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RAD 466-L 8 by Dr. Halima Hawesa

RAD 466-L 8 by Dr. Halima Hawesa. SPECT/CT TECHNOLOGY & FACILITY DESIGN. Objective. To become familiar with basic SPECT/CT technology, and review considerations in establishing a new SPECT/CT facility. Content. SPECT cameras Image Quality & C amera QA SPECT/CT scanners

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RAD 466-L 8 by Dr. Halima Hawesa

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  1. RAD 466-L 8byDr. Halima Hawesa SPECT/CT TECHNOLOGY & FACILITY DESIGN

  2. Objective To become familiar with basic SPECT/CT technology, and review considerations in establishing a new SPECT/CT facility

  3. Content • SPECT cameras • Image Quality & Camera QA • SPECT/CT scanners • Design of SPECT/CT facilities

  4. What is SPECT Camera gamma cameras. • The most widely used gamma cameras are the so-called Anger cameras, in which a series of phototubes detects the light emissions of a large single crystal, covering the field of view of the camera. • SPECT imaging systems consist of single- or multiple-head gamma cameras which rotate around the patient, thereby acquiring the projections necessary for reconstruction of axial slices. • SPECT stand for Single Positron Emitting Computing Tomography.

  5. SPECT Camera Components • Collimator • NaI(Tl) crystal • Light Guide (optical coupling) • PM-Tube array • Pre-amplifier • Position logic circuits (differential & addition etc.) • Amplifier (gain control etc) • Pulse height analyser • Display (Cathode Ray Tube etc).

  6. Scintillators Density Z Decay Light Atten . (g/cc) time yield length (ns) (% NaI) (mm) Na(Tl) I 3.67 51 230 100 30 BGO 7.13 75 300 15 11 LSO 7.4 66 47 75 12 GSO 6.7 59 43 22 15 • Na(Tl) I works well at 140 keV, and is the most common scintillator used in SPECT cameras

  7. Scintillation detector Amplifier PHA Scaler

  8. Pulse height analyzer Pulse height (V) UL LL Time The pulse height analyzer allows only pulses of a certain height (energy) to be counted. counted not counted

  9. Gamma camera Used to measure the spatial and temporal distribution of a radiopharmaceutical

  10. GAMMA Camera

  11. Gamma camera(principle of operation) Position X Position Y Energy Z PM-tubes Detector Collimator Types of collimator Pinhole Parallel hole Diverging Converging collimators.

  12. GAMMA CAMERA Photons are selected by a collimator, hits the detector crystal, which produce light flashes that are detected and amplified by the photomultipliers, then send to digitizer, and then to computer processor for image reconstruction, then to display on monitor.

  13. PM-tubes Detect and amplify the light flash produced by the scintillation crystal.

  14. Light gamma-Rays GAMMA-ray Scintillation Detector • gamma-ray energy converted to light • Light converted to electrical signal Photomultiplier Tube Electrical Signal Scintillation Crystal

  15. Photomultiplier Tubes • Light incident on Photocathode of PM tube • Photocathode releases electrons + - Light gamma-Rays Scintillation Crystal Photocathode PM Tube Dynodes

  16. Photomultiplier Tubes • Electrons attracted to series of dynodes • each dynode slightly more positive than last one + + + - + + Light gamma-Rays Scintillation Crystal Photocathode PM Tube Dynodes

  17. Gamma cameraData acquisition • Static • Dynamic • ECG-gated • Wholebody scanning • Tomography • ECG-gated tomography • Wholebody tomography

  18. Scintigraphy seeks to determine the distribution ofa radiopharmaceutical

  19. SPECT cameras are used to determine the three-dimensional distribution of the radiotracer

  20. Tomographic acquisition

  21. Tomographic planes

  22. Myocardial scintigraphy

  23. ECG GATED TOMOGRAPHY

  24. 12.2 Image Quality & Camera QA

  25. Factors affecting image formation • Distribution of radiopharmaceutical • Collimator selection and sensitivity • Spatial resolution • Energy resolution • Uniformity • Count rate performance • Spatial positioning at different energies • Center of rotation • Scattered radiation • Attenuation • Noise

