RADI 1130 Week 1 Readings PDF

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RADI 1130: Week 1 – Readings Chapter 25 The Imaging Process (CAB) Phase 1 – image acquisition  Unique to each imaging modality for both film-screen imaging and digital imaging  Creation of x-ray beams and x-ray images are common to both types  Creating the beam – radiation concepts, electricity, electromagnetism, x-ray tube, x-ray equipment, auto exposure controls, x-ray production o Film screen imaging – film and screen, imaging and processing o Digital imaging – computed radiography, digital radiography Phase 2 – image processing  Divided into film/hard copy and monitor/soft copy  Film screen images can be recorded on film/hard copy or digitized into DICOM-forma images  Digital images can be processed for monitor/soft copy methods or produced as film/hard copy by a laser or dry imaging system Phase 3 – image archiving  Consist of storing images for reference  Can be physically stored or digitized and stored electronically Phase 4 – image display  Way to view images  Can change spatial resolution, brightness, contrast Phase 5 – image analysis  Analyse image quality  Looks at IR exposure, contrast, spatial resolution, distortion Professional Imaging Standards: The pyramid Problem:  Pyramid Problem – roadblock in overcoming complex problems  Acceptable image need to look at technical factor selection, subject density, contrast, pathology, digital processing Analytical Process: Diagnosing and Treating Image:  Diagnosing and treating are out of scope practices  We must obtain pertinent info for the physician  Physician – experts in science of anatomy and physiology  Radiologist – physicians who are experts in diagnosing through anatomical images  Radiographers – experts of creating and analyzing the image Diagnostic Process:  To solve pyramid problems you must breakdown the whole into individual parts  Attention to detail is important  Diagnosing needs highest level of mental acuity o Analysis, synthesis, evaluation to some complex problems  Narrowing Search Field – start with large area, find abnormality and then shrink  Hypothesis Activation – formulate hypothesis to explain cues  Information Seeking – hypothesis is tested by finding more info  Hypothesis Evaluation – predict the solution to the problem Acceptance Limits: Graphing Acceptance Limits:  Fit the limits of the radiographs that will be accepted against those that will not  Acceptance Limit – 1

Main goal is to produce a diagnostic-quality image, suboptimal images are also accepted for diagnosis  Extra radiation is not good Striving for Perfection: Factors Affecting Acceptance Limit Curves  If image is over-exposed it is possible to change it digitally  If image is under-exposed, no method to fix it  EI values are extremely important 

Chapter 12: Prime Factors (CAB)  X-ray photons from an x-ray tube is controlled by a number of factors  Tube housing, target material, filtration, voltage waveform  Principal Factors that affect x-ray emission are under direct control of the radiographer o Milliamperage-second (mAs) o Kilovoltage (kVp) o Distance (d)  X-Ray beam is both quantity and quality  X-Ray Quantity – measure of the number of x-ray photons in the useful beam o Also called x-ray output, intensity or exposure o Unit of measurement is Roentgen (R)  X-Ray Quality – measurement of the penetrating ability of the x-ray beam o Describes the distance of the x-ray beam travels in matter o High energy x-ray photons travel farther in matter and are more penetrating than low energy photons o High penetrating x-rays are called hard x-rays o Low penetrating x-rays are called soft x-rays o Numerically represented by the half-value layer (HVL)  The thickness of absorbing material needed to reduce the x-ray intensity (quantity)to half its original value o Factors that directly affect the quality are kilovoltage and filtration Factors Affecting X-Ray Emission Quantitative Factors Qualitative Factors mAs kV kV Filtration Distance Filtration Milliamperage-Second:  Milliamperage (mA) – measurement of x-ray tube current (number of electrons crossing the tube from cathode to anode) o mA is the number of electrons per second o changes in length of time of exposure will affect total number of electrons flowing from cathode to anode  Amperage = to an electric charge of 1 coulomb flowing through a conductor per second o 1 ampere = 6.3 x 1018 o 1 milliamperage = 6.3 x 1015  As mA increases, # of electrons increases that cross the tube to reach the x-ray target  Milliamperage is directly proportional to tube current o mA doubles, so does # of electrons  # of electrons is controlled by the length of time the tube is energized 2

