rad tech midterm 2 cards Flashcards
how many screen in one cassette?
2
how many emulsion layers are in one cassette?
2, 1 on each side of the polyester
Over 99% of the x-ray image is formed by
screen light
Luminescence
The emission of light from a substance bombarded by radiation
Fluorescence
process of glowing only while being excited (during irradiation) and will cease glowing at completion of the X-??ray exposure
Phosphorescence
afterglow
radioparent
not have a habit of absorbing X-??rays
Reflective layer of screens is made of
titanium dioxide
are rare earth phosphors and are about 4X more efficient than the old Calcium Tungstate technology
Gadolinium, lanthanum, yttrium
Adjusting mAs for changing screen speed is done by
Speed1/ speed 2 X mAs1 = mAs2
Screens should be cleaned
monthly unless busier practice
Focal areas of exposed film in the shape of a
bolt of lightening
Mammography film is an example of
?single emulsion film?
The emulsion on film is
Silver halide microcrystals
latent image
The pattern of exposed and unexposed crystals on a film; -this is BEFORE development in the processor
The following can cause exposure of film:
X-??Rays Heat Certain chemicals or chemical fumes Pressure Age
Latitude
used to describe the range of densities that can be recorded on the film
Wide latitude film is best when
you desire low contrast radiographs (i.e. chest radiograph)
film Contrast & Latitude are?
inversely related
go over character curves
seriously do it
Contrast Index
is the difference in radiographic density between the Speed Index reading and the optical density reading (using the densitometer) that is two steps darker on the sensitometric strip
Gross Fog Index
is (film) Base plus Fog. It is the inherent optical density of a film when it has not been exposed at all.
Usual value for Gross Fog Index =
0.15-??0.20
Faster films have a higher
Gross Fog Index
Safe Lights inside dark rooms need to be:
Covered by filter that only allows light of a spectral emission that is not within the sensitive range of the film you?re using
Film should not be exposed to ?safe light? more than
3 min-
Developer Activator
Sodium carbonate-?? Softens gelatin protective cover on film
Developer Reducing Agents
Hydroquinone Reduces EXPOSED silver halide to black metallic silver
Developer Preservative
Sodium sulfite
Developer Restrainer
Potassium bromide; Acetic acid
Fixer Clearing Agent
Ammonium thiosulfate Dissolves undeveloped silver halide
Fixer Tanning Agent
Potassium alum
Fixer Activator
Acetic Acid Neutralizes the developer, stopping the development process & Maintains acid pH
Under-replenishment of Automatic Developer systems causes
Loss of contrast (grey appearing) & Loss of film density
Every 1?2 months:
Complete chemical change and tank cleaning; Check replenisher rates
Dark room causes of apparently lowered contrast on a film
Safe light fog, Room temperature/humidity too high, Chemical fog from processor too hot, Chemical fog from chemicals too concentrated, Film past expiration date
3 interactions of X?rays with matter:
Coherent Scattering, Compton Effect, Photoelectric Effect
Things that affect scatter production:
Tissue volume, Increased kVp, Increased mAs
the greater the tissue volume:
the greater the interactions= increased scatter
how does an increase of kVp increase scatter radiation?
increase energy increases the number and energy of scattered photons (each photon can cause multiple scattered photons of various types when the incident photon has sufficient energy)
how does an increase of mAs increase scatter radiation?
increased numbers of photons = increase in scattered photons
Scatter control or reduction on the film
Grid device, Air Gap technique, Minimize exposure field size, Decrease kVp
what is the Air Gap technique?
increase OID results in diminished scatter intensity at film (must increase SID to compensate for magnification distortion
Grid ratio?
height of lead strips/ width of interspacing material; 10:1 or 12:1 is best for spinal radiography
what are focused grids?
lead strips are aligned to the direction of the diverging primary x-??ray beam
what is the Grid radius?
the specific SID focused grid is aligned to
what is the Grid focal range?
range of source-image distances at which the grid will work acceptably- in other words the range of distances it will not absorb significant amounts of remnant radiation (primary beam after it has gone through the patient)
Cross?hatch grid?
lamination of 2 grids with lead strips perpendicular to each other
Stationary grids should have at least this many lines per inch?
103 lines per inch
Grid cut?off:
Undesirable attenuation of the primary x-??ray beam by the grid
when is a grid advisable?
when the body part exceeds 12 cm
Roentgen (R)=
Coulombs per kilogram (C/kg)
rad=
Gray (Gy): 1 Rad = .01 Gy; 1 Gy = 100 rad
rem=
Seivert (Sv): 1 rem = .01 Sv; 1 Sv = 100 rem (this is the one that uses the quality factor to multiply times the # Gy)
Curie=
Becquerel
Roentgen is the measurement of?
ionization of dry air by an X-ray beam
rad =
radiation absorbed dose-Measures dose to a specific tissue
rem =
radiation equivalent in man. X-??rays have a quality factor of 1.
Entrance skin exposure (ESE) doses are highest in
spinal radiography as compared to other plain film studies.
95% of cell damage is repaired within
3 days if it is going to repair at all
in The Laws of Bergonie and Tribondeau-Cell sensitivity depends on:
age, differentiation, mitotic rate, metabolic rate
how does cell age change the sensitivity?
the younger= more sensitive
how does cell differentiation change the sensitivity?
simple= more sens
how does cell mitotic rate change the sensitivity?
more rapidly dividing= more sens
how does cell metabolic rate change the sensitivity?
cells that use energy rapidly are more sens
what is Somatic effects of radiation
Affecting the irradiated individual
Stochastic
Probabilistic, random, Probability of experiencing the effect is proportional to the exposure volume, but the severity of the effect is not really affected
are stochastic effects somatic or genetic?
BOTH
Nonstochastic:
Deterministic, predictable, Severity of the effect is proportional to the exposure volume. There is a threshold beneath which effects generally aren?t seen
are nonstochastic effects somatic or genetic?
Only somatic
what is LD 50/30 =
death to 50 percent of an exposed population within 30 days
Human mortality (LD 50/30) =
~ 300 rad whole body dose
what is Hormesis?
Hypothesis that radiation can be good for you in small doses
what does ALARA stand for?
as low as reasonably achievable
Highest fetal doses are due to
lumbar and pelvic radiography
The 10 day rule is:
Direct pelvic radiation to fertile females should be done only during the first 10 days of the menstrual cycle
is the 10 day still valid?
It is not valid any longer? pregnancy can occur during any part of the cycle
Personnel radiation exposure monitoring is only legally required when?
a radiation monitoring expert deems it possible that an individual would receive as much as 25% of the maximum permissible dose
Effective Dose Equivalent (EDE) limit
Maximum Permissible Dose (MPD)
EDE Adult non-??pregnant workers:
5 rem / yr. (limited to 1.25 rem per calendar quarter)
EDE Pregnant workers:
0.5 rem / 9 mos.
EDE Workers under age 18:
.5 rem / yr.
When should occupationally exposed persons hold patients or films during exposures?
NEVER
who owns the radiographs?
the facility/ practitioner
