Radiology final study guide PDF

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Radiology final study guide...

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Before Exposure When to prescribe radiographs? Ideal PID? Collimator? 2.75 inch – collimator, 16in Rectangular PID o Filtration Define half value layer: Thickness of the aluminum in the x-rays path reduces intensity by onehalf Inherent versus added filtration Inherant: o 0.5-1.0mm of aluminum o in x-ray tubehead, does not meet state/federal filtration alone Added: o Added in 0.5mm increments to machine as needed for compliance o Placed b/w tubehead & collimator o Results in high-penetrating x-ray beam Minimum filtration at different kVp settings Machines operating at/below 70 kVp o Min of 1.5mm aluminum filtration Machines operating above 70 kVp o Min of 2.5mm aluminum filtration During Exposure Fast Film What makes some films faster than other films? o Size and amount of crystals o Fast film is the most effective method of reducing a pt’s exposure to x-radiation o F-speed is 20% faster than e-speed film o Digital receptor – fastest method of exposure Lead apron o Protects reproductive cells and blood-forming tissues (Radiosensitive organs) o Protects from scatter radiation o Must be at least 0.25mm of lead thick o Thyroid collar only recommended for intra-oral radiography bc results in obscured data and non-diagnostic radiography Etc Protection ALARA o As low as reasonably achievable o Exposure to radiation must be kept at a minimum How the radiographer is protected o Leave room during exposure

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Avoid standing in primary beam (90-135 degree angle to the beam) Stand 6 ft away from tubehead Several thickness dry wall or shielded (lead) Film exposure badges

MPD (in 1 yr) / MAD (lifetime) o MPD – maximum dose of radiation an individual can receive w/in a given period of time w/ little or no injury o MPD for occupationally exposed person – 5.0 rem/year (0.05 Sv/year) o MPD for non-occupationally exposed – 0.1rem/year (0.001 Sv/year) MAD o Occupationally exposed personnel to determine lifetime absorbed dose. Over age 18 o M.A.D = (N-18) x 5rem/year (occupationally exposed) o M.A.D = (N-18) x 0.005 Sv/year  “N” refers to age Characteristics of x-rays What types of radiation produced at the tungsten target? Characteristic & braking radiation. Define each separately. Cathode to anode. o General (Breaking) (Bremsstrahlung) Radiation  Sudden stopping of high-speed electrons at the tungsten target, produced when electrons come very close to, or hit, the nucleus of a tungsten atom  Rarely hit the nucleus  Higher energy this close to the nucleus causes the electron to slow down  Most x-rays produced this way (70%)

o Characteristic radiation: o Produced when a high-speed electron dislodges an inner-shell electron from the tungsten atom o Results in ionization of the tungsten atom o Only occurs at or above 70kV

Parts of the tube & their function Aluminum disks  Filter out penetrating long wave lengths, sheet of .5mm thick aluminum disks Anode: Made of a copper stem and focal spot; +, focal spot is made of tungsten; converts bombarding electrons into x-ray photon  positive electrode  converts electrons into x-ray photons  has tungsten target & copper stem  99% heat, 1% x-ray photon Cathode: Made of a tungsten filament an molybdenum cup; - , filament: heated to give off a cloud of electrons; thermionic emission, cup: focuses electrons toward the anode  negative electrode  supplies electrons necessary to generate x-rays  has tungsten filament, molybdenum cup, step up transformer Copper stem  Dissipates heat away from TT Insulating Oil  Surrounds x-ray tube and transformers, prevents overheating Lead Collimator  Restricts size and shape of x-ray beam  2.75 inch Leaded glass housing  Prevents x-rays from escaping in all directions  One area has a “window” that permits the x-ray beam to exit the tube and directs the beam toward the aluminum disks, lead collimator, PID Metal Housing

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Surrounds the x-ray tube and transformers, protects the tube and grounds high voltage components

Molybdenum cup  Focuses electrons into a narrow beam and directs the beams toward the tungsten target PID 

