Radiology Physics & Instruments (RMI216) Lecture 1 PDF

RADIOLOGY PHYSICS& INSTRUMENTS (RMI216) INTRODUCTION TO RADIOLOGY PHYSICS (LEC.1) Dr. Mohammed Sayed Mohammed National Cancer Institute, Cairo University Faculty of Applied Health Sciences, Galala University. Qualified Expert of Radiologic Sciences, Ministry of Health, Egypt. Former Supervisor o...

RADIOLOGY PHYSICS& INSTRUMENTS (RMI216) INTRODUCTION TO RADIOLOGY PHYSICS (LEC.1) Dr. Mohammed Sayed Mohammed National Cancer Institute, Cairo University Faculty of Applied Health Sciences, Galala University. Qualified Expert of Radiologic Sciences, Ministry of Health, Egypt. Former Supervisor of Diagnostic Radiology Department, College of Applied Medical Sciences, University of Hail, KSA. Former STEM Ambassador, University of Reading, UK.  ATOMIC STRUCTURE, X-RAYS PRODUCTION, AND RADIOACTIVITY. Atomic structure: Atoms are made up of 3 main particles: Protons(+ charge) inside the nucleus. 2 Neutrons(+/- charge) inside the nucleus. Electrons(- charge) orbit around the nucleus. In Radiology: Electrons interact with radiation to create medical images. The behavior of atoms is critical for understanding how X-rays are produced. Nucleus (protons and neutrons) ENERGY LEVELS& IONIZATION Key points: Electron energy levels. 3 Ionization process. Role in X-rays production. Fundamental physical constants: Avogadro’s number: NA = 6.022 × 1023 atoms/mol Speed of light in vacuum: c ≈ 3 × 108 m/s Electron charge: e = 1.602 × 10–19 C Proton rest mass: NA = 6.022 × 1023 atoms/mol c ≈ 3 × 108 m/s e = 1.602 × 10–19 C  Electron/positron rest mass: me = 0.511 MeV/c2 mp = 938.3 MeV/c2  Neutron rest mass: IAEA mn = 939.6 MeV/c2 Basic quantities and several derived physical quantities and their units in SI units: 4 Classification of ionizing radiation Ionizing radiation carries enough energy per quantum to Ionizing Radiation remove an electron from an atom or molecule Introduces reactive and potentially damaging ion into the environment of the irradiated medium 5 Can be categorized into two types: Directly ionizing radiation Indirectly ionizing radiation Both can traverse human tissue Directly ionizing Indirectly ionizing radiation radiation Can be used in medicine for imaging & therapy es reactive and potentially damaging ion into the environment of the irradiated medium Classification of indirectly ionizing photon radiation Consists of three main categories: Ultraviolet: limited use in medicine X ray: used in disease imaging and/or treatment Emitted by orbital or accelerated electrons 6 γ ray: used in disease imaging and/or treatment Emitted by the nucleus or particle decays Difference between X and γ rays is based on the radiation’s origin. The origin of these photons fall into 4 categories: Characteristic (fluorescence) X rays From nuclear transitions Bremsstrahlung X rays Annihilation quanta  Characteristic X rays Orbital electrons inhabit atom’s minimal energy state An ionization or excitation process leads to an open vacancy An outer shell electron transitions to fill vacancy (~nsec). 7 Liberated energy may be in the form of: Characteristic photon (fluorescence) Energy = initial state binding energy - final state binding energy Photon energy is characteristic of the atom Transferred to orbital electron that Emitted with kinetic energy = transition energy - binding energy Called an Auger electron  Bremsstrahlung Translated from German as 'breaking radiation’  Light charged particles (β− & β+) slowed down by interactions with other charged particles in matter (e.g. atomic nuclei) 8  Kinetic energy loss converted to electromagnetic radiation  Bremsstrahlung energy spectrum Non-discrete (i.e. continuous) Ranges: zero - kinetic energy of initial charged particle  Central to modern imaging and therapeutic technology Can be used to produce X rays from an electrical energy source  Gamma rays Nuclear reaction or spontaneous nuclear decay may leave product (daughter) nucleus in excited state  The nucleus can transition to a more stable state by emitting a γ ray 9  Emitted photon energy is