X-Ray Production and Interaction Flashcards

Comprehensive vocabulary flashcards covering x-ray production, emission spectra, quantity/quality factors, and interactions with matter.

Kinetic energy

The energy of motion, calculated using the equation $KE = \frac{1}{2}mv^2$ where $m$ is mass and $v$ is velocity.

Projectile electron

An electron accelerated from the cathode to the anode in an x-ray tube that interacts with the target atoms.

Anode heat production

The result of projectile electrons interacting with outer-shell electrons of target atoms, where approximately $99\%$ of kinetic energy is converted to thermal energy.

Excitation

The process where outer-shell electrons are raised to a higher energy level and then drop back to normal, emitting infrared radiation (heat).

Efficiency of x-ray production

A measurement independent of tube current that increases with increasing kVp; it is approximately $1\%$ at $100\,kVp$.

Characteristic x-rays

Radiation produced when a projectile electron ionizes a target atom by removing an inner-shell electron, and an outer-shell electron fills the void.

K-shell binding energy (Tungsten)

The energy required to remove a K-shell electron from tungsten, which is exactly $69\,keV$.

K x-rays

Characteristic x-rays resulting from outer-shell electron transitions into the K shell; they are the only tungsten characteristic x-rays useful for imaging.

L x-rays

Characteristic x-rays resulting from electron transitions to the L shell, possessing much less energy (approximately $12\,keV$) than K x-rays.

Bremsstrahlung radiation

A German word meaning "braking radiation," produced when a projectile electron is slowed by the nuclear field of a target atom nucleus.

Continuous emission spectrum

A spectrum that contains all possible values, characteristic of bremsstrahlung x-rays which range from zero energy to the peak electron energy.

Discrete emission spectrum

A spectrum containing only specific, precisely fixed values; characteristic x-rays of tungsten form this at specific energies like $69\,keV$.

X-ray emission spectrum

A plot of the relative number of x-rays emitted as a function of the energy of each individual x-ray.

Integration

The process of adding together the number of x-rays emitted at each energy over the entire spectrum, represented by the area under the curve.

Spectrum Amplitude

The height of the curve on an emission spectrum graph, representing x-ray intensity or quantity.

15% Rule

A rule of thumb stating that a $15\%$ increase in kVp is equivalent to doubling the mAs to maintain constant exposure to the image receptor.

Added filtration effect

Results in a relative increase in average energy (hardening) and a reduction in x-ray intensity, primarily by absorbing low-energy x-rays.

Target material effect

As the atomic number ($Z$) of the target increases, the efficiency of bremsstrahlung production and the energy of characteristic x-rays both increase.

Voltage ripple effect

As ripple decreases (e.g., in high-frequency generators), x-ray intensity and effective energy increase due to more efficient operation.

X-ray intensity

The number of x-rays in the useful beam, measured in milligray in air ($mGya$), also known as radiation quantity or radiation exposure.

Air kerma

An expression of x-ray intensity, measured in $mGya$, representing the kinetic energy released in matter (air).

mAs relationship to intensity

X-ray intensity is directly proportional to the milliampere seconds ($mAs$); doubling mAs doubles the x-ray quantity.

kVp relationship to intensity

X-ray intensity is proportional to the square of the ratio of the kilovolt peak ($kVp$), mathematically expressed as $\frac{kVp_2^2}{kVp_1^2}$.

Inverse square law

A law stating that x-ray intensity is inversely proportional to the square of the distance from the source: $\frac{I_1}{I_2} = (\frac{d_2}{d_1})^2$.

The Square Law

Used to maintain constant image receptor exposure when distance is changed: $\frac{mAs_1}{mAs_2} = (\frac{SID_1}{SID_2})^2$.

Penetrability

The ability of x-rays to penetrate deeper into tissue and be transmitted to the image receptor; synonymous with x-ray quality.

High-quality x-rays

X-rays with high energy and high penetrability.

Attenuation

The reduction in x-ray intensity that results from a combination of absorption and scattering as the beam passes through matter.

Half-Value Layer (HVL)

The thickness of absorbing material (usually Aluminum) necessary to reduce the x-ray intensity to half of its original value; the best specifier of x-ray energy.

Inherent filtration

Filtration provided by the glass or metal enclosure of the x-ray tube, typically approximately $0.5\,mm\,Al$ equivalent.

Compensating filter

A filter used to produce a uniform intensity on an image receptor when a body part varies greatly in thickness or tissue composition.

Wedge filter

A common compensating filter used for body parts that vary in thickness, such as the foot during an anteroposterior projection.

Trough filter

A bilateral wedge filter sometimes used in chest radiography to compensate for the radiopaque mediastinum and radiolucent lung fields.

