Radiology ch 3-5
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carolammons7 on November 13, 2009
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91 terms
Terms | Definitions |
|---|---|
 object density | teeth, bone, soft tissue- determined by the structure of the object being radiographed |
| film density | the degree of blackness on a film |
| contrast | the difference in the degrees of blackness on the film between adjacent areas |
| object contrast is determined by | thickness of the object, density of the object, chemical composition of the object, quality of the x-ray beam and scatter radiation |
| short scale contrast films | high-contrast films, appear mainly in black and white, 65 kVp, may not reveal early pathologic changes |
| long scale contrast films | low contrast films, many gray tones, 90 to 100 kVp, early detection of bone loss and incipient decay |
| image detail | the visual quality of a radiograph that depends on definition or sharpness, measured in line pairs per millimeter |
| factors that influence detail | size of the tube focal or target area, FFD, OFD, movement of patient, film or tube, type of intensifying screen(if used) and image contrast |
| penumbra | the unsharpness or blurring that surrounds the edge of a radiographic image |
| umbra | the sharp area of a radiographic image |
| how to keep the penumbra as small as possible | using a small focal spot, angulation of the target, an increased FFD and a small OFD |
| size of tube focal area | the smaller the focal area at the anode, the better the image detail will be, the heat produced limits how small the focal area can be |
| how is the focal area in the tube tilted | usually at an angle of 20 degrees to the cathode |
| an ideal radiograph can be made by | establishing a maximum FFD, determining a minimal OFD and positioning the object and the film parallel to each other in their long axes and the central ray perpendicular to both |
| maximum FFD | the distance between the focal spot at the anode and the film in the patients mouth, the maximal distance allows the more parallel rays from the center of the x-ray beam to strike the object and the film |
| minimal OFD | the tooth and the film should be as close together as possible- the closer they are, the less enlarged the image is on the film |
| best FFD choice | 16 inches |
| most common FFDs | 8, 12 and 16 inches |
| FFD that may cause magnification | 8 inches or less |
| inverse square law | an expression of the relationship between the exposure time and FFD. " the intensity of radiation is inversely proportional to the square of the distance between a point source and the irradiated surface " |
| paralleling technique | the film is held parallel to the long axis of the tooth, results in an increased OFD in most areas of the mouth, to compensate, use a increased FFD |
| bisecting-angel technique | the film is held as close to the tooth as possible, the central x-ray is directed vertically perpendicular at an imaginary line that bisects the angle formed by the long axis of the tooth and the film packet |
| first x-ray package | 1896-1913/ consisted of glass photographic plates or film cut into pieces and hand wrapped by the dentist in black paper or rubber dam |
| year Kodak introduced first prepackaged x-ray film | 1913/ still made by hand |
| year first machine-made x-ray packet was introduced | 1921 |
| child size film packet # | #0 |
| narrow anterior film packet # | #1 |
| adult size film packet # | #2 |
| Occlusal film packet # | #4 |
| long bitewing packet # | #3 |
| film packet contents | waterproof outer layer, black paper, film, lead foil |
| double film packet | a film packet that contains two pieces of film |
| x-ray film is composed of | a clear cellulose acetate film base that is coated with an emulsion of silver halide(usually silver bromide) grains suspended in a layer of gelatin |
| film sensitivity | determines how much radiation for what period of time(mAs) is needed to produce an image on the film |
| film speed is designated by | American National Standards Institute (ANSI) |
| film speed we use at school/slowest film recommended for use | D-speed film |
| fastest film speed | F-speed film |
| film contrast | the characteristic of the x-ray film that enables it to portray differences in subject contrast |
| film fog | all or part of the radiograph is darkened by sources other than the primary beam |
| film fog may be from | imbalanced or exhausted processing solutions, unintentional exposure from light leaks, scatter radiation |
| duplicating film | a reversal film used to replicate original images |
| intensifying screen | a coating of flourescent material on a suitable base that intensifies the radiation, thus permitting a decrease in exposure time |
| What is the patient objective in taking dental x-rays? | to use the least possible amount of radiation to obtain the greatest diagnostic yield |
| What is the dental professional objective in taking dental x-rays? | to achieve occupational radiation as close to zero as possible |
| X-rays interact with | all forms of matter |
| interaction can result in | absorption of energy and thus attenuation of the x-ray beam( a reduction in the intensity of the beam) and the production of secondary radiation |
| X-ray energy absorbed by the tissue causes | chemical changes that result in tissue damage, two mechanisms for this change are ionization and free radical formation |
| The thicker the material that an x-ray beam must penetrate | the more x-ray will be absorbed |
| what determines x-ray absorption? | thickness of material, the atomic configuration- the number of orbiting electrons and the numbers of protons and neutrons in the nucleus of the atom |
