Radiology Final Study Guide 2021 PDF

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A cumulative final study guide for Dental Radiography...

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Key topics on the 2021 Final- Radiography Chapters 1-21

Components of x-ray tube Cathode: Consists of tungsten filament and molybdenum focusing cup. Negatively charged. Anode: Consists of tungsten target embedded in a copper stem. Positively charged. Copper: Anode; Thermal conductor removes heat from tungsten target and reduces risk of target from melting Tungsten: Filament (on Cathode (-)) and Tungsten Target (focal spot) on anode (+) has a high atomic number (74) allowing for sufficient x-ray production, has a high melting point (3422 degrees C), High thermal conductivity and low vapor pressure. Molybdenum: Cathode focusing cup which is negatively (-) charged. Lead: Collimator Oil: Surrounds x-ray tube and transformers, conducts heat away from the x-ray tube Vacuum: Glass envelope or tube that is evacuated contains x-ray tube (cathode and anode) – prevents collision of fast-moving electrons w/gas molecules which would significantly reduce their speed and prevents oxidation/burnout of tungsten filament. Aluminum: Filter Transformers: Provide a low-voltage current to heat the x-ray tube filament AND generate a high potential difference to accelerate electrons from cathode to anode. Thermionic Emission: The burning off of electrons from the tungsten filament. Target/Focal Spot: Tungsten target on copper anode converts kinetic energy of colliding electrons into photos. >99% of this is heat produced. < 1% is photons produced.

mAs/kVps mAs: (Density/Quantity) Milliampere seconds (tube current + exposure time). The higher the mA, the more x-rays will strike the film. (quantity). Affects density (darkness). kVp: (Contrast/Quality) Kilovoltage or penetrating power of the xray beam and influences density. Higher kV will cause higher radiographic density if all other factors remain the same. (quality). Affects contrast (degrees of light and dark).

Density: The degree or gradation of “blackness” on a radiographic image. It depends on the amount of radiation reaching a particular area on the film. > x-ray energy reaching the image, the

> blackness/density. The greater amnt of blackness=the greater # of light absorbed (rather than transmitted through). Contrast: The difference in densities seen on an image. Affected primarily by kVp. Contrast cannot be varied by a change in mA unless the kVp is also altered. If mA is increased, the kVp would need to be decreased to maintain the same density. General Radiation: Bremsstrahlung “braking” radiation: Decelerate high speed e. Kinetic energy lost by e is emitted in the form of x-radiation. Characteristic Radiation: Ionized unstable atom is ejected. For atoms to return to normal state, electron drops off, energy given off is an x-ray photon. “59 KeV characteristic of tungsten”. Characteristic Radiation: A form of radiation originating from an atom following removal of an electron or excitation of the atom. The wavelength of the emitted radiation is specific for the element concerned and the particular energy levels that are involved.

Beam: 2.75 inches

Units of measure Exposure (X) (unit): A measure of the amount of ionization produced in air by an x-ray beam; measured in milliroentgens (mR) or Roentgens (R), new SI unit of measurement is Coulombs/kg. Exposure (definition): Amount of radiation that comes out of the x-ray unit and reaches a person. Dose/Absorbed Dose (D): Amount of x-ray energy absorbed by a unit of mass of tissue. How much energy is deposited into the tissues. Measured by rads (old) or grays (new SI). Absorbed dose: The amount of energy imparted by ionizing radiation to a unit mass of irradiated material at a place of interest. The unit of absorbed dose in a traditional system is the RAD (100 erg/g). The SI unit of absorbed dose is the gray (Gy) (1Gy=1 J/kg). NEW UNIT: SI: new International System (SI). Gray: The SI unit for dose is the gray (Gy). It is the amount of energy (Joules) absorbed per kg of tissue. (1Gy= 1 J/kg). Gray (mGy): 1 gray = 100 rads Sievert (mSv): A dose equivalent unit defined as the absorbed dose Gray (Gy) times the quality factor (QF). For dental x-rays, 1 Sv = 1 Gy. 1 rem = 100 Sv. Coulomb: measure of electrical charge in a certain mass of air. OLD UNITS: (R)Roentgen: quantity of photons that will produce a defined number of ion pairs (about 2 billion) in a cubic centimeter of *air at standard temperature and pressure. Physicists convert

