LC232 X-ray Physics

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LC232 X-ray Physics Principles

• Russell L. Wilson C.R.T.

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Week 1a Chapter 1 Concepts of Radiologic Science
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Our Surroundings

• Everything in the universe can be classified as
  matter or energy.
• Matter is anything that occupies space and has a
  shape or form.
• Matter has Mass. This is the quantity of
  matter.The physical properties can be transformed
  in size, shape and form.

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Energy

• Energy is the ability to do work. Energy can
  exist in many forms.
• Potential Energy is the ability to do work by
  virtue of position.
• Kinetic energy is the energy of motion. It is
  possessed by all matter in motion.

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Energy

• Chemical Energy is the energy released by way of
  a chemical reaction.
• Electrical Energy represents the work that can be
  done when an electron or an electronic charge
  moves through an electronic potential.

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Energy

• Thermal (heat) Energy is the energy of motion at
  the atom or molecule level. Thermal energy is
  measured by temperature. The faster the atoms or
  molecule are moving, the more thermal energy or
  heat will be produced.

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Energy

• Nuclear Energy is the energy contained in the
  nucleus of the atom.
• Electromagnetic Energy is the most important
  type of energy for radiology.It is the type of
  energy in an x-ray. In addition to x-ray,
  electromagnetic energy includes radio waves,
  microwaves and visible light.

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Energy

• Like matter, energy can be transformed from one
  type to another.
• Then taking an x-ray, we start with electrical
  energy that is transformed to electromagnetic
  energy. After the x-ray passes through matter, it
  is converted to chemical energy in the film.

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Mass-Energy Equivalence

• Frequently matter and energy exist side by side.
  The interchangeability was theorized by Albert
  Einsteins Emc2.
• The Mass-Energy Equivalence is the basis of
  nuclear power, nuclear medicine and the atom bomb.

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Radiation

• Energy emitted and transferred through matter is
  called Radiation.
• Like ripples or waves are generated when a stone
  is dropped into a still pond.
• Visible light is a form of electromagnetic energy
  radiated from the sun.

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Radiation

• Electromagnetic radiation is referred to as just
  radiation.
• Matter that intercepts radiation and absorbs part
  or all of it is said to be exposed or irradiated.
• During radiography, the patient is irradiated.

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Ionizing Radiation

• Ionizing radiation is a special type of radiation
  that includes x-rays. It is any kind of
  radiation capable of removing an orbital electron
  from an atom with which it interacts.

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Ionizing Radiation

• Ionizing radiation passes close enough the the
  atom with sufficient energy to remove an electron
  from the atom. The free orbiting electron and
  atom become Ion Pairs.

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Ionizing Radiation

• X-ray and Gamma Rays are the only forms of
  electromagnetic energy with sufficient energy to
  ionize matter.

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Other forms of Ionizing Radiation.

• Alpha and Beta Particles are capable of
  Ionization. These are fast moving particles of
  matter and Not electromagnetic radiation.

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Sources of Ionizing Radiation

• Many forms or radiation are harmless but Ionizing
  radiation can injure humans.
• Natural sources of radiation results in the
  annual exposure of about 300 mrad (3 mGy)
• A mrad is 1/1000 of a rad. The Rad is the unit of
  radiation absorbed dose.

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Sources of Ionizing Radiation

• Radon is the largest component of natural
  radiation. All earth-based materials such as
  concrete, wall board and bricks contain radon. It
  emits alpha particle and therefore contributes
  dose only to the lungs.
• Naturally occurring radioactive materials
  contribute to natural exposure.

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Sources of Radiation Exposure
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Sources of Ionizing Radiation

• Elevation from sea level will impact exposure to
  natural gamma exposure.
• Flying cross country or living in the mountains
  will result in a higher level of background
  exposure.
• During the era of above ground nuclear testing,
  everyone was exposed to 5 mrads/ year.

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Sources of Ionizing Radiation

• During the Chernobyl Disaster, the populations
  near the plant received very high exposures.
• In some areas of India, background radiation is
  over 500 mrads from uranium.
• Medically employed x-rays constitute the largest
  source of man-made ionizing radiation.

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The Development of Radiology

• A brief history

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Wilhelm Konrad Roentgen, Ph. D

• Born March 27, 1945
• Died February 10, 1923
• The father or modern radiography.
• Won the Nobel Prize for Physics in 1901

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History

• Like Chiropractic, X-ray was discovered in 1895.
• One November 8, 1895, Dr. Wilhelm Roentgen in
  Germany was experimenting with a Crookes or
  cathode ray tube.
• The room was dark and the tube was enclosed with
  black photographic paper.