Aims and shapes the x-ray beam

Step down transformer  Used to decrease voltage from the incoming 110 or 220 line voltage to the 3-5 volts used by the filament circuit  Location: Anode o More wire coils in the primary coil than in the secondary  Controlled by kVp Step up transformer  Used to increase incoming voltage to 65,000 to 100,000 volts used by the high-voltage circuit  Location: Cathode o More wire coils in the secondary than in the primary  Controlled by kVp Transformers o Alters voltage of incoming electricity, controls the voltages of electricity that is entering the x-ray tube Tubehead o Contains the x-ray tube that produces dental x-rays Tubehead seal o Permits exit of x-rays from tubehead, seals the oil, filters x-ray beam Tungsten filament o Produces electrons when heated, forming electron cloud o Location: cathode Thermionic emission: o Release of electrons from the tungsten filament when the electrical urrent passes through it and heats the filament How do x-rays interact with cells? Which ones cause ionization? Cause scatter? No interaction – No ionization No scatter Coherent – scatter w/ no ionization. Interaction w shell changes path of x ray but no interaction. Compton (more common) – causes scatter. Ionization. Dislodges outer shell electron Absorption – xray absorbed by pt cells – Ionization. Photoelectric effect

Ionization- what is it? Atom that has lost or gained an electron kVp (long/short scale) o Changes density and contrast 

Increase kVp- higher intensity, long grey scale - LOW contrast image * LONG grey scale, periodontal or periapical disease

Decrease kVp – less intensity, less density, higher contrast, short grey scale - High contrast * caries detection o If you increase kVp by 15, you must decrease the exposure time by ½ o If you decrease kVp by 15, you must increase exposure time by 2 

mA o Overall darkness or blackness of an image o Increase mA = increase density o Decrease mA = decrease density If exposure time increased, mA must be decreased to maintain diagnostic density Density: Controlled by kVp & mA o To increase density: increase kVp/mA o To decrease density: decrease kVp/mA Contrast: Controlled by kVp o To increase contrast: decrease kVp o To decrease contrast: increase kVp Exposure Time: Changes w/ kVp/ mA o Increased exposure time: decrease kVp/mA o Decrease exposure time: Increase kVp/mA Penumbra o Fuzzy, unclean areas on radiograph o Unsharpened or blurred edges Sharpness influenced by 3 factors: 1. Focal spot size (tungsten target): Smaller the focal spot, sharper the image a. ~0.6-1.0mm tungsten target 2. Film composition: Size of crystals in emulsion 3. Movement: Movement of pt or tubehead Fuzziness, impacted by movement, film (larger crystals)

Intensity What makes a beam more or less intense? o Product of the quantity and quality of the beam per unit of distance (area) and time o Affected by mA, kVp, time, and distance of the beam o Categorization of intensity?  High kVp resulting in short wavelengths  High mA increasing # of x-rays produced  Longer exposure time  Shorter distance from the anode to target Time Distance Kvp mA How can you change this? Inverse Square Law Divide by ½ multiply by 4 = beam is 4x as intense multiply by 2, divide by 4 = beam is 1/4th as intense Types of Injury Ionization – o x-ray strikes pt tissue o Ejected electron interacts w/pt cells and is absorbed by tissue Free radicals (primary way) – o x-ray photon ionizes water around pt’s cells, changing the water into free radicals o Free radicals - neutral atoms w/ unpaired electrons in their outermost cell Dose Response Curve  Determines what level of radiation exposure is acceptable  DRC – used to correlate the damage in pt tissue to the radiation dose they received  graph used to chart damage against tissue Linear Relationship: o Tissue damage is directly proportional to dose of radiation received Non-Threshold: o No matter how small the dose of radiation is, there will always be biologic damage to pt tissues Sequence of Injury Latent o Time b/w exposure to x-rays and appearance of clinical signs of injury o Depends on dose received o More radiation = shorter latent period Injury

