HSMI L2 Atomic Structure and Medical Imaging PDF

HSMI 1211 INTRODUCTION TO MEDICAL IMAGING LECTURE 2: ATOMIC STRUCTURE AND MEDICAL IMAGING DATE : OCTOBER 17, 2024 INSTRUCTOR: LIYANA MUSA (PhD) DEPARTMENT OF DIAGNOSTIC IM...

HSMI 1211 INTRODUCTION TO MEDICAL IMAGING LECTURE 2: ATOMIC STRUCTURE AND MEDICAL IMAGING DATE : OCTOBER 17, 2024 INSTRUCTOR: LIYANA MUSA (PhD) DEPARTMENT OF DIAGNOSTIC IMAGING & RADIOTHERAPY DAY: THURSDAY KULLIYYAH OF ALLIED HEALTH SCIENCES INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA OVERVIEW OF ATOMIC STRUCTURE ATOMIC STRUCTURE Definition of atom Basic unit of matter, consisting of nucleus surrounded by electrons.  COMPONENT OF AN ATOM Nucleus contains proton (positively charged) & neutron (neutral) account for most of the atom’s mass Electrons negatively charged orbit the nucleus in various energy levels ATOMIC NUMBER & Same number of protons but different number of neutron. MASS NUMBER Atomic Number (Z) ISOTOPE the number of protons in the Different type of atom but nucleus same element. defining the element STANDARD ATOMIC Mass Number (A) NOTATION total number of protons and neutrons in the atom’s nucleus IMPORTANCE OF ATOMIC STRUCTURE the arrangement of subatomic particle determines the atom’s chemical properties, stability and behaviour in interaction with radiation ELECTRON BINDING ENERGY The energy of the electrons as they orbit the nucleus in their respective orbits (shells) LINK TO MEDICAL IMAGING The number of electrons per shell is fixed; (2n2). X-ray interaction: the photoelectric The closer an electron is to the nucleus, the effect and compton scattering more tightly it is bound to the orbit or shell (higher the electron binding energy) involves interaction with an atom’s electron, escpecially those in the >more energy is needed to remove the electron. inner and outer shells RADIATION  TYPES OF IONISING Alpha RADIATION Beta Gamma RADIATION-definition X-ray Occurs when energy is emitted by a source, then travels High energy Neutrons through a medium, such as air, until it is absorbed by matter. TYPES OF RADIATION NON-IONIZING NON-IONISING - do not cause ionisations in the atom they interact. does not have enough energy to remove electrons from Ultraviolet atoms or molecules. Visible light less harmful. Infrared Microwave IONIZING Radio waves - cause ionisations in the atoms of matter that they interact. carries enough energy to ionize atoms or molecules by detaching electrons. can cause damage to biological tissue. ELECTROMAGNETIC SPECTRUM RADIOACTIVITY  DEFINITION The process by which unstable atomic nuclei spontaneously break down or decay, releasing energy in the form of radiation. This occurs because certain isotopes (known as radioactive isotopes or radionuclides) are not stable and seek a more stable state. TYPES RADIOACTIVITY Alpha decay Beta decay Gamma decay LINK TO MEDICAL IMAGING Nuclear Medicine - Radioactive Isotopes (Technitium-99m) used in SPECT for imaging skeleton, hearts and other organs. Radiation Therapy - Radioactive sources (Iodine-131) to treat cancer by damaging cancerous cells with focused ionizing radiation. SOURCE OF RADIATION IN MEDICAL IMAGING NATURAL SOURCES ARTIFICIAL SOURCES Diagnostic Imaging: Radiation Therapy: Includes cosmic rays from the sun. X-ray machines (e.g., in High-energy X-rays or radiography, fluoroscopy, gamma rays used to kill Terrestrial CT scans). cancer cells while sparing radiation from surrounding healthy tissue. naturally occurring Nuclear Medicine: Uses elements like gamma-emitting radon. radioisotopes injected or ingested into the body (e.g., Internal radiation Technetium-99m in SPECT, from radioactive Fluorine-18 in PET). isotopes within our bodies. HOW X-RAY IS PRODUCED CATHODE (ELECTRON SOURCE) A heated filament releases electrons through thermionic emission (high temperature) ANODE (TARGET) Electrons are accelerated towards the anode (often made of tungsten) by a high voltage difference.  