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CHAPTER 1 CONCEPTS OF RADIOLOGIC SCIENCE NATURE OF OUR SURROUNDINGS Thermal/Heat Energy  The energy in motion at the molecular level Matter  Anyth...

CHAPTER 1 CONCEPTS OF RADIOLOGIC SCIENCE NATURE OF OUR SURROUNDINGS Thermal/Heat Energy  The energy in motion at the molecular level Matter  Anything that occupies space & has mass Nuclear Energy  The energy that is contained within the Atoms nucleus of an atom  The building blocks of matter Electromagnetic Energy Mass  The type of energy that is used in an x-rays  The quantity of matter as described by its energy equivalence Theory of Relativity  The distinguishing characteristic of matter  Albert Einstein  States that matter and energy are Weight interchangeable  The force exerted on a body under the influence of gravity Matter-Energy Equivalence  Formula: E=mc2 MATTER AND ENERGY Radiation Matter  The energy emitted & transferred through  Material substance with mass of which space physical objects are composed Visible Light Atoms & Molecules  Radiated by the sun  The fundamental, complex, building blocks of matter Exposed/Irradiated  Matter that intercepts & absorbs radiation Energy  The ability to do work UV Light  SI Unit: joules (J)  It causes sunburn  In Radiology: electron volt (eV) Ionizing Radiation Potential Energy  Any type of radiation that is capable of  The ability to do work by virtue of position removing an orbital electron from the atom with which it interacts Kinetic Energy  Examples: x-rays, gamma rays & UV light  The energy in motion Ionization Chemical Energy  The removal of an electron from an atom  The energy released by a chemical reaction 1 Particulate-type Ionizing Radiation Page Electrical Energy  Examples: alpha & beta particles  The work that can be done when an electron moves through an electric potential difference (V) STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 1 CONCEPTS OF RADIOLOGIC SCIENCE SOURCES OF IONIZING RADIATION Fluorescence  The emission of visible light only during Natural Environmental Radiation stimulation  Annual Dose: 300 mrem/yr  Cosmic Rays: emitted by sun & stars 1901  Terrestrial Radiation: deposits of uranium,  Roentgen received Nobel Prize in Physics thorium & other radionuclides  Internally-deposited Radionuclides: February 1896 potassium-40 (natural metabolites)  He published and produced the first medical  Radon: largest source x-ray image  The first x-ray examination Man-made Radiation  Annual Dose: 60 mrem/yr DEVELOPMENT OF MODERN RADIOLOGY  Diagnostic X-rays: largest source (39 mrem/yr) Radiography  Uses x-ray film & x-ray tube mounted from NCRP the ceiling  National Council on Radiation Protection &  Provides fixed images Measurements Fluoroscopy MSCT  Conducted with an x-ray tube located under  Multislice Spiral Computed Tomography the examination table  Provide moving images Medical Applications of Ionizing Radiation  Annual Dose: 50 mrem/yr X-ray Voltage  Measured in kVp DISCOVERY OF X-RAYS To provide an x-ray beam that is satisfactory Cathode Rays for imaging, you must supply the x-ray tube  Electrons with a high voltage & sufficient electric current! Sir William Crookes  He invented crookes tube X-ray Current Wilhelm Roentgen  Measured in mA  He discovered x-rays Image Blur November 8, 1895  Caused: long exposure time  Discovery of x-rays  Wurzburg University in Germany Michael Pupin (1896) 2  He demonstrated the use of radiographic Page Barium Platinocyanide intensifying screen  The fluorescent material used by Roentgen Charles L. Leonard (1904)  He demonstrated the use of double emulsion film STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 1 CONCEPTS OF RADIOLOGIC SCIENCE Thomas A. Edison (1898) 1970  He developed fluoroscope  PET & CT were developed  Original Fluorescent Material: Barium platinocyanide 1980  Most Recent: Zinc cadmium sulfide &  MRI become an accepted modality calcium tungstate MEG Clarence Dally (1904)  Magnetoencephalography  The first x-ray fatality Because of effective radiation protection William Rollins practices, radiology is now considered a safe  He demonstrated the first application of occupation! collimation & filtration H.C. Snook (1907) Always practice ALARA: keep radiation  He introduced interrupterless transformer exposures As Low As Reasonably Achievable!  Snook transformer Filtration William D. Coolidge (1913)  It absorbs low energy x-rays  He introduced coolidge x-ray tube  Aluminum or copper Radiology emerged as a medical specialty Collimation because of the snook transformer & the  It restricts the useful x-ray beam Coolidge x-ray tube!  It reduces scatter radiation  It improves image contrast Gustav Bucky (1913)  Example: adjustable light-locating  He invented stationary grid collimators (common)  “glitterblende” Intensifying Screen Hollis Potter (1915)  It reduces x-ray exposure by more than 95%  He invented moving grid Protective Apparel 1921  Lead-impregnated material  Potter-Bucky grid was introduced  Examples: gloves & apron Light Amplifier (1946) Gonadal Shielding  He demonstrated at Bell Telephone  It is used with all persons of childbearing Laboratories age 1950 Protective Barriers 3  Light amplifier was adapted for fluoroscopy  Lead-lined with a leaded-glass window Page  Example: radiographic control console 1960  Diagnostic UTZ & gamma camera appeared ARRT  American Registry of Radiologic Technologists STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 1 CONCEPTS OF RADIOLOGIC SCIENCE TEN COMMANDMENTS OF RADIATION PROTECTION 1. Understand & apply the cardinal principles of radiation control: time, shielding & distance. 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. 5. Always wear an occupational radiation monitor and position it outside the protective apron at the collar. 6. Never hold a patient during radiographic examination. Use mechanical restraining devices when possible. Otherwise, have parents or friends hold the patient. 7. The person who is holding the patient must always wear a protective apron and, if possible, protective gloves. 8. Use gonadal shields on all people of child bearing age when such use will not interfere with the examination. 9. Examination of the pelvis and lower abdomen of a pregnant patient should be avoided whenever possible, especially during the first trimester. 