the number of ion pairs released into an electrical charge that they measure in a unit called coulombs (C ). The new unit of exposure is called the exposure unit (X). The X unit is the # of photons that will produce 1 coulomb (# of ion pairs released in an electrical charge) of charge per kg of air. (1X Unit= 1 C/kg air). RAD (Radiation absorbed dose) : The old R unit for dose/absorbed dose. It is the energy absorbed per gram of tissue. (1 rad = 100 erg/gm). 1 Gy = 100 Rads. Rem (Roentgen equivalent man) – A unit of dose equivalence/unit of dose of any radiation to body tissue in terms of its estimated biologic effects relative to an exposure of 1 Roentgen of x- or gamma-radiation. 100 Rems = 1 Sv. Curie: (Ci) (old unit) The original unit used to express the decay rate of a sample of radioactive material. The curie is equal to that quantity of radioactive material in which the number of atoms decaying per second is equal to 37 billion (3.7×1010). It was based on the rate of decay of atoms within one gram of radium. Becquerel (Bq): is the SI unit of radioactivity. One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. Rad=Gray Rem=Seivert Roentgen=Coulomb Curie=Becquerel Kerma (kinetic energy released in matter): Measured by the gray. MPD Maximum Permissable Dose: Radiation Workers including RDH = 50 mSv or 5 rads Public, pregnant – 5 mSv or 0.5 rads.

Underdevelopment/overdevelopment Underdevelopment: Film appears light/thin; Inadequate development time or temperature Time = too little Temperature = too cold! Depleted/contaminated developer solution Overdevelopment: Film appears dark/dense; Excess development time or temperature Time = too long Temperature = too hot! Concentrated developer solution

Underexposure/overexposure Overexposure: Image is too dark, reduce exposure time Underexposure: Image is too light, increase exposure time

Radiolucent/radiopaque Radiolucent: A black or dark area seen on a radiograph; structures that appear radiolucent lack density and permit the passage of the x-ray beam. Examples: maxillary sinus, nasal fossae, median palatine suture, incisive canal foramen, lip line, lingual foramen, mental foramen, mandibular canal, submandibular gland fossa, soft tissue shadow. Caries, fractures, periodontal ligament. Sinuses, acrylic, silicate. Muscle. Radiopaque: A white or light area on a radiograph; structures that appear radiopaque are dense and resist the passage of the x-ray beam. Examples: Lateral pterygoid plate, hamular process, coronoid process, maxillary tuberosity, zygoma malar bone, walls and fl of max. sinus, nasal septum, walls and fl of nasal fossa, anterior nasal spine, shadow of nose, genial tubercles, border of mandible, internal and external oblique ridges. Enamel, dentin, lamina dura, alveolar bone. Restorations. Bone.

Anatomy Filters/collimators Collimator: Controls size and shape of useful x-ray beam. Lead collimator. A common term for a variable aperture, beam-limiting device for restricting the field of x-ray photons in a beam to a desired shape and size. Rectangular reduces radiation more than round. *Most dangerous is the primary beam. Filter: Aluminum filter Filters secondary and scatter radiation. Inherent filtration built into machine: 1.5mm aluminum < 70 or 2.5mm > 70 Half Value Layer: Quality of x-ray beam measured by HVL. Thickness of aluminum needed to get ½ of its original value. Ex: 1.5 mm aluminum < 70 and 2.5mm aluminum > 70

Radiation Health Hormesis: Beneficial low doses of radiation. Threshold dose: The minimum exposure that will produce a detectable degree of any given effect. Small exposures produce no visible damage. With increasing levels of exposure, a threshold will be reached, at which time a specific radiation effect will become visible. Threshold dose depends on the kind of tissue exposed.

Deterministic (nonstochastic) Effects: Threshold dose, nonlinear (curved-line) type of radiation effects such as epilation (hair loss), erythema (skin reddening), cataracts (opacity on lens of eye), and sterility. Somatic tissues: tissues of the body that are not inherited from parent to child. Ex: Salivary glands, muscles, bones, skin. Radiation damage to somatic tissues only influences the individual exposed. Genetic/reproductive tissues: tissues responsible for producting the next generation of offspring and specifically include the oocytes in the female and spermatogonia. Radiation damage to genetic/reproductive tissues is inherited from one generation to the next and is considered to be harmful. Stochastic Effects: Number of mutations increases as the exposure to radiation increases. Result of linear effects of radiation. Leukemia, Cancer, Tumors, Genetic Mutations. Compton Scatter Radiation: Occurs when a photon interacts with an outer orbital electron. 57% of interactions are Compton Scattering. The incident photon collides with an outer electron, the photon is then deflected and is scattered in a new direction. Radiation that has been deflected from its path by impact during its passage through matter. This form of secondary radiation is emitted or deflected in all directions by the tissues of the patient’s head during exposure to x-radiation. The incident radiation has sufficient energy to dislodge a bound electron but attacks a loosely bound electron. The remaining radiation energy proceeds in a different direction as scatter radiation.