HOW X-RAY IS PRODUCED -SUMMARY- High Voltage Filament heated Electron released from cathode Electrons accelerate Electron interact with towards target atom from anode X-RAY (RADIATION ) RELEASED  1. BREMSSTRAHLUNG RADIATION (BRAKING RADIATION) PRIMARY PROCESSES IN Process: When high-speed electrons from the cathode are accelerated towards the anode, they pass near the nucleus of THE ATOMS OF the atoms (typically tungsten) in the anode target. The strong positive charge of the nucleus slows down or "brakes" the THE ANODE incoming electrons. THAT GIVE RISE Energy Release: As the electrons decelerate, they lose kinetic TO X-RAY energy, which is emitted in the form of X-ray photons. This PRODUCTION IN process produces a broad spectrum of X-rays with varying energies. X-RAY TUBE Characteristics: The majority of X-rays produced in an X-ray tube are Bremsstrahlung radiation, and these X-rays have a continuous spectrum of energies, ranging from very low to the maximum energy set by the tube voltage (kVp).  1. BREMSSTRAHLUNG RADIATION (BRAKING RADIATION) PRIMARY PROCESSES IN THE ATOMS OF THE ANODE THAT GIVE RISE TO X-RAY PRODUCTION IN X-RAY TUBE  2. CHARACTERISTIC RADIATION PRIMARY Process: When high-energy electrons from the cathode collide PROCESSES IN with inner-shell electrons in the atoms of the anode target THE ATOMS OF (usually the K-shell or L-shell electrons), they can knock these inner-shell electrons out of their orbit. This creates a vacancy in THE ANODE the inner shell. THAT GIVE RISE Energy Release: To fill this vacancy, electrons from higher energy shells (outer shells) drop down to the lower energy level. TO X-RAY As they transition to the lower energy shell, they release energy PRODUCTION IN in the form of X-ray photons. The energy of these X-rays corresponds to the difference in energy levels between the X-RAY TUBE shells. Characteristics: Characteristic X-rays have discrete energies, specific to the target material's atomic structure (e.g., tungsten). These X-rays are responsible for a small portion of the X-rays produced, but they have specific, sharp energy peaks.  2. CHARACTERISTIC RADIATION PRIMARY PROCESSES IN THE ATOMS OF THE ANODE THAT GIVE RISE TO X-RAY PRODUCTION IN X-RAY TUBE PROPERTIES OF RADIATION COMMON PROPERTIES OF ALL TYPES OF RADIATION 1. In free space, they travel at the speed of light. 2. in free space, they travel in a straight line. 3. in free space they obey the inverse square law. 4. When interacting with matter they experience attenuation. 5. Radiation cannot be stopped completely. INVERSE SQUARE LAW The intensity of radiation decreases proportionally to the square of the distance from the source. This means that as you move away from a radiation source, the amount of radiation you receive reduces rapidly. ATTENUATION Gradual reduction in the intensity of radiation as it passes through a material. This decrease in intensity occurs due to the absorption and scattering of radiation within the material. ATTENUATION in the context of medical imaging and its relation to human anatomy INTERACTION OF X-RAY WITH TISSUE INTERACTION OF X-RAY WITH TISSUE PHOTOELECTRIC EFFECT Definition: occurs when an incoming X-ray photon completely transfers its energy to an inner-shell electron of an atom, ejecting the electron from the atom. The ejected electron is called a photoelectron. Process: An X-ray photon interacts with an inner-shell electron (usually K or L shell). The photon transfers all its energy to the electron, which overcomes its binding energy and is ejected from the atom. The ejected electron leaves a vacancy in the inner shell. An outer-shell electron fills the vacancy, and in doing so, releases characteristic radiation (secondary X-rays or fluorescence). Energy Considerations: The energy of the incident photon must be equal to or greater than the binding energy of the electron in the inner shell. The probability of the photoelectric effect is higher with lower-energy X-rays and denser atoms (like bone or metal).. INTERACTION OF X-RAY WITH TISSUE COMPTON SCATTERING Definition: Compton scattering occurs when an X-ray photon collides with a loosely bound outer-shell electron, transferring part of its energy to the electron and causing the photon to scatter in a different direction with reduced energy. Process: An X-ray photon interacts with an outer-shell electron. The photon transfers part of its energy to the electron, which is ejected from the atom (called a Compton electron). The photon, now with reduced energy, changes direction (scatters). Energy Considerations: The scattered photon has less energy than the incident photon because part of the energy was transferred to the ejected electron. Compton scattering is more likely with higher-energy X-rays and is less dependent on the atomic number of the material..  THANK YOU!