| four possibilities can occur when an x-ray photon interacts with tissue | No interaction, Thompson scatter, Photoelectric effect, Compton effect |
| No interaction when a x-ray photon interacts with tissue | 9% of the time, no ionization |
| Thompson scatter when a x-ray photon interacts with tissue | 8% of the time, no ionization |
| Photoelectric effect when a x-ray photon interacts with tissue | x-ray photon can collide with an orbiting electron, giving up all its energy to dislodge the electron from its orbit. photoelectron produced has a negative charge and remaining atom has a positive. 30% of time, Ionizing |
| Compton effect when a x-ray photon interacts with tissue | x-ray photon can collide with a loosely bound electron in an outer shell of the atom and only give up part of its energy in ejecting the electron from its orbit. results in a negative charged, ejected Compton electron , a photon of scattered radiation, and a remaining atom that is positively charged. 62% of time, Ionizing |
| Radiobiology | the study of the effects of ionizing radiation on biologic tissue |
| Free radical | an uncharged molecule with a single unpaitred electron in its outer ring, very unstable, exists for only about 10 seconds |
| How do free radicals stabilize themselves? | by recombining to form a stable molecule that will not cause tissue damage or by combining with other free radicals, which will cause changes or the production of a tissue toxin such as hydrogen peroxide |
| damage to biologic molecules- indirect effect | by far the most prevalent, the free radicals that are formed as the result of the ionization of water go on to form toxins that injure or alter cells |
| damage to biologic molecules- direct effect | x-ray photons directly hit critical areas within the cell and cause damage to those particular cells (e.g., DNA) |
| Conventional units of radiation measurement | roentgen, radiation absorbed dose (rad) and Roentgen equivalent man (rem) |
| new units of radiation measurement/ International system of Units (SI) | Coulomb per kologram (C/kg), Gray (Gy), and Sievert (Sv) |
| 1 rad= ? Gy | 0.01 |
| 1 Gy= ? rad | 100 |
| millirem= ? rem | 1/1000 |
| dose equivalent | a concept that allows for the fact that not all radiations are identical in biologic effects. expressed in rems or sieverts |
| 1 rem= ? Sv | .01 |
| 1 Sv= ? rem | *100 |
| In terms of the effects of dental radiation, the rad (gray) is identical to the | rem(sievert) |
| In terms of the effects of dental radiation the roetegen is approximately equal to both | roentegen=rad=rem |
| Exposure | the amount of ionization in the air produced by x-rays or gamma radiation, it is the quantity of radiation in an area to which the patient is exposed, expressed in roentgens (C/kg) |
| Dose | the amount of energy absorbed per unit mass of tissue at a particular site, expressed in rad(grays) or rem (sieverts) |
| localized exposure | the measurement of radiation to the area of the body that is in the path of the direct beam of radiation, A rad of radiation to the localized area means that each gram of body tissue in that area absorbs 1 rad |
| total body exposure | each gram of of tissue in the entire body absorbs the rad(s) |
| total body exposure from a dental radiograph is | 1/10,000 of the facial exposure |
| Dose area | different parts of the body that absorb radiation other than the main target; IE skin dose, thyroid dose , etc |
| Dose-response curve | illustrates the possible biologic responses to a harmful agent such as ionizing radiation; can be linear (response is directly proportional to the dose) or non linear (response not proportional to dose), threshold or non-threshold |
| The prevailing consensus is that low-dose, ionizing radition is a | liner, nonthreshold relationship |
| Somatic effects | effectt on all cells in the body with the exception of reproductive cells |
| Genetic effect | changes in the genetic cells cannot be detected in the exposed patient but are passed on to succeeding generations; also called mutations |
| Acute (short term) effects | result from high doses of whole body radiation; effects vary from mild to death and may take minutes, hours, days or weeks to show themselves; lethal whole body dose is 450 RAD |
| Chronic (long term) effects | may be seen years after the original exposure; acute and/or chronic exposures may produce cumulative effects on both the somatic and/or genetic cells |
| Latent period | the time that elapses between the exposure to ionizing radiation and the appearance of clinical symptom; time can vary from hours to years depending on exposure and tissues involved |
| Critical organs | designated as critical because they are exposed to more radiation than others when dental radiographs are taken; skin, thyroid, eye lens, hematopoietic tissue, genetic tissue |
| ALARA principle | As Low As Reasonably Acheivable; the radiation exposure to our patients should be reduced as much as possible within the dental office without excessive cost or inconvenience to the patient |
| Maximum permissible dose for the dental professional | 5000mrem (50mSv) |
| Skin exposure risk | erythema (reddening of the skin); 250R in 14 days; |
| exposure risk for eyes | 200,000-500,000 mrem |
| Thyroid exposure risks | cancer; 6rad |
| Bone marrow exposure risks | FMX would only affect 5% of total red bone marrow in body; FMX every four months for the rest of your life would be the same as living in Denver |
| Gonads exposure risk | sterilization; impossible in dentistry; 400R in male, 625 in female |
| Pregnancy exposure risks | none except possible low birth weight due to thyroid exposure which can be reduced to 0 with thyroid collar; dental professional has no exposure risk and can carry out job duties |
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