Paralleling/bisecting Paralleling technique – aka. Long cone technique, right angle technique. *Film placed parallel to the long axis of teeth being radiographed. *Central ray is directed at right angles to both teeth and receptor. *Achieve Parallelism by placing film away from teeth. *Compensate for increased object-to-receptor (teeth to receptor) distance by increasing source-to-film distance with long BID (16 inches). USES: Technique: Patient upright with sagittal plane perpendicular to the floor.Maxillary apices lie on the ala-tragus line while mandibular apices are .5cm from the lower border of the mandible. For Maxillary projections: Ala-tragus line parallel to floor For Mandibular projections: Occlusal plane parallel to floor. Angulation: BID parallel to floor = 0 degrees

Tip of BID tilted toward the floor is positive angulation. BID pointed toward ceiling is negative angulation Vertical Angulation: excessive vertical angulation with paralleling technique causes foreshortening, while insufficient vertical angulation causes elongation. Bisecting technique – aka short cone technique *The angle formed by the long axis of the tooth and the plane of the film must be bisected. *Beam is directed perpendicularly through the apex of the tooth toward the bisecting line *Dimensional distortion is inherent in the technique Uses: Can be used when it's nearly impossible to place the film parallel to the teeth e.g. children, patients with small mouths, low palatal vault, cleft palate. Technique: Position patient head w/sagittal plane perpendicular to floor. Maxillary projection: Ala-tragus line parallel to floor Mandibular projection: Commissure-tragus line parallel to floor Periapical: Show apices of teeth and 2mm of surrounding bone Bitewings: show the coronal portion of teeth in both arches and the alveolar crest of bone. Occlusal: shows an entire arch on the film in cross-section

Short/long scale contrast The lower the kilovoltage = short-scale contrast (60-65 kV). The higher the kilovoltage = long-scale contrast (80-90 kV). Short Scale Contrast: If kV is low (60-65 kV), then penetration of tissue is less and the density differences between adjacent areas will be greater. Best for bitewings and visualization of dental caries. (less gradual/more severe changes/jumps from light to dark). Reduced range of grays. Fewer gradients of white/gray/black. Long-Scale Contrast: If kV is high ((80-90kV), then penetration of tissue is greater and the density differences on adjacent areas on the radiograph will be small. Increased range of grays. More gradients of light, grey, dark gray, black. Best for periapical films, osseous changes such as periodontal and periapical disease.

Penetrometer/Step-Wedge: a radiographic testing device made of aluminum and built up in steps of varying thickness. Demonstrates how long-scale contrast compares with short-scale contrast.

Localization Localization of a 3D object in a 2D radiographic image using different techniques. 3 Different Ways to Localize: 1) Examine two conventional images projected at right angles to each other 2) Use the tube shift technique employing conventional periapical views (SLOB) 3) Image the anatomic region with a 3D imaging modality.

Distance Operator positioning at least 6 feet away and around the corner. Source-receptor distance: The shorter the distance between the focal spot (source of xrays) and the image receptor (film/sensor/psp/cassette), the greater the quantity of x-rays that strike the film, and therefore the higher the density. Ex: Doubling the distance gives ¼ the density and halving the distance give 4X the density. Inverse Square Law – The intensity of the beam depends on the distance of the measuring device (BID) to the focal spot. The intensity is inversely proportional to the square of the distance from the source. If distance increases, beam intensity decreases. If distance decreases, beam intensity increases. Example: 1 gy / 4 gy = 1m^2/2m^2.

Film Faster film F-speed = less radiation exposure 68-70 degrees chem reducing silver/dissolved salts Silver Halide: A salt compound used in photographic emulsions because of its sensitivity to light and other forms of radiation. Halides are compounds of metals with halogen elements of bromine, chlorine, and iodine.

Digital BASICS OF DIGITAL IMAGING *Composed of pixels (picture elements) which are characterized by 3 numbers

*These numbers are stored in an image file in the computer *Measurement of root length for Endo *Digital subtraction radiography *Advantages *Immediate image with CCD sensor/Ability to manipulate the image *Storage with software systems/Security of backup and off-site archiving of images *Ease of transfer by email/Security of the original image *Eliminates chemicals/Hazardous wastes are eliminated *Dose Reduction? *Once promoted as a “huge advantage” digital imaging *Why the dose reduction is not as large as suggested *Dose per exposure *Reduction of 0% to 50% as compared with “F” speed film *Increase in the number of radiographs made *Increase in the number of retakes due to the ease of exposing additional images Disadvantages *The electronic x-ray receptor are susceptible to rough handling Digital Image Receptors Solid state technology “sensors” *Charge-coupled device (CCD) *Thin silicon crystals *More sensitive to light than x-rays *Contains a layer of scintillating materials-increasing the absorption efficiency of the detector Analog vs. digital *Analog- conventional film images that have differences in the size and distribution of black metallic silver result in a continuous density *Digital- is a numeric format of the image content and its discreetness *Discrete in 2 ways: spatial distribution (pixels) and different shades of gray each of the pixels.

