Radiology Flashcards
Milliampere (mA)
AMOUNT or number of electrons
Measures the AMOUNT of current passing through the wires of the circuit
The AMOUNT of x-rays produced
Kilovolt peak (kVp)
The power or speed of electrons
Determines the PENETRATING ability
What is the yoke?
Connects extension arm and tube head
Can revolve 360 degrees
High kVp vs low kVp
High kVp= long scale contrast(many shade of black and white)
Low kVp=short scale contrast (few shades of black and white)
Direct current
Electricity continuously flows in one direction
*Good for DIGITAL radiography
Alternating current
Changes direction of flow 60x/second
What do most dental xray units operate on
110-120 V alternating current
7mA-15mA
65kVp-100kVp
Voltage
The electrical pressure between two electrical charges
Step-down transformer
Decreases voltage
Heats filament and produces electron cloud
Step-up transformer
Increases voltage
What percent of energy is converted to x-rays and what percent is lost in heat
1% converts to X-ray
99% loss is heat
Ionizing radiation
Any radiation that produces ions
Electromagnetic radiation
Movement of wave-like energy through space as a combination of electric and magnetic field
How are wavelength and frequency related
Inversely
Long wavelength= low frequency
Short wavelength=high frequency
Velocity
The speed of the wave
Compton effect
Causes x-rays to scatter in all directions
Called Secondary radiation
Coherent scattering is also known as
Thompson scattering
What is the occupational exposure limit in one year
50 mSv (5rem)
What is the occupational lifetime exposure limit
10mSv x age
Pregnant Dental personnel occupational exposure limit is
0.5 mSv/month
General public is permitted how much radiation in one year
5mSv (0.5rem)
Organs with high radiosensitivity
Lymphoid organs, bone marrow, ovaries, small intestine, fetal cells
Organs with low radiosensitivity
Muscle, brain, spinal cord
ALARA
As low as reasonably achievable
What is the single most effective method of reducing radiation to the patient
Rectangular collimator
Reduces radiation up to 70%***
Federal regulations state the X-ray beam needs to be how far from the skin surface
2.75 in or 7cm
How thick is the added filtration (aluminum discs in the pathway of the X-ray beam)
0.5mm
Is a longer or shorter PID more safe
Long PID= less radiation
How much thickness of lead needs to be in the lead apron and thyroid collar
0.25 mm
What is the second most effective method of reducing radiation to the patient
Film speed
Faster film=less radiation needed to expose it
What is the correct distance away from the x-ray beam for the operator
6 feet at 90° to 135° from the head of the patient
The walls blocking the x-ray should be
2.5-3 in of drywall
Silver halide crystals
Retain the latent image when exposed to X-ray beam
larger the crystal=faster film speed***
Thicker emulsion= faster film speed
Manual film processing steps
Develop, rinse, fix, wash, dry
Automatic film processing steps
Develop, rinse, dry
The Safelight should be a minimum of how far from the working area
4feet
A white ceiling light may cause what to the film
Foggy film
Inverse square law
I(1) D(2)^2
—— = ————
I(2) D(1)^2
I(1)=original intensity
I(2)= new intensity
D(1)= Original distance
D(2)= new distance
SLOB rule
Same=lingual
Opposite=buccal
The size and shape of the focal trough is determined by
The manufacturer
**Structures positioned outside of the focal trough will be blurred
During a pano where should the tongue be placed
Roof of mouth
On a panoramic x-ray if the chain is too low what will happen
Exaggerated smile appearance
On a panoramic x-ray if the chin is too high what will happen
Frown appearance
When the Patient’s chin is tipped too low on a panoramic x-ray the teeth on the anterior will be positioned how
Farther from the film
What causes a black film
Light leaking
An unexposed film will be what color
White
What is the earliest clinical signs of radiation over exposure
Erythema
If the kVp is set higher is there more or less scatter radiation
Less
kVp effects what
mA effects what
kVp= contrast
mA=density
If anterior teeth look short and fat, that means
The teeth were BEHIND the focal trough