Exposure time is directly proportional to the number of electrons crossing the tube and is directly proportional to the number of x-rays created (x-ray quantity)  Number of x-rays that will be created at the target is product of number of electrons crossing the tube (tube current) and how long the electrons are allowed to cross (exposure time)  Milliamperage-second (mAs) – unit used to describe the product of tube current and exposure time o mAs = mA x s o primary controller of x-ray quantity o mAs doubles = x-ray exposure doubles (measured in roentgens) Image Receptor (IR) Exposure Relationship to mAs:  records images that is then displayed on a monitor for viewing  Density – used to describe the level of brightness on the monitor (how light/dark the image is), the relationship is this brightness level does not correspond to the IR exposure  Radiographic Density – degree of blackening of an x-ray film o Created by deposits of black metallic silver within the emulsion of an x-ray film that has been exposed to light or x-ray and then processed  Digital imaging System exposure to IR must be assessed with exposure index (EI) o This tells if an image is over or under exposed and must be repeated o Digital systems do not automatically correct the errors in selecting an mAs Kilovoltage (kVp):  Controls both quantity and quality of x-ray beam  Increasing the kV will cause an increase in the speed and energy of the electrons applied across the x ray tube  kV affects quantity (intensity) because more interactions occur at target as kVp increases o quantity is approximately directly proportional to the square of the ratio of the change in kVp  if kVp is doubled, the amount of x-ray photons increase about 4x  kV affects quality because each electron gas more energy, resulting in a beam with greater penetrability IR Exposure Relationship to kVp:  both quantity and quality will vary with changes in kV applied across x-ray tube  kVp is the primary controller of the differences in densities/IR exposures (contrast)  as kVp increases, penetrability increases = result in a image with less contrast  15 percent rule o Increase in kVp by 15% will cause a doubling in exposure, the same effect as doubling the mA or doubling exposure time o kVp decreased by 15% = exposure decreases by ½ o a smaller change in kVp will have a greater impact on x-ray emission in the lower kVp ranges than a higher kVp range o 15% of 40 kVp = 6 kVp exposure o 15% of 80 kVp = 12 o 15% of kVp = kVp exposure o 15% change (increase or decrease) kVp has same effect as doubling or ½ of the mAs on density  So if kVp was increased by 15% to maintain exposure, mAs would have to be ½ o Ex. Radiograph of pelvis is produced using 25 mAs at 70kVp. What kVp would be needed to double the exposure?  15% of 70 kVp = 10.5 kVp  70 + 10.5 – 80.5 or 81 kVp 

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o

Ex. An acceptable radiograph of the knee is produced using 10 mAs at 60 kVp. If the kVp is increased by 15% to 69 kVp, what mAs would be neeed to maintain the exposure?  Half of 10 mAs = 5 mAs

Distance:  Intensity of rays varies with changes in distance  X-ray intensity will decrease as the distance from the tube is increased  X-ray intensity (exposure) is measured in roentgens (R) or milliroentgens (mR)  X-ray photons are most concentrated at the target and from there they spread out n all directions  As the beam spreads and widens, x=ray intensity or quantity begins to diminish 

Inverse Square Law = o o o o o o

I1 I2

=

D2

2

D1

2

I1 = original intensity (mR) I2 = new intensity (mR) D1 = original distance D2 = new distance Intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance Ex. X-ray exposure of 240 mR is recorded at a distance of 20 inches. If the same technical factors are used, what will the exposure be if the distance is increased to 40 inches.  

240 I2

=

=

240 x 20 402

402 202

2

==

240 x 400 = 60mR 1600

IR Exposure Relationship to Distance:  Since distance effects x-ray intensity, it will affect IR exposure  As distance increase, intensity and IR exposure decreases  As distance decreases, intensity and IR exposure increases

mAs1 mAs2

D 22



Exposure Maintenance Formula (Direct Square Law) = =



mAs is the primary controller of x-ray intensity and IR exposure, mAs can be adjusted to compensate for changes in distance Ex. Acceptable radiograph of the abdomen is taken using 25 mAs at 80 kVp at a distance of 40 inches. The Second radiograph is required to be taken at 56 inches. What mAs should be used to produce an acceptable radiograph if the distance is increased to 56 inches?



o

25 mAs2

=

562 402

25 x 402 562

=

D 12

= 49 mAs

 Use to compensate for effects that changes in distance will have on IR exposure of the image Image Quality Factors:  With digital image detecto systems , image quality properties of density and contrast to mAs, kVp, and distance does not exist  It is possible to change mAs, kVp and distance and have no effect on brightness or contrast on monitor  Digital image receptors can respond to exposures fro 0.01mR to 100mR Summary:  Prime factors are under control of radiographer  Prime factors have a significant impact on x-ray photon emission from the tube 4

