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Review of Last Week: Counting Statistics & Error Propagation This week : • Types of Error – systematic error; eg bias in experiment, error with fixed tendency, cannot be treated with statistics, can be corrected for if known (calibration) -- effects accuracy – random error; inherent to instruments and/or nature of measurement (eg biological variability), cannot be ‘corrected’ but can be minimized with large samples/trials, treated with statistical approaches -- effects precision Scintillation Cameras for single-photon imaging (Planar and SPECT) • Statistical Descriptions of Random Error – probability distribution functions • Binomial; probability of observing certain outcome in N attempts when probability of single outcome is p. • Poisson (limiting case of binomial: p small, N large); mean = variance = (standard deviation)2, asymmetric, positive means only • Gaussian (Normal); widely used, symmetric, approximates Poisson for large means, mean and SD can be independent William Hunter, PhD# University of Washington# Department of Radiology# • Reporting Statistics/Error - consistency in significant figures Suggested reading: Chapters 13&14.Physics in Nuclear Medicine by Cherry et al. • Propagation of Error - errors from independent sources add in ‘quadrature’; error in f(x, y) due to errors in x (x) and y (y) is f2 = |∂f/∂x|2x2 + |∂f/∂y|2y2 simplest case: f = ax ± by, then error in f: f2 = (ax)2 + (by)2 (a, b = const.) The Planar Gamma Camera Planar and SPECT Cameras - Summary • System components: – CollimatorDetectorElectronics • Collimator – Types: Parallel, Converging, Diverging, Pinhole, Multi-pinhole – Performance: Penetration, Resolution, Efficiency • Detector: – Components: Scintillator crystal, Optical spacer, PMTs – Performance: Efficiency, Intrinsic (spatial) resolution, Energy resolution • Acquisition modes: – Frame vs List mode – Static (single), Dynamic (TAC), Gated (cardiac / respiration) • Camera QA corrections: – Uniformity, Linearity, Photo-peak window, Multi-energy registration • SPECT QA/QC: – Center-of-rotation, Head tilt, uniformity Siemens e.cam 1 Gamma Camera Instrumentation# Signal# The Scintillation Camera: Detector System# acquisition &# processing# computer# processing# electronics# PMT# Lightguide# Scintillator# Collimator# Detection Efficiency# Light response function versus position# (spatial resolution)# E Intrinsic spatial Resolution: <4 mm FWHM x1 x2 x3 x4 x5 x6 x7 x 0.64 PMT# LG# Crystal# 2 Gamma Camera Energy Spectra# Scatter# PMTs detector - NaI(Tl) Gamma Camera Energy Spectra# Nai(Tl) Energy Spectra (140 keV) 6 104 • Tc99m # #140.5 keV # # 6.03 hours# 4 104 • I-131 # #364, 637 keV # 8.06 days# 3 104 • I-123 # #159 keV # # 13.0 hours# • I-125 # #35 keV # # 60.2 days# • In-111 # #172, 247 keV # 2.81 days# • Th-201 # #~70, 167 keV # 3.044 days# • Ga-67 #93, 185, 300 keV# 3.25 days# 5 104 Counts 10% ER 20% ER List of Nuclear Medicine ʻSingle Photonʼ Radionuclides 2 104 1 104 0 0 50 100 150 energy (keV) 140 keV photons, 9.5 mm crystal# 200 # From: Physics in Nuclear Medicine (Sorenson and Phelps) 3 Parallel Hole Collimator# PMTs# The Scintillation Camera: Collimators# Collimators - Septal Penetration# Detector Collimator septa l d t detector - NaI(Tl)# l e# Collimator Efficiency# Collimators typically absorb well over 99.95% of all photons emitted from the patient. Trade-off between spatial resolution and detection efficiency.