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. INTRODUCTION Lecture 9: Nuclear Imaging-I An imaging system
must determine, Photon flux Density Direction of the detected
photon
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
17. Gamma Camera Design Lecture 9: Nuclear Imaging-I Front side
of Gamma Camera Head without collimator. A
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. 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. 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. 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. 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. 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. Gamma Camera Analogue Design Lecture 9: Nuclear Imaging-I
Electronic circuits of a fully analog scintillation camera.
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Gamma Camera hybrid Design Lecture 9: Nuclear Imaging-I
Electronic circuits of a hybrid analog-digital scintillation
camera.
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. Gamma Camera Model Digital Design Lecture 9: Nuclear
Imaging-I Electronic circuits of a modern digital scintillation
camera.
38. Gamma Camera Model Digital Design Lecture 9: Nuclear
Imaging-I Even if the cameras are digital but you have to identify
radionuclide.
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. 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. 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. 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. NUCLEAR IMAGING-I Lecture 9: Nuclear Imaging-I Curie was
the passion and Becquerel was the passion however radiation are
still at large. (SY)