Test #3 Flashcards
Why do you use intensifying screens?
Because they amplify the remnant radiation & they decrease pt dose
These convert the energy of the x-ray beam into visible light by utilizing certain chemical compounds which produce light when expose to x-ray photons
Intensifying screens
This covers & protects the phosphor layer. Helps resist abrasions & static electricity
Protective Coating
This is the active layer that emits light when stimulated by x-rays
Phosphor
Type of active layer that emits blue light. Used w/ blue sensitive film. Oldest type.
Calcium tungstate
Type of active layer that emits green light. Used w/ green sensitive film
Rare earth
Why are rare earth screens better than calcium tungstate screens?
3-4x better at converting photon energy into light = decrease pt. dose.
Better light producing charac. over the range of kilovolt values.
What is the reflective layer made out of?
Magnesium oxide or titanium oxide
What does the reflective layer do?
Redirects the light toward the film - double the photons reaching the film
This layer provides the mechanical support for the phosphor
Base
What is the base layer made out of?
Polyester, metal, or card board
This is the relative number used to quantitate the efficiency of conversion of x-rays to light
Screen speed
What are the charac. of a faster screen speed?
More light emitted for the same exposure
Decrease pt dose
Have poorer recorded detail
Increase density
Angiography rare earth screens have what two advantages?
Require less exposure time = decrease pt dose & decrease pt. motion
Increase tube life
Holder that contains the screens & holds the film
Cassettes
What are the front & back of cassettes made of?
Front - plastic or graphite
Back - lead lined to prevent back scatter
What are examples of how to care for screens & cassettes?
Mark the outside of cassette & inside of screen w/ # Mark date of purchase on cassette (last 7 yr) Use proper film/screen combo Do screen test Clean screens at least every 3 mos. Don't touch screens Don't stand on plastic cassettes Light leaks indicate black edges on film
What is involved in image acquisition in CR?
Filmless cassette
Imaging plate: latent image is formed in the photostimulable phosphor
Wider latitude than conventional x-ray = better visualization of soft tissue & bone
What are the 3 primary stages of computed radiography (CR)?
Image acquisition
Image processing
Image display
What is the advantages of image display in CR?
Displayed on a high resolution monitor
Can print onto film
Can send to distant location
Can store on a disc
What are the steps involved in manual (hand tanking) processing?
Wetting Developing Stop Bath Fixer Wash Dry
What is the purpose of wetting during manual processing?
Causes the emulsion to swell allowing for chemicals to penetrate
What occurs during the developing step of manual processing?
Converts the latent image to manifest image
Chemically reduces the silver ions to metallic silver
If film oxidizes w/ air, it turns brown
What is the active ingredient in the Stop Bath?
Acetic acid
This stops development by neutralizing the developer & removes excess chemicals from the emulsion
Stop bath
This treats films so the image will not fade & will remain permanent. Ammonium thiosulfate clears undeveloped silver halide.
Fixer
During this step, water removes any residual fixer.
Wash (if fixer isn’t completely removed film could turn brown)
What steps are different b/w automatic processing & manual processing?
Wetting occurs during the Developer step
Acetic acid is in the fixer so no Stop Bath step
Overall, automatic occurs much faster than manual (90secs vs 1hr)
The removal of silver from the used fixer solution as fixer removes the unexposed silver halide from the film
Silver Recovery
What are the two types of Silver Recover?
Metallic replacement: steel wool or foam that is impregnated w/ steel wool
Electrolytic: Electrically charged disc or drum to attract the silver (most efficient & expensive type)
Type of artifact that run the length of the travel direction of the film, usually 1” apart
Guide shoe marks
What causes Guide Shoe Marks?
Rough handling of rollers during cleaning, warped plastic rollers
Lines are black = developer section
Lines are white = fixer or wash section
This artifact is caused by kinking film w/ finger or fingernail
Crescent moon marks
This artifact is caused by inadequate or improper chemistry
Chemical Fog
This artifact is when there are yellow, green, blue, or purple runs on the film. It is caused by chemistry not being squeezed from film d/t warped rollers or processor is running to slow
Curtain effect
This artifact causes tree-like black jagged lines or smudges.
Static (caused by static in the room, carpet)
This artifact is caused by light leaks, primary beam, safe light too close
Light or radiation fog
This artifact is when there is greater density (darker) than the area of the x-ray surrounding it
Plus density
This artifact is when there is less density (lighter) than the area of the x-ray surrounding it
Minus density
What is Emulsion Pick Off (artifact) caused by?
