radiology test 3 pt 1

wave length 

determines the energy and penetrating power of radiation

true

X rays with shorter wave lengths have more penetrating power 

quality

used to describe the mean energy or penetrating ability of the x-ray beam

What is quality controlled by?

Kilovoltage

What is voltage and what happens when it is increased?

Voltage is the potential difference between two electrical charges. When voltage is increased, the speed of electrons also increases, causing them to strike the target with greater force and energy.

What is voltage measured in and what do volts and kilovolts represent?

Voltage is measured in volts or kilovolts. A volt is a unit that describes the potential driving an electrical current through a circuit, and one kilovolt equals 1,000 volts.

What voltage range is used in dental imaging and what happens outside that range?

Dental imaging uses 65 to 100 kV. Less than 65 kV results in inadequate penetration, while more than 100 kV causes overpenetration.

What controls the quality, wavelength, and energy of the X-ray beam?

The quality, or wavelength and energy of the X-ray beam, is controlled by the kilovolt peak (kVp)

What is density in an X-ray image?

Density is the overall darkness or blackness of an image.

How does kilovoltage affect the density of an X-ray image?

When kilovoltage is increased, the image appears darker. When kilovoltage is decreased, the image appears lighter.

What is contrast in an X-ray image?

Contrast is how sharply dark and light areas are differentiated on an X ray image.

What kind of contrast and image appearance do low kilovoltage settings (65–70 kVp) produce, and what are they used for?

Low kilovoltage settings produce high contrast images with many black and white areas and few shades of gray. They are good for detecting caries.

What kind of contrast and image appearance do high kilovoltage settings (≥90 kVp) produce, and what are they used for?

High kilovoltage settings produce low contrast images with many shades of gray. They are good for detecting periodontal or periapical disease.

Exposure time

interval of time during which x rays are produced

What is amperage in an X-ray machine?

Amperage determines the amount of electrons passing through the cathode filament.

What happens when amperage is increased in an X-ray machine?

Increasing amperage increases the number of electrons traveling from the cathode to the anode, producing more X-rays.

What controls the quantity of X-rays produced?

The quantity of X-rays produced is controlled by milliamperage (mA).

What is an ampere and what does it measure in an X-ray machine?

An ampere (A) is a unit of measure used to describe the number of electrons, or current, flowing through the cathode filament.

What is the typical milliamperage range in dental imaging and what happens if it is exceeded?

In dental imaging, milliamperage ranges from 7 to 15 mA. Exceeding this range produces excessive heat.

What does milliamperage regulate in an X-ray machine?

Milliamperage regulates the temperature of the cathode filament.

What happens when milliamperage is increased in an X-ray machine?

Increasing milliamperage increases the overall density of the image, resulting in a darker image.

What is the inverse relationship between milliamperage and exposure time?

When milliamperage is increased, exposure time must be decreased. When milliamperage is decreased, exposure time must be increased.

What are the three exposure factor settings on all dental X-ray machines?

Kilovoltage (kV), milliamperage (mA), and exposure time.

What does kilovoltage control in an X-ray machine?

Kilovoltage regulates the penetrating power of the X-ray beam by controlling the speed of electrons traveling from the cathode to the anode. Higher kVp produces an X-ray beam with more energy, shorter wavelengths, and increased intensity.

What does milliamperage control in an X-ray machine?

Milliamperage controls the number of electrons produced in the X-ray tube and the number of X-rays produced, affecting the intensity of the beam. Higher mA produces more energetic and intense X-rays.

How does exposure time affect X-ray production?

Longer exposure time produces more X-rays and a more intense X-ray beam.

How does distance affect the intensity of the X-ray beam?

The intensity decreases as distance increases. Key distances are target-surface, target-object, and target-receptor.

What is the Inverse Square Law in radiography?

The intensity of radiation is inversely proportional to the square of the distance from the source. Doubling the distance reduces intensity to one quarter, halving the distance increases intensity four times.

What is the purpose of the half-value layer (HVL) in dental X-ray machines?

Aluminum filters remove low-energy, less penetrating X-rays, increasing the mean penetrating ability while reducing intensity. The half-value layer (HVL) is the thickness of material that reduces the beam’s intensity by half.

What does radiolucent mean in a dental X-ray image?

Radiolucent refers to the dark or black areas of a processed image. A structure that appears black lacks density, allowing X-rays to pass through freely.

What does radiopaque mean in a dental X-ray image?

Radiopaque refers to the white areas of a processed image. A structure that appears white is dense and absorbs or resists the passage of X-rays.

What makes a diagnostic dental image ideal?

It has proper density and contrast, sharp outlines, and the same shape and size as the object radiographed.

How do air spaces and dense structures appear on dental X-rays?

Air spaces appear radiolucent (dark) because X-rays pass through freely. Dense structures like enamel, dentin, and bone appear radiopaque (white) because they resist X-rays.

What is density in a dental X-ray image and what factors influence it?