  26. SPATIAL RESOLUTION Sum of intrinsic resolution and the collimator resolution Intrinsic resolution depends on the positioning of the scintillation events (detector thickness, number of PM-tubes, photon energy) Collimator resolution depends on the collimator geometry (size, shape and length of the holes)

  27. SPATIAL RESOLUTION Object Image Intensity

  28. NON-UNIFORMITY (Contamination of collimator)

  29. NON UNIFORMITYRING ARTIFACTS Good uniformity Bad uniformity Difference

  30. NON-UNIFORMITY Defect collimator

  31. Scattered radiation Scattered photon photon electron

  32. The amount of scattered photons registered Depends on 1- Patient size 2- Energy resolution of the gammacamera 3- Window setting

  33. PATIENT SIZE

  34. Counts 140 120 100 80 Tc99m 60 40 20 0 120 100 140 160 20 60 Energy Pulse height distribution Full energy peak Scattered photons The width of the full energypeak (FWHM) is determined by the energy resolution of thegamma camera. There willbe an overlap between thescattered photon distributionand the full energy peak,meaning that some scatteredphotons will be registered. FWHM Overlappingarea

  35. Window width 20% 40% 10% Increased window width will result in an increased number ofregistered scattered photons and hence a decrease in contrast

  36. ATTENUATION CORRECTION • Transmission measurements • Sealed source • CT

  37. ATTENUATION CORRECTION Ficaro et al Circulation 93:463-473, 1996

  38. NOISE Count density

  39. Gamma camera • Operational considerations • Collimator selection • Collimator mounting • Distance collimator-patient • Uniformity • Energy window setting • Corrections (attenuation, scatter) • Background • Recording system • Type of examination

  40. QC GAMMA CAMERA Acceptance Daily Weekly Yearly Uniformity P T T P Uniformity, tomography P P Spectrum display P T T P Energy resolution P P Sensitivity P T P Pixel size P T P Center of rotation P T P Linearity P P Resolution P P Count losses P P Multiple window pos P P Total performance phantom P P P: physicist, T:technician

  41. Sensitivity • Expressed as counts/min/MBq and should be measured for each collimator • Important to observe with multi-head systems that variations among heads do not exceed 3%

  42. Multiple Window Spatial Registration • Performed to verify that contrast is satisfactory for imaging radionuclides, which emit photons of more than one energy (e.g. Tl-201, Ga-67, In-111, etc.) as well as in dual radionuclides studies

  43. Count Rate Performance • Performed to ensure that the time to process an event is sufficient to maintain spatial resolution and uniformity in clinical images acquired at high-count rates

  44. Total performance Total performance phantom. Emission or transmission. Compare result with reference image.

  45. Phantoms for QC ofgamma cameras • Bar phantom • Slit phantom • Orthogonal hole phantom • Total performance phantom

  46. QUALITY CONTROLANALOGUE IMAGES Quality control of film processing: base & fog, sensitivity, contrast

  47. QUALITY ASSURANCECOMPUTER EVALUATION Efficient use of computers can increase the sensitivity and specificity of an examination. * software based on published and clinically tested methods * well documented algorithms * user manuals * training * software phantoms

  48. SPECT/CT System

  49. TYPICAL SPECT/CT CONFIGURATION The most prevalent form of SPECT/CT scanner involves a dual-detector SPECT camera with a 1-slice or 4-slice CT unit mounted to the rotating gantry; 64-slice CT for SPECT/CT also available

  50. SPECT/CT • Accurate registration • CT data used for attenuation correction Localization of abnormalities • Parathyroid lesions (especially for ectopic lesions) • Bone vs soft tissue infections • CTCA fused with myocardial perfusion for 64-slice CT scanners

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