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  • 1. ‫ברפואה‬ ‫פיסיקה‬ ‫ישומי‬ ‫גרעינית‬ ‫רפואה‬
  • 2. ‫גרעינית‬ ‫רפואה‬ ‫ברפואה‬ ‫פיסיקה‬ ‫ישומי‬ * Introduction Atomic and Nuclear Physics Radioactivity Interaction of photons and matter Photon Detectors Radiopharmaceuticals Radiation Safety Study Types Gamma Cameras
  • 3. Introduction Nuclear Medicine combines Physics and Medicine in a very strong way. Nuclear Medicine uses non-invasive methods to image the physiology of human body by detecting the radiation emitted by radiopharmaceuticals inside the body. Understanding how radiation is detected is important in order to use optimally Nuclear Medicine detectors. In the following hour we hope to describe in sufficient detail the basics of the phenomena of the emission of radiation and its detection.
  • 4. Electromagnetic Waves Characterized by wavelength. Wavelength related to frequency and energy: 1 ev = 1.6 x 10e-19 joules 1 kev = 1000ev ; 1 Mev = 1000000 ev wavelength frequency Energy Comments [m] [Hz] [eV] 3.0e+03 1.0e+05 6.6e-11 LF, MF 3.0e+00 1.0e+08 6.6e-08 VHF,UHF,FM 3.0e-03 1.0e+11 6.6e-05 m-wave,radar 3.0e-06 1.0e+14 6.6e-02 IR,Light, UV 3.0e-09 1.0e+17 6.6e+01 UV, X-ray 3.0e-12 1.0e+20 6.6e+04 X-ray,gamma 3.0e-15 1.0e+23 6.6e+07 gamma
  • 5. Atomic Physics The Atom can be divided into the nucleus and the electron envelope. The electrons generate all chemistry (and biology) and are in large responsible for interaction between radiation and matter. All radiation detectors are mainly based on the interaction between radiation and the electron envelope. NucleusNucleus ElectronsElectrons
  • 6. Atomic Physics The electrons are arranged in “layers” (or “shells”) each with its binding energy. (For each layer n there 2n-1 sublayers , and 2 electrons sit in each sublayer) . The innermost layer has an index of 1 and is called the K layer. The next layer is called L layer and so on. LL KK “Free” Electrons 4-5 keV 33.2 keV Binding Energy
  • 7. Atomic Emissions The electrons tend to fill the atomic layers from the bottom up, i.e. if a K shell electron is kicked out , an outer shell electron will move to take its place, releasing energy. This energy can be released in two ways: – Characteristic X-ray photons E=BK-BL – Auger electrons E=BK-2BL LL Nucleus K-shell Vacancy Auger Electron KKCharacteristic X-ray
  • 8. Ionization Exitation Ground state kev 100 200 300 400 400 kev gamma 800
  • 9. The Nucleus The nucleus is comprised of protons and neutrons: – Z = number of protons – N = number of neutrons – A = Z + N , the total mass of the Nucleus Z defines the number of electrons in an atom, therefore defining which element it is. The atom is noted by A ZxN. A X is sufficient to define a nucleus. For example Iodine 131: 131 53I78 131 I
  • 10. The Nucleus The nucleus is kept together by the strong nuclear force, which is active at short distances. The protons and the neutrons in the nucleus can be arranged in energy shells, not much different from the arrangement of electrons in atoms. The nucleus can be on: # Excited state: Unstable, decays promptly to ground state # Ground state: Stable # Metastable state: Unstable decays slowly (lifetime > 10-12 sec) to ground state Metastable nuclei are very important in nuclear medicine: 99m Tc is a metastable nucleus.
  • 11. Isotopes Isotopes are nuclei with the same number of protons , but different number of neutrons. Many elements exist in nature with different number of neutrons in the nucleus. Examples:238 U and 235 U, 36 Cl and 35 Cl. All isotopes of an element have the same chemical characteristics. Isotopes have different nuclear properties, i.e.. some are ground state, some are in excited states etc..
  • 12. Radioactivity Unstable isotopes will try to reach the ground state by emitting radiation There are 4 main types of radiation: – alpha rays: nuclei of helium, 2 protons and 2 neutrons – beta rays: electrons – gamma rays: electromagnetic radiation of short wavelength – neutrons alpha rays: change the number of protons and neutrons by 2: A ZXN A-4 Z-2YN-2 beta- rays: turn a neutron into a proton: A ZXN A Z+1YN-1 gamma rays: keep the same nuclear numbers, just the state change. neutron emission is usually associated with fission, when a heavy nucleus break into lighter parts.
  • 13. Radionuclides Natural Exist in an unstable state in nature ( Z > 82 ) Artificial Produced by bombarding stable nuclides with high- energy particles.
