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RTEC 111
Bushong Ch 2, 3 &15
Technique Math
Fundamentals ofFundamentals ofRadiologic ScienceRadiologic Science
RTEC 111RTEC 111
Bushong Ch. 2Bushong Ch. 2
Units of Measurement
This allows scientists to describe quantities.
The fundamental units of measurement are mass, length and time.
Two widely used systems of measurement
UNITS OF RADIATION MEASUREMENT
• TO QUANTIFY THE AMOUNT OF RADIATION A PATIENT OR WORKER RECEIVES.
Conventional (British)Units vs. SI Units
Conventional (British) Units Used Since The 1920’s (foot, pound, second) also called the US customary system
1948 - A System Of Units Based On Metric Measurements Was Developed By The International Committee For Weights And Measures. SI Units
Commonly Used SI Prefixes
Important Radiology Units
Roentgen (R) is coulomb per kilogram (C/kg)
Radiation absorbed dose (rad) is gray (Gy)
Radiation equivalent man (rem) is seivert (Sv)
Conv. Units SI Units
RADS
REMS
R - ROENTGEN
GRAYS
SIEVERT
C/KG
ROENTGEN (R)
SI = coulomb per kilogram (C/kg) or air kerma Gya
The quantity of X-ray radiation Only exposure in air Output of the x-ray tube Does not indicate actual patient exposure or
absorption
RADIATION ABSORBED DOSE (RAD) SI = GRAY (Gy)
Measures the amount of energy absorbed in any medium (the patient)
1 Gy = 100 rads1/100 or 0.01 Gy = 1 rad1 centigray = 1 rad
REM / SIEVERT
1 Sv = 100 rem 1/100 Sv = 1 rem 1 centisievert = 1 rem Used for occupational exposure
EMPLOYEE EXPOSURE
RADIATION EQUIVALENT MAN(rem) OR Effective dose
SI UNITS = SIEVERT Not all types of radiation produce the
same responses in living tissue
The unit of dose equivlaence, as expressed as the product of absorbed dose in RAD and the quality factor
Rem OR Sievert
SI UNITS = SIEVERT
1 Sv = 100 rem
THE PRODUCT OF THE GRAY AND THE QUALITY FACTOR.
Rad VS. Rem
RAD’S X QUALITY FACTOR = REM
GRAY’S X QUALITY FACTOR = SIEVERT
QUALITY FACTOR FOR X-RAYS = 1
So…… Rads = Rems
Rems & Rads
Sieverts & Grays
PAtient = rAds & grAys
Employee (technologists) = rEms & siEvErts
U.S. to S.I. Conversiona trick to remember
U.S. = rads & rems
Pennies
S.I. = grays & sieverts
Dollars
Metric System
milli m
10-3
5 mrem =
0.005 rem
5000 mrem = 5 rems
500 mrem = 0.5 rems
50 mrem = 0.05 rems
5 mrem = 0.005 rems
Radiology – units of measurement
What units correlate with: Exposure Dose Effective dose
The Structure of MatterThe Structure of Matter
RTEC 111RTEC 111
Radiology Mechanics
Velocity The motion of an object can be
described by the use of two terms velocity and acceleration.
Velocity = speed What is the speed of x-rays in a
vacuum?
X-Ray Properties
Travel in straight lines.
Travel at the speed of light, 3 X 108 meters per second in a vacuum or 299,792,458 m/s
or 29,979,245,800 cm/s
Can ionize matter.
Kinetic energy (KE)
The energy associated with the motion of an object
Kinetic energy depends on the mass of the object and the square of its velocity
Potential energy (PE)
The stored energy of position or configuration
Heat
Is the kinetic energy of the random motion of molecules
Atoms
Elements: 112 substances have been identified 92 are naturally occurring and 20
more have been artificially produced The atom is the smallest particle of
matter that has the properties of an element
Atomic Structure
What does Z # mean?
Atomic mass?