Dirty rollers
This artifact is when yellow/brown stains appear over time. Caused by not all of the (fixer) thiosulfate is removed in the wash. Wash-water contaminated, not clean
Hypo/Hyporetention
What equipment is used to monitor the processor?
Thermometer
Sensitometer
Densitometer
Dedicated film supply
This measures the light transmitted through the tablet (film). It detects small changes in optical density that occur when the film is fogged.
Densitometer
This places a known light exposure onto the film & results in an image gradient of 21 different steps/degrees on the film
Sensitometer
What 3 factors are used when analyzing the tablet?
Base + fog density
Speed index
Contrast index
What is involved w/ base + fog density?
Read at the zero exposure step (step #1)
Normal should not be >0.30 OD
If > 0.25 the problem may be in the imaging system itself or the film storage facilities
What is involved w/ the Speed Index (Mid density)?
Record the step # that reads 1.00-1.20 OD (should #11)
Same step should be used each time that you do the test
Increasing what processing factors will increase density?
Processing temp
Development time
What processing factors would decrease density?
Under replenishment of the developer
Oxidation of processing chemicals
Too low processing temp.
Too short development time
This artifact occurs every 3.14”. Caused by dirty rollers or flat edge on roller.
Pi Lines
Increasing what technical factors would increase density?
mAs
kVp
Film screen speed
Increasing what factors would decrease contrast?
kVp
mAs
Development time
Unit of radiation exposure that will liberate a charge of 2.58x10(-4) coulombs per kg of air. It is the approx. exposure to the body surface for a radiographic view. Intensity of the beam
Roentgen (R)
Radiation measuring instruments are calibrated in what? Output of x-ray machines are also specified in this unit of measure
Roentgens
This is the amount of radiation energy absorbed into a given mass of tissue.
Rad (Radiation absorbed Dose)
1 Rad is equal to what?
Radiation necessary to deposit 100 ergs(?) in 1 gram of irradiated material
The number of Rads deposited per roentgen of exposure varies w/ what two factors?
Energy of the x-ray beam
Composition of the absorber
1 joule/kg is equal to how many Grays?
1 Gray (gy)
1 Gray is equal to how many Rads?
100 Rads
The avg CXR gives a dose of what?
10 millirads (mrad)
What amount of Grays delivered to the whole body over a short period of time can be deadly?
3-4 Gray
The unit of absorbed dose equivalent. Measures the energy per unit mass times adjustments for the type of radiation involved (quality factor) & the biological response in the tissue (a weighted factor)
REM (Rad Equivalent Man)
What are 3 features of REM (Rad Equivalent Man)?
It converts dose into a measured risk
It is only used in radiation protection
It is a measure of biological effectiveness of radiation
Why are personnel monitoring devices (Dosimeters/film badges) analyzed in REMs?
b/c it takes into account the biological effects of different types of radiation
1 Sievert (Sv) is equal to how many mrem?
100,000 mrem
This is a device used for the measurement of exposed dose
Dosimeter
The effectiveness of a dose is dependent on what?
Dose-rate
This is a dose of radiation that in light of presnet knowledge would not expect to produce significant radiation effects
MPD (maximum permissible dose)
Cumulative MPD is equal to what?
5(n-18)rem n=age in years
What is the annual MPD?
5 rem = 5000mrem = 50m SV/year
This is a unit of radioactivity. It quantifies the amount of radioactive material & not the radiation emitted. It is the amount of material in which 3.7x10(10) atoms disintegrate every second
Curie (C)
This type of radiation is somewhat shielded by the atmosphere so the dose is higher at higher altitudes
Cosmic Radiation
For every 200ft increase in altitude, cosmic radiation dose increases to what?
Increase dose of 1 mrem/yr
What are 3 types of rocks that emit radiation?
Uranium
Coal
Granite
What is an example of a nutrient that emits radiation?
Potassium
This is a radioactive gas that comes from inside the earth. Sometimes it gets trapped inside of homes coming through foundations & basements
Radon
What are examples of things that cause man-made background radiation?
X-rays Medical isotopes TV Smoke detectors Nuclear fuel Weapons fallout
What is the normal annual exposure from natural radiation?
300 mrem/yr
What is the normal annual exposure from man-made radiation?
70 mrem/yr
The biological effect of radiation is what?
Ionization (free radicals which can change chemicals in the body)
What are effects of DNA damage sustained from radiation?