  • 14. Interaction of Radiation and Matter Gamma and Beta rays interact with the electrons in the Atom Alpha rays interact both with electrons and nuclei Neutrons interact only with the nucleus Atoms are either Ionized or excited by radiation LL Nucleus KK Excitation Ionization EM Radiation
  • 15. Interaction of Photons and Matter Photons interact with matter through 3 processes: – Photoelectric effect – Compton Scattering – Pair production LL KKPhoton Electron Nucleus Photoelectric Photon Electron Compton Photon Anti-Electron Electron Pair Production > 1.02 Mev ! Photon
  • 16. Radiation Detectors Detectors are devices that translate radiation into recognizable signals The signals can be electric, light or even visual Ideal detector is: – Fast – Precise – Linear in Energy – Efficient All radiation detectors work by the principle that radiation deposits energy in matter. Atoms are ionized and free negative charges (electrons) and positive charges (cations or holes) are created. 3 types of detectors: – Gas detectors : Geiger - Muller counter – Solid State detectors – Scintillation detectors
  • 17. Scintillation Detectors Scintillators produce light in presence of radiation ∗ Scintillators have to be: – Efficient – Generate light proportional to Energy – Transparent (Low Absorption) – Fast ∗ Among the Scintillation detectors, NaI(Tl) is the most popular in NM. NaI(Tl) - Thallium-activated sodium iodide crystal. The purpose of thallium impurities to create activator centers to trap electrons “kicked out” by gamma rays.
  • 18. Scintillators NaI(Tl) scintillation: holes radiation electrons Drift to impurity center and Ionize it Free Holes and electrons recombine producing excited atoms Light radiation
  • 19. Gamma Ray CollimatorCollimator NaI(Tl) Crystal Light Electrons Dynodes Dynodes Anode HighVoltageSupply Photocathode Signal Pre - Amp Amp 념넮녈넮녁
  • 20. Summary Emission of radiation Absorption and Detection of Radiation Scintillation Detectors Transformation of Scintillator Light into electric pulses We have all the ingredients needed to start with Nuclear Medicine devices Gamma Camera
  • 21. Radiopharmaceuticals Radiopharmaceuticals are radioactive agents or drugs used for diagnostic or therapeutic procedures. Consist of two parts: 1. A radioactive substance to provide the signal. 2. A ligand that determines the molecule’s distribution in the body. Purpose: To follow their absorption, distribution, metabolism, and excretion through the use of detection device.
  • 22. Physical Properties Gamma or x-ray emission with an energy between 60 and 400 kev Physical half - life between 1 hour and 1 year. Almost ideal agent: Tc-99m: 140 kev & 6.02 hour half life.
  • 23. Radiopharmaceuticals Ideal properties: Readily available. Easy to prepare. Short half - life. Pure gamma emitter. Localization in only the tissue or organ desired. No significant radiation exposure to critical organs.
  • 24. Common Radionuclides Nuclide Half-Life Application 67 Ga 78 hr Tumor/infection imaging 201 Tl 73 hr Myocardial imaging 131 I 8 days Thyroid imaging & therapy 99m Tc 6 hr Nuclide for majority of radionuclide imaging 123 I 13 hr Thyroid imaging 133 Xe 5.2 days Ventilation imaging 111 In 68 hr Labeling white blood cells, antibodies
  • 25. Radiation Safety Radiation Exposure: Intensity of ionizing radiation, The number of ions produced when radiation passes through a specific volume of air at a standard temperature and pressure. Exposure is measured in roentgens (R) Radiation Absorbed Dose: Measured the amount of energy that is deposited per gram of substance. 1 Rad=1 erg/gram tissue 1Gy=100 Rads
  • 26. Radiation Safety Radiation Dose Equivalent accounts for the quality of radiation. Quality Factor is a measurement of relative biologic damage caused by a specific type and energy of radiation. 1 Rem (Roentgen equivalent man) = 1 Rad * Q.F (quality factor). x-rays, gamma rays and beta particles are assigned a quality factor of 1.
  • 27. Radiation Protection Natural Exposure ( 300mRem/yr) 150 - 250 mRem/yr (W. Body) Radiation worker - 5000 mRem/yr 1 chest X rays - 80 - 150 mRem C.T - 1500 - 2000 mRem W.B Bone Scan - 750 mRem, ALARA - As Low As Reasonably Achievable. To reduce radiation exposure: Time Distance Shielding
  • 28. Study Types Static Imaging Dynamic Imaging Whole Body Scan Gated Imaging SPECT Imaging PET Imaging TET Imaging
  • 29. APEX 409
  • 30. 03-5643367

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