-
What are characteristics of electromagnectic radiation?
- invisibe
- 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?
3.60 mSv/year
-
What is the greatest source of man-made ionizing radiation to individuals?
medical/dental xrays
-
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?
- Reproductive
- Lymphatic
- Circulatory
- Endocrine
- Respiratory
- Digestive
- Nervous
- (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
- age/health
- 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 erythema?
skin reddening
-
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=5(36-18)
- 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
|
|