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  • ישומי פיסיקה ברפואה רפואה גרעינית
  • ישומי פיסיקה ברפואה רפואה גרעינית
    • Introduction
    • Atomic and Nuclear Physics
    • Radioactivity
    • Interaction of photons and matter
    • Photon Detectors
    • Radiopharmaceuticals
    • Radiation Safety
    • Study Types
    • Gamma Cameras
  • 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.
  • 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
  • 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.
    Nucleus Electrons
  • 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.
    L K “ Free” Electrons 4-5 keV 33.2 keV Binding Energy
  • 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=B K -B L
      • Auger electrons E=B K -2B L
    L Nucleus K-shell Vacancy Auger Electron K Characteristic X-ray
    • Ionization
    • Exitation
    Ground state kev 100 200 300 400 400 kev gamma 800
  • 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 Z x N.
    • A X is sufficient to define a nucleus.
    • For example Iodine 131:
    • 131 53 I 78 131 I
  • 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.
  • 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..
  • 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 Z X N A-4 Z-2 Y N-2
    • beta - rays: turn a neutron into a proton: A Z X N A Z+1 Y N-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 .
  • Radionuclides
    • Natural
    • Exist in an unstable state in nature ( Z > 82 )
    • Artificial
    • Produced by bombarding stable nuclides with high-energy particles.
  • 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
    L Nucleus K Excitation Ionization EM Radiation
  • Interaction of Photons and Matter
    • Photons interact with matter through 3 processes :
      • Photoelectric effect
      • Compton Scattering
      • Pair production
    L K Photon Electron Nucleus Photoelectric Electron Compton Photon Anti-Electron Electron Pair Production > 1.02 Mev ! Photon Photon
  • 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
  • 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.
  • Scintillators
    • NaI(Tl) scintillation :
    holes radiation electrons Drift to impurity center and Ionize it Free Holes and electrons recombine producing excited atoms Light radiation
  • Gamma Ray Collimator Collimator NaI(Tl) Crystal Light Electrons Dynodes Dynodes Anode High Voltage Supply Photocathode Signal Pre - Amp Amp 념넮녈넮녁
  • 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
  • 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.
  • 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.
  • 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 .
  • 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
  • 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)
    • R adiation A bsorbed D ose:
    • Measured the amount of energy that is deposited per gram of substance.
    • 1 Rad=1 erg/gram tissue
    • 1Gy=100 Rads
  • 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 ( R oentgen e quivalent m an) = 1 Rad * Q.F (quality factor).
    • x-rays, gamma rays and beta particles are assigned a quality factor of 1.
  • 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
  • Study Types
    • Static Imaging
    • Dynamic Imaging
    • Whole Body Scan
    • Gated Imaging
    • SPECT Imaging
    • PET Imaging
    • TET Imaging
  • APEX 409
  • 03-5643367