Hardening the x-ray beam

The process of increasing the average energy of the beam by adding filtration to remove low-energy x-rays.

Coherent Scattering

Also called classical or Thompson scattering; occurs at energies below $10\,keV$ where the incident x-ray changes direction with no loss of energy.

Compton Scattering

An interaction with outer-shell electrons that scatters the x-ray, reduces its energy, and ionizes the atom; the primary source of occupational exposure.

Compton electron

The electron ejected from an atom's outer shell during a Compton interaction.

Backscatter radiation

X-rays scattered in the direction back toward the incident x-ray beam at angles up to $180$ degrees.

Compton energy equation

$E_i = E_s + (E_b + E_{KE})$, where $E_i$ is incident energy, $E_s$ is scattered energy, $E_b$ is binding energy, and $E_{KE}$ is electron kinetic energy.

Photoelectric Effect

Total x-ray absorption occurring when an incident x-ray interacts with an inner-shell electron and is completely absorbed, ejecting a photoelectron.

Photoelectron

The electron removed from an inner shell during a photoelectric interaction, possessing kinetic energy equal to $E_i - E_b$.

Photoelectric probability (Atomic Number)

The probability of this effect is directly proportional to the third power of the atomic number ($Z^3$) of the absorbing material.

Photoelectric probability (Energy)

The probability of this effect is inversely proportional to the third power of the x-ray energy ($\frac{1}{E^3}$).

Pair Production

An interaction requiring at least $1.02\,MeV$ where an x-ray disappears near the nucleus and is replaced by a positron and an electron.

Annihilation radiation

The process where a positron unites with a free electron, converting the mass of both particles back into electromagnetic energy.

Photodisintegration

An interaction occurring above $10\,MeV$ where an x-ray is absorbed by the nucleus, causing it to enter an excited state and emit a nuclear fragment.

Differential absorption

The difference between x-rays absorbed photoelectrically and those transmitted to the image receptor; it determines image contrast.

Radiopaque

Structures with high x-ray absorption characteristics (like bone) that result in light areas on an x-ray image.

Radiolucent

Structures with low x-ray absorption (like air-filled lungs) that results in dark areas on an x-ray image.

Image noise

A generalized dulling of the image (fog) caused by scattered x-rays (primarily Compton) reaching the image receptor.

Mass density

The quantity of matter per unit volume, specified in $kg/m^3$. Increased density results in a proportional increase in x-ray interactions.

Positive contrast agent

High atomic number materials like Barium ($Z=56$) or Iodine ($Z=53$) used to increase differential absorption.

Negative contrast agent

Materials like air used in double-contrast examinations to create differences in mass density.

Exponential attenuation

The mathematical description of how x-rays are reduced in number by a given percentage for each incremental thickness of tissue they penetrate.

Barium ($Z=56$)

A contrast agent used primarily for gastrointestinal imaging due to its high atomic number and high mass density.

Molybdenum (Mo)

A target material used in mammography because of its low atomic number ($Z=42$) and production of low-energy characteristic x-rays ($19\,keV$).

Voltage waveform effect

Three-phase or high-frequency operation yields more intense x-ray emission and higher effective energy than single-phase operation.

Electron mass

The mass of an electron, which is approximately $9.1 \times 10^{-31}\,kg$.

Maximum energy of bremsstrahlung

In keV, this value is numerically equal to the operating kVp of the x-ray imaging system.

Primary function of x-ray imaging system

To accelerate electrons from the cathode to the anode in the x-ray tube.

Diagnostic range of x-rays

Typically between $20\,kVp$ and $150\,kVp$.

Filtration hardening

The result of removing low-energy x-rays, which increases the average energy and the penetrability of the beam.

Crossover point (Soft Tissue)

The energy ($20\,keV$) at which the probability of photoelectric effect equals the probability of Compton scattering in soft tissue.

Crossover point (Bone)

The energy ($40\,keV$) at which the probability of photoelectric effect equals the probability of Compton scattering in bone.

Beryllium ($Z=4$)

Material used for thin x-ray tube windows in mammography to provide low inherent filtration ($0.1\,mm\,Al$).

Secondary radiation

Radiation, such as characteristic x-rays produced in the body, that results from interactions of the primary beam with atoms.

Spectrum position shift

A shift to the right on the energy axis indicates higher effective energy or quality of the x-ray beam.

Tungsten ($Z=74$)

The primary component of most x-ray tube targets due to its high atomic number and high melting point.

Effect of SID on mAs

When SID is increased, mAs must be increased by the square of the distance ratio to maintain constant exposure.

One-third rule (Spectrum)

The greatest number of x-rays in a bremsstrahlung spectrum is emitted with energy approximately one-third of the maximum energy.