10. Always collimate to the smallest field size appropriate for the examination. 4 Page STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 2 FUNDAMENTALS OF RADIOLOGIC SCIENCE STANDARD UNITS OF MEASUREMENT  Recent Definition: measured by an atomic clock Physics  The study of interactions of matter & energy Measurement  It has a magnitude & a unit Three Base Quantities  Mass, Length & Time Four Systems of Units  MKS Secondary/Derived Quantities  CGS  The combination of one or more base  British quantities  SI Special Quantities SPECIAL QUANTITIES OF RADIOLOGIC  Exposure, Dose, Equivalent Dose & SCIENCE & THEIR UNITS Radioactivity Radiographic Special Units SI Quantities IBWM Exposure C/kg Air kerma (Gya)  International Bureau of Weights & Dose J/kg Gray (Gyt) Measures Equivalent J/kg Sievert (Sv) Dose Length Radioactivity s-1 Becquerel (Bq)  It is based on speed of light  SI Unit: meter (m) The same system of units must always be used  Platinum-Iridium Bar: represents the when one is working on problem or reporting standard unit of length answers!  Redefinition: wavelength of orange light emitted from an isotope of krypton-86 MECHANICS  One Meter: distance traveled by light in 1/299,792,468 Mechanics  The segment of physics that deals with Mass motion at rest (statics) & objects in motion  One Kilogram: mass of 1000 cm3 of water at (dynamics) 4o C  SI Unit: kilogram (kg) Velocity (V)  Platinum-Iridium Cylinder: represents the  It is sometimes called speed standard unit of mass  The rate of change of its position with time  Units of Weight: Newton (N) & pounds (lb)  Formula: V = d/t o d = distance Time o t = time  It is based on the vibration of atoms of  SI Unit: m/s 5 cesium  British Unit: ft/s Page  Original Definition: based on rotation of Earth on its axis (mean solar day) Velocity of Light  Redefinition: a certain fraction of the  Symbol: c tropical year 1900  c = 3x108 m/s or 1.86x105 mi/s STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 2 FUNDAMENTALS OF RADIOLOGIC SCIENCE Average Velocity Newton’s Third Law: Action/Reaction  Symbol: ῡ  For every action, there’s an equal &  Formula: ῡ = (Vf + Vo)/2 opposite reaction o Vf = final velocity o Vo = initial velocity Weight  SI Unit: m/s  A force on a body caused by the pull of  British Unit: ft/s gravity on it  Symbol: Wt Acceleration  Formula: Wt = mg  The rate of change of velocity with time o m = mass  Symbol: a o g = acceleration due to gravity  Formula: a = (Vf – Vo)/t  SI Units: N or lb o Vf = final velocity o Vo = initial velocity Acceleration Due to Gravity o t = time  Symbol: g  SI Unit: m/s2  Constant in SI Unit: 9.8 m/s2  British Unit: ft/s2  Constant in British Unit: 32 ft/s2  Constant Velocity: zero acceleration Weight is the product of mass & the Isaac Newton (1686) acceleration of gravity on earth: 1 lb = 4.5 N!  He presented the fundamental laws of motion Momentum  The product of mass of an object & its Newton’s First Law: Inertia velocity  A body will remain at rest or will continue  Symbol: p to move with constant velocity in a straight  Formula: p = mv line unless acted on by an external force o m = mass o V = velocity Inertia  SI Unit: kg-m/s  The property of matter that acts to resist a  British Unit: lb-ft/s change in its state of motion  Total p before interaction = Total p after interaction Newton’s Second Law: Force  The force (F) that acts on an object is equal Work to the mass (m) of the object multiplied by  The force applied times the distance the acceleration (a) produced  Symbol: W  Formula: W = Fd Force o F = force  A push or pull on an object o d = distance  Symbol: F 6  SI Unit: J  Formula: F = ma Page  British Unit: ft/lb o m = mass o a = acceleration Power  SI Unit: newton (N)  The rate of doing work  British Unit: pounds (lb)  The quotient of work over time  Symbol: P STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 2 FUNDAMENTALS OF RADIOLOGIC SCIENCE  Formula: P = Work/t = Fd/t Calorie o F = force  The heat necessary to raise the temperature o d = distance of 1 g of water through 1o C o t = time  SI Units: J/s or W Three Ways of Heat Transfer  British Unit: hp  Conduction, Convection & Radiation  One hp: 746 W Conduction Energy  The transfer of heat through a material by  The ability to do work touching Law of Conservation of Energy Convection  States that energy may be transformed from  The mechanical transfer of “hot” molecules one form to another but it cannot be created in a gas or liquid from one place to another or destroyed Thermal Radiation Two Forms of Mechanical Energy  The transfer of heat by the emission of  Kinetic & Potential Energy infrared radiation  An x-ray tube cools primarily by radiation Kinetic Energy  The energy associated with the motion of an Temperature object  It is measured with a thermometer  Symbol: KE  3 Scales: Celsius, Kelvin & Fahrenheit  Formula: KE = ½mv2 o m = mass Converting Fahrenheit (F) to Celsius (C) o v2 = velocity squared  Formula: Tc = 5/9(Tf - 32)  SI Unit: J o Tc = temperature in celsius  British Unit: ft-lb o Tf = temperature in fahrenheit Potential Energy Converting Celsius to Fahrenheit  The stored energy of position or  Formula: Tf = 9/5(Tc) + 32 configuration  Symbol: PE Converting Celsius to Kelvin (K)  Formula: PE = mgh  Formula: K = Tc + 273 o m = mass o K = temperature in Kelvin o g = acceleration due to gravity o h = height Approximate Temperature Conversion  SI Unit: J  From oF to oC: subtract 30 & divide by 2  British Unit: ft-lb  From oC to oF: Double, then add 30 7 Cryogens Page Heat  The KE of the random motion of molecules  The cooling agents used in MRI  Unit: calorie  Liquid Nitrogen: boils at 77 K  Liquid Helium: boils at 4 K STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 2 FUNDAMENTALS OF RADIOLOGIC SCIENCE MATHEMATICS FOR RADIOLOGIC Step 3: x = c/a SCIENCE  Second Rule: when numbers are added to an unknown x, subtract that number from both Fractions sides of the equation  The quotient of two numbers Step 1: x + a = b  x/y: numerator/denominator Step 2: x + a – a = b – a Step 3: x = b – a Proper Fraction  Third Rule: when an equation is presented in  The quotient is less than one the form of a proportion, cross-multiply & then solve for the unknown x Improper Fraction Step 1: x/a = b/c (cross-multiplication)  The quotient is greater than one Step 2: cx = ab Step 3: x = ab/c Adding/Subtracting Fractions  Find a common