X-ray Flashcards
what property of the body does it measure
tissue density. Denser tissue attenuates xrays a fewer pass through
how is the signal produced (physics)?
thermionic electron emission from wire. Focusing on the cup to get tight beam. Anode/cathode cahrge pulls electrons towards tungsten anode. Anode is a spinning disk with angled edged. When electrons hit it, they produce characteristic radiation/Bremmstralung/compton scattering.
what is characteristic emission of x-ray
electron knocks out inner electron, upper one falls down and emits x-rays
what is Bremsstrahlung emission of x-rays
electron swings off path due to nuclear attraction, slows down & emits energy x-ray
what happens to collimated x-rays
they pass through patient, some are attenuated, some are scattered, some reach detector below.
What is the photoelectric effect
x-ray in, and electron is knocked out. Proportional to Z^3/E^3 used in mammography- so this is lower energy
What is the Compton scatter
x-ray in, electron knocked out with another x-ray- diagnostic normal
what is Rayleigh scatter
x-ray in, x-ray out at a different angle
what does the image look like if more x-rays are hitting the detector
brighter image
what are the key components of the system
anode (tungsten), filter, collimator, grid, detectors
what anode is used for mammography and why
molybdenum because it has a Z that is better for differentiating fat from ductal cells
what parameters do we control on x-ray
kVp, mA, time, magnification/SID, focal spot size, grid sizes, AEC (automatic exposure control)
what image quality parameters do we look at?
spatial resolution (point spread function), contrast, temporal resolution, noise/SNR, heel effect (lower intensity x-rays through back side of anode)
what is the heel effect and draw how it affects an image
it lower intensity x-rays through the back side of the anode
what can increasing kvP do to an image
it increases the x-ray energy, which means less attenuation, higher dose, but less noise
what does increasing current do to an image
it increases the number of x-rays but it increases the signal to noise ratio
what does a shorter SID do
it increases the magnification and skin dose, but not the total dose because of the inverse square rule adn there is a bigger penumbra
what happens if you increase the focal spot?
it just increases the penumbra, but it can take an image of more at a time
what are the trade-offs with increasing kvp
dose vs. contrast
what are the trade-offs with current
dose vs. SNR
what are the trade-offs with the anode angle
greater focal spot size, but more heel effect
what are the trade-offs with SID
magnification vs. penumbral blur
what are the stochaistic effects of x-ray
probability increases with dose
what are the deterministic effects of xray
severity increases with dose (acute radiation poisoning)