Digital Image Receptors Photostimulable phosphor technology “PSP” *-phosphor coated on top of a plate in which a latent image is formed after x-ray exposure. The latent image is converted to a digital image by a scanning device through stimulation by laser light. *PSP materials: barium, iodine, chlorine or bromine and europiumdope (barium fluorohalide) forms a crystal lattice PSP (con’t) *Exposure to energetic source of radiation *Valence electrons absorb energy and move into conduction band *Electrons migrate to nearby halogen vacancies in the fluorohalide lattice and become trapped *The # of electrons trapped is proportional x-ray exposure = latent image PSP ( con’t) *PSP plates must be erased to eliminate “ghost images” *Sealable polyvinyl envelopes *May be stored for 12-24 hours Digital Image Receptors *Silicone based semiconductors, differing from the CCD’s in the way the pixel’s are read. Spatial Resolution *The capacity for distinguishing fine detail in an image. *Measured as line-pairs per millimeter *A space and a line is called a line pair *PSP systems allows reduction in exposure to radiation by 50% in comparison to F speed film

Cone beam CBCT *Unlike panoramic and cephalometric, CBCT acquires data volumetrically, providing 3D images for the assessment of the dental and maxillofacial complex facilitating diagnosis. *With use of software formats like DICOM file format, the role of CBCT has expanded to image guidance of op and surg procedures, as well as biomodels and surgical guides. *3 Main Processes: 1) Image production 2)Visualization

3) Interpretation *In all CT techniques, a collimated x-ray source and a detector revolve around the patient. The detector records photon attenuation by measuring the number of photons that exit the patient, registering this information at several hundred angles through the rotational arc. These recordings constitute “raw data” that is reconstructed by a computer algorithm to create a 3D data set composed of volumetric elements (Voxels) from which images are derived *The basic component of resultant grayscale images is the picture element (pixel) value. The grayscale value or intensity of each pixel is related to the intensity of the photons incident on the detector. Although providing similar images, CBCT and MDCT represents separate evolutionary arms of CT imaging.

Processing /errors Umbra: A complete shadow produced by light, with sharply demarcated margins. In radiography, a sharply delineated image detail. Penumbra: Fuzzy margin surrounding image. The secondary shadow, produced by light, that is the periphery of the primary shadow. In radiography, the penumbra is blurred or ill-defined margin of an image detail; also called geometric unsharpness.

Patient management Parallel technique: ● Narrow arch ● Mandibular torus Bisecting angle technique: ● Shallow palate ● Large tight lingual frenulum Occlusal: ● Palatal torus *Stimulating the posterior dorsum of the tongue and the soft palate can stimulate the gag reflex. ***Primary dentition exam of a child 3-6 years old may consist of: ● 2 anterior occlusal images, ● 2 posterior bitewing images, and ●

4 posterior periapical images.

Exposure Increasing exposure time increased the amount of xrays produced. 1 impulse= 1/60seconds

Extraoral radiography (panoramic, lateral, waters, etc) Intensifying screen: A device used to convert x-ray energy to light energy. It consists of a card or plastic sheet coated with fluorescent material, positioned singly or in pairs in a cassette to contact the film. When the cassette is exposed to x-radiation, the light emitted from the fluorescent intensifying screen exposes the film and produces the latent image. Panoramic – A radiograph that shows a large area of the mandible and maxilla on a single film. Screen film 5 or 6 x 12 in is used in rigid or flexible cassette PURPOSE AND USES Dentist uses to : a.) examine large areas of face and jaws b.) locate impacted teeth c.) evaluate trauma, lesions d.) evaluate growth and development ADVANTAGES - Radiation dose is approximately 10x less than full mouth series using long, round PID and E+ speed film (7 ΦSv vs 70) - Increased coverage of dental arches and structures – more complete view of structures - Reduces superimposition of anatomical image - Mounting time is eliminated DISADVANTAGES - Not used to detect and evaluate caries and periodontal disease – poor detail - Difficult to obtain good im...