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x-ray interactions

chapter 7

QuestionAnswer
image formation dependent on the quantity and quality of the x-ray beam along with composition of anatomic tissues.
what type of radiation comprises the image on the image receptor? exit radiation
exit radiation consists of transmitted and scatter x-ray photons. Forms the diagnostic image on the image receptor.
transmitted x-rays Incoming x-ray photon passes through the anatomic part with any interactions with the atomic structures. Only 1% of the x-ray beam is transmitted.
image receptor Any device that receives the radiation leaving the patient and records a latent image.
relationship between beam attenuation and x-ray photon energy increased energy=decreased attenuation
relationship between beam attenuation and tissue thickness increased part = increased attenuation
relationship between beam attenuation and tissue density increase density = increased attenuation
relationship between beam attenuation and tissue material increased atomic # = increased attenuation
half value layer The amount of material required to reduce the amount of x-ray beam intensity to one-half its original value. affected by kvp and filtration.
filtration purpose is to remove "soft x-rays" (low energy x-rays generated in the tube).removing soft x-rays hardens the beam.
bean attenuation The removal of x-ray photons from the beam due to absorption or scattering
why does beam attenuation occur? occurs as a result of photon interactions with the atomic structures that compose the tissue.
what are the 2 types of attenuation? 1.absorption 2.scatter
what are they 5 types of x-ray interactions in the body? 1.Photoelectric effect 2.comptoon scattering 3.coherent/classical scattering 4.pair production 5.photodisintegration
photoelectric effect complete absorption of the x-ray by knocking out the inner shell e- producing a photoelectron. The photoelectron leaves the atom. an electron from another shell drops down to fill the void and generates a secondary electron photon.
what does the secondary photon in the photoelectric effect become? generally becomes scatter in the body and are absorbed which contributes to patient dose
compton effect occurs when the outer shell e- is ejected by x-ray photon (creates a secondary/secondary e-). The now lower energy photon changes direction and interacts with the image receptor.
what interaction is it when some x-ray photons interact with tissue but aren't absorbed and loses energy? Compton effect
what is the probability of photoelectric effect happening depend on? Probability depends on both the energy of beam and the composition of the anatomy.The energy of the beam must be greater than or equal to the binding force if the inner shell e-.Atoms with higher atomic #'s absorb more x-rays
what is the probability of Compton effect happening depend on? The probability depends solely on energy of incoming photon.just as likely to occur in soft tissue as in bone because it interacts with outer shell e-
what kind of energies does coherent/classical scatter occur? occurs between very low energy x-ray photons and matter
What energy level must it be for a coherent/classical interaction to occur? less than or equal to 10 KeV
Does coherent/classical scatter cause ionization of the atom? no
What is the process of coherent/classical scatter? the incident photon interacts with electrons in an atom and causing the electrons to become excited and vibrate. The excited atom releases the excess energy as a scatter x-ray photon wit the same wavelength as the incident photon.
Is coherent/classical scatter diagnostic in radiology? no
What are the 2 types of coherent/classical scatter? 1.Thomson 2.Rayleigh
What is the difference between Thomson and Rayleigh? Thomson involves a single e- of the atom and Rayleigh involves all of the electrons in the atom.
what happens when scatter reaches film? If it reaches film it only contributes to fog not diagnostic quality.
what does scatter do to patient dose? increases it
What happens if scatter leaves the patient and doesn't strike the image receptor? scatter can contribute to radiation exposure of anyone near the patient.
define- differential absorption different tissues absorb more or less radiation depending on thickness, atomic number and compactness of bone.
what are the 4 factors that image formation is the direct result of? 1.differential absorption 2.photo electric 3.scatter interactions 4.transmitted x-rays
What is pair production used for? Used only in radiation therapy
what is the process of pair production? x-ray photon of 1.02 mev comes close to the strong nuclear field of an atom and loses all of its energy in the interaction. The energy reappears a negative e- w/.51 charge and a positive e- w/.51 charge.
what makes pair production an annihilation reaction? The negative and positive electrons continue to be attracted to each other and continue to annihilate each other each time their energy is reformed.
What is photo disintegration used for? occurs only in radiation therapy.
In photo disintegration what does the x-ray interact with? The nucleus of the atom
In photo disintegration how much photon energy is required? greater than or equal to 10 MeV
What is the process of photo disintegration? The high energy photon interacts with the nucleus and all of the energy of the photon is absorbed. The nucleus rids itself of the excess energy by emitting a nuclear fragment.
define- ionization A characteristic of x-ray that is caused by the ejection of an electron.
3 Factors that cause ioniztion 1.gamma radiation 2.x-ray radiation 3.ultra violet radiation
Created by: lchadderton