Density is the overall darkness or blackness of the image, determined by the distribution of black silver particles in the emulsion. Influencing factors include kilovoltage, milliamperage, exposure time, and subject thickness.

What is contrast in a dental X-ray image?

Contrast is the difference in degrees of blackness between adjacent areas. Increasing kilovoltage affects contrast by producing higher energy X-rays.

What is high contrast versus low contrast in dental images?

• High contrast: very dark and very light areas (short-scale contrast, low kVp)

• Low contrast: many shades of gray (long-scale contrast, high kVp)

What determines overall contrast in a dental X-ray?

• Film contrast: inherent qualities of the film and processing

• Subject contrast: characteristics of the subject affecting radiographic contrast

What is sharpness in a dental X-ray image?

Sharpness is the ability of the X-ray receptor to reproduce distinct outlines of an object. Some lack of sharpness (penumbra) is always present.

What factors influence sharpness in dental X-rays?

1. Focal spot size: smaller spots produce sharper images

2. Film composition: faster films with larger crystals reduce sharpness

3. Movement: causes loss of sharpness

How does target-receptor distance affect image magnification?

A longer PID and longer target-receptor distance results in less image magnification.

How does object-receptor distance affect image magnification?

Increasing the object-receptor distance results in greater image magnification.

What is distortion in dental radiography?

Distortion is a variation in the true size and shape of the object being radiographed, caused by unequal magnification of different parts due to improper receptor alignment or X-ray beam angulation.

What factors influence distortion in dental X-rays?

• Object-film alignment: the object and film must be parallel to avoid distortion.

• X-ray beam angulation: the beam must be directed perpendicular to the tooth and film

What happens if the tooth and receptor are not parallel in dental radiography?

If the tooth and receptor are not parallel, an angular relationship forms, causing a distorted image. To limit distortion, the central ray must be perpendicular to both the tooth and the receptor.

What are the two possible mechanisms of radiation injury?

1. Ionization – produced when X-rays strike tissue via the photoelectric effect or Compton scatter.

2. Free Radical Formation – occurs when an X-ray photon ionizes water, forming highly reactive, unstable free radicals that damage cells.

What is a free radical and how does it cause cell damage?

A free radical is an uncharged atom or molecule with a single, unpaired electron in its outer shell. Free radicals react with cellular components, leading to cell damage. Most cell damage occurs via free radical formation in water-containing cells.

How can radiation damage living tissue?

• Direct hit: absorption of an X-ray photon by critical cell structures.

• Indirect hit: absorption of an X-ray photon by water in a cell, forming free radicals that create toxins damaging the cell.

What are the two theories describing radiation damage to cells?

• Direct Theory – cell damage occurs when radiation directly hits critical areas; occurs infrequently.

• Indirect Theory – X-rays absorbed by water form free radicals that combine into toxins, which damage cells.

What is the dose-response curve in radiation biology?

• It correlates tissue damage with radiation dose.

• Linear, non-threshold curve: tissue response is proportional to dose; any dose, no matter how small, can cause some biologic damage.

What are stochastic and nonstochastic radiation effects?

• Stochastic effects: no dose threshold; probability increases with dose; examples include cancer and genetic mutations.

• Nonstochastic (deterministic) effects: have a threshold; severity increases with dose; examples include erythema, hair loss, cataracts, and decreased fertility.

What are the stages in the sequence of radiation injury?

• Latent period – time between exposure and observable clinical signs; depends on total dose and exposure time.

• Period of injury – various cellular injuries occur.

• Recovery period – cells can repair damage depending on several factors.

• Cumulative effects – unrepaired damage accumulates over time.

What factors determine the severity of radiation injury?

• Total dose of radiation

• Dose rate

• Amount of tissue irradiated

• Cell sensitivity

• Age

What are short-term and long-term effects of radiation?

• Short-term effects: occur with large doses over a short period (acute radiation syndrome – nausea, vomiting, diarrhea, hair loss, hemorrhage).

• Long-term effects: occur with small, repeated doses over years; effects include cancer, birth abnormalities, and genetic defects.

What is the difference between somatic and genetic effects of radiation?

• Somatic effects: occur in the irradiated individual; not passed to future generations.

• Genetic effects: occur in reproductive cells; not seen in the exposed individual but passed to future generations.

What determines a cell’s radiosensitivity?

A cell’s response to radiation depends on:

• Mitotic activity (more dividing = more sensitive)

• Cell differentiation (less specialized = more sensitive)

• Cell metabolism (higher metabolic activity = more sensitive)

Which tissues and organs are radiosensitive and which are radioresistant?

• Radiosensitive: lymphoid tissue, bone marrow, testes, intestines.

• Radioresistant: salivary glands, kidney, liver.

What is a critical organ in dental radiography?

A critical organ is one that, if damaged, diminishes the quality of a person’s life.

Which critical organs are exposed during dental radiographic procedures?

The skin, thyroid gland, lens of the eye, and bone marrow.

What does a roentgen measure?

A roentgen measures radiation by determining the amount of ionization that occurs in air. It does not measure the amount of radiation absorbed by tissues.

