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Chapter 9
Key concepts
24
Health Care
Undergraduate 3
10/30/2014

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Term
what is coherent scattering also known as?
Definition
classical or Thompson
Term
coherent scatter occurs at what energy level?
Definition
energy below 10 keV
Term
relationship between incident x-ray and scatter x-ray in coherent scatter
Definition
same energy and same wavelength
Term
what is the result of coherent scatter
Definition
change in direction of x-ray without a change in energy (no ionization)
Term
coherent scatter in relation to diagnostic radiology
Definition
little importance but does contribute slightly to film fog
Term
in compton scatter what does the incident x-ray interact with
Definition
an outer shell electron, ionizing the atom
Term
in compton scatter what is the ejected electron called
Definition
the compton electron or secondary electron
Term
what is the relationship between energy and wavelength in compton scattering
Definition
the scattered electron has less energy and longer wavelength
Term
at what angle does the scattered x-ray defelct at in compton scatter
Definition
can be deflected at any angle
Term
how does compton scatter affect an image?
Definition
reduces the contrast
Term
compton scatter is the source of what type of radiation exposure
Definition
occupational dose by the rad tech (mainly during fluoro)
Term
what type of electron does an incident ray interact with during photoelectric effect
Definition
an inner-shell electron and then ejects it causing ionization
Term
what happens to the incident ray in photoelectric effect
Definition
it is totally absorbed, releasing all of it's energy to the ejected electron
Term
what is the ejected electron called in photoelectric effect
Definition
photoelectron
Term
in photoelectric effect what happens when outer-shell electron fill in the spaces of void left by ejected electron
Definition
characteristic x-rays (secondary radiation and behave the same as scatter radiation)
Term
how does photoelectric effect effect the image
Definition
it is responsible for image contrast (white areas)
Term
how much energy is necessary for pair production
Definition
1.02 MeV => it has to be that high to get close to the nucleus of the atom (does not occur in diagnostic imaging)
Term
what happens in pair production
Definition
the interaction between the x-ray and the nuclear electric field causes the x-ray to disappear, and in its place two electrons appear, one positively charged (positron) and one negatively charged
Term
what energy level do you need for photodisintegration
Definition
10 MeV in order to interact with nucleus of an atom (not in diagnostic x-ray)
Term
what happens in photodisintegration
Definition
the energy is absorbed by the nucleus and the nucleus emits a nuclear fragment
Term
what is differential absorption
Definition
the difference in x-ray interaction resulting from the differences between x-rays that are absorbed photoelectrically in the patient and those that are transmitted to the image receptor
Term
what 2 types of interactions with matter cause differential absorption
Definition
compton scattering and photoelectric effect, and x-rays transmitted through the patient
Term
how many x-rays reach the image receptor
Definition
approximately 1%
Term
how many of the x-rays that reach the image receptor interact to form an image
Definition
less then half
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