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Lecture 2: Radiation and the atom
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Radiation is energy that travels through space or matters
Two types of radiation in medical imaging:Electromagnetic(EM)
andparticulate radiation
1. EM radiation (EMR) is pure energy, has no mass, and
travels at c
EMR used in medical imaging can be: radiofrequency radiation
x-rays
gamma rays
2. Particulate radiation energy is function of the
particulate
mass and speed
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EM radiation is commonly characterized byfrequency,
wavelength, andphoton energy.
%There is some overlap in frequency (energy) for gamma and
X-rays.
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When discussingpropagation in space, it is convenient totreat EM
radiation as a wave.
When discussing interactions of the EM with matter, it is
convenient to view EM radiation with respect to itsparticle-like
behavior, and express its energy in units of eV.
For medical imaging, generally deal with energy levels
expressed as keV or MeV.
6
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All waves are characterized by their amplitude (maximal height,
intensity
of the wave), wavelength (@, the distance between any two
identical pointson adjacent cycles),frequency (!, number of periods
that occur per
second), andperiod (the time required to complete one cycle of a
wave).
Phase is the temporal shift of one wave with respect to
theother.
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