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What are characteristics of electromagnectic radiation?
- no mass/weight
- can damage tissue
- emit energy in wave form
- travel @ speed of light (186,000 mi/sec)
What is ionization?
- when atom gains or loses an electron;electron displaced from its orbit
- process by which xrays cause damage
What is the significance of ionization?
process by which ionizing radiation produces biological damage
How much backround ionizing radiation is the average person exposed to annually?
What is the greatest source of man-made ionizing radiation to individuals?
Define wavelength & frequency & list significance?
- wavelength-distance between crests--determine penetrating power
- frequency-number of crests passing a fixed point per second--works hand in hand with wavelength(if u alter 1 u alter the other)so determines penetrating power *the shorter the wavelength higher the energy
Describe wavelengths & frequencies produced by low & hi kVp's?
- (HI)kVp=(low)wavelength & (HI)frequency
- (low)kVp=(HI)wavelength & (low)frequency
What should you do with your xray badge when you are having xrays exposed on urself?
you shouldn't wear it
What is LD(lethal dose) 50/30 for xrays?
LD 50/30 for humans= 450 RADS
List the cells in order of sensitivity going most to least sensitive to radiation?
- (Real Love Constitutes Entire Respect, Dont Namecall)
Define threshold exposure?
lowest dose that will produce a biological effect
Define latent period?
lag time between exposure and effect
What factors influence amount of damage produced by exposure to ionizing radiation?
- type of radiation
- toal dose
- dose rate
- cell type(radiosensitivity)
- volume of tissue exposed
- biological variations between species/people
Define primary & secondary radiation? Which do we as operators protect ourselves from?
- primary-radiation produced @ target(focal spot)
- secondary-radiation formed by interaction of xrays & matter
- (primary or useful beam??)
Define useful beam & who should be in it's path?
useful beam-radiation that is allowed to leave tubehead after collimation & filtration;only patient should be in path
What are characteristics of radiosensitive cells?
- immature (young/primative)
- not highly specialized
- high mitotic rate
What are characteristics of radioresistant cells?
- opposite of radiosensitive
- (old, specialized, low mitotic rate?)
Define acute & chronic effects of radiation? & what causes each?
- Acute(short term)- erythema, vomit, rear, disorientation, loss of hair & muscle tone. Caused by localized dose of radiation therapy or high dose of total body exposure.*not possible with dental xrays
- Chronic(long term)- genetic:passed on to offspring/somatic-all other cells in person radiated. Caused from earlier large doses or repeated low level doses.
Define somatic & genetic cells and give examples of each?
- somatic- all other cells besides genetic, occur in radiated patient, can repair within 24 hours
- genetic- passed to offsring, DNA, female/male chromosomes & genes, cannot repair
What do xerostomia & resulting radiation caries in a person recieving radiation therapy result from?
xerostomia(dry mouth), resulting caries, difficult swallowing, inflammed tissues all effects of radiation therapy due to: dysfunction of salivary glands
Define direct hit theory of ionization?
photon hits & damages a critical cell componant
Define indirect hit theory of ionization?
photon hits & damages a non-critical cell componant (H2O) produces free radicals
Define threshold & non threshold response theories of radiation exposure;which one do scientists believe in?
- threshold-lowest dose that will produce a biological effect
- non threshold-assumes some level of hazard is associated with all doses regardless of how small; scientists believe in this one that any dose produces damage
Define ALARA priciple?
- To keep radiation exposure- As Low As Resonably Acceptable
- responsibility of maximizing the quality of radiograph while minimizing the risk to the patient
What is formula for figuring the maximum accumulated dose?
- MAD=5(n-18) ex:36 yr old
- MAD=90 Rems
What is MPD for occupationally exposed persons per year? who belongs in this catagory?
- MPD(max. permissible dose)= 5 Rems/yr (or 50 mSv)
- in this catagory those 18 & up & not pregnant
What is MPD for non-occupationally exposed persons per year? who belongs in this catagory?
- MPD(max. perm. dose)= .5 Rems/yr (or 5 mSv)
- those not working with radiation, occupationally exposed- under 18, an operator that is pregnant
What catagory of MPD exposed does a fetus belong to?
civilian (non-occ. exp.) MPD= .5 Rems/yr
What is the most effective way to reduce radiation exposure to a person?
- For patient: *fast speed film/ collimatation(open-ended, lead lined, rectangular is best)/ filtration/ lead aprons(all films)/ thyroid collar(intraoral only)/ film holder/ good technique in exposing & processing
- For operator: stand behind barrier or rec. distance(6ft. & 90-135 degree from path)/ never hold film or tubehead during exposure
What are examples of personal monitoring devices? which is most reliable?
- ionization chamber(dosimeter)
- film badge
- thermoluminescent dosimeter(TLD)-most reliable
What is standard & international unit for measuring radiation exposure?
- standard unit- Roentgen (R)
- international unit- Coulomb
What is the standard & international unit for measuring the radiation absorbed dose?
- standard unit- radiation absorbed dose (RAD)
- international unit- Gray (Gy)
- *conversion 100 R's = 1 Gray
What is standard & international unit for measuring the biological effect(aka the dose equivalent)?
- standard unit- Roentgen equivalent man (REM)
- international unit- Sievert (Sv)
- *conversion 100 REMs = 1 Sv (xrays so small often expressed as millisieverts- mSv)
- *RADs x qualifying factor = REMs
What is recommended minimum distance & direction an operator should stand from source of radiation?
6 ft. away/ 90-135 degrees to side of beam
What is total body dose of exposure to radiation compared to localized dose?
- total body dose- total max. permissible dose & max. accumulated dose (MPD&MAD)
- localized dose -xrays are restricted/localized dose
- *total body dose = 1/10,000 of localized dose
Define filter & collimator?
- filter- (protective device) from unnecessary radiation by filtering out weak, non-penetrating xrays that would otherwise be absorbed by patient's face;made of aluminum
- collimator-(protective device) from unnecessary radiation by reducing volume of tissue exposed by restricting beam size to 2.75 inches; made of lead
Define Contrast? What factor causes hi contrast? lo contrast? and to maintain density?
- Contrast- differences in densities within a film that make image
- (HI)contrast & mnt. density= (de.)kVp + ^ time&mA
- (LO)contrast & mnt. density= ^ kVp + (de.)time&mA
Define density? What 2 control factors cause low & high density?
- density-overall blackness of image
- (HI)density= ^ mA or time
- (LO)density= decrease mA or time
When are xrays generated?
when electrons strike the tungsten target (focal spot)
What factor determine the quality of xrays? What factors effect quantity?
- quality- kVp
- quantity- mA & time
Define Bremsthrahlen & Characteristic radiation?
- Bremsthrahlen- electrons interact with nucleus of target atom
- Characteristic- electrons interact with outter shell electron
Define foreshortening & elongation?
- forshortening- appear shorter caused by excessive vertical angulation
- elongation- appear longer caused by insufficiant vertical angulation
What is MAS & MAI?
- MAS- mA/second
- MAI- mA/impulse
What is Inverse Square Law?
- the intensity of the xray beam varies inversely with the square of the change in distance
- if distance is halved, the square of the chnage in distance is 1/4 & new intensity is 4x greater than original
- if distance is doubled, the square of the change in distance is 4 & the new intensity is 1/4 as great as original