denominator then add or Proportion subtract  It expresses the equality of two ratios  x/y + a/b = xb/yb + ay/yb = (xb + ay)/yb Decimal System Multiplying Fractions  System of numbers that is based on  Simply multiply numerator & denominator multiples of 10  (x/y) x (a/b) = xa/yb Decimal to Exponential Form Dividing Fractions  If there are digits to the left of the decimal  Invert the second fraction & multiply point, the exponent will be positive  x/y ÷ a/b = (x/y) x (b/a) = xb/ya  If there are no nonzero digits to the left of the decimal point, the exponent will be Ratio negative  It expresses the mathematical relationship between two similar quantities Planck’s Constant  Symbol: h  Constant: In addition & subtraction, round to the same o 4.15 x 10-15 Ev-s number of decimal places as the entry with the o 6.63 x 10-34 Js least number of digits to the right of the decimal point! Rules of Exponents  Multiplication: 10x x 10y = 10(x+y)  Division: 10x ÷ 10y = 10(x-y) In multiplication & division, round to the  Raising to a Power: (10x)y = 10xy same number of digits as the entry with the least number of significant digits!  Inverse: 10-x = 1/10x  Unity: 100 = 1 8 Page Three Principal Rules of Algebra Graphing  First Rule: when an unknown x is multiplied  It is based on two axes: x-axis & y-axis by a number, divide both sides of the equation by that number Origin Step 1: ax = c Step 2: ax/a = c/a  The point where the two axes meet STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 2 FUNDAMENTALS OF RADIOLOGIC SCIENCE Ordered Pairs  1 Ci: 3.7 x 1010 nuclei disintegration per  (x-axis, y-axis) second (Bq) Radiologic Units TERMINOLOGY FOR RADIOLOGIC  Roentgen, Rad, Rem, & Curie SCIENCE Roentgen/Exposure STANDARD SCIENTIFIC & ENGINEERING  The unit of radiation exposure or intensity PREFIXES  It is defined as a unit of radiation quantity Multiple Prefix Symbol (1928) 1018 exa E  Applies only to x-rays & gamma rays & 1015 peta P 12 their interaction with air 10 tera T  Symbol: R 109 giga G  SI Unit: air kerma (Gya) 106 mega M o Adoption of Wagner/Archer Method 103 kilo k 2  1 R: 2.08 x 108 ip/cm3 of air 10 hecto h  1 R: 2.58 x 10-4 C/kg (official) 101 deka da 10-1 deci d Rad/Dose 10-2 centi c -3  The unit of radiation absorbed dose 10 milli m 10-6 micro µ  The quantity of radiation received by the 10-9 nano n patient 10-12 pico p  It is used for any type of ionizing radiation 10-15 femto f & exposed matter, not just air -18 10 atto a  Symbol: rad  SI Unit: gray (Gyt)  Special Unit: J/kg Diagnostic radiology is concerned primarily  1 Rad: 100 erg/g or 10-2 Gyt with x-rays. We may consider:  Erg (J): a unit of energy 1 R = 1 rad = 1 rem or 1 mGya = 1 mGyt = 1 mSv)! Rem/Equivalent Dose  The unit of occupational radiation exposure  It is used to expressed the quantity of radiation received by radiation workers & populations  Symbol: rem  SI Unit: Sievert (Sv)  Special Unit: J/kg  Application: occupational radiation monitors 9 Page Curie (Ci/Bq)  A unit of radioactivity  The unit of quantity of radioactive material  Symbol: Ci  SI Unit: Becquerel (Bq)  Special Unit: s-1 STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 3 THE STRUCTURE OF MATTER CENTURIES OF DISCOVERY  Pudding: a shapeless mass of positive electrification Greek Atom  Atomos means indivisible J.J. Thomson (1890)  Four Substances: earth, water, air, & fire  He investigated the physical properties of  Four Essences: wet, dry, hot, & cold cathode rays (electrons)  He concluded that electrons were integral Substances/Elements parts of all atoms  112 identified  92 naturally occurring Ernest Rutherford (1911)  20 artificially produced  Nuclear model  He disproved Thomson’s model An atom is the smallest particle that has all the  He described the atom as containing a small, properties of an element! dense, positively charged center surrounded by a negative cloud of electrons Subatomic Particles  He called the center of the atom the nucleus  Particles smaller than atom Bohr Atom (1913) Dalton Atom  Miniature solar system  Hook-and-eye affair  He improved Rutherford’s description of the atom John Dalton (1808)  The electrons revolved about the nucleus in  He showed that elements could be classified prescribed orbits or energy levels according to integral values of atomic mass Quantum-chromodynamics (QCD) Dmitri Mendeleev  More accurately described the details of  First periodic table of elements atomic structure Alkali Metals FUNDAMENTAL PARTICLES  Group 1 elements  All soft metals that combine readily with Particle Accelerator oxygen & react violently with water  Atom smasher  It is used in mapping the structure of atomic Halogens nucleus  Group VII elements  Easily vaporized & combine with metals to Nucleons form water-soluble salts  Protons (+) & neutrons (O)  It is composed of quarks & gluons Noble Gas (subatomic particles) 10  Group VIII elements  Highly resistant to reaction with other Page The fundamental particles of an atom are the elements electron, proton & the neutron! Thomson Atom  Plum pudding  Plum: negative electric charges (electrons) STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 3 THE STRUCTURE OF MATTER Electron Number of Protons  Location: orbital shells  Determine the chemical behavior of an atom  Relative: 1  Determine the chemical element  Mass in kg: 9.1 x 10-31  Mass in amu: 0.000549 Isotopes  Number: 0  Same number of protons, but different  Charge: -1 number of neutrons  Symbol: - In their normal state, atoms are electrically Proton neutral; the electric charge on the atom is  Location: nucleus zero!  Relative: 1836 Electron Arrangement  Mass in kg: 1.673 x 10-27  The number of electrons in the outermost  Mass in amu: 1.00728 shell of an atom = group in the periodic  Number: 1 table & determines the valence of an atom  Charge: 1  The number of outermost electron shell of  Symbol: + an atom = period in the periodic table Neutron Maximum Electrons Per Shell  Location: nucleus  Formula: 2n2  Relative: 1838  Mass in kg: 1.675 x 10-27 Principal Quantum Number  Mass in amu: 1.00867  The shell number (n)  Number: 1  Charge: 0 No outer shell can contain more than eight  Symbol: O electrons! Atomic Mass Unit Orderly Scheme of Atomic Progression  The mass of a neutral atom of an element  Interrupted in fourth period  Symbol: amu  1 amu: ½ the mass of a carbon-12 atom Transitional elements  Atoms associated with the phenomenon Atomic Mass Number mentioned above  Number of protons plus number of neutrons in the nucleus Centripetal Force  Symbol: A  Center-seeking force  Formula: protons + neutrons  The force that keeps an electron in orbit 11 ATOMIC STRUCTURE Centrifugal Force  Flying-out-from-the-center force Page The atom is essentially empty space!  