Flashcards in Radiology Deck (71):
Rank from least to most radiopaque
most __ lesions are well-defined unilocular
90% of the time, diffuse radiolucencies indicate __
CANCER - if there is a loss of cortical plates, the first dx is cancer
most common factors precipitating osteoradionecrosis are (2)
necrosis of bone produced by ionizing radiation that is more common in the mandible > max (cause richer vascular supply to max)
factors - pre and post-irradiation extractions and perio disease
damage to __ predisposes a pt to developing osteoradionecrosis
it's a complication that can occur in pts taking what meds?
IV bisphosphonates, or oral bisphosphonates > 3yrs (ex. Fosomax)
bony projection that arises from the sphenoid bone and extends down and posteriorly is the
coronoid process usually seen on which films?
PAs of molars in maxilla
tapered or triangular radiopaque below or superimposed on molars of maxilla
how long should dental xrays be retained?
legally, radiographs are property of who?
the dentist! but pt has right to reasonable access
pts can refuse dental xrays, but entist must decide if an accurate dx can be provided or tx can be provided
why do digital xrays require less radiation?
reduced by what %?
sensor is more sensitive to xrays
storage phosphor imaging system uses what instead of a sensor?
reversible imaging plate, more flexible and comfortable
a direct digital imaging system works using
intraoral sensor attached to a fiberoptic cable
indirect digital imaging system works by
scanning an existing xray and digitizes the image
the most common digital image recptor is the
charge-coupled device (CCD)
-solid state detector with silicon chip
-also used in home video cameras, fax machines, telescopes
primary radiation is generated at the __ of the xray tube
ANODE, and is attenuated by the filter and object
secondary radiation "Scattered"
from interactions of primary radiation beam with atoms in the object
-major source of image degradation
in secondary radiation (scattered) what 3 interactions can occur
photo electric absorption
Compton scattering <-- cause most scattered xrays in dx imaging
how can you best reduce the amt of scatter radiation? by using a __, __ cone
leaded, rectangular cone (PID)
in normal dental dx procedures, who receives the greatest hazard from secondary scatter radiation?
collimation is the control of ___ and ___
the control of SIZE and SHAPE of the xray beam
the diameter of a circular beam of radiation at the pt's skin can't be larger than __ inches
xray beam is composed of rays of diff. wavelengths and penetrating power (polychromatic) because
the potential across the xray tube constantly changes as the kilovoltage changes
are short or long wavelength xrays useful?
SHORT are useful, and long are useless!
Short ones (high energy) have good penetrating power, are produced at higher kilovoltages, and form the image on the film.
Long ones don't reach the film in reasonable quantities, and only add onto the radiation the pt gets! Use ALUMINUM discs to "filter" these out.
filtration reduces 3 things:
3 types of filtrations:
reduces: pt dose, contrast, film density
1. inherent filtration - incl. OIL around xray tube to dissipate heat, ~0.51 mm aluminum
2. added filtration - added aluminum sheets in cone
3. total filtration = inherent + added
recommended total filtration = __ mm aluminum below 50 kVp, and __ mm over 70 kVp
0.5 mm < 50 kVp
2.5 mm > 70 kVp
when taking xrays, operator should stand at least __ feet away, and behind a lead shield
and be at __ angle from the beam
6 feet away
what film provides the most effective way to reduce exposure time, amt of radiation reaching pt and amt of scatter radiation to the dentist?
standards: 1 year radiation exposure, max. dose = __ REM for someone who works near radiation
__ REM for a non-occupationally exposed person
5 REM (0.1 REM per week)
sequence of radiation injury (3)
1. Latent period - btw exposure and onset of symptoms
2. Period of cell injury - cell death, changes in fxn, abnormal mitosis
3. Recovery period - some cells recover
are effects of radiation additive?
damage that remains non-repaired accumulates -> can lead to carcinogenesis -> carcinomas, genetic mutations, leukemias, cataracts
the greater/lesser rate of potential for miosis and the more mature/immature the cells are, the MORE susceptible the cells are to radiation
greater mitosis and immature
radiosensitive cells incl
small lymphocytes (immature), bone marrow, reproductive cells, immature bone cells
prostate gland, hemopoietic tissue (most sensitive)
radioresistant cells incl
mature bone, muscle (most resistant), nerve (pulp)
measure of the energy imparted by radiation; traditional unit is called
RAD - radiation absorbed dose
what measure is used by the dentist to compare biologic risk effects/estimates of diff types of radiation damage?
equivalent dose "dose equivalent"
effective dose measures risk in
__ is the traditional unit of radiation exposure measured in air and only applies to __ rays and __ rays
only applies to xrays and gamma rays
electromagnetic radiation includes
microwaves, x-rays, visible light, gamma rays
xrays and gamma rays are NON-PARTICULATE radiation energy
a sialolith in Wharton's duct is best viewed with which radiograph?
what xray is designed to dx basilar skull fractures? when you suspect a fracture of the zygomatic arch?
gives dx info about the zygoma, zygomatic arches, mandible
source below mandible, film above head
the standard radiograph for showing an ANTERIOR view of the paranasal sinuses and mid-face and orbits is?
posterior-anterior projection, face against film and xray behind head
dx mid-facial fractures, sinus infxns, lesions of max sinus
the best film to visualize CONDYLES and NECK OF MANDIBLE is?