characteristic of nuclear energy transition  γ ray energy typically > 100 keV & wavelengths < 0.1 Å Annihilation quanta Positron results from: β+ nuclear decay high energy photon interacts with nucleus or orbital electron electric field 10 Positron kinetic energy (EK) loss in absorber medium by Coulomb interactions: Collisional loss when interaction is with orbital electron Radiation loss (bremsstrahlung) when interaction is with the nucleus Final collision (after all EK lost) with orbital electron (due to Coulomb attraction) called positron annihilation Annihilation quanta During annihilation Positron & electron disappear Replaced by 2 oppositely directed annihilation quanta (photons) 11 Each has energy = 0.511 MeV Conservation laws obeyed:  In-flight annihilation 2 quanta emitted Electric charge, linear momentum, angular momentum, total energy Annihilation can occur while positron still has kinetic energy Not of identical energies Do not necessarily move at 180º Radiation quantities and units  Exposure: X Ability of photons to ionize air  Kerma: K (acronym for Kinetic Energy Released in Matter) 12 Energy transferred to charged particles per unit mass of the absorber Defined for indirectly ionizing radiation  Dose (also referred to as absorbed dose): Energy absorbed per unit mass of medium Radiation quantities and units  Equivalent dose: 𝐻T Dose multiplied by radiation weighting factor wR When different types of radiation are present, 𝐻T is the sum of all of the individual weighted contributions 13  Effective dose: E 𝐻𝑇 multiplied by a tissue weighting factor wT  Activity: A Number of nuclear decays per unit time Its SI unit, becquerel (Bq), corresponds to one decay per second Radiation quantities and units 14 BASIC DEFINITIONS FOR ATOMIC STRUCTURE 15 BASIC DEFINITIONS FOR ATOMIC STRUCTURE 16 BASIC DEFINITIONS FOR ATOMIC STRUCTURE 17 BASIC DEFINITIONS FOR ATOMIC STRUCTURE 18 BASIC DEFINITIONS FOR NUCLEAR STRUCTURE 19 BASIC DEFINITIONS FOR NUCLEAR STRUCTURE 20 BASIC DEFINITIONS FOR NUCLEAR STRUCTURE 21 BASIC DEFINITIONS FOR NUCLEAR STRUCTURE 22 BASIC DEFINITIONS FOR NUCLEAR STRUCTURE 1. Nuclear binding energy 23  How X-rays are produced 24 X-rays are created when high-energy electrons hit a metal target(usually tungsten) inside an Xray tube. Two types of radiation are produced: Bremsstrahlung Radiation: electrons slow down as they approach the nucleus, emitting energy in the form of Xray. Characteristic Radiation: electrons knock out inner-shell electrons fill the gap, releasing energy as X-rays. Both types are important in diagnostic imaging. Properties of X-ray Key points: Invisible 25 Penetrates soft tissue, absorbed by bones Produces diagnostic images Types of radiation Alpha: blocked by paper 26 Beta: penetrates skin Gamma : High penetration, used in diagnostics  Types of radiation Alpha particles: 1. Large & heavy, can be stopped by a sheet of paper. Not used in medical imaging due to low penetration. Beta Particles: 27 Smaller, can penetrate skin but stopped by materials like plastic. Sometimes used in radiation therapy. Gamma Rays: Highly penetrating, can pass through the body. Commonly used in nuuclear medicine to trace radioactive substances in the body. Understanding these types is important for using radiation safely in diagnostics. Conclusion Key points: Atomic structure &energy levels X-ray production processes Radioactive decay & its role in imaging We’ve covered the atomic structure & its role in radiology. 28 We discussed x-ray production through ionization & the types of radiation used in diagnostics. Understanding these concepts is crucial as we move forwared with more advanced imaging techniques.  THANK YOU Dr. Mohammed Sayed Mohammed National Cancer Institute, Cairo University Faculty of Applied Health Sciences, Galala University. Qualified Expert of Radiologic Sciences, Ministry of Health, 29 Egypt. Former Supervisor of Diagnostic Radiology Department, College of Applied Medical Sciences, University of Hail, KSA. Former STEM Ambassador, University of Reading, UK. [email protected] www.gu.edu.eg