Gene expression Gene mutation Chromosome Aberrations Genomic Instability Cell killing
This type of DNA damage from radiation is when the gene responds by changing its signal to produce protein; this may be protective or damaging
Gene expression
This type of DNA damage from radiation is when a gene may be changed so that it can’t make its corresponding protein properly
Gene mutation
This type of DNA damage from radiation may trigger programmed cell death. If only a few cells are affected, this prevents reproduction of damaged DNA & protects the tissue
Cell Killing
This is caused by damage to organs or systems after very high whole body doses. The symptoms depend upon the dose & time of exposure
Radiation Sickness
Give examples of the effects of radiation sickness based on time of exposure i.e. minutes, days, weeks, months, years
Minutes = CNS Syndrome Days = GI Syndrome Weeks = Hematopoietic Syndrome Months = Birth defects, LD 50 Years = Cancer
According to the U.N. Health Agency, this poses a greater long term health risk than radioactive particles in the air
Contaminated food
What are some effects of fetal radiation?
Prenatal death Neonatal death Congenital malformation Childhood malignancy Diminished growth & development
What is the Law of Bergonie & Tribondeau?
Radiosensitivity is a function of the metabolic state of the tissue being irradiated
What are examples of cells/tissues that are more radiosensitive than other?
Stem cells as compared to mature cells
Younger tissues & organs
Cells w/ high metabolic activity
Cells w/ a high rate of proliferation
What are 4 cell types that have a high radiosensitivity?
Lymphocytes
Spermatogonia
Erythroblasts
Intestinal crypt cells
What are 4 cell types that have an intermediate radiosensitivity?
Endothelial cells
Osteoblasts
Spermatids
Fibroblasts
What are 3 cell types that have a low radiosensitivity?
Muscle cells
Nerve cells
Chondrocytes
This is the dose of radiation to the whole body that will result in death w/i 30 days to 50% of the subjects irradiated
LD 50/30
What is the LD 50/30 for a human?
300 rad
This is the rate energy is deposited in tissue as ionizing radiation
L.E.T. (Linear Energy Transfer)
What is the L.E.T. of diagnostic x-rays?
3 ke V/um
Why is it difficult to determine if low doses cause cancer?
Background radiation is often higher than the level of added exposure
There is a high & variable rate of cancer in human populations
There is no way to tell a radiation induced cancer from a spontaneous cancer
Low doses show different biological responses than high doses. Name 3
Increased activity of repair genes
Adaptive response
Cell/cell communication
What are 3 cardinal principles of radiation protection?
Time: keep the time of exposure as short as possible
Distance: maintain a large distance b/w the exposed person & source of radiation
Shielding: Insert shielding b/w the source & exposed person (lead/concrete)
10 rads during the first 2 wks of pregnancy can have what effect?
1/10 will experience spontaneous abortion, if not, preg. goes to term w/o ill effects
10 rads during the 2-8 wks of pregnancy can have what effect?
1% will have congenital abnormalities
At what dose of rads should a pregnant woman consider an abortion?
> 25 rads
When a x-ray tech. becomes pregnant, what should they do?
Inform employer ASAP
Wear lead apron w/ monitoring badge on collar & one under apron to record fetal dose
What are some preventative measures used to protect pregnant women?
Have a consent signed for preg. release by all females of childbearing age Practice 10 day rule Gonandal shielding Control access to x-ray room Preg. tests Post signs in the x-ray room
What is the 10 day rule?
10 day interval following the onset of menstruation is the only time when it is most unlikely a woman could become preg. It is only during this time that you should x-ray the Lsp, pelvis, hips, sacrum or coccyx
When should gonadal shielding be used?
When the gonads lie w/i the primary x-ray field or w/i 5cm off the edge of colimation
What level of attenuation of x-rays should gonadal shielding provide?
At least equivalent of .25mm of lead
Increasing what technical factors would decrease density?
Body part thickness Mass density of body part Grid ratio SID Collimation
Increasing what factors would increase contrast?
Film speed
Collimation
Grid ratio
This type of DNA damage from radiation is when the entire chromosome may break, recombine in an abnormal way or sometimes parts of two different chromosomes may be combined
Chromosome aberrations
This type of DNA damage from radiation may produce later changes that contribute to cancer
Genomic Instability
What are the 10 basic radiation control principles?
Understand & apply the principles of time, distance, & shielding
Don’t allow familiarity to result in a false sense of security
Never stand in the primary beam
Always wear protective apparel when not behind a barrier
Always wear a personnel monitoring device
Never hold a pt
Person holding a pt should wear a lead apron
Used gonadal shielding
Observe 10 day rule
Always collimate to the smallest field size
