1. Nuclear Medicine Principles & Technology_I
Dr. Mohammed Alnafea

2. Nuclear medicine images
Single photon imaging
Planar 2D image
Single Photon Emission Computed Tomography (SPECT) 3D image
Positrons Emission Tomography (PET).
All reveal the spatial and temporal distribution of target-specific pharmaceuticals in the human body.
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3. Nuclear Medicine Principles & Technology
Non-invasive determination of physiologic processes
Tracer principle:
Radiopharmaceuticals are distributed, metabolized, and excreted according to their chemical structure
Display of biological functions as:
-Images
-Numerical data
-Time-activity curves
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4. Nuclear medicine images
Depending on the application, the nuclear medicine data can be interpreted to yield information about physiological processes such as :
glucose metabolism.
blood volume, flow and perfusion.
tissue and organ uptake.
receptor binding, and oxygen utilization.
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5. Tracer Principle
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6. Common Radio-nuclides
Energy (keV)
Type
Half lives
Nuclides
140 
6 h
TC-99m 70
73 h
Tl-201
159
13 h
I-123
364
8 d
I-131
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7. Radiopharmaceutical
Selection of pharmaceutical based on organ-specific question.
Labeling of pharmaceutical with radioactive isotopes.
Radiopharmaceuticals should not disturb the process under investigation
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8. Ideal Radiopharmaceuticals
Low radiation dose
High target/non-target activity
Safety
Convenience
Cost-effectiveness
Only emit gamma
Produced by generator
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10. Mechanisms of Localization
Compartmental localization and leakage
Cell sequestration
Phagocytosis
Passive diffusion
Metabolism
Active transport
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11. Localization (cont.) Capillary blockade Perfusion Chemotaxis
Antibody-antigen complexation
Receptor binding
Physiochemical adsorption
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12. Half-Life (HL) Physical Half-Life Biological Half-Life
Time (in minutes, hours, days or years) required for the activity of a radioactive material to decrease by one half due to radioactive decay
Biological Half-Life
Time required for the body to eliminate half of the radioactive material (depends on the chemical form)
Effective Half-Life
The net effect of the combination of the physical & biological half- lives in removing the radioactive material from the body
Half-lives range from fractions of seconds to millions of years
1 HL = 50% 2 HL = 25% 3 HL = 12.5%
9. Half-Life
In any sample of radioactive material, the amount of radioactive material constantly decreases with time because of radioactive decay.
The physical half-life is the amount of time required for a given amount of radioactive material to be reduced to half the initial amount by radioactive decay.
The biological half-life is the time required for the human body to eliminate half of the radioactive material taken into it. For many radioactive materials, the elimination from the body occurs via urination. However, depending on the chemical composition of the radioactive material, other pathways can also help to eliminate the radioactive material from the body.
The effective half-life is a measure of the time it takes for half the radioactive material taken into the body to disappear from the body. Both the physical half-life and the biological half-life contribute to the elimination of the radioactive material from the body. The combination of these two half-lives is called the effective half-life.
After one half-life, half of the material remains. After a second half-life, a half of a half, i.e. 25% of the initial amount remains. After 10 half-lives, about 1/1000 remains. After 20 half-lives, only one millionth of the material remains.
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13. Nuclear Imaging
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14. Interaction of Photons with Matter
Pass through unaffected (i.e. penetrate)
Absorbed (and transfer energy to the absorbing medium)
Scattered (i.e. change direction and possibly lose energy)
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15. Main Interactions of gamma-rays with matter when used for imaging
Photo-electric absorption
Compton Scattering
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16. Photoelectric absorption
An incident photon is completely absorbed by an atom in the absorber material, and one of the atomic electrons is ejected. This ejected electron is known as a photoelectron.
The electron must be bound to the atom, to conserve energy and momentum.
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17. The Photoelectric Effect
In the photoelectric effect the photon interacts with an orbital electron and disappears, while the electron is ejected from the atom thus ionising it. The energy of the photoelectron is given by
Ek = hν – EB
Where Ek is the kinetic energy of the ejected electron, hν the energy of the photon and EB the binding energy of the electron.
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18. Compton Scattering
In this case, an incident gamma ray scatters from an outer shell electron in the absorber material at an angle , and some of the gamma ray energy is imparted to the electron.
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19. All interaction
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20. 9th lecture General-Purpose Circular Detector
                                     
High-Performance Circular Detector
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21. The gamma camera
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22. Gamma Camera Components
Photomultipliers
Scintillator
Collimator
Organ to be imaged
Typically: 40cm × 55cm NaI(Tl) scintillator
Spatial resolution ~ a few mm
Use of large collimator not efficient  relatively large radiation dose needed to be given to patient.
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23. The modern gamma camera consists of:
- multihole collimator
- large area NaI(Tl) (Sodium Iodide - Thallium activated) scintillation crystal
- light guide for optical coupling array (commonly hexagonal) of photo-multiplier tubes
- lead shield to minimize background radiation
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24. Features and parameters of the scintillation crystal
The following are the typical features of the scintillation crystal used in modern gamma cameras
most gamma cameras use thallium-activated (NaI (Tl))
NaI(Tl) emits blue-green light at about 415 nm
the spectral output of such a scintillation crystal matches well the response of standard bialkali photomultipliers .
the linear attenuation coefficient of NaI(Tl) at 150 KeV is about 2.2 1/cm . Therefore about 90% of all photons are absorbed within about 10 mm
NaI(Tl) is hyrdoscopic and therefore requires hermetic encapsulation
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25. digital and/or analog methods are used for image capture
NaI(Tl) has a high refractive index ( ~ 1.85 ) and thus a light guide is used to couple the scintillation crystal to the photomultiplier tube
the scintillation crystal and associated electronics are surrounded by a lead shield to minimize the detection of unwanted radiation
digital and/or analog methods are used for image capture
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26. Camera component
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27. The action of a parallel hole collimator
A crucial component of the modern gamma camera is the collimator. The collimator selects the direction of incident photons. For instance a parallel hole collimator selects photons incident the normal.
The action of a parallel hole collimator
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28. Detail of the pin-hole collimator
Other types of collimators include pinhole collimator often used in the imaging of small superficial organs and structures (e.g thyroid,skeletal joints) as it provides image magnification.
Detail of the pin-hole collimator
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29. Collimator
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30. Collimator
Defines the spatial resolution of the system
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31. Collimator Septa designed for specific gamma ray energy:
e.g. length 35 mm
distance 1.5 mm
thickness 0.2 mm
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32. Again Camera components
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33. Gamma Camera Components
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34. Principle of Scintillation detector
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35. Scintillator
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36. Anger (gamma) camera
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37. Energy Signal
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38. Ideal Energy Spectrum
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39. Projections
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40. Real Energy Spectrum
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41. Camera specification Detector size ca. 50 cm x 60 cm
ca. 60 photomultiplier tubes per detector
Energy keV< 10%
Intrinsic spatial resolution: 3,5 -4 mm
Extrinsic spatial resolution (Collimator): mm
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42. Examples
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43. Nuclear medicine image
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44. Renal Scan
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45. My time is up!
Any questions ??
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