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13 Cards in this Set
- Front
- Back
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exposure time |
interval at which x-rays are being produced controls the quantity of the x-ray beam double the exposure, double the number of x-ray photons exposure unit is roentgen (R) |
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tube current |
same function as exposure time in controlling quantity of x-ray beam higher tube current, more electrons released from filament, more x-ray photons produced double the tube current, double the x-ray photons produced |
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beam quantity |
expressed as the product of exposure time and tube current |
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tube voltage |
as tube voltage is increased, there is increase in kinetic energy of each electron, thus an increase in: number of photons generated mean energy max energy tube voltage controls beam quality |
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filtration |
removes lower energy photons from x-ray beam common materials: aluminum, copper filtration required for dental x-rays: 1.5mm of aluminum up to 70kVp 2.5mm of aluminum for all higher voltages half-value layer: absorber thickness required to reduce the intensity of the original beam by one half |
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collimation |
collimator reduces size of beam, scatter radiation, patient exposure made of metal (usually lead) PID is used as a collimator in dental radiography |
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influence of source-object on x-ray beam |
distance from object to source of radiation is increased >> x-ray intensity at object decreases relationship between distance and intensity of radiation is known as inverse square law |
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inverse square law |
intensity of radiation is inversely proportional to the square of the source-object distance I1/I2 = (D2/D1)squared increased distance decreases intensity: attenuation and divergence |
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beam attenuation |
reduction in intensity of x-ray beam absorption attenuation: x-ray beam deposited in absorber electrons deflection (scatter) attenuation: x-ray photons that are deflected from their original path different attenuation of tissues to x-ray beam is what forms the diagnostic base of x-ray machines 3 factors of attenuation: object's thickness object's density kVp |
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three x-ray interactions with matter |
coherent scatter (simple scatter): more in low energy photons 10% photoelectric effect: the most significant, contributes to diagnostic dental radiograph 30% incoherent scatter (compton interaction): scatter radiation that degrades image 60% |
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dose or absorbed dose |
measure of energy that is absorbed per unit mass measured in units of Gray (Gy) 1Gy = 100 rads |
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equivalent dose |
same as absorbed dose different linear energy transfer (LET) causes a different biologic effect used to compare biologic effect of different types of radiation on different tissues or organs measured in units of sievert 1 sievert = 100 rems used to estimate the risk in humans, different tissues have different sensitivities to radiation exposure |
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dosimetry |
determination of the quantity of x-ray exposure or dose ionization chamber: consists of air and electrodes measures exposure or absorbed dose film badge: measures film density (blackness) good for professional monitoring fluorescence (???) |
