Term
| characteristics of X-rays |
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Definition
| travel in straight lines but can be diverted, electromagnetic radiation, ionizing radiation, able to penetrate matter if energy is high enough, energy can be absobed by matter if energy is too low to penetrate |
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Term
| types of pathways x-rays can take |
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Definition
| absoption, penetration, partial absorption and forward scatter, partial absoption and backward scatter |
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Term
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Definition
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Term
| what do differences in attenuation between different tissues allow? |
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Definition
| allows the image to be established....radiographs are shadow-graphs |
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Term
| 3 parts of an xray device in clinic |
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Definition
| 1: anode, x-ray tube, cooling oil and step up transformer 2: beam indicating device/spacer cone 3: timer, settings, mA and kV changes |
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Term
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Definition
| an x-ray tube characteried by a vacuum glass tube in an oil bath...for cooling purposes |
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Term
| differences between anodes in dental and medical machines |
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Definition
| dental machines have stationary anodes while medical machines have rotating anodes which move so as to reduce the heat and therefore wear of the machine so it lasts longer bc x-rays are taken over a longer period of time |
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Term
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Definition
| filters the lower energy x-rays out of the specturm which results in an overall higher x-ray energy output producing a more quality picture |
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Term
| what does no filtering of x-rays lead to? |
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Definition
| results in more radiation absorption by the patient's tissues (the low energy x-rays will not penetrate the tissues and subsequently hit the image receptor). Produces a poor image |
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Term
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Definition
| via beam collimation through differnt shaped filters and shape focusing attachments |
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Term
| smaller surfaces irradiated results in what |
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Definition
| less scattered radiation and lower radiation dose |
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Term
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Definition
| it reduces the surface that is being irradiated. The latter results in less scatter (better image quality) and lower rdaiation dose |
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Term
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Definition
| analog films, photostimulable phosphor storage plates (PPSPs), solid state sensors (CCD) |
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Term
| what are solid state sensors |
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Definition
| CCD - charged coupled devices and CMOS-complementary mtal oxide semiconductors = active pixel size) |
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Term
| pros and cons of solid state sensors aka direct digital radiography |
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Definition
| cons: volume of the sensor is substantial, hardware and cable limits which patients can handle them. Also, the actual size of the sensor is significantly smaller than the size of the captor which is a serious limitation Pros: easy to use and fast image acquisition and no possibility of double images |
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Term
| pros and cons of photo stimulable phosphor plates aka indirect digital radiography |
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Definition
| cons: latent image is captures and is sensitive to white light (erases image). Red helium neon laser scan is needed, a photomultiplier tube captures the light and via an analog digital converter the image is displayed on a computer screen. Double images ARE POSSIBLE. Pros: all sizes are available and physical dimensions like analog intraoral film packet |
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Term
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Definition
| the latitude of an image receptor is the difference in minimal and maxilmal exposure time to which the receptor can be exposed |
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Term
| what does minimal exposure time correspond to |
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Definition
| to the minimal grey value that will still be detectable. |
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Term
| what does maximal exposure correspond to |
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Definition
| to the maximum grey value that will still be detectable |
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Term
| what happens below the minimal exposure time or above the maximum? |
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Definition
| below the minimal...shows a white image (no exposure detected). Above the maximum exposure time the immage receptor will show a pitch black image (too much exposure detected)...meaning there is a happy medium to be found in x-ray exposure |
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Term
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Definition
| has a wider latitude than a solid state sensor, because the relationship between optical density and exposure time is truly linear in PSPP |
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Term
| solid state sensors and latitude |
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Definition
| shows a linear relationship between optical density and exposure time, but its slope is very steep. This results in a more narrow latitude compared to PSPP |
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Term
| overexposure of a solid state sensor |
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Definition
| results in over saturation of the sensor with light and hence a shiny black image on the screen. The software cannot change that. The PSPP is more "forgiving" |
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Term
| why can one gain a usable diagnostic image after unintentionally exposing a patient too long |
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Definition
| because of the wider latitude of PSPP..due to the true linear relationship between optical density and exposure time |
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Term
| justification principle of x-rays |
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Definition