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History

• On a table next to the tube was a plate coated
  with barium platinocynide a fluorescent material.
• Dr. Roentgen observed that when the Crookes tube
  was on, the fluorescent material luminated
  regardless of how far the plate was from the
  tube.

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History

• He placed various materials between the tube and
  the plate. The X-light easily penetrated
  cardboard, books, wood and cloth.
• He had more trouble penetrating metals with the
  densest being opaque.

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History

• When he placed his hand near the plate, he
  discovered that skin was almost transparent while
  bone was fairly opaque.
• In his experiments, he discovered many of the
  principles that we use today.
• The discovery of X-ray was basically an accident.

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The X-Ray Tube Development

• Dr. Roentgen used a Crookes-Hittorf tube to make
  the first x-ray image.
• Note that there is no shielding around the tube.

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The first x-ray image

• The first human radiograph was taken or Mrs.
  Roentgen.
• It was a 15 minute exposure.

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The first x-ray image

• For the first time, we were able to see inside
  the body without surgery.
• Early x-rays were taken on glass photographic
  plates

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Early X-ray Machine

• First U.S. x-ray exam on Feb. 3, 1896 was a wrist
  x-ray taken at Dartmouth College.
• The maximum power was 50 kV or 50,000 volts and
  low mA.

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The Development of Modern Radiography

• Coil and battery type x-ray machine used in the
  Spanish American War of 1898.
• A series of batteries provided DC power to a
  coil. Operating cost 0.11 per hour

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The Development of Modern Radiography

• Static type machine also used by the US Army
  during the Spanish American War.
• A motor produced DC power for the x-ray tube.

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The X-Ray Tube Development

• The Coolidge Hot cathode tube was a major
  advancement in tube Design. The radiator at the
  end of the anode cool the anode.

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The Development of Modern Radiography

• This was the recommended design of an early x-ray
  room.
• The operator had to watch the glow of the tube
  and adjust power during the exposure.

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The Development of Modern Radiography

• Lead was placed between the tube and the
  operator.
• A mirror was used to observe the patient and
  tube.
• To test the machine, the operator x-rayed their
  forearm.

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The Development of Modern Radiography

• If they could see a button through the radius, it
  was operating properly.
• Another test was to see a watch through the
  patients skull with fluoroscopy.

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The Development of Modern Radiography

• 1896 First medical applications of x-ray in
  diagnosis therapy.
• 1905 Einstein introduced his theory of relativity
• 1907 Snook interrupterless transformer to make
  high voltage. The capabilities of the transformer
  exceeded the capacity of Crookes tubes.

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Development of Modern Radiography

• 1913 Bohr theorizes his model of the atom.
• 1913 The Crookes cathode ray tube was replaced by
  Coolidge hot cathode tube.
• 1913 Dr. Gustave Bucky built the first grid.
• 1918 Double emulsion film by Kodak.
• 1920 Dr. Hollis Potter put a Grid in a moving
  cabinet to remove grid lines.

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Development of Modern Radiography

• 1922 Compton describes scattering of x-rays
• 1928 The roentgen is defined as the unit of
  measurement of x-ray intensity.
• 1929 Rotating anode x-ray tube introduced.
• 1930 Tomography is demonstrated by several
  investigators.

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The X-Ray Tube Development

• This is the variety of tube designs available in
  1948.
• The Coolidge tube was still available.

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The X-Ray Tube Development

• Two major hazards plagued early radiography.
• Excessive radiation exposure
• Electric Shock

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Development of Modern Radiography

• 1942 Morgan exhibits the first electronic
  phototimer.
• 1942 First automatic film processor
• 1948 First fluoroscopic image intensifier.
• 1953 Rad is officially adopted as the unit of
  absorbed dose.

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Development of Modern Radiography

• 1956 First automatic roller transport film
  processor introduced by Kodak
• 1963 Single photon emission computed tomography
  demonstrated.
• 1965 Ninety second film processor introduced.

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Development of Modern Radiography

• 1966 Diagnostic ultrasound enters routine use.
• 1972 Rare earth radiographic intensifying screen
  are introduced.
• 1973 Hounsfield completes development of the
  first computed tomography (CT) scanner (EMI)

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Development of Modern Radiography

• 1973 Damadian and Lauterbur produce the first
  magnetic resonance image (MRI)
• 1980 First superconductor MR imager introduced
• 1981 The International System of Units (SI) is
  adopted by the ICRU
• 1983 First tabular grain film emulsion

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Development of Modern Radiography

• 1983 First tabular grain film emulsion
  ( Kodak) introduced.
• 1984 Laser stimulable phosphors for direct
  digital radiographs appear.

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Reports of Injury

• The first fatality from radiography occurred in
  1904 when Clarence Daly died from complications
  from experiments in fluoroscopy.
• Injuries were frequent in the early years in the
  form of
• Burns, loss of hair and anemia.
• By 1910, the more powerful Coolidge tube and
  Snook transformer reduced the superficial tissue
  injuries.

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Reports of Injury

• Years later blood disorders such as aplastic
  anemia and leukemia were developing in
  radiologists.
• This resulted in the development of lead aprons
  and gloves.
• Workers were routinely evaluated for signs of
  effects of radiation exposure and provided
  detection devices.

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Radiation Safety

• The attention of radiation safety has been very
  effective. Today it is considered as a safe
  occupation.
• Today the emphasis has shifted back to the
  patient.
• The principle of radiation safety is called ALARA
  or As Low As Reasonably Achievable.

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Ten Commandments of Radiation Protection

1. Understand and apply the cardinal principles of
   radiation control time, distance and shielding.
2. Do not allow familiarity to result in false
   security.
3. Never stand in the primary beam.
4. Always wear protective apparel when not behind a
   protective barrier.

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Ten Commandments of Radiation Protection

1. Always wear a radiation monitor and position it
   outside the protective apron at the collar.
2. Never hold a patient during a radiographic
   procedure. Use mechanical restraining devices
   when possible. Otherwise, have parents or friends
   hold the patient.

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Ten Commandments of Radiation Protection

1. The person hold the patient must wear a
   protective apron and if possible protective
   gloves.
2. Use gonadal shields on all patients of child
   bearing age when it will not interfere with the
   examination.
3. Examinations of the abdomen or pelvis should be
   avoided on pregnant patients especially during
   the first trimester.

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Ten Commandments of Radiation Protection

• Always collimate to the smallest field size
  appropriate to the examination.
• California regulation require three borders of
  collimation visible on the film.

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Chapter 2

• Radiologic Quantities and Units

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Basic math in radiography

• In radiography, some basic math skill are
  required.
• Some x-ray controls use fractions or decimals to
  enter exposure factors.
• The geometry of radiography also requires some
  basic math skill.
• Adjusting factors for changes in distance or
  patient size requires math skill.

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Fractions

• Fractions are used generally for exposure time on
  older single phase machines. Therefore the
  ability to multiply a fraction and a whole number
  is important.
• numerator
• Fraction ----------------- x/y
• denominator

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Fractions

• A special application of fractions in radiology
  is the ratio.
• A ratio expresses the mathematical relationship
  between similar quantities.
• Fractions can be easily converted to decimals if
  the denominator is a power of 10. Otherwise a
  calculator can be used.

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Decimal Points

• One can easily get carried away with decimal
  points when using a calculator.
• Too many points imply greater precision that is
  really there.
• Addition and subtraction round to the same number
  of points as the entry with the least number of
  decimal points to the right of the decimal place.

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Decimal Points

• In multiplication and division, round to the same
  number of digits as the entry with the least
  number of significant figures.
• 17.24 x 0.3836.585686.59
• 3.1416/1.052.9922.99

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Algebra

• The rules of algebra provides definite ways to
  manipulate fractions and equations to solve for
  an unknown.
• When an unknown, x, is multiplied by a number,
  divide both sides of the equation by that number.
• AXC ax/ac/a x c/a

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Algebra

• When numbers are added to an unknown, x, subtract
  that number from both sides of the equation.
• X AB X A - A B-A X B - A

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Algebra

• When an equation is presented in the form of a
  proportion, cross multiply and then solve for the
  unknown, x.
• x/a b/c cxab x ab/c
• If a grid height is 800 µm and the inter-space is
  80µm what is the ratio?
• 800/80 101

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Number systems

• We use a decimal system where the number is based
  upon multiples of 10.
• While used in many applications in science and
  physics, the logarithmic for of a number has
  little use in radiology except for some
  characteristics of radiographic film.

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Number systems

• 1010
• The superscript on 10 in the exponential form
  of numbers is called the exponent.
• It is also referred to as the power of ten
  notation or scientific notation.
• It makes it easier to write very large or very
  small numbers.

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Numeric Prefixes

• In radiology we often must describe very large
  or very small multiples of a standard unit. The
  two most common units are milliapmeres (mA) and
  kilovolt peak (kVp).
• 70,000 volts 70 x 103 volts 70 kVp
• The size of a blood cell is about 10 micrometers
  (µ)
• 10µ 10 x 10-6m 105 0.00001m

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Numeric Prefixes
Multiple 106 103 102 10 10-1 10-2 10-3 10-6 Prefix mega kilo hecto deka deci centi milli micro Symbol M K h da d c m µ
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Radiology Terms

• The four most common terms for defining radiation
  exposure are
• Exposure Roentgen Air kerma or gray in air
• Absorbed dose rad gray in tissue
• Effective dose rem Seivert
• Radioactivity currie becquerel

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Radiologic Units

• The four units used to measure radiation should
  become a familiar part of your vocabulary. The SI
  International System equivalents will be shown in
  parenthesis.
• In 1981 the International Commission on Radiation
  Units and Measurement (ICRU) issues standard
  units and they were adopted by all countries
  except the United States. Scientific journal
  usually use the SI but regulatory agencies and
  the governments used the standard units.

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Roentgen (R) (Gya) Air Kerma

• The intensity of radiation is measured in
  roentgen or R.
• One R equals the intensity of radiation that will
  create 2.08 x 1018 ion pairs in a cubic
  centimeter of air.
• Official definition is 1R 2.58 x 10-4 C/kg
• To convert R to Gya multiply R x 0.01

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Roentgen (R) (Gya)

• Roentgen refers to x-rays and gamma rays and
  their interaction with air.
• X-ray out put is generally referred to as mR.
• Radiation exposure rate meters are calibrated in
  R.

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Rad (rad) (Gyt)

• For all practical purposes, in diagnostic
  radiology 1R 1 rad 1 rem
• Biologic effects are usually related to the
  absorbed dose. The rad is the term used to
  describe the amount of radiation received by the
  patient.
• Roentgen used for gamma or x-ray exposure in air.
  

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Rad (rad) (Gyt)

• The rad is used for any type of ionizing
  radiation and any exposed matter.
• 1 rad 100 erg/g where erg (joule) is a unit of
  energy and gram ( kilogram) is a unit of mass.
• 1rad 10-2 Gyt or 0.01 Gyt The t refers to
  tissue where the a stands for air.

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Rem (rem) Seivert (Sv)

• The rem is used to express the quantity of
  radiation received by radiation workers and
  populations.
• Some types of radiation produce more damage than
  x-rays. The rem accounts for these differences
  in biologic effectiveness.
• The rem is the unit of occupational radiation
  exposure express as effective dose (E).
• 1 rem 10-2 Sv 0.01 Sv

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Curie (Ci) Becquerel (Bg)

• The curie is the unit of radioactivity.
• One curie is the quantity of radioactivity in
  which 3.7 x 1010 nuclei disintegrate every
  second.
• One Becquerel 3.7 x 1010 Ci
• The milliCurie (mCi) and microcurie (µCi) are the
  most common quantities of radioactive material.
• Radioactivity and curie have nothing to do with
  x-ray.

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Special quantities of Radiologic Sciences
Quantity Name Symbol SI Name Symbol
Exposure Roentgen R Air kerma Gya
Absorbed Dose Rad Rad Gray Gyt
Effective Dose Rem Rem Seivert Sv
Radioactivity Curie Ci Becquerel Bq
Multiply R Times 0.01 To obtain Gya
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Occupational Exposure
Old (rem) 100 rem 50 rem 10 rem 1 rem 500 mrem 100 mrem 1 mrem New (Seivert) 1 Sv 500 mSv 100 mSv 10 mSv 5 mSv 1 mSv 1µSv
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Biologic affects of X-radiation

• Common affects of early radiography included
• burns
• loss of hair
• anemia
• aplastic anemia
• leukemia

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Basics Radiation Protection

• It is easy to reduce exposure for the patient
  and operator when items designed for this purpose
  are used and understood.
• Filtration usually aluminum will absorb the soft
  rays to harden the beam.
• Collimation or cones will restrict the beam.

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Basics Radiation Protection

• Collimation will restrict the beam. The use of
  adjustable lead shutters with light control or
  cone will limit the beam to the area of interest.
  
• Intensifying screen Today it is the light from
  the screens inside the cassette that produces the
  image on the film.

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Basics Radiation Protection

• Intensifying screen Exposure is reduced by 95
  compared to exams performed without screens.
• Protective apparel Lead impregnated rubber
  aprons are used to protect the operator inside
  the x-ray room.

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Basics Radiation Protection

• Gonad shielding Lead is used to block the beam
  from exposing the gonads.
• Protective barrier Lead is used to protect the
  operator. When behind the barrier, the operator
  should not receive any exposure.
• Restricted access Only the patient should be in
  the room during exposure.

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Basics Radiation Protection

• Restricted access Only the patient should be in
  the room during exposure.
• If the patient needs to be held during an
  x-ray, The family of the patient and not the
  operator should hold the patient.
• Lead apron and gloves should be worn by those
  holding the patient. Stay out of the path of the
  beam.

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End of Lecture

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