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

 

Prime factors are: mAs, kVp, distance X-Ray emission are both its quantity (amount) and quality (penetrability) X-ray quantity affected by mAs, distanc, kVp and filtration X-Ray quality affected by kVp and filtration mAs is directly proportional to the number of x-ray photons created in the tube kV affects both quantity and quality kV is approximately proportional to the square of the ratio of the changed kVp o kVp is doubled, x-ray quantity would increase by a factor of 4 o but increased penetrability of beam with increasing kVp o IR exposure is affected Maintain exposure with changes in kVp, 15% rule o 15% rule states that increase in kVp by 15% will cause an approximate doubling of the exposure o Maintain IR exposure, if kVp is increased by 15%, mAs must be reduced to ½ its original value Quantity of x-ray photon is inversely proportional to the square of the distance As distance increases, exposure decreases in an inverse proportion to the square of the change in distance

Chapter 2: Radiation Concepts (CAB) Matter and Energy:  Radiography – recording images created by x-ray energy  Natural Science – study of universe and its contents o Non-Living Matter – physical science o Living Matter – biological science  Physics – studies matter and energy and their interrelationship  Matter – anything that has mass and occupies space Matter:  Describe the substance that comprises all physical objects  Principle characteristic of matter is mass o Mass – quantity of matter contained in an object  Described by energy equivalence or weight  Weight – force that an object exerts under the influence of gravity  Unit of mass is kilograms (kg) = 1000cm3 of water an 0℃  Matter is most commonly found found as a mixture of substances  Sustances – material that has a definite andconstant composition o Can be simple or complex o A simple substance is an element  Elements – substance that cannot be broken down into any simpler substances by ordinary means (92 naturally occurring elements) o A complex substance is a compound  Compound  Mixture – when two of more substances are combined o Air is oxygen, hydrogen, nitrogen and variety of other substances  Atom – smallest particle of an element that possess chemical properties  Molecule – two or more atoms are chemically united, which is the smallest particle of a compound  Atoms are tightly bonded to each other whena molecule is formed  Degree of attraction between atoms or molecules determines if the substance is a solid, liquid or gas 5

o o

Weakest (gas) – strongest (solid) State is determined by heat or thermal energy that the substance possesses

Energy:  Energy – ability to do work  Unit of energy is joule (J)  Radiation – energy is emitted and transferred through matter o Applied to heat and light  When any form of matter is struck up a form of radiant energy, it is described as being exposed or irradiated  E = mc2 o E = energy, m = mass, constant = speed of light in a vacuum Atomic Energy:  Atoms can be subdivided into three basic subatomic particles o Protons (p+), Neutrons (n0), Electrons (e-) Basic Atomic Particles:  Nucleus – small dense center which is surrounded by electrons that orbit it at various levels o Contains protons and neutrons which are responsible for most the mass of an atom o Nucleons – protons and neutrons together o Electrons on outside the nucleus and has a tiny mass o Electrons cannot be divided into smaller part o Quarks – protons and neutrons both comprise even smaller subnuclear structures  M Theory – postulates that electrons and quarks may not be particles but extremely small loops of rapidly vibrating string like matter  String Theory – matter behaves differently depending on vibrations of the string  Subatomic particles possess electrical charges o Positive – proton o Negative – electron o Neutron has no charge o When positives and negatives equal they are neutral or stable o Atoms are constantly vibrating because of the strong positive nuclear forece field, which is surrounded by negatively charged spinning and orbiting electrons  Each element has specific number of nuclear protons o Atomic Number (Z Number) – number of nuclear protons  Isotope – when atom gains or loses neutrons o Have same number of protons but different number of neutrons  Ion – if an atom gains or loses an electron o Ionization – process of adding or removing an electron from an atom Atomic Mass:  Mass of am atom is extremely small  Atomic Mass Unit (AMU) – mass of particles of an atom  Atomic Mass Number (A) – equal to the number of protons and neutrons in the nucleus Orbital Electrons:  Electron Binding Energy (Eb) – binding energy f an electron is defintied as that amount of energy needed to remove the electron from the atom  Free electron at rest has energy of zero so total energy of an orbital electron would be zero minus the binding energy or the negative of the binding energy  Closer an electron is to the nucleus, more tight to its orbit or shell  Stability of electrons is by centrifugal force and attractive electrostatic force  Closer the electron is th nucleus, higher binding energy 6