Combining atoms
Atom + Atom = molecule
Molecule + Molecule = Compound
The smallest particle of an element is an atom; the smallest particle of a compound is a molecule
Elements
Chemical elements – determined by the # of protons
Isotopes – neutrons, atomic mass
Shells – electron orbits Ion or Ionization?
e- shell configuration
is dependent
on the size
of the atom
Ionization of carbon
Ion pair
34 eV of energy
is required
Electron Arrangement
The maximum number of e- that can exist in each shell increase with distance from the nucleus
See table
No outer shell can contain more than eight e-
Periodic table of the elements
The table is organized by the number of e- in the outer or valence shell of an atom
# of e- in the outermost shell = the period of that atom on the table
The valence shell is important because it determines how that element will react and interact with other elements
Electrons
Can exist only in certain shells
Each shell has different electron binding energies or energy levels
Electron binding energy
The closer the e- is to the nucleus the more tightly it is bound and the higher the binding energy
Also the larger the Z# of the atom the higher the binding energy for any given shell….therefore more difficult of ionize larger atoms
Ionization potential
The energy required to ionize tissue atoms
How much energy is required to ionize tungsten’s K shell?
Pg 46
Types of Ionizing Radiation
All ionizing radiation can be classified into two categories Particulate or electromagnetic radiation
What type of radiation is used for diagnostic ultrasound or magnetic resonance imaging? Ionizing or Nonionizing?
ParticulateRadiation
The emission of particles and energy from the nucleus in order to become stable
Radioactive elements are called radionuclides or radioisotopes
Radioisotopes
Occur when atoms have too many or too few neutrons
Can occur naturally or can be man made
Radioisotope decay
Decay from the nucleus to become stable Beta emission and Alpha emission
Alpha & Beta particles can cause ionization because of high kinetic energy
What form of energy does x-rays use to ionize
Radioactive Half-Life
The time required for a quantity of radioactivity to be reduced to one-half its original value
For radiology: Half-value layer To reduce the strength of the x-ray beam
by 1/2
Photons vs Particles
Particles cause ionization through kinetic energy
Photons have no mass, no charge, travel at the speed of light and are considered energy disturbances in space. A form of EM energy. Photons travel at the speed of light or not at all.
X-rays vs Gamma rays
Forms of EM energy Only difference between x-rays and
gamma rays is their origin Only difference between alpha and
beta particles is their origin
Origins
X-rays = outside the nucleus in the e- shells
Alpha & Beta particles = from the nucleus
Gamma rays = from the nucleus As part of radioactive decay
X-rays have low ionization rates and a very long range in tissue
Technique Calculations
What happens to primary?
When x-rays pass through a patient's body, three things can happen: (1) the x-ray photon is transmitted, passing through the body, interacting with the film, and producing a dark area on the film; (2) the x-ray photon is absorbed in an area of greater tissue density, producing lighter areas on the film; and (3) the x-ray photon is scattered and reaches the film causing an overall gray fog.
Density
The degree of overall blackening from the black metallic silver deposited in the emulsion.
Optical Density: range of human visibility
Densitometer
Density
.25 TO -2.5
The straight line of the H&D curve
(Hurter & Driffield)
Optical Density
Controlling factor: mAs mAs determines the quantity of x-
rays What is the formula to determine
quantity of x-rays?
mAs
mA X time (sec) = mAs
The quantity of x-rays produced
To see changes in optical density
In order to see changes in optical density on a radiograph you must increase you mAs by at least 20 – 30%
To double the density on a radiograph you must double your mAs
kVp
Kilovolts peak
kVp Controls the Contrast
(for analog/film imaging)
Low vs High contrast
As a radiologic technologist, you will learn to distinguish between low- and high-contrast radiographs. A radiograph with large differences in density is a high-contrast, or short-scale, radiograph. If the density differences aren't as great, you have a low-contrast, or long-scale, radiograph.
kVp: Effects density & contrast
a. 15% rule: 15% kVp = doubling of exposure to the film
15% kVp = halving of exposure to the film
b. 15% rule will always change the contrast of the image because kV is the primary method of changing image contrast.
Its math time……