Chapter 9 Flashcards
What are the 5 basic interactions with matter?
Coherent scattering Photoelectric interaction* Compton interaction* Pair production Photodisintrigration
Which 2 of the 5 basic interactions with matter pertain to diagnostic x-ray?
Photoelectric interaction
Compton interaction
Photons of electromagnetic radiation interact with structures of similar ___ and ___ of the radiation
Size and wavelength
Low energy x-rays tend to interact with what?
Whole atoms
Moderate energy x-rays tend to interact with what?
Electrons
High energy x-rays tend to interact with what?
Nuclei
What are the two other names for coherent scattering?
Classical scattering
Thompson scattering
Term for an interaction between low-energy x-rays and atoms. The xray loses no energy but changes direction slightly. The wavelength of the scattered x-ray is equal to the wavelength of the incident x-ray
Coherent scattering
The result of coherent scattering is a change in _____ of the xray without a change in its ____.
Direction
Energy
The general graying of an image that reduces image contrast
Image noise
Term for when the incident x-ray interacts with an outer-shell electron not only scattering the x-ray but reducing its energy and ejecting it from the atom thereby ionizing the atom.
Compton scattering
X-rays scattered back in the direction of the incident x-ray beam.
Backscatter radiation
The probability of Compton scattering ____ as x-ray energy increases.
Decreases
What does Compton scattering do to image contrast?
Reduces
Radiation which is the source of most of the occupational radiation exposure that radiographers receive
Compton Scattering
Term for x-rays in the diagnostic range undergoing ionizing interactions with inner shell electrons in which the x-ray is not scattered but is totally absorbed.
Photoelectric effect
Term for the electron removed from the atom during a photoelectric effect that escapes with kinetic energy equal to the differecne between the energy of th incident x-ray and the binding energy of the electron
Photoelectron
The photoelectric effect is…
Total x-ray absorption
The k shell electron binding energy (keV) ____ as atomic number ____
Increases
Increases
A photoelectric interaction cannot occur unless the incident x-ray has what?
Energy equal to or grater than the electron binding energy
The probability of the photoelectric effect is directly proportional to what?
The third power of the atomic number of the absorbing material
K shell electron binding energy
keV
Atomic number affects the probability of ______ interaction but not _____ interaction
Photoelectric
Compton
Pair production does not occur during what?
X-ray imaging
Positively charged electron
Positron
Interaction of a high energy photon and the electromagnetic field of the nucleus (nuclear field) in which the photon disappears and 2 electrons appear; one positively charged (positron) and one negatively charged.
Pair production
An electron with less that 1.02 MeV cannot undergo what?
Pair production
Pair production is not an important factor in x-ray imaging but IS important in what diagnostic imaging?
PET scans (Positron emission tomography)
When x-rays with energy above approximately 10 MeV escape interaction with electrons and the nuclear field and are absorbed directly by the nucleus and is raised to an excited state and instantly emits a nucleion or other nuclear fragment.
Photodisintegration
Photodisintegration does not occur in what?
Diagnostic imaging
Differential absorption occurs because of what?
Compton scattering, photoelectric effect and x-rays transmitted through the patient.
What three types of x-rays are important to the making of a radiograph?
Those scattered by Compton interaction
Those absorbed photoelectrically
Those transmitted through the patient without interaction
The difference in x-ray interaction between those x-rays absorbed photoelectrically in the patient and those transmitted by the image receptor
Differential absorption
Differential absorption increases as what is reduced?
kVp
Reducing the kVp to increase differential absorption and therefor image contrast results in what?
Increased radiation doseage to the patient
With higher x-ray energy, _____ interactions occur, so ____ x-rays are transmitted without interaction
Fewer, more
Compton scattering is ____ of the atomic number of tissue. (Dependent or independent)
Independent
At low energies, most x-ray interaction with tissue are _____. At high energies most x-ray interaction with tissue is ______
Photoelectric, Compton
To image small difference in soft tissue, one must use ____ kVp to get maximum differential absorption
Low
___ kVp = high contrast
Low
____ kVp technique is used for examination of barium studies and chest radiography in which the intrinsic subject contrast is ___, resulting in much lower patient radiation dose
High, high
A beam containing x-rays that all have the same energy
Monoenergetic
Clinical xrays are ___ meaning they are emitted over an entire spectrum of energies
Polyenergetic
Quantity of matter per unit volume (specified in kilograms per cubic meter) aka number of atoms present per unit volume of material; basically tells how tightly the atoms of a substance are packed
Mass density
The total reduction in the number of x-rays remaining in an x-ray beam after penetration through a given thickness of tissue
Attenuation
An interaction such as the photoelectric effect is called _____ because the x-ray disappears
Absorption
Absorption + scattering =
Attenuation
A change in the direction of an incident x-ray without a loss of energy
Coherent scattering
This type of scattering occurs when incident x-rays ionize atoms and the x-ray then changes direction with a loss of energy
Compton scattering
This occurs when the incident x-ray is absorbed into one of the inner electron shells and emits a photoelectron
Photoelectric effect
This occurs when the incident x-ray interacts with the electric field of the nucleus. The x-ray disappears, and two electrons appear - one positively charged (positron) and one negatively charged (electron)
Pair production
This occurs when the incident x-ray is directly absorbed by the nucleus. The x-ray disappears and the nuclear fragments are released
Photodisintegration
What controls the contrast of the x-rays image?
Differential absorption
Differential absorption and attenuation of the x-ray beam depend on what 3 factors?
The atomic number of atoms in tissue
The mass density of tissue
The x-ray energy
What constrast agent is used in vascular, renal, and biliary imaging and why?
Iodine has a greater atomic number and mass density greater than that of soft tissue
What radiologic contrast agent is used for gastrointestial imaging and why?
Barium; it has a greater atomic number and mass density greater than that of soft tissue