AP projection, pt on back and film under head, xray from front and rotated 30 deg from Frankfort plane, directed at condyles
-assess status of condyles, condylar neck rami because often superimposed by MASTOID and ZYGOMA
reverse Towne's view is used to identify fractures of the __ and __
developer solution fxn is to reduce __ crystals to __
silver halide crystals -> black metallic silver
xray developing solution has 4 chemicals
1. developing agent (hydroquinone)
2. antioxidant preservative (sodium sulfite)
3. accelerator (sodium carbonate)
4. restrainer (potassium bromide)
as developing solution gets weaker, the films get lighter
yellow brown film is caused by
fogged film is from
low solution levels will appear as?
bad fixing (brown) or rinsing
improper film storage, outdated films
developer cut-off (straight clear border) or fixer cut-off (straight black border)
xray fixing solution fxn is to
stop development and remove remaining unexposed crystals
time is 2x as long as developing time
4 chemicals in fixing solution
1. clearing agent (sodium or ammonium thiosulfate) - removes underdeveloped crystals
2. antioxidant preservative (sodium sulfite)
3. acidifier (acetic acid)
4. hardener (potassium alum)
incorrect vertical angulation will cause __ and __
1. foreshortening - excess vertical angulation, teeth appear too short
2. elongation - most common error!
general rule for horizontal angulation is the central ray should be __ to the mean antero-posterior plane of teeth being xrayed
overlapping interproximal areas are from incorrect ___ angulation
central ray is 0 if the tube is adjusted so the ray is __ to the floor
positive angulation is when the tube is directed up/down?
positive - at floor
negative - at ceiling
bisecting angle technique
based on geometric rule of isometry, image on film is equal to length of tooth when central ray is 90 deg to imaginary bisector
what is the advantage to the bisecting angle technique?
decreased exposure time
image might be distorted, SHORT cone so not true img, can't judge correct alveolar bone height
film is placed parallel to long axis of tooth, central ray is perpendicular or at right angles to long axis of tooth and plane of film
no superimposition on max molar view, accurate dx of periodontal bone height, image accurate
requires INCR exposure time (LONG cone), object-film distance needs to be increased
cervical burnout is caused by
relatively low x-ray absorption
inverse square law is
intensity if inversely proportional to square of the distance from the source
intensity of xray beam depends on distance from the FOCAL SPOT
focal spot is
tungsten on the ANOE (target) from which xrays emanate
size of the focal spot influences radiographic DEFINITION
the short cone is how big?
20 cm (8 in) - exposes more tissue, more divergent beam
41 cm (16 in) - reduces amt of exposed tissue, less divergent beam
target film distance (source to film) is determined by?
length of the cone
half-value layer (HVL) is the
amt of material required to reduce the intensity of an xray beam to HALF
normally expressed in aluminum or copper thickness
~2 mm aluminum ( 50% of xrays are absorbed by 2 mm aluminum), doubling this thickness doesn't absorb all the xrays but one HALF of the remaining xrays
what indicates the QUALITY of an xray beam?
half-value layer (HVL)
intensifying screens convert xray energy into?
used for what kind of radiographs?
visible light, so radiation pt receives is decreased
for all extra-oral xrays
radiograph operator controls what 3 factors?
1. kilovoltage (kVp) - quality or penetrating power of xray beam that controls speed of ELECTRONS, alters CONTRAST quality
2. milliamperage (mA) - controls # of xrays produced, usually 7-15 mA
3. exposure time
# of e- determines what?
QUANTITY of xrays produced, controlled by temperature of tungsten filament
how can you increase film density? 4 factors
doing what to kVp will cause the xray to have a longer scale of contrast?
how do you increase subject contrast?
density is the __
it increases as these 3 factors increase, and vice versa
overal DARKNESS of a radiograph
mA, kVp, exposure time
image magnification is minimized by using a __ cone
where is the stream of electrons produced?
what houses the tungsten filament?
electron stream travels from __ to __
filament (tungsten in the CATHODE)
from filament (cathode +) to tungsten target (anode -)
the anode (-) that stops the stream of electrons is the
part of the tungsten target struck by the e- beam is?
occult diseases are
small carious lesions, cysts, tumors that present NO clinical signs or symptoms
rare, so xray exam of jaws should not be done to look for it when no signs! (except for caries)