| one does not take a radiograph if the same information can be obtained in any other way. One does not take a radiograph if the patient is not capable of coping with the procedure. The benefit has to outweigh the risk for the patient. |
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Term
| limitation principle of radiographs |
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Definition
| one should always strive to keep the dose to the patient as low as possible...ALARA - as low as reasonably achievable |
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Term
| optimization principle of radiographs |
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Definition
| one should always strive to obtain the best image quality possible, but with both previous principles in mind |
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Term
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Definition
| never hold the receptor/sensor/film. If someone has to help holding the detector, let a parent or care giver do it, while that person wears a lead apron. Never stand in the primary beam. Brick wall/lead equivalent thickness wall. if you cannot keep safe distance, wear lead apron with thyroid shielding |
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Term
| what is the inverse square law |
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Definition
| at a distance of 2 meters, the radiation beam is only at 1/4 of its original energy anymore...at 3 meters its 1/9th etc. |
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Term
| if no barrier is available how should a practicioner stand? |
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Definition
| at least 6 feet from the patient, at an angle of 90135 degrees to the central ray of the x-ray beam when the exposure is made |
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Term
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Definition
| its the measure of the amount of energy absorbed from the radiation beam per unit mass of tissue. AKA 1 unit = gray (Gy) = J/kg |
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Term
| what is the equivalent dose |
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Definition
| this is the measure which allows the differnt radiobiological effectiveness of different types of radiation to be taken into account. unit = sievert (Sv). Each type of radiation obtains a radiation weighting factor "Wr" |
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Term
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Definition
| a radiation weighing factor. Wr for x-rays = 1. Wr for alpha particles is 20 while the Wr for protons and fast neutrons = 10 |
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Term
| what is the effective dose |
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Definition
| this measurement allows doses of different investigations of different parts of the body to be compared, by converting all doses to an equivalent whole body dose. SEveral tissues are assigned a so called tissue weighting factor "Wt"...the more radiosensitive the organ, the higher the Wt...adding all the Wt results in a value of 1 |
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Term
| equation for the effective dose |
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Definition
| E = H x Wt....where H equals D (radiation dose) and E = the dose refferred to in general terms. |
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Term
| important concept to keep in mind regarding the number of dental exposures and the individual |
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Definition
| the individual doses encountered in a dental radiology may appear very small, however, one should never forget that the diagnostic burdne is an additional radiation burden to that which the ptient is already receiving from all types of backround radiation. Never forget that the number of dental exposures is significantly higher than from any other diagnostic radiation investigation |
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Term
| organs and ionizing radiation |
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Definition
| not all our organs are sa sensitive to ionizing radiation because of the tissue weighting factors. The younger, the more sensitive and vulnerable. The faster the tissues or cells grow and multiply, the ore sensitive and vulnerable...especially the head and neck (salivary glands, thyroid, lens of the eye, brain) |
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Term
| deterministic effects of ionizing radiation |
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Definition
| effect of ionizing radiatoin is proportional to the energy of the raditaion. There is a certain threshold dose under which no results will appear - but once that threshold is exceeded, the results will definitely occur |
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Term
| the is the stochastic effect of ionizing radiation |
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Definition
| there is a probability that certain effects will appear - the effect is not proportionte to the energy of the ionizing radiation. there is no threshold dose, so the effect can occur with any dose |
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Term
| the dentists responsibility in administering an x-ray |
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Definition
| the dental profession is committed to delivering the highest quality of care to each of its individual patients and applying advancements in technology and science to continually improve the oral health status of the US popoulation. However, the dentist must weigh the benefits of taking dental radiographs against the risk of exposing a patient to X-rays, the effects of which accumulate from multiple sources over time |
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Term
| what are guidlines of radiation intended for |
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Definition
| intended to serve as a resource for the practitioner and are not intended as standars of care requirements or regulation. |
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Term
| ways to limit radiation exopsure - advise |
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Definition
| 1: fastest detectors, 2: collimation of the X-ray beam 3: proper exposure techniques 4: protective aprons and thyroid collars when appropriate 5: limit the number of images 6: receptor holders for BW and peri-apicals 7: staff and operator protection 8: hand-held devices (always protection shield)!! |
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Term
| maximum permissible anual dose of ionizing radiation for health care workers |
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Definition
| 50 mSv...equivalent of 25,000 peri-apicals |
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Term
| maximum life time dose of IR |
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Definition
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Term
| if the annual radiation dose s more than 1 mSv/y, a health care worker should do what |
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Definition
| wear a doimeter, while pregnant health care workers should ALWAYS wear a dosimeter |
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