1. 1. Lecture 9: Nuclear Imaging-I Shahid Younas NUCLEAR IMAGING The Scintillation Camera- Design Performance
2. 2. INTRODUCTION Lecture 9: Nuclear Imaging-I Nuclear imaging produces images of the isotropicaly distributed of radionuclides in patients. Uses gamma rays, characteristic x-rays, or annihilation photons to form images
3. 3. INTRODUCTION Lecture 9: Nuclear Imaging-I An imaging system must determine, Photon flux Density Direction of the detected photon
4. 4. INTRODUCTION Lecture 9: Nuclear Imaging-I Instruments designed to image gamma ray and x-ray emitting radionuclides use collimators. Vast majority (over 99.95%) of emitted photons is wasted.
5. 5. Development- Rectilinear Scanner Lecture 9: Nuclear Imaging-I Earliest successful imaging device was the rectilinear scanner A single moving radiation detector sampled the photon fluence at a small region at a time
6. 6. Development- Rectilinear Scanner Lecture 9: Nuclear Imaging-I The output was recorded on white paper with a series of black marks. Intensity of exposure or depth of color, corresponded to the concentration of radioisotope.
7. 7. Development- Rectilinear Scanner Lecture 9: Nuclear Imaging-I Benedict Cassen invented the rectilinear scanner. Do you know which was the first organ scanned on this scanner? Thyroid
8. 8. Development- Rectilinear Scanner Lecture 9: Nuclear Imaging-I Improved upon by use of a large-area positron-sensitive detector (indicating the location of each interaction) to sample simultaneously the photon fluence over the entire image plane. More expensive; permits more rapid image acquisition
9. 9. Development- Anger Gamma Camera Lecture 9: Nuclear Imaging-I Developed by Hal Anger from 1952 to 1958 Significantly replace rectilinear scanners in the late 1960s Spatial resolution became comparable to that of rectilinear scanners. Tc-99m-labeled radiopharmaceuticals became commonly used Replacing I-131 and Hg-203
10. 10. Development- Anger Gamma Camera Lecture 9: Nuclear Imaging-I Do you know what was the main short-coming of Anger Gamma Camera? Continuous motion.
11. 11. Development- Anger Gamma Camera Lecture 9: Nuclear Imaging-I Simultaneous collection of data over large area. Permits more rapid acquisition of images and enables dynamic studies. More flexible in its positioning, permitting images to be obtained from almost any angle
12. 12. Development- Anger Gamma Camera Lecture 9: Nuclear Imaging-I Scintillation camera wastes fewer photons. Images have less quantum mottle (statistical noise). Can be used with higher resolution collimators, producing images of better spatial resolution
13. 13. Development- Anger Gamma Camera Lecture 9: Nuclear Imaging-I What is the suitable photon energy range of usage of gamma camera? 100 to 200 keV
14. 14. Gamma Camera Design Lecture 9: Nuclear Imaging-I Scintillation camera contains a disk-shaped or rectangular NaI(Tl) crystal, ~ 0.95 cm thick, optically coupled to ~37 to 91 PMTs 5.1- to 7.6-cm diameter
15. 15. Gamma Camera Design Lecture 9: Nuclear Imaging-I Some designs incorporate a Lucite light-pipe between the glass cover of the crystal and the PMTs; in others, the PMTs are directly coupled to the glass cover. In most cameras, a preamp is connected to the output of each PMT
16. 16. Nuclear Stability Tests Lecture 9: Nuclear Imaging-I
17. 17. Gamma Camera Design Lecture 9: Nuclear Imaging-I Front side of Gamma Camera Head without collimator. A
18. 18. Gamma Camera Design Lecture 9: Nuclear Imaging-I Between the patient and the crystal is a collimator, usually made of lead. A scintillation camera without a collimator does not generate meaningful images
19. 19. Gamma Camera -Design Lecture 9: Nuclear Imaging-I Septa absorbs most of the photons ( 99.95%). Photons approaching the collimator from a nearly perpendicular direction pass through the holes. Those absorbed in NaI(Tl) causes emission of visible and ultraviolet light.
20. 20. Gamma Camera -Design Lecture 9: Nuclear Imaging-I Lights photons are converted into electrical signals. Amplification by PMTs. Further amplified by pre-amplifiers (preamps). Amplitude of the amplified pulse ~ amount of interaction light
21. 21. Gamma Camera -Design Lecture 9: Nuclear Imaging-I The pattern of photon interactions in the crystal forms a 2D projection of the 3D activity distribution in the patient. The PMTs closest to each photon interaction in the crystal receive more light producing larger voltage pulses
22. 22. Gamma Camera -Design Lecture 9: Nuclear Imaging-I Relative amplitude of the pulses from the PMTs contain sufficient information to determine the location of the interaction in the plane of the crystal.
23. 23. Gamma Camera -Design Lecture 9: Nuclear Imaging-I Why Sodium Iodide is doped with Thallium? Pure NaI is scintillator only at Liquid Nitrogen temperature. Thallium (0.1-0.4 mole %) is added to create activity centers to scintillate at room temperature.