K-shell is closest to nucleus. Has 2 electrons in shell o Shells grow by =2n2  Octet Rule – number of electrons in outermost shell never exceeds 8  Electron Volt (eV) – binding energy of an electron (same as x-ray energy) o 1keV = 1000 electron volts (eV) Periodic Table:  Valence – elements with only one electron in its outermost shell has a valance of +1 Types of Energy:  Energy is the ability to do work  Work = force x distance  Mechanical Energy – action of machine or physical movement o Two types: mechanical and kinetic  Potential Energy – energy that an object has because of its position (stored)  Kinetic Energy – energy in motion (moving)  Chemical Energy – form of energy released during chemical reaction  Thermal Energy – quality of heat result of the motion of atoms and molecules o Temperature – measure of thermal energy  Electrical Energy (Electricity) – movement of electrons (electrical charges) o Electricity – study of resting or moving electrical charges  Nuclear Energy - stored in nucleus of each atom that holds nuclear particles in a tight bond Electromagnetic:  Electromagnetic Energy – form of energy from electric and magnetic disturbances in space o Travels through space with electric and magnetic fields and is produced y acceleration of a charge  Radio waves, microwaves, infrared light, visible light, cosmic rays  X-rays are human-made electromagnetic energy created in an x-ray tube when highs speed electrons are suddenly stopped  Identical to gamma rays o Gamma rays are from nucleus of radioactive materials Electromagnetic Spectrum:  Electromagnetic Radiation (EM) – natural part of environment in which we live  Visible light has both electric and magnetic properties  Electromagnetic radiation has a wide range of magnitudes of energy  Electromagnetic Spectrum – details all various forms of EM radiation o Common form is velocity – equal to speed of light  UV, x-ray, gamma are all capable of ionization  Excitation – electrons in an atom are moved to a higher state without actually being removed from the atom  Dual nature is know as the wave-particle duality of radiation o Understand x-rays, need to consider them as both waves and particles of energy Wave Theory:  EM energy travels through space in form of waves o Wave are disturbances in medium o Can travel in a vacuum  All waves have wavelength, frequency, amplitude and period  Sine waves  Wavelength – distance between any two successive points on wave  Amplitude – intensity of the wave ( max height)  Frequency – number of waves that pass a particular point in a given time frame  Period – time required to complete one cycle of the wave 

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 Velocity = frequency x wavelength  Frequency and wavelength are inversely proportional Particle Theory:  High frequency electromagnetic radiation interacts with matter, it behaves like a particle than a wave  EM radiation acts like small bundle of energy known as photon or quantum  Photon energy and frequency are directly proportional  E = hv Discovery of X-Rays:  1895 German physicist Wilhelm Conrad Rontgen discovered x-rays  Was experimenting with cathode rays  Died of carcinoma of the bowels in 1923 X-Ray Properties: X-Rays are: 1. Highly penetrating, invisible rays that are a form of EM radiation 2. Electrically neutral and not affected by electric or magnetic fields 3. Can be produced over a variety of energies and wavelengths (polyenergetic and heterogeneous) 4. Release very small amount of heat upon passing through matter 5. Travel in straight lines 6. Travel at the speed of light in a vacuum 7. Can ionize matter 8. Cause fluorescence (emission of light) of certain crystals 9. Cannot be focused by a lens 10. Affect photographic film 11. Produce chemical and biological changes in matter through ionization and excitation 12. Produce secondary and scatter radiation Chapter 6: X-Ray Equipment (Pg 97-99) (CAB) Types of X-Ray Equipment:  Medical x-ray units are classified as diagnostic or therapeutic  Most are made for specific procedures such as general radiographic procedures, cardiac catheterization, head procedures and fluoroscopy  Range 10-1200 milliamperes (mA), 0.001-10 seconds, at peak kilovoltage (kVp) of 25-150 Tables:  Support patients to enhance radiographic exam  Comfort is not the primary purpose  Tabletop are uniformly radiolucent to easily permit x-rays to pass through  Use carbon graphite fiber to reduce absorption of photons  Flat or curved( fluoroscopic) tops o Curved top has two disadvantage  Difficult for radiographer to maintain a patient accurately in an oblique or later position  Top is entirely useless ...