Radiation Characteristics

Radiation characteristics include what? The x-ray beam ________

• quality

• quantity

• intensity

Variations in the character of the x-ray beam influence what?

the quality of the resulting image

Current dental x-ray units have control panels. These come with preset what?

predetermined exposure factors like kV, mA, and time for various anatomical areas

What was different about older x-ray  units?

exposure factors could be manually adjusted by operator

Do today’s x-ray units allow for exposure factors to be adjusted?

yes, limited

The wavelength of an x-ray determines what?

the energy and penetrating power of radiation

X-rays with shorter wavelengths have ______ penetrating power, whereas those with longer wavelengths are ______ penetrating and _______ likely to be absorbed by matter. 

more, less, more

In dental imaging, the term quality is used to describe what?

the mean energy or penetrating ability of the x-ray beam. 

The quality, or wavelength and energy, of the x-ray beam is controlled by what?

kilovoltage

What is a measurement of force that refers to the potential difference between two electrical charges?

voltage

Inside the dental x-ray tubehead, voltage is the measurement of ________ that causes electrons to move from the negative cathode to the positive anode

electrical force

Voltage determines what about the electrons in the x-ray tubehead?

the speed they move

Voltage can be measured in what?

volts or kilovolts

What is the unit of measurement that is used to describe the potential that drives an electrical current through a circuit?

volt

Dental x-ray equipment requires the use of what type of voltage?

high

What is the conversion between kilovolts and volts?

1 kilovolt = 1000 volts

What term is the maximum voltage, or peak voltage of an alternating current (AC)?

kilovoltage

When the kV is adjustable in modern x-ray units, what two kilovoltages can you switch between?

60 kV and 70 kV

In modern x-ray units, when the kilovoltage is it adjustable, it is fixed to what kilovoltage?

70 kV

Kilovoltage regulates what two things of the electrons? What does it determine about the x-ray beam?

speed and energy; penetrating ability

What is the overall darkness or blackness of an image?

density

Can an adjustment of kilovoltage result in a change in the density of a dental image?

yes

If the kV is increased while the other exposure factors remain constant, what happens?

the image exhibits an increased density and appears darker

If the kV is decreased while the other exposure factors remain constant, what happens?

the image exhibits a decreased density and appears lighter

If an image is too dark or light and is nondiagnostic, what can be done to make it diagnostic

use special image enhancement software, retake image with adjusted exposure factors

What refers to how sharply dark and light areas are differentiated or separated on an image?

contrast

An adjustment in _______ results in a change in the contrast of a dental image

kilovoltage

When lower kilovoltage settings are used, what type of image will result?

a high-contrast image

An image with “high” contrast has what?

many black and white areas, with few shades of gray

A high contrast image is useful for detecting and determining what?

the progression of dental caries

With higher kilovoltage settings, what contrast results?

low contrast image

An image with what type of contrast has many shades of gray instead of areas that are predominantly black and white?

low contrast

An image with low contrast is useful for detecting what?

periodontal or periapical disease

What type of contrast is desirable in dental imaging?

between high and low contrast

What can change the contrast of an image when needed?

special image enhancement software

What term refers to the interval of time during which x-rays are produced?

exposure time

The timer controls what?

length of exposure time

The timer determines what?

how long the x-rays will be emitted from the machine

What exposure factor is recommended to adjust to lighten or darken an image?

time

A larger person may require ______ exposure time, whereas a smaller patient may require ______ x-ray exposure time

more, less

The timer may be calibrated in either _______ or _______, depending on when the unit was manufactured

seconds, impulses

On older units, exposure time is indicated by what?

pulses, impulses

What’s a term of measurement that refers to the fact that x-rays are created in a series of bursts or pulses rather than in a continuous stream?

impulse

How often does one impulse occur?

Every 1/60 of a second

Newer x-ray units designed to be used with digital imaging use exposure times how often?

Every 1/100 of a second

How are kilovoltage and exposure time related?

inversly

When kilovoltage is increased, the exposure time is ________.

decreased

When kilovoltage is decreased, the exposure time is ________

increased

What refers to the number of x-rays produced in the dental x-ray unit?

quantity

What determines the amount of electrons passing through the cathode filament?

amperage

An increase in the number of electrons available to travel from the cathode to the anode results in the production what?

an increased number of x-rays

The quantity of the x-rays produced is controlled by what?

milloamperage

What’s the unit of measure used to describe the number of electrons, or current, flowing through the cathode filament?

ampere

Whats the conversion for milliamperes and amperes?

1 milliampere = 1/1,000 ampere

Milliamperage and milliamperes can both be abbreviated by what?

mA

Current intraoral x-ray units may include adjustable settings that have what range? What if it’s fixed?

6 - 8 mA; 7 mA

What regulates the temperature of the cathode filament?

Milliamperage?

What does a high milliampere setting do to the temperature of the cathode filament?

increases the temperature, which increases the number of electrons produced

An increase in the number of electrons that strike the anode increase what?

the number of x-rays emitted from the tube

As the milliamperage is increased, ______ electrons pass through the filament, and _________ x-rays are produced. 

more, more

what trick can be used to remember quality vs quantity?

KLMN; kV = quality mA = quantity

What term can be defined as the product of the quantity (number of x-ray photons) and quality (energy of each photon) per unit of area per unit of time of exposure

intensity

What is the formula for intensity?

intensity = (No. of photons) x (Energy of each photon) / (Area) x (Exposure rate)

the distance from the source of radiation to the patient’s skin

target-surface distance

The distance form the source of radiation to the tooth

target-object distance

The distance from the source of radiation to the receptor

target-receptor distance