24. 24. Gamma Camera Analogue Design Lecture 9: Nuclear Imaging-I Electronic circuits of a fully analog scintillation camera.
25. 25. Gamma Camera -Design Lecture 9: Nuclear Imaging-I Single Channel Analyzer produced a logic pulse (a voltage pulse of fixed amplitude) only if the Z pulse received was within a preset range of energies. Different Energy Setting ranges for different radionuclides.
26. 26. Gamma Camera Analogue Design Lecture 9: Nuclear Imaging-I Have you heard that in old cameras there used to be a manual dial which is changed by technologist? That was actually SCA Shift
27. 27. Gamma Camera NaI(Tl) Crystal Lecture 9: Nuclear Imaging-I Scintillator is a transparent material that converts the energy lost by ionization into pulse of light. Higher conversion efficiency Short decay time of excited state Transparent to its own emissions High Detection Efficiencies Rugged, hygroscopic free, inexpensive
28. 28. Gamma Camera NaI(Tl) Crystal Lecture 9: Nuclear Imaging-I Property NaI (Tl) BGO LSO (Ce) CsI (Tl) BaF2 Density 3.67 7.13 7.4 4.15 4.89 Effecitve No. 50 74 66 54 54 Decay time (nsec) 230 300 40 1000 0.8 Photon Yield Per KeV 38 8 20-30 52 10 Hygroscopic Yes No No Slightly No
29. 29. Gamma Camera NaI(Tl) Crystal Lecture 9: Nuclear Imaging-I Good absorber and Efficient Detector due to , Relative Density 3.67 g /cm3 Higher Z of Iodine ( 53) Sensitivity > 85 % at 140 keV Moderate Energy Resolution 9-10 % Well matched in to peak response to PMT.
30. 30. Gamma Camera NaI(Tl) Crystal Lecture 9: Nuclear Imaging-I At higher gamma ray energies (>300 KeV) needs larger volume for better detection. Fragile Hygroscopic Temperature Range
31. 31. Gamma Camera Analogue Design Lecture 9: Nuclear Imaging-I Do you know the desirable Temerature and humidity range for efficient camera working? 18-24 1.5 oC 30-60 5%
32. 32. Gamma Camera NaI(Tl) Crystal Lecture 9: Nuclear Imaging-I NaI is doped with 0.1-0.4 mole % Thallium to scintillate. Single, Large area usually, 6-12.5 mm ( ~ 9.5 mm) thick Increased Sensitivity but Resolution decreases. 25-50 cm diameter or 60 x 40 cm dimensions if rectangular. Surrounded by highly reflective material TiO2 or Mag-Oxide to maximize light output.
33. 33. Gamma Camera hybrid Design Lecture 9: Nuclear Imaging-I Late 1970s hybrid analog-digital scintillation cameras introduced Analog X, Y, and Z pulses converted to digital signals by analog- to-digital converters (ADCs) Digital signals sent to digital correction circuits
34. 34. Gamma Camera hybrid Design Lecture 9: Nuclear Imaging-I Corrected digital X, Y, and Z signals converted back to analog voltage pulses. Energy discrimination done in the analog domain by SCAs. Output to CRT as with display on a computer monitor.
35. 35. Gamma Camera hybrid Design Lecture 9: Nuclear Imaging-I Electronic circuits of a hybrid analog-digital scintillation camera.
36. 36. Gamma Camera Model Digital Design Lecture 9: Nuclear Imaging-I Corrected digital X, Y, and Z signals converted back to analog voltage pulses. Energy discrimination done in the analog domain by SCAs. Output to CRT as with display on a computer monitor.
37. 37. Gamma Camera Model Digital Design Lecture 9: Nuclear Imaging-I Electronic circuits of a modern digital scintillation camera.
38. 38. Gamma Camera Model Digital Design Lecture 9: Nuclear Imaging-I Even if the cameras are digital but you have to identify radionuclide.
39. 39. Gamma Camera Collimators Lecture 9: Nuclear Imaging-I Collimator forms the projection image by permitting gamma ray photons to reach the crystal while absorbing most of the other photons. Most common collimator is the parallel-hole collimator
40. 40. Gamma Camera Collimators Lecture 9: Nuclear Imaging-I Holes may be round, square, or triangular. Most state-of-the-art collimators have hexagonal holes and are usually made from lead foil. Septa must be thick enough to absorb most of the photons incident upon them
41. 41. Gamma Camera Collimators Lecture 9: Nuclear Imaging-I Inherent compromise between spatial resolution and efficiency (sensitivity) of collimators. Reducing size of holes or lengthening collimator to improve spatial resolution reduces efficiency.
42. 42. Gamma Camera Collimators Lecture 9: Nuclear Imaging-I Most scintillation cameras are provided with a selection of parallel-hole collimators: low-energy, high-sensitivity low-energy, all-purpose (LEAP) low-energy, high-resolution (LEHR)
43. 43. NUCLEAR IMAGING-I Lecture 9: Nuclear Imaging-I Curie was the passion and Becquerel was the passion however radiation are still at large. (SY)