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principles of diagnostic imaging questions and answers graded A+
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principles of diagnostic imaging questions and answers graded A+
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principles of diagnostic imagingwhy is electromagnetic radiation best for image formation? - correct answer ✔✔travels in straight lines
velocity of EM radiation? - correct answer ✔✔speed of light (this stays constant)
energy of EM radiation? - correct answer ✔✔inversely proportional to wavelength
(shorter wavelength = higher energy)
how are x-rays different from gamma rays? - correct answer ✔✔different based on how they're formed:
>Xrays: produced by interaction of fast moving electrons with metal (tungsten) target and used in
radiography
>gamma rays: produced by decay of radioactive elements and used in nuclear medicine (scintigraphy)
what does heating the cathode of a x-ray machine do? - correct answer ✔✔'thermionic emission' =
cloud of electrons around cathode
how is a xray produced? - correct answer ✔✔>tungsten wire filament heated by small electric current =
cloud of free electrons around cathode
>electrons are focused in beam by a negatively charged focusing cup around the cathode
>electrons then accelerated towards anode by application of high PD between anode and cathode
>electrons rapidly decelerated upon interaction with anode atoms = x ray production
why is tungsten used in the cathode? - correct answer ✔✔used due to high atomic number (74) and
melting point (3380'C)
what is mA? - correct answer ✔✔AMOUNT OF XRAY
>alters the small current heating the cathode filament
,>the higher the filament current (mA), the higher the temperature heating the cathode = greater
number of electrons produced = more xray
what is the normal potential difference applied to accelerate electrons towards the anode? - correct
answer ✔✔50-100,000V
what is kV? - correct answer ✔✔STRENGTH/PENETRATING POWER OF XRAY: alters the PD across the
tube, between the anode and cathode
(max energy of x-ray = kV across tube)
what is the focal spot (FS)? - correct answer ✔✔electrons from cathode are focused so they impinge on
small area (FS) of the anode
what is the general emission method of x-ray formation? - correct answer ✔✔>aka 'braking radiation'
>interaction of electrons = x-ray production
what is the characteristic emission method of x-ray formation? - correct answer ✔✔>electron knocked
out of target atom
>another falls down through shells to replace it → loss of energy = X-ray photon
why is x-ray production inefficient? what can be done to prevent this? - correct answer ✔✔Interaction
between electrons and anode = 99% heat and 1% x-rays so have to try and remove heat produced from
focal spot
what are the 2 methods of removing heat from the focal spot? - correct answer ✔✔1. stationary anode
(lower output machine)
>tungsten target embedded in block of copper = conduction of heat away from anode target
2. rotating anode (higher output machines)
>anode = disc (molybdenum or graphite- doesn't have to be conducting) with angled edge
>tungsten track runs round angled edge
>disc is mounted on a molybdenum rod rotated by electric motors (motors outside of the tracks)
>heat lost by convection from surface of disc as molybdenum is a poor conductor
, >have to 'prep' the x-ray machine as this starts the anode spinning and heats the cathode
what is the x-ray tube made of? - correct answer ✔✔evacuated pyrex tube containing anode and
cathode
>immersed in oil- helps heat conduction and electrical insulation
>entire tube surrounded by lead, except for a small window where useful X-ray beams emerge
how are the exposure factors of an x-ray altered? - correct answer ✔✔control panel on X-ray machine
what are the 4 exposure factors of an x-ray? - correct answer ✔✔>on/off button
>mA control
>kV control
>timer
why is the on/off button an xray exposure factor? - correct answer ✔✔>when X-ray machine is
connected to power supply, area around = 'controlled area' with access restrictions by law
what does the step up transformer do in the xray machine? - correct answer ✔✔increases voltage from
mains to supply the kV across the tube
what happens in the xray producing mechanism when you increase the kV? - correct answer ✔✔=
greater potential difference across X-ray tube = faster electrons between cathode and anode = more
kinetic energy when they hit anode = higher energy in resultant X-rays
when would you increase the kV and/or mA? - correct answer ✔✔thicker bodies
why is kV not linear? - correct answer ✔✔increase of 10kV = double energy
what happens in the xray producing mechanism when you increase the mA? - correct answer ✔✔=
hotter cathode filament = more electrons available to accelerate across tube = more electrons hit anode
= more X-rays produced (energy of xray = unchanged)
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