# Minimum septa thickness, t, for <5% septal penetration:# From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps)# 4 Collimator Resolution Gamma Camera - spatial resolution Rs = (R 2 int 2 + Rcol ) From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps) From: The Essential Physics of Medical Imaging (Bushberg, et al)# Types of Collimators# Collimator: Resolution and Sensitivity# magnification From: The Essential Physics of Medical Imaging (Bushberg, et al)# From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps) 5 The Scintillation Camera: Corrections and QA Gamma Camera Processing Electronics (energy correction)# 19 8 Energy channel vs. event location 9 6 104 5 104 17 7 6 2 1 10 3 4 104 11 Counts 18 3 104 2 104 1 104 16 5 4 10% ER (between) 10% ER (over) 12 0 0 50 100 150 200 energy (keV) 15 14 13 How was this image produced? Gamma Camera Processing Electronics (linearity correction) Gamma Camera Processing Electronics (linearity correction) 19 18 17 8 7 6 16 2 1 5 15 9 10 3 4 14 11 12 13 From: Physics in Nuclear Medicine (Cherry, Sorenson and Phelps) 6 Additional Gamma Camera Corrections (sensitivity / uniformity) Daily Gamma Camera QA Tests# Acquired from long uniform flood after energy and linearity corrections have been applied# # Multiplicative correction# # Adjusts for slight variation in the detection efficiency of the crystal# # Compensates for small defects or damage to the collimator# Flood uniformity# # Should not be used to correct for large irregularities# Photopeak window# From: The Essential Physics of Medical Imaging (Bushberg, et al)# Multienergy spatial registration (e.g., Ga-67 (93-, 185-, and 300 keV) gamma rays)# properly adjusted# Spatial Resolution Test# improperly adjusted# FWHM of LSF = 1.7 x (size of smallest bar resolved)# From: The Essential Physics of Medical Imaging (Bushberg, et al)# From: The Essential Physics of Medical Imaging (Bushberg, et al)# 7 Pulse Pile-up# The Scintillation Camera: Image Acquisition# Pile-up in image Energy spectra From: Physics in Nuclear Medicine (Sorenson and Phelps) and (Cherry, Sorenson and Phelps) Image Acquisition Gated Acquisition • Frame mode (data stored as an image)# - static# - single image acquisition# - can have multiple energy windows# - dynamic# - series of images acquired sequentially# - gated# - repetitive, dynamic imaging# - used for cardiac imaging# • List-mode (data stored event by event)# - time stamps are included within data stream# - allows for flexible post-acquisition binning# - can result in very large data files# From: The Essential Physics of Medical Imaging (Bushberg, et al)# 8 Region of Interest (ROI) and Time-Activity Curves (TAC) The Scintillation Camera: SPECT Imaging From: The Essential Physics of Medical Imaging (Bushberg, et al) Gamma Camera Imaging (SPECT) Gamma Camera Imaging (SPECT) Siemens e.cam (http://www.medical.siemens.com) www.medical.philips.com GE MG (http://www.gehealthcare.com) www.medical.philips.com 9 Gamma Camera Imaging (gated cardiac SPECT) Additional QA/QC Tests for SPECT Center-of-Rotation (COR) Alignment Artifact Small COR misalignement will blur image, while larger misalignement will cause donut shape artifacts. • Images obtained during individual phases of cardiac cycle • Gating based on EKG • 8-16 frames per cycle • Allows assessment of global and regional LV function www.cardiology.utmb.edu/ slides/Gated%20Cardiac%20SPECT.htm www.medical.siemens.com/siemens/en_INT/ gg_nm_FBAs/files/ brochures/Cardiology_Insert_4DMSPECT.pdf Additional QA/QC Tests for SPECT Camera Head Tilt From: The Essential Physics of Medical Imaging (Bushberg, et al) Additional QA/QC Tests for SPECT Detector non-uniformity artifact Rings around center of rotation (transverse view) This artifact differs from a COR-misalignment artifact in that it only appears around the AOR. From: The Essential Physics of Medical Imaging (Bushberg, et al) From: The Essential Physics of Medical Imaging (Bushberg, et al) 10 Planar and SPECT Cameras - Summary • System components: – CollimatorDetectorElectronics • Collimator – Types: Parallel, Converging, Diverging, Pinhole, Multi-pinhole – Performance: Penetration, Resolution, Efficiency • Detector: – Components: Scintillator crystal, Optical spacer, PMTs – Performance: Efficiency, Intrinsic (spatial) resolution, Energy resolution • Acquisition modes: – Frame vs List mode – Static (single), Dynamic (TAC), Gated (cardiac / respiration) • Camera QA corrections: – Uniformity, Linearity, Photo-peak window, Multi-energy registration • SPECT QA/QC: – Center-of-rotation, Head tilt, uniformity 11