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Rad Protection Ch.3
Interaction of X-Radition with Matter
| Question | Answer |
|---|---|
| Absorbed Dose (D) | The amount of energy per unit mass absorbed by an irradiated object. This absorbed energy is responsible for an biologic damage resulting from the tissues being exposed to radiation. The gray (Gy) is the SI unit of this radiation quantity. |
| Absorption | Transference of electromagnetic energy from an x-ray beam to the atoms or molecules of the matter through which it passe. |
| Attenuation | Is the reduction in the number of primary photons in the x-ray beam through absorption and scatter. |
| Auger Effect | When an inner-shell vacancy occurs in an atom, the energy liberated when this vacancy is filled can be transferred to another electron of the atom, thereby ejecting the electron. |
| Characteristic Photon | A quantum or quantity of radiant energy given off by an atom when an electron from an outer-shell drops down to fill an inner-shellvacancy. |
| Characteristic X-ray | Energy is directly related to the shell structure of the atom from which it was emitted. |
| Compton scattered electron, or secondary, or recoil, electron | An energetic electron dislodged from the outer shell of an atom of the irradiated object as a result of a Compton interaction with an incoming x-ray photon. |
| Coherent Scattering | The process wherein a low-energy photon interacts with an atom of human tissue and does not lose kinetic energy. |
| Coherent Scattering: | The atom responds by releasing the energy it has receive in the form of a scattered photon that has the same wavelength and energy as the original incident photon. The emitted photon changes direction by 20 degrees or less. |
| Compton Scattering | An interaction between an incoming x-ray photon and a loosely bound outer-shell electron of an atom in the irradiated object |
| Compton Scattering: | The photon surrenders a portion of it kinetic energy to dislodge the electron from its outer-shell orbit, thereby ionizing the atom, and then continues in a new direction. |
| Contrast Media | Consists of solutions containing elements having a higher atomic number than surrounding soft tissue. |
| Effective Atomic Number (Zeff) | A composite Z value for when multiple chemical elements comprise a material. |
| Exit, or Image-formation, Photons | All the x-ray photons that reach their destination after passing through the patient being radiographed. |
| Fluorescent Rdiation | Characteristic x-ray photon. |
| Fluorescent Yield | The number of x-rays emitted by an atom per inner-shell vacancy. |
| Mass Density | Quantity of matter per unit volume. It is generally specified in unity of kilograms per cubic meter or grams per cubic centimeter. |
| Millampere-Seconds (mAs) | The product of electron tube current and the amount of time in seconds that the x-ray tube is activated. |
| Peak Kilovoltage (kVP) | The highest energy level of photons in the x-ray beam. |
| Pair Production | Interaction between an incoming photon of at least 1.022 MeV and an atom of irradiated biologic tissue in which the photon approaches, strongly interacts with the nucleus of the atom of the irradiated tissue, and disappears. |
| Photodisintegration | An interaction that occurs above 10 MeV in high energy radiation therapy treatment machines. In the interaction, a high energy photon collides with the nucleus of an atom, which directly absorbed all the photon's energy. |
| Photodisintegration: | This energy excess in the nucleus creates an instability that in most cases is alleviated by the emission of a neutron from the nucleus. |
| Photoelectron | The electron ejected from its inner-shell orbit during the process of photoelectric absorption. It possesses kinetic energy an can ionize other atoms it encounters until its energy is spent. |
| Primary Radiation | Radiation that emerges directly from the x-ray tube collimator and moves without deflection toward a wall, door, viewing window, and so on. |
| Radiographic Contrast | Differences in gray levels between adjacent anatomic structures on a completed image. |
| Radiographic Fog | Undesirable additional darkness on a completed radiographic image caused by scattered radiation reaching the image receptor. |
| Radiographic Image Receptor | Phosphor plate, digital radiography receptor, or radiographic film. |
| kVp | - Controls penetration. - It is the highest level of photons in the x-ray beam. |
| mAs | A product of the # of photons and time factor. |
| The combination of the glass envelope and the aluminum in the collimator is called _____________________. | Permanent inherent filtration. |
| Primary Beam | Is what comes through the window of the x-ray tube. |
| What reduces resistance in the x-ray tube? | Glass envelope. |
| Where are the x-rays produced? | On the target of the anode. |
| When x-rays basses through an object it goes through a process called? | Attenuation. |
| Direct Transmission | X-rays that pass through the patient without interaction. |
| Indirect Transmission | X-rays that pass through but after striking an image through scatter. |
| Photodisintegration | - An interaction that occurs at more than 10 MeV in high-energy radiation therapy treatment machines. - Process of photodisintegration. |
| What type of interaction accounts for most of the white appearance of the radiograph? | Photoelectric absorption. |
| Use of Contrast Media to Ensure Visualization of Anatomic Structures | - If tissues or structures are similar in Z, and mass density must be distinguished, use of appropriate contrast media may be needed to ensure visualization of those tissues or structures in the radiographic image. |
| Use of Contrast Media to Ensure Visualization of Anatomic Structures: | - Use of positive contrast medium. - Use of negative contrast medium. |
| Effects of Attenuation on Radiographic Images: | - The less a structure attenuates radiation, the darker the image will be and vice versa. - An image must have a sufficient amount of variation in densities to clearly visualize anatomic structures of interest. |
| Examples of contrast media: | IVP GI studies. |
| Impact of PE absorption on Radiographic contrast: | - The greatest x-ray energy that permits adequate radiographic contrast should be used to protect patients. - Contrast media has high atomic numbers so low Z number structures visualization may be enhanced. |
| Impact of PE absorption on Radiographic contrast | - Lower kVp exams shows a greater PE absorption. - Greater PE absorption increases patient dose. |
| Probability of Occurrence of Photoelectric Absorption: | Depends on - Atomic number of irritated item. - Higher atomic numbers have higher incidence of absorption. - Mass density of body structure. |
| Probability of Occurrence of Photoelectric Absorption | Depends on - As density increases so does photoelectric absorption. - Body part thickness. - As body part thickness increases so does photoelectric absorption. |
| Auger Effect | - Discovered by Pierre Victor Auger in 1925. - Produces an Auger electron. - Is a radiationless effect. |
| There are 5 interactions between X-radiation and matter are possible; but only 2 are in diagnostic range? | Compton and Photoelectric. |
| The __________ is responsible for the clear parts of the radiographic image due to this absorption. | PE. |
| Another thing that happens in the _________________________ is the production of Auger electrons. Form the ejected inner shell electrons, as it exits from the shells, the ejection of an additional outer shell electron is called an Auger electron. | Photoelectric effect. |
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