W2 Flashcards
Describe the History of Dental Radiology in brief
X-rays…
* Discovered by Professor Wilhelm Conrad Roentgen in 1895. Named them, Unknown rays (X-rays). published the article on X-rays on 5th Jan, “A Sensational Discovery”
* 2 weeks after Roentgen’s publication Dr Otto Walkhoff made the first picture of teeth - intraoral radiograph after an exposure of 25 min.
* Dr Edmund Kells - FIRST to expose dental radiograph in the United States
Describe the Atomic structure
7 protons (postitive charge) and 7 neutrons (neutral charge) in the nucleus
7 electrons (negative charge) orbiting around the nucleus
number of electrons = number of protons in an atom = atom has no net charge/electrically neutral
Define electromagnetic radiation and list the types (including x-rays)
Electromagnetic radiation: movement of energy through space as a combination of electric and magnetic fields
Types: X-ray, radiowaves, visible light, microwaves and gamma rays, travel at the speed of light (3X10^8m per second)
What is Electrostatic force?
Will electrons closer to the nucleaus have greater or less electrostatic force?
Attraction between the positive protons and negative electrons
Electrons in the orbit closest to the nucleus (the K-shell) will have a greater electrostatic force.
What is radiation? List the two types.
Radiation is the transmission of energy through space and matter
1. Particulate radiation: Alpha particles, Betaparticles and cathode rays
2. Electromagnetic radiation
What is ionisation and ionisation energy? How does it occur?
If an atom loses an electron, the nucleus becomes a positive ion and the free electron a negative ion = process of forming an ion pair = ionization.
Binding energy (ionization energy); is the amount of energy required to overcome the electrostatic force to remove an electron from its orbit
What does the left side and right side represent on this electromagnetic spectrum?
TEST
Ionising radiation = LEFT SIDE (strong waves, short wavelength, high freq., high penetrating ability = easily ionise)
Non-ionising radiation = RIGHT SIDE (long wavelength, low freq., low penetrating ability)
Compare Ionizing and Non-ionizing radiation
Ionizing radiations - Radiation consisting of particles, X-rays, or gamma rays with sufficient energy to cause ionization in the medium through which it passes.
Nonionizing radiations - ex. visible light, infrared, and microwave radiation, and radio waves do not have sufficient energy to remove bound electrons from their orbitals.
What does wavelength, frequency, distance and energy represent in electromagnetic radiation,
The wavelength (W) is the distance from the crestof one wave to the crest of the next wave.
The frequency (F) is the number of waves in a given distance (D).
Energy of a wave of electromagnetic radiation represents the ability to penetrate an object. Shorter W = greater energy
top wave above has a shorter wavelength, higher frequency and greater energy than the wave below it
Explain the characteristics of an X-ray
- X-rays are high energy waves, with very short wavelengths (0.1 – 0.001 nm), and travel at the speed of light.
- X-rays have no mass (weight) and no charge (neutral).
- You cannot see x-rays; they are invisible.
- X-rays travel in straight lines;
- X-rays are differentially absorbed by the materials they pass through.
- X-rays will cause certain materials to fluoresce (give of flight)
- X-rays can be harmful to living tissue. therefore keep the number minimum
What does it mean by X-rays are differentially absorbed by the materials they pass through.?
More dense materials (like an amalgam restoration) will absorb more x-rays than less dense material (like pulp tissue)
List the three basic components of an X-ray
the X-ray tubehead, which produces the x-rays
Support arms, which allow you to move the tubehead
The control panel, which allows you to alter the duration of the x-ray beam (exposure time)
List the components of an x-ray tube
- Focusing cup (Molybdenum): focuses electrons on target
- Tungsten Filament: releases electrons when heated
- Electron stream: electrons cross from filament to target
- Vacuum: to prevent collision of the moving electrons with gas molecules which can reduce the speed of electrons & prevents oxidation and burnout ofthe filament.
- Tungsten Target: x-rays produced when electrons strike target
- Copper stem: Houses the target and helps remove heat from target
- Leaded glass: Keeps x-rays from exiting tube in wrong direction
- **X-rays **produced in target are emitted in all directions
- Beryllium window: this non-leaded glass allows x-rays to pass through. The PID would be located directly in line with this window
What parts of the x-ray tube make up the cathode and anode.
Cathode = Negatively charged
Anode = Positively charged
What is thermionic emission?
When we depress the exposure button -> electricity flows through the filament -> hot -> electrons released
Why is the target made of Tungsten?
Tungsten = Only metal that has high atomic number, high melting point, high thermal conductivity and low vapor pressure
Describe the Line Focus Principle
target is placed at an angle of 20 degree to the X-ray beam = smaller source of X-rays and sharper image
Compare the two types of x-rays that are produced
Two types of x-rays produced in the target of the x-ray tube…
1. Bremmstrahlung/general radiation (majority): high-speed electrons pass close to, or strike, the nuclei of the target atoms. Electrons are slowed down and change direction = E released in form of X-rays
The higher the speed of the electrons, the higher the average energy of the x-rays produced
2. Characteristic radiation: High energy electron hits inner most electron (K shell) knocking off the electron. The elctron from L takes its place. The energy of X-Ray will be equal to the difference between the binding energies of the target electrons involved
What are the three factors that absorb the excess heat produced by X-rays?
