radio chapter 5
Quantity
the number of x-rays produced in the dental x-ray unit
wavelength
determines the energy and panetrating power of radiation
x-ray with shorter wavelength
have more penetrating power
longer wavelength
are less panetrating and are more likely to be absorbed by matter
the term quality
is used to discribe the mean energy or penetrating ability of the x-ray beam
quility or wavelength and energy of x-ray beam
controlled by kilovoltage
voltage
is the measurment of force that refers to the potential diff between 2 electrical charges
inside the tubehead voltage
is measured of electrical force that causes electrons to move from the negative cathode to the positive anode
when voltage is increased
the speed of electrons is increased
the elctrons strike the target with greater force resulting in
penetrating x-ray beam with a short wavelngth
voltage is measured in
volts or kilovolts
dental x-ray equipment requires the use
of high voltage, most radiographers unit use 1 kilovolts is equal to 1000 volts
the term kilovoltage is the
maximum voltage or peak voltage of an alternating current
current intraoral x-ray units include adjustable setting that range from
60 to 70 kv
increasing kilovoltage results in
a higher energy x-ray beam with increased penetrating ability
Density and kilovoltage ---> density is
the overall darkness or blackness of an image
if kilovoltage is inceased while other fcators remain constant
image exhibits an icreased density and appear darker
if kilovoltage is decreased
image exhibits a decreased density and appears lighter
contrast and kilovoltage---> contrast refers to
how sharply dark and light areas are differentiated or separated on an image
when lowering kilovoltage setting are used
a high contrast image result---> an image with high contrast has many black areas , many white areas, and few shades of gray
an image with high contrast is useful for
detecting and determining the progression of denta caries
with higher kilovoltage setting
low contrast results-----> with many shades of gray rather then black and white
an image low contrast is useful for
detecting of periodontal or periapical disease
exposure time and kilovoltage -----> exposure time refers to
the interval of time during which x-ray are produced
the longer the exposure time
the more x-ray are delivered and darker image result
the timer exposure is recommended to
adjust in order to lighten or darken an image
an impulse is a term of *used by older units
measurment that refers to the fact that x-ray are created in a series of bursts or pulses rather than in a continuous stream
1 pulse occurs in every *used by older units
1/60 seconds
kilovoltage was increased, the exposure time was. *older units
decreased
when kilovoltage is decreased,the exposure time is. *olderunits
increased
amperage and milliamperage--> amperage determines
the amount of electrons passing through the cathode filament
an increase in the # of electrons travel fromcathode to anode result in
production of inceased # of x-rays
the quantity of x-ray produced is controlled by
milliamperage
Ampere (mA) id the unit measure used to describe
number of electrons flowing through the cathode filament
current intraoral units may include adjustable setting rage from
6-8mA or else a fixed setting of 7 mA
older units were availabe with adjustable setting rage from
7 mA to 15 mA
A higher milliampere setting
increases the temp of the cathode filament and increase the numb of electrons that strike the anode increases the numb of x-rays emitted from the tube
the quantity or the numb of x-ray is emitted is controlled by
milliamperage
increase in mA increase the overall
density and result in a darker image
decrease in mA
decreases the over all density and image appear lighter
increased kv
decreases exposure time
decreases kv
increase exposure time
increased mA
decreases exposure time
decreases mA
increases exposure time
kv =
quality
mA =
quantity
all dental x-ray machines have 3 eposure factor setting
kV,mA and time
the exposure time is adjusted based onpatient size
it should be decreased with children and increased with adults with large jaws
Quality + quantity =
intensity
intensity defined as
th product of the quantity( numb of x-ray photon) and quality(energy of each photon) per unit of area per unit of the time exposure
intensity = # of photon x energy of each photon / area x exposure rate
Distance
target-surface distance: the distance from the source of radiation( tungsten target in anode) to the patient's skin
target-object distance:---> the distance from the source of radiation( tungsten target in anode) to the patient's tooth
target-receptor :---> the distance from the source of radiation(tungsten target in anode) to the receptor
Inverse square law state
the intensity o radiation is inversly proptional to the square of the distance from the source of radiation
inversely proportional means
one variable increase the other decreases
when the source- to- receptor distance increase the intensity of the beam decreases
according to the invrse law
when target-receptor distance is doubled ----> the result is 1/4 as intense
when the target-receptor distance is reduced by half ---> result is 4x as intense
beam will be 1/4 intense if the
target to receptor distance is changed from 8 to 16 inches
half-value layer
ex. if the half value layer is 3mm --> than a 3mm thickness of aluminum is required to decrease the intensity by half