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……