High melting point of tungsten target
Conductive properties of copper stem
Oil surrounding X-ray tube
List the factors controlling X-Ray beam
kVp control: increase = number of X-rays and kinetic energy (greater penetration and contrast)
mA setting: increase = increase number of X-rays (sharper)
Exposure time: increase = increase number of X-rays (sharper)
Filtration: = only high energy X-rays
Collimation = reduce radiaton scope
Describe the three filters used in Inherent filtration. Describe the factor needed to achieve total filtration
Beryllium window, oil surrounding tube head, barrier material
= filter low energy X-rays = High E X-rays
Sometimes manafacture can add filter of Al = Total Filtration
What is collimation?
metallic barrier (lead disc) with anaperture in the middle used to reduce the size of the X-ray beam and therefore the volume of the irradiatedtissue in a patient
Explain the Interaction of X-Rays with matter
90% of X-Rays get absorbed
B - Of the absorbed X-rays, 70% undergo scattering within the tissues (compton and coherent scattering). These scattered radiations reach the film and degrade the image quality
C - The rest 30% of absorbed X-rays are critical in diagnostic imaging. More X-rays are absorbed by bone (causing bone to appear white on radiograph) than by soft tissues (which appear dark in radiograph)
(A) - 10% directly reach the film without interacting with the tissues
Define Attenuation and list and describe the three ways in which it can occur.
Attenuation = Reduction of x-ray beam intensity (thatr eaches film) by interaction with matter (tissues)
It occurs by…
1. Coherent scattering: X-ray beam hits outer shell electron causing vibration (8%)
2. Compton scattering: X-ray beam knocks out outer shell electron (62%)
3. Photoelectric absorption: X-ray beam knocks out innermost electron and electron from next shell drops to fill vacency (30%)
How does Ionizing radiation cause damage?
2 ways
Direct effect: Energy of photon is transferred directly to biological macromolecules (DNA/RNA)
Indirect effect: 75% of our cells contain H20. Radiolysis of water (Radiation interacts with H2O = H2O2 (Hydrogen peroxide) = damage the cell by breaking down proteins or DNA)
TEST
Radiation effects at cellular level
Effect on…
* Proteins: Changes in the secondary and tertiary structure, disruption of the side chains, breakage of hydrogen and sulfide bonds
* Nucleus: DNA - change or loss of base, disruption of Hydrogen bonds, breakage of DNA strands.
* Chromosomes: type of damage that is visualized depends on stage of cell cycle
* Cytoplasm: high doses are required to cause visible damage = increased permeability to Na and K = changes in cellular mechanisms
* Mitosis: delayed mitosis
* Cell death
* Cell recovery
List the three radiation effects at tissue and organ level
TEST - 3 effects of radiation on tissue
Deterministic effects => Somatic Deterministic effects
Stochastic effects => Somatic Stochastic effects OR Genetic stochastic effects
Define Somatic Deterministic effects and list examples
Damaging effects to the body of the person exposed that will definitely result from high dose radiation
* threshold dose below which there will be no effect
* Severity of effect is directly proportionate to the dose of radiation
* Ex. Radiotherapy -> Skin reddening, Cataract, Mucositis
Effects of Radiotherapy on oral cavity
TEST?
Can somatic deterministic effects be seen with Dental Radiology?
No somatic deterministic effects due to small dose (well below threshold)
Define Somatic Stochastic effects and list examples
TEST
Effects (carcinogenesis) that may (probability of occurrence) develop as a result of exposure to radiation
Probability of getting cancer depends on amount of radiation exposure. Higher the dose = higher probability of getting a cancer.
* There is no threshold dose
* Severity of effect is not proportionate to the dose of radiation
Ex. Japanese atom bomb survivors developed cancer, irradiation treatment for postpartum mastitis
Since there is no evidence of a lower threshold for the appearance of Somatic Stochastic Effects, the prudent course of action is to ensure that all radiation exposures follow a principle known as….
ALARA (As Low As Reasonable Achievable)
Effects of Diagnostic dose (very low) of radiation ‐ eg ‐Dental X‐Ray radiation is not much but considered as a risk factor therefore avoid unnecessary exposure of radiation to patients therefore avoid unnecessary exposure of radiation to patients
List the various radio-sensitivity of different tissues/organs
High = high mitotic activity (cell division)
Describe Acute Radiation Syndrome
Effects of whole body irradiation
Somatic Deterministic effect
Collection of signs and symptoms experienced by humans exposed by medical radiotherapy, atom bomb blastsand radiation accidents.
Describe the two sources of radiation
Is the statement “having 2 intraoral radiographies = 1/2 million risk of cancer” considered to be
1) Equivalent natural exposure
2) Probability of stochastic effect
2) Probability of stochastic effect
Describe the two sources of radiation
Describe the two sources of radiation
Describe the two sources of radiation
Describe the two sources of radiation