The force that causes an electron to travel straight and leave the atom Neutral Atom  Same number of electrons & protons STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 3 THE STRUCTURE OF MATTER Electron Binding Energy Protocol for Representing Elements in a Molecule  The strength of attachment of an electron to  Upper Left: atomic mass (A) the nucleus  Lower Left: atomic number (Z)  Symbol: Eb  Upper Right: valence state (+/-)  Lower Right: number of atoms/molecules Tungsten (W-74) & Molybdenum (Mo-42)  The primary constituents of x-ray tube target CHARACTERISTICS OF SOME ELEMENTS IMPORTANT TO RADIOLOGIC SCIENCE Barium (Ba-56) & Iodine (I-53) Naturally  Radiographic & fluoroscopic contrast agents Chemical Element Z A Occurring Symbol Isotopes Carbon (C-6) Beryllium Be 4 9 1  The important component of human tissue Carbon C 6 12 3 Oxygen O 8 16 3 Ionization Potential Aluminum Al 13 27 1  The amount of energy (34 keV) necessary to Calcium Ca 20 40 6 ionize tissue atoms Iron Fe 26 56 4 Copper Cu 29 63 2 ATOMIC NOMENCLATURE Molybdenum Mo 42 98 7 Ruthenium Ru 44 102 7 Chemical Symbols Rhodium Rh 45 103 5  The alphabetic abbreviations of an element Silver Ag 47 107 2 Tin Sn 50 120 10 Number & Arrangement of Electrons Iodine I 53 127 1  It determines the chemical properties of an Barium Ba 56 138 7 element Tungsten W 74 184 5 Rhenium Re 75 186 2 Atomic number Gold Au 79 197 1  Number of Protons Lead Pb 80 208 4  Symbol: Z Uranium U 92 238 3 Atomic Mass Number CHARACTERISTICS OF VARIOUS  Number protons plus number of neutrons NUCLEAR ARRANGEMENTS  Symbol: A Atomic Atomic Neutron Arrangement Mass Number Number The atomic number & the precise mass of an Number atom are not equal! Isotope same different different Isobar different same different Carbon-12 Atom Isotone different different same  Its A & Z are equal 12 Isomer same same same  Rationale: it is the arbitrary standard for Page atomic measure Technetium-99m (Tc-43)  It decays to technetium-99 Elemental Mass  Energy Emitted:140 keV gamma rays  It is determined by the relative abundance of isotopes & their respective atomic masses STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 3 THE STRUCTURE OF MATTER COMBINATIONS OF ATOMS transforms itself into another atom to reach stability Molecules  It occurs when the nucleus contains too few  The group of atoms of various elements or too many neutrons  The smallest unit of a compound Radioisotopes  Radioactive atoms that have the same Sodium chloride (NaCl) number of protons  Common table salt Uranium (U-92) & Carbon-14 Chemical Compound  Two primary source of naturally occurring  Any quantity of one type of molecule radioisotopes CHON (C-6, H-1, O-8, N-7) Beta Emission  Carbon, Hydrogen, Oxygen, Nitrogen  It occurs in all radioisotopes  90% of the human body  It occurs more frequently than alpha emission Water  Results:  80% of the human body o Loss of small quantity of mass & one unit of negative electric charge Covalent Bond o To increase the Z by one while A  The chemical union between atoms formed remains the same by sharing one or more pairs of electrons o Changing of an atom from one type  Example: H2O of element to another  Neutron undergoes conversion to a proton Ionic Bond  The bonding that occurs because of an Alpha Emission electrostatic force between ions  It occurs only in heavy radioisotopes  Example: NaCl  It is much more violent process  It is consists of 2 protons & 2 neutrons Sodium bicarbonate (NaHCO3)  Atomic Mass Number: 4  Baking soda  Results: o Nucleus loses 2 units of positive The smallest particle of an element is an atom; charge & 4 units of mass the smallest particle of a compound is a o Chemically different atom & an molecule! atom lighter than 4 amu RADIOACTIVITY Radioactive Half-life  The time required for a quantity of Radioactivity radioactivity to be reduced to one-half its  The emission of particles & energy in order 13 original value to become stable  Symbol: T1/2 Page  I-131: T1/2 = 8 days Radioactive Decay/Radioactive Disintegration  C-14: T1/2 = 5730 days  The process by which the nucleus spontaneously emits particles & energy & STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 3 THE STRUCTURE OF MATTER Radioactive Decay Law  Antimatter  It described the rate of radioactive decay & the quantity of material present at any given Electromagnetic Radiation time  Examples: x-rays & gamma rays  Formula: Activity Remaining = Original  They only differ in origin Activity (0.5)n  It is often called photons  n: number of half lives  It has unlimited range in matter TYPES OF IONIZING RADIATION Photons  No mass & no charge Five Physical Characteristics  Travel at the speed of light (c)  Mass, Energy, Velocity, Charge & Origin  c: 3 x 108 m/s or 1.86 x 105 mi/s Particulate Radiation X-rays and gamma rays are the only forms of  It has finite range in matter ionizing electromagnetic radiation of  Examples: alpha & beta Particles radiologic interest! Alpha Particle X-rays  Equivalent to a helium nucleus  Symbol: X  It contains 2 protons & 2 neutrons  Mass: 0  Symbol: α  Charge: 0  Mass: 4 amu  Origin: electron cloud  Charge: +2  Energy: 0-25 MeV  Origin: nucleus of heavy radioactive nuclei  Range: 0-100 m (air); 0-30 cm (soft tissue)  Energy: 4-7 MeV  Ionization Rate: 100 ip/cm (equal to beta  Range: 1-10 cm (air); Primary Voltage  It allows a wide range of time intervals to be (V) selected  Secondary Current (mA) < Primary Current  It is used for rapid serial exposures (A)  Secondary Windings > Primary Windings Most exposure timers are electronic & are  Voltage Waveform: sinusoidal controlled by a microprocessor!  