o Cellular injury Recovery o Cells repair from the damage caused by x-rays Cumulative – ex. cataracts o Additional radiation exposure occurs, unrepaired damage accumulate in tissues o Body cannot repair What characteristics make a cell sensitive to radiation? 1.Mitotic activity: How fast the cell divides 2.Cell differentiation: How mature/specialized a cell is 3.Cell metabolism: Cell’s metabolic rate Long term versus short term radiation effects Long term: Small amounts of radiation exposure over a long period of time - Seen after years, decades, or generations - Ex. Cancer, birth defects Short term: Large amount of radiation in a short period of time - Seen w/in minutes, days, weeks - Ex. Acute Radiation Syndrome “ARS” (nausea,vomit, hair loss, hemorrhage) Linear non threshold – stochastic What is the process of reduction? o Removal of exposed & energized silver halide crystals o Results in conversion of crystals into black metallic silver Steps in automatic processing 1. Prepare dark room (unless using daylight loader) Turn off overhead light, turn on safelight 2. Open Film(s) Unwrap packages carefully Recycle lead foil 3. Insert Film(s) Feed film into slot on machine for processing 1 at a time Allow ~10 seconds between each film to prevent overlapping 4. Retrieve Processed Film(s) Steps in manual processing 1. Development (radiolucent areas) Reduction of crystals to black metallic silver Softens emulsion

2. Rinse Remove rest of developing solution 3. Fixation (radiopaque areas) Clear unexposed crystals from film Hardens emulsion 4. Wash Remove rest of chemicals 5. Dry For handling Developing solution  Developing agent – Converts crystals into black metallic silver o Hydroquinone (black tones) & Elon (gray tones) 

Preservative – Prevents oxidation of the developer agents o Sodium sulfite

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Accelerator – Activates developer agents & softens emulsion o Sodium carbonate

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Restrainer - Prevents development of unexposed crystals o Potassium bromide

Fixing solution 

Fixing agent – Clears unexposed halide crystals o Sodium thiosulfate, ammonium thiosulfate

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Preservative - Prevents deterioration of the fixer agents o Sodium sulfite

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Hardening agent – Hardens gelatin o Potassium alum

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Acidifier – Neutralizes and stops further development o Acetic acid, sulfuric acid

Dark room o Safelights o Composed of long-wave re-orange light o Place 4 ft away from working area

Concepts of Panoramic Imaging 

Tomography: Image of one layer of the body while blurring other structures in other planes o Receptor and tubehead move around the patient 

Tubehead rotates in opposite direction of the receptor

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Pt remains stationary

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Rotational center o The axis (pivotal point) around which the receptor and tubehead rotate

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Focal trough “image layer” o 3D zone where structures are clearly demonstrated on a pano image

Panoramic versus Intra-oral Machines Collimator (Pano) – Lead plate with an opening shaped as a narrow vertical slit. Allows x-rays to pass through slit at about -10 degrees upward Lead apron (pano) – no thyroid collar, double-sided Traditional-Based Panoramic Type of film – Screen film Where film is loaded – w/in a cassette b/w 2 intensifying screens Intensifying screens – convert x-ray energy into light to expose the film 

Calcium tungstate (emit blue light) or rare earth (green light)

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Rare earth – faster, requires less x-ray exposure

Steps to taking Panoramic 1. Disinfect the panoramic machine Wipe-wipe machine, place barriers on exposure buttons Insert bite-block (sterilized, barriered, single use) If using film, load cassette in darkroom under safelight 2. Turn on the machine If digital, connect it to the digital software If the machine was already on/used, be sure to re-align the machine*** 3. Explain the procedure to the patient 4. Prepare the patient for exposure Place lead apron on the patient Have patient remove all objects from head and neck area that may interfere with exposure I.e. glasses, hearing aid, hairpins, any jewelry, intra-oral prosthesis

5. Adjust the machine to the patient Change the height of the machine to the patient Adjust the exposure settings to the patient 6. Position patient in the panoramic Patient to stand tall as possible Patient bites on the bite block Position **midsagittal plane perpendicular to the floor Position **frankfort plane parallel with the floor – from external auditory meatus to floor of orbit. Tragus of ear to ala of nose 7. Give patient final instructions Machine is going to rotate around head Emergency button if needed Keep still for entire exposure Position their tongue to the roof of their mouth during exposure Close lips around bite block 8. Leave room, expose image while watching patient What planes must be aligned Position **midsagittal plane perpendicular to the floor Position **frankfort plane parallel with the floor – from external auditory meatus to floor of orbit. Tragus of ear to ala of nose Errors of improper patient alignment - Frankfort plane upward o Chin is too high, reverse smile line - Frankfort plane downward o Chin is to low, exaggerated smile line - Midsagittal plane error o If pt’s head isn’t centered teeth appear un-equally magnified Panoramic machines can be modified w/ a cephalostat extension arm Lateral Jaw Projections o Body of mandible projection

