Radiation Characteristics

What are the three main radiation characteristics?

X-ray beam quality, quantity, and intensity.

What is x-ray beam quality?

The penetrating power or mean energy of the x-ray beam.

What controls x-ray beam quality?

Kilovoltage (kV).

What is voltage?

The measurement of force between two different electrical charges.

What happens to wavelength when voltage increases?

Wavelength decreases.

What happens to penetrating power when kVp increases?

Penetrating power increases.

What kV settings are commonly used for intraoral dental x-ray units?

60–70 kV.

What does kVp stand for?

Kilovoltage peak.

What does kVp measure?

The peak voltage during x-ray production.

Why is the x-ray beam polychromatic?

Voltage fluctuates, producing x-rays with different wavelengths.

What is radiographic density?

The darkness of a radiographic image.

How does increasing kVp affect film density?

It increases density because more photons penetrate the subject and reach the receptor.

How does decreasing kVp affect film density?

It decreases density.

What is radiographic contrast?

The difference between light and dark areas on a radiograph.

What is low contrast?

Many shades of gray with greater detail.

What is high contrast?

Mostly black and white with very few shades of gray.

Which contrast is useful for diagnosing periodontal disease and apical lesions?

Low contrast.

Which contrast is useful for diagnosing caries?

High contrast.

How does low kVp affect contrast?

It produces high contrast.

How does high kVp affect contrast?

It produces low contrast.

What controls radiographic contrast?

kVp.

Does mA affect radiographic contrast?

No.

How are kVp and exposure time related?

Inversely; higher kVp requires less exposure time.

What happens to exposure time when kVp increases?

Exposure time decreases.

What happens to exposure time when kVp decreases?

Exposure time increases.

What is an impulse?

A burst of x-ray photons.

How long is one impulse?

1/60 of a second.

What is a typical dental x-ray exposure in impulses according to the lecture?

6–8 impulses.

What is the 15% kVp rule described in the lecture?

Increasing kVp by 15 allows exposure time to be cut in half while maintaining density; decreasing kVp by 15 requires doubling exposure time.

If kVp decreases from 90 to 75 and the original exposure was 8 impulses, what is the new exposure time?

16 impulses.

If kVp increases from 75 to 90 and the original exposure was 12 impulses, what is the new exposure time?

6 impulses.

What is x-ray beam quantity?

The number of x-ray photons produced.

What controls x-ray beam quantity?

Amperage (mA).

How does amperage affect x-ray production?

It controls filament temperature and the number of electrons released.

What happens when filament temperature increases?

More electrons are released.

What happens when more electrons strike the tungsten target?

More x-ray photons are produced.

What does mA stand for?

Milliamperage.

How much is 1 mA?

1/1000 of an ampere.

What mA range is commonly used in dental radiography according to the lecture?

6–8 mA.

How does increasing mA affect beam quantity?

It increases the number of photons produced.

How does decreasing mA affect beam quantity?

It decreases the number of photons produced.

How does increasing mA affect film density?

It increases density.

How does decreasing mA affect film density?

It decreases density.

Why does mA not affect contrast?

It changes the number of photons, not their wavelengths.

How are mA and exposure time related?

Inversely; increasing mA allows exposure time to decrease.

What happens to exposure time when mA increases?

It decreases to maintain the same density.

What happens to exposure time when mA decreases?

It increases to maintain the same density.

What does mAs stand for?

Milliampere-seconds.

What is the formula for mAs?

mAs = mA × exposure time in seconds.

What does mAs determine?

The total quantity of x-rays produced during an exposure.

What is the mAs for 15 mA and 2 seconds?

30 mAs.

If 10 mA for 1.5 seconds produces good density, what exposure time is needed at 15 mA?

1 second.

If 12 mA for 2 seconds produces good density, what exposure time is needed at 8 mA?

3 seconds.

What is x-ray beam intensity?

The combined effect of beam quality, quantity, exposure time, and distance.

What four factors affect x-ray beam intensity?

kVp, mA, exposure time, and distance.

How does kVp affect intensity?

It controls the penetrating power of the beam.

How does mA affect intensity?

It controls the number of electrons and photons produced.

How does exposure time affect intensity?

It controls how many photon bursts are released.

What happens to film density when kVp, mA, or exposure time increases?

Film density increases.

How does distance affect x-ray beam intensity?

As distance increases, intensity decreases.

What happens to x-rays as they travel away from their source?

They spread out and lose intensity.

What are the three distances considered in dental radiography?

Target-surface, target-object, and target-film distance.

What is target-surface distance?

The distance from the tungsten target to the patient's skin.

What is target-object distance?

The distance from the tungsten target to the patient's tooth.

What is target-film distance?

The distance from the tungsten target to the image receptor.

What happens to intensity when distance decreases?

Intensity increases.

What happens to intensity when distance increases?

Intensity decreases.

What does the inverse square law state?

Radiation intensity is inversely proportional to the square of the distance from its source.

What is the inverse square law formula?

Original intensity / New intensity = New distance² / Original distance².

What happens to intensity when distance doubles?

Intensity decreases to one-fourth.

What happens to intensity when distance is cut in half?

Intensity increases four times.

What happens to intensity when distance triples?

Intensity decreases to one-ninth.

What happens to intensity when distance decreases to one-third?

Intensity increases nine times.

If a person moves from 6 feet to 2 feet from the tubehead, how does intensity change?

It increases 9 times.

If a person moves from 4 feet to 16 feet from the tubehead, how does intensity change?

It decreases to 1/16.

If Sandy stands 5 feet from the tubehead and Patrick stands 10 feet away, who receives greater intensity?

Sandy receives 4 times the intensity.

According to the inverse square law, what happens when target distance changes from 16 inches to 8 inches?

Intensity increases four times.

According to the inverse square law, what happens when target distance changes from 8 inches to 16 inches?

Intensity decreases to one-fourth.

How can a flashlight help explain the inverse square law?

Moving it closer concentrates light in a smaller area, while moving it farther away spreads the light and reduces intensity.

What is filtration?

The removal of low-energy x-ray photons from the beam.

How does aluminum filtration affect beam quantity?

It decreases quantity.

How does aluminum filtration affect average beam quality?

It increases average penetrating power.

How does filtration affect beam intensity?

It decreases intensity.

Are intensity and penetrating power the same thing?

No. Intensity depends on multiple factors, while penetrating power depends on wavelength and energy.

What does HVL stand for?

Half-value layer.

What is the half-value layer?

The thickness of aluminum needed to reduce x-ray beam intensity by one-half.

What does an HVL of 4 mm mean?

4 mm of aluminum is required to reduce beam intensity by half.

What does a larger HVL indicate?

Greater average penetrating power.

How can beam intensity be increased?

Increase mA, exposure time, or kVp, or decrease distance.

How can beam intensity be decreased?

Decrease mA, exposure time, or kVp, or increase distance.

How does patient size affect exposure settings?

Smaller patients generally require less intensity.

What exposure factor can students adjust on the lecture's dental x-ray units?

Exposure time.

How should exposure time be adjusted for smaller patients?

Reduce the number of impulses.

What is the easiest way to remember kVp versus mA?

kVp = quality; mA = quantity.