Amplitude: only difference in the primary & secondary waveform mAs Timer  Functions: Turns Ratio o Monitors the product of mA &  The ratio of the number of secondary exposure time windings to the number of primary windings o Terminates exposure when desired  Examples: 500:1 & 1000:1 mAs value is attained  Directly proportional to the voltage o Provides the highest safe tube  Inversely proportional to the current current for the shortest exposure for any mAs selected Voltage Rectification  Location: secondary side of the high-voltage  It ensures that electrons flow from cathode transformer to anode only  Applications: o Falling-load Rectification o Capacitor discharge imaging system  The process of converting alternating current (AC) to direct current (DC) Automatic Exposure Control (AEC)  A device that measure the quantity of Rectifier radiation that reaches the image receptor  An electronic device that allows current  It automatically terminates the exposure flow in only one direction when the image receptor has received the required radiation intensity Diode  An electronic device that contains two Solid-state Detectors electrodes  It is used to check timer accuracy (as short as 1 ms) Valve Tube  A vacuum tube (original rectifier) HIGH VOLTAGE GENERATOR  It replaced by solid-state rectifier o Composition: silicon High Voltage Generator  It increases the output voltage from the 27 Semiconductor autotransformer to the kVp necessary for x-  Lies between insulators & conductors Page ray production  2 Types: p-type & n-type Three Primary Parts P-type Semiconductor  High Voltage Transformer, Filament  Have loosely bound electrons (free to move) Transformer & Rectifiers  Have spaces called holes (no electrons) STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 6 THE X-RAY IMAGING SYSTEM  Holes: as mobile as electrons Extinction Time  Ending an exposure Solid-state p-n Junction  N-type material placed in contact with p- High Frequency Generator type crystal  It produces a nearly constant potential  It conducts electricity in only one direction voltage waveform  Solid-State Diode: a rectifier  Advantages: o Much smaller & less costly & more Electron flow is used when medical imaging efficient systems are described! o Improves image quality at lower patient radiation dose Half-Wave Rectification  It uses inverter circuits  The voltage is not allowed to swing negatively during the negative half of its Inverter Circuit cycle  A high-speed switchers or choppers that  Diodes: 0, 1 or 2 convert DC into a series of square pulses  60 pulses/second  Disadvantages: Full-wave rectification or high-frequency o It wastes half the supply of power voltage generation is used in almost all o It requires twice the exposure time stationary x-ray! Full-Wave Rectification Capacitor Discharge Generator  The negative half-cycle corresponding to the  Tube voltage falls during exposure inverse voltage is reverse  Approximately 1 kV/mAs  Diodes: 4  120 pulses/second Grid-Controlled X-ray Tube  Advantage:  An automatic lead beam stopper o Exposure time reduced in half  It stops continues x-ray emission of capacitor bank Single-Phase Power  It is designed to be turned on & off very  It results in a pulsating x-ray beam rapidly  Disadvantage:  Applications: o X-ray produced has a value near zero o Portable capacitor discharge imaging systems Three-Phase Power o Digital subtraction angiography  The voltage impressed across the x-ray tube o Digital radiography is nearly constant o Cineradiography  6 pulses/1/60 second  Grid: it refers to an element in the tube that  Advantage: acts as a switch 28 o Voltage never drops to zero during exposure Less Voltage Ripple Page  Disadvantages:  Greater radiation quantity o Its size & cost o Higher efficiency of x-ray production Initiation Time  Starting an exposure STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 6 THE X-RAY IMAGING SYSTEM  Greater radiation quality o Fewer low-energy projectile electrons pass from cathode to anode CHARACTERISTICS OF HIGH FREQUENCY X-RAY GENERATORS Frequency Range Inverter Features Incident X-ray λ  Energy: Ei = Es (Eb + EKE) The probability of the photoelectric effect is o Ei = incident x-ray energy inversely proportional to the third power of the o Es = scattered x-ray energy x-ray energy (1/E)3! o Eb = electron binding energy STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 10 X-RAY INTERACTION WITH MATTER FEATURES OF PHOTOELECTRIC EFFECT The probability of the photoelectric effect is With inner-shell electron directly proportional to the third power of the With tightly bound atomic number (Z3)! electrons Most likely to occur When x-ray energy is just higher than electron Z & K-SHELL Eb OF RADIOGRAPHICALLY binding energy (Eb) IMPORTANT ELEMENTS Increased penetration Atomic Electron Binding through tissue without Element Number (Z) Energy (Eb) interaction Hydrogen 1 0.02 As x-ray energy Less photoelectric effect Carbon 6 0.3 increases relative to Compton Nitrogen 7 0.4 effect Oxygen 8 0.5 Reduced absolute Aluminum 13 1.6 photoelectric effect (1/E3) Calcium 20 4.1 Increases proportionately Molybdenum 42 19 As atomic number of with the cube of atomic Rhodium 45 23 absorber increases number (Z3) Iodine 53 33 As mass density of Proportional increase in Barium 56 37 absorber increases photoelectric effect Tungsten 74 69 Rhenium 75 72 Pair Production Lead 82 88  The incident x-ray interacts with the nuclear force field  Results: x-ray disappears & two electrons EFFECTIVE Z OF MATERIALS with opposite charge appear (positron & IMPORTANT TO RADIOLOGICAL SCIENCE electron) Type of Substance Effective Z  Occur At: 1.02 MeV x-rays HUMAN TISSUE  It is useful in PET Fat 6.3 Soft Tissue 7.4 Pair production does not occur during x-ray Lung 7.4 imaging! Bone 13.8 CONTRAST MATERIAL Annihilation Radiation Air 7.6  A process wherein the mass of positron & Iodine 53 electron is converted to energy Barium 56 OTHER Photodisintegration Concrete 17  The incident x-ray interacts directly into the Molybdenum 42 nucleus 42 Tungsten 74 Lead 82  Results: x-ray is absorbed by the nucleus & Page nucleon/nuclear fragment is emitted  Occur At: 10 MeV x-rays Photodisintegration does not occur in diagnostic radiology! STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 10 X-RAY INTERACTION WITH MATTER DIFFERENTIAL ABSORPTION CHARACTERISTICS OF DIFFERENTIAL ABSORPTION Differential Absorption Fewer Compton  Different degrees of absorption in different interactions (1/E) tissues Many fewer As x-ray energy  Results: image contrast & formation of the photoelectric increases x-ray image interactions (1/E3)  It occurs because of: More transmission o Compton scattering through tissue o Photoelectric effect No change