 Evaluates fractures, impacted teeth, lesions o Ramus of Mandible Projection  Evaluate impacted 3rd molars, lesions, fractures of posterior mandible TMJ Projections o Transcranial Projection “Lindblom technique”  Evaluates superior surface of the condyle and articular eminence o TMJ Tomography  Examines TMJ Skull Projections o Lateral cephalometric  Eval facial growth, development, trauma, disease, developmental abnormality o Posteroanterior 

Eval facial growth, development, trauma, disease, developmental abnormality

o Waters 

Eval max sinus (sinus drips liquid)

o Submentovertex 

Identify position of condyles, base of the skull, fractures of the zygomatic arch

o Reverse Towne 

Identify fractures of the condylar neck and ramus region

3-D Imaging o Type of image – CBCT (cone beam computed tomography) o Advantages and disadvantages o Advantages 

Low radiation

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Pt cooperation

 More true image o Disadvantages 

Metal restorations interfere w/ imaging

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Lack of practitioner knowledge of interpretation

Direct versus Indirect Imaging o Direct Imaging 

Uses sensor that is exposed to radiation, then transfer info directly on the computer software to view

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Connected to computer w/fiber optic cable of wi-fi cordless

o Indirect Imaging 

Scans a sensor after exposure to radiation, then converts into digital form to be viewed on a computer

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Extra step of scanning

PSP (storage phosphor imaging plate) – Indirect imaging  Records diagnostic data  High-speed scanner converts info into electron files  Laser scans info from plate to computer as image  Less rapid than digital imaging o Reusable plate w/ phosphor coating o Flexible o Plate converts energy into light to create image o Must erase image after scanning o Careful handling and wrapping o Use 50x or more CCD (couple-charged device) – Direct imaging o Pixels on silicon chip size 20-40 um o When x-ray contacts CCD, results in release of electronic charge from electronic potential wells (specially arranged crystals) CMOS-APS (Complimentary Metal-Oxide Semiconductor-Active Pixel Sensor) – Direct o Built in control functions o Smaller pixels, lower power requirement o Has built in amplifying transistor in each pixel to improve signal output o Less expensive, connects thru USB to computer Silicone Chip Characteristics o Sensitive to x-radiation or light o Electrons on chip are divided into pixels, where electrons produced by x-ray exposure are deposited

o Pixel sizes vary based on sensor, influence image resolution Pros and Cons of Digital o Pros 

Superior grey-scale resolution 

256 grey shades

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Reduced pt exposure

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Speed

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Cost effective in long run

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Productivity and efficiency

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Enhanced diagnostics 

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Digital subtraction reverses black and white shades

Effective pt tool

o Cons 

Initial cost setup

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Sensor size

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Infection control

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Legal issues

Toothache triage Cold – recession (generalized) (NO XRAY), caries (localized, pain from sweets) (BWs) Hot – pulp inflammation (PA) Sweet – caries (BW) Bite – occusion (light pain on bite), PA abscess (severe pain on bite) Pt jumps during percussion test – infection, fracture Swollen/ Constant – periodontal abscess Panoramic film New box of film Darkroom Safelight Developer and fixer strength

Quality Assurance Panoramic film New box of film – Darkroom Safelight – check every 6 months for light leak 

Correct w/ weather stripping or black tape

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Coin test o Place coin on unwrapped film in darkroom for 3-4min. Remove coin o Process film; if there is no visible image of the coin- safelight is working

Developer and fixer strength o Developer strength  Reference radiographs to ensure unfogged & match densities  Stepwedge radiographs using aluminum step device to match densities  Normalizing device – monitors strength of chemicals and film density o Fixer Strength 

Prepare film and check for clearing, should clear w/in 2 min

Special needs pts o Gagging patient  Dental radiographer must remain confident in their ability & patience  Do not bring up gagging or ask  Limit time the sensor is in the patient’s mouth  Take molars PA’s last to prevent gag as long as possible  Reduce tactile sensation  Distract the patient How long to retain dental radiographs? indefinitely Refusal of radiographs 

Inability to treat pt

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Signing a refusal paper does not release dentist of liability

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Pt cannot sign to negligent care

Treating pregnant patients

 Cancer risks 

1 in 3 mil chance of developing cancer. No case reported...