RadProd Flashcards
The amount of energy absorbed per unit mass
Absorbed Dose
When electromagnetic energy is transferred from the x-rays to the atoms of the patient’s biologic material
Absorption
The reduction in the number of primary photons in the x-ray beam through absorption (a total loss of radiation energy) and scatter (a change in direction of travel that may also involve a partial loss of radiation energy) as the beam passes through the patient in its path.
Attenuation
The “released” energy that is carried off in the form of a photon. It’s energy is directly related to the shell structure of the atom from which it was emitted.
Characteristic photon
The “released” energy that is carried off in the form of a photon. It’s energy is directly related to the shell structure of the atom from which it was emitted. Also known as fluorescent radiation.
Characteristic x-ray
A simple process that results in no loss of energy as x-rays scatter.
The incoming low-energy x-ray photon (<10 keV) interacts with an atom and transfers its energy by causing some or all of the electrons of the atom to vibrate momentarily. The electrons then radiate energy in the form of electromagnetic waves. These waves nondestructively combine with one another to form a scattered wave, which represents the scattered photon. Its wavelength and energy, or penetrating power, are the same as those of the incident photon. Generally, the emitted photon may change in direction less than 20 degrees with respect to the direction of the original photon.”
Coherent scattering
The freed electron that possesses excess kinetic energy and is capable of ionizing other atoms.
Compton scattered electron, or secondary, or recoil electron
Compton scattering
In the Compton process, an incoming x-ray photon interacts with a loosely bound outer electron of an atom of the irradiated object. On encountering the electron, the incoming x-ray photon surrenders a portion of its kinetic energy to dislodge the electron from its outer-shell orbit, thereby ionizing the biologic atom.
Compton scattering
Compton scattering is also called…
• Incoherent scattering
• Inelastic scattering
• Modified scattering
Photons (1 and 2) that emerge from the tissues and strike the radiographic IR below it.
Exit, or image-formation, photons
Synonymous with characteristic x-rays.
Fluorescent radiation
Term that replaces density in the digital environment. It is used because radiographic film is no longer used as the primary IR.
Image receptor (IR) exposure
Measurement of different body structures denoted in grams per cubic centimeter.
Mass density
The product of electron tube current and the amount of time in seconds that the x-ray tube is activated.
Milliampere-seconds (mAs)
The incoming photon (equivalent in energy to at least 1.022 MeV) strongly interacts with the nucleus of the atom of the irradiated object and disappears. In the process, the energy of the photon is transformed into two new particles: a negatron (electron) and a positron. The negatron eventually recombines with any atom that needs another electron. The positron interacts destructively with a nearby electron. During the interaction, the positron and the electron annihilate each other, with their rest masses converted into energy, which appears in the form of two 0.511-MeV photons, each moving in the opposite direction.
Pair Production
Example of unstavle nuclei ised in PET scanning
Fluorine-18 (F18), Carbon-11 (11C), Nitrogen-13 (N13)
The highest energy level of photons in the x-ray beam.
Peak kilovoltage (kVp)
An interaction that occurs at more than 10 MeV in high-energy radiation therapy treatment machines. High-energy photons collide with the nucleus of an atom, which directly absorbs the photon’s energy. This energy excess in the nucleus creates an instability that in most cases is alleviated by the emission of a neutron by the nucleus.
Photodisintegration
A, On encountering an inner-shell electron in the K or L shells, the incoming x-ray photon surrenders all its energy to the electron, and the photon ceases to exist. B, The atom responds by ejecting the electron, called a photoelectron, from its inner shell, thus creating a vacancy in that shell. C, To fill the opening, an electron from an outer shell drops down to the vacated inner shell by releasing energy in the form of a characteristic photon. Then, to fill the new vacancy in the outer shell, another electron from the shell next farthest out drops down and another characteristic photon is emitted, and so on until the atom regains electrical equilibrium. There is also some probability that instead of a characteristic photon, an Auger electron will be ejected.
Photoelectric absorption
By products of photoelectric absorption
- Photoelectrons (those induced by interaction with external radiation and the internally generated Auger electrons).
- Characteristic x-ray photons (fluorescent radiation).
The ejected orbital electron that possesses kinetic energy equal to the energy of the incident photon less the binding energy of the electron shell.
Photoelectron
The emerging x-ray photon beam.
Primary radiation
Differences in densities and the absorption properties among different body structures.
Radiographic contrast
Degree of overall blackening on a radiographic film.
Radiographic density
Undesirable, additional exposure that degrades the appearance of a completed radiographic image.
Radiographic fog
Object that catches exit radiation.
- Phosphor plate
- Digital radiography receptor
- Radiographic film
Radiographic image receptor (IR)
Methods that have been devised to limit the effects of indirectly transmitted x-ray photons…
The most common methods include the following:
•Air gap techniques
•Radiographic grids
Photons (2) that on their path before they hit the IR. They degrade the appearance of a completed radiographic image by blurring the sharp outlines of dense structures.
Small-angle scatter
The midpoint of the range of densities visible on the image. Adjusting the window level, also known as windowing, refers to changing the brightness, either to be increased or decreased throughout the entire range of densities
Window level
Differentiate between peak kilovoltage (kVp) and milliampere-seconds (mAs)
kVp is the highest energy level of photons in the x-ray beam. It controls the penetrating ability of the x-ray beam.
mAs is the the product of electron tube current and the amount of time in seconds that the x-ray tube is activated.
Describe the process of absorption, and explain the reason why absorbed dose in atoms of biologic matter should be kept as small as possible.
X-ray photons can interact with atoms of the patient’s body and transfer energy to the tissue. The amount of energy absorbed per unit mass is referred to as the absorbed dose (D). This dose should be kept low to prevent the possibility of biologic damage in the patient.
Differentiate among the following: primary radiation; exit, or image-formation, radiation; and scattered radiation.
Primary radiation: The emerging x-ray photon beam.
Exit, or image-formation radiation: Noninteracting and small-angle scattered photons that pass through the patient and hit the IR.
Scatter radiation: photons that change directions, involve a partial loss of energy, and do not hit the IR
List two types of x-ray photon transmission, and explain the difference between them.
List two types of x-ray photon transmission, and explain the difference between them.
Direct: When photons transverse the patient without interacting and still reach the image receptor.
Indirect: When photons transverse the patient, undergo Compton and/or coherent interactions that may cause them to scatter or deflect with a potential loss of energy before striking the IR.
The anode target is made of the metal tungsten or a metal alloy tungsten rhenium because…
- High melting point
- High atomic number (Tungsten: 74, Rhenium: 75)
List the events that occur when x-radiation passes through matter.
When x-rays pass through matter, they are either attenuated (meaning they interact with the atoms of the patient’s biologic tissue and are absorbed or scattered), or they pass through the patient as small-angle scatter photons or exit, image-forming radiation that hits the image receptor.
The atomic numbers of compact bone, soft tissue, and air…
Compact bone: 13.8
Soft tissue: 7.4
Air: 7.6
Describe the impact of positive contrast media on photoelectric absorption, and identify its effects regarding absorbed dose in the body structure that contains it.
Positive contrast media has a high atomic number that significantly enhances the occurrence of photoelectric interaction relative to similar adjacent structures that do not have contrast media. It also leads to an increase in absorbed dose in the body structures that contain it.