in Compton o X-rays transmitted through the interactions patient (independent) As tissue atomic Many more number increases Three Types of X-ray Important in Making a photoelectric Radiograph interactions (Z3)  Those scattered by Compton interaction Less x-ray transmission o Doesn’t provide diagnostic Proportional increase in information Compton interactions o Result: image noise As tissue mass density Proportional increase in  Those absorbed photoelectrically increases photoelectric interaction o Provides diagnostic information Proportional reduction o Appearance: radiopaque in x-ray transmission  Those transmitted by the patient without interaction To image small differences in soft tissue, one o Provides diagnostic information must use low kVp to get maximum differential o Appearance: radiolucent absorption! Two Other Factors Important in Making a Mass Density Radiograph  The quantity of matter per unit volume  X-ray emission spectrum  Units: kg/m3 or g/cm3  Mass density of patient tissue  Water: 1000 kg/m3 Image Noise The interaction of x-rays with tissue is  A generalized dulling of the image by x- proportional to the mass density of the tissue rays not representing diagnostic information regardless of the type of interaction! Radiographic Image CONTRAST EXAMINATION  It results from approximately 0.5% of the x- rays emitted by the x-ray tube Contrast Agent  Compounds used as an aid for imaging 43 internal organs with x-rays Differential absorption increases as the kVp is  Positive Contrast Agent: higher Z than the Page reduced! surrounding tissue e.g. barium (Z-56) & iodine (Z=53)  Negative Contrast Agent: lower Z than the surrounding tissue e.g. air STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 10 X-RAY INTERACTION WITH MATTER MASS DENSITY OF MATERIALS  An all-or-none condition for x-ray IMPORTANT TO RADIOLOGIC SCIENCE interaction Mass Density Substance (kg/m3) Scattering Process HUMAN TISSUE  The interaction in which x-ray is partially Lung 320 absorbed Fat 910  Examples: Compton effect & coherent Soft tissue, muscle 1000 scattering Bone 1850 CONTRAST MATERIAL Attenuation Air 1.3  The total reduction in the number of x-rays Barium 3500 remaining in an x-ray beam after penetration Iodine 4930 through a given thickness of tissue OTHER Calcium 1550 Concrete 2350 Attenuation is the product of absorption & Molybdenum 10,200 scattering! Lead 11,350 Rhenium 12,500 Tungstate 19,300 Low-kVp Technique  It produces excellent high-contrast radiographs of the organs of GI tract High-kVp Technique  It is used to outline the organ under investigation & penetrate the CM to visualized the lumen of the organ more clearly Double Contrast Examination  Examination that uses air & barium for contrast  Examples: pneumoencephalography & ventriculography EXPONENTIAL ATTENUATION Absorption Process 44  The interaction in which x-ray disappears  Example: photoelectric interaction, pair Page production & photodisintegration Absorption  The removal of x-ray from a beam via the photoelectric effect STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 11 RADIOGRAPHIC FILM Image Forming X-rays No unwanted pattern or  Those that exit the patient and interact with shading on image the image receptor o Semirigid o Tinted with blue dye Exit Beam  Reduces eyestrain & fatigue  The x-rays that remain as the useful beam exits the patient Glass Plate  The original film base Image Receptor  The medium that converts the x-ray beam Cellulose Nitrate into a visible image  Standard base  Characteristic: FILM CONSTRUCTION o Flammable Radiographic Film Cellulose Triacetate (mid-1920s)  Basic Parts: base & emulsion  Safety base  Other Parts: adhesive layer & overcoat  Characteristic:  Thickness: 150-300 μm o Not as flammable as cellulose nitrate Adhesive Layer Polyester (1960)  A thin coating located between the emulsion  Film base of choice & base  Characteristics:  Purpose: o More resistant o Allows emulsion & base to maintain o Superior dimensional stability proper contact & integrity Emulsion Overcoat  The heart of the x-ray film  A protective covering of gelatin that  Composition: enclosed the emulsion o Gelatin & Silver Halide Crystal  Purposes:  Thickness: 3-5 μm o Protects the emulsion from scratches, pressure & contamination Gelatin o Allows rough manipulation of x-ray  It holds the silver halide crystal uniformly film before exposure dispersed in place  Characteristics: Base o Clear & sufficiently porous  The foundation of radiographic film  Principal Function:  Purpose: o To provide mechanical support for o To provide a rigid structure onto silver halide crystals 45 which the emulsion can be coated  Characteristics: Silver Halide Crystal Page o Flexible & fracture resistant  The active ingredient of the emulsion o Dimensional stability  Characteristic:  Maintain its size & shape o High atomic number (Z) o Uniform lucency  Composition:  Transparent to light o Silver bromide (98%) STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 11 RADIOGRAPHIC FILM o Silver iodide (2%) Gurney-Mott Theory  Shapes: tabular (mostly used), cubic,  The accepted, incomplete, explanation of octahedral, polyhedral & irregular latent image formation Tabular Silver Halide Crystals Silver Halide Crystal  Size: 0.1 μm  Crystal Lattice: silver, bromide & iodine  Diameter: 1 μm atoms  Cross section: triangular, hexagonal or  Positive Ion: silver higher-polygonal  Halide/Negative Ions: bromide & iodide  Arrangement of Atoms: cubic o Found in greatest concentration along the surface of the crystal Silver Halide Crystal Formation AgNO3 + KBr AgBr + KNO3 An ion is an atom that has too many or too few electrons & therefore has electric charge! Double Emulsion Film  Film coated with emulsion on both sides Frankel Defect  An inherent defect in the structure of silver Silver Sulfide halide crystals  A chemical contaminant responsible for the physical imperfection of the silver halide Photon Interaction With Silver Halide Crystal crystal Latent Image  Photoelectric Interaction: x-ray is totally Sensitivity Center absorbed  Physical imperfection in the lattice of the  Compton Interaction: x-ray is partially emulsion layer absorbed  The latent image center Secondary Electron Formation Factors Affecting the Performance of Radiographic Br + photon Br + e- Film  The number of sensitivity center per crystals The result is the same whether the interaction  The concentration of crystals in the involves visible light from an intensifying emulsion screen or direct exposure by x-rays!  