What is the SI equivalent of the roentgen?

There is no exact SI equivalent; exposure is stated in coulombs per kilogram (C/kg).

What does a rad measure, and what is its SI equivalent?

A rad (radiation absorbed dose) measures the amount of energy absorbed by tissue. The SI equivalent is the gray (Gy), where 1 Gy = 100 rads.

What is a sievert (Sv) and how is it related to rems?

A sievert (Sv) is the SI unit used to measure dose equivalent (biologic effect of radiation). 1 Sv = 100 rems.

What does “milli” mean in dental imaging measurements?

“Milli” means one-thousandth (1/1000) and is used to express the small radiation doses used in dental imaging.

What are the sources of natural background radiation?

Natural background radiation comes from:

• Cosmic radiation (stars and the sun)

• Terrestrial radiation (radioactive materials in the earth and air)

How much background radiation does an average person in the U.S. receive per year?

Between 150 to 300 millirads (mrads) per year.

When should dental images be prescribed?

Dental images should be prescribed only when the benefit of disease detection outweighs the risk of biologic damage.

Why are dental X-rays considered safe when properly used?

When properly prescribed and exposed, the benefit of detecting disease far outweighs the risk of radiation damage.

What is inherent filtration in dental radiography?

Inherent filtration occurs when the primary x-ray beam passes through the glass window of the x-ray tube, the insulating oil, and the tubehead seal.

How much aluminum equivalent is inherent filtration?

Approximately 0.5 to 1.0 mm of aluminum.

Does inherent filtration meet legal standards?

No, inherent filtration does not meet state and federal requirements—added filtration is required.

What is added filtration?

Added filtration uses aluminum disks placed between the collimator and the tubehead seal to filter out longer wavelength, lower-energy x-rays.

What is the result of added filtration?

It produces a higher-energy and more penetrating useful x-ray beam.

What is total filtration?

The sum of inherent and added filtration in an x-ray machine.

What are the legal requirements for total filtration?

• Machines ≤ 70 kVp → minimum 1.5 mm aluminum

• Machines > 70 kVp → minimum 2.5 mm aluminum

What is collimation?

Collimation restricts the size and shape of the x-ray beam to reduce patient exposure.

What does a round collimator produce?

A cone-shaped beam about 2.75 inches in diameter.

What does a rectangular collimator produce?

A rectangular beam slightly larger than a #2 film.

What is a Position-Indicating Device (PID)?

An extension of the x-ray tubehead used to direct the x-ray beam.

What are the types of PIDs?

Conical, rectangular, or round.

• Conical PIDs: no longer used (cause scatter radiation).

• Rectangular/Round PIDs: 8- or 16-inch, open-ended and lead-lined.

What is a thyroid collar and what does it protect?

A flexible lead shield placed around the neck to protect the thyroid gland from scatter radiation.

When is the thyroid collar recommended or not recommended?

• Recommended: all intraoral exposures

• Not recommended: extraoral exposures

What is the purpose of a lead apron?

Protects the reproductive organs and blood-forming tissues from scatter radiation.

Which image receptors reduce patient radiation exposure?

Digital receptors and fast film (F-speed) require less radiation.

What is the most effective way to reduce a patient’s radiation exposure?

Use of a digital image receptor.

Why is proper technique important in dental radiography?

Nondiagnostic images must be retaken, increasing patient exposure. Avoid retakes when possible.

What distance should the operator maintain during exposure?

At least 6 feet from the tubehead.

What position should the operator stand in relation to the x-ray beam?

Perpendicular or at a 90°–135° angle to the primary beam.

What is equipment monitoring in dental radiography?

Ensuring dental x-ray machines are checked regularly for leakage radiation.

What is personnel monitoring?

Use of a radiation monitoring badge to measure a radiographer’s exposure over time.

Where should a radiation badge be worn?

At waist level when taking x-rays.

How often is a radiation monitoring badge evaluated?

Monthly — mailed with a control badge to the monitoring company for evaluation.

What is the MPD for occupationally exposed persons?

50 mSv/year (0.05 Sv/year or 5.0 rem/year).

What is the MPD for nonoccupationally exposed persons?

1 mSv/year (0.1 rem/year).

What is the MPD for occupationally exposed pregnant women?

0.5 mSv per month during pregnancy.

What is Cumulative Occupational Dose (COD)?

The total radiation dose accumulated over a radiographer’s lifetime.

What formula is used to calculate a worker’s cumulative occupational dose limit?

Age (in years) × 10 mSv.

What is cortical (compact) bone?

Dense outer layer of bone that appears radiopaque on an image.

What is cancellous bone?

Soft, spongy bone located between two layers of dense cortical bone; appears radiolucent.

What fills the spaces within cancellous bone?

Bone marrow within numerous bony trabeculae that form a lattice-like network.

How does trabecular pattern differ between the maxilla and mandible?

• Maxilla: small, dense, granular pattern

• Mandible: larger, coarser trabeculae