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adionuclide Imaging Radionuclide Imaging amma Camera Gamma Camera • Planar Imaging vs. SPECT • Radio-tracers for SPECT • Small animal SPECT • Positron Imaging ET systems PET systems • Radio-chemistry
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he Gamma Camera The Gamma Camera
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hoton Interactions Photon Interactions
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ompton Scatter Compton Scatter E sc = E 0 /[1 + (E 0 /0.511)(1 – cos )]
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ollimator Collimator ifferent Types Different Types
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ollimator (cont.) Collimator (cont.) nergy Dependence Energy Dependence • Sensitivity • High Resolution vs. Low – Thickness of Septa – Length of Septa – Septal Penetration
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he Effect of Collimator The Effect of Collimator with collimator without collimator
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cintillation Scintillation
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cintillation Crystal Scintillation Crystal hickness Thickness • Energy Dependence • Resolution and Sensitivity Trade off • Crystal Types – LSO, NaI, CsI, BGO arameter aI(Tl) sI(Tl) GO SO Parameter NaI(Tl) CsI(Tl) BGO LSO Effective Atomic Number 51 75 66 Density(gm/cc) 3.67 4.51 7.13 7.4 Decay Time ns 230 600 to 340 300 48 Light Output (NaI(Tl) = 100) 100 45 15 75
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hoto Multiplier Tube (PMT) Photo Multiplier Tube (PMT)
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lectronics (cont.) Electronics (cont.) WHM (Full Width at Half Max) FWHM (Full Width at Half Max) – Average Variation in Pulse Size ulse Height Analyzer (PHA) • Pulse Height Analyzer (PHA) – Windowing
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dverse Effects on Imaging Adverse Effects on Imaging catter Scatter • Attenuation in Patient and Collimator Key: --- = scatter = total spectrum
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lanar Imaging and SPECT Planar Imaging and SPECT
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omputed Tomography Computed Tomography rojections Projections • Sinogram
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SPECT Reconstruction imple Back Projection Simple Back Projection
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ore Reconstruction More Reconstruction iltered Back Projection • Filtered Back Projection – Modify Sinogram Before Back Projection i U filt d i Filt d Sinogram Unfiltered Sinogram Filtered Unfiltered Back Projection Filtered Back Projection
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erative Reconstruction Iterative Reconstruction asic Iterative Method • Basic Iterative Method – Make an initial guess (uniform image) – Compute error sinogram Error sinogram = Measured sinogram Estimated sinogram – Backproject error sinogram Pixel values are correction factors – Iterate
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Spatial Resolution R = SQRT( Ri 2 + Rg 2 + Rs 2 + …) Ri : intrinsic resolution (4mm for Tc-99m) Rg : geometric resolution (collimator) - g = + + Rg d ( t e b c )/ t e Rs : scatter resolution (distance, others…)
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Collimator Resolution
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Detection Efficeincy Efficiency = fi x fp x fg x Ni fi : intrinsic efficiency fp : photopeak efficiency geometric efficiency fg : geometric efficiency Ni : abundance of the radiation in question
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Collimator Efficiency 4 d 2 2 ) ( a d t K E e g :024~028 K: 0.24 ~ 0.28 LEAP: ~ 0.01%
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SPECT handout - Nuclear Nuclear Medicine Imaging Zhenghong...

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