The size & distribution of the crystals Radiographic Film Metallic Silver Formation  It is manufactured in total darkness e- + Ag Ag FORMATION OF THE LATENT IMAGE Steps in the Production of Latent Image & Conversion of Latent Image into a Manifest Image A. Radiation interaction releases electrons 46 Latent Image B. These electrons migrate to the sensitivity  The invisible change that is induced in the Page center silver halide crystal C. At the sensitivity center, atomic silver is formed by attraction of an interstitial silver Photographic Effect ion  The formation of the latent image D. This process is repeated many times, resulting in the buildup of silver atoms STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 11 RADIOGRAPHIC FILM E. The remaining silver halide is converted to  Characteristics: thermally-sensitive silver during processing  Applications: “dry” printers F. The silver grain results Characteristics That Must be Considered in Latent Image Center Selecting Screen-Film  Group of silver atoms  Contrast, Speed, Spectral Matching, Anticrossover/Antihalation Dyes & Processing Safelight  The term applied to the chemical reactions that transform the latent image into a Contrast visible/manifest image  Degree of difference between the light & dark areas of a radiograph TYPES OF FILM  High Contrast Film: o It produces black & white image Types of Film Used in Medical Imaging o Smaller grains  Screen-film, Laser Printing,  Low Contrast Film: Copy/Duplicating, Dental, Radiation o It produces images with shades of Monitoring & Dry Transfer gray o Larger grains Screen-Film  It is inversely proportional to its exposure  The most widely used IR latitude  Emulsions: two  Characteristics: blue or green sensitive Latitude  Applications: general radiography  The range of exposure techniques (kVp &  Advantages: reduce technique & dose mAs) that produce an acceptable image  Disadvantage: image is blurred Speed Copy/Duplicating Film  The sensitivity of the screen-film  Emulsion: single with antihalation backing combination to x-rays & light  Characteristics: pre-exposed to Dmax  Fast IS: needs fewer x-rays to produce a  Applications: duplicating radiographs diagnostic image Dental Film Principal Determinants of Film Speed  Emulsions: two packed in sealed envelope  For Direct Exposure: concentration & total  Characteristics: has lead foil to reduce number of silver halide crystals backscatter  For Screen-Film: silver halide grain size &  Applications: dentistry shape Radiation Monitoring Film Large grain emulsions are more sensitive than 47  Emulsions: two packed in sealed envelope small grain emulsion!  Characteristics: one emulsion can be Page sloughed off to increase OD scale Double Emulsion Film  Applications: radiation monitoring  An emulsion is layered on either side of the base Dry Transfer Film  It is used to optimize the speed  Emulsions: one  It is flat after processing STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 11 RADIOGRAPHIC FILM Covering Power Panchromatic  The more efficient use of silver in the  Film that is sensitive to the entire visible emulsion spectrum Crossover Reciprocity Law  The exposure of an emulsion caused by light  Principle that states that optical density on a from the opposite radiographic intensifying radiograph is proportional only to the total screen energy imparted to the radiographic film  Effect: blurring of image  Formula: o Exposure = Intensity x Time = Ways to Reduce Crossover Constant Optical Density  Tabular grain emulsions:  Applicable: film exposed directly to x-ray o Increase covering power  Failure: when film exposed to light from IS  Light-absorbing dye:  Important: when exposure times are long o Added in a crossover control layer (mammography) & short (angiography) o It reduces crossover to near zero  Result: reduce speed & increase technique  IS that emits short-wavelength light (Blue or UV) APPROXIMATE RECIPROCITY LAW FAILURE Three Critical Characteristics of Crossover Control Exposure Time Relative Speed Layer 1 ms 95  It absorbs most of the crossover light 10 ms 100  It does not diffuse into the emulsion but 100 ms 100 remains as a separate layer 1s 90  It is completely removed during processing 10 s 60 Spectral Matching Safelight  The most important consideration  It provides enough light to illuminate the  The color of light emitted by the screen must darkroom while ensuring that the film match the response of the film remains unexposed  Calcium Tungstate: blue & blue-violet  Composition: incandescent lamp with filter  Rare Earth: ultraviolet, blue, green & red  Watts: 15 W  Distance: 5ft (1.5m) from work surface Rare Earth screens are made with rare Earth  Amber Filter: for blue sensitive film (>550 elements – those with atomic numbers of 57 to nm) 71!  Red Filter: for both green & blue sensitive film (>600 nm) All silver halide films respond to violet & blue light but not to green, yellow, or red unless Direct-Exposure Film 48 they are spectrally sensitized!  Film used without the use of IS  Characteristics: Page Orthochromatic Film o Thicker emulsion than screen-film  Film that is green-sensitive o Higher concentration of silver halide crystals  Purpose: to improve direct x- ray interaction STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 11 RADIOGRAPHIC FILM o Back side of the base is coated with Line Artifact clear gelatin (for single emulsion  Cause: creasing of the film film)  Purpose: to balance emulsion Specular Artifact swelling & shrinking  Cause: dirt on the hands or IS Mammography Film Static Artifact  Emulsion: single with antihalation backing  Cause: dry environment Halation Heat & Humidity  Reflection of screen light transmitted  Storage Temperature: 5000 rad (> 5 Gyt) Spinal Transaction 101 Page STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 33 FUNDAMENTAL PRINCIPLES OF RADIOBIOLOGY Principal Aim of the Study of Radiobiology Radiation Weighting Factor (WR)  To understand radiation dose-response  Factor used in radiation protection that relationships accounts for differences in biologic effectiveness between different radiations Dose-Response Relationship  Former Name: quality factor  A mathematical & graphic function that relates radiation dose to observed response Relative Biologic Effectiveness (RBE)  Ratio of the dose of standard radiation Jean Bergonie & Louis Tribondeau (1906) necessary to produce a given effect to the  Theorized & observed that radiosensitivity dose of test radiation needed for the same was a function of metabolic state of tissue effect being irradiated  Formula: Dose of standard radiation necessary LAW OF BERGONIE & TRIBONDEAU to produce a given effect  Stem cells are radiosensitive; Mature cells RBE = Dose of test radiation necessary to are radioresistant produce the same effect  Younger tissues and organs are radiosensitive  Tissues with high metabolic activity are Orthovoltage X-rays radiosensitive  The standard radiation by convention  A high proliferation rate for cells & a high  Range: 200-250 kVp growth rate for tissues result in increased  It was used in radiation oncology radiosensitivity The RBE of diagnostic x-rays is 1! Physical Factors That Affect Radiosensitivity  Linear Energy Transfer (LET), Relative LET & RBE OF VARIOUS RADIATION Biologic Effectiveness (RBE), Protaction & DOSES Fractionation LET TYPE OF RADIATION RBE (keV/μm) Linear Energy Transfer (LET) 25 MV x-rays 0.2 0.8  A measure of the rate at which energy is 60Co gamma rays 0.3 0.9 transferred from ionizing radiation to soft 1 MeV electrons 0.3 0.9 tissue Diagnostic x-rays 3.0 1.0  Another Method of: 10 MeV protons 4.0 5.0 o Expressing radiation quality Fast neutrons 50.0 10 o Determining the value of the 5 MeV alpha particles 100.0 20 radiation weighting factor (WR) Heavy nuclei 1000.0 30  Used in radiation protection  Expressed in: keV/μm Protraction 102  Diagnostic X-rays: 3 keV/μm  The dose is delivered continuously but at a  As LET Increases: lower dose rate o Increases the ability to produce Page biologic damage Fractionation o Increases the probability of  The dose is delivered at the same dose in interaction with the target molecule equal portions at regular intervals  It reduces the effect STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 33 FUNDAMENTAL PRINCIPLES OF RADIOBIOLOGY o Rationale: cells undergo repair & Interphase Death recovery between doses  It occurs when the cell dies before replicating Dose protraction & fractionations cause less effect because time is allowed for intracellular Intracellular Repair repair & tissue recovery!  It is due to a repair mechanism inherent in the biochemistry of the cell Biologic Factors That Affect Radiosensitivity  Oxygen Effect, Age, Recovery, Chemical Repopulation Agents & Hormesis  Replication by surviving cells Oxygen Effect The combined processes of intracellular repair  Oxygenated/Aerobic State: tissue is more & repopulation contribute to recovery from sensitive to radiation than anoxic & hypoxic radiation damage! Oxygen Enhancement Ratio (OER) Chemical Agents  Ratio of the dose necessary to produce a  Radiosensitizers: agents that enhance the given effect under anoxic conditions to the effect of radiation dose necessary to produce the same effect o Examples: under aerobic conditions  Halogenated pyrimidines  Formula:  Methotrexate Dose necessary under anoxic  Actinomycin D conditions to produce a given effect  Hydroxyurea OER =  Vitamin K Dose necessary under aerobic  Radioprotectors: agents that reduces the conditions to produce the same effect effect of radiation  LET dependent o Not found human application  Low LET: higher OER  Rationale: it must be administered at toxic levels Hyperbaric/High Pressure Oxygen o Examples:  It has been used in radiation oncology  Cysteine o Purpose: to enhance the  Cysteamine radiosensitivity of nodular & avascular tumors Hormesis  A little bit of radiation is good for us Diagnostic x-rays imaging is performed under o Rationale: it stimulates hormonal & conditions of full oxygenation! immune responses to other toxic environmental agents Age  RADIATION DOSE-RESPONSE 103 Before Birth: most radiosensitive  After Birth: radiosensitivity decreases RELATIONSHIPS  Maturiry: most radioresistant Page  Old Age: somewhat more radiosensitive Radiation Dose-Response Relationship  A mathematical relationship between Recovery various radiation dose levels & magnitude if  Intracellular Repair + Repopulation the observed response STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 33 FUNDAMENTAL PRINCIPLES OF RADIOBIOLOGY Two Important Applications in Radiology S-Type/Sigmoid-Type  It is used to design therapeutic treatment  Example: skin effects resulting from high routines for patient with cancer dose fluoroscopy  It revealed provide the basis for radiation control activities Diagnostic radiology is concerned almost exclusively with the late effects of radiation Two Types of Radiation Responses exposure & therefore, with linear,  Deterministic/Nonstochastic nonthreshold dose-response relationships! o It follows a high-dose exposure o Early radiation response CONSTRUCTING A DOSE-RESPONSE o Example: skin burn RELATIONSHIP  Stochastic o It follows a low-dose exposure A dose-response relation is produced when o Late radiation response high-dose experimental data are extrapolated o Examples: cancer, leukemia & to low doses! genetic effects Extrapolation Two Characteristic of Dose-Response Relationship  Estimation of value beyond the range of  Linear or Nonlinear known values  Threshold or Nonthreshold  Results in: linear, nonthreshold dose- response relationship Threshold Dose  The level below which there is no response Linear Dose-Response Relationship  The response is directly proportionate to the dose  Linear Nonthreshold Type: intersects at zero or below  Linear Threshold Type: intercept the dose axis at some value greater than zero Radiation-induced cancer, leukemia, & genetic effects follow a linear-nonthreshold dose-response relationship! Nonlinear Dose-Response Relationship  It is used in establishing radiation protection guidelines for diagnostic imaging 104  The response is not directly proportional to the dose  Nonlinear Nonthreshold: large response Page results from a very small radiation dose  Nonlinear Threshold Type: below the threshold, no response is measured STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 34 MOLECULAR & CELLULAR RADIOBIOLOGY Radiation Interaction With Water  The principal radiation interaction in